Acoustically Stimulated Electromagnetic Response in Biomedical Tissues

Ultrasonic irradiation induces alternating electromagnetic polarization through electro- or magneto-mechanical coupling. It follows that electromagnetic fields are generated from a variety of materials when they are acoustically stimulated. In this paper, the acoustically stimulated electromagnetic response is investigated in biomedical tissues that consist of piezoelectric collagen. The response signal is detected through a capacitive resonant antenna tuned to an ultrasonic frequency of 9.0 MHz. First, we have measured an artificial oriented and unoriented collagen. The response signal is definitely observed in thin collagen sheets with a thickness of 300 $\mu \text{m}$. The signal amplitude in the oriented collagen sheet is several times as large as that in the unoriented one. Next, we have investigated the response signal in bone (rat femur). The ASEM signal is definitely observed even when the bone is decalcified, indicating that the origin of the signal is attributed to collagen. These findings may pave the way for noninvasive medical inspection to evaluate fibrosis or collagen degradation in biomedical tissues.