Multilayer Transducers Research Articles

Synthesis of single-phase perovskite Pb(Zn1/3Nb2/3)O3 using Pb3Nb2O8 and ZnO

Relaxor ferroelectrics have large dielectric constant maximum with broad phase transition regions due to the complex perovskite structure. Lead zinc niobate Pb(Zn1/3Nb2/3)O3 (PZN), a member of ABO3 structural family, where A = mono or divalent ions, B = tri, tetra or pentavalent ions, has a complex perovskite structure in which Zn2+ and Nb2+ are disordered at the B-site, which results in composition variations and corresponding fluctuations in the phase transition temperature from region to region [1, 2]. As a result the phase transition is broad and occurs over a range of temperatures called the Curie region. The Curie region for PZN occurs near 140 ◦C (crystal form) and shows many desired dielectric and piezoelectric properties for multilayer capacitor, transducer and actuator applications [3–6]. This is due to its larger electrostrictive strains, which are of an order of magnitude larger than those of BaTiO3 based ceramics and piezoelectric PZT ceramics [7, 8]. The formation of the compound in the perovskite structure should satisfy the charge neutrality and tolerance factor, t [9] as

A wavelength-tunable dispersion equalizer using a nonlinearly chirped fiber Bragg grating pair mounted on multilayer piezoelectric transducers

We realized a wavelength-tunable dispersion equalizer using a pair of nonlinearly chirped fiber Bragg gratings mounted on multilayer piezoelectric transducers. The operation region can be continuously tuned up to 7 nm by applying 50 V. This device enables us to equalize the second- and third-order dispersion of dispersion-shifted fibers with different zero dispersion wavelengths over 6 mn. This performance shows that our equalizer can be employed for adaptive equalization.

Pyroelectric PVDF sensor modeling of the temporal voltage response to arbitrarily modulated radiation

Our design of transducer arrays for custom pyroelectric sensors is mainly devoted to IR laser beam characterization and control. It benefits from some of the properties of PVDF film such as low cost, low weight, mechanical flexibility, chemical stability (inert), and compatibility of thick film interconnection technologies on metallized films. By using the temporal characteristics of the source intensity and starting from a standard equivalent one-dimensional model of a multilayer thick-film transducer in the frequency domain, we developed a computer model of the PVDF sensor that determines the temporal response to arbitrarily modulated radiation. The validation of the model accuracy has been carried out with a simulation procedure performed on a PVDF sensor designed for accurate beam alignment of low power laser beams. In this case, an iterative algorithm also was developed to estimate some thermal and physical properties of the front absorbing and the metallization layers that are generally barely known. We present a fitting procedure to determine these properties by using the temporal pyroelectric response to a square wave modulated laser diode that provides a reliable reference signal.

Model of electro-acoustic channel of a flaw detector equipped with emitting and receiving transducers

Using the model of the electro-acoustic channel for a multilayered slanted bidirectional transducer, which was developed previously, parameters of the acoustic channel equipped with the emitting and receiving transducers have been calculated. The calculations have been performed in the asymptotic approximation (ray acoustics) in the far-field zone. The calculations have been compared to experimental results.

Ultrasound transducer modeling-received voltage signals and the use of half-wavelength window layers with acoustic coupling layers

A general set of modeling equations for lossless one-dimensional multilayer ultrasound transducers is presented based on first principles. In particular, a direct relationship between ultrasound transducer results and the underlying physical principles of electroacoustics is given. As such, the model may provide better physical understanding for designers not fully versed in electrical circuits theory or in linear system analyses. The model is suitable for time-domain analysis and monofrequency design. Special attention is given to the determination of the time-dependent voltage across the receiver electrodes subject to a general voltage input, but information on any (dynamic) variable of interest is provided. The basic equations governing the dynamics of the multilayer structure acting as transmitter as well as receiver are solved by Fourier analysis and by imposing continuity of velocity and pressure between layers. Sound transmission between the two piezoelectric circuits is assumed to take place in a water bath such that the Rayleigh equation can be used to obtain the incoming pressure at the receiver aperture from the acceleration of the opposing transmitter aperture. Comparison with experimental results is possible by allowing coupling to external electric impedances. A numerical test case using a multilayered 1-MHz transducer for flow meter applications was considered and good agreement with experiments was obtained in terms of voltage signals. The transducer contains a half-wavelength stainless steel layer needed to resist corrosion, the ability to operate at temperatures in a wide range from 20 to 150 degrees Celsius, resistance to impact from flowing particles in the medium, high pressure or vacuum, and pH values up to 10 in some locations. The influence of epoxy glue and grease acoustic coupling layers-between the piezoceramics and the stainless steel layer-in the range from 1 to 70 mum was examined. It was shown that, for the same layer thickness, epoxy glue is preferred as compared with grease, both in terms of signal shapes and amplitudes. Finally, inclusion of appropriate electric impedances in the transmitter and receiver circuits is found to affect signal pulses strongly.

Multi-layer composite ultrasonic transducer arrays

A piezoelectric transducer chip comprising a plurality of transducer elements. At least one of the transducer elements is a multi-layer element which comprises a plurality of piezoelectric layers, each of which is separated from the adjacent piezoelectric layers by an electrode layer so that a plurality of capacitive elements is electrically connected in parallel. The plurality of piezoelectric layers are comprised of a plurality of piezoelectric members separated from adjacent members by a gap to form a composite piezoelectric layer. Also disclosed is a method of making a multilayer transducer of a composite piezoelectric material. Alternate embodiments include two-dimensional ultrasonic transducer arrays having multilayer elements formed of a composite piezoelectric material.

Method of manufacturing multilayer array ultrasonic transducers

A method for fabricating "1.5D" and "2D" multilayer ultrasonic transducer arrays employs dicing saw kerfs, which provide acoustic isolation between rows. The kerfs are metallized to provide electrical connection between surface electrode layers and buried internal electrode layers. A multilayer piezoceramic transducer element for a "1.5D" or "2D" array produced by this method has higher capacitance, and accordingly provides better transducer sensitivity, in comparison to a single layer element.

Electrical interconnect for multilayer transducer elements of a two-dimensional transducer array

A multilayer two-dimensional array of ultrasonic transducer elements includes four via segments at the four corners of each transducer element. A first pair of diagonally opposed via segments provide signals to signal electrode layers of each transducer element. A second pair of diagonally opposed via segments interconnect ground electrode layers. Thus, a redundant interconnection scheme is achieved. If the transducer elements include piezoelectric layers having a square cross section parallel to a transducer radiating surface, four-fold symmetry is maintained, despite the formation of the four via segments. Also disclosed is a method of forming a two-dimensional array.

Unidimensional modeling of multi-layered piezoelectric transducer structures

Multi-layered transducer structures offer the potential of improved performance in terms of increased transmit sensitivity, greater bandwidth, and enhanced reception characteristics. Unfortunately, the successful design of such devices is often difficult, owing to the complex interaction between the active piezoelectric layers and passive intermediate interface layers. Furthermore, in many practical applications, the loading effects imposed by the electrical drive circuitry often limit the performance improvements that may be physically realized. This paper describes the development of a comprehensive, unidimensional modeling approach. This model may be employed to facilitate the analysis and subsequent optimization of laminated transducer assemblies. The devices currently under consideration include both piezoceramic and piezopolymer configurations, as well as alternative piezocomposite designs. The effects of varying bondline thickness and the introduction of passive interface layers are examined, as is the influence of the electrical load circuitry on overall system response. The ability to accurately predict the response of stacked piezoelectric structures is demonstrated through extensive comparison of experimental and theoretical responses. This paper concludes by highlighting the important role that modeling plays in the design, fabrication, and optimization of complex multi-layered transducer assemblies.

Multiple frequency steerable acoustic transducer

A multiple frequency acoustic transducer is constructed as a stacked confration of N groups of multi-layer transducer elements separated from one another by an electrical insulating material. Each multi-layer transducer element in an n-th one of the N groups has a layer of acoustically transparent electroacoustic transducer material whose thickness is determined by the n-th frequency of operation. Each multi-layer transducer element has opposing planar surfaces with electrically conductive material deposited thereon. For each multi-layer transducer element, the electrically conductive material is formed into parallel strips electrically isolated from one another on at least one of each element's opposing planar surfaces. The parallel strips associated with each multi-layer transducer element in any one of the n-th groups have a unique angular orientation in the n-th group.

Modeling of piezoelectric multilayer ceramics using finite element analysis

For medical ultrasound imaging, 2-D array transducers have greater versatility than linear arrays. Unfortunately, the tiny array elements in a 2-D array have poor signal-to-noise ratio (SNR). We have previously shown that SNR is increased in 2-D array transducers made from piezoelectric multilayer ceramics. Conventional one-dimensional models provide accurate results when comparing multilayer ceramic performance relative to single layer transducers. However, these models are not accurate when comparing simulations directly to measurements. Because multilayer ceramics have a complex structure, a 3-D model, such as finite element analysis, is needed for accurate simulations. We modeled four arrays that were previously fabricated: a single layer and multilayer 1 MHz, 2-D array element, and a single layer and multilayer 2.25 MHz, 1.5-D array element that can focus and steer in azimuth but only steer in the elevation dimension. We compared the simulated and measured impedance plots for each transducer. The finite element analysis plots accurately predicted the impedance for each vibration mode. On the other hand, the one dimensional KLM transmission line model could simulate only the thickness mode vibrations and the results were inaccurate compared to measurements. We also simulated the transmit output pressure for the 2.25 MHz arrays and compared the results to measurements. The simulated pressure vs. time plots and their spectra were accurate when compared to measurements. Finally, we obtained a series of images that show the impulse response vibrations for the 2.25 MHz, arrays. These animations show the vibration modes in the complex multilayer ceramic structure. Measurements were not available to confirm the animations. Our results show that finite element analysis in three dimensions is a valuable tool to predict the performance of multi-layer transducers.

Selective Modal Transducers for Anisotropic Rectangular Plates: Experimental Validation

A general selective modal transducer (SMT) design methodology recently introduced by the authors for piezolaminated anisotropic plate systems is validated through an experimental test on a cantilevered orthotropic composite piezolaminated plate. Fundamental aspects of the SMT theory are reviewed. The SMT theory is extended to provide the means to predict the modal character of multilayered piezolaminated transducers embedded in an anisotropic plate in which the active subelements are both bidirectional and spatially varying. An experimental procedure is described involving a 10-layered orthotropic plate constructed from four graphite-epoxy layers sand(

PVDF transducers-a performance comparison of single-layer and multilayer structures

To improve the pulse-echo sensitivity of a piezopolymer transducer while preserving its broad bandwidth property, several multilayer transducer design approaches have been suggested. This paper presents formulae derived to describe three types of multilayer transducers: a folded multilayer-, Barker-coded, multilayer-, and switchable Barker-coded multilayer transducer. The pulse-echo responses of the multilayer transducers under various excitation signals were calculated and compared with those achievable with an equivalent PZT transducer. Also, the influence of a tissue layer on the transducer responses was examined. The simulation results indicated that the switchable Barker coded transducer design outperforms all other transducer designs analyzed with respect to the axial resolution and overall sensitivity in the medical imaging frequency range. To verify the simulation results, several prototypes of multilayer Barker coded transducers were fabricated and tested in water. A good agreement between the experimental results and the corresponding computer predictions was achieved.

Transmission and reception performance of multilayered transducer structures

Multilayered transducer structures offer the potential for greater performance in terms of increased radiated acoustic power and improved reception characteristics. In earlier work, a unidimensional modeling approach was presented, that was shown to provide a means of accurately predicting the in-air electrical impedance characteristics of a range of different laminated transducer structures [J. Acoust. Soc. Am. 97, 3299(A) (1995)]. These prototype devices have since been encapsulated within polyurethane rubber ready for in-water acoustic testing. This paper presents a theoretical and experimental analysis of both the transmission and reception performance characteristics of this group of multilayered devices. The effects of intermediate bondlines and electrode layers will be considered in terms of changes to both the device’s sensitivity and its resonant frequency. Transducer performance will be assessed via the standard figures of merit, TVR and FFVS, in conjunction with its pulse-echo transient response. Theoretical predictions from the unidimensional model are in good agreement with experimentally obtained values. The polyurethane encapsulant was found to have detrimental effects on overall transducer performance. Beam profiles for the laminated devices have been recorded experimentally and are compared to the responses of their single-layer counterparts. [Work sponsored by the Office of Naval Research.]

PVDF polymers: Imaging transducers and ultrasonic hydrophone probes

Abstract This paper presents practical applications of PVDF polymers in biomedical ultrasonics. The applications discussed entail both miniature hydrophone probes for sensing ultrasonic fields and a new generation of non-resonant pulse-echo imaging transducers, which use multilayer polymer films. The multilayer PVDF transducer structure discussed here represents a relatively unconventional approach to the pulse-echo imaging transducer design. The non-resonant design provides exceptionally wide bandwidth and is suitable for operation at the clinically relevant frequencies. The design described uses multiple active piezopolymer layers arranged according to a Barker code pattern and is adapted for pulse echo imaging. The operation principle of the switchable Barker code transducer (SBCT) is outlined and it is shown that not only SBCTs pulse-echo sensitivity is on a par with that achievable with the resonant PZT or PZT composite transducer design but also the bandwidth achievable with SBCTs is twice as large ...

Multi-layered ultrasonic transducers employing air-gap structure

Aiming at developing miniaturized ultrasonic image sensors with high spatial resolution, this paper proposes multi-layered ultrasonic transducers employing air-gap structure. Theoretical analysis suggests that if the device is optimally designed, its performance is little affected by the layer supporting the air-gap structure, and that low-loss, wide-bandwidth transducers having practical mechanical strength could be developed. The transducer consisting of polymer/Pyrex-glass/ZnO/Pyrex-glass layers was fabricated, and a conversion loss of 11.6 dB and -3 dB relative bandwidth of 7.8% were obtained. The transducer was also applied to nondestructive testing, and its basic performance was shown. >

Optimization of Signal-to-Noise Ratio for Multilayer Pzt Transducers

In medical ultrasound imaging, two-dimensional (2-D) array transducers are desirable to implement dynamic focusing and phase aberration correction in two dimensions as well as volumetric imaging. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near the resonance frequency. This results in poor signal-to-noise ratio (SNR) of the array elements. It has previously been demonstrated that transducers made from multilayer PZT ceramics have lower electrical impedance and greater SNR than comparable single layer elements. A simplified circuit model has been developed to optimize the SNR for multilayer ceramic (MLC) transducers. In this model, an electronic transmitter excites the array element and in the receive mode, the element drives a coaxial cable load terminated by a high impedance preamplifier. The transducer impedance is Zt/N2, where N is the number of piezoelectric layers. Maximum transmit signal is obtained when N = Ntx such that the transducer impedance, Zt/Ntx2, is matched to the source impedance. Maximum receive signal is obtained when N = Nrx such that the transducer impedance, Zt/Nrx2, is matched to the coaxial cable reactance. For maximum pulse-echo signal, the transducer should be designed with N = square root of Ntx Nrx, the geometric mean of Ntx and Nrx. Using this optimization technique, a 1.5-D array was designed with 3 layers for maximum pulse-echo SNR. Results of simulations from the simplified circuit analysis were consistent with those of the KLM model. The 3 layer array was fabricated as well as a single layer control array. The measured transmit signal and receive signal agreed with the simulation results.

Optimization of Signal-to-Noise Ratio for Multilayer PZT Transducers

In medical ultrasound imaging, two-dimensional (2-D) array transducers are desirable to implement dynamic focusing and phase aberration correction in two dimensions as well as volumetric imaging. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near the resonance frequency. This results in poor signal-to-noise ratio (SNR) of the array elements. It has previously been demonstrated that transducers made from multilayer PZT ceramics have lower electrical impedance and greater SNR than comparable single layer elements. A simplified circuit model has been developed to optimize the SNR for multilayer ceramic (MLC) transducers. In this model, an electronic transmitter excites the array element and in the receive mode, the element drives a coaxial cable load terminated by a high impedance preamplifier. The transducer impedance is Z t/N 2, where N is the number of piezoelectric layers. Maximum transmit signal is obtained when N = N tx, such that the transducer impedance, Z t/N tx 2, is matched to the source impedance. Maximum receive signal is obtained when N = N rx such that the transducer impedance, Z t/N rx 2 is matched to the coaxial cable reactance. For maximum pulse-echo signal, the transducer should be designed with N = [formula] the geometric mean of N tx and N rx. Using this optimization technique, a 1.5-D array was designed with 3 layers for maximum pulse-echo SNR. Results of simulations from the simplified circuit analysis were consistent with those of the KLM model. The 3 layer array was fabricated as well as a single layer control array. The measured transmit signal and receive signal agreed with the simulation results.

Performance of Multilayered Ultrasonic Transducers Comprising Vinylidene Fluoride and Trifluoroethylene Copolymer Films and Ferroelectric Ceramic Plates

Frequency and impulse response characteristics of multilayered ultrasonic transducers comprising forward films of vinylidene fluoride and trifluoroethylene copolymer (P(VDF-TrFE)) and backward ferroelectric ceramic plates of lead-zirconate-titanate (PZT) and a backing load, are studied both theoretically and experimentally. These transducers can be driven in three operation modes: (1) P(VDF-TrFE) as a transmitter and a receiver, (2) PZT as a transmitter and a receiver, and (3) PZT as a transmitter and P(VDF-TrFE) as a receiver. It is found that, owing to the great difference in their acoustic and dielectric properties, PZT plates and P(VDF-TrFE) films operate independently at different frequencies, and that, in operation mode (3), the multilayered transducers exhibit broad frequency bandwidth or shorter impulse response characteristics with high sensitivity and high S/N ratio.

New transmission line analogy applied to single and multilayered piezoelectric transducers

It is shown that a piezoelectric element vibrating in an extensional or shear mode can be modeled rigorously by systematic use of the transmission line analogy and the superposition theorem. A schematic representation of such an element which is in a way more intuitive than others representations is introduced. The stresses on the electroded faces are considered as sources of stress applied at the two ends of an acoustic transmission line, since the acoustical perturbations may be considered as originating on these faces. Using transmission line theory, a complete set of expressions is found for electrical impedance, acoustic stresses, and velocities. Computed results are exactly the same as those given by the classical method, even if the computation sequence is almost entirely different. An intuitive graphical model for a piezoelectric element is proposed. It is also shown that the acoustic velocities on opposite faces of an asymmetrical loaded piezoelectric plate are exactly equal at the antiresonance frequency when internal losses are neglected. The programs developed can be used efficiently for practical multilayered transducer design.