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Optimisation of the pulse-echo method with an application to acoustic thermometry
Author(s)
Burger, Gert Cloete
Date Issued
2010
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
In acoustics, pulse echo methods are well known as a means of measuring time of Hight. Traditional
techniques for generating acoustic waves in solid ferromagnetic waveguides include piezoelectric,
capacitive and magnetostriction. Piezoelectric and capacitive techniques are preferred
due to the inefficiency of magnetostriction caused by electro-mechanical coupling losses and the
fact that most ferromagnetic materials show low levels of magnetostriction. The aim of this
study was to optimise the magnetostrictive effects for sensing applications based on a ferromagnetic
waveguide using the pulse echo method. The results obtained were implemented in the
design of an acoustic thermometer.
Two configurations for signal generation and recovery were examined, the use of a single
wound copper coil acting as a transceiver coil, and the use of separate transmit and receive
coils. Results obtained using the latter configuration indicated better signal to noise ratio's and
provided the flexibility to manipulate the point of signal recovery. The pulse echo method was
implemented and optimised.
An acoustic thermometer based on an existing design was developed by inducing a partial
reflection from a set position in the waveguide, defining a sensing probe. Awareness of the elastic
properties of the waveguide material enabled the guaging of its temperature by measuring the
acoustic pulse velocity in the probe.
The accuracy of the instrument was increased through signal conditioning, examined together
with cross correlation and an increased sampling frequency. Systematic errors were resolved
through calibration, giving the instrument an overall accuracy of ±O.56"C for the range of
temperatures between 2O"C and 400"C.
techniques for generating acoustic waves in solid ferromagnetic waveguides include piezoelectric,
capacitive and magnetostriction. Piezoelectric and capacitive techniques are preferred
due to the inefficiency of magnetostriction caused by electro-mechanical coupling losses and the
fact that most ferromagnetic materials show low levels of magnetostriction. The aim of this
study was to optimise the magnetostrictive effects for sensing applications based on a ferromagnetic
waveguide using the pulse echo method. The results obtained were implemented in the
design of an acoustic thermometer.
Two configurations for signal generation and recovery were examined, the use of a single
wound copper coil acting as a transceiver coil, and the use of separate transmit and receive
coils. Results obtained using the latter configuration indicated better signal to noise ratio's and
provided the flexibility to manipulate the point of signal recovery. The pulse echo method was
implemented and optimised.
An acoustic thermometer based on an existing design was developed by inducing a partial
reflection from a set position in the waveguide, defining a sensing probe. Awareness of the elastic
properties of the waveguide material enabled the guaging of its temperature by measuring the
acoustic pulse velocity in the probe.
The accuracy of the instrument was increased through signal conditioning, examined together
with cross correlation and an increased sampling frequency. Systematic errors were resolved
through calibration, giving the instrument an overall accuracy of ±O.56"C for the range of
temperatures between 2O"C and 400"C.
Additional information
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009
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Optimisation of the Pulse-Echo method with an application to acoustic thermometry.pdf
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