Mode Electromechanical Coupling Coefficient Research Articles

Design and Analysis of Lithium–Niobate-Based Laterally Excited Bulk Acoustic Wave Resonator with Pentagon Spiral Electrodes

In this paper, we present a comprehensive study on the propagation and dispersion characteristics of A1 mode propagating in Z-cut LiNbO3 membrane. The A1 mode resonators with pentagon spiral electrodes utilizing Z-cut lithium niobate (LiNbO3) thin film are designed and fabricated. The proposed structure excites the A1 mode waves in both x- and y-direction by utilizing both the piezoelectric constants e24 and e15 due to applying voltage along both the x- and y-direction by arranging pentagon spiral electrode. The fabricated resonator operates at 5.43 GHz with no spurious mode and effective electromechanical coupling coefficient (Keff2) of 21.3%, when the width of electrode is 1 µm and the pitch is 5 µm. Moreover, we present a comprehensive study of the effect of different structure parameters on resonance frequency and Keff2 of XBAR. The Keff2 keeps a constant with varied thickness of LiNbO3 thin film and different electrode rotation angles, while it declines with the increase of p from 5 to 20 µm. The proposed XBAR with pentagon spiral electrodes realize high frequency response with no spurious mode and tunable Keff2, which shows promising prospects to satisfy the needs of various 5 G high-band application.

Improving fatigue resistance of PIMNT single crystal via two-step poling process

The fatigue resistance of pseudo-ternary single crystal 0.22Pb(In1/2Nb1/2)O3-0.53Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 (PIMNT) is tested by a “two-step poling process” – alternate current poling (ACP) with different cycles followed by direct current poling (DCP). The remnant polarization of the hysteresis loop decreases significantly and then does not change, and the coercive field raises with increasing polarization cycles. However, the two-step poling process contributes to the optimization and stability of fatigue resistance. Before 700 cycles, the piezoelectric constant d33 of the crystal is obviously promoted compared with the conventional DCP sample of d33 = 2200 pC/N, which increases by 40.9%–3100 pC/N, while the average thickness mode electromechanical coupling coefficient Kt remains at 0.518. With the increase in number of polarization cycles, the d33 and Kt are larger and more stable than for the ACP only sample. This improvement is due to nanoscale denser and smaller domains induced by the two-step poling process.

Fabrication and high acoustic performance of high frequency needle ultrasound transducer with PMN-PT/Epoxy 1-3 piezoelectric composite prepared by dice and fill method

In this paper, we reported the fabrication and high acoustic performance of high frequency needle ultrasound transducer based on 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal/Epoxy 1–3 piezoelectric composite, which was prepared by using the dice and fill (DAF) method. The as-prepared 0.70PMN-0.30 PT/Epoxy 1–3 composite has high thickness extension mode electromechanical coupling coefficient with the value of 67.3 %. The transducer is designed by PMN-PT/Epoxy 1–3 piezoelectric composite with a dimension of 550 μm × 450 μm × 35 μm. The fabricated transducer has not only a high center frequency larger than 42 MHz, but also high bandwidth of -6 dB of 90.6 %, the insertion loss with the value of 16 dB and excellent transmitting sensitivity of 314 mV/V. The results are in good agreement with the values simulated by PiezoCAD software. In addition, the acoustic performance of the transducer was also obtained by measuring the acoustic filed distribution in purified water. The -3 dB acoustic beam dimension width, the value of focal length and the acoustic power were 0.38 mm × 0.42 mm, 2.3 mm and 4.4 × 10−3mW, respectively. The performance PMN-PT/Epoxy 1–3 piezoelectric composite ultrasound transducer fabricated by dice and fill method (DAF) achieved the effect of ultrasonic transducer fabricated by deep reactive ion etching (DRIE). The excellent acoustic performance demonstrated that the DAF prepared PMN-PT/Epoxy 1–3 piezoelectric composite have great industry application potential in high frequency ultrasonic electronics, such as microelectronics NDT and biomedical imaging.

The Simulation of Resonant Mode and Effective Electromechanical Coupling Coefficient of Lithium Niobate Crystal with Different Orientations

At present, the proportion and role of thin film bulk acoustic wave (FBAR) filters in mobile communication products are becoming more and more obvious due to its higher work frequency and smaller size. As a commonly used piezoelectric material, aluminum nitride (AlN) limits the bandwidth of the FBAR filter because of its small electromechanical coupling coefficient (kt 2) of ~6.5%. On contrast, lithium niobate (LiNbO3, LN) crystals with some certain specific orientations have much better acoustic properties, making this type of material the promising candidate for FBAR applications. In this work, the acoustic resonant mode in LN crystal is analyzed by FEM simulations. In order to obtain the optimal orientations with good longitudinal wave property, Euler angle (EA) method is used to simulate the resonant modes and calculate the corresponding kt 2 of different orientations. Besides, the correctness of EA method has been demonstrated in this work by comparing the displacement change under electrostatic field with the traditional matrix transformation operation depending on the piezoelectric effect. The simulations show that the 43°Y-cut LiNbO3 has a high kt 2 and a pure longitudinal wave vibration mode simultaneously, making this orientation the most proper candidate for FBAR filters application with large bandwidth.

Ultrahigh Electromechanical Coupling and Its Thermal Stability in (Na1/2Bi1/2)TiO3-Based Lead-Free Single Crystals

In this work, we report the ultrahigh electromechanical coupling performance of NBT-6BT-KNN lead-free single crystal at room temperature. The thickness mode electromechanical coupling coefficient (kt) and the 31 mode electromechanical coupling coefficient (k31) reach 69.0% and 45.7%, respectively, which are superior to the PZT-5H lead-based ceramics of kt~60% and k31~39%. In addition, the evolution of the crystal structure and domain morphology is revealed by Raman scattering spectra, a polarizing microscope and piezoelectric force microscopy characterization.

Optimizing the piezoelectric vibration of Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 single crystal by alternating current polarization for ultrasonic transducer

Alternate current poling (ACP) is an effective method to enhance the piezoelectric performance of Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals dramatically. For their application in piezoelectric transducers for medical imaging, the beam mode vibration of PMN-0.25PT single crystal resonators after ACP was investigated by combining experimental impedance measurements and finite element simulation. The complete material coefficients of PMN-0.25PT single crystals were obtained by using pulse-echo ultrasound and inverse impedance spectroscopy. Compared to traditional direct current poling (DCP), the beam mode electromechanical coupling coefficient (k33′) of PMN-0.25PT for ACP reaches up to 89.1% from 84.5% of DCP. As the attribution of the special periodic stripe domain structure (109° domain), the lateral vibration will be suppressed effectively in the array transducer. This indicates that AC-poled PMN-0.25PT single crystals can be an efficient strategy to obtain higher sensitivity and a larger bandwidth in ultrasonic transducers.

Temperature dependence of mode coupling effect in piezoelectric vibrator made of [001]c-poled Mn-doped 0.24PIN–0.46PMN–0.30PT ternary single crystals with high electromechanical coupling factor**Project supported by the Basic Scientific Research Foundation of College and University in Heilongjiang Province, China (Grant No. 2018QNL-16), the Guiding Science and Technology Project of Daqing City (GSTPDQ), China (Grant No. zd-2019-03), and the National Natural Science Foundation

The influence of temperature on mode coupling effect in piezoelectric vibrators remains unclear. In this work, we discuss the influence of temperature on two-dimensional (2D) mode coupling effect and electromechanical coupling coefficient of cylindrical [001]c-poled Mn-doped 0.24PIN–0.46PMN–0.30PT piezoelectric single-crystal vibrator with an arbitrary configuration ratio. The electromechanical coupling coefficient kt decreases with temperature increasing, whereas k33 is largely invariant in a temperature range of 25 °C–55 °C. With the increase of temperature, the shift in the ‘mode dividing point’ increases the scale of the poling direction of the piezoelectric vibrator. The temperature has little effect on coupling constant Γ. At a given temperature, the coupling constant Γ of the cylindrical vibrator is slightly greater than that of the rectangular vibrator. When the temperature changes, the applicability index (M) values of the two piezoelectric vibrators are close to 1, indicating that the coupling theory can be applied to piezoelectric vibrators made of late-model piezoelectric single crystals.

(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics Synthesized by a Gel-Casting Method

(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) powder was synthesized by a solid-state reaction method, then the ceramics were fabricated by gel-casting and die-pressing routes, respectively. Piezoelectric coefficient (d33) was measured by the d33 m; Planar mode electromechanical coupling coefficient (kp), dielectric loss (tanδ) and relative permittivity (er) were measured by the impedance analyzer. Results of measurements showed that in the range of tested sintering temperature (1300–1500°C), gel-casting samples showed better piezoelectric and electromechanical coupling coefficients (d33 = 395 pC/N, kp = 0.44) compared with die-pressing samples, and comparable dielectric properties were also observed. (tanδ = 0.037, er = 3267).

Sb5+ Modified Phase Transition in (Li, Na, K)(Nb1-xSbx)O3 Piezoelectric Ceramics

The modified behavior of the phase transition temperatures (TO-T and/or TC) between orthorhombic (O), tetragonal (T) and cubic (C) that caused by doping Sb5+ in (Li0.052Na0.493K0.455)(Nb1-xSbx)O3 (LNKNSx) ceramics was reported in the present investigation. The results show that differing from the insensitive TO-T to the Sb5+ content, TC splits into two peaks TCI and TCII when doping Sb5+. The decreased TCI by raising x may be ascribed to the Sb-rich grains and the settled TCII round 480 °C resulting from the Sb-lack ones. The enhanced piezoelectric coefficient d33 value of 263 pC/N and planar mode electromechanical coupling coefficient kp value of 42.5% at x=0.052 can be attributed to the polymorphic phase boundary (PPB) behavior with an appropriate ratio between T and O phases without any second phase.

Templated grain growth and piezoelectric properties of 〈001〉-textured PIN–PMN–PT ceramics

Abstract

Tapered Two-Layer Broadband Vibration Energy Harvesters

Two-layer piezoelectric vibration energy harvesters using convergent and divergent tapered structures have been developed for broadband power output. The harvesters consist of a base cantilevered beam, which is attached to an upper beam by a spacer to develop a two-layer configuration. Two masses are attached to each layer to tune the resonance frequencies of each harvester and one of these masses also serves as the spacer. By varying the positions of the masses, the convergent and divergent tapered harvesters can generate close resonance frequencies and considerable power output in the first two modes. A broadband harvester design strategy is introduced based on a modal approach, which determines the modal performance using mass ratio and modal electromechanical coupling coefficient (EMCC). The required modal parameters are derived using the finite element method. Mass ratio represents the influence of the modal mechanical behavior on the power density directly. Since the dominant mode causes the remaining modes to have smaller mass ratios, smaller EMCC, and poor performance, the design strategy involves the selection of the harvester configurations with close resonances and favorable values of mass ratio initially, and deriving the EMCC and power density of those selected configurations.

Effects of Sr substitution on the structural, dielectric, ferroelectric, and piezoelectric properties of Ba(Zr,Ti)O3 lead-free ceramics

We have systematically studied the effects of Sr substitution on the microstructure, crystal structure, Curie temperature, dielectric, ferroelectric, and piezoelectric properties of (Ba1−xSrx)(Zr0.05Ti0.95)O3 (0 ≤ x ≤ 0.40) ceramics prepared by the conventional solid-state reaction method. Both X-ray diffraction and dielectric measurements reveal that with increasing Sr content, the room-temperature crystal structure of the samples evolves from tetragonal to orthorhombic around x = 0.2 where the two phases coexist. Dielectric measurements show that Sr doping significantly reduces the Curie temperature (TC) linearly from 114 °C for x = 0 to 10 °C for x = 0.4 with dTC/dx ≈ −265 °C/mol. Moreover, Sr doping causes linear shrinkage of the lattice constants and unit cell volume as well as considerable changes in the ferroelectric and piezoelectric properties. At room temperature, the sample with x = 0.11 exhibits enhanced piezoelectric properties with d33 ~ 380 pC/N and the planar mode electromechanical coupling coefficient kp = 0.38. Our results provide useful reference for the optimization of Ba(Zr,Ti)O3-based lead-free piezoelectric materials.

2P1-7 Shear mode electromechanical coupling coefficient of c-axis parallel oriented ZnO films by sputtering with H2O

2P1-7 Shear mode electromechanical coupling coefficient of c-axis parallel oriented ZnO films by sputtering with H2O

Electromechanical coupling and gigahertz elastic properties of ScAlN films near phase boundary

The electromechanical coupling, elastic properties, and temperature coefficient of elastic constant c33D of ScxAl(1−x)N films with high Sc concentration (x) of 0–0.70 were experimentally investigated. Near the phase boundary, a Sc0.41Al0.59N film exhibited a maximum thickness extensional mode electromechanical coupling coefficient kt2 of 12% (kt = 0.35), which is almost double the value of 6.4% for typical pure AlN films. In the region of 0 < x < 0.2, the electromechanical coupling was confirmed to increase without any detectable deterioration in the temperature stability of c33D (=−54.5 ppm/ °C). This region is favorable in terms of temperature stability and is suitable for wideband resonator filter applications.

A general modal approach for the development of optimal multi-layer stacked vibration energy harvesters

Piezoelectric vibration energy harvesters with multi-layer stacked structures have been developed. They consist of multi-layer beams, of zigzag configurations, with rigid masses attached between the beams. The rigid masses, which also serve as spacers, are attached to each layer to tune the frequencies of the harvester. Close resonance frequencies and considerable power output can be achieved in multiple modes by varying the positions of the masses. A modal approach is introduced to determine the modal performance conveniently using the mass ratio and the modal electromechanical coupling coefficient, and the required modal parameters are derived using the finite element method. Mass ratio represents the influence of modal mechanical behaviour on the power density. Since the modes with larger mass ratios cause the remaining modes to have smaller mass ratios and lower power densities, a screening process using the modal approach is developed to determine the optimal or near-optimal performance of the harvesters when altering mass positions. This procedure obviates the need for full analysis by pre-selecting the harvester configurations with close resonances and favourable values of mass ratio initially. Furthermore, the multi-layer stacked designs using the modal approach can be used to develop harvesters with different sizes with the power ranging from microwatts to milliwatts.

Enhanced piezoelectricity in YbGaN films near phase boundary

Weak piezoelectricity in GaN is a problem in bulk acoustic wave filters and heterostructure field-effect transistors. In this study, enhancement of piezoelectricity in c-axis direction by substituting Yb for Ga was experimentally demonstrated. Thickness extensional mode electromechanical coupling coefficient kt for the YbxGa1−xN films increases with the Yb concentration from x = 0 to 0.3. Yb0.30Ga0.70N film near the phase boundary exhibited a maximum kt of 3.1%, which is approximately 2.5 times larger than that for a pure GaN.

Optimal design of two-layer vibration energy harvesters using a modal approach

Piezoelectric vibration energy harvesters (VEHs) with two-layer structures are developed. The attached masses are used to tune the frequencies and as spacers between the two layers. By changing the dimensions of the layers and masses and relocating the positions of the masses, the VEHs can generate close resonance frequencies and considerable power output. The modal approach is introduced to determine the modal performance using the mass ratio and the modal electromechanical coupling coefficient, where the mass ratio represents the influence of the modal mechanical behaviour on the power density directly, and the modal parameters required are derived using the finite element method. The findings indicate that a mode with too large mass ratio will cause the remaining modes to have small mass ratios and poor performance. Then, a screening process for the identification of the configurations of VEHs with optimal or near-optimal performance is developed using the modal approach. This procedure facilitates the selection of VEH configurations with close resonances and favourable values of mass ratio initially before carrying out full analysis. Furthermore, the approach can be used to develop VEHs of different sizes ranging from a few millimeters to hundreds of millimeters with the power ranging from microwatts to milliwatts.

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.

SmAlO 3 -modified (K 0.5 Na 0.5 ) 0.95 Li 0.05 Sb 0.05 Nb 0.95 O 3 lead-free ceramics with a wide sintering temperature range

Lead-free ceramics (1 − x)(K0.5Na0.5)0.95Li0.05Sb0.05Nb0.95O3-xSmAlO3 (KNLNS-xSA) were prepared by conventional sintering technique. The phase structure, dielectric and piezoelectric properties of the ceramics were investigated. All compositions show a main perovskite structure, exhibiting room-temperature symmetries of tetragonal at x ≤ 0.0075, of pseudo-cubic at x = 0.0100. The Curie temperature of KNLNS-xSA ceramics decreases with increasing SmAlO3 content. Moreover, the addition of SmAlO3 can effectively broaden the sintering temperature range of the ceramics. The KNLNS-xSA ceramic with x = 0.0050 has an excellent electrical behavior of piezoelectric coefficient d33 = 226 pC/N, planar mode electromechanical coupling coefficient kp = 38%, dielectric loss tan δ = 3.0%, mechanical quality factor Qm = 60, and Curie temperature TC = 327 °C, suggesting that this material could be a promising lead-free piezoelectric candidate for piezoelectric applications.

Robust electromechanical finite element updating for piezoelectric structures effective coupling prediction

A robust electromechanical updating methodology for piezoelectric structures effective coupling prediction is first presented. It combines a finite element design experiment–based a priori sensitivity analysis, a response surface method–based meta-modelling and a genetic algorithm–based multi-objective optimization procedure. Then, this methodology is applied to cantilever aluminium thick plate and thin beam structures that are bonded, respectively, with two oppositely poled large and oppositely and same poled small piezoceramic patches on their upper and lower surfaces. In order to correlate corresponding first few effective modal electromechanical coupling coefficients, a mechanical updating is first considered; it consists of identifying the stiffness parameters of linear springs, modelling the clamp, so that relative deviations between the first few experimental and finite element short-circuit frequencies are minimized; then, an electric updating is considered; it consists of finding the patches’ relative transverse blocked dielectric constants that minimize the first few experimental and finite element open-circuit frequencies relative deviations. Free vibrations are simulated using ANSYS®-coupled piezoelectric three-dimensional finite element. The obtained results have partially confirmed those from a former ad hoc updating method since the sensitivity analyses led to same stiffness parameters’ irreducible number and only some effective modal electromechanical coupling coefficient test–model correlations were enhanced.