Knowledge Box

Vol.3 Wireless Power Transfer Systems for Wireless Healthcare Devices

Smartphones and tablet devices incorporate a variety of sensing elements, including acceleration, gyro, pressure, temperature, and GPS sensors, and their number continues to increase from year to year. This development has even led to the creation of a new term, "sensor hub" that is heard quite frequently these days. In a conventional arrangement, where information from each individual sensor is processed by the CPU, power consumption will increase with the number of sensors. By contrast, having the data from multiple sensors processed together by a low-power "sensor hub" chip will help to conserve power and prolong battery life. The progress of smartphone technology is unstoppable. Smartphones featuring an array of high-performance sensors are destined to evolve further, while also incorporating aspects of AI (artificial intelligence) and robot technology. This is expected to eventually result in "smartphone type robots" or "robot type smartphones" that can be a boon for improving our daily life and work.

Wearable blood pressure meter allowing 24-hour monitoring soon to be a reality

The task of a sensor is to detect information or energy from an object and convert it into an electrical signal. Various types of sensors corresponding to the human five senses (sight, hearing, smell, taste, touch) are being used extensively in electronic devices and electrical equipment. Going beyond simply processing the sensor signal for output, it is also possible to provide feedback to the sensor side, thereby achieving optimized control and enabling capabilities such as autonomous driving.

Sensors for vital signs including respiratory rate and heart rate, blood pressure and blood sugar levels will be indispensable for wearable health care devices. People are growing more health conscious, and in keeping with this trend, various activity meters for example in wristband or wristwatch form have come onto the market. A low-power pairing technology called Bluetooth Low Energy (BLE) is being used to wirelessly connect smartphones and similar to such hub devices. Simply by wearing suitable device on one's body, it is possible to realize 24-hour, 365-day health management through sensors for vital signs including number of steps walked, distance traveled, heart rate, calories consumption, and more.

A variety of new components for wearable applications have also been developed. One of these is the SESUB-PAN-T2541 from TDK which harnesses proprietary semiconductor embedded substrate (SESUB) technology to realize a tiny BLE communication module. In combination with a battery and suitable sensor, it can becomes a wearable pulse rate meter. TDK also supplies atmospheric pressure sensors and a variety of other sensor products. For example, by incorporating a combination of small sensors TDK also supplies acceleration sensors, atmospheric pressure sensors and similar products. For example, by using an acceleration sensor to provide attitude information and incorporating it in a fashionable bracelet or necklace type wearable device, a system for protecting elderly persons from falls can be devised.

However, one vital sign that is still difficult to measure while a person is in motion is blood pressure. In addition to traditional blood pressure meters using a mercury column (Korotkoff method), electronic blood pressure monitors (oscillometric method) for home use have been developed, but all of these require a cuff (pneumatic tourniquet) to put pressure on the upper arm or wrist, temporarily stopping the blood flow for measurement. Until recently, no meter for continuously measuring blood pressure without oppression was available.

However, wearable cuff-less blood pressure monitors are now being developed. A prototype created by Nihon University is a new kind of blood pressure meter that uses the phase shift method to perform measurement by simple touch. Near infrared light from a LED source irradiates the skin, and changes in the waveform of the reflected light are detected to calculate the blood pressure value using a unique algorithm. The dedicated chip for the system measures a mere square centimeter, which should enable integration into a wearable device of the wristband or wristwatch type, thereby realizing continuous blood pressure monitoring.