Improved High Frequency Calibration for Dosimetry in Focussed Ultrasound Surgery (360G-Wellcome-202566_Z_16_Z)

Ultrasound at high intensities can cause tissue damage, therefore knowing the intensities used in clinical application is paramount. Ultrasound source outputs are calibrated using hydrophones, following a primary standard calibration at the National Physical Laboratory (NPL) in the UK. Yet uncertainty in the primary calibrations is surprisingly high: around 10% and growing with frequency (NPL 2014). The primary calibration uses optical interferometry for the measurements. This project will investigate one source of uncertainty in this procedure: the effect of the tension in the optically-reflecting membrane. The rig for these experiments will be designed and built following the design shown in Figure (1). There are three key goals: a) Create a measurement rig that can measure the normal incidence acoustic pressure transmission coefficient of a stretched mylar membrane as a function of frequency, membrane tension, and membrane thickness. b) Based on previous work in the literature (Thomas 1976; Romilly 1969; Lamb 1957; Ingard 1954; Chen et al. 2014), construct a mathematical and/or numerical model of the motion of a membrane under tension when a sound wave is incident, and make for comparison with the measurements. c) Formulate advice to the National Physical Laboratory on how to minimize this uncertainty.