Acoustic Self-Demodulation of Predistorted Pulsed Carriers.
TEXAS UNIV AUSTIN ELECTRONICS RESEARCH CENTER
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Nonlinear effects cause demodulation of a pulsed carrier such that a signal proportional to the second time derivative of the square of the pulse envelope develops in the insonified medium. If the pulse envelope function is predistorted by time integrating it twice and taking its square root, the resulting pulsed carrier should demodulate into the original envelope function. Several different types of pulse envelopes were used to modulate a 450 KHz carrier in order to verify the self-demodulation phenomenon. The pulse envelopes were then predistorted integrated twice and square rooted and used to modulate the carrier which then drove a 3 ince diameter circular piston projector. The transmission medium was water. In all experiments, a low pass filter was used to absorb the carrier frequency. The self-demodulation phenomenon was experimentally demonstrated for several envelope pulse shapes. When the pulses were predistorted, the original pulse envelope was recovered within the bandwidth limitations of the transmitter and receiver. Author
- Non-Radio Communications