A simple physical model of 1-3 composite piezoelectrics is advanced for the material properties that are relevant to thickness-mode oscillations. This model is valid when the lateral spatial scale of the composite is sufficiently fine that the composite can be treated as an effective homogeneous medium. Expressions for the composite's material parameters in terms of the volume fraction of piezoelectric ceramic and the properties of the constituent piezoelectric ceramic and passive polymer are derived. A number of examples illustrate the implications of using piezocomposites in medical ultrasonic imaging transducers. While most material properties of the composite roughly interpolate between their values for pure polymer and pure ceramic, the composite's thickness-mode electromechanical coupling can exceed that of the component ceramic. This enhanced electromechanical coupling stems from partially freeing the lateral clamping of the ceramic in the composite structure. Their higher coupling and lower acoustic impedance recommend composites for medical ultrasonic imaging transducers. The model also reveals that the composite's material properties cannot be optimized simultaneously; tradeoffs must be made. Of most significance is the tradeoff between the desired lower acoustic impedance and the undesired smaller electromechanical coupling that occurs as the volume fraction of piezoceramic is reduced. >

Modeling 1-3 composite piezoelectrics: thickness-mode oscillations

Advantages and Challenges of Relaxor-PbTiO3 Ferroelectric Crystals for Electroacoustic Transducers- A Review.

Piezoelectric Fiber Composites were previously introduced as an alternative to monolithic piezoceramic wafers for structural actuation applications. This manuscript was an investigation into the improvement of piezoelectric fiber composite performance through a nonconventional electroding scheme. Two microelectromechanical models were developed that predict the composite properties. These models were used to examine the trends of composite properties versus fiber volume fraction for various constituent materials. Several etched electrode PZT fiber composites, with fiber volume fractions ranging from 7% to 58%, were manufactured and tested. Experimental measurements showed excellent agreement with both the trends and magnitude of model predicted values. The maximum fiber volume fraction composites demonstrated a capacitance (E3 /Eo) of 550, piezoelectric free strain constants (d33 and d31) of 150 pm/V and-70 pm/V, and piezoelectric clamped stress (e33) of 5 C/m2, showing a substantial improvement over prev...

Piezoelectric Fiber Composites with Interdigitated Electrodes

Abstmcr-The objective of the present work was to gain a deeper mensions of the transducer are much smaller than the understanding of the behavior of lead zirconate titanate (PZT) polymer composites for applications such as ultrasonic medical diagnosis in the megahertz frequency range. These composites were originally developed for low-frequency hydrophone applications. The PZT rod-polymer composites have been prepared with five to 30 volume percent PZT using 0.28 mm and 0.45 mm rods. In a disc of PZT rod-polymer composite material, there are three principal types of resonance: the planar mode, the thickness mode, and various lateral modes caused by the regular periodicity of the PZT rod in the composite. These resonance modes have been studied with the following techniques: 1) electrical impedance measurement as a function of frequency and 2) laser probe dilatometry of the dynamic displacement as a function of frequency and position in the composite lattice. The observed resonance behavior is found to be a result of lateral interactions in the composite through the epoxy medium. The effect of temperature on the electromechanical properties of the composite has also been investigated. Implications of these results for optimizing the design of ultrasonic transducers are discussed.

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Piezoelectric Composite Materials for Ultrasonic Transducer Applications. Part I: Resonant Modes of Vibration of PZT Rod-Polymer Composites

The main objective of this article is to present an overview of the modelling that has been proposed by various workers in the field of smart or intelligent structures. Before the main discussion o...

L.J. Bowen

Papers

Composite piezoelectric transducers

Composite Piezoelectric Transducers