ULTRASONIC INTENSITY MEASUREMENT METHOD

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The objective is to conduct basic research on original methods for accurate measurement of ultrasonic intensity with high spatial resolution, detecting independently and simultaneously the instantaneous pressure and particle velocity in an acoustic field over broad ranges of amplitude and frequency. The long term goal is an instrument that would be, on the one hand, accurate, and on the other it would be compact, east to use and cost effective such that accurate characterization of acoustic and ultrasonic fields could be regularly employed in the design and safe use of instruments, and in the conduct of biophysical experimentation. As it is, designers of ultrasound systems often must rely on theory and inaccurate measurements. The problem is especially accute in relation to imaging and blood flow systems, therapy machines, and lithotripters in medicine. Variations of the order of 100% in any particular measurement are common despite a decidedly high level of technological competence. Such difficulties are very costly to the government and to instrument manufacturers and researchers, and can prevent adequate protection of the population supposedly at risk. They also greatly hinder accurate investigations using ultrasonics in biology, physics, and other applied fields such as nondestructive testing. The principal method to be explored will be a spatial superposition of optical interferometric measurements, which measure local particle displacement, with thin-film piezoelectric devices which effectively measure local acoustic pressure. Intensity is the vector product of particle velocity, which can be calculated from the displacement, and pressure. It is proposed that such a measurement concept can overcome the inaccuracies and instabilities of thin piezoelectric films for pressure measurement, since the optical subsystem can be used for periodic recalibration. Simultaneous measurement of the acousto-optic effect will be investigated as it applies to this problem. Measurement of particle displacement, independent of pressure, is necessary to calculate the intensity in near-fields and in other non-planar fields for which the velocity and pressure may not be in phase.