-
[show abstract]
[hide abstract]
ABSTRACT: This work describes an investigation into the first order parasitic mode (i.e., that closest to the fundamental thickness mode) that can occur in 2-2 and 1-3 thickness drive piezoelectric composite transducers. Specifically, the authors compare the performance of piezoceramic and piezocrystal composites with a common passive phase. A local Lamb wave approach is used to describe the generation of such modes, and the validity of this theory is investigated over the entire volume fraction range. It is shown that, when the parasitic mode is primarily generated by Lamb wave activity in the passive phase, both active materials demonstrate similar behavior. However, at higher volume fractions, the first order mode is related to the lateral resonance of the active material, and quite different behavior may be observed between the two sets of devices. The phase velocity of the parasitic modes in each device configuration was investigated by a combination of experimental measurement on a number of transducers along with simulations using the finite-element code PZFlex. Both 2-2 and 1-3 composites made from the single crystal materials pzn-4.5%pt, pzn-8%pt, and pmn-30%pt were investigated along with composites made from pzt5h ceramic. The PZFlex results are compared with experimental impedance analysis and laser scanning of surface displacement, with good agreement demonstrated. By comparing two very different active materials, additional insight into parasitic resonant activity within composite devices is demonstrated
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 09/2006; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Piezoelectric composite transducers have many recognised advantages for medium frequency (0.2 MHz-20 MHz) ultrasound applications. However, the extension to lower frequency bands has not been straightforward, especially with regard to active (i.e. transmission) behaviour. Manufacture from single ceramic blocks is problematic, due to polarisation limitations and inevitably, the low capacitance compromises transmit sensitivity. Alternative configurations, based on multilayered stacks can overcome most of these problems but introduce additional complexities with device manufacture and operational robustness. This paper presents a different method for manufacture of low frequency composites, utilising the fundamental symmetric Lamb mode (S0) in a conventional thickness drive piezoelectric plate. A composite plate, with electrodes positioned on the major faces, is driven at the fundamental frequency corresponding to the plate length dimension. This is shown to correspond with the S0 mode and demonstrates low loss, longitudinal wave propagation, with uniform surface displacement at the end faces that are normal to the direction of wave travel. A combination of experiment and finite element modelling using PZFlex is used to demonstrate the validity of this approach for low frequency (10 kHz-100kHz) 2-2 piezoelectric composite arrays. Measured coupling coefficients of approximately 0.5 for pzt5h ceramic and 0.8 for single crystal pmn-pt are shown to provide good agreement with theory as do laser scans of the radiating surface profile. The simulated TVR is superior to ceramic based tonpilz configurations of a similar frequency.
Ultrasonics Symposium, 2004 IEEE; 09/2004
-
[show abstract]
[hide abstract]
ABSTRACT: Ultrasonic array technology is used in many imaging applications across a wide range of industrial sectors, including underwater sonar. Lead based single crystal materials such as pzn-pt and pmn-pt provide the possibility of manufacturing sonar arrays with significantly increased sensitivity and bandwidth, compared to conventional arrays based on piezoelectric ceramic designs. To take full advantage of single crystal materials, it is essential that the active transducer array should be efficient, unimodal over the frequency range of operation and demonstrate a wide directional response from individual array elements. One solution, which offers significant advantages, involves piezoelectric composites, comprising a matrix of active piezoelectric elements embedded within a passive, usually polymeric, material. This paper describes a theoretical and experimental investigation into mechanical cross talk within 1-3 and 2-2 connectivity piezoelectric composite array configurations. The study incorporates both piezoelectric ceramic, lithium niobate and pmn-pt single crystal array designs, with the theoretical and experimental comparison based on impedance characteristics and cross talk between array elements. The electrical impedance and mechanical cross talk predicted using PZFlex with good agreement demonstrated. The design techniques obtained from PZFlex, are shown to produce arrays with low cross talk and therefore desirable beam patterns.
Ultrasonics, 2003 IEEE Symposium on; 11/2003
-
[show abstract]
[hide abstract]
ABSTRACT: This paper investigates suppression of Lamb waves in piezoelectric composite transducers by matching their frequency to the even harmonics of the device thickness mode. This was done by a combination of experimental measurement on a number of transducers along with simulations using the finite element code PzFlex. Both 2-2 and 1-3 composites made from the single crystal materials pzn-4.5 % pt and pzn-8 % pt were investigated along with composites made from pzt5h ceramic. The theory is supported by means of experimental impedance analysis and laser scanning of surface displacement, with good agreement demonstrated.
Ultrasonics Symposium, 2002. Proceedings. 2002 IEEE; 11/2002
