Thesis Presented for the Degree of
Magister Technologiae
in the Department of Electrical Engineering
Cape Peninsula University of Technology
2006 / Because of the nature of piezoelectric ceramics and the physical construction pf high
power piezoelectric transducers, such devices are inherently non-linear and become unpredictable
when driven at high power. To drive an ultrasonic transducer or an array
thereof efficiently, specific resonant points are used. These poin~s are characterised by the
devices' mechanical modes of oscillation. At high electrical power levels, the resonance
points of PZT transducers vary. The movement of the resonances points in the frequency
domain, coupled with the transducers high Q, is severe enough to seriously hamper the
devices' efficiency. The problem is specifically apparent when multiple transducer arrays
are driven at power. The electrical fluctuations and interactions of the characteristics of
separate transducers cause arrays to be driven efficiently at a single resonance point.
To efficiently drive an array of PZT transducers it is necessary to employ a .suitable
technique. Although several methods exist in the literature, each is designed for a specific
configuration of transducers and dedicated matching circuitry. The fundamental
flaw in most methods is that they are conceived with the assumption all PZT transducers
are identical and can be driven as such. Inherent nonlinearities caused by poling
and construction methods, result in each transducer to be slightly different causing a
superposition of resonance frequencies for each transducer array.
Existing methods cannot be used to efficiently drive generic transducer arrays and
a novel approach has been adopted to accommodate transducer nonlinearities. This
novel approach can be described as a culmination of two driving techniques and has been
named, Swept Frequency Dwelling (SFD). This thesis examines five different driving
techniques and quantifies their effectiveness by means of experimental evaluation proficiencies.
The driving techniques are grouped into two categories - straight driving
techniques and frequency sweeping techniques - which are compared and evaluated.
In conclusion, a novel method for driving ultrasonic transducer arrays was established
with the aim of eliminating some detrimental effects of other driving techniques, while
exploiting some of their positive attributes and was found to be effective.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/1089 |
| Date | January 2006 |
| Creators | Smith, Tarren MJ |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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