Development And Performance Testing Of Milliwatts-levers Standard Piezoelectric Ultrasonic Transducer

In the ultrasonic diagnosis and treatment, large ultrasonic power may lead to thedestructive deformation and cavitation effect of human cells. So the safety of medicalultrasonic instruments has gradually been a critical issue of this field. In China, themetrological service to all kinds of ultrasonic instruments is mainly done bymeasuring their output power utilizing ultrasonic power meter at watts or milliwattslevel, and the ultrasonic power meter is tested and calibrated regularly by the superiormeasuring department. Therefore, the accuracy of ultrasound quantity transmissionprovides guarantee for the reliability of the ultrasonic technology application.In this paper, the vibration model and piezoelectric equation of piezoelectricresonators and the piezoelectric mechanism of lithium niobate single crystal materialwere analyzed based on the working principle of piezoelectric ultrasonic transducer.And then, the electro-mechanical equivalent circuits of piezoelectric transducer underthe vibration mode of thickness expansion were obtained from the piezoelectricequation. In the selections of piezoelectric material, the vibration characteristics andelectro-mechanical coupling coefficient of lithium niobate single crystal underdifferent cutting direction were studied, and the best cutting type and vibration modeof piezoelectric wafer were achieved at last. In the design of piezoelectric vibrator,the author designed the reasonable proportion of the thickness and diameter in thevibrator, and plated the surface of piezoelectric vibrator with a layer of goldmembrane using sputtering techniques. In the finally manufacture of the transducer,the transducer shell was designed with a consideration of the whole assembly andelectrode welding. In this paper, a standard ultrasonic transducer of5MHz wasdeveloped complying with the requirements of "Milliwatts Ultrasonic Power MeterVerification Regulations" strictly.The performance testing of lithium niobate piezoelectric ultrasonic transducermainly included two parts—the acoustic field characteristics and ultrasonic poweroutput. The sound field characteristics were measured by hydrophone method. In order to identify the working frequency of the transducer, an experiment wasdesigned and the sound field distribution characteristics under the working frequencywere tested. According to the calibration requirement of standard ultrasonic source atmilliwatts level, the radial force balance method was used to measure the outputpower of the ultrasonic transducer on the basis of the national reference device atmilliwatts level, and the uncertainty of the experimental results was evaluated at last.The experimental results show that the transducers developed in this study meet therequirements of "Milliwatts Level Standard Ultrasound Source". It overcomes thedrawback of standard quartz crystal ultrasonic transducer and achieved the desireddesign index.