Transducer Applications Research Articles

Development of Polymer-Ceramic-Metal Graded Acoustic Matching Layers via Cold Sintering.

A family of three phase, polymer-ceramic-metal (Poly-cer-met) electrically conducting composites was developed via cold sintering for acoustic matching application in medical ultrasound transducers. A range of acoustic impedance ( Z ) between MRayl with low attenuation (<3.5 dB/mm, measured at 10 MHz) was achieved in composites of zinc oxide, silver, and in thermoplastic polymers like Ultem polyetherimide (PEI) or polytetrafluoroethylene (PTFE) at sintering pressure less than 50 MPa and temperature of 150 °C. Densities exceeding 95% were achieved, with resistivities less than 1 Ω -cm. The acoustic velocity was homogeneous across the part (variations <5%). The acoustic velocities exceeded 2500 m/s for Z above 12 MRayl. The experimentally measured acoustic impedance of ZnO/Ag/PEI composites was observed to be in close agreement with the theoretical logarithmic model developed for different volume fractions of individual phases at the percolation limit for Ag. Thus, the acoustic properties of this family of matching layers (MLs) can be predicted to a good approximation before experimental realization. Additionally, a non-conducting low Z (5 MRayl MRayl) with acoustic velocities exceeding 2000 m/s was achieved using hydrozincite as the ceramic component. Scaling of the composites to 2'' diameter was demonstrated. A -6 dB bandwidth greater than 85% was measured for a three ML ultrasound transducer, fabricated using a single cold sintered layer ( Z = 19 MRayl) and two other commercial layers in the stack. Finally, a co-cold sintered graded prototype consisting of three tape-casted formulations corresponding to Z = 5 , 9, and 19 MRayl, while still retaining the correct distributions of the components was demonstrated.

Recent advances in piezoelectric materials for electromechanical transducer applications

Recent advances in piezoelectric materials for electromechanical transducer applications

Dependence of coercive field of PIN–PMN–PT single crystal on temperature and frequency

The effective coercive field Eceff of [001]c oriented 0.24Pb(In1/2Nb1/2)O3–0.45Pb(Mg1/3Nb2/3)O3–0.31PbTiO3 (PIN–PMN–PT) single crystals has been investigated as a function of temperature T and frequency f. The results show that the Eceff vs f curve exhibits two different regimes separated at about 400 kHz, which may be attributed to the relaxation of non-180° domain switching. It is found that Eceff linearly decreases with T at any given frequency but increases with frequency at a given temperature. These quantitative results demonstrate that the PIN–PMN–PT single crystals have good thermal stability and can be operated at a field level much beyond the conventional coercive field, revealing a great potential for high-frequency ultrasonic transducer applications.

Recent advances in piezoelectric materials for electromechanical transducer applications

Recent advances in piezoelectric materials for electromechanical transducer applications

Experimental investigation on the tribological behavior and surface damage due to embedment of ceramic proppant – analog mudrock composite systems

The analysis of interface problems involving proppants and rocks is of major interest in unconventional reservoir exploitation and modeling as well as in geophysics, mining engineering and rock mechanics. Despite the significant progresses that have been reported in hydraulic fracturing, there has been given less attention in the fundamental understanding of the interactions between proppants and rocks, which can provide enhanced input parameters in computational-based analyses involving complex multi-phase processes. In this study, the tribological behavior of three types of contacts including ceramic-ceramic (analog) proppants, kaolinite-kaolinite blocks (analog mudrock) and ceramic-kaolinite composite interfaces was investigated performing laboratory tests using a custom-developed loading apparatus and the experiments involved force and displacement measurements by the application of high-precision transducers. Based on a series of normal loading tests, it was observed that the ceramic beads exhibited a completely elastic behavior, whereas the kaolinite blocks showed a softer response with, predominantly, plastic deformations. The results of the shearing tests indicated that for the ceramic-kaolinite composite contacts, the arrangement of the clay microfabric significantly affected the shearing load-displacement response in terms of the post-peak softening behavior, the development of the microslip regime as well as the dynamic friction. It was also shown that even though the interface friction was controlled, predominantly, by the softer kaolinite block, the interface tangential stiffness had different involved mechanisms, in which case the kaolinite blocks showed the highest stiffness specifically at greater magnitudes of normal load, whereas the ceramic-kaolinite composite interfaces had the lowest values of stiffness.

High-Performance Curved Piezoelectric Single-Crystal Composites via 3D-Printing-Assisted Dice and Insert Technology for Underwater Acoustic Transducer Applications.

Piezoelectric single-crystal composites (PSCCs) have been studied and applied because of their improved resolution and power source level performance in underwater acoustic transducer applications relative to traditional piezoelectric ceramic composites (PCCs). Currently, the methods to fabricate curved PSCCs are mostly derived from PCCs, including molding with flexible backing, molding with heating, and molding with the casting rubber method. Unfortunately, the methods mentioned above are not suitable for preparing curved PSCCs for underwater acoustic transducer applications because of their brittleness, the large anisotropy of piezoelectric single crystals, and the high thickness (>2 mm) of PSCCs for achieving the low operating frequency (<700 kHz). In the present work, we proposed a preparation method, 3D-printing-assisted dice and insert technology, and successfully prepared curved PSCCs with high performance. Although the PSCCs have a low volume fraction of single crystals in this work (∼33%), a high thickness electromechanical factor kt of 86% and a large piezoelectric coefficient d33 of 1550 pC/N were achieved in the curved 1-3 PSCCs, which are superior to other reported PSCCs and PCCs with nearly the same volume fraction of single crystals and piezoelectric ceramics. This work presents a paradigm for fabricating curved PSCCs for underwater acoustic transducers, and this method shows the potential for large-area, special-shaped PSCCs, which are key materials for next-generation underwater acoustic transducers.

Optical ultrasound sensors for photoacoustic imaging: a narrative review.

Optical ultrasound sensors have been increasingly employed in biomedical diagnosis and photoacoustic imaging (PAI) due to high sensitivity and resolution. PAI could visualize the distribution of ultrasound excited by laser pulses in biological tissues. The information of tissues is detected by ultrasound sensors in order to reconstruct structural images. However, traditional ultrasound transducers are made of piezoelectric films that lose sensitivity quadratically with the size reduction. In addition, the influence of electromagnetic interference limits further applications of traditional ultrasound transducers. Therefore, optical ultrasound sensors are developed to overcome these shortcomings. In this review, optical ultrasound sensors are classified into resonant and non-resonant ones in view of physical principles. The principles and basic parameters of sensors are introduced in detail. Moreover, the state of the art of optical ultrasound sensors and applications in PAI are also presented. Furthermore, the merits and drawbacks of sensors based on resonance and non-resonance are discussed in perspectives. We believe this review could provide researchers with a better understanding of the current status of optical ultrasound sensors and biomedical applications.

SPICE Modeling of a High-Power Terfenol-D Transducer Considering Losses and Magnetic Flux Leakage.

Of great importance is modeling for transducer design and application to predict its performance and simulate key characteristics. The equivalent circuit modeling (ECM), one of the most powerful tools, has been widely used in the transducer industry and academia due to its outstanding merits of low simulation cost and easy usage for multi-field simulation in both time and frequency domains. Nevertheless, most of the existing equivalent circuit models for Terfenol-D transducers normally ignore three material losses, namely elastic loss, piezomagnetic loss, and magnetic loss. Additionally, the magnetic leakage due to the intrinsic poor magnetic permeability of Terfenol-D is rarely considered into the piezomagnetic coupling. Both loss effects will produce substantial errors. Therefore, an improved SPICE model for a high-power Terfenol-D transducer considering the aforementioned three losses and magnetic flux leakage (MFL) is proposed in this article, which is implemented on the platform of LTspice software. To verify the usefulness and effectiveness of the proposed technique, a high-power Terfenol-D tonpilz transducer prototype with a resonance frequency of around 1 kHz and a maximum transmitting current response (TCR) of 187.1 dB/1A/ μ Pa is built and tested. The experimental results, both in the air and water of the transducer, are in excellent agreement with the simulated results, which well validates our proposed modeling methods.

Recent advances in piezoelectric materials for electromechanical transducer applications

Recent advances in piezoelectric materials for electromechanical transducer applications

Design and fabrication of non-periodic 1–3 composite structure for ultrasonic transducer application

Piezoelectric composite materials (PCMs), combing the advantages of both piezoelectric materials and polymers, have been extensively used in piezoelectric material ultrasonic transducers (PCUTs). However, PCMs induce lateral modes in PCUTs, which can degrade their performance. In this study, a mathematical model for the lateral mode frequency was deduced. A novel 1–3 composite structure with non-periodicity in one dimension was designed based on the proposed model to eliminate the effect of the lateral mode. In addition, the PZFlex software was used to simulate and verify the performance of the PCUT. The non-periodic 1–3 PCM was fabricated and used to package 4 MHz PCUT. A PCUT with a normal 1–3 PCM was fabricated for comparison. Then, the electrical and acoustic properties of the PCUTs were then systematically characterized. The PCUT with the non-periodic 1–3 PCM had a broader −6 dB bandwidth (38.9 %), larger electromechanical coupling coefficient (0.68), higher peak-to-peak voltage (2.44 V) and smaller insertion loss (-17.40 dB) than those of the PCUT with normal 1–3 PCM (28.4 %, 0.55, 1.19 V and –22.86 dB). The results show that non-periodic 1–3 composite structure can break the limits of the lateral mode and has great potential for the development of high-performance PCUTs.

Effect of Sm2O3 addition on the dielectric behaviour of BaTiO3

BaTiO3 is a widely used ferroelectric ceramic having applications in transducers, capacitors, thermistors, non linear optics etc. BaTiO3 exhibits Curie temperature (Tc) of 120 °C. Recent research in BaTiO3 based thin films has resulted in a significant rise in their Tc. The most prominent increase in Tc has been reported in BaTiO3 – Sm2O3 system in which Sm2O3 nanorods were incorporated in BaTiO3 matrix resulting in the Tc ∼ 800 °C. Such a remarkable increase in the Tc was attributed to the high elastic modulus of Sm2O3 (E = 125 GPa) w.r.t. that of BaTiO3 (E = 67 GPa). Higher elastic modulus of the second phase resulted in the generation of strain in the matrix thereby delaying the onset of tetragonal – cubic transition. The improvement in the Tc of BaTiO3 thus opened possibilities of use of BaTiO3 based systems for high temperature piezoelectric applications. Since BaTiO3 based thin films exhibited a remarkable increase in the Tc, it needed to be studied if such a phenomenon could be replicated in bulk ceramics. Hence, BaTiO3 – Sm2O3 ceramics were prepared by the conventional ceramics processing route. Submicron-sized BaTiO3 and Sm2O3 powders were used as starting materials and compositions with Sm2O3 content varying between 5 and 30 wt% were prepared. BaTiO3 and Sm2O3 powders were milled using a jar mill for 48 h in ethanol followed by drying of slurries and room temperature uniaxial pellet pressing. Green pellets were sintered by pressureless sintering at 1350 °C for 4 h. X-ray diffraction (XRD) analysis of BaTiO3 and BaTiO3 – 5 wt% Sm2O3 ceramics confirmed the presence of tetragonal phase. However, further increase in Sm2O3 content resulted in the transformation of tetragonal BaTiO3 to cubic BaTiO3. Since cubic phase is centrosymmetric and cannot exhibit ferroelectricity, compositions with Sm2O3 > 5 wt% became redundant for any ferroelectric application. Moreover, BaTiO3 – 5 wt% Sm2O3 exhibited Tc of just 100 °C with lower dielectric constant thereby making this composition ineffective for high temperature piezoelectric application. While it had been anticipated that incorporation of Sm2O3 in bulk BaTiO3 ceramics would increase their Tc as in thin films, none of these compositions exhibited the anticipated behaviour. This paper discusses why BaTiO3 – Sm2O3 bulk ceramics failed to exhibit similar dielectric behaviour to their thin film counterparts in light of the phase formation, microstructure and dielectric behaviour.

Application of Matrix Array Transducer for Non-destructive Photoacoustic Imaging

In general, it is challenging to evaluate subsurface flaws of a target material because of a dead zone of surface echo in nondestructive ultrasonic testing. In this study, photoacoustic (PA) imaging using a matrix array transducer was applied to reconstruct the three-dimensional shape of subsurface flaws in carbon fiber reinforced plastic (CFRP). The matrix array transducer can receive the scattered signal individually and enhance the total intensity by setting a delay for each element. In this study, we selected several focal depths and reconstructed the flaw shape using the synthetic aperture focusing technique. The result showed that adequate delay design was necessary for accurate flaw imaging.

Vibrational Characteristics of Au‐Doped Si Nanowires: A Molecular Dynamics Study with a Modified Embedded Atom Method Potential Developed for Si‐H‐Au Systems

Silicon nanowires (SiNWs) are promising structures as resonators for applications in ultrasensitive force and mass transducers. In the present work, large‐scale molecular dynamics simulations were conducted to explore the effect of gold (Au), a commonly used catalyst, on the vibrational properties of [1 0 0] and [1 1 0] SiNWs. The force field was established using the modified embedded atom method (MEAM) formalism. The parameterization focused on the properties of the hydrogen‐covered SiNWs doped with Au, involving the formation energy as well as the structural and vibrational characteristics. The vibrational characteristics of a clamped‐clamped SiNW were examined through excitation using a sinusoidal velocity field after energy minimization and thermal equilibration. Different doping concentrations and distributions can significantly change the frequency response, quality factor Q, and beat phenomenon. The natural frequency f0 decreased with increasing Au concentration, whereas the effect of the impurity distribution on f0 was negligible. Furthermore, Q was sensitive to the Au concentration and distribution, and the increased concentration led to an overall increment in Q, accompanied by considerably increased scattering. Besides, the beat period of [1 1 0] SiNWs showed a strong positive correlation with the concentration. The vibration along the elementary axes cannot produce the beat phenomenon. Deflection of the elementary axes in a very small range would lead to a higher energy dissipation rate. In addition, owing to the considerable difference between the atomic masses of Au and Si, randomly distributed Au atoms significantly disturb the symmetry of the SiNWs. However, the elementary axes of the [1 1 0] SiNWs remained stable, even in the models with extremely radial or longitudinal impurity segregation. In contrast, we failed to capture the distinguishable elementary axes for most of the doped [1 0 0] samples. The features described above indicate that the impurity Au can effectively tune the resonant frequency of the [1 1 0] SiNWs, meanwhile, causes no large frequency shift that could be potentially caused by the deflection of the elementary coordinate system.

Twelve modified figures of merit of 2–2-type composites based on relaxor-ferroelectric single crystals

Twelve modified figures of merit are studied for the first time for 2–2-type composites based on relaxor-ferroelectric single crystals such as [001]-poled (1 – x)Pb(A1/3Nb2/3)O3 – xPbTiO3, where A = Mg or Zn. These modified figures of merit are related to the piezoelectric coefficients d3j* of the composite (j = 1, 2 and 3) and characterise the effectiveness of energy harvesting and transduction along the three co-ordinate axes OXj of a piezoelectric composite under a constant mechanical stress or strain. The volume-fraction dependencies of the modified figures of merit are analysed for parallel-connected 2–2 and 2–2–0 composites, and the effect of porosity (i.e. the volume fraction and shape of air pores in each polymer layer) on these figures of merit is considered for 2–2–0 composites. Linkages between the modified figures of merit and traditional energy-harvesting figures of merit d3j*g3j* are discussed for the studied 2–2-type composites. New diagrams are developed to indicate important volume-fraction ranges that correspond to a large anisotropy of exemplar modified figures of merit. Due to the large effective parameters and large anisotropy of specific figures of merit, the studied composites are of interest in piezoelectric sensor, transducer and energy-harvesting applications.

2PL Advances in Development and Applications of Pb-Free Piezoelectric Materials for Transducer Applications

2PL Advances in Development and Applications of Pb-Free Piezoelectric Materials for Transducer Applications

Ultrasonic energy harvester: Biocompatible material selection

In the current scenario, most countries are facing power shortage issues due to an increase in demand for power supply and a lack of viable alternative power generation methods. Predominantly, conventional non-renewable energy sources are used in the world today. Primary energy sources such as oil, coal, and natural gases are getting depleted fast and may come to an end soon. There is an urgent need for non-conventional renewable, and green energy sources. In the last three decades, there have been more studies on alternative energy sources such as energy harvesting using piezoelectricity. In this paper, the focus is on energy harvesting from ambient ultra-sonic sound sources with the help of piezoelectric devices. Ultra-sonic sound is abundantly available in UV scanners used in hospitals, rocket stations, and so on. This high-frequency mechanical energy can be converted into electrical energy with the help of proper piezoelectric materials. For the selection of suitable piezoelectric materials for ultra-sonic energy harvesting, a study was done using the simulation of an ultrasonic transducer. Various parameters such as lowest eigenmode, surface electric potential, susceptance, stress developed, total energy, and displacement were analyzed for different materials and the different metal electrodes. For the study, different types of materials such as natural piezoelectric materials, polymers, semiconductors, and ceramics were considered. Since the piezoelectric energy harvesting devices also be worn on the human body, a literature study was done to avoid hazardous materials. Our studies indicate that poled Barium Titanate can be used as a suitable biocompatible piezoelectric material along with Silver or Copper as the electrode for ultrasonic transducer applications.

Call for papers: Recent advances in piezoelectric materials for electromechanical transducer applications

Call for papers: Recent advances in piezoelectric materials for electromechanical transducer applications

Smart materials for ultrasonic piezoelectric composite transducer: A short review

At every step of development, advanced composite combinations are found, resulting in a material revolution. Smart materials, with their many classifications and characteristics, play an important part in today's research. The vast majority of dielectric, electro-magnetic, fatigue, and electric attributes were completely studied. These factors influence the working performance of piezoelectric composite materials. For various stiffness ratio the breakage point of the material changes does affects the fatigue cycle is explained. For ultrasonic transducer applications, we may design the structure to produce materials with better electromechanical coupling and lower acoustic impedance than traditional piezoelectric ceramics. The requirement for composites in piezoelectric transducers explains the high performance and high-end applications. The interaction of the main factors was displayed under various situations, majority of changes happens in the mechanical and chemical property changes and that can be recovered by treating the material and the results were explained.

Generalized homogenization model of piezoelectric materials for ultrasonic transducer applications

Although piezocomposite (PC) materials have increasingly attracted researchers, there is still a need to properly and easily derive their properties. We develop a generalized homogenization model (GHM) that accounts for Smith and Cha approaches to evaluate the equivalent characteristics of piezocomposites. This method could be applied to all connectivities patterns, but restricted herein to 2-2 and 1-3 piezocomposites for comparison with Smith (1-3) and Cha (2-2) analytical results. In the proposed GHM is a parameter θ, is changed for various connectivities. The 1-3 and 2-2 PZT-7A/Araldite D (PCs) data are used and equivalent characteristics of these Pcs are determined as function of volume fraction of PZT-7A piezoelectric. Results show that the electromechanical coefficients are well fitted by Voigt and Reuss models. Results obtained for some parameters show that the proposed GHM is consistent with the analytical existing models used for the 1-3 and 2-2 connectivities and is in line with measured values from Chan and Unsworth (1989). Based on the GHM 2-2 configuration results of piezocomposite materials, the electroacoustic responses of transducers having some of these properties are simulated using the KLM model. A performance trade-off was chosen, resulting in an improved thickness coupling coefficient and a lowered acoustical impedance, and a similar approach as that on a pure PZT-7A.

Optimization of Ferroelectric Ordering and Thermal Stability in Na1/2Bi1/2TiO3-Based Lead-Free Single Crystal through Defect Engineering.

Environmentally friendly lead-free piezoelectric materials have been attracting significant attention in recent years. Na1/2Bi1/2TiO3-based relaxor ferroelectrics have found acceptance for application in promising lead-free transducers in high-power ultrasonic devices. However, their low thermal stability, i.e., their relatively low ferroelectric-relaxor transition temperature (TF-R), hinders their practical application. Herein, a thermal-quenching approach is applied on a Na1/2Bi1/2TiO3 (NBT)-based single crystal, which yields a large increase in TF-R and dramatic enhancement of its ferroelectric ordering, leading to excellent thermal stability of its dielectric, ferroelectric, and piezoelectric properties. This behavior is mainly attributed to quenching-induced domain evolution as well as its octahedral tilt, which is linked to the increased oxygen vacancies. The substitution of long-range ordered ferroelectric domains for short-range polar nanodomains contributes to its increased coherence length and, consequently, enhancement of TF-R. This work provides an approach to the optimization of the ferroelectric ordering and thermal stability of NBT as well as an in-depth understanding of the quenching effect on the local structure, which could be applied to other relaxor-based ferroelectrics for optimization of their macroscopic properties.