陶瓷骨架对3-3型复合材料压电性能的影响

本工作研究了压电陶瓷的化学组成对3-3型复合材料介电、压电性能的影响。选用了三种类型的压电陶瓷:“硬性”压电陶瓷(PZT-F)、“软性”压电陶瓷(PZT-N)和“稳定型”压电陶瓷(PZT-C)。实验结果指出:以PZT-F 和 PZT-C 为骨架制成的复合材料仍然具有较低的体积密度、较高的静水压灵敏度、小的机械品质因数和较小的介质损耗,同时其耐静水压稳定性也有所改善。这种复合材科已装配成发射型换能器,成功地用于地震模拟试验。这类材料的问世将有助于宽带换能器的发展。     

Acoustic emission in a composite copper NbTi conductor

Acoustic emission generated in a composite copper multifilamentary NbTi conductor has been measured. Its source appears to be dissipation associated with the Lorentz force induced flux motions. It is demonstrated that acoustic emmision transducers can be used to detect a superconducting-to-normal transition.     

Functional composites for sensors,actuators and transducers

Following the trend in structural applications, composite structures are being used more commonly in transducer applications to improve acoustic, mechanical and electrical performance of piezoelectric devices. Functional composite transducers for actuators and sensors generally consist of an active ceramic phase incorporated with a passive polymer phase, each of which has a phase transition associated with it. In this paper, several polymer–piezoelectric ceramic composite transducers, mostly designed for sensing hydrostatic waves, are discussed based on the connectivity of the constituent phases. Also discussed are some recent examples of metal–ceramic composites, and single element ceramic transducers with modified shapes for improved performance. A comparison of these designs is given based on their hydrophone figure of merit (d_h·g_h).     

Lamb Waves for Damage Localisation in Panels

Abstract: In this study, Lamb wave propagation phenomena have been used to localise discontinuities in aluminium and composite panels. For that purpose, piezoelectric transducers have been used to excite and register Lamb waves in the panels. Excited waves that propagate and reflect from the panel edges and discontinuities were registered by piezoelectric sensors as voltage changes in time. Three different experiments have been conducted to investigate the wave propagation phenomena. In the first experiment, the attenuation and dispersion of Lamb waves in the aluminium panel has been studied. The second experiment has been oriented to localise an additional mass attached to the same panel. A dedicated signal‐processing algorithm has been developed to aid the localisation procedure that allowed to extract relevant features of the discontinuity. The algorithm has been tested on signals from the panel with and without the additional mass. The results obtained have been compared to find the position of the discontinuity. The third experiment concerned a more realistic damage scenario when piezoelectric transducers have been arranged as a clock‐like array to find a crack in a composite panel.     

Single Sided Inspection of Composite Materials Using Air Coupled Ultrasound

A single sided, air coupled ultrasonic NDT system based on the generation and reception of the a₀ Lamb mode is described. 1–3 composite ultrasonic transducers are employed, transmitting and receiving transducers being oriented at the appropriate coincidence angle for the generation and detection of the mode; they are placed close together and scanned over the surface of the plate to produce a C-scan image. Tests have been carried out on carbon fiber composite plates with delamination defects, the damaged areas being readily detected. The measurements have also been compared with numerical predictions based on a finite element model, good agreement being obtained.     

Diffraction effects in hydrophone measurements

Theoretical and experimental methodology are presented for accurately determining the effective radii of unfocused, circular plane piston transducers as well as using tone burst hydrophone measurements to verify steady-state theoretical calculations. Experiments using two specially fabricated unfocused, composite piezoelectric transducers demonstrate the validity of the methodology. For spherically focused circular transducers, a simple model is used to estimate the transient diffraction encountered in co-axial flat hydrophone measurements.     

Single element high frequency (<50 MHz) PZT sol gel composite ultrasound transducers

A sol gel composite process has been used to produce lead zirconate titanate coatings in the thickness range of 3 to 100 mum on aluminum substrates. The complex permittivity (epsilon(33)(S )), elastic stiffness (c(33)(D)), and the piezoelectric constant (h(33)) of the coating and the complex elastic stiffness (c(33)(D)) of the substrate have been determined using impedance measurements and a commercially available software program [Piezoelectric Resonance Analysis Program PRAP 2.0, TASI Technical Software, Kingston, Ontario, Canada]. The complex components of the material parameters account for the losses within the film and the substrate. Sol gel composite films on aluminum have a dielectric constant of 220 with an imaginary component of 1% and an electromechanical coupling coefficient of up to 0.24 with an imaginary component of 3%. These films are applied to the fabrication of a high frequency transducers suitable for ultrasound biomicroscopy (UBM). By combining the sol gel composite material with existing transducer fabrication techniques, single-element focusing transducers have been produced that operate in the frequency range of 70 to 160 MHz. Devices have -6-dB bandwidths up to 52% and minimum insertion losses ranging from -47 to -58 dB. Real-time images of phantom materials and ex vivo biological samples are shown.     

Health monitoring of concrete structures strengthened with advanced composite materials using piezoelectric transducers

An active damage interrogation (ADI) method which uses an array of piezoelectric (PZT) transducers attached to a structure was used to detect and localize disbonds and delaminations of advanced composite reinforcement from concrete structures. The ADI system provides the ability to detect, localize, and estimate the extent of the disbond by actively exciting the structure with PZT transducers and processing the structural response as measured by the PZT transducers. The ADI system makes use of both amplitude and phase information from various actuator/sensor transfer functions, and also provides a unique method for determining when the transducer/structure bond has degraded. This paper investigates the feasibility of using the ADI method for health monitoring of concrete structures repaired with composite materials, and the advantages and limitation of this method are discussed.     

A review on the development of piezoelectric composites forunderwater acoustic transducer applications

For future sonar transducer applications that emphasize the detection of acoustical signals in a hydrostatic mode, new piezoelectric composite materials have been developed. Ceramic-polymer composites having `1-3' and `0-3' connectivity patterns are shown to exhibit much higher sensitivities than conventional PZT ceramics. Glass-ceramic composites are free of aging, and have potential applications in standard transducers     

The performance and applications of PZT composite transducer with 3-3 connectivity

The performance of 3-3 connectivity composite piezoelectric transducers is discussed. This type of transducer has been successfully used in ultrasonic imaging (frequency range: 150~600 kHz). Using a simple hardware system, this type of transducer can recognize a very thin aluminum plank (6 mm in thickness) in water, and it can clearly recognize a multilayer body.     

Radially composite piezoelectric ceramic tubular transducer in radial vibration

The radially composite piezoelectric tubular transducer is studied. It is composed of radially poled piezoelectric and a long metal tube. The electro-mechanical equivalent circuit of the radially poled piezoelectric and metal tube in radial vibration is obtained. Based on the force and velocity boundary conditions, the six-port electro-mechanical equivalent circuit for the composite tubular transducer is given and the resonance/anti-resonance frequency equations are obtained. The relationship between the resonance frequency and the dimensions is analyzed. Numerically simulated results obtained by the finite element method are compared with those from the analytical method. Composite piezoelectric tubular transducers are designed and manufactured. The resonance/anti-resonance frequencies are measured, and it is shown that the theoretical results are in good agreement with the simulated and experimental results. It is expected that radially composite piezoelectric tubular transducers can be used as high-power ultrasonic radiators in ultrasonic applications, such as ultrasonic liquid processing.     

Avoiding diffraction grid effect in ultrasonic fields of 1-3 PZT polymer piezocomposite transducers

Improvement of sensitivity in ultrasonic fields of piezocomposite transducers is limited because of diffraction effects arising from the periodic structure. We present a theoretical and experimental study of ultrasonic fields of 1-3 PZT polymer piezocomposite transducers. The relation between the composite grid periodicity and the wavelength is critical in order to obtain a far field similar to that of homogeneous transducers. If diffraction grid effect is present, it results in an important energy loss in the higher diffraction orders. These higher orders perturb the central field of the transducer because of multipath contributions to the main lobe caused by reflections from the boundaries of the test sample.     

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO₃) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO₃) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 Ω for the PZT fiber composite and PbTiO₃ ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO ₃ and PbTiO₃ transducers provided better image contrast than the other materials     

Modeling 1-3 composite piezoelectrics: thickness-mode oscillations

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.     

Dynamic characteristics of 2-2 piezoelectric composite transducers

Lateral resonant modes associated with specific lateral structures in piezoceramic-polymer composites are the main drawback that interferes with performance of ultrasonic transducers utilizing the composites as driving elements. This paper presents a field solution to characterize dynamic behavior of lateral modes in composite transducers with 2-2 connectivity. The solution is derived based on a concept of Lamb wave propagation along piezoceramic and polymer layers in the thickness direction of the composite transducers. The behavior of 2-2 composite is investigated over a broad spectrum ranging from quasi-static stage up to mode transition zones. Dispersion curves for various modes were calculated and compared with experimental results. A safe zone can be identified from the dispersion curves where the interference of lateral modes to thickness oscillation is negligible. Strong interactions between thickness modes and lateral modes are observed in the transition zones where two modes merge together in the frequency domain. Electromechanical thickness coupling coefficient, k_t, is calculated for the first time to include the effect of aspect ratio of the composite. Results show that the coupling coefficient, k_t, varies dramatically as a function of both ceramic volume fraction and the aspect ratio. As k_t reaches its maximum value, the vibration of the ceramic phase is completely decoupled from that of the polymer phase     

Comparative analysis between active and passive current transducersin sinusoidal and distorted conditions

Current measurements are a critical item in the monitoring of modern electrical power plants, since the quantities to be measured often show high harmonic content. The current transducers should therefore guarantee a good accuracy even when they operate with distorted waveforms. In this paper, the behavior of some devices commonly used for current measurement is examined, considering either sinusoidal or distorted conditions. Traditional current transformers, transducers based on the Hall effect, and resistive shunts combined with isolation amplifiers have been considered. The comparison is performed by evaluating a synthetic error index, called composite error, which allows all the main causes of uncertainty (amplitude errors, time shifts, and distortion) to be taken into account. The proposed investigation aims to find out the main characteristics that make each transducer suitable or unsuitable in different practical situations     

Feasibility on fiber orientation detection of unidirectional CFRP composite laminates using one-sided pitch–catch ultrasonic technique

It is important to assess fiber orientation, material properties and part defect because strength and stiffness of composites depend on fiber orientation of CFRP (carbon fiber reinforced plastics). A one-sided pitch–catch setup was used in the detection and evaluation of ultrasonic wave behavior and fiber orientation in the unidirectional CFRP composite laminates. Two Rayleigh wave transducers were joined head-to-head and used in the pitch–catch mode on the surface of the composites. The pitch–catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composite. Especially, one-sided ultrasonic measurement was made with using a Rayleigh wave transducers and the Rayleigh ultrasonic waves were extensively characterized in the CFRP composite laminates. Also, a conventional scanner was used in an immersion tank for extracting fiber orientation information in the unidirectional laminate. Therefore, it is thought that the proposed method is useful to evaluate integrity of CFRP laminates.     

Characterization of air-coupled transducers

This paper describes a theoretical and experimental study for determination of the through-air system impulse response and insertion loss with different air-coupled ultrasonic transducers. Wide-band piezopolymer transducers (PVDF) are employed in both transmission and reception modes and their behavior assessed by means of mathematical modeling and experiment. Specifically, a linear systems approach, modified to include the influence of attenuation in the propagation medium, was used to design suitable PVDF transducers for wide-band operation in air. Suitable devices were then manufactured for determination of the transmission and reception response characteristics of piezocomposite and electrostatic transducers when operating in the air environment. A range of transducers was evaluated, including 1-3 connectivity composites of different ceramic volume fraction and mechanical matching conditions, in addition to electrostatic devices of varying design. To complement the investigation, relative performances for narrow-band operation are also presented under transmission and transmit-receive conditions. Despite the obvious measurement difficulties, good agreement between theory and experiment was observed and the methodology is shown to provide a convenient and robust procedure for comparison of through-air transducers operating in the frequency range 50 KHz to 2 MHz. Although highly resonant, the most effective composite transducers under consideration demonstrate an improvement in two-way insertion loss of 22.4 dB and 11.5 dB over a corresponding electrostatic pair, under narrow-band and wide-band operation, respectively     

Acoustic emission for in situ monitoring in metal-matrix composite processing

The attractive elevated-temperature properties of metal-matrix composities (MMCs) have not been exploited in commercial applications partly because of the high processing cost and lack of reliability in fabrication. In this exploratory study, the feasibility of using acoustic emission (AE) as an in-process, non-destructive quality control technique is examined. A variation of the squeeze casting technique is selected for investigation. Acoustic emission is employed with the intent of non-intrusively establishing whether complete infiltration has occurred during composite fabrication. The problems due to the background noise during AE monitoring are overcome by using transducers with different frequency responses. The acoustic signatures of machine noise, preform crushing and metal solidification are obtained by employing suitable transducers in a series of tests that systematically evaluate the individual processes that comprise infiltration casting. The results form a strong basis for the development of an in situ AE sensor for the infiltration process.     

Solid freeform fabrication of piezoelectric sensors and actuators

The last two decades have witnessed the proliferation piezoelectric composite transducers for an array of sensor and actuator applications. In this article, a concise summary of the major methods used in composite making, with special emphasis on Solid Freeform Fabrication (SFF), is provided. Fused Deposition of Ceramics (FDC) and Sanders Prototyping (SP) are two SFF techniques that have been utilized to make a variety of novel piezocomposites with connectivity patterns including (1-3), (3-2), (3-1), (2-2) and (3-3). The FDC technique has also been used to prototype a number of actuators such as tube arrays, spiral, oval, telescoping, and monomorph multi-material bending actuators. It has been demonstrated that SFF technology is a viable option for fabricating piezocomposite sensors and actuators with intricate geometry, unorthodox internal architecture, and complex symmetry. The salient aspects of processing of such composite sensors and actuators are summarized, and structure-processing-property relations are elaborated on.