High Electromechanical Coupling Coefficient Research Articles

Influence of a silver epoxy dopant on the performance of broken piezoelectric ceramic transducer based on an analytical model

Over the past decade, an unprecedented increase in the types of, the methods of using, and the demand for piezoelectric ceramic transducers (PCTs) has been observed in the market. These factors increase the probability of PCTs being subjected to breakage. Therefore, this study proposes a simple, low-cost procedure which uses available components to repair and reinstall five broken PCTs and then tests them as emitters and receivers in bulk and surface wave detection. An SM211 PCT with a 7.2 MHz frequency, a high damping and electromechanical coupling coefficient, and two silver electrodes were selected for the experiment. A Mason circuit was used for the procedure, the Laplace transform was used as a mathematical analysis method, and MATLAB was the technical computing language used to model the new transfer function for this type of PCT. This study proved that silver electrodes are a significant load on PCTs, particularly at high frequencies. Very good identity correlations between this mathematical and the experimental responses of the standard PCT were obtained. Later this mathematical model was used to prove the explanations provided by this research. The response of the standard PCT was compared with that of the samples of PCT that have been repaired (SPCTR). Through this comparison, many conclusions were obtained, and several recommendations were made, which can be taken advantage of by people who are interested in this field of research. Such recommendations include analyzing the response of SPCTR and explaining the types of ultrasonic tests in which SPCTR can be used.

Theoretical investigation of conductivity sensitivities of SiC-based bio-chemical acoustic wave sensors

The phase velocities, electromechanical coupling coefficients, conductivity sensitivities, insert losses, and minimum detectable masses of Rayleigh and Lamb waves sensors based on silicon carbide (SiC) substrates are theoretically studied. The results are compared with the performances of the sensors based on conventional silicon substrates. It is found that the sensors using SiC substrates have higher electromechanical coupling coefficients and conductivity sensitivities than the conventional silicon-based sensors in virtue of piezoelectricity of the SiC. Moreover, higher phase velocities in SiC substrates can reduce the insert losses and minimum detectable masses of the sensors. In this case, in the detection of the gas with the tiny mass as the hydrogen, in which the conductivity sensitivity is more important than the mass sensitivity, the sensor based on the SiC substrate has a higher sensitivity and exhibits the potential to detect the gas with the concentration below the ppm level. According to the results, the performances of the sensors based on the Rayleigh and Lamb waves using the SiC substrates can be optimized by properly selecting piezoelectric films, structural parameters, and operating wavelengths.

Fabrication and geometrical factors of a novel piezoelectric composite

A novel 0.25PZN–0.75PLZT ceramic/epoxy resin composite with spiral ceramic structure was fabricated by the roll forming-curling method. The composites were investigated for dielectric and piezoelectric properties, while the volume fraction of ceramic phase and the ratio of width to thickness lw/lt of the ceramic ring were varied. In addition to a high electromechanical coupling coefficient (Kt=89%)with a 25% volume fraction and low acoustic impedances, the composite was found to yield optimum figure of merit (FOM) value of 77.1×10−12m2/N with a 11% volume fraction when the ratio of width to thickness lw/lt of the ceramic ring was 0.4. Furthermore, for a given volume fraction of the ceramic phase, the properties electromechanical coupling coefficient (Kt) and the figure of merit (FOM) were all dependent on the ratio of width to thickness lw/lt of the ceramic ring.

Synthesis and Electrical Properties of 1-x(Na<sub>0.5</sub>K<sub>0.5</sub>NbO<sub>3</sub>)-x(CoFe<sub>2</sub>O<sub>4</sub>)

Magnetoelectric (ME) effect is a coupled two-field effect in which application of an electric field induces magnetization and a magnetic field induces electrical polarization. However, it is difficult for a single material to have this combination of the ferromagnetic and ferroelectric properties. Thus, ferromagnetic–ferroelectric/dielectric composite materials become an attractive subject. Na1−xKxNbO3(NKN) is a combination of ferroelectric KNbO3and antiferroelectric NaNbO3, and forms a morphotropic phase boundary (MPB) near 50/50 composition (x=0.50) separating two orthorhombic phases. NKN has high electromechanical coupling coefficient (k2) and high phase transition temperature (Tc = 425 °C), especially near the morphotropic phase boundary (MPB). CoFe2O4(CFO), on the other hand, is well known spinel ferrite with high Curie temperature. We have synthesized ceramic composites, 1-x(Na0.5K0.5NbO3)-x(CoFe2O4) with x = 0.0 to 1.0 (in step of 0.2) by standard solid state reaction route. Powder XRD show a mixed cubic phase without impurity peaks for the samples under study. In low frequency range the dielectric properties of the NKN/CFO composites show Maxwell–Wagner relaxation. Systematic change in the electrical polarization with increasing x was observed at various applied fields at room temperature.

Surface acoustic wave in temperature compensated NdCa 4 O(BO 3 ) 3 crystal

A two-port synchronous resonator was used for measurements of surface acoustic wave (SAW) parameters in the Y-plane of NdCa4O(BO3)3 crystal. For YX–5°, YX and YX + 5° orientations, the SAW phase velocity under free surface, electromechanical coupling coefficient, second-order temperature coefficient of frequency and turnover temperature (T O) of about 3481, 3502 and 3503 m/s; 0.68, 0.63 and 0.6%; −37, −32 and −70 ppb/°C2 and 80, 25 and −35 °C, respectively, were obtained. The crystal was assessed as attractive in SAW applications due to temperature compensation and high electromechanical coupling coefficient.

Surface and quasi-longitudinal acoustic waves in KTiOAsO4 single crystals

Surface and quasi-longitudinal acoustic wave properties have been investigated in potassium titanyl arsenate (KTiOAsO4, KTA) single crystals for the first time. Surface acoustic wave (SAW) velocity, electromechanical coupling coefficient and power flow angle characteristics have been obtained in rotated Y-cut of KTA crystals. High SAW electromechanical coupling coefficient (0.4%) is found in Z-cut of KTA crystals. For high-frequency devices it is promising the resonators on quasi-longitudinal acoustic wave in X-cut of KTA crystals with sharp response in interdigital transducer conductance at resonance frequency.

Modal electromechanical optimization of cantilevered piezoelectric vibration energy harvesters by geometric variation

The design studies of cantilevered piezoelectric vibration energy harvesters have been focused on the optimization of the power output of rectangular cantilevered beam vibration energy harvesters. However, without clarifying the influences of the modal electromechanical coupling and mechanical behaviour clearly, the power outputs cannot be adequately optimized. In this article, a distributed parameter electromechanical model is used to predict the power output with resistive loads, and the parameters are derived using the finite element method. First, a parametric study is presented to investigate the effects of the two factors on the volumetric power of cantilevered vibration energy harvesters. Then, an optimization strategy is implemented to investigate the modal electromechanical coupling coefficient and mass ratio separately using geometric parameter study. Mass ratio represents the influences of modal mechanical behaviour on the power density directly. The findings indicate that the convergent and divergent tapered cantilevered and rectangular cantilevered beam designs with partial coverage of piezoelectric layer are able to generate higher electromechanical coupling coefficient than conventional rectangular cantilevered designs with full coverage. Besides, using convergent tapered cantilevered designs can actually decrease the power density significantly. Both using divergent tapered cantilevered structures and attaching reasonable extra masses with varied locations on vibration energy harvesters can generate larger power density.

Study on the electromechanical coupling coefficient of Rayleigh-type surface acoustic waves in semi-infinite piezoelectrics/non-piezoelectrics superlattices

The electromechanical coupling coefficient of Rayleigh-type surface acoustic waves in semi-infinite piezoelectrics/non-piezoelectrics superlattices is investigated by the transfer matrix method. Research results show the high electromechanical coupling coefficient can be obtained in these systems. The optimization design of it is also discussed fully. It is significantly influenced by electrical boundary conditions on interfaces, thickness ratios of piezoelectric and non-piezoelectric layers, and material parameters (such as velocities of pure longitudinal and transversal bulk waves in non-piezoelectric layers). In order to obtain higher electromechanical coupling coefficient, shorted interfaces, non-piezoelectric materials with large velocities of longitudinal and transversal bulk waves, and proper thickness ratios should be chosen.

Piezoelectric behavior of (1−x)(PbMgNbO3–PbZrTiO3)–x(BaTiO3) ceramics for energy harvester applications

Abstract The Pb(Mg 1/3 Nb 2/3 )O 3 –Pb(Ti,Zr)O 3 system near morphotropic phase boundary (MPB) can be expected to provide a high piezoelectric charge coefficient and electromechanical coupling coefficient. Therefore, it has been used as an excellent candidate for piezoelectric applications, including energy harvester applications. In this study, electric field-induced phase transition in (1− x )(PbMgNbO 3 –PbZrTiO 3 )– x (BaTiO 3 ) ceramics in a relatively low field of 40 kV/cm will be discussed. XRD analysis showed tetragonal and rhombohedral perovskite structure of PbMgNbO 3 –PbZrTiO 3 with BaTiO 3 , indicated that phase transition was occurred with increasing BaTiO 3 , component. Measurement of room temperature dielectric constant indicated a gradual increase with increasing BaTiO 3 content. The results show that the addition of BaTiO 3 is very effective in improving the dielectric and electric properties of Pb(Mg 1/3 Nb 2/3 )O 3 –Pb(Ti,Zr)O 3 system.

Theoretical investigation of acoustic wave devices based on different piezoelectric films deposited on silicon carbide

Performances of acoustic wave (AW) devices based on silicon carbide (SiC) substrates are theoretically studied, in which two types of piezoelectric films of ZnO and AlN deposited on 4H-SiC and 3C-SiC substrates are adopted. The phase velocities (PV), electromechanical coupling coefficients (ECC), and temperature coefficients of frequency (TCF) for three AW modes (Rayleigh wave, A0 and S0 modes of Lamb wave) often used in AW devices are calculated based on four types of configurations of interdigital transducers (IDTs). It is found that that the ZnO piezoelectric film is proper for the AW device operating in the low-frequency range because a high ECC can be realized using a thin ZnO film. The AlN piezoelectric film is proper for the device operating in the high-frequency range in virtue of the high PV of AlN, which can increase the finger width of the IDT. Generally, in the low-frequency Lamb wave devices using ZnO piezoelectric films with small normalized thicknesses of films to wavelengths hf/λ, thin SiC substrates can increase ECCs but induce high TCFs simultaneously. In the high-frequency device with a large hf/λ, the S0 mode of Lamb wave based on the AlN piezoelectric film deposited on a thick SiC substrate exhibits high performances by simultaneously considering the PV, ECC, and TCF.

PIN-PMN-PT Single-Crystal-Based 1–3 Piezoelectric Composites for Ultrasonic Transducer Applications

In this work, Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal/epoxy 1–3 composites with different thicknesses (400 μm to 825 μm) were fabricated using the conventional dice-and-fill method. Their properties were compared with the corresponding lead zirconate titanate (PZT) ceramic 1–3 composites. Excellent properties for ultrasonic transducer applications have been achieved, such as high electromechanical coupling coefficient (kt ≈ 78% to 83%), high piezoelectric strain coefficient (d33 ≈ 1000 pm/V), and lower acoustic impedance (Z ≈ 20 Mrayl). The strain levels of PIN-PMN-PT composites were almost constant (1000 pm/V) with decreasing thickness, being much higher than those of PZT composites (650 pm/V). However, an increase in strain hysteresis was observed with decreasing thickness, reaching 25.3% for the 400-μm single-crystal 1–3 composite, which is lower than the corresponding PZT composites (44.1% for 350-μm PZT ceramic 1–3 composite). These results show that PIN-PMN-PT single-crystal 1–3 composites have great potential for use in advanced ultrasound transducer applications.

Performance of tonpilz transducers with segmented piezoelectric stacks using materials with high electromechanical coupling coefficient

Tonpilz acoustic transducers for use underwater often include a stack of piezoelectric material pieces polarized along the length of the stack and having alternating polarity. The pieces are interspersed with electrodes, bonded together, and electrically connected in parallel. The stack is normally much shorter than a quarter wavelength at the fundamental resonance frequency so that the mechanical behavior of the transducer is not affected by the segmentation. When the transducer bandwidth is less than a half octave, as has conventionally been the case, for example, with lead zirconate titanate (PZT) material, stack segmentation has no significant effect on the mechanical behavior of the device in its normal operating band near the fundamental resonance. However, when a high coupling coefficient material such as lead magnesium niobate-lead titanate (PMN-PT) is used to achieve a wider bandwidth with the tonpilz, the performance difference between a segmented stack and a similar piezoelectric section with electrodes only at the two ends can be significant. This paper investigates the effects of stack segmentation on the performance of wideband underwater tonpilz acoustic transducers. Included is a discussion of a particular tonpilz transducer design using single crystal piezoelectric material with high coupling coefficient compared with a similar design using more traditional PZT ceramics.

Wideband Lithium Niobate FBAR Filters

Filters based on film bulk acoustic resonators (FBARs) are widely used for mobile phone applications, but they can also address wideband aerospace requirements. These devices need high electromechanical coupling coefficients to achieve large band pass filters. The piezoelectric material LiNbO3 complies with such specifications and is compatible with standard fabrication processes. In this work, simple metal—LiNbO3—metal structures have been developed to fabricate single FBAR elements directly connected to each other on a single chip. A fabrication process based on LiNbO3/silicon Au-Au bonding and LiNbO3 lapping/polishing has been developed and is proposed in this paper. Electrical measurements of these FBAR filters are proposed and commented exhibiting filters with 8% of fractional bandwidth and 3.3 dB of insertion losses. Electrical measurements show possibilities to obtain 14% of fractional bandwidth. These devices have been packaged, allowing for power handling, thermal, and ferroelectric tests, corresponding to spatial conditions.

Performance of transducers with segmented piezoelectric stacks using materials with high electromechanical coupling coefficient

Abstract underwater acoustic transducers often include a stack of thickness polarized piezoelectric material pieces of alternating polarity interspersed with electrodes and bonded together. The stack is normally much shorter than a quarter wavelength at the fundamental resonance frequency, so that the mechanical behavior of the transducer is not affected by the segmentation. When the transducer bandwidth is less than a half octave, as has conventionally been the case, stack segmentation has no significant effect on the mechanical behavior of the device. However, when a high coupling coefficient material such as PMN-PT is used to achieve a wider bandwidth, the difference between a segmented stack and a single piezoelectric piece with the same overall dimensions can be significant. This paper investigates the effects of stack segmentation on the performance of wideband underwater acoustic transducers, particularly tonpilz transducer elements. Included is discussion of transducer designs using single crystal piezoelectric material with high coupling coefficient compared with more traditional PZT ceramics.

Calculation and analysis of surface acoustic wave properties of ZnO film on diamond under different excitation conditions

In the last twenty years, the ZnO/diamond layered structure for surface acoustic wave (SAW) devices have been widely studied and have attracted great attention, due to its advantages of high acoustic velocity, high electromechanical coupling coefficient and high power durability. Distinguished from the conventional single-crystal substrate (such as quartz, lithium niobate), ZnO/diamond layered structure shows dispersive SAW properties, which can be excited by four ways: interdigital transducer (IDT)/ZnO/diamond, IDT/ZnO/shorting metal/diamond, ZnO/IDT/diamond, and shorting metal/ ZnO/IDT/diamond. In this paper, the formulation based on the stiffness matrix method for calculating the effective permittivity of ZnO/diamond layered structure under four excitation conditions is given first. Then, by using this formulation, the SAW properties of the monocrystalline ZnO (002) film on polycrystalline diamond and the polycrystalline ZnO (002) film on polycrystalline diamond are calculated respectively. Based on the results of calculation, the ZnO film thicknesses qualified to design and fabricate SAW device are analyzed in detail. Finally, we discuss the function of diamond film thickness of ZnO/diamond/Si layered structure so as to avoid the influence of the silicon substrate on the SAW properties.

(1-x)(PbMgNbO3-PbZrTiO3)-x(BaTiO3) Piezoelectric Ceramics

The Pb(Mn1/3Nb2/3)O3-Pb(Ti,Zr)O3 system near the morphotropic phase boundary (MPB) can be expected to provide high piezoelectric constant and electromechanical coupling coefficient. Therefore it has used as an excellent candidate for piezoelectric applications including the high-power application. In this study, electric field-induced phase transition in PMN-PZT-based ceramics at a relatively low field of 40 kV/cm will be discussed. The structural and electrical properties of (1-x)(PMN-PZT)-xBT ceramics were investigated as a function of the BaTiO3 content (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). Phase formation behavior was studied by an X-ray diffraction method. Room temperature SEM investigation revealed common trends in the grain structure with increasing BaTiO3 content.

Characterization of piezoelectric polymer composites for MEMS devices

Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (k). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low k value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2–2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.

Lead-free piezoelectric single crystal based 1–3 composites for ultrasonic transducer applications

In this work, lead-free 1–3 composites based on piezoelectric 0.947Na0.5Bi0.5TiO3–0.053BaTiO3 (NBT–0.053BT) single crystal and epoxy are fabricated for ultrasonic transducer applications by a modified dice-and-fill method. Excellent properties for ultrasonic transducer applications have been achieved, such as high electromechanical coupling coefficient (kt=73%), lower acoustic impedance (Z=16MRayl) and moderate dielectric constant. Based on this lead-free piezoelectric single crystal composite, single-element ultrasonic transducer and linear array have been fabricated and characterized. Both types of transducers exhibit similar performance with broad bandwidth of exceeding 100%. The promising results show that these lead-free composites have the potential to be used for high-performance ultrasonic transducers.

Surface Acoustic Wave Propagation in Relaxor-Based Ferroelectric Single Crystals 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 Poled along [011

Surface acoustic wave (SAW) propagation in relaxor-based ferroelectric single crystals 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 (PZN-7%PT) poled along [011]c has been analyzed theoretically. The results show that PZN-7%PT single crystals have excellent SAW properties, such as low phase velocities, very high electromechanical coupling coefficients and small power flow angles. It is also found that the SAW properties strongly depend on the propagation direction and the characteristic curves of SAW phase velocity, and the electromechanical coupling coefficients are symmetric with respect to θ = 90°. Considering all related factors, the X-cut PZN-7%PT single crystal has the best performance. Based on our results, the X-cut PZN-7%PT single crystals poled along [011]c are an excellent candidate for ultra-wide bandwidth low-frequency SAW devices.

Effect of Low-Temperature Frit on the Sintering Behavior and Properties of 0.95K<sub>0.49</sub>Na<sub>0.51</sub>NbO<sub>3</sub>-0.05LiSbO<sub>3</sub> Lead-Free Piezoceramics

The effects of low-temperature frit Li2O-Na2O-K2O-B2O3-SiO2-CaO-BaO-ZnO (abbreviated as BS) on the sintering behavior and electrical properties of 0.95K0.49Na0.51NbO3- 0.05LiSbO3 (abbreviated as KNN-LS) lead-free piezoceramics were investigated. The sintering temperature of the KNN-LS ceramics can be reduced from 1080 °C to 1000 °C due to the addition of BS frit. For the 0.5 wt% BS-doped KNN-LS ceramics, which are sintered at reduced temperature of 1000 °C for 2 h, remain relatively high piezoelectric constant d33 (195 pC/N) and planar electromechanical coupling coefficient kp (40.7%). In addition to other optimization effects, such as reduction of dielectric loss from 3.6% to 2.7% and increment of mechanical quality factor Qm from 48 to 70, this BS frit was experimentally proved to be good for low temperature sintering of KNN-based ceramics while maintaining high piezoelectric response.