A Primary Level Ultrasonic Power Measurement System Developed at National Institute of Metrology, Thailand

The total output power from a medical ultrasound transducer has to be measured due to various reasons but in general they are related to assessment of performance and safety of equipment. The objective of this work was to develop a primary level ultrasonic power measurement system to establish standards for ultrasonic power measurement in Thailand. This system is being set up at the National Institute of Metrology, Thailand (NIMT) and it will be capable of determining the ultrasonic output power in the frequency range from 1 MHz to 20 MHz, and in the power range from 1 mW to 20 W. The implementation of the system utilizes a radiation force balance technique based on the method recommended in IEC 61161. Three ultrasound transducers with three different resonance frequencies, 1 MHz, 5 MHz and 10 MHz were used as an ultrasound source to test the performance of the developed system. The results of the measurements from the developed primary system are presented in comparison with those measured from the commercial ultrasound power meter (UPM). It is shown that the measurements yielded results that were consistent and the developed system is currently able to determine the ultrasonic output power in the frequency range from 1 MHz to 10 MHz, and in the power range from 1 mW to 500 mW. Current efforts are being made to focus on evaluating the measurement uncertainty for each component of the system, testing the frequency measurement range of the system up to 20 MHz and extending the power measurement region of the system to 20 W.