to generate audio sound from ultrasound?
This is possible due to the non-linear property of air. When two collimated
waves of neighboring frequencies are transmitted into air, non-linear
interaction of these two waves will occur. As a result of this, the sum and
difference frequency waves will be generated. By utilizing this non-linear
property of air, when an amplitude modulated (AM) audio signal is transmitted
in air, the original audio signal can be obtained when air self-demodulate the