Acoustic cloaking technology could be used to stop a sonar-using observer from detecting the presence of an object that would normally be detectable as it reflects or scatters sound waves. Ideally, the technology would encompass a broad spectrum of vibrations on a variety of scales. The range might be from miniature electronic or mechanical components up to large earthquakes. Although most progress has been made on mathematical and theoretical solutions, a laboratory metamaterial device for evading sonar has been recently demonstrated. It can be applied to sound wavelengths from 40 to 80 kHz.