Spatial Calibration of Airborne Ultrasonic Phased Arrays with Two-Dimensional Visualization of Ultrasound Emissions

In order to expand the applications of electronically controllable intense mid-air ultrasonic fields generated with airborne ultrasonic phased arrays (AUPA), a precise spatial calibration method between multiple AUPAs is in great demand. However, the conventional methods, such as manual fine-tuning and acoustic beam scanning, take a long time to complete. Here, we propose a quicker calibration method using thermal imaging. By placing an acoustically translucent screen in the AUPAs’ sound field containing narrow and straight sound beams, acoustic energy in the field is converted into a two-dimensional heat map. By shooting several images with a thermal camera changing the beam position, information about the relative spatial information between the screen and the AUPAs is promptly visualized. We developed the algorithm to estimate the postures of AUPAs from the obtained image. We conducted a preliminary experiment about thermal imaging and a numerical simulation of the AUPA posture estimation algorithm and verified the effectiveness of our proposed method.