27. 超音波水診器（hydrophone）的校正關係式是：
(A) 電壓（voltage）與聲壓（acoustic pressure）關係
(B) 密度（density）與溫度（temperature）關係
(C) 速度（velocity）與聲壓（acoustic pressure）關係
(D) 加速度（acceleration）與聲壓（acoustic pressure）關係

[解釋]

The hydrophone sometimes is called a microprobe. The hydrophone is used inntwo forms：(1) a small transducer element (with a diameter of 1 mm or less) mounted on the end of a hollownneedle, or (2) a large piezoelectric membrane with small metallic electrodesncentered on both sides.

Using the hydrophone calibration (relationshipnbetween the voltage and the acoustic pressure), pressure amplitudenalso may be determined. In addition, wavelength, spatial pulse length, andnintensities also can be calculated.

[出處]

Seventh Edition Diagnostic Ultrasound CH9, Output Measurements(p.315 andnp.319)