Conference Paper

P5F-2 Improved Fiber Optic Hydrophone Sensors

DOI: 10.1109/ULTSYM.2007.583 Conference: Ultrasonics Symposium, 2007. IEEE
Source: IEEE Xplore

ABSTRACT

Broadband fiber optic hydrophones are an attractive solution for characterization and measurement of high intensity acoustic fields which are encountered in clinical ultrasound applications upto 100 MHz. A small sensing area avoids spatial acoustic field averaging and provides sub-millimeter resolution required for enhanced imaging in diagnostic applications. In this paper we present analytical and experimental performance results of broadband down-tapered fiber optical hydrophone sensors based on reflection type sensing and intensity detection scheme. Both uncoated as well as gold coated down-tapered fibers have been fabricated. Experimental results employing these fiber sensors for a 1.6 MHz acoustic signal, at 1 MPa pressure have corroborated the analytical predictions that thin metal coating can improve the sensitivity by almost 15 dB over that of uncoated tapered fiber. Such improvement in sensitivity is due to enhanced reflectance from the thin metal layer that senses the incident acoustic pressure.

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Available from: P.A. Lewin, Jun 24, 2015
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    ABSTRACT: The primary objective of this research was to develop and optimize the calibration techniques for ultrasonic hydrophone probes in acoustic field measurements up to 100 MHz. Dependable, 100 MHz calibration method was necessary to examine behavior of the sub-millimeter fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also of interest was to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (High Intensity Focused Ultrasound) applications. The innovative elements of this research include implementation of a prototype FO sensor with an active diameter of about 10 mum that exhibits uniform frequency range and does not require any spatial averaging correction procedure up to about 75 MHz. The sensor is also sufficiently robust to measure fields generated by HIFU transducers. Accordingly, to test the FO probe behavior a novel 100 MHz bandwidth calibration technique was developed. This technique provided the sensitivity of conventional, finite aperture piezoelectric hydrophone probes as a virtually continuous function of frequency and allowed the verification of the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined initially to be about plusmn12% up to 40 MHz, plusmn20% up to 60 MHz and plusmn25% up to 100 MHz. Comparison of these data with those obtained from an independent laboratory is presented and a possibility of using the FO sensor as a reference tool to determine the phase response of finite aperture hydrophones is briefly discussed. Finally, the attempt is made to answer the question posed in the title. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will form an important breakthrough in acoustic measurements of both diagnostic and therapeutic fields.
    No preview · Conference Paper · Dec 2007
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    [Show abstract] [Hide abstract]
    ABSTRACT: The primary objective of this work was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100 MHz. A dependable, 100 MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (high intensity focused ultrasound) applications. In addition to the development and validation of a novel, 100 MHz calibration technique the innovative elements of this research include implementation and testing of a prototype FO sensor with an active diameter of about 10 microm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75 MHz. The results of the calibration measurements are presented and it is shown that the optimized calibration technique allows the sensitivity of the hydrophone probes to be determined as a virtually continuous function of frequency and is also well suited to verify the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about +/-12% (+/-1 dB) up to 40 MHz, +/-20% (+/-1.5 dB) from 40 to 60 MHz and +/-25% (+/-2dB) from 60 to 100 MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100 MHz bandwidth.
    Full-text · Article · Nov 2008 · Ultrasonics

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