Hydrophone spatial averaging corrections from 1-40 MHz

The spatial averaging model was developed and experimentally verified in the frequency range 1-40 MHz. The model is applicable to focused sources of circular geometry, accounts for the effects of hydrophone finite aperture and allows calibration by substitution to be performed when the active elements of reference and tested hydrophone differ significantly. The effective diameters of the ultrasonic hydrophone probes calibrated in the focal plane of the sources with different f-numbers ranged from 150-500 /spl mu/m. The probes with diameters smaller than that of the reference hydrophone exhibited experimentally determined absolute sensitivity higher than the true one. The model was capable of predicting the correct sensitivity with an overall uncertainty of +1 dB. It is now being extended to be applicable to frequencies beyond 40 MHz and rectangular acoustic sources.