Tip‐sensitive fibre‐optic Bragg grating ultrasonic hydrophone for measuring high‐intensity focused ultrasound fields

Abstract

A tip-sensitive fibre-optic Bragg grating ultrasonic hydrophone (TSFBGUH) with high spatial resolution for measuring high-intensity focused ultrasound (HIFU) fields is reported. When measuring a HIFU field, the sensitive axis of the TSFBGUH with a flexible fibre-optic sensor holder should be in parallel with the acoustic axis of the HIFU transducer to ensure the measured ultrasound impinges on the tip of the TSFBGUH. The TSFBGUH system has been established and tested. The experimental results show that the acoustic pressure sensitivity of the TSFBGUH system is about 31.3 mV/MPa within the measurement range of 10 MHz and the noise equivalent pressure is about 10.4 kPa.Introduction: High-intensity focused ultrasounds (HIFUs) have been used to cure cancers non-invasively by destroying tumours through heating and acoustic cavitations. To ensure the treatment safety, the acoustic pressure distributions and the size of the focal regions of HIFU fields need to be measured and characterised accurately. At present, HIFU fields are commonly measured and characterised by piezoelectric needle hydrophones, fibre-optic hydrophones etc. [1][2][3][4]. The fibre-optic hydrophones possess the merits of simple configuration, miniaturisation and immunity to electromagnetic interference. The fibre-optic Bragg gratings (FBGs) have been developed into various sensors for measuring static pressures [5], ultrasonic pressures [6-13] and other physical parameters. The FBG hydrophones, possessing the capability of multiplexing and withstanding high acoustic pressure, have attracted much interest [9-13]. All the above-mentioned FBG hydrophones sensed ultrasounds through the lateral side of FBGs, which could break the hydrophones by the ultrasonic wave and limit the spatial resolution [2,8]. Up to now, we have not found the literature about the tip-sensitive FBG hydrophones for measuring HIFU fields.In this Letter, a tip-sensitive FBG ultrasonic hydrophone (TSFBGUH) for measuring HIFU fields is described. The TSFBGUH system and the experimental setup have been built to measure the HIFU fields generated by a 0.965 MHz HIFU transducer in continuous mode.

Fiber Optic Sensors for Temperature Monitoring during Thermal Treatments: An Overview

“…Other FOSs based on FBGs and Fabry-Pérot interferometers have also been employed in this application, but for the measurement of HIFU field [ 95 , 96 , 97 ]. For instance, an all-silica Fabry-Pérot FOS has been developed by Wang et al, with a very low wavelength change with temperature (0.000858 nm·°C −1 ), and good signal to noise ratio (42.8 dB) [ 96 ].…”

Semiconductor Infrared Devices and Applications

“…In resonator-based technique, a micron-scale optical resonator detects ultrasound waves (see Figure 4a(iv)); using this technique, miniaturization of the ultrasound detection unit is feasible. The optical resonator geometries that are most frequently used in photoacoustic imaging are Fabry-Pérot interferometers (FP) [161][162][163], micro-ring resonators (MRRs) [164][165][166], and π-phase-shifted fiber Bragg gratings (π-FBGs) [167][168][169]. Refractometric methods can be classified as intensity sensitive, beam deflectometry, and phase sensitive [41,42].…”

Overview of Ultrasound Detection Technologies for Photoacoustic Imaging

“…In resonator-based technique, a micron-scale optical resonator detects ultrasound waves (see Figure 4 a(iv)); using this technique, miniaturization of the ultrasound detection unit is feasible. The optical resonator geometries that are most frequently used in photoacoustic imaging are Fabry–Pérot interferometers (FP) [ 161 , 162 , 163 ], micro-ring resonators (MRRs) [ 164 , 165 , 166 ], and π-phase-shifted fiber Bragg gratings (π-FBGs) [ 167 , 168 , 169 ]. Refractometric methods can be classified as intensity sensitive, beam deflectometry, and phase sensitive [ 41 , 42 ].…”