The application of scanning vibrometer in mapping ultrasound fields

Optical interferometry has been used for calibrating hydrophones at frequencies greater than 500 kHz for many years with very small uncertainties. Optical method have been found to be an effective non-perturbing method for detecting ultrasound fields with very fine spatial and temporal resolution; ultrasound fields can be mapped using a membrane and a scanning vibrometer, and two-dimensional fields can be imaged when the optical beam from a Laser Doppler Vibrometer (LDV) is aligned normal to the axis of the sound beam from a arbitrarily shaped projector. This paper presents a theoretical analyses for using a LDV system to detect ultrasound fields and further presents the result of some initial optical scan measurements performed using an LDV system. Results are presented of the particle velocity distributions produced by a focused ultrasound projector measured using a scanning LDV on an acoustically compliant, optically reflective membrane using a scanning LDV. Further measurement results are also presented of two-dimensional field maps obtained by positioning the laser beam perpendicular to the acoustic axis of a projector and detecting the line-integral acousto-optic effect. Visual maps of the acoustic waves radiating from the projector and the reflected and scattered propagating field by objects in water were obtained using this method and are presented in this paper