High Coupling Coefficient Research Articles

Research on Stacked Piezoelectric Cymbal Vibrator.

As demand for haptic feedback increases, piezoelectric materials have become one of the best candidate materials due to their small size, high electromechanical coupling coefficient, and fast response. A stacked piezoelectric cymbal vibrator is proposed based on the common cymbal-type transducer, which is composed of a piezoelectric stack to drive and a cymbal disk to amplify displacement. A coupling theoretical model between the piezoelectric stack and the cymbal-type structure is established. The longitudinal and radial displacements of the stacked piezoelectric cymbal vibrator are calculated in the low frequency range (<1000 Hz) by the theoretical model and the finite element method. The theoretical and numerical results are in good agreement. The results show that the radial displacement can be converted into longitudinal displacement and then effectively amplified by the cymbal disk with an amplification ratio of 30. The feature is conducive to its widespread application in the field of consumer electronics.

Active acoustic field modulation of ultrasonic transducers with flexible composites

The simple acoustic field generated by conventional transducers limits the development of ultrasound applications. Current methods rely on passive acoustic lenses or active arrays to manipulate ultrasonic waves, but they face challenges such as low transmission efficiency with bulky morphology for lenses, and complex systems with high-cost for arrays. Here, we propose a method exploiting flexible piezoelectric ultrasonic transducers (FPUT) with 1-3 PZT8/PDMS composites to achieve a high-frequency and diversified ultrasonic field. The FPUT at a center frequency of 1.5 MHz exhibits a high electromechanical coupling coefficient (kt ~ 0.74), excellent transmission efficiency, and mechanical conformability. We showcase two dynamic functionalities of our setup, namely variable acoustic focus and multi-order vortex generated by circular and spiral shape transducers. Finally, we show that the FPUT achieves high-resolution underwater ultrasonic imaging at a wide spatial range (>12λ) via ultrasonic collimation, offering a viable technological alternative for active acoustic fields manipulation and ultrasonic applications.

Film bulk acoustic resonators with 400 MHz ultrawide-range tunability using crystalline PZT thin film

Tunable and switchable film bulk acoustic resonators (FBARs) have great application potential owing to their much-increased flexibility in radiofrequency (RF) circuits. Here, we report on the design and fabrication of a tunable and switchable FBAR based on a thin crystalline lead zirconate titanate (PZT, Pb[Zr0.6Ti0.4]O3) film. The FBAR device has a resonant frequency of 2.42 GHz with a high effective electromechanical coupling coefficient keff2 of 30%. The frequency tunable range of the device is up to 400 MHz (2.11–2.51 GHz, 16.6%) with a DC bias voltage of less than 12 V, and the device can also be switched off when the polarization intensity in the PZT film is zero. Through the investigation, a relationship between the ferroelectric nature of PZT material and the wide tuning range of FBAR is established, providing a theoretical and experimental guideline for further development.

Phononic crystals for Love waves based on thin-film lithium niobate

This paper presents a type of surface acoustic wave (SAW) phononic crystals based on thin-film lithium niobate (LN). They are created by forming micro-pillar or micro-well structures on the LN, resulting in significant Rayleigh and Love SAW bandgaps. Especially for Love waves, they offer an irreplaceable advantage because they overcome the inability of conventional electrodes to reflect Love waves effectively. This enables the creation of high-quality, compact, high electromechanical coupling coefficient, stable and power-resistant acoustic resonators based on Love waves, potentially leading to a new generation of high-performance SAW filters and sensors. In this paper, we demonstrate the feasibility of such phononic crystals using xy-cut LN-on-SiC. However, it is worth noting that other piezoelectric materials such as lithium tantalate can also be used instead of LN, and high acoustic velocity substrates such as sapphire and diamond can be substituted for SiC.

Compact Bandwidth-Enhanced 180-Degree Phase Shifter Using Edge-Coupled Multi-Microstrip and Artificial Transmission Line.

Compactness has obtained sufficient importance in wideband phase shifter design considerations, as it is directly related to fabrication cost. In this paper, a novel structure was presented to create compact broadband 180-degree phase shifter, which has the advantages of enhanced bandwidth and significantly reduced chip area. The proposed configuration consists of edge-coupled multi-microstrip lines (ECMML) and an artificial transmission line (ATL) with dual-shorted inductors, both of which have the periodic shunt load of capacitors. The ECMML can provide a high coupling coefficient, leading to an increase in the bandwidth, while the introduced capacitors can greatly reduce the line length (35.8% of the conventional method). To verify the relevant mechanisms, a wideband switched network with compact dimensions of 0.67 × 0.46 mm2 was designed via 0.15-micrometer GaAs pHEMT technology. Combined with the measured switch transistor, it was shown that the proposed phase shifter exhibits an insertion loss of less than 2 dB, a return loss of greater than 12 dB, a maximum phase error of less than 0.6° and a channel amplitude difference of less than 0.1 dB in the range of 10 to 20 GHz.

Misalignment tolerance improvement and high efficiency design for wireless power transfer system based on DDQ‐DD coil

SummaryThis paper addresses misalignment tolerance improvement and high‐efficiency maintenance for wireless power transmission systems. Firstly, a receiving coil is designed according to Standard J2954, published by the Society of Automotive Engineers. Next, a DDQ transmitting coil is designed to accommodate a constrained operating space. The structure and parameters of the transmitting coils are determined to obtain a high coupling coefficient when offset occurs. Subsequently, an analysis is carried out to determine the relationship between the coupler magnetic fields and power transmission ability. A current phase control strategy is developed to deal with the mismatched magnetic fields, and a switching threshold is selected to obtain high power transmission efficiency. Finally, an experimental system is set up using the designed coil. The experimental results demonstrate that the system can maintain high efficiency even when lateral misalignment occurs in different directions. A maximum transmission efficiency of 89.63% is obtained, which validates the effectiveness of the proposed method.

Theoretical study on luminescence properties of a series of iridium complexes with high spin orbit coupling coefficients

AbstractIn this paper, several Ir (III) complexes with transition metal as the central atom formed by the corresponding combination of two main ligands and three auxiliary ligands have been studied theoretically. The electronic structure, frontier molecular orbital, and spin orbit coupling data are used to analyze its application value in light emitting devices. The density functional theory is used to study (tbi)2Ir(bpp), (tbi‐c)2Ir(bpp), (tbi)2Ir(dbm), (tbi‐c)2Ir(dbm), (tbi)2Ir(pic), and (tbi‐c)2Ir(pic). bpp = (2Z)‐3‐hydroxy‐13‐diphenylprop‐2‐en‐1‐one; dbm = 1,3‐di‐phenyl‐1, 3‐propanedione; pic = picolinate.

Simulation and Optimization of Surface Acoustic Wave Devices With High Electromechanical Coupling Factor and Zero Temperature Coupling Coefficient by Pattern Piezoelectric Layer

Recently, a more popular patterned surface acoustic wave (SAW) device with better performance was proposed. This structure has a large electromechanical coupling factor. To make surface acoustic wave devices easy to be applied to integrated circuit technology, a multilayer structure based on patterned Al/ZnO/Si is designed by using finite element method (FEM). Firstly, dependence of ZnO piezoelectric material on electromechanical coupling factor is studied systematically. The results show that Al/ZnO/Si structure excites Rayleigh mode and Sezawa mode with high electromechanical coupling factor. The patterning of piezoelectric materials could be achieved by etching. The electromechanical coupling factor of Rayleigh mode is as high as 7.98%, and the electromechanical coupling factor of Sezawa mode is up to 9.68%. As we all know, temperature will affect the characteristics of SAW devices. Therefore, the temperature characteristics based on this structure are systematically studied. To achieve zero temperature coupling coefficient, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is used as an intercalation layer for temperature compensation. The structure of Rayleigh mode and Sezawa mode with the thinner SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is easier to achieve zero temperature coupling coefficient than that of conventional structure. Meanwhile, the electromechanical coupling factor of Sezawa mode based on patterned Al/ZnO/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si structure does not change significantly with the increase of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness, with the maximum value of 10.78%, and the minimum value of 10.62%, which is 1.1% larger than that of structure without SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Parameter sensitivity analysis and efficiency optimization design of wireless charging system

Electric vehicle (EV) wireless charging technology has recently attracted a lot of attention and has a broad potential for commercial application development. A fundamental performance indicator of wireless charging systems is efficient transmission. Magnetic coupling mechanism design and circuit parameters have the greatest effects on the transmission efficiency of the system. In this study, the output power and efficiency of the wireless power transfer (WPT) circuit were theoretically computed based on the LCC-type resonant network. Simulation studies demonstrate that the transmission efficiency and output gain deviate significantly from the expected value when circuit parameters are changed. To improve transmission efficiency, the optimal impedance configuration was created using a semi-controlled rectifier circuit. Based on electromagnetic field theory and equivalent magnetic circuit model, a new contactless transformer structure was optimized and created, and the new contactless transformer had a higher coupling coefficient. The coil offset had a greater impact on the transmission efficiency. The results indicate that within a certain distance, the coupling coil offset had no impact on transmission efficiency, and beyond that distance, the transmission efficiency was almost non-existent. Both the feasibility of the practical verification and the accuracy of the theoretical study were tested using a low-power wireless charging experimental setup. This paper provides design guidelines for wireless charging systems using circuit parameter sensitivity analysis and contactless transformer optimization design.

Research on a high-frequency unfilled layered symmetrical piezoelectric material with a high effective electromechanical coupling coefficient

As the demand for high-performance hydrophones for marine communication systems grows, this paper develops a high-frequency unfilled layered symmetrical piezoelectric material with high effective electromechanical coupling coefficient. The vibration mode of piezoelectric material is converted into vibration mode of the piezoelectric pillar to improve the effective electromechanical coupling coefficient of the material. The material is determined by the equivalent circuit method and ANSYS finite element simulation method. Test results show that the resonant frequency is 117.8 kHz and the effective electromechanical coupling coefficient is 0.67, which shows that the developed material has a good electromechanical conversion performance.

An Efficient and Stable Embedded Multi-U-Shaped Column Rotary Transformer

Inductively Coupled Power Transfer (ICPT) technology can be used to solve the problems of high friction loss, overheating and low stability caused by conductive slip rings on rotating power supply equipment. An improved Embedded Multi-U-Shaped Column Rotary Transformer (EMUCRT) based on the ICPT and spliced core structure is proposed in this paper. It has a higher coupling coefficient and can transmit power more efficiently and stably due to the primary magnetic core is embedded inside the secondary magnetic core. Compared with the one-piece core structure, the spliced type is more flexible due to its loose magnetic core arrangement. Its primary coil can still transmit energy stably after offset by a certain distance, so the structure has good anti-misalignment ability. On the basis of analyzing its magnetic core arrangement and magnetic circuit model, the optimal magnetic core specifications and quantities of primary and secondary side are obtained by theoretical calculation and simulation. In order to verify the high efficiency, rotational stability and anti-misalignment characteristics of the structure, an experimental prototype was built. The results show that EMUCRT can transmit energy efficiently and has good rotational and offset stability.

Adaptation of Inductive Power Transfer to Small Household Appliances That Can Operate on Induction Heating Cooktops: Wireless Electric Kettle

In this paper, an inductive power transfer (IPT) system without compensation elements is presented for small house appliances. The proposed system’s transmitter side is an independent induction heating cooktop. IPT can be achieved when the kettle with the receiving coils is placed on the transmitter coil. The coils are designed with a high coupling coefficient. The magnetic system model consisting of aligned transmitter and receiver coils is created in the Maxwell program. In the created model, the analysis depends on the air gap and frequency, which are the variables that affect the wireless power transfer. The electronic circuit simulation uses the coil model to examine the system’s dynamic behavior. The design of the transmitter/receiver coils of the IPT system is made with a cylindrical coil with a diameter of 145 mm, taking into account that it is compatible with the dimensions of the existing kettle and induction heating cooktops coil. A half-bridge series resonant converter circuit is used to adjust the power transferred to the load. To verify the simulation results and test the designed system, an experimental circuit using a 2200 W kettle is carried out. In the experiments, the air gap between the coils is kept constant at 7 mm, and measurements are taken for different powers. Experimental results confirm the magnetic model and simulation results. As a result, wireless power transfer is realized in a wide range without loss of performance in the kettle. System efficiency is greater than the 90% specified in the Ki cordless kitchen standard, and the harmonic currents drawn from the mains are lower than the values determined by the IEC 61000-3-2 standard.

Flexible 1-3 Piezoelectric Composites with Soft Embedded Conductive Interconnects for Underwater Acoustic Transducers

1-3 Piezoelectric composites have been widely used in underwater acoustic transducers because of their advanced electromechanical coupling properties relative to bulk piezoelectric ceramics. However, the existing applied composites are mainly rigid 1-3 PZT–epoxy resin composites, which have rigid structures and cannot be adapted to various sonar carriers with complex surfaces. Here, we design and develop a flexible 1-3 PZT–silicone rubber composite (PSC) for the first time. PSC combines a soft silicone rubber polymer in PZT with flexible embedded island-bridge conductive interconnects to enable the flexibility of both the piezoelectric sensing core and the electrical layer. The flexible wide bridge structure embedded in the polymer can cope with the large bending deformation of PSC with good conductive property, while the rigid thin island structure ensures the high acoustic performance of piezoelectric materials. A PSC sample is prepared with its structural parameters optimized via finite element analysis and is experimentally verified to have good flexibility, high electromechanical coupling coefficient (kt = 0.7), great thermal stability (from 25 to 105 °C), and bending stability (bending angle up to 215°). In addition, a preparation method for flexible 1-3 PSC is introduced, which has the advantages of high efficiency, low cost, no sample size restriction, and no high-temperature operation. The flexible 1-3 PSC in this work paves an important way for the development and application of the next generation of flexible underwater acoustic transducers.

A Novel Planar Nonlinear Coupled Inductor for Improving Light and Intermediate Load Efficiency of DC/DC Converters

With the development of data center, the two-stage voltage regulator module (VRM) is paid considerable attention. Since CPU goes into sleep mode frequently and spends a lot of time working at intermediate load in our daily use, it is important to have high light and intermediate load efficiency. This article proposes a novel planar nonlinear coupled inductor with a three-layer sandwiched structure, in which a middle layer made of high permeability material is sandwiched between two side layers made of low permeability material. Its nonlinearity can be controlled by configuring permeability, saturation flux density, and thickness of the high permeability middle layer. Benefitting from the structure, it can improve light and intermediate load efficiency, due to high self-inductance and low coupling coefficient. Besides, an analytic model is derived to calculate self-inductance and coupling coefficient for quick design, and design guidelines are summarized. A nonlinear coupled inductor and a conventional inductor with constant coupling coefficient are fabricated to compare the performance. Compared with the conventional constant coupling coefficient inductor, the proposed nonlinear coupled inductor could effectively improve the efficiency at light and intermediate load.

Fabrication and characterization of hybrid bulk and surface acoustic wave resonators with Ag/patterned-AlN/Mo/diamond/Si layered structure

Hybrid bulk acoustic wave and surface acoustic wave (BAW/SAW) devices attract extensive interests due to their high electromechanical coupling coefficient and quality factor. In this study, longitudinal BAW coupled SAW resonators with piezoelectric AlN inter-digital transducers (IDT) were simulated and fabricated on diamond substrates to increase the working frequency as well. The simulated figure of merit value is 104, 123 % improved comparing with the corresponding metal IDT of 46.5. The frequency response spectrum of single port reflection (S11) shows dominant harmonic resonance at 913 MHz with electromechanical coupling coefficient of 2.16 % and quality factor of 913. These results indicate mutual transductions between BAW and SAW occur with sufficient efficiency in hybrid structures, which is analyzed and interpreted by equivalent acoustic impedance theory.

The Versatility of Piezoelectric Composites

Piezoelectric materials possess the capability to interchangeably convert electrical energy into a mechanical response. While current piezoelectric materials exhibit strong properties, known limitations have inhibited further development. This review describes the ability to combine different piezoelectric materials into a composite to create well-rounded properties. The different types of connectivity classes are described as well as important design considerations and theoretical models. The contributions from the active and passive phases are outlined, focusing primarily on ferroelectric ceramics and polymer-based composites. The key advantage of piezoelectric composites is their ability to combine the flexibility of polymers with the high electromechanical coupling and piezoelectric coefficients of ferroelectric ceramics or single crystals appropriate for a variety of applications. Composites are prominent in medical ultrasound imaging and therapy, underwater acoustic sensing, industrial structural health monitoring, energy harvesting, and numerous other emerging applications.

Fuzzy logic based active vibration control using novel photostrictive composites

Although conventional actuators like piezoelectric and electrostrictive are efficient, but they required hard wiring, which contaminates the control signal and adds to the weight of the structure. The current study presents a wireless control strategy using photostrictive actuators. Owing to the fortunate combination of photovoltaic effect and converse piezoelectric effect, a photostrictive actuator can generate mechanical strain, when irradiated with light intensity. Limited choices of photostrictive material with high electromechanical coupling coefficient give the motivation to design photostrictive composites. The finite element-based formulation incorporating fuzzy logic controller is employed to study the active vibration control response of cantilever structure when equipped with photostrictive composite actuator. A parametric study has been carried out to study the influence of inclusion’s volume fraction on wireless active vibration control of the structure. Control merits have been defined to compare the control performance of different composites. It is found that particulate composites are the better choice for lightweight structure and fiber composites are better if there is no weight constraint.

ScAlN Film-Based Piezoelectric Micromechanical Ultrasonic Transducers with Dual-Ring Structure for Distance Sensing

Piezoelectric micromechanical ultrasonic transducers (pMUTs) are new types of distance sensors with great potential for applications in automotive, unmanned aerial vehicle, robotics, and smart homes. However, previously reported pMUTs are limited by a short sensing distance due to lower output sound pressure. In this work, a pMUT with a special dual-ring structure based on scandium-doped aluminum nitride (ScAlN) is proposed. The combination of a dual-ring structure with pinned boundary conditions and a high piezoelectric performance ScAlN film allows the pMUT to achieve a large dynamic displacement of 2.87 μm/V and a high electromechanical coupling coefficient (kt2) of 8.92%. The results of ranging experiments show that a single pMUT achieves a distance sensing of 6 m at a resonant frequency of 91 kHz, the farthest distance sensing registered to date. This pMUT provides surprisingly fertile ground for various distance sensing applications.

High electro-mechanical coupling coefficient SAW device with ScAlN on diamond

In this study, Sc concentration dependence of Sc x Al1−x N/AlN/poly-crystalline diamond/Si surface acoustic wave (SAW) characteristics at high Sc from 23.8% to 44.3% was investigated by fabricating one-port SAW resonator at high frequency. 3.8 GHz one-port resonator fabricated on Sc0.43Al0.57N showed an excellent performance of electro-mechanical coupling coefficient (K 2) as high as 6.34% for 2nd mode Sezawa wave, which enables a wide bandwidth in high frequency applications. The temperature coefficient of frequency was approximately −40 to −50 ppm deg−1 for the device fabricated with Sc concentration of 42.9%. This is a smaller value compared to conventional high K2 bulk materials such as LiNbO3. As the result, a high K2 6.34% material system at a higher Sc concentration of ScAlN/AlN/PCD was found to be possible at a high phase velocity of 7000 m s−1. Combined with the extremely high-power durability of diamond based device, high-power durable wideband SAW device at high frequency can be expected.

Wideband Surface Acoustic Wave Filter at 3.7 GHz With Spurious Mode Mitigation

As an essential functional block in radio frequency (RF) front-ends, surface acoustic wave (SAW) filters with large fractional bandwidth (FBW), high center frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> ), and low loss are highly sought-after in 5G new radio (NR). To address this end, 32°Y-X LiNbO3/SiO2/Si heterostructure with high electromechanical coupling coefficient of 23% was constructed, while the propagation characteristics as well as spurious resonance were analyzed through finite element method (FEM) and one-port resonators measurement. It is revealed that by using thin electrodes in the series resonator and thick electrodes in the parallel resonator, spurious modes are successfully eliminated out of the passband. As a result, the SAW filters formed by the above resonators are capable of several superb RF performances: a large bandwidth of 730 MHz (FBW of 19.5%) at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> of 3.74 GHz, a small insertion loss (IL) of 3.03 dB, and a flat passband. Furthermore, since our devices were fabricated by standard photolithography process, this work advances commercial implementation of SAW filter in 5G NR.