Broadband unidirectional ultrasound propagation
A passive, linear arrangement of a sonic crystal-based apparatus and method including a 1D sonic crystal, a nonlinear medium, and an acoustic low-pass filter, for permitting unidirectional broadband ultrasound propagation as a collimated beam for underwater, air or other fluid communication, are described. The signal to be transmitted is first used to modulate a high-frequency ultrasonic carrier wave which is directed into the sonic crystal side of the apparatus. The apparatus processes the modulated signal, whereby the original low-frequency signal exits the apparatus as a collimated beam on the side of the apparatus opposite the sonic crystal. The sonic crystal provides a bandpass acoustic filter through which the modulated high-frequency ultrasonic signal passes, and the nonlinear medium demodulates the modulated signal and recovers the low-frequency sound beam. The low-pass filter removes remaining high-frequency components, and contributes to the unidirectional property of the apparatus.
1. An apparatus for generating a collimated, unidirectional acoustic signal having a frequency f m or a band of frequencies centered at f m , from an input carrier signal having a frequency f c >f m amplitude modulated by f m , comprising:
a low-loss acoustic bandpass filter for receiving the modulated carrier signal, and having a bandwidth larger than an amplitude modulated sideband of the amplitude modulated f c ;
an acoustic nonlinear medium for receiving and demodulating the amplitude modulated f c from said acoustic bandpass filter, whereby a collimated acoustic signal having a frequency f m is generated; and
a low-pass acoustic filter for preventing the carrier signal or the amplitude modulated carrier signal from being transmitted through said apparatus in the direction opposite to the generated collimated acoustic signal.
2. The apparatus of claim 1 , wherein said input carrier signal f c amplitude modulated by f m is generated by an acoustic transducer.
3. The apparatus of claim 1 , wherein said acoustic bandpass filter comprises a phononic crystal.
4. The apparatus of claim 1 , wherein said acoustic bandpass filter comprises a sonic crystal.
5. The apparatus of claim 1 , wherein the amplitude modulation of said input carrier signal f c amplitude modulated by f m is chosen from carrier suppressed double sideband modulation, single sideband modulation, and double sideband modulation.
6. The apparatus of claim 1 , wherein said acoustic nonlinear medium comprises a nonlinear acoustic liquid.
7. A method for generating a collimated, unidirectional acoustic signal having a frequency f m or a band of frequencies centered at f m , from an input carrier signal having a frequency f c >f m amplitude modulated by f m , comprising:
passing the modulated carrier signal through a low-loss acoustic bandpass filter having a bandwidth larger than an amplitude modulated sideband of the amplitude modulated f c ;
demodulating the bandpass filtered amplitude modulated f c from said acoustic bandpass filter, whereby a collimated acoustic signal having a frequency f m is generated; and
passing the collimated acoustic signal having a frequency f m through a low pass filter, whereby the carrier signal or the amplitude modulated carrier signal are prevented from being transmitted through the bandpass filter in the direction opposite to the generated collimated acoustic signal.
8. The method of claim 7 , wherein said step of demodulating the bandpass filtered amplitude modulated f c is performed by a nonlinear acoustic medium.
9. The method of claim 8 , wherein the nonlinear acoustic medium comprises a nonlinear acoustic liquid.
10. The method of claim 7 , wherein the input carrier signal f c amplitude modulated by f m is generated by an acoustic transducer.
11. The method of claim 7 , wherein the acoustic bandpass filter comprises a phononic crystal.
12. The method of claim 7 , wherein the acoustic bandpass filter comprises a sonic crystal.
13. The method of claim 7 , wherein the amplitude modulation of the input carrier signal f c amplitude modulated by f m is chosen from carrier suppressed double sideband modulation, single sideband modulation, and double sideband modulation.