Thesis
Modelling and design of 1-3 piezoelectric composite transducers
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2001
- Thesis identifier
- T10361
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- In any ultrasonic system, the transducer is responsible for electro-mechanical energy conversion during the generation and detection of signal data. Arguably, it is the most important element of the system, since front-end data quality is pivotal to subsequent processing and analysis stages. Conventionally, ultrasonic transducers are fabricated from solid, piezoceramic materials. These are mechanically stiff and usually demonstrate resonant behaviour with low intrinsic loss. The resultant mechanical matching to fluid media is thus problematic and much attention has been devoted to improving bandwidth and sensitivity in such situations. Piezoelectric composite transducers, comprising a controlled combination of active and passive materials, were developed originally to improve matching, bandwidth and efficiency for operation into liquid load media. The 1-3 structure consists of an array of active piezoceramic pillars, embedded within a passive (usually polymeric) host matrix. In this case the complementary properties of the constituent phases may be used to lower mechanical impedance, thereby improving interface matching to a fluid load medium. At the same time, transducer efficiency may be improved when compared to the solid piezoceramic device, due to the reduced lateral clamping of the active pillars. Bandwidth is also extended, since the increased energy transfer into the load medium reduces the overall cavity resonance of the transducer. Although only two phases are involved, the behaviour of 1-3 piezoelectric composite transducers is a complex combination of phase volume fraction, piezoceramic pillar dimensions, shape, periodicity and material properties, in addition to the elastic and viscoelastic characteristics of the passive filler material. Moreover, introduction of a polymeric or urethane material invariably increases the internal mechanical wave absorption, leading to an increase in electrical (thermal) noise and potential problems with thermal dissipation at higher operating power levels. Consequently, for a given application, the design compromises may be extremely sophisticated and system optimisation can be very difficult. This Thesis describes the rationale and progress made during 18 years of research into the understanding of 1-3 piezoelectric composite behaviour. A major objective has been the creation of design guidelines for a range of different applications. In the present context, these relate specifically to underwater sonar and through air non-destructive testing. The research has received significant international recognition in both application areas. The Thesis is divided into 3 main sections, embracing mathematical modelling of the 1-3 structures, 1-3 piezoelectric composite design, and finally, a section detailing the engineering applications output of the research.
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