Development of ultrasonic power measurement standards in Thailand

Measurement of power output levels of diagnostic and therapeutic ultrasound equipment has become increasingly important to determine exact patient exposure levels in case a potential risk exists to the patient and to ascertain whether the ultrasound devices are performing satisfactorily. The objective of this work was to establish standards for ultrasonic power in Thailand by developing a primary level ultrasonic power measurement system. This system is being set up at the National Institute of Metrology, Thailand (NIMT) and it will be able to determine 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 the International Electrotechnical Commission (IEC 61161). Three ultrasonic transducers with three different resonance frequencies, 1 MHz, 5 MHz and 10 MHz were used as an ultrasonic source to test the performance of the developed system. The results of the measurements from the developed primary system at the National Institute of Metrology, Thailand (NIMT) 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 within a measuring uncertainty of ±5%. In addition, the results also show that the developed system is currently capable of determining 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.