University College London
5 files

Rapid Spatial Mapping of Focused Ultrasound Fields Using a Planar Fabry–Pérot Sensor

posted on 2021-03-16, 15:01 authored by Elly MartinElly Martin, Edward ZhangEdward Zhang, James Guggenheim, Paul BeardPaul Beard, Bradley TreebyBradley Treeby

The data was acquired in order to investigate the potential of a robust planar Fabry–Pérot sensor for measurement of high acoustic pressures. The sensor was formed from all hard dielectric materials, and designed to operate at 1550 nm, coupled with a C-L (1516–1610 nm) band wavelength tunable laser and rapid scanning system. A set of measurements of the field of a single element spherically focusing HIFU transducer (H101, Sonic Concepts) driven at 1.1 MHz with a 4 cycle burst, was made with the sensor at a variety of drive levels, which at the lower end was compared against hydrophone measurements (0.2 mm PVDF needle hydrophone, Precision Acoustics), and at the higher end was beyond the damage threshold of conventional commercially available PVDF hydrophones, and was compared with KZK simulations of the field. Volume scans were also performed to demonstrate the feasibility of these given the rapid scan times.

The transducer was mounted pointing downwards into a small temperature controlled tank filled with degassed, deionised water, with manually adjustable xyz position. The Fabry-Perot sensor was mounted in the bottom of the tank in a fixed position, and measurements were taken over the sensor area by scanning the interrogation laser beam.

The directional frequency response of the sensor is included in the frequency response field in the sensor dataset. This has size [1002, 978, 3], where [:, 1, :] contains the frequency, [1, :, :] contains the angles, [2:end, 2:end , 1] is the magnitude response, [2:end, 2:end, 2] is the phase response, and [2:end, 2:end, 3] is the smoothed/corrected magnitude correction (1/mag response) that as applied to the data.

In total, this records contains 5 data files:

1. Planar field scan acquired with the Fabry Perot sensor at the focal plane at low level, for comparison with hydrophone scans (Fig4).

2. Planar scans at the focal plane at three drive levels (Fig 5).

3. Small area planar scans at the focal plane at 22 different drive levels, 6 repeats up to level 13, 3 repeats at levels 13-22: 94 datasets (Fig 6).

4. Planar scans at three different axial positions at an intermediate drive level. (Fig 7).

5. Hydrophone scans: a planar scan used to define the source boundary condition for KZK simulations performed as a comparison with scans in file 2. A lateral line scan acquired for comparison with the Fabry-Perot scan in file 1.


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