Cushman, Darby & Cushman
Acoustic holography apparatus
 Apparatus and method for forming acoustic hologram patterns, comprising a receiver transducer for detecting acoustic waves scattered by an object, a scanning system for moving the receiver relative to the object, a sampling system for taking samples of a signal derived from the receiver transducer at selected instants relative to the phase of the acoustic signals at the transmitter, the selected instants being determined according to the phase of a chosen notional reference wave at the position of the receiver transducer relative to the phase of the chosen notional reference wave at a datum point, and a system for plotting the samples versus the displacement of the receiver transducer so as to form a graphical diagram representing an acoustic hologram of the object. The receiver signals are preferably applied to a phase-locked frequency-multiplier circuit and the samples taken from the output of this circuit. The sampling system may include a switch circuit arranged to apply a series of predetermined voltages in sequence to a comparator controlling a sampling gate. 
National Research Development Corporation
G
G01S
inventional
David Trevor
Green