Broadband unidirectional ultrasound propagation using sonic crystal and nonlinear medium

The development of a passive, sonic crystal-based device with unusual properties is reported in this study. This device combines a 1D sonic crystal, a nonlinear medium and an acoustic low-pass filter to allow unidirectional broadband ultrasound propagation as a collimated beam for specialized underwater communication. The signal (220–400 kHz) to be transmitted is first amplitude modulated with a high-frequency ultrasonic carrier wave (2·7–3·25 MHz) and applied to one side of the device. The device then demodulates this signal, and consequently, the original low-frequency signal appears as a collimated beam on the other side. The sonic crystal provides a band-pass acoustic filter through which the high-frequency ultrasonic signal can pass through, and the nonlinear medium then demodulates the signal and also generates the low-frequency sound beam through the parametric array concept. The low-pass filter strips off any remaining high-frequency components and also contributes to the unidirectional property of the device. Design details of the device and experimental data are presented.