Evaluation of transient and highly localized acoustic fields using acoustooptic phase contrast imaging.

摘要

A comprehensive study of the generation and optical imaging of highly localized acoustic fields is presented. A phase-contrast imaging method is described which reconstructs a pressure field of arbitrary waveform in space at a constant time. The method resembles the existing pulsed-schlieren technique, but reconstructs the true pressure field, where schlieren returns the absolute value of the field. The phase-contrast imaging system is constructed and tested with the aid of numerical simulation and experiment. To allow efficient global reconstruction of the phase-contrast imaged fields, a temporal backward planar projection algorithm is devised. The algorithm projects spatially dependent field data from an initial time t0, forward or backward to a new time t. This temporal projection method is compared with standard wave-vector/time domain techniques. Generation of radially-dependent transient signals is accomplished through the construction of a backed PZT 1--3 composite piezoceramic transducer array. The array consists of a center disk and four concentric rings patterned onto a single composite. The electromechanical transduction problem for broad-band ultrasonic signals produced by the transducer is addressed. Appropriate electric potentials for producing a number of finite approximations to nondiffracting solutions to the linear acoustic wave equation, or acoustic bullets, are calculated. These potentials are physically generated by an arbitrary waveform generator (AWG), input to the array, imaged, and projected. These experimental results are compared with theoretical values.