Effective Coupling Factor Research Articles

Tuning of vibration absorbers by an effective modal coupling factor

The simplest family of vibration absorbers comprise inertia absorbers, with an inerter in series with a parallel or series dashpot–spring element, and stiffness absorbers, for which inerter and spring are interchanged. Vibration absorbers are tuned to a structure’s critical resonance, for which scalar structure-absorber equations are derived from an expansion in vibration modes with the absorber in either a free or clamped state. It is demonstrated that the influence from non-targeted residual modes is consistently represented by an effective modal coupling factor (EMCF), evaluated as the relative difference between free and clamped natural frequencies squared. While closely related to the coupling factor for shunted electromechanical transducers, the use of EMCFs determines an entirely new direction for the tuning of mechanical vibration absorbers on a flexible structure. For inertia and stiffness absorbers, the EMCF represents apparent mass or stiffness ratios that also account for the influence from residual modes. Therefore, analytical tuning expressions can be obtained from the derived modal frequency response functions, as demonstrated for a pole-placement method with the EMCF as a new governing absorber parameter. The accuracy of the proposed absorber tuning is validated by a simple numerical example, which shows that analytical tuning expressions can be used directly for vibration damping of flexible structures, provided that the EMCF is included correctly to compensate for the inherent modal interaction.

Inkjet-printed P(VDF-TrFE) film for high-frequency annular array.

An innovative processing to deposit P(VDF-TrFE) film on silicon wafers by an inkjet printing method was used to fabricate high-frequency annular array prototype. This prototype has a total aperture of 7.3 mm and 8 active elements. A polymer-based lens with low acoustic attenuation was added to the flat deposition on the wafer, setting the geometric focus to 13.8 mm. With a thickness of around 11 μm, the electromechanical performance of P(VDF-TrFE) films was evaluated with an effective thickness coupling factor of 22%. Electronics allowing all elements to simultaneously emit as a single element transducer was developed. In reception, a dynamic focusing, based on eight independent amplifying channels, was preferred. The center frequency of the prototype was 21.3 MHz, the insertion loss was 48.5 dB and the -6 dB fractional bandwidth was 143%. The trade-off sensitivity/bandwidth has rather favored the large bandwidth. Dynamic focusing on reception was applied and allowed to improvements in the lateral-full width at half maximum as shown on images obtained with a wire phantom at several depths. The next step, for a fully operational multi-element transducer, will be to achieve a significant increase of the acoustic attenuation in the silicon wafer.

Resonance properties of shear-horizontal surface acoustic waves on Ca3TaGa3Si2O14 at room and high temperatures

The resonance properties of shear-horizontal surface acoustic waves on Ca3TaGa3Si2O14 (CTGS) with Au or Al interdigital transducers (IDTs) were investigated. IDT-type resonators were fabricated on CTGS (0°, 134° or 155°, 90°) using Au- or Al-IDT, and the strong resonance properties and near-zero temperature coefficient of frequency (TCF) were measured at a certain electrode film thickness. From the measured and simulated results, an effective coupling factor of approximately 1.2% and zero TCF can be simultaneously obtained by using not only a high-density Au-IDT but also an Al-IDT and by adjusting the cut angle and electrode film thickness. Moreover, the resonance properties on Au-IDT/CTGS were evaluated at temperatures up to 570 °C. From the cut-angle dependences of the frequency shift calculated using the determined second-order temperature coefficients of the elastic constants, the potential for sensor applications that measure not only temperature but also pressure in such high-temperature environments can be expected.

Enhancement of coupling factor in 0th to 4th mode Rayleigh surface acoustic waves on polarity inverted multilayered ScAlN film/AlN and BN substrates

The rapid development of mobile communications requires high performance surface acoustic wave (SAW) filters. ScAlN film SAW resonators have a high coupling factor (K 2) and high phase velocity, enabling them to function as effective SAW filters. We theoretically investigated high-order mode Rayleigh SAWs (RSAWs) on single-layered or polarity inverted two-layered ScAlN film/AlN or BN substrate structures to find the optimal structure to achieve a higher K 2 and higher frequency. The K 2 and phase velocity for the single-layered ScAlN film/BN substrate structure were higher than those for the corresponding AlN substrate structure. The K 2 was enhanced in the polarity inverted ScAlN film/AlN or BN substrate structure. Finite element method analysis revealed that the effective coupling factor K eff 2 for the 2nd to 4th mode RSAWs on polarity inverted multilayered ScAlN films was enhanced by setting the boundary of the polarity inverted structure at the all positions where the particle displacements were concentrated.

Analysis of propagation characteristics of Rayleigh surface acoustic waves on Yb0.33Al0.67N piezoelectric films/high-velocity substrates

Piezoelectricity of YbAlN films has recently been shown to be almost as high as that of ScAlN films. YbAlN film surface acoustic wave (SAW) resonators are expected to have a high coupling factor. We theoretically investigated the propagation characteristics of first-mode Rayleigh SAWs (RSAWs) on Yb0.33Al0.67N film/high-velocity Si, sapphire, AlN, SiC, BN, and diamond substrates. The first-mode RSAWs on the YbAlN layered structures had high coupling factors, higher than those on ScAlN layered structures. An enhancement of the effective coupling factor of the first-mode RSAWs was observed in polarity inverted YbAlN film/BN or diamond substrate structures.

Surface acoustic wave modes characteristics of CMOS compatible SiO2/AlN/SiO2/Si multilayer structure with embedded electrodes

In this work, a CMOS compatible surface acoustic wave (SAW) device has been simulated and analyzed on SiO2/AlN/SiO2/Si. The simulation results have been used to characterize a typical fabricated device as well. The phase velocity, coupling coefficient, and temperature coefficient of frequency (TCF) of surface acoustic waves in the proposed structure have been investigated using the finite-element (FE) simulation. The simulation results show that a high velocity and a large effective coupling factor can be simultaneously obtained. Besides, the excellent nearly zero TCF is also achieved. The analysis further shows potential for designing high-frequency SAW devices that are CMOS compatible and temperature stable utilizing the Sezawa wave mode.

Characterization of magnetomechanical properties in FeGaB thin films

Layered magnetic/piezoelectric heterostructures have drawn a great amount of interest for their potential use in ultra-sensitive magnetoelectric (ME) sensors, ME antennas, voltage tunable inductors, magnetic tunable resonators, etc. It is critically important to characterize the saturation magnetostriction, piezomagnetic coefficient, ΔE effect, and magnetomechanical coupling factor of magnetic thin films, which determine the performance of these ME devices. In this work, a sensitive system has been developed to measure these magnetomechanical properties, on which several different magnetostrictive thin films on the silicon substrate cantilever were characterized. A 0.015 ppm limit of detection of the magnetostriction tester and a frequency resolution of 0.01 Hz of the ΔE tester have been achieved. After magnetic anneal treatment, a record high piezomagnetic coefficient of 12 ppm/Oe, a giant magnetic field induced Young's modulus change of 153 GPa, and a high effective magnetomechanical coupling factor of 0.84 have been measured in FeGaB thin films.

Comparison of Tripolar and Circular Pads for IPT Charging Systems

Recently, a magnetic pad called the tripolar pad (TPP) has been introduced for inductive power transfer (IPT) systems. This paper evaluates the effective coupling factor and leakage magnetic field of a 20-kW IPT system that uses a combination of TPP and circular pad (CP) topologies over a range of lateral displacements. The results show that the effective coupling factor and the leakage magnetic field of the TPP–TPP system are substantially better when the secondary is displaced away from ideal alignment. Leakage magnetic field is reduced up to 43% compared to the CP–CP system at the worst-case misalignment, which is due to the ability of the TPP–TPP system to generate and capture different types of magnetic field shapes. Simulation methods for both the TPP and CP are validated in the laboratory using a 2-kW system operating at 85 kHz.

Melting and thermal ablation of a silver film induced by femtosecond laser heating: a multiscale modeling approach

The femtosecond laser pulse heating of silver film is investigated by performing quantum mechanics (QM), molecular dynamics (MD) and two temperature model (TTM) integrated multiscale simulation. The laser excitation dependent electron thermophysical parameters (electron heat capacity, electron thermal conductivity, and effective electron-phonon coupling factor) are determined from ab initio QM calculation, and implemented into TTM description of electron thermal excitation, heat conduction, as well as electron-phonon coupled thermal energy transport. The kinetics of atomic motion is modeled by MD simulation. Energy evolution of excited electron subsystem is described by TTM in continuum. The MD and TTM are coupled by utilizing the effective electron-phonon coupling factor. Laser heating with varying laser fluence is systematically studied to determine the thresholds of the homogeneous melting and ablation. The thermal ablation induced by faster expansion of locally and excessively superheated silver is reported. This paper provides a basis for interpreting the phase change process induced by laser heating, and facilitates the advancement of femtosecond laser pulse processing of material.

Tripolar Pad for Inductive Power Transfer Systems for EV Charging

A recently proposed magnetic structure called Tripolar Pad (TPP) is investigated as a primary pad in an inductive power transfer battery charging system for electric vehicles. In this paper, a TPP primary is evaluated for 3.3 kW power transfer to both a circular pad and a bipolar pad as secondary pads. A mathematical model is presented to describe the power transfer from the TPP primary to the secondary pads then a control scheme is proposed which exploits the mutual decoupling between the TPP coils to find optimal primary currents. The optimization of the primary currents in the TPP improved the effective coupling factor over traditional topologies, particularly when the secondary was misaligned, and maintained leakage magnetic flux below International Commission on Non-Ionizing Radiation Protection guidelines. The result for the proposed TPP is validated with practical measurements.

Effective Coupling Factors for Series and Parallel Tuned Secondaries in IPT Systems Using Bipolar Primary Pads

Inductive power transfer is a method of delivering power from a source to a load by resonating inductive coils in proximity with each other. Two main pad topologies exist: one that can generate nonpolarized and one that can generate polarized fields. Multicoil pads such as bipolar pads (BPPs) have been proposed as a pad topology that is interoperable with both polarized and nonpolarized pads. BPPs comprise two ideally overlapped mutually decoupled coils, which can be driven in any relative magnitude or phase. A polarized pad structure, such as a double d pad, is not equivalent to a BPP, and the polarized pad is a subset of the multicoil pad. It also shows that the effective coupling factor ( $k_{\mathrm {eff}}$ ) between the BPP primary and the secondary depends on the coupling factors that exist between each primary coil and the secondary coil, the reflected impedances, and the relative magnitude and phase of currents between the primary coils. An equation that describes $k_{\mathrm {eff}}$ is proposed and considers all these factors to show how each coil in a BPP can be energized to control VA transfer.

Enhancement of effective electromechanical coupling factor by mass loading in layered surface acoustic wave device structures

This paper describes a drastic enhancement of the effective coupling factor by mass loading in layered surface acoustic wave (SAW) device structures such as the ScAlN film/Si substrate structure. This phenomenon occurs when the piezoelectric layer exhibits a high acoustic wave velocity. The mass loading decreases the SAW velocity and causes SAW energy confinement close to the top surface where an interdigital transducer is placed. It is shown that this phenomenon is obvious even when an amorphous SiO2 film is deposited on the top surface for temperature compensation. This enhancement was also found in various combinations of electrode, piezoelectric layer, and/or substrate materials. The existence of this phenomenon was verified experimentally using the ScAlN film/Si substrate structure.

SAW Characteristics of AlN/SiO2/3C-SiC Layered Structure With Embedded Electrodes.

A layered structure of aluminum nitride (AlN)/silicon dioxide (SiO2)/cubic silicon carbide with embedded electrodes, which enables the growth of high-quality AlN thin films, is proposed and studied. The phase velocity, coupling factor, and temperature coefficient of frequency (TCF) of surface acoustic waves in the proposed structure have been investigated using the finite-element method. The simulation results show that a high velocity of 5485 m/s and a large effective coupling factor ( K2<sup/>) of 1.45% can be simultaneously obtained for the first mode. The dramatic enhanced K2 of 10.5% is also obtainable on the proposed structure employing Sc0.4Al0.6N thin film. Besides, the excellent zero TCF is also achieved without deteriorating the coupling factor by adding an amorphous SiO2 overlay.

Electrical properties and temperature behavior of ZnO-doped PZT–PMnN modified piezoelectric ceramics and their applications on therapeutic transducers

Pb 0.98Ca 0.01Sr 0.01[(Mn 1/3Nb 2/3) 0.054Cu 0.006–(Zr 0.52Ti 0.48) 0.94]O 3 (PMNCZT) + x wt.% ZnO (PMNCZT–Z10 x) ceramics were prepared and sintered at a low temperature 980 °C, using the modified mixed-oxide method. The phase structure and microstructure evolutions were examined by XRD and SEM analyses. Effects of ZnO additives on the dielectric relaxation, piezoelectric, temperature stability, and ferroelectric properties were systematically investigated. The results showed that the ZnO doping increased the tetragonality ratio, tetragonal phase fraction, and long-range order degree of crystal structure. In addition, the electromechanical coupling factors, and the temperature stability of resonance frequency and resonant resistance were improved with increasing the ZnO amounts until x = 1. Beside these properties, the decrease of Q m was related to decreasing in normalized change value of space charge. This developed compositions had k p and k t of 0.56 and 0.55, Q m of 1280, d 33 of 285 pC/N, ε 33 T / ε 0 of 980, tan δ of 0.0023, coercive field ( E c) of 11 kV/cm, and remnant polarization ( P r) of 28 μC/cm 2. Their corresponding transmission coefficient of intensity exhibited from value of 60.12% ( x = 0) to value of 68.56% ( x = 2) by the acoustic model calculation. To evaluate the dynamic performance of developed piezoceramics, a 3 MHz therapeutic transducer was fabricated using the trade-off ceramics with x = 0.5. Its properties exhibited that the average effective coupling factors k eff 2 of 5.6%, electro-acoustic efficiencies of 34.1%, and dynamic acoustic power 0.75 W were better than those of a commercial transducer.

The third-order nonlinear optical properties of novel styryl dyes

The third-order nonlinear optical properties of two novel styryl dyes, namely, 1,3-diethyl-5-(4-methoxybenzylidene)-2-thioxodihydropyrimidine-4,6(1 H,5 H)-dione and 5-(3,4-dimethoxybenzylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1 H,5 H)-dione were studied using the Z-scan technique employing 7 ns laser pulses at 532 nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of effective third-order susceptibility and coupling factor were determined. The optical power limiting behavior of the colorants was ascribed to two-photon absorption phenomenon. Nonlinear absorption cross-section increased with increase in π electron density and the effective two-photon absorption cross-section was two orders of magnitude larger than those of commercially available azo compounds. The results suggest that these colorants offer promise as nonlinear optical materials for device applications.

Improvement of composite sol–gel process for manufacturing 40 μm piezoelectric thick films

In this study, high performance piezoelectric thick films were prepared by depositing only a few sol–gel infiltrated composite layers on Si/SiO 2/Ti/Pt wafers. Lead zirconate titanate (PZT) powder, binder and infiltration sol were synthesised from the same-laboratory made time-stable polymeric PZT sol. Adding coarse powder (50 wt%) to the sol precursor, crack-free coatings were prepared by dip coating in the 30–50 μm thickness range in only 3–6 layers. The results showed that good performance can be achieved by controlling sol concentration, powder charge, composite sol ageing, number of infiltrations and heat treatments. The initial results showed that only a limited number of infiltrations are needed in the final stack to obtain high piezoelectric performance. For instance, a 40 μm thick film was prepared with 6 composite layers with a 0.7 M PZT sol charged with 50 wt% PZT powder after 2 months’ ageing. Poling was performed for 5 min under 15 V/μm in an oil bath at 170 °C after 5 infiltrations and final annealing at 700 °C for 10 min in RTA. Despite substrate clamping, this coating reached an effective thickness coupling factor up of to 39% at a resonance frequency of 30 MHz. This result was obtained with a non-doped PZT powder.

Single-crystal lead magnesium niobate-lead titanate (PMN/PT) as a broadband high power transduction material

Two experimental underwater acoustic projectors, a tonpilz array, and a cylindrical line array, were built with single crystal, lead magnesium niobate/lead titanate, a piezoelectric transduction material possessing a large electromechanical coupling factor (k33 = 0.9). The mechanical quality factor, Q(m), and the effective coupling factor, k(eff), determine the frequency band over which high power can be transmitted; k(eff) cannot be greater than the piezoelectric material value, and so a high material coupling factor is a requisite for broadband operation. Stansfield's bandwidth criteria are used to calculate the optimum Q(m) value, Q(opt) approximately 1.2 (1-k(eff)2 1/2/k(eff). The results for the tonpilz projector exhibited k(eff) = 0.730, Q(m) = 1.17 (very near optimal), and a fractional bandwidth of 0.93. For the cylindrical transducer array, k(eff) = 0.867, Q(m) = 0.91 (larger than the optimum value, 0.7), and the bandwidth was 1.16. Although the measured bandwidths were less than optimal, they were accurately predicted by the theory, despite the highly simplified nature of the Van Dyke equivalent circuit, on which the theory is based.

Synthesis of 10‐μm‐Thick Lead Zirconate Titanate Films on 2‐in. Si Substrates for Piezoelectric Film Devices

To achieve micro‐machined piezoelectric film devices, crack‐free and dense 10‐μm‐thick lead zirconate titanate (PZT) films were successfully deposited onto 2‐in. Pt/Ti/SiO2/Si substrates using an automatic coating system, and disk‐shaped structures with a diameter from 20 to 100 μm were fabricated by an RIE process. The prepared PZT thick film disks showed well‐saturated P–E hysteresis curves and butterfly‐shaped longitudinal displacement curves. The AFM‐measured piezoelectric constant of the 30‐μm‐diameter PZT thick film disk after poling at 100 V for 10 min was AFM d33=290 pm/V. The resonant and anti‐resonant frequencies of the thickness oscillation mode were observed at 180 MHz. The calculated thickness mode effective coupling factor was (keff)2=0.1 for the poled 30‐μm‐diameter PZT thick film disks. These results suggest that the prepared PZT thick film disks are applicable for piezoelectric micro devices such as micro‐machined ultrasonic transducers.

FINITE ELEMENT ANALYSIS OF UNDERWATER CYMBAL TRANSDUCERS WITH LARGE DISPLACEMENT AND FAST RESPONSE TIME

ABSTRACT A new-style, piezocomposite cymbal transducer is presented in this paper. The single cymbal element is packaged in an ultra-high frequency (UHF) connector and sealed with epoxy, plugged by a coaxial-cable, which is more portable and miniature compared with conventional ones. Several kinds of cap heights are designed and the theory model of class V flextensional transducer is used to study their performance based on the cavity depth and caps thickness. The effect of dimensional changes on fundamental resonant frequencies has been investigated by finite element analysis. It is found that the cymbal transducer exhibits large displacement amplification, fast response time and high effective coupling factor through theoretical calculation, which are coincident with measurements. The results show that this design would have more potential application of low frequency and high energy transmission.

The effect of biaxial texture on the effective electromechanical constants of polycrystalline barium titanate and lead titanate thin films

Effective electromechanical constants as a function of biaxial crystallographic texture in polycrystalline films are modeled using a self-consistent approach. The film is modeled by assuming Gaussian distributions of two Euler angle textures about perfect orientation with varying spread, or full width at half maximum. We see that independent in-plane texturing has little effect on the piezoelectric displacement tensor. Increased out-of-plane texturing gives rise to an enhanced piezoelectric effect for barium titanate films, but not for lead titanate. Twist texturing about these out-of-plane angles shows a further enhancement in the non-shear components of the piezoelectric displacement tensor for both materials. Finally, we use the effective piezoelectric coupling factor as the primary figure of merit for the effective piezoelectric properties of polycrystal devices, thus utilizing all electromechanical constants of this simulation. This quantity shows a primary dependence on the out-of-plane texture.