Theory, Instrumentation and Applications of Magnetoelastic Resonance Sensors: A Review
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paper_title: Wireless Magnetoelastic Resonance Sensors: A Critical Review

paper_content:

This paper presents a comprehensive review of magnetoelastic environmental sensor technology; topics include operating physics, sensor design, and illustrative applications. Magnetoelastic sensors are made of amorphous metallic glass ribbons or wires, with a characteristic resonant frequency inversely proportional to length. The remotely detected resonant frequency of a magnetoelastic sensor shifts in response to different physical parameters including stress, pressure, temperature, flow velocity, liquid viscosity, magnetic field, and mass loading. Coating the magnetoelastic sensor with a mass changing, chemically responsive layer enables realization of chemical sensors. Magnetoelastic sensors can be remotely interrogated by magnetic, acoustic, or optical means. The sensors can be characterized in the time domain, where the resonant frequency is determined through analysis of the sensor transient response, or in the frequency domain where the resonant frequency is determined from the frequency-amplitude spectrum of the sensor.
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paper_title: Characterization of nano-dimensional thin-film elastic moduli using magnetoelastic sensors

paper_content:

Abstract Application of magnetoelastic thick-film sensors to the measurement of thin-film elastic moduli is described in this study. An analytical model is derived, that relates the resonant frequency of a magnetoelastic sensor to the elasticity and density of an applied thin-film. Limits of the model are analyzed, and related to experimental measurements using thin-films of silver and aluminum. For 500 nm thick-films, the measured Young’s modulus of elasticity for Al and Ag is found to be within 1.6% of standard data. Using commercially available magnetoelastic sensors, the elasticity of coatings, approximately 30 nm thick, can readily be measured.
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paper_title: The frequency response of magnetoelastic sensors to stress and atmospheric pressure

paper_content:

Earlier work demonstrated that the characteristic resonant frequency of magnetoelastic thick-film sensors shifts linearly downwards in response to increasing atmospheric pressure. In this paper, the response mechanism is detailed and shown to be a function of both pressure and the way that the sensor is mechanically stressed. Stressing the sensor, in either the elastic or plastic regime, induces out-of-plane vibrations that act as a pressure-dependent damping force to the longitudinal sensor oscillations excited by the interrogation field. This damping force, in turn, acts to shift the resonant frequency of the magnetoelastic sensor lower in response to increasing pressure.
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paper_title: Magnetoelastic sensors in combination with nanometer-scale honeycombed thin film ceramic TiO2 for remote query measurement of humidity.

paper_content:

Ribbonlike magnetoelastic sensors can be considered the magnetic analog of an acoustic bell; in response to an externally applied magnetic field impulse the sensors emit magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected external to the test area using a pick-up coil, enabling query remote monitoring of the sensor. The characteristic resonant frequency of a magnetoelastic sensor changes in response to mass loads. [L.D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986). p. 100].Therefore, remote query chemical sensors can be fabricated by combining the magnetoelastic sensors with a mass changing, chemically responsive layer. In this work magnetoelastic sensors are coated with humidity-sensitive thin films of ceramic, nanodimensionally porous TiO2 to make remote query humidity sensors.
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paper_title: Monitoring blood coagulation with magnetoelastic sensors.

paper_content:

The determination of blood coagulation time is an essential part of monitoring therapeutic anticoagulants. Standard methodologies for the measurement of blood clotting time require dedicated personnel and involve blood sampling procedures. A new method based on magnetoelastic sensors has been employed for the monitoring of blood coagulation. The ribbon-like magnetoelastic sensor oscillates at a fundamental frequency, which shifts linearly in response to applied mass loads or a fixed mass load of changing elasticity. The magnetoelastic sensors emit magnetic flux, which can be detected by a remotely located pick-up coil, so that no direct physical connections are required. During blood coagulation, the viscosity of blood changes due to the formation of a soft fibrin clot. In turn, this change in viscosity shifts the characteristic resonance frequency of the magnetoelastic sensor enabling real-time continuous monitoring of this biological event. By monitoring the signal output as a function of time, a distinct blood clotting profile can be seen. The relatively low cost of the magnetoelastic ribbons enables their use as disposable sensors. This, along with the reduced volume of blood required, make the magnetoelastic sensors well suited for at-home and point-of-care testing devices.
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paper_title: Remote query pressure measurement using magnetoelastic sensors

paper_content:

Two magnetostriction-based methods for measuring atmospheric pressure are presented. Each technique correlates changes in pressure with the characteristic resonant frequency of a magnetoelastic magnetostrictive thick-film sensor. In each case the sensor is monitored remotely, using an adjacently located pickup coil, without the use of physical connections to the sensor.
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paper_title: A remote query magnetoelastic pH sensor.

paper_content:

A remote query magnetoelastic pH sensor comprised of a magnetoelastic thick-film coated with a mass-changing pH-responsive polymer is described. In response to a magnetic query field the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the attached polymer layer. As the magnetoelastic sensor is magnetostrictive the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely from the sensor using a pickup coil. The pH responsive copolymer is synthesized from 20 mol% of acrylic acid and 80 mol% of iso-octyl acrylate and then deposited onto a magnetoelastic film by dip-coating. For a 1 micrometer polymer coating upon a 30 micrometer thick Metglas [The Metglas alloys are a registered trademark of Honeywell Corporation. For product information see: http://www.electronicmaterials.com:80/businesses/sem/amorph/page5_1_2.htm.] alloy 2826MB magnetoelastic film between pH 5 and 9 the change in resonant frequency is linear, approximately 285 Hz/pH or 0.6%/pH. The addition of 10 mmol/l of KCl to the test solution decreases the sensitivity of the polymer approximately 4%.
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paper_title: A wireless micro-sensor for simultaneous measurement of pH, temperature, and pressure

paper_content:

In response to a magnetic field impulse, magnetostrictive magnetoelastic sensors mechanically vibrate. These vibrations can be detected in several ways: optically from the amplitude modulation of a reflected laser beam, acoustically using a microphone or hydrophone, and by using a pickup coil to detect the magnetic flux emitted from the sensor. Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts in response to different environmental parameters, including temperature, pressure, fluid flow velocity and mass loading, with each parameter determined in an otherwise constant environment. To extend the utility of the sensor technology in this work we report on the fabrication and application of a miniaturized array of four magnetoelastic sensors that enable the simultaneous remote query measurement of pH, temperature, and pressure from a passive, wireless platform.
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paper_title: Magnetoelastic Immunosensors: Amplified Mass Immunosorbent Assay for Detection of Escherichia coli O157:H7

paper_content:

A mass-sensitive magnetoelastic immunosensor for detection of Escherichia coli O157:H7 is described, based on immobilization of affinity-purified antibodies attached to the surface of a micrometer-scale magnetoelastic cantilever. Alkaline phosphatase is used as a labeled enzyme to the anti-E. coli O157:H7 antibody, amplifying the mass change associated with the antibody−antigen binding reaction by biocatalytic precipitation of 5-bromo-4-chloro-3-indolyl phosphate in a pH 10.0 PBS solution. The detection limit of the biosensor is 102 E. coli O157:H7 cells/mL. A linear change in the resonance frequency of the biosensor was found to E. coli O157:H7 concentrations ranging from 102 to 106 cells/mL.
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paper_title: A remote query magnetostrictive viscosity sensor.

paper_content:

Magnetically soft, magnetostrictive metallic glass ribbons are used as in-situ remote query viscosity sensors. When immersed in a liquid, changes in the resonant frequency of the ribbon-like sensors are shown to correlate with the square root of the liquid viscosity and density product. An elastic wave model is presented that describes the sensor response as a function of the frictional forces acting upon the sensor surface.
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paper_title: Measurement of temperature and liquid viscosity using wireless magneto-acoustic/magneto-optical sensors

paper_content:

Remote query magneto-acoustic and magneto-optical sensors are used to measure liquid temperature, viscosity and density. Sensors comprising magnetoelastic Metglas(R) 2826MB thick-films, alloy composition Fe/sub 40/Ni/sub 38/Mo/sub 4/B/sub 18/, oscillate in response to an externally applied, time-varying magnetic field. The sensor oscillations are strongest at the characteristic mechanical resonant frequency of the sensor. Depending upon the physical geometry and surface roughness of the magnetoelastic films, the mechanical sensor-vibrations launch an acoustic wave that can be detected remotely using a hydrophone or microphone. Furthermore, the sensor oscillations act to modulate the intensity of a laser beam reflected from the sensor surface. The sensor vibrations were optically monitored using a photo detector placed in the path of a laser beam back-scattered off the sensor ribbon. Using a Fast Fourier Transform, the signal obtained in the time-domain from acoustical or optical detectors is converted into the frequency-domain from which the resonant frequency of the sensor is determined. The resonant frequency shifts linearly with temperature and, when immersed in a liquid, with the frictional damping forces associated with liquid viscosity and density, thus allowing a remote measurement of temperature and liquid viscosity.
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paper_title: A wireless, remote query glucose biosensor based on a pH-sensitive polymer

paper_content:

This paper describes a wireless, remote query glucose biosensor using a ribbonlike, mass-sensitive magnetoelastic sensor as the transducer. The glucose biosensor is fabricated by first coating the magnetoelastic sensor with a pH-sensitive polymer and upon it a layer of glucose oxidase (GOx). The pH-responsive polymer swells or shrinks, thereby changing mass, respectively, in response to increasing or decreasing pH values. The GOx-catalyzed oxidation of glucose produces gluconic acid, inducing the pH-responsive polymer to shrink, which in turn decreases the polymer mass. In response to a time-varying magnetic field, a magnetoelastic sensor mechanically vibrates at a characteristic resonance frequency, the value of which inversely depends on sensor mass loading. As the magnetoelastic films are magnetostrictive, the vibrations launch magnetic flux that can be remotely detected using a pickup coil. Hence, changes in the resonance frequency of a passive magnetoelastic transducer are detected on a remote query ...
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paper_title: Theory of elasticity

paper_content:

A walking beam pumping unit is provided for pumping liquid from wells having gas pressure therein. The unit is driven by gas pressure from the well reciprocating the piston of a pneumatic cylinder up and down to swing the walking beam correspondingly and pump the liquid from the well. Gas under pressure is directed from the wellhead through a two-way valve to the opposite ends of the hydraulic cylinder in alternating fashion, so the piston has power strokes in opposite directions. Each power stroke, besides moving the walking beam, serves to recompress the gas used for the preceding power stroke sufficiently to inject it into the sales line. The setting of the two-way valve is controlled by a pneumatic actuator supplied with gas under pressure from the wellhead and having a thimble valve responsive to the up and down movement of the walking beam by means of adjustable stops carried thereon. The horsehead is counter-balanced by weights or by a pneumatic cylinder attached to the horsehead and actuated by movement thereof to provide counter-balancing gas pressure. In one form of the invention, the counter-balancing gas pressure is stored in a hollow skid assembly.
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paper_title: A magnetoelastic bioaffinity-based sensor for avidin.

paper_content:

Abstract A magnetoelastic bioaffinity sensor coupled with biocatalytic precipitation is described for avidin detection. The non-specific adsorption characteristics of streptavidin on different functionalized sensor surfaces are examined. It is found that a biotinylated poly(ethylene glycol) (PEG) interface can effectively block non-specific adsorption of proteins. Coupled with the PEG immobilized sensor surface, alkaline phosphatase (AP) labeled streptavidin is used to track specific binding on the sensor. This mass-change-based signal is amplified by the accumulation on the sensor of insoluble products of 5-bromo-4-chloro-3-indolyl phosphate catalyzed by AP. The resulting mass loading on the sensor surface in turn shifts the resonance frequency of the magnetoelastic sensors, with an avidin detection limit of approximately 200 ng/ml.
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paper_title: Elastic modulus measurement of thin films coated onto magnetoelastic ribbons

paper_content:

A model is presented to describe the change of the resonant frequency of a magnetoelastic sensor when the sensor is coated with a material of given elasticity. With a mass load coated on the surface of the sensor, its characteristic resonant frequency changes depending on the ratio of the sound velocities in the sensor and the coating. A measurement technique is derived that allows the determination of Young's modulus of elasticity of thin film coatings, with thickness greater than approximately 75 nm, based on the measurement of mass and resonant frequency of a sensor before and after coating. Comparing the measurement to the model delivers the value of Young's modulus of elasticity for a coating of known density.
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paper_title: Remote query measurement of pressure, fluid-flow velocity, and humidity using magnetoelastic thick-film sensors

paper_content:

Abstract Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al 2 O 3 that reversibly changes mass in response to humidity.
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paper_title: Simultaneous measurement of liquid density and viscosity using remote query magnetoelastic sensors

paper_content:

Earlier work [C. A. Grimes et al., Smart Mater. Struct. 8, 639, (1999)] has shown that upon immersion in liquid the resonant frequency of a magnetoelasticsensor shifts linearly in response to the square root of the liquid density and viscosity product. It is shown that comparison between a pair of magnetoelasticsensors with different degrees of surface roughness can be used to simultaneously determine the liquid density and viscosity.
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paper_title: Magnetoacoustic remote query temperature and humidity sensors

paper_content:

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al2O3 ceramic thin film, the in situ measurement of humidity levels.
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paper_title: A staphylococcal enterotoxin B magnetoelastic immunosensor.

paper_content:

A magnetoelastic immunosensor for detection of staphylococcal enterotoxin B (SEB) is described. The magnetoelastic sensor is a newly developed mass/elasticity-based transducer of high sensitivity having a material cost of approximately $0.001/sensor. Affinity-purified rabbit anti-SEB antibody was covalently immobilized on magnetoelastic sensors, of dimensions 6 mm x 2 mm x 28 microm. The affinity reaction of biotin-avidin and biocatalytic precipitation are used to amplify antigen-antibody binding events on the sensor surface. Horseradish peroxidase (HRP) and alkaline phosphatase were examined as the labeled enzymes to induce biocatalytic precipitation. The alkaline phosphatase substrate, 5-bromo-4-chloro-3-indolyl phosphate (BCIP) produces a dimer, which binds tightly to the sensor surface, inducing a change in sensor resonance frequency. The biosensor demonstrates a linear shift in resonance frequency with staphylococcal enterotoxin B concentration between 0.5 and 5 ng/ml, with a detection limit of 0.5 ng/ml.
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paper_title: A wireless magnetoelastic micro-sensor array for simultaneous measurement of temperature and pressure

paper_content:

Magnetoelastic thick film sensors mechanically deform when subjected to a magnetic field impulse, launching elastic waves within the sensor the magnitude of which is greatest at the mechanical resonant frequency. As the sensors are magnetostrictive, the mechanical deformations launch magnetic flux that can be detected remotely. The characteristic resonant frequency of a magnetoelastic sensor, which is a function of the length, density, elasticity and Poisson's ratio of the sensor material, changes in response to temperature, pressure, ambient flow rate and, in combination with a mass changing, chemically responsive layer different analyte concentrations. By using an array of such sensors different environmental parameters can be simultaneously determined in a complex environment; we have designed and fabricated such an array for the simultaneous measurement of temperature and pressure.
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paper_title: A wireless, remote query ammonia sensor.

paper_content:

Abstract This paper presents a wireless, remote query ammonia sensor comprised of a free-standing magnetoelastic thick-film coated with a polymer, poly(acrylic acid-co-isooctylacrylate), that changes mass in response to atmospheric ammonia concentration. The mass of the polymer layer modulates the resonant frequency the ferromagnetic magnetoelastic substrate, hence by monitoring the frequency response of the sensor, atmospheric NH 3 concentration can be determined remotely, without the need for physical connections to the sensor or specific alignment requirements. The effect of copolymer composition, polymer film thickness, and relative humidity level (RH) on the sensitivity of the sensor were investigated. The sensor linearly tracks ammonia concentration below 0.8 vol.%, and tracks higher concentrations logarithmically; within the linear calibration range, a 0.02 vol.% change in NH 3 concentration can be detected.
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paper_title: Design and application of a wireless, passive, resonant-circuit environmental monitoring sensor

paper_content:

Abstract A wireless, passive, remote query sensor platform is presented capable of monitoring the complex permittivity of a surrounding medium, temperature, humidity, and pressure. The sensor is a planar two-dimensional inductor–capacitor circuit, of scaleable-size, that resonates at a characteristic frequency the value of which is dependent upon the parameters of interest. The resonant frequency of the sensor is detected remotely with one or a pair of loop antennas by measuring the impedance or voltage spectrum of the antenna(s), with the environmental parameters of interest then calculated from the measured resonant frequency. The wireless, remote query nature of the platform enables the LC sensor to monitor the environmental conditions from within sealed opaque containers. The paper describes the operational principles, design criteria, illustrative applications, and performance limitations of the sensor platform.
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paper_title: A remote query magnetostrictive viscosity sensor.

paper_content:

Magnetically soft, magnetostrictive metallic glass ribbons are used as in-situ remote query viscosity sensors. When immersed in a liquid, changes in the resonant frequency of the ribbon-like sensors are shown to correlate with the square root of the liquid viscosity and density product. An elastic wave model is presented that describes the sensor response as a function of the frictional forces acting upon the sensor surface.
---
paper_title: Measurement of temperature and liquid viscosity using wireless magneto-acoustic/magneto-optical sensors

paper_content:

Remote query magneto-acoustic and magneto-optical sensors are used to measure liquid temperature, viscosity and density. Sensors comprising magnetoelastic Metglas(R) 2826MB thick-films, alloy composition Fe/sub 40/Ni/sub 38/Mo/sub 4/B/sub 18/, oscillate in response to an externally applied, time-varying magnetic field. The sensor oscillations are strongest at the characteristic mechanical resonant frequency of the sensor. Depending upon the physical geometry and surface roughness of the magnetoelastic films, the mechanical sensor-vibrations launch an acoustic wave that can be detected remotely using a hydrophone or microphone. Furthermore, the sensor oscillations act to modulate the intensity of a laser beam reflected from the sensor surface. The sensor vibrations were optically monitored using a photo detector placed in the path of a laser beam back-scattered off the sensor ribbon. Using a Fast Fourier Transform, the signal obtained in the time-domain from acoustical or optical detectors is converted into the frequency-domain from which the resonant frequency of the sensor is determined. The resonant frequency shifts linearly with temperature and, when immersed in a liquid, with the frictional damping forces associated with liquid viscosity and density, thus allowing a remote measurement of temperature and liquid viscosity.
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paper_title: Correction for longitudinal mode vibration in thin slender beams

paper_content:

This letter reports on a correction to the theoretical prediction of longitudinal mode vibration in thin, slender beams. Thin magnetostrictive strips were fashioned from Metglas™ and subjected to a modulated magnetic field to determine resonant frequency and acoustic wave propagation speed. The results indicated that current analytical solutions were not adequate to predict behavior. Numerical simulations were performed that adjusted Poisson’s ratio until the acoustic wave speed matched that measured in the experiments. The results indicated that the current equations, formulated using the plane-strain modulus, should be modified by using the plane-stress or biaxial modulus.
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paper_title: Remote query measurement of pressure, fluid-flow velocity, and humidity using magnetoelastic thick-film sensors

paper_content:

Abstract Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al 2 O 3 that reversibly changes mass in response to humidity.
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paper_title: Simultaneous measurement of liquid density and viscosity using remote query magnetoelastic sensors

paper_content:

Earlier work [C. A. Grimes et al., Smart Mater. Struct. 8, 639, (1999)] has shown that upon immersion in liquid the resonant frequency of a magnetoelasticsensor shifts linearly in response to the square root of the liquid density and viscosity product. It is shown that comparison between a pair of magnetoelasticsensors with different degrees of surface roughness can be used to simultaneously determine the liquid density and viscosity.
---
paper_title: Magnetoacoustic remote query temperature and humidity sensors

paper_content:

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al2O3 ceramic thin film, the in situ measurement of humidity levels.
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paper_title: Magnetomechanical damping in amorphous ribbons with uniaxial anisotropy

paper_content:

We have investigated the magnetomechanical damping and the resonant amplitude of the longitudinal vibrations of amorphous ribbons with a uniaxial anisotropy induced transverse to the ribbon axis by magnetic field annealing. The damping and herewith the resonant amplitude are governed by eddy current losses. Yet, classical eddy current theory fails to describe the experimental results, in particular, when the sample is biased by a constant magnetic field. This failure ultimately originates in the commonly used assumption of an isotropic permeability tensor. This is not true in uniaxial ferromagnets where magnetization changes by rotation. Thus, within a domain, a change of magnetization along the ribbon axis is inevitably accompanied by a change of magnetization transverse to the ribbon axis. The latter produces excess eddy current losses which become increasingly important the more the equilibrium position of the magnetization vector is declined towards the ribbon axis by the bias field. Taking this into account, a straight forward calculation ends up in analytic expressions capable to describe correctly the experimental findings starting from the basic material parameters.
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paper_title: A wireless magnetoelastic micro-sensor array for simultaneous measurement of temperature and pressure

paper_content:

Magnetoelastic thick film sensors mechanically deform when subjected to a magnetic field impulse, launching elastic waves within the sensor the magnitude of which is greatest at the mechanical resonant frequency. As the sensors are magnetostrictive, the mechanical deformations launch magnetic flux that can be detected remotely. The characteristic resonant frequency of a magnetoelastic sensor, which is a function of the length, density, elasticity and Poisson's ratio of the sensor material, changes in response to temperature, pressure, ambient flow rate and, in combination with a mass changing, chemically responsive layer different analyte concentrations. By using an array of such sensors different environmental parameters can be simultaneously determined in a complex environment; we have designed and fabricated such an array for the simultaneous measurement of temperature and pressure.
---
paper_title: Design and application of a wireless, passive, resonant-circuit environmental monitoring sensor

paper_content:

Abstract A wireless, passive, remote query sensor platform is presented capable of monitoring the complex permittivity of a surrounding medium, temperature, humidity, and pressure. The sensor is a planar two-dimensional inductor–capacitor circuit, of scaleable-size, that resonates at a characteristic frequency the value of which is dependent upon the parameters of interest. The resonant frequency of the sensor is detected remotely with one or a pair of loop antennas by measuring the impedance or voltage spectrum of the antenna(s), with the environmental parameters of interest then calculated from the measured resonant frequency. The wireless, remote query nature of the platform enables the LC sensor to monitor the environmental conditions from within sealed opaque containers. The paper describes the operational principles, design criteria, illustrative applications, and performance limitations of the sensor platform.
---
paper_title: Characterization of nano-dimensional thin-film elastic moduli using magnetoelastic sensors

paper_content:

Abstract Application of magnetoelastic thick-film sensors to the measurement of thin-film elastic moduli is described in this study. An analytical model is derived, that relates the resonant frequency of a magnetoelastic sensor to the elasticity and density of an applied thin-film. Limits of the model are analyzed, and related to experimental measurements using thin-films of silver and aluminum. For 500 nm thick-films, the measured Young’s modulus of elasticity for Al and Ag is found to be within 1.6% of standard data. Using commercially available magnetoelastic sensors, the elasticity of coatings, approximately 30 nm thick, can readily be measured.
---
paper_title: Theory of elasticity

paper_content:

A walking beam pumping unit is provided for pumping liquid from wells having gas pressure therein. The unit is driven by gas pressure from the well reciprocating the piston of a pneumatic cylinder up and down to swing the walking beam correspondingly and pump the liquid from the well. Gas under pressure is directed from the wellhead through a two-way valve to the opposite ends of the hydraulic cylinder in alternating fashion, so the piston has power strokes in opposite directions. Each power stroke, besides moving the walking beam, serves to recompress the gas used for the preceding power stroke sufficiently to inject it into the sales line. The setting of the two-way valve is controlled by a pneumatic actuator supplied with gas under pressure from the wellhead and having a thimble valve responsive to the up and down movement of the walking beam by means of adjustable stops carried thereon. The horsehead is counter-balanced by weights or by a pneumatic cylinder attached to the horsehead and actuated by movement thereof to provide counter-balancing gas pressure. In one form of the invention, the counter-balancing gas pressure is stored in a hollow skid assembly.
---
paper_title: Elastic modulus measurement of thin films coated onto magnetoelastic ribbons

paper_content:

A model is presented to describe the change of the resonant frequency of a magnetoelastic sensor when the sensor is coated with a material of given elasticity. With a mass load coated on the surface of the sensor, its characteristic resonant frequency changes depending on the ratio of the sound velocities in the sensor and the coating. A measurement technique is derived that allows the determination of Young's modulus of elasticity of thin film coatings, with thickness greater than approximately 75 nm, based on the measurement of mass and resonant frequency of a sensor before and after coating. Comparing the measurement to the model delivers the value of Young's modulus of elasticity for a coating of known density.
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paper_title: Characterization of nano-dimensional thin-film elastic moduli using magnetoelastic sensors

paper_content:

Abstract Application of magnetoelastic thick-film sensors to the measurement of thin-film elastic moduli is described in this study. An analytical model is derived, that relates the resonant frequency of a magnetoelastic sensor to the elasticity and density of an applied thin-film. Limits of the model are analyzed, and related to experimental measurements using thin-films of silver and aluminum. For 500 nm thick-films, the measured Young’s modulus of elasticity for Al and Ag is found to be within 1.6% of standard data. Using commercially available magnetoelastic sensors, the elasticity of coatings, approximately 30 nm thick, can readily be measured.
---
paper_title: Monitoring blood coagulation with magnetoelastic sensors.

paper_content:

The determination of blood coagulation time is an essential part of monitoring therapeutic anticoagulants. Standard methodologies for the measurement of blood clotting time require dedicated personnel and involve blood sampling procedures. A new method based on magnetoelastic sensors has been employed for the monitoring of blood coagulation. The ribbon-like magnetoelastic sensor oscillates at a fundamental frequency, which shifts linearly in response to applied mass loads or a fixed mass load of changing elasticity. The magnetoelastic sensors emit magnetic flux, which can be detected by a remotely located pick-up coil, so that no direct physical connections are required. During blood coagulation, the viscosity of blood changes due to the formation of a soft fibrin clot. In turn, this change in viscosity shifts the characteristic resonance frequency of the magnetoelastic sensor enabling real-time continuous monitoring of this biological event. By monitoring the signal output as a function of time, a distinct blood clotting profile can be seen. The relatively low cost of the magnetoelastic ribbons enables their use as disposable sensors. This, along with the reduced volume of blood required, make the magnetoelastic sensors well suited for at-home and point-of-care testing devices.
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paper_title: Time domain characterization of oscillating sensors: Application of frequency counting to resonance frequency determination

paper_content:

A frequency counting technique is described for determining the resonance frequency of a transiently excited sensor; the technique is applicable to any sensor platform where the characteristic resonance frequency is the parameter of interest. The sensor is interrogated by a pulse-like excitation signal, and the resonance frequency of the sensor subsequently determined by counting the number of oscillations per time during sensor ring-down. A repetitive time domain interrogation technique is implemented to overcome the effects of sensor damping, such as that associated with mass loading, which reduces the duration of the sensor ring-down and hence the measurement resolution. The microcontroller based, transient frequency counting technique is detailed with application to the monitoring of magnetoelastic sensors [C. A. Grimes, D. Kouzoudis, and C. Mungle, Rev. Sci. Instrum. 71, 3822 (2000)], with a measurement resolution of 0.001% achieved in approximately 40 ms.
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paper_title: Frequency-domain characterization of magnetoelastic sensors: a microcontroller-based instrument for spectrum analysis using a threshold-crossing counting technique

paper_content:

This work presents a novel instrumentation technique for frequency-domain characterization of magnetoelastic sensors. By applying threshold-crossing counting to the transient response of a magnetoelastic sensor excited by sinusoidal pulses, frequency-domain analysis is accomplished without the necessity of using lock-in amplifier or FFT facilities as required in the conventional instrumentation techniques. The threshold-crossing counting technique is discussed and its electronic implementation described. The resulting compact and cost-effective microcontroller-based instrument is capable of frequency-domain analysis, and time-domain analysis including frequency counting and determination of the damping ratio.
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paper_title: A wireless micro-sensor for simultaneous measurement of pH, temperature, and pressure

paper_content:

In response to a magnetic field impulse, magnetostrictive magnetoelastic sensors mechanically vibrate. These vibrations can be detected in several ways: optically from the amplitude modulation of a reflected laser beam, acoustically using a microphone or hydrophone, and by using a pickup coil to detect the magnetic flux emitted from the sensor. Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts in response to different environmental parameters, including temperature, pressure, fluid flow velocity and mass loading, with each parameter determined in an otherwise constant environment. To extend the utility of the sensor technology in this work we report on the fabrication and application of a miniaturized array of four magnetoelastic sensors that enable the simultaneous remote query measurement of pH, temperature, and pressure from a passive, wireless platform.
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paper_title: Magnetic field tuning of the frequency–temperature response of a magnetoelastic sensor

paper_content:

Abstract Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts linearly in response to temperature [Sens. Actuat. A 84 (2000) 205]. In this work it is shown that over the temperature range examined, 20–60 °C, the temperature–frequency response is dependent upon the magnitude of an applied DC magnetic biasing field, and can be switched from negative, through zero, to positive. Experimental results are compared with a theoretical model that describes the effects of temperature and applied DC magnetic field on both the mechanical and magnetoelastic properties of the sensor material.
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paper_title: The frequency response of magnetoelastic sensors to stress and atmospheric pressure

paper_content:

Earlier work demonstrated that the characteristic resonant frequency of magnetoelastic thick-film sensors shifts linearly downwards in response to increasing atmospheric pressure. In this paper, the response mechanism is detailed and shown to be a function of both pressure and the way that the sensor is mechanically stressed. Stressing the sensor, in either the elastic or plastic regime, induces out-of-plane vibrations that act as a pressure-dependent damping force to the longitudinal sensor oscillations excited by the interrogation field. This damping force, in turn, acts to shift the resonant frequency of the magnetoelastic sensor lower in response to increasing pressure.
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paper_title: Remote query pressure measurement using magnetoelastic sensors

paper_content:

Two magnetostriction-based methods for measuring atmospheric pressure are presented. Each technique correlates changes in pressure with the characteristic resonant frequency of a magnetoelastic magnetostrictive thick-film sensor. In each case the sensor is monitored remotely, using an adjacently located pickup coil, without the use of physical connections to the sensor.
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paper_title: Magnetoelastic sensors in combination with nanometer-scale honeycombed thin film ceramic TiO2 for remote query measurement of humidity.

paper_content:

Ribbonlike magnetoelastic sensors can be considered the magnetic analog of an acoustic bell; in response to an externally applied magnetic field impulse the sensors emit magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected external to the test area using a pick-up coil, enabling query remote monitoring of the sensor. The characteristic resonant frequency of a magnetoelastic sensor changes in response to mass loads. [L.D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986). p. 100].Therefore, remote query chemical sensors can be fabricated by combining the magnetoelastic sensors with a mass changing, chemically responsive layer. In this work magnetoelastic sensors are coated with humidity-sensitive thin films of ceramic, nanodimensionally porous TiO2 to make remote query humidity sensors.
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paper_title: Higher-order harmonics of a magnetically soft sensor: Application to remote query temperature measurement

paper_content:

This letter describes the application of magnetically soft ribbons for remote query temperature monitoring based upon amplitude changes in the higher-order harmonics emitted by the sensor in response to a magnetic interrogation signal. The harmonic-based temperature sensor is placed, or rigidly embedded since there are no moving parts, within the region of interest where it is remotely monitored using a single interrogation and detection coil. Taking the amplitude ratio between two or more different-order harmonics eliminates the effect of relative orientation between the sensor and monitoring coil, enabling wide-area monitoring. Remote query monitoring of temperature from within a concrete block is demonstrated. The wireless and passive nature of the described sensor platform makes it ideally suited for long-term monitoring applications, such as measuring the temperature inside a concrete roadway or building structure.
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paper_title: A wireless micro-sensor for simultaneous measurement of pH, temperature, and pressure

paper_content:

In response to a magnetic field impulse, magnetostrictive magnetoelastic sensors mechanically vibrate. These vibrations can be detected in several ways: optically from the amplitude modulation of a reflected laser beam, acoustically using a microphone or hydrophone, and by using a pickup coil to detect the magnetic flux emitted from the sensor. Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts in response to different environmental parameters, including temperature, pressure, fluid flow velocity and mass loading, with each parameter determined in an otherwise constant environment. To extend the utility of the sensor technology in this work we report on the fabrication and application of a miniaturized array of four magnetoelastic sensors that enable the simultaneous remote query measurement of pH, temperature, and pressure from a passive, wireless platform.
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paper_title: Measurement of temperature and liquid viscosity using wireless magneto-acoustic/magneto-optical sensors

paper_content:

Remote query magneto-acoustic and magneto-optical sensors are used to measure liquid temperature, viscosity and density. Sensors comprising magnetoelastic Metglas(R) 2826MB thick-films, alloy composition Fe/sub 40/Ni/sub 38/Mo/sub 4/B/sub 18/, oscillate in response to an externally applied, time-varying magnetic field. The sensor oscillations are strongest at the characteristic mechanical resonant frequency of the sensor. Depending upon the physical geometry and surface roughness of the magnetoelastic films, the mechanical sensor-vibrations launch an acoustic wave that can be detected remotely using a hydrophone or microphone. Furthermore, the sensor oscillations act to modulate the intensity of a laser beam reflected from the sensor surface. The sensor vibrations were optically monitored using a photo detector placed in the path of a laser beam back-scattered off the sensor ribbon. Using a Fast Fourier Transform, the signal obtained in the time-domain from acoustical or optical detectors is converted into the frequency-domain from which the resonant frequency of the sensor is determined. The resonant frequency shifts linearly with temperature and, when immersed in a liquid, with the frictional damping forces associated with liquid viscosity and density, thus allowing a remote measurement of temperature and liquid viscosity.
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paper_title: Magnetoacoustic remote query temperature and humidity sensors

paper_content:

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al2O3 ceramic thin film, the in situ measurement of humidity levels.
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paper_title: A wireless magnetoelastic micro-sensor array for simultaneous measurement of temperature and pressure

paper_content:

Magnetoelastic thick film sensors mechanically deform when subjected to a magnetic field impulse, launching elastic waves within the sensor the magnitude of which is greatest at the mechanical resonant frequency. As the sensors are magnetostrictive, the mechanical deformations launch magnetic flux that can be detected remotely. The characteristic resonant frequency of a magnetoelastic sensor, which is a function of the length, density, elasticity and Poisson's ratio of the sensor material, changes in response to temperature, pressure, ambient flow rate and, in combination with a mass changing, chemically responsive layer different analyte concentrations. By using an array of such sensors different environmental parameters can be simultaneously determined in a complex environment; we have designed and fabricated such an array for the simultaneous measurement of temperature and pressure.
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paper_title: Magnetic field tuning of the frequency–temperature response of a magnetoelastic sensor

paper_content:

Abstract Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts linearly in response to temperature [Sens. Actuat. A 84 (2000) 205]. In this work it is shown that over the temperature range examined, 20–60 °C, the temperature–frequency response is dependent upon the magnitude of an applied DC magnetic biasing field, and can be switched from negative, through zero, to positive. Experimental results are compared with a theoretical model that describes the effects of temperature and applied DC magnetic field on both the mechanical and magnetoelastic properties of the sensor material.
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paper_title: Theory of elasticity

paper_content:

A walking beam pumping unit is provided for pumping liquid from wells having gas pressure therein. The unit is driven by gas pressure from the well reciprocating the piston of a pneumatic cylinder up and down to swing the walking beam correspondingly and pump the liquid from the well. Gas under pressure is directed from the wellhead through a two-way valve to the opposite ends of the hydraulic cylinder in alternating fashion, so the piston has power strokes in opposite directions. Each power stroke, besides moving the walking beam, serves to recompress the gas used for the preceding power stroke sufficiently to inject it into the sales line. The setting of the two-way valve is controlled by a pneumatic actuator supplied with gas under pressure from the wellhead and having a thimble valve responsive to the up and down movement of the walking beam by means of adjustable stops carried thereon. The horsehead is counter-balanced by weights or by a pneumatic cylinder attached to the horsehead and actuated by movement thereof to provide counter-balancing gas pressure. In one form of the invention, the counter-balancing gas pressure is stored in a hollow skid assembly.
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paper_title: Simultaneous measurement of liquid density and viscosity using remote query magnetoelastic sensors

paper_content:

Earlier work [C. A. Grimes et al., Smart Mater. Struct. 8, 639, (1999)] has shown that upon immersion in liquid the resonant frequency of a magnetoelasticsensor shifts linearly in response to the square root of the liquid density and viscosity product. It is shown that comparison between a pair of magnetoelasticsensors with different degrees of surface roughness can be used to simultaneously determine the liquid density and viscosity.
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paper_title: Characterization of nano-dimensional thin-film elastic moduli using magnetoelastic sensors

paper_content:

Abstract Application of magnetoelastic thick-film sensors to the measurement of thin-film elastic moduli is described in this study. An analytical model is derived, that relates the resonant frequency of a magnetoelastic sensor to the elasticity and density of an applied thin-film. Limits of the model are analyzed, and related to experimental measurements using thin-films of silver and aluminum. For 500 nm thick-films, the measured Young’s modulus of elasticity for Al and Ag is found to be within 1.6% of standard data. Using commercially available magnetoelastic sensors, the elasticity of coatings, approximately 30 nm thick, can readily be measured.
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paper_title: A remote query magnetoelastic pH sensor.

paper_content:

A remote query magnetoelastic pH sensor comprised of a magnetoelastic thick-film coated with a mass-changing pH-responsive polymer is described. In response to a magnetic query field the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the attached polymer layer. As the magnetoelastic sensor is magnetostrictive the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely from the sensor using a pickup coil. The pH responsive copolymer is synthesized from 20 mol% of acrylic acid and 80 mol% of iso-octyl acrylate and then deposited onto a magnetoelastic film by dip-coating. For a 1 micrometer polymer coating upon a 30 micrometer thick Metglas [The Metglas alloys are a registered trademark of Honeywell Corporation. For product information see: http://www.electronicmaterials.com:80/businesses/sem/amorph/page5_1_2.htm.] alloy 2826MB magnetoelastic film between pH 5 and 9 the change in resonant frequency is linear, approximately 285 Hz/pH or 0.6%/pH. The addition of 10 mmol/l of KCl to the test solution decreases the sensitivity of the polymer approximately 4%.
---
paper_title: Magnetoelastic sensors in combination with nanometer-scale honeycombed thin film ceramic TiO2 for remote query measurement of humidity.

paper_content:

Ribbonlike magnetoelastic sensors can be considered the magnetic analog of an acoustic bell; in response to an externally applied magnetic field impulse the sensors emit magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected external to the test area using a pick-up coil, enabling query remote monitoring of the sensor. The characteristic resonant frequency of a magnetoelastic sensor changes in response to mass loads. [L.D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986). p. 100].Therefore, remote query chemical sensors can be fabricated by combining the magnetoelastic sensors with a mass changing, chemically responsive layer. In this work magnetoelastic sensors are coated with humidity-sensitive thin films of ceramic, nanodimensionally porous TiO2 to make remote query humidity sensors.
---
paper_title: Magnetoacoustic remote query temperature and humidity sensors

paper_content:

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al2O3 ceramic thin film, the in situ measurement of humidity levels.
---
paper_title: A wireless, remote query ammonia sensor.

paper_content:

Abstract This paper presents a wireless, remote query ammonia sensor comprised of a free-standing magnetoelastic thick-film coated with a polymer, poly(acrylic acid-co-isooctylacrylate), that changes mass in response to atmospheric ammonia concentration. The mass of the polymer layer modulates the resonant frequency the ferromagnetic magnetoelastic substrate, hence by monitoring the frequency response of the sensor, atmospheric NH 3 concentration can be determined remotely, without the need for physical connections to the sensor or specific alignment requirements. The effect of copolymer composition, polymer film thickness, and relative humidity level (RH) on the sensitivity of the sensor were investigated. The sensor linearly tracks ammonia concentration below 0.8 vol.%, and tracks higher concentrations logarithmically; within the linear calibration range, a 0.02 vol.% change in NH 3 concentration can be detected.
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paper_title: Ethylene Detection Using Nanoporous PtTiO2 Coatings Applied to Magnetoelastic Thick Films

paper_content:

This paper reports on the use of nanoporous Pt-TiO2 thin films coated onto magnetoelastic sensors for the detection of ethylene, an important plant growth hormone. Five different metal oxide coatings, TiO2, TiO2+ZrO2, TiO2+TTCN(1,4,7-Trithiacyclononane)+Ag, SiO2+Fe, and TiO2+Pt, each having demonstrated photocatalytic activity in response to ethylene, were investigated for their ability to change mass or elasticity in response to changing ethylene concentration. Pt-TiO2 films were found to possess the highest sensitivities, and coupled with the magnetoelastic sensor platform capable of sensing ethylene levels of < 1 ppm.
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paper_title: A remote query magnetoelastic pH sensor.

paper_content:

A remote query magnetoelastic pH sensor comprised of a magnetoelastic thick-film coated with a mass-changing pH-responsive polymer is described. In response to a magnetic query field the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the attached polymer layer. As the magnetoelastic sensor is magnetostrictive the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely from the sensor using a pickup coil. The pH responsive copolymer is synthesized from 20 mol% of acrylic acid and 80 mol% of iso-octyl acrylate and then deposited onto a magnetoelastic film by dip-coating. For a 1 micrometer polymer coating upon a 30 micrometer thick Metglas [The Metglas alloys are a registered trademark of Honeywell Corporation. For product information see: http://www.electronicmaterials.com:80/businesses/sem/amorph/page5_1_2.htm.] alloy 2826MB magnetoelastic film between pH 5 and 9 the change in resonant frequency is linear, approximately 285 Hz/pH or 0.6%/pH. The addition of 10 mmol/l of KCl to the test solution decreases the sensitivity of the polymer approximately 4%.
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paper_title: A wireless pH sensor based on the use of salt-independent micro-scale polymer spheres

paper_content:

Abstract Poly(vinylbenzylchloride-co-2,4,5-trichlorophenyl acrylate) (VBC-TCPA) spheres, approximately 725 nm in diameter, were prepared by dispersion polymerization then derivatized with diethanolamine to realize a mass changing pH-responsive polymer. While the pH-responsive polymer spheres are suitable for use with any mass-sensitive sensor platform, in this work, the polymer spheres are combined with magnetoelastic thick films to achieve a remote query pH sensor. The magnetoelastic pH sensors were fabricated by spin-coating the aminated polymer spheres onto the surface of a magnetoelastic ribbon. The pH response of these sensors was examined by monitoring changes in sensor resonance frequency as a function of test-solution pH. The sensors demonstrate a linear pH response from pH 3.0 to 9.0, with a change in resonance frequency f r of 0.2% f r per pH for a 1.5-μm thick polymer layer. Measurements were virtually independent of background potassium chloride concentration.
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paper_title: A wireless micro-sensor for simultaneous measurement of pH, temperature, and pressure

paper_content:

In response to a magnetic field impulse, magnetostrictive magnetoelastic sensors mechanically vibrate. These vibrations can be detected in several ways: optically from the amplitude modulation of a reflected laser beam, acoustically using a microphone or hydrophone, and by using a pickup coil to detect the magnetic flux emitted from the sensor. Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts in response to different environmental parameters, including temperature, pressure, fluid flow velocity and mass loading, with each parameter determined in an otherwise constant environment. To extend the utility of the sensor technology in this work we report on the fabrication and application of a miniaturized array of four magnetoelastic sensors that enable the simultaneous remote query measurement of pH, temperature, and pressure from a passive, wireless platform.
---
paper_title: A wireless pH sensor using magnetoelasticity for measurement of body fluid acidity.

paper_content:

The determination of body fluid acidity using a wireless magnetoelastic pH-sensitive sensor is described. The sensor was fabricated by casting a layer of pH-sensitive polymer on a magnetoelastic ribbon. In response to an externally applied time-varying magnetic field, the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the pH polymer film, which varies as the film swells and shrinks in response to pH. As the magnetoelastic sensor is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely using a pickup coil. The sensor can be used for direct measurements of body fluid acidity without a pretreatment of the sample by using a filtration membrane. A reversible and linear response was obtained between pH 5.0 and 8.0 with a measurement resolution of pH 0.1 and a slope of 0.2 kHz pH(-1). Since there are no physical connections between the sensor and the instrument, the sensor can be applied to in vivo and in situ monitoring of the physiological pH and its fluctuations.
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paper_title: A wireless and sensitive sensing detection of polycyclic aromatic hydrocarbons using humic acid-coated magnetic Fe3O4 nanoparticles as signal-amplifying tags

paper_content:

Abstract A wireless magnetoelastic-sensing device for the detection of polycyclic aromatic hydrocarbons (PAHs) with anthracene as the model target is reported using humic acid-modified magnetic Fe 3 O 4 nanoparticles (HMNPs) as signal-amplifying tags. A sandwich-type detection strategy involves the humic acid (HA)/chitosan composite self-assembled on the polyurethane-protected sensor surface and HMNPs, both of which flank the anthracene target in sequence. As the HMNPs-combined anthracene absorbs to the sensor surface, there is an increase in the mass load on the sensor, and consequently a decrease in resonance frequency. Under optimal conditions, the sensor shows a linear response to polycyclic aromatic hydrocarbons with sensitivity depending on the benzene rings. The sensor shows the largest sensitivity to benzo[ a ]pyrene due to its 5 ring with a detection limit of 3 nM. Tap water, river water and spring water were analyzed with this sensor.
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paper_title: Magnetoelastic Immunosensors: Amplified Mass Immunosorbent Assay for Detection of Escherichia coli O157:H7

paper_content:

A mass-sensitive magnetoelastic immunosensor for detection of Escherichia coli O157:H7 is described, based on immobilization of affinity-purified antibodies attached to the surface of a micrometer-scale magnetoelastic cantilever. Alkaline phosphatase is used as a labeled enzyme to the anti-E. coli O157:H7 antibody, amplifying the mass change associated with the antibody−antigen binding reaction by biocatalytic precipitation of 5-bromo-4-chloro-3-indolyl phosphate in a pH 10.0 PBS solution. The detection limit of the biosensor is 102 E. coli O157:H7 cells/mL. A linear change in the resonance frequency of the biosensor was found to E. coli O157:H7 concentrations ranging from 102 to 106 cells/mL.
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paper_title: A wireless magnetoelastic biosensor for rapid detection of glucose concentrations in urine samples

paper_content:

Abstract A wireless magnetoelastic glucose biosensor is fabricated by co-immobilizing glucose oxidase (GOx) and catalase onto a pH-sensitive-polymer-coated magnetoelastic sensor with chitosan as a supporting substrate. The GOx-catalyzed hydrolyzation of glucose produces gluconic acid, resulting in shrinking and corresponding mass decrease in the pH-responsive polymer, and consequently the resonance frequency of the magnetoelastic sensor increasing. The glucose biosensor is applied to measurement of glucose concentrations within urine samples; the shift in resonance frequency is found proportional to the glucose concentration, with a linear response obtained between 1 mM and 15 mM. The presence of acetaminophen, lactose, saccharose and galactose do not significantly interfere with glucose detection; ascorbic acid does, as expected, however its effect can be eliminated through cross-correlation with a pH-responsive magnetoelastic reference sensor or by pre-adjusting the sample to pH 7.0. A L 9 (3 4 ) orthogonal array based on the Taguchi method is used to optimize the sensor fabrication process and to determine the key factors that affect sensor performance. Assays of 15 clinical urine samples give glucose levels that are in accordance with the results by an urine analyzer, showing the proposed sensor can be applied for glucose assay in urine.
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paper_title: Determination of glucose using bienzyme layered assembly magnetoelastic sensing device

paper_content:

Abstract A bienzyme layered assembly on magnetoelastic sensor, consisting of horseradish peroxidase and glucose oxidase is used to sense glucose by the horseradish peroxidase-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine, by H 2 O 2 , and the formation of the insoluble product on the sensor surface. A horseradish peroxidase is used to analyze hydrogen peroxide (H 2 O 2 ) via the biocatalyzed oxidation of tetramethylbenzidine and the precipitation of the insoluble product. The glucose oxidase catalyzed oxidation of glucose produces gluconic acid and H 2 O 2 , and the generated H 2 O 2 effects the formation of the insoluble product in the presence of horseradish peroxidase. The insoluble product accumulated on the sensor surface resulting in shifts of the sensor resonance frequency which are correlated with the amount of H 2 O 2 or glucose. The biosensor response is linear in the range of glucose concentrations of 5–50 mM, with a detection limit of 2 mM at a noise level of ∼10 Hz. The biosensor is applied to determine glucose concentration in urine sample.
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paper_title: A wireless, remote query glucose biosensor based on a pH-sensitive polymer

paper_content:

This paper describes a wireless, remote query glucose biosensor using a ribbonlike, mass-sensitive magnetoelastic sensor as the transducer. The glucose biosensor is fabricated by first coating the magnetoelastic sensor with a pH-sensitive polymer and upon it a layer of glucose oxidase (GOx). The pH-responsive polymer swells or shrinks, thereby changing mass, respectively, in response to increasing or decreasing pH values. The GOx-catalyzed oxidation of glucose produces gluconic acid, inducing the pH-responsive polymer to shrink, which in turn decreases the polymer mass. In response to a time-varying magnetic field, a magnetoelastic sensor mechanically vibrates at a characteristic resonance frequency, the value of which inversely depends on sensor mass loading. As the magnetoelastic films are magnetostrictive, the vibrations launch magnetic flux that can be remotely detected using a pickup coil. Hence, changes in the resonance frequency of a passive magnetoelastic transducer are detected on a remote query ...
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paper_title: Measurement of Glucose Concentration in Blood Plasma Based on a Wireless Magnetoelastic Biosensor

paper_content:

Abstract A wireless magnetoelastic glucose biosensor in blood plasma is described, based on using a mass sensitive magnetoelastic sensor as transducer. The glucose biosensor was fabricated by coating the ribbon‐like, magnetoelastic sensor with a pH sensitive polymer and a biolayer of glucose oxidase (GOx) and catalase. The pH response polymer swells or shrinks, thereby changing sensor mass loading, respectively, in response to increase or decrease of pH values. The GOx–catalyzed oxidation of the glucose in blood plasma produces gluconic acid, resulting in the pH sensitive polymer shrinking, which in turn decreases the sensor mass loading. The results show that the proposed magnetoelastic glucose biosensor can be successfully applied to determine the concentration of glucose in blood plasma. At glucose concentration range of 2.5–20.0 mmol/l, the biosensor responses are reversible and linear, with a detection limit of 1.2 mmol/l. Since no physical connections between the sensor and the monitoring instrument...
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paper_title: A magnetoelastic bioaffinity-based sensor for avidin.

paper_content:

Abstract A magnetoelastic bioaffinity sensor coupled with biocatalytic precipitation is described for avidin detection. The non-specific adsorption characteristics of streptavidin on different functionalized sensor surfaces are examined. It is found that a biotinylated poly(ethylene glycol) (PEG) interface can effectively block non-specific adsorption of proteins. Coupled with the PEG immobilized sensor surface, alkaline phosphatase (AP) labeled streptavidin is used to track specific binding on the sensor. This mass-change-based signal is amplified by the accumulation on the sensor of insoluble products of 5-bromo-4-chloro-3-indolyl phosphate catalyzed by AP. The resulting mass loading on the sensor surface in turn shifts the resonance frequency of the magnetoelastic sensors, with an avidin detection limit of approximately 200 ng/ml.
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paper_title: A wireless magnetoelastic biosensor for convenient and sensitive detection of acid phosphatase

paper_content:

This paper describes a wireless and low-cost biosensor for the sensitive detection of acid phosphatase (ACP) using a thick-film magnetoelastic transducer. In response to an externally applied time-varying magnetic field, the magnetoelastic ribbon-like sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the attached film. As the ribbon material is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux as a return signal that can be detected remotely using a pickup coil. The measurement is based on the enzymatic hydrolysis of 5-bromo-4-chloro-3-indolyl phosphate (BCIP), producing a dimer which binds tightly to the sensor surface, resulting in a change in the sensor resonance frequency. The biosensor demonstrates a linear shift in resonance frequency with ACP concentration ranging from 1.5 to 15 U/l, with a detection limit of 1.5 U/l at a noise level of ∼20 Hz. The sensitivity achieved is comparable to spectrometry and surface acoustic wave sensors. The effect of substrate concentration and BSA immobilization are detailed.
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paper_title: A wireless magnetoelastic-sensing device for in situ evaluation of Pseudomonas aeruginosa biofilm formation

paper_content:

A wireless, passive magnetoelastic-sensing device is presented for the in situ, continuous, and real-time evaluation of the formation of Pseudomonas aeruginosa biofilms. The sensor, a polyurethane-coated magnetostrictive ribbon, is placed in a flowing system, and both the resonance frequency and amplitude of the sensor are wirelessly monitored through magnetic field telemetry. The sensor platform appears to be of great utility for the in situ evaluation of biofilms formation.
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paper_title: The detection of Mycobacterium tuberculosis in sputum sample based on a wireless magnetoelastic-sensing device.

paper_content:

This paper presents a real-time detection of Mycobacterium tuberculosis (M. TB) using a wireless magnetoelastic sensor. The sensor is fabricated by coating a magnetoelastic ribbon (Metglas 2826MB) with a polyurethane protecting film. M. TB consumes the nutrients of a liquid culture medium in growing and reproducing process, which results in properties changes (viscosity, density, elasticity, ion concentration, etc.) of the culture medium, and consequently changes in the resonance frequency of the magnetoelastic sensor. Using the described technique M. TB is quantified and sensor response is proportional to logarithmic values of the M. TB concentration from 10(4) to 10(9)cells ml(-1), with a detection limit of 10(4)cells ml(-1) at a noise level of approximately 10 Hz. The sensor can be used effectively for monitoring the bacterial growth and good results were obtained when used in sputum sample. The drug-resistance of isoniazid (INH) and rifampin (RFP) on M. TB growth in culture medium was evaluated based on this proposed method. The wireless nature of the presented device facilitates the aseptic operations.
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paper_title: Quantification of multiple bioagents with wireless, remote-query magnetoelastic microsensors

paper_content:

This paper presents a micromagnetoelastic sensor array for simultaneously monitoring multiple biological agents. Magnetoelastic sensors, made of low-cost amorphous ferromagnetic ribbons, are analogous and complementary to piezoelectric acoustic wave sensors, which track parameters of interest via changes in resonance behavior. Magnetoelastic sensors are excited with magnetic ac fields, and, in turn, they generate magnetic fluxes that can be detected with a sensing coil from a distance. As a result, these sensors are highly attractive, not only due to their small size and low cost, but also because of their passive and wireless nature. Magnetoelastic sensors have been applied for monitoring pressure, temperature, liquid density, and viscosity, fluid How velocity and direction, and with chemical/biological responsive coatings that change mass or elasticity, various biological and chemical agents. In this paper, we report the fabrication and application of a six-sensor array for simultaneous measurement of Escherichia coli O157:H7, staphylococcal enterotoxin B, and ricin. In addition, the sensor array also monitors temperature and pH so the measurements are independent from these two parameters
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paper_title: A staphylococcal enterotoxin B magnetoelastic immunosensor.

paper_content:

A magnetoelastic immunosensor for detection of staphylococcal enterotoxin B (SEB) is described. The magnetoelastic sensor is a newly developed mass/elasticity-based transducer of high sensitivity having a material cost of approximately $0.001/sensor. Affinity-purified rabbit anti-SEB antibody was covalently immobilized on magnetoelastic sensors, of dimensions 6 mm x 2 mm x 28 microm. The affinity reaction of biotin-avidin and biocatalytic precipitation are used to amplify antigen-antibody binding events on the sensor surface. Horseradish peroxidase (HRP) and alkaline phosphatase were examined as the labeled enzymes to induce biocatalytic precipitation. The alkaline phosphatase substrate, 5-bromo-4-chloro-3-indolyl phosphate (BCIP) produces a dimer, which binds tightly to the sensor surface, inducing a change in sensor resonance frequency. The biosensor demonstrates a linear shift in resonance frequency with staphylococcal enterotoxin B concentration between 0.5 and 5 ng/ml, with a detection limit of 0.5 ng/ml.
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paper_title: A remote-query sensor for predictive indication of milk spoilage

paper_content:

Abstract Described is application of the remote-query (wireless, passive) magnetoelastic sensor platform for direct detection and monitoring of bacterium contamination of milk within hermetically sealed containers. Specific application is made to the quantification of Staphylococcus aureus ssp. anaerobius ( S. aureus ) concentrations in milk. S. aureus growth changes milk viscosity, in turn changing the resonance frequency of the liquid immersed sensor allowing S. aureus concentrations of 10 3 to 10 7 cells ml −1 to be directly quantified.
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paper_title: Eliminating unwanted nanobubbles from hydrophobic solid/liquid interfaces: a case study using magnetoelastic sensors.

paper_content:

Air bubbles are known to form at the liquid/solid interface of hydrophobic materials upon immersion in a liquid (Holmberg, M.; Kdühle, A.; Garnaes, J.; Mørch, K. A.; Boisen, A. Langmuir 2003, 19, 10510-10513). In the case of gravimetric sensors, air bubbles that randomly form at the liquid-solid interface result in poor sensor-to-sensor reproducibility. Herein a superhydrophilic ZnO nanorod film is applied to the originally hydrophobic surface of a resonance-based magnetoelastic sensor. The superhydrophilic coating results in the liquid completely spreading across the surface, removing unwanted air bubbles from the liquid/sensor interface. The resonance amplitude of uncoated (bare) and ZnO-modified sensors are measured in air and then when immersed in saline solution, ethylene glycol, or bovine blood. In comparison to the bare, hydrophobic sensors, we find that the standard deviation of the resonance amplitudes of the liquid-immersed ZnO-nanorod-modified sensors decreases substantially, ranging from a 27% decrease for bovine blood to a 67% decrease for saline. The strategy of using a superhydrophilic coating can be applied to other systems having similar interfacial problems.
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paper_title: Monitoring blood coagulation with magnetoelastic sensors.

paper_content:

The determination of blood coagulation time is an essential part of monitoring therapeutic anticoagulants. Standard methodologies for the measurement of blood clotting time require dedicated personnel and involve blood sampling procedures. A new method based on magnetoelastic sensors has been employed for the monitoring of blood coagulation. The ribbon-like magnetoelastic sensor oscillates at a fundamental frequency, which shifts linearly in response to applied mass loads or a fixed mass load of changing elasticity. The magnetoelastic sensors emit magnetic flux, which can be detected by a remotely located pick-up coil, so that no direct physical connections are required. During blood coagulation, the viscosity of blood changes due to the formation of a soft fibrin clot. In turn, this change in viscosity shifts the characteristic resonance frequency of the magnetoelastic sensor enabling real-time continuous monitoring of this biological event. By monitoring the signal output as a function of time, a distinct blood clotting profile can be seen. The relatively low cost of the magnetoelastic ribbons enables their use as disposable sensors. This, along with the reduced volume of blood required, make the magnetoelastic sensors well suited for at-home and point-of-care testing devices.
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paper_title: The effect of TiO2 nanotubes in the enhancement of blood clotting for the control of hemorrhage.

paper_content:

Abstract The main biological purpose of blood coagulation is formation of an obstacle to prevent blood loss of hydraulic strength sufficient to withstand the blood pressure. The ability to rapidly stem hemorrhage in trauma patients significantly impacts their chances of survival, and hence is a subject of ongoing interest in the medical community. Herein, we report on the effect of biocompatible TiO 2 nanotubes on the clotting kinetics of whole blood. TiO 2 nanotubes 10 μm long were prepared by anodization of titanium in an electrolyte comprised of dimethyl sulfoxide and HF, then dispersed by sonication. Compared to pure blood, blood containing dispersed TiO 2 nanotubes and blood in contact with gauze pads surface-decorated with nanotubes demonstrated significantly stronger clot formation at reduced clotting times. Similar experiments using nanocrystalline TiO 2 nanoparticles showed comparatively weaker clot strengths and increased clotting times. The TiO 2 nanotubes appear to act as a scaffold, facilitating fibrin formation. Our results suggest that application of a TiO 2 nanotube functionalized bandage could be used to help stem or stop hemorrhage.
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Title: Theory, Instrumentation and Applications of Magnetoelastic Resonance Sensors: A Review

Section 1: Introduction
Description 1: Provide an overview of magnetoelastic sensors, their composition, operational principle, and various applications.

Section 2: The Equation of Motion of a Magnetoelastic Sensor
Description 2: Explain the theoretical model, including the equation of motion for magnetoelastic sensors, and discuss the boundary conditions and resonant frequency derivation.

Section 3: Effect of Mass Loading on a Magnetoelastic Sensor
Description 3: Discuss how mass loading affects the resonance frequency of magnetoelastic sensors and provide experimental data demonstrating these effects.

Section 4: Instrumentation: Early Developments
Description 4: Describe the initial instrumentation used with magnetoelastic sensors, including the types of circuits and measurement approaches used in early research.

Section 5: Modern Microcontroller Based Instrumentation
Description 5: Detail advancements in instrumentation, focusing on modern microcontroller-based designs and their components.

Section 6: Pressure Sensing
Description 6: Explain the application of magnetoelastic sensors in pressure sensing, including theoretical background and experimental results.

Section 7: Temperature Sensing
Description 7: Discuss the use of magnetoelastic sensors for temperature measurement, including the effects of temperature on resonance frequency.

Section 8: Measurement of Liquid Viscosity and Density
Description 8: Provide insights into how magnetoelastic sensors measure liquid viscosity and density, including theoretical models and practical examples.

Section 9: Monitoring Fluid Flow Rate
Description 9: Describe the application of magnetoelastic sensors in monitoring fluid flow rates and the principles behind this measurement.

Section 10: Measurement of Elastic Modulus of Thin Film
Description 10: Discuss the use of magnetoelastic sensors to measure the elastic modulus of thin films coated on their surface.

Section 11: Humidity Measurement Using a Magnetoelastic Sensor
Description 11: Explain the application of magnetoelastic sensors in humidity measurement, including coating materials and experimental data.

Section 12: Ethylene, CO2 and NH3 Sensors
Description 12: Describe the use of magnetoelastic sensors for detecting gases like ethylene, CO2, and NH3, including the coating materials and detection principles.

Section 13: Magnetoelastic pH Sensor
Description 13: Discuss the application of magnetoelastic sensors in pH measurement, including the responsive materials used and experimental findings.

Section 14: Detection of Escherichia coli O157:H7
Description 14: Explain the use of magnetoelastic sensors for detecting E. coli O157:H7, including methods for enhancing detection sensitivity.

Section 15: Magnetoelastic Glucose Biosensor
Description 15: Describe the application of magnetoelastic sensors in glucose detection, detailing the sensor design and performance in different environments.

Section 16: Magnetoelastic Avidin Biosensor
Description 16: Discuss the use of magnetoelastic sensors for detecting avidin, including the biochemical interactions and methods used for signal amplification.

Section 17: Other Bio-Sensing Applications
Description 17: Provide an overview of other bio-sensing applications of magnetoelastic sensors, including pathogens, bacterium, and biochemical agents detection.

Section 18: Magnetoelastic Sensor for Monitoring Milk Quality
Description 18: Explain how magnetoelastic sensors are used to monitor milk quality, including the detection of lactose and bacterial growth.

Section 19: Magnetoelastic Sensor for Lipoprotein Detection
Description 19: Discuss the use of magnetoelastic sensors in detecting lipoprotein particles, including the biochemical reactions involved and the challenges faced.

Section 20: Magnetoelastic Sensors for Monitoring Blood Coagulation
Description 20: Describe how magnetoelastic sensors are used to monitor blood coagulation, including clotting time, clot strength, and aggregation tests.

Section 21: Conclusions
Description 21: Summarize the versatility and potential applications of magnetoelastic sensing technology, highlighting the advancements and future directions.