Acoustically stimulated electromagnetic method for sensing electric and magnetic properties

A measurement technique for detecting acoustically induced polarization is introduced. Ultrasonic irradiation can generate alternating electric or magnetic polarization in materials via electromechanical or magnetomechanical coupling, respectively. It follows that electromagnetic fields are often emitted to the surrounding environment when materials are acoustically stimulated. The first harmonic response of the acoustically stimulated electromagnetic (ASEM) field is detected by a resonant antenna tuned to the ultrasound frequency. Ultrasound can temporally modulate the magnetic polarization (magnetization) in ferromagnetic materials, resulting in magnetic imaging and magnetic hysteresis measurements via ultrasonic stimulation. Ultrasonic probing of local magnetic properties gives unique magnetic measurements and is a promising tool in steel inspection. Furthermore, the ASEM response is generated in not only inorganic crystals but also biological tissues such as bones, tendons, and the aortic wall. The response signal is well explained by stress-induced electric polarization of biological tissues, which depends on the crystallinity of fibrous proteins. Therefore, the ASEM method opens possibilities for unique noninvasive sensing in medical fields. In this talk, we will discuss the origin of the ASEM response in various materials and its applications including steel and human measurements.