High temperature, high power piezoelectric composite transducers (original) (raw)
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Improving the thermal stability of 1-3 piezoelectric composite transducers
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2005
The effect of temperature on the behaviour of 1-3 piezoelectric composites manufactured using various polymeric materials was assessed experimentally through electrical impedance analysis and laser vibrometry. Device behaviour varied with temperature irrespective of the polymer filler. Most significant changes in the piezoelectric composites were recorded around the glass transition temperature (T g) of the polymer; movement to lower fundamental resonant frequencies and higher values of electrical impedance minima were observed at higher temperatures. Decoupling of the pillars from the polymer matrix was observed by laser vibrometry at high temperatures. The use of high T g polymer extended the operational temperature range of a piezoelectric composite and a high T g polymer with improved thermal conductivity also proved beneficial. For all devices, at temperatures very close to room temperature, subtle changes in device performance, linked to polymer softening, were observed. Particulate filled materials have been investigated and it is recognised that the high viscosities and low mechanical damping of such materials could be problematic for piezoelectric composite manufacture. Finally, the thermal solver of the PZFlex finite element code has been used to predict the temporal and spatial temperature response of a selection of the devices presented. The simulated and experimental data compare favourably.
Piezocomposite transducer design and performance for high resolution ultrasound imaging transducers
International Journal of Computational Materials Science and Engineering
Piezocomposite design for dedicated ultrasonic imaging applications requires precise homogenization models for predicting the electromechanical characteristics of the new material. Thus, several homogenization models have been developed. As part of this work, we applied several analytical homogenization models for piezocomposite of 2–2 and 1–3 connectivities. To validate these analytical models, a comparative study was made between various models and experimental measurements. As a result, these homogenized electromechanical properties are effectively used for the calculation and comparison of electroacoustic response for typical transducers aimed at ultrasound imaging applications. An optimal design of transducer aimed at ultrasound imaging applications is proposed as a dedicated imaging performance index, elaborated through a trade-off between sensitivity and bandwidth.
Physics Letters A, 2021
Analytical models can be useful tools to develop efficient transducers dedicated to a specific application field. This work proposes a homogenization technique for establishing the effective coefficients and parameters of 1-3 piezocomposite whose both phases are piezoelectrically active. Such piezocomposite materials may have homogenized electromechanical properties resulting from positive hybrid effect. A numerical simulation of the effective parameters resulting from a PZT-5A / PVDF-TrFE composition shows that, volume fraction influences significantly on the properties of the piezocomposite and consequently on its behavior in service. As an end-user application for ultrasound imaging, those piezocomposite materials are effectively integrated in a piezocomposite transducer, coupled with a dedicated backing. The resulting characteristics in terms of impulse response and associated electroacoustic echo are compared and discussed for typical configurations. A method for the optimization of the design of such piezocomposite transducer is presented. Specific estimators based on the bandwidth flatness BWF and bandwidth amplitude product BWA are proposed as stable and smooth criteria for an optimization procedure.
Design considerations for 1-3 composites used in transducers for medical ultrasonic imaging
Ceramic polymer piezoelectric composites with 1-3 connectivity have become an important tool in the design and manufacture of thickness mode transducers for medical diagnostic ultrasonic imaging. The major reasons for this are that, relative to piezoelectric ceramics alone, the composite can be designed with higher thickness coupling coefficient. acoustic impedance can be more closely matched to human tissue, arid low frequency lateral resonances can be suppressed. These improvements can lead to higher sensitivity and bandwidth in the transducer and reduce ringing due to unwanted modes of vibration. This paper compares annular array transducers made from ceramics alone to those made with composites to demonstrate the advantages of composites, and examines some of the trade-offs involved in optimizing composite designs for this application. Effects of varying Young's modulus and Poisson's ratio of the polymer phase on coupling coefficient and high frequency lateral resonances of the composite are presented.
High Efficiency Non-Contact Transducers and a Very High Coupling Piezoelectric Composite
Despite the usefulness of ultrasound for materials analysis, this age-old method has been stifled by direct or indirect transducer contact to the test media, generally by liquids. Consequently, a branch of materials that are porous, liquid-sensitive, food, pharmaceuticals, wood lumber, concrete, consolidated powders, or in early stages of formation cannot be analyzed by ultrasound without adversely affecting them. While Non-Contact Ultrasound (NCU) is highly desired, yet its realization calls for overcoming natural barrier of massive Zmismatch between NTP coupling air and solids, which can be between <3 to >7 orders of magnitude! This is only possible if transducers are characterized by phenomenally high transduction efficiency in air. After a struggle of more than 20 years, in 1997 we finally succeeded in creating ultrasound devices between <60kHz to ~10MHz, capable of generating 10s to 100s of Pa/V acoustic pressure in air-US and internationa lly patented. In practical terms, the NCU transducers are capable of driving ultrasound through any material even with relatively low energy excitation and amplification. This paper presents acoustic characteristics of NCU transducers, experimental evidence of their exceptionally high efficiency, and applications possibilities for NDT, sensing, proximity analysis, and more. Here we also introduce a new piezoelectric composite that is characterized by the highest coupling, zero cross-talk, broad bandwidth, very low dielectric constant, and several other advantages-US and international patents pending. NCU and other transducers based upon this material are characterized by efficiency that is twice that of conventional piezoelectric composites. Realities that defy Non-Contact Ultrasound: In order for NCU to become a reality for analytical and other applications of ultrasound, the significance of transducer efficiency cannot be overestimated. Assuming that the first medium of ultrasound propagation is ambient air before it encounters a solid medium, two natural phenomena defy the NCU reality, Fig. 1. These are absorption of ultrasound by air and near total reflection of
Piezoelectric materials for high frequency medical imaging applications: A review
Journal of Electroceramics, 2007
The performance of transducers operating at high frequencies is greatly influenced by the properties of the piezoelectric materials used in their fabrication. Selection of an appropriate material for a transducer is based upon many factors, including material properties, transducer area, and frequency of operation. This review article outlines the major developments in the field of piezoelectrics with emphasis on materials suitable for the design of high frequency medical imaging ultrasonic transducers. Recent developments in the areas of fine grain and thin film ceramics, piezo-polymers, single crystal relaxor piezoelectrics, as well as lead-free and composite materials are discussed.
Ultrasonics …, 2004
Potential applications of high frequency ultrasound exist because of the high spatial resolution consequent upon short wavelength. The frequencies of interest, typically from 25 MHz upwards, are easily supported by modern instrumentation but the capabilities of ultrasonic transducers have not kept pace and the transducers in high frequency commercial ultrasonic systems are still made with single-phase crystal, ceramic or piezopolymer materials. Despite potential performance advantages, the 1-3 connectivity piezoelectric ceramic-polymer composite materials now widely used at lower ultrasonic frequencies have not been adopted because of manufacturing difficulties. These difficulties are centred on fabrication of the 1-3 piezoceramic bristle-block comprising tall, thin pillars upstanding from a supporting stock. Fabrication techniques which have been explored already include injection moulding, mechanical dicing, and laser machining. Here, we describe an alternative technique based on viscous polymer processing (VPP) to produce net shape ceramic bristle-blocks. VPP produces green-state ceramic with rheological properties suitable for embossing. We outline how this can be created then report on our work to fabricate PZT bristle-blocks with lateral pillar dimensions of the order of 50 lm and height-to-width ratios of the order of 10. These have been backfilled with low pre-cure viscosity polymer and made into complete 1-3 piezocomposite transducer elements. We outline the performance of the transducers in terms of electrical impedance and pulse-echo behaviour and show that it corresponds well with computer modelling. We conclude that VPP is a promising technique to allow the established advantages of piezocomposite material to be exploited at higher frequencies than have been possible so far.
High frequency piezo-composite transducer array designed for ultrasound scanning applications
Proceedings of the IEEE Ultrasonics Symposium
A 20 MHz high density linear array transducer is presented in this paper, This array has been developed using an optimized ceramic-polymer composite material. The electro-mechanical behaviour of this composite, especially designed for high frequency applications, is characterised and the results are compared to theoretical predictions. To support this project, a new method of transducer simulation has been implemented. This simulation software takes into account the elementary boundary phenomena and allows prediction of inter-element coupling modes in the array. The model also yields realistic computed impulse responses of transducers, A miniature test device and water tank have been constructed to perform elementary acoustic beam pattern measurements. It is equipped with highly accurate motion controls and a specific needle-shaped target has been developed. The smallest displacement available in the three main axes of this system is 10 microns. The manufacturing of the array transd...
Characterization of multilayered piezoelectric ceramics for high power transducers
Ultrasonics, 2002
In some circumstances, large vibrational displacements at ultrasonic frequency must be generated using a low voltage drive. This result cannot be obtained with monolithic PZT ceramics which require voltages larger than 1000 V to produce displacements of the micrometer order at resonance. The use of multilayered hard lead zirconate titanate ceramics as transduction material in resonant devices is experimentally investigated for Langevin-type transducers. Large amplitudes are obtained under low drive (5 lm under 10 V). Material constant (compliance, losses) variations under large dynamic stress are, at least, one order of magnitude larger than for monolithic ceramics. Depolarization is found to be a critical issue when the transducer is driven continuously. It is demonstrated that this problem can be solved by polishing the interfaces between different parts of the device and applying an electrical DC bias to the transducer. Ó