Acoustical Science and Technology
A Calibrator of Miniaturized Hydrophone
Aconvenient calibration apParatus for a minia . turized hydrophone is described which is primarily intended for intracard 至 ac , intravascular , intrauterine and var 玉 ous other uses in vivo . The present apparatus is composed of two parts to calibrate in a vibrating column of water shown in Fig ,2and in a closed water −filled chamber shown in Fig.8. As the 五rst step of the calibration process , a monitor hydrophone ( Fig. 5)to be used forasecond . ary standard is calibrated at low −audio
... at low −audio frequencies by immersing the hydrophone in the vibrating column of water . When the water column is vibrated vertical 董 y and sinusoidally , the pressure in the water 呈 sproportional to the water height h and the accele . ration as given by Eq . ( 4 ) . The values of the cor . rection factor for this apparatus due tQ wave effects are tabulated in Table 1. The sensitivity of a monitor hydrophone is − 125. 4dB re .1V / μbar at 100Hz , and the fτequency response is shown in Fig . 7. The secondary calibration of a miniaturized hydro . phone is performed by comparing the unknown output with that of the mon 菫 tor hydrophone in a closed water filled chamber shown in Fig.8. Sinusoidal pressure is obtained by driving the diaphragm of the chamber by an electrodynamic vibrator excited by abeat frequency oscillator . Two factors for design・ ing the closed chamber are represented by Eqs .( 12) and ( 13 ) with a nondirnensional parameter Z . The response frequency characteristics of a minia − turized hydrophone was measured by the apparatus mentioned above over the frequency range from 20Hz to 5 kHz at a sound pressure level over 104 μ bar. The results of the calibrations are shown in Fig .13 and 14. Furthermore , the response to a static pressure fair 且 y agreed with tllat to a sinusoida ! pressure . The sensitivity has been measured with an accuracy of about ± 1dB .