Close-proximity, real-time thermoacoustic sensors: Design, characterization, and testing

This paper describes the design, characterization, and testing of a close-proximity, real-time thermoacoustic sensor for ultrasound intensity measurements. Plexiglass sensors, 20 mm diameter and 3.3 mm length, absorbed ultrasound with a frequency of 1.5 MHz, a 20% duty cycle, and a 1 kHz pulse repetition frequency, at intensities between 30 and 100 mW/cm². An embedded system design fit thermistor temperature data to a curve relating the temperature rise averaged across the backside of the sensor to the applied ultrasound intensity, and calculated the corresponding ultrasound intensity. Good linearity was demonstrated between the ultrasound intensity measured using a radiation force balance, and intensity measured using the thermoacoustic sensor when placed in contact with the acoustic transducer: accuracy within 5% of the target value and standard deviation of 4.55% or less. The sensor has an operational temperature range of 22°C to 26°C. This design makes for a quick and convenient method of checking ultrasound intensity, and also presents the possibility of integrated sensor and ultrasound generator systems using feedback loops to achieve auto-calibration.