ASA 127th Meeting M.I.T. 1994 June 6-10

4pEA2. Absolute calibration of high-intensity focused transducers used in pulsed mode.

George Kapodistrias

Sameer I. Madanshetty

Aerosp. and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215

Absolute calibration of high-intensity focused transducers is attempted. The difficulty with using the high-intensity focused fields in underwater applications is that at the high pressure amplitudes involved, cavitation can occur, which can destroy the reference transducer used for calibration. Reference transducers of the PVDF membrane type are expensive and cannot be sacrificially used for calibration purposes. A robust alternative to using the sacrificial reference transducer is to use an economical needle type Dapco(trademark) transducer to pick the acoustic pulses to be calibrated. It is used to measure the relative positive and negative peak amplitude variations with increasing input voltage. [At high intensities the nonlinearities on the acoustic pulse manifest as heightened positive pressure peak accompanied by shallow negative pressure (tensile) peaks.] Additionally, a radiation force balance is used to measure the net acoustic output. Knowing the beam profile and applying a nonlinearity correction factor developed absolute magnitudes of the positive and the negative pressure peaks can be inferred for pulsed applications. It is to be noted that for cavitation studies one needs to know the peak negative pressure (the tensile component).