Comparison of the input electrical power measurement methods for HIFU transducers

HIFU (High Intensity Focused Ultrasound) transducers are attractive tools for cancer therapy. They must be used carefully for operator and patient safety as they produce very high powers up to a few hundred watts, and characterized in many ways. The ultrasonic power of a transducer is directly proportional to the applied input electrical voltage, current and consequently electrical power. Internationally accepted methods for measurements of ultrasonic output power up to 10 W are well established in the IEC 61161 standards [1]. The same method was used for higher powers up to 150 W with an uncertainty of 4.7% for 1.1 MHz and 5.0% for 3.3 MHz in an intercomparison between national metrology institutes [8]. In this paper, input electrical power of the HIFU transducer, which is mainly converted into ultrasonic energy, was determined. 3 methods for the measurement of electrical power delivered to a reactive ultrasonic (HIFU) transducer were compared. Electrical power measurements were realized with an expanded uncertainty of 3.3 % for up to 50 W and 4.3 % for up to 100 W in the frequency range between 0.93 MHz and 3.1 MHz. Measurement devices were calibrated and verified by establishing traceability to electrical and ultrasonic standards at TUBITAK UME (The Scientific and Technological Research Council of Turkey, National Metrology Institute) primary laboratories. Electrical power measurement results obtained by this method were also compared with two different conventional power meters. Electrical power measurement results detailed in this paper showed an agreement with each other and conventional power meters.