Precise control of the relative phases of two ultrasonic purses using digital logic circuitry
John M. Mills, Thomas Carolus · The Journal of the Acoustical Society of America · 1979
Description is given of a recently constructed device for use in ultrasonic experiments that employ two matched transducers. The device produces two sinusoidal bursts of substantially identical waveform, but with an adjustable delay between their starting times. The bursts are derived digitally from an external frequency standard (crystal clock), with a frequency of 5 MHz; the master frequency for sine wave synthesis can be any integer fraction of this clock frequency. The period of each cycle is ten times the reciprocal of that integer fraction of the master frequency. Any integer number of sinusoidal cycles, from one to nine cycles, are generated as a burst. A delay counter is started coincident with the sinusoidal waveform generator. Upon completion of this preset delay interval a second sine counter is started, which then generates the same number of cycles as there were in the first burst. The delay interval may be adjusted to any integer number of master clock cycles. Thus the two sine wave pulses can be delayed by any integer multiple of one tenth of a period of one sinusoid. The three-decade delay counter allows the total delay between the two pulses to be as much as 100 cycles. Sinusoidal output frequency, the number of cycles in a burst, and the delay between two successive bursts are all adjustable during the course of an experiment. [Work supported by NASA.]