Acoustic field characterization of the focal plane of a focused transducer based on thin-film temperature rise

The selection of absorbing materials is essential for accurately measuring the acoustic field of focused ultrasound transducers using infrared thermography. This study is based on the physical properties of plastic absorbing films that efficiently absorb sound energy and rapidly convert it to heat. A three-layer medium simulation model based on the principle of sound intensity superposition is established, and a theoretical linear relationship between temperature rise and acoustic intensity is derived within the linear sound field model. In addition, an experimental setup for infrared sound field measurement is developed and the results are validated using the hydrophone scanning method. The results show that the difference in the −6 dB width between the infrared measurements at a power of 30 W for 0.2 s and the acoustic field scanning results is within 0.34%. Under low-power conditions, as the output power increases, the focal temperature rises and the −6 dB width of the focal plane gradually decreases. Over time, the −6 dB width first decreases and then increases, with better matching observed at 0.2 s compared to later stages.