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Investigation of high frequency applications for PVDF and optical hydrophones for measurements of the acoustic output of diagnostic medical ultrasonic devices

Objective



Background

Ultrasonic devices used in medical diagnostics are
increasingly employing ultrasound frequencies beyond 15
MHz. For dosimetry of these systems there is the need for
appropriate means and methods of measurement. So far PVdF
hydrophones are used for these measurements and fibre
optical detection schemes are tested. Concerning
measurements with PVdF hydrophones IEC standards only
cover the frequency range up to 15 MHz (there exists a
draft standard for the range up to 40 MHz). Fibre optical
detectors are not yet dealt with in any IEC standard.

Objectives

The overall objectives of the project are
to develop a new miniature PVdF needle hydrophone with
about 50#m diameter. Due to its size it is expected to be
better suited for detecting high-frequency ultrasound
than larger hydrophones.
to further develop and improve the techniques of a
fibre optical pressure sensor as a standard measurement
device for ultrasonic diagnostic and surgical systems.
The fibre optical sensor to be employed (Laser Probe
Hydrophone LPH) is based on the principle invented by
Eisenmenger and Staudenraus.
to further improve the measurement methods and
techniques for acquisition of important acoustic field
parameters with respect to IEC standard 1157 employing
(and mutually relating) the above described optical and
piezo-electrical detectors.
The particular objectives of the first stage of the
project are
Production and characterisation of acoustically well
defined ultrasonic sources
Design of the miniature PVdF hydrophone
Establishing the LPH system for defined and
reproducible measurements

Work programme

The programme to meet the above objectives comprises the
following stages:
Optimisation of the LPH for the detection of diagnostic
ultrasonic pressures.
Exact calibration of the LPH in the frequency range 2 -
20 MHz.
Production of a miniature PVdF Hydrophone.
Mutual comparison of the properties of both detection
schemes.
Exploration of the properties of both systems in the
frequency range beyond 20 MHz.
Measurement of acoustic field parameters with
commercially available ultrasonic diagnostic devices in
the frequency range 20-50 MHz.

State of progress

An LPH system has been set up to reliably determine its
physical properties when measuring pressure transients in
the frequency range of 3 to 20 MHz and the pressure range
of 0.1 to 10 MPa. For the future calibration procedure
especially diffraction effects are being worked on. In
parallel the miniaturised piezo-electric hydrophone has
been designed towards an active element diameter of 40
microns. Also, appropriate means of measurement have been
set up to precisely evaluate the properties of the
optical as well as of the piezo-electrical hydrophones.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Rheinische Friedrich-Wilhelms-Universität Bonn
Address
25,Sigmund-freud-straße
53105 Bonn
Germany

Participants (1)

Precision Acoustics Ltd
United Kingdom
Address
1 Colliton Walk
DT1 1TZ Dorchester