Design of a dual chamber heat conduction calorimeter for ultrasonic beam measurement

This thesis describes a device that is capable of measuring ultrasonic output power quickly and accurately. The device is a dual chamber heat conduction calorimeter (HCC) designed, built, and tested for the purpose of measuring ultrasonic output power of clinical diagnostic ultrasound devices. The HCC is composed of two identical water filled aluminum wells housed in two separated compartments of an insulated box. The two compartments form the measuring and reference chambers of the calorimeter. The wells are sealed with plastic membranes that constitute the entrance window for the ultrasound. The bottom of each well is stuffed with a 4 cm layer of 0.5 cm thick rubber pads. These pads serve as a sonic-to-heat energy converter. In both chambers, a small resistive heater is embedded between the first and the second layer of rubber pads for calibration purposes. Heat is measured with a series of Seebeck effect thermoelectric devices (thermopiles) sandwiched between the well and the heat sink surrounding the wells. The performance and sensitivity of the HCC was measured, initially with the embedded resistive heaters, then with an experimental transducer, and lastly with transducers from clinical ultrasound scanners. The minimum detectability and the measurement uncertainty of the HCC was determined to be 1.2 mW and 6.6%, respectively.