Materials For Ultrasonic Transducers Research Articles

Preparation of ZnO Piezoelectric Thin-Film Material for Ultrasonic Transducers Applied in Bolt Stress Measurement

The measurement of bolt preload by using ultrasound can be accurate, convenient, and can realize the real-time monitoring of the change in the residual axial stress of a bolt during use. In order to realize the ultrasonic measurement of bolt preload, the use of zinc oxide (ZnO) piezoelectric thin-film material as an ultrasonic transducer material to stimulate an ultrasonic signal on the bolt is a feasible solution. In this paper, we choose to use RF magnetron sputtering technology to prepare ZnO piezoelectric thin-film materials and study the effects of sputtering power and target substrate distance on the structure and ultrasonic properties of ZnO piezoelectric thin films during the preparation process, in order to lay the foundation for realizing the application of ZnO piezoelectric thin films in the field of bolt preload measurement. The experimental results show that too-large sputtering power or too-small target substrate distance will result in the particles having too much kinetic energy during sputtering and exhibiting a structure of multiorientation growth, which excites ultrasonic longitudinal–transverse waves. A sputtering power of 600 W, sputtering time of 4 h, and target substrate distance of 100 mm are ideal experimental parameters for a ZnO piezoelectric thin-film material to be excited by an ultrasonic longitudinal wave signal, and its ideal operating frequency is 41 MHZ. These research results of bolt stress detection demonstrate good application prospects.

Valorization of eggshell waste in designing flexible polyurethane-based piezoelectric composite materials for ultrasonic transducers

Valorization of eggshell waste in designing flexible polyurethane-based piezoelectric composite materials for ultrasonic transducers

Preparation of polyvinyl acetate composite as a new backing material for the manufacture of ultrasonic transducers

Polyvinyl acetate (PVAc) composites were loaded with varying amounts of nano-metal alloy (Ag–Sn–Cu–Pt) and stearic acid. They are used as backing materials for ultrasonic transducers to prevent back-echoes from reverberating into the piezoelectric element and to reduce noisy echoes. The novelty of this work is the usage of these newly prepared PVAc/alloy composites as backing material in ultrasonic transducers with a polyvinylidene fluoride (PVDF) active element. The X-ray diffraction (XRD) technique was used to examine the structure of the composites. The ultrasonic technique investigated the ultrasonic attenuation coefficient, the acoustic impedance, the mechanical properties, and other parameters. The transducers with the new backing composites gained high sensitivity, broadband, short ringing, and so on. These characteristics were improved by increasing the nano-metal alloy content in the backing composites. The study also proved the efficiency of the PVAc/alloy composite as new backing material in ultrasonic transducers.Graphical abstractSketch of fabricated ultrasonic transducers with backing materials from PVAc/alloy composites (B1, B2, B3, B4, B5, and B6) and their important features (BW is transducers’ band width and S is transducers’ sensitivity).

Novel 1–3 (K,Na)NbO3-based ceramic/epoxy composites with large thickness-mode electromechanical coupling coefficient and good temperature stability

The 1–3 piezoelectric composites are an important type of artificial functional materials for ultrasonic transducers. Currently, there are increasingly strong demands to replace the lead-containing materials. Excellent 1–3 0.96(K0.48Na0.52) (Nb0.96Sb0.04)O3−0.03BaZrO3−0.01(Bi0.50Na0.50)ZrO3 ceramic/epoxy (abbreviated hereafter as KNNS-0.03BZ-0.01BNZ/epoxy) piezoelectric composites were prepared by a modified dice-and-fill technique. Compared to the monolithic KNNS-0.03BZ-0.01BNZ ceramic, the developed composites possess much larger electromechanical coupling coefficient kt of 0.54–0.67 and piezoelectric voltage coefficient g33 of 64–91 × 10−3 Vm/N. In addition, these composites also possess other favorable properties such as low values of acoustic impedance Z of 6.9–13.4 Mrayl, dielectric coefficient ε33 of 130–400 and mechanical quality factor Qm of 1.3–4. More importantly, kt is weakly temperature-dependence in the common usage temperature range between −30 °C and 100 °C. The result indicates that the 1–3 KNNS-0.03BZ-0.01BNZ/epoxy piezoelectric composites have a great potential for high-frequency ultrasonic transducers.

Piezoelectric Materials for Ultrasonic Transducers of Shock–wave Therapy Machines

Piezoelectric Materials for Ultrasonic Transducers of Shock–wave Therapy Machines

Lead-Free NKN-Based Materials for Ultrasonic Therapeutic Transducers: Resistance to Temperature and Humidity

In this study, CuF2 and LiNbO3 modified lead-free (Na, K)NbO3 (NKN)-based ceramics (NKNCF and NKLN) were synthesized using solid-state reaction methods. The influence of doping materials on the electrical properties and stability of the synthesized ceramics was then investigated. The ceramics synthesized with CuF2 and LiNbO3 dopants were of higher density than pure NKN ceramics and far more stable under the effects of temperature and humidity. NKNCF ceramics sintered at 1000°C exhibited excellent “hard” piezoelectric properties (kp = 35%, kt = 45%, d33 = 88 pC/N, Qm = 2800, and tanδ = 0.1%). In contrast, NKLN ceramics sintered at 950°C exhibited excellent “soft” piezoelectric properties (kp = 50%, kt = 53%, d33 = 150 pC/N, Qm = 168, and tanδ = 4%). The ceramics were then used in the fabrication of 3-MHz ultrasonic therapeutic transducers driven by a self-tuning circuit to investigate the dynamic performance. Our results clearly demonstrate that the resonance resistance, Qm, and tanδ play a more important role in the generation of acoustic power of ultrasonic therapeutic transducers than the electromechanical coupling coefficient (k). The CuF2-doped ceramics were found to easily generate a greater acoustic power, which makes them suitable for applications in therapeutic transducers.

A study of the conversion of ultrasonic energy and their transducers

This paper essay offers a survey of research on interconvertibility of the conversion of ultrasonic energy with other energy, and their transducers, the conversion materials. Furthermore, it mainly gives piezoelectric ultrasonic transducer and piezoelectrical ultrasonic transducer material. Finally, some problems of ultrasonic energy and transducers, especially microelectronic materials and its acoustoelectric devices used for the ultrahigh-frequency (UHF) ultrasonic which need further research are pointed out.

Transparent lead lanthanum zirconate titanate (PLZT) ceramic fibers for high-frequency ultrasonic transducer applications

This paper presents fabrication of transparent lanthanum zirconate titanate (PLZT) fibers using extrusion technique. The diameter of the sintered PLZT fiber is about 400-μm, and the fibers exhibit very good transparency. Measured dielectric constant, remnant polarization and coercive field of PLZT fiber were found to be 2340, 22.5-μC/cm2, and 9.8-kV/cm, respectively. The transparent piezoelectric materials may exhibit great potential for Photoacoustic (PA) imaging and hybrid intravascular imaging combining OCT and ultrasound imaging by using the transparent fiber as the path of light propagation and ultrasonic transducer material. In our study, these transparent PLZT fibers were designed to fabricate two types of high-frequency ultrasonic transducers: small aperture single PLZT fiber/epoxy composite and large aperture 1–3 PLZT fiber/epoxy composite ultrasonic transducers. Besides, a 20-μm tungsten wire phantom and the cornea of the porcine eye were also imaged with the 1–3 PLZT fiber/epoxy composite ultrasonic transducer to demonstrate its imaging capability.

Nuclear Radiation Tolerance of Single Crystal Aluminum Nitride Ultrasonic Transducer

Ultrasonic technologies offer the potential for high accuracy and resolution in-pile measurement of a range of parameters, including geometry changes, temperature, crack initiation and growth, gas pressure and composition, and microstructural changes. Many Department of Energy-Office of Nuclear Energy (DOE-NE) programs are exploring the use of ultrasonic technologies to provide enhanced sensors for in-pile instrumentation during irradiation testing. For example, the ability of small diameter ultrasonic thermometers (UTs) to provide a temperature profile in candidate metallic and oxide fuel would provide much needed data for validating new fuel performance models, (Rempe et al., 2011; Kazys et al., 2005). These efforts are limited by the lack of identified ultrasonic transducer materials capable of long term performance under irradiation test conditions. To address this need, the Pennsylvania State University (PSU) was awarded an Advanced Test Reactor National Scientific User Facility (ATR NSUF) project to evaluate the performance of promising magnetostrictive and piezoelectric transducers in the Massachusetts Institute of Technology Research Reactor (MITR) up to a fast fluence of at least 1021 n/cm2. The irradiation is also supported by a multi-National Laboratory collaboration funded by the Nuclear Energy Enabling Technologies Advanced Sensors and Instrumentation (NEET ASI) program. The results from this irradiation, which started in February 2014, offer the potential to enable the development of novel radiation tolerant ultrasonic sensors for use in Material Testing Reactors (MTRs). As such, this test is an instrumented lead test and real-time transducer performance data is collected along with temperature and neutron and gamma flux data. Hence, results from this irradiation offer the potential to bridge the gap between proven out-of-pile ultrasonic techniques and in-pile deployment of ultrasonic sensors by acquiring the data necessary to demonstrate the performance of ultrasonic transducers. To date, very encouraging results have been attained as several transducers have continued to operate under irradiation. The irradiation is ongoing and will continue to approximately mid-2015.

Irradiation Testing of Ultrasonic Transducers

Ultrasonic technologies offer the potential for high accuracy and resolution in-pile measurement of numerous parameters, including geometry changes, temperature, crack initiation and growth, gas pressure and composition, and microstructural changes. Many Department of Energy-Office of Nuclear Energy (DOE-NE) programs are exploring the use of ultrasonic technologies to provide enhanced sensors for in-pile instrumentation during irradiation testing. For example, the ability of single, small diameter ultrasonic thermometers (UTs) to provide a temperature profile in candidate metallic and oxide fuel would provide much needed data for validating new fuel performance models. Other efforts include an ultrasonic technique to detect morphology changes (such as crack initiation and growth) and acoustic techniques to evaluate fission gas composition and pressure. These efforts are limited by the lack of existing knowledge of ultrasonic transducer material survivability under irradiation conditions. To address this need, the Pennsylvania State University (PSU) was awarded an Advanced Test Reactor National Scientific User Facility (ATR NSUF) project to evaluate promising magnetostrictive and piezoelectric transducer performance in the Massachusetts Institute of Technology Research Reactor (MITR) up to a fast fluence of at least 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sup> n/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (E>0.1 MeV). This test will be an instrumented lead test; and real-time transducer performance data will be collected along with temperature and neutron and gamma flux data. By characterizing magnetostrictive and piezoelectric transducer survivability during irradiation, test results will enable the development of novel radiation tolerant ultrasonic sensors for use in Material and Test Reactors (MTRs). The current work bridges the gap between proven out-of-pile ultrasonic techniques and in-pile deployment of ultrasonic sensors by acquiring the data necessary to demonstrate the performance of ultrasonic transducers.

Phase fragility and mechatronic reliability for Pb(Mg1/3Nb2/3)O3–PbTiO3 ferroelectric single crystals — A review

Single crystals of (1-x) Pb ( Mg 1/3 Nb 2/3) O 3–x PbTiO 3( PMN –x PT ) near their morphotropic phase boundaries (MPBs) are under extensive investigations for their extraordinary high dielectric and piezoelectric behavior. Applications of those single crystals facilitated the breakthrough in ultrasonic transducer materials and devices. Ferroelectric materials are known to be fragile which often leads to various reliability failures in applications involving electric loadings. In a mechanical sense, the failure modes concern the fracture under an intensive electric field, and the fatigue crack propagation under an alternating electric field. In an electrical sense, the failure is exhibited by degenerated hysteresis loop by shrinking the remnant polarization and expanding the coercive field. All these modes degrade the performance for ferroelectric devices. As a departure from the tetragonal (T) ferroelectric materials, exemplified by BaTiO 3 and Pb ( ZrTi ) O 3, the domain structures of PMN–PT around the MPB are versatile and intricate, depending sensitively on the composition variation, orientation and previous loading history. In this review, the attention is mainly focused on three aspects. First, the phase fragility and multiphase coexistence are presented for both [100]- and [101]-oriented PMN–PT single crystals. Second, investigations on electric field-induced fatigue crack propagation are described, along with the orientation effect on the crack propagation behavior. Third, the inverse effects of the phase transition and fatigue crack growth on the polarization behavior, or the interaction between the mechanical and electrical degradations will be elucidated. The review aims for better understanding the underlying mechanism for the ultrahigh performance of the PMN–PT single crystals, to bridge the studies of ferroelectric materials from the mechanical and electrical senses, as well as to evaluate the reliability of PMN–PT single crystals under device applications.

Note: Piezoelectric polymers as transducers for the ultrasonic-reflection method and the application in mechanical property-screening of coatings

In the last years, non-destructive ultrasonic testing methods are more and more frequently employed in order to investigate the drying and curing processes of different coatings. Among them an ultrasonic reflection method was developed allowing the simultaneous measurement with longitudinal and transversal waves. In order to generate the ultrasonic pulse, piezoelectric ceramics or oxides are usually used as transducer materials which are connected to a delay line. Here, we demonstrate a similar approach for the ultrasonic reflection method installing piezoelectric polymers as ultrasonic transducer materials. In detail, poly(vinylidene fluoride and trifluoroethylene) [P(VDF-TrFE)] copolymers were prepared as piezoelectric transducer layers directly onto the metallization of glass delay lines avoiding additional bonding processes. The film preparation was carried out by solvent casting the polymer onto an area with a diameter of 12 mm and is optimized so that relatively homogeneous polymer layers with thicknesses between 14 and 35 μm are adjusted by the deposited amount of the polymer. Electrical poling renders the polymer piezoelectric. The ultrasonic properties of the P(VDF-TrFE) transducer and their usability for the ultrasonic reflection method are described also in comparison to previous measurements using LiNbO(3) transducer.

Cellular polypropylene polymer foam as air-coupled ultrasonic transducer materials

Cellular polypropylene polymer foams, also known as ferroelectrets, are compelling candidates for air-coupled ultrasonic transducer materials because of their excellent acoustic impedance match to air and because they have a piezoelectric d(33) coefficient superior to that of PVDF. This study investigates the performance of ferroelectret transducers in the generation and reception of ultrasonic waves in air. As previous studies have noted, the piezoelectric coupling coefficients of these foams depend on the number, size, and distribution of charged voids in the microstructure. The present work studies the influence of these parameters both theoretically and experimentally. First, a three-dimensional model is employed to explain the variation of piezoelectric coupling coefficients, elastic stiffness, and dielectric permittivity as a function of void fraction based on void-scale physics and void geometry. Laser Doppler vibrometer (LDV) measurements of the effective d(33) coefficient of a specially fabricated prototype transmitting transducer are then shown which clearly indicate that the charged voids in the ferroelectret material are randomly distributed in the plane of the foam. The frequency-dependent dynamic d(33) coefficient is then reported from 50 to 500 kHz for different excitation voltages and shown to be largely insensitive to drive voltage. Lastly, two ferroelectret transducers are operated in transmit-receive mode and the received signal is shown to accurately represent the corresponding signal generated by the transmitting transducer as measured using LDV.

Magnetic and magnetoelastic properties of Ni–Cu–Mn–Ti–Mo alloys

The results on magnetic and magnetoelastic properties of some Ni-based alloys containing copper, manganese, titanium and molybdenum are reported. The values of saturation magnetic induction, Curie temperature, saturation magnetostriction and magneto-mechanical coupling coefficient, obtained in the case of thermally treated samples, show the possibility to use these materials for ultrasonic transducers.

Porous piezoelectric ceramics: Materials for ultrasonic flaw detection and medical diagnostics

The key features of the piezoelectric materials for ultrasonic transducers are considered. A procedure is described for the fabrication of porous piezoelectric ceramics. It is shown that, owing to their high piezoelectric performance and ease of fabrication, porous ceramics may compete with lead niobate and piezoelectric composites in the fields of medical diagnostics and ultrasonic flaw detection.

High frequency properties of passive materials for ultrasonic transducers.

The acoustic properties of passive materials for ultrasonic transducers have been measured at room temperature in the frequency range from 25 to 65 MHz using ultrasonic spectroscopy. These materials include alumina/EPO-TEK 301 composites and tungsten/EPO-TEK 301 composites. Experimental results showed that the acoustic impedance of the composites monotonically increased with the volume fraction of the particle filler, which is in agreement with the Denavey model. The attenuation, however, peaked between 7 and 9% volume fraction of particle filler. For comparison, several other passive materials were also fabricated and measured. The results suggest that materials that possess a higher attenuation also appear to have a larger velocity dispersion.

Dielectric properties of PZT aerogels

Due to their low sound velocity and high porosity PZT aerogels have an exceptional low acoustic impedance. Therefore they are promising materials for impedance-matched ultrasonic transducers that can be used for ranging and sonar systems or medical imaging devices. Monolithic, nanostructured and open porous PZT aerogels of morphotropic stoichiometry (Pb1.05Zr0.53Ti0.47O3) were prepared by sol-gel synthesis and subsequent supercritical drying. Porosities up to 70% could be adjusted by the sintering conditions. The resulting material can be described as an interpenetrating 3-3 composite of PZT and air. The porosity of the PZT aerogels decreases with increasing sintering time and temperature. The relative dielectric permittivity at 1 kHz depends non-linearly on porosity. The dielectric permittivity could be monitored over two decades by the sintering conditions. For samples with comparable porosity the dielectric permittivity increases with sintering time. This behavior can be simulated by Looyenga's formula using different values for the dielectric permittivity of the PZT backbone as parameter. A comparison between the experimental and theoretical data suggests, that the dielectric permittivity of the PZT backbone material is mainly influenced by the sintering time. The porosity is adjustable both by sintering time and temperature. This offers the possibility to tailor the porosity and dielectric permittivity of the PZT backbone in a wide range for the given application.

Acoustic characterization of ultrasonic transducer materials: II. The effect of curing agent in binary epoxy blends on acoustic properties

The acoustic properties of seven new series of binary epoxy blends as a function of the composition of the flexible epoxy were studied at room temperature in the low-MHz frequency range. Each blend was composed of a flexible epoxy resin, DER 736, mixed with one of four rigid epoxies, DER 330, DER 331, DER 332 or DEN 431, and crosslinked with one of four curing agents, DEH 26, DEH 29, DEH 39 or Thermoset 310. All elastic moduli and Poisson's ratios were calculated by using longitudinal velocity, shear velocity and density. This paper focuses on the effect of curing agents on the epoxy blends throughout the entire range of epoxy mix ratios. It has been found that there are basically two types of acoustic properties in these formulations depending on whether their glass transition temperature is above or below the temperature at which the measurements are made. The acoustic properties were strongly influenced by the curing agent and the amount of DER 736. However, for a given curing agent, the selection of the specific rigid epoxy did not have a large effect on the properties.

Acoustic characterization of ultrasonic transducer materials: I. Blends of rigid and flexible epoxy resins used in piezocomposites

Five different types of Dow epoxy blends were studied with differential scanning calorimetry. Each epoxy blend consists of a flexible epoxy resin, DER 736 or DER 732, with one of four different rigid epoxies, DER 317, DER 331, DER 332 and DEN 431, crosslinked by 1,4-bis (3-aminopropyl)-piperazine (BAPP). Longitudinal and shear wave acoustic properties of these epoxy resin blends as a function of the composition were measured at room temperature and an ultrasonic frequency range. All moduli and Poisson's ratios were calculated by using longitudinal velocity, shear velocity and density. These systems all have similar behavior. By increasing the amount of flexible epoxy in a mixture of hard and flexible epoxies a critical composition was found (∼50% by weight for DER 736 and ∼30% for DER 732), below which the acoustic properties, the elastic moduli and Poisson's ratios kept an almost constant value, and above which the velocities, impedances and all moduli decreased, whereas attenuations and Poisson's ratios increased gradually. Many epoxy materials ranging from soft and flexible to hard and rigid have been obtained by epoxy blend technology. Some of them have been applied to make 1–3 composites for medical ultrasound transducers.

Calculations of the elastic compliance and piezoelectric constants of PVDF and P(VDF-TrFE) crystals using molecular mechanics

The selection and/or design of projector materials for ultrasonic transducers requires knowledge of their elastic, piezoelectric, and dielectric properties. These properties can be measured directly; however, in order to minimize the fabrication and measurement of many different materials, it would be useful to compute these properties from the chemical composition and structure of the material. In molecular mechanics, a force field is used to describe short- and long-range interactions between atoms in a crystal. The most favored state occurs when the total energy, i.e., the sum of the interaction energies, is minimized. This paper presents calculated compliance and piezoelectric constants for β-phase crystals of polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene, P(VDF/TrFE). The constants were derived by minimizing the energy of the unit cell while varying the stress. The model was validated using experimental and theoretical values for the properties of PVDF. The behavior of the compliance and piezoelectric constants of P(VDF/TrFE) are examined as a function of the molecular percentage of VDF. It was found that an optimum value for d33 exists between 55 and 65 mol % VDF. The implications of these results for the use of P(VDF/TrFE) copolymer in ultrasonic projectors will be discussed.