Measurement of the Instantaneous Acoustic Power of Diagnostic Ultrasound Equipment by Piezoelectric-Array Acoustic Power Meter

The bounded-square (1 x 1 cm) instantaneous acoustic power for most ultrasound imaging devices can reach several hundred or even thousand watts, which has a strong possibility of causing inertial cavitation, chromosome damage, fetus stimulation, or other biological impacts. Hence, the instantaneous acoustic power should be accurately measured. Up until now, the radiation force balance (RFB) is the only commercially available instrumentation for measuring acoustic power. However, the RFB, which measures the acoustic power based on a spatiotemporal averaging approach, cannot acquire the instantaneous acoustic output power directly. To measure the instantaneous acoustic output power, a new instrumentation named piezoelectric-array acoustic power meter based on piezoelectric effect is proposed. To analyze the operating mechanism of the piezoelectric-array acoustic power meter, a dynamic model of acoustic-structure interaction is established. The relationship between instantaneous acoustic power and the output voltage on piezoelectric arrays is derived. To verify the theory, a sample of piezoelectric acoustic power meter with nine arrays is fabricated using 1-3 piezoelectric composites. Experimental results show that the error between the proposed method and RFB is less than 10% below 20 W, proving the accuracy of our proposed instrumentation. The maximum bounded-square (1 x 1 cm) instantaneous acoustic output power of a B-mode ultrasonic diagnostic device we obtained reaches 46.41 +/- 0.30 W, approximately two times higher than the estimated value obtained from RFB. Moreover, it is interesting to note that the maximum acoustic output power of an ultrasonic source operating in continuous mode in the experiments reaches 42.07 +/- 0.20 W, which is about two times higher than the IEC standard. The proposed method overcomes the limitation of the RFB method, which can only obtain the spatiotemporal averaged acoustic output power. It provides a new instrumentation to measure both the instantaneous acoustic output power and the high acoustic output power as well