Admittance Curves Research Articles

RF Analysis of Fruit and Vegetables using Equivalent Circuits Deduced from S-parameters

We deduced equivalent circuits of the electrical properties of five fruit and eight vegetable samples from the S-parameters. The S-parameters were measured at a frequency range from 1 MHz to 100 MHz using a portable VNA and a tiny three-pin SMA probe. Admittance values calculated from the S-parameters were plotted on the admittance Smith chart, and the equivalent circuits with four parallel sub-circuits were synthesized by curve fitting. The admittance curves for the fruit and vegetable samples have two parts with different lengths split at a frequency of about 30 MHz. The admittance in the low-frequency range was determined mainly by two large capacitive and two small resistive elements of the equivalent circuit related to the plant cell wall and membrane. When the plant cell wall and membrane were decomposed by grating and 30µm-filtering, the specific part of the admittance curve was eliminated, and the admittance value increased. The measured and calculated admittance curves were in good agreement. About 30 samples of plant cultivars were classified as fruit and vegetables according to four criteria deduced from the RF analysis. S-parameter spectroscopy (SPS) is an effective analytical method for evaluating the electrical properties of plant tissues.

Numerical analysis and experimental measurement on segmented ring transducer acoustic fields

In order to overcome the shortcomings of the two traditional methods of finite element method (FEM) and direct coupling of mechanical FEM and acoustic boundary element method (BEM) in the comprehensive simulation of acoustic characteristics of non-two-dimensional axisymmetrical transducers, the acoustic FEM and acoustic BEM coupling method is adopted in this study to model, calculate and analyze the three-dimensional (3D) model of the segmented ring transducer. Firstly, the basic theory of FEM, BEM and FEM-BEM coupling calculation of the transducer is introduced. Secondly, a 1/8 3D model of the segmented ring transducer is built to simulate the underwater electro-acoustic characteristics of the transducer. Finally, a transducer prototype is manufactured according to the numerical model, and the electro-acoustic performance of the transducer is measured in the anechoic tank. The numerical results of transmission voltage response (TVR), admittance and radiation directivity curves are in good agreement with the experimentally measured results, which indicate that the proposed method is correct and effective. Therefore, the method could be used to comprehensively calculate the acoustic characteristics of the segmented ring transducer. In addition, the method could be used not only to study the acoustic problems of other transducers or transducers arrays with complex structures that are non-two-dimensional axisymmetrical, but also to comprehensively analyze and predict the near-field and far-field acoustic characteristics of any transducers including two-dimensional (2D) axisymmetrical transducers.

Theoretical Analysis of Dynamic Response of Pipe Pile with Multi-Defects

A mathematical model for an outer soil, multi-defects pipe pile, and inner soil dynamic interaction system is established to research the influences of multi-defects on the vibration of a pipe pile. The dynamic impedance of the pipe pile is deduced by applying a Laplace transformation method and an impedance recursive technique. Then, the velocity response at the pile head is further obtained using the inverse Fourier transform method. Moreover, parametric analyses are conducted to research the influences of the type, degree, distribution, length, and depth of multi-defects on the vibration of the pipe pile. The results indicate that the characteristics of multi-defects appear different, with amplitude differences and reflected signal features on the velocity admittance and velocity response curve, respectively. This means that the obtained analytical solutions and relevant results can be used to detect multi-defects of pipe piles using the different appearances of the velocity admittance and velocity response curve, as measured in engineering practice.

Quality Factor Enhancement of Piezoelectric MEMS Resonator Using a Small Cross-Section Connection Phononic Crystal

Anchor loss is usually the most significant energy loss factor in Micro-Electro-Mechanical Systems (MEMS) resonators, which seriously hinders the application of MEMS resonators in wireless communication. This paper proposes a cross-section connection phononic crystal (SCC-PnC), which can be used for MEMS resonators of various overtone modes. First, using the finite element method to study the frequency characteristics and delay line of the SCC-PnC band, the SCC-PnC has an ultra-wide bandgap of 56.6–269.6 MHz. Next, the effects of the height h and the position h1 of the structural parameters of the small cross-connected plate on the band gap are studied, and it is found that h is more sensitive to the width of the band gap. Further, the SCC-PnC was implanted into the piezoelectric MEMS resonator, and the admittance and insertion loss curves were obtained. The results show that when the arrangement of 4 × 7 SCC-PnC plates is adopted, the anchor quality factors of the third-order overtone, fifth-order overtone, and seventh-order overtone MEMS resonators are increased by 1656 times, 2027 times, and 16 times, respectively.

3D resistor-network modeling of infiltrated SOFC electrodes

For first time a 3D simulation for infiltrated electrodes taking into account the charge transfer resistance (CT) for computing the admittance is developed. By employing a three-dimensional voxelised resistor network, we study the electrode resistance as a function of electrode microstructure and material conductivities. The simulated electrodes consist of pores, metal and ion conductor material and were generated from a random sphere insertion model which emulates the experimental procedure of the infiltration process. To both evaluate and validate the proposed model, a comparison with numerical models and experimental results from the literature is used. More accurate results closely related to those observed experimentally and the use of the main characteristics of the infiltrated electrodes as input parameters are benefits of 3D modeling. The results show that the model for the admittance and TPBL curves have the same behavior as a function of the amount of infiltrated material. This similarity is fulfilled when the diffusion of gas in the pores of the electrode is not the limiting process for the calculation of the admittance, and when the percolation of the ionic and electronic conducting phases are considered in the calculation for TPBL.

Multi-Modal Scattering and Propagation Through Several Close Periodic Grids

The presented method describes reflection and transmission of electromagnetic waves at multiple closely stacked metal grids using multimodal S-parameter propagation. For that, the periodic surface admittance curve of every metal layer was determined through a novel semianalytic approach that uses simple Fourier transformations instead of solving an integral equation. The modal components of this surface admittance were used to express the generalized scattering matrices of the individual grids. By applying multimodal propagation techniques to the resulting scattering parameters, it was possible to model the electromagnetic interactions within a multilayer stack of periodic impedance sheets. Resulting reflection and transmission parameters perfectly matched the corresponding full-wave simulations even above the grating lobe regime. In the end, the universal mode propagation method enabled modeling of a layer stack, connected to lumped components.

Sensitivity Analysis of NVH Simulations with Stochastic Input Parameters for a Car Body

<div class="section abstract"><div class="htmlview paragraph">Uncertainties play a major role in vibroacoustics - especially in car body design in the preliminary development because of the overall spread in the production that should be covered with one simulation model. Therefore, we use uncertain input parameters to determine the stochastically distributed admittance of the car body before each part of the car is fully designed. To gain a stochastic result - the stochastically distributed admittance curve - we calculate a deterministic finite element simulation several times with sets of stochastically distributed input parameter values. To reduce simulation time and cost of the car model with many million degrees of freedom we focus on the uncertain parameters that show a significant influence on the admittance curve. It is therefore necessary to be able to accurately estimate for each parameter if its influence on the admittance of the car body plays a major role for the noise vibration harshness simulation. A sensitivity analysis describes the connection between model input and output and the influence of the input on the output. We conduct a two-step global sensitivity analysis which is based on the generalized polynomial chaos expansion to determine the sensitivity of the parameters. Since the less sensitive parameters hardly influence the admittance curve of the car body, we can simulate them as deterministic values. In the further research, we will focus on the most sensitive parameters.</div></div>

Simulation research on vibration parameters model of drill string

The study of transmission characteristics of drill string is the key to complete acoustic teletransmission while drilling. In this paper, by analyzing the influence of structural cross-section changes on acoustic transmission characteristics in drill string, using acoustic vibration theory, the transfer matrix of vibration parameters at four ends of tapered cross-section rod is analyzed, and the channel model of vibration parameters of drill string is constructed. Through simulation comparison, the transfer admittance curve of the drill string structure is obtained, which can accurately characterize the resistance characteristics of the channel structure, and can more accurately reflect the influence of the transition zone structure in the drill string on the channel, making the results closer to the actual system characteristics.

Coupled longitudinal-flexural vibration characteristics of a piezoelectric structure with losses

The dynamic characteristics studies of piezoelectric structures usually focus on the single vibration modes such as the longitudinal or the flexural mode, and the losses that cause heat generation and energy waste are generally neglected, which leads to discrepancies compared with experiments. In the present paper, a beam-type piezoelectric structure with four kinds of losses under coupled longitudinal-flexural vibration mode is investigated. In this approach, first, impedance matrix of the structure is obtained based on the motion equation and the electrical-mechanical boundary conditions. Secondly, admittance curves of this piezoelectric structure under different boundary conditions are simulated by the equivalent circuit methods that contain four losses—piezoelectric and dielectric losses, as well as two elastic losses. The simulation results by equivalent circuit methods has good agreement with COMSOL results, which demonstrate the effectiveness of the proposed method.

Depolarization field effect on elasticity of unpoled piezoelectric ceramics

Multiple poling steps and complex electrode configurations are indispensable for high-performance state-of-the-art piezoelectric devices, yet those create partially poled or utterly unpoled regions that significantly change behaviors of piezoelectric devices. Several studies have dealt with method to obtain elastic compliance, yet little attention has been paid to method to obtain elastic loss. Furthermore, physical mechanism to explain the behavior of unpoled piezoelectric ceramic is missing. In this study, we experimentally obtain both effective elastic compliance and elastic loss of unpoled piezoelectric ceramics, using recently developed method called partial electrode (PE), and propose physical mechanism to explain the elasticity. The derivation process for analytical admittance equation for PE is explained and verified with finite element analysis (FEA) simulation. The complex elastic compliance was determined by fitting experimental admittance curve with derived analytical solutions. With the aid of intensive and extensive elastic compliances and elastic losses, we concluded that elasticity of unpoled piezoelectric material lies in between intensive-ness and extensive-ness. We explained this “elastic intermediacy” with depolarization field effect, which is one of the most important phenomena in piezoelectricity.

Design of a Hyperbolic Metamaterial as a Waveguide for Low-Loss Propagation of Plasmonic Wave

A stratiform hyperbolic metamaterial comprises multiple units of symmetrical metal-dielectric film, stacked to have a precisely equivalent refractive index, admittance, and iso-frequency curve. A metamaterial that is composed of stacks of symmetrical films as a waveguide to couple a diffracted wave into a horizontally propagating plasmonic wave is designed herein. By tuning the parameters of the constituent thin films within a hyperbolic metamaterial, both the loss of the plasmonic wave and admittance matching are minimized and optimized, respectively.

Structural damage detection system based on FPGA and EMI method

This paper designs a miniaturized structure health detection system based on the electro-mechanical impedance (EMI) method. The system uses two orthogonal signals of the same frequency as the excitation source, which effectively solves the problem of determining the phase difference in phase detection. According to the characteristics of the piezoelectric sensor, the FPGA is used as the main control chip, the measurement frequency range is adjustable by the user, and transmitted through the wireless serial port. The admittance curve of the piezoelectric sensor is displayed on the host computer, and real-time calculation of the RMSD value and relative RMSD value of the admittance curve. Compared with the current impedance analyzer on the market, it has the characteristics of wide measurement frequency range, small size and low cost.

Structural Health Monitoring for Concrete Structure using Impedance Chip

Structural Health monitoring plays a vital role in all generations for the safety of life and property. The method of Electromechanical Impedance (EMI) method and sensors are used in damage detection of civil and mechanical structures. The structure deteriorates due to ageing and environmental factors. This study represents the detection of damage in concrete structure using piezo electric transducer and EMI method. The piezo sensor is bonded to the concrete structure using epoxy resin and damage is created by using flexural testing machine. The force is applied using flexural testing machine at different KiloNewton. The output from the impedance chip is noted at undamaged state and at all levels of applied force. The impedance, admittance, conductance and susceptance curves are drawn with different levels of frequency. Root mean square deviation is also calculated for the detection of damage. The results conclude that Impedance chip is highly reliable and accurate in damage detection of concrete structure.

Response of open-end pipe piles to vertical dynamic load considering the effects of soil plug and soil disturbance during driving

This paper presents an analytical solution for the vertical dynamic response of an open-ended pipe pile considering the radial inhomogeneity caused by soil disturbance. The governing equation of the surrounding soil is deduced on the basis of incremental deformations superimposed on an initial finite deformation, i.e. the soil disturbance. The effect of the radial expansion pressure of the soil plug after pile driving is investigated for the first time. By treating the soil plug as the additional mass attached to the pile shaft using the Voigt model, the densification of the soil plug is also considered. A parametric study is performed to illustrate the influence of the expansion pressure of both inner and outer sides of the pile wall and the soil plug on the vertical dynamic response of the pipe pile. The results indicate that the expansion pressure enhances the fluctuation of velocity admittance curves and the peak amplitudes of the reflected signal at both the pile toe and the soil plug top. Wall thickness of the pile influences the dynamic effects of expansion pressure and soil plug on the pile.

3D FEM simulation of SAW resonators using hierarchical cascading technique and general purpose graphic processing unit

This paper proposes an application of a general purpose graphic processing unit (GPGPU) to the finite element method analysis based on the hierarchical cascading technique (HCT). It is proved that GPGPU can accelerate the HCT significantly, especially for large scale problems. Thanks to significant acceleration, full three-dimensional simulation is possible for practical surface acoustic wave (SAW) device structures. Besides admittance curve, the displacement field is calculated. It is shown that SAW scattering occurs at the boundary at busbar spaces between the interdigital transducer (IDT) and reflector regions.

A micro dual-frequency transducer based on contour-extensional vibration and thickness mode

This paper presents a single piezoelectric transducer with dual-frequency characters by utilizing contour-extensional mode and thickness mode. A 2.5 MHz and 8.5 MHz frequency transducer prototype is designed by Finite element method (FEM) analyses and verified by experiment. Performance of the transducer is then evaluated through the measurement of admittance curves and pulse-echo responses. It’s demonstrated experimentally that the proposed transducer has -6dB bandwidth of 39.4% @1.0 Vpp at 2.4 MHz and 34.6% @1.1 Vpp at 8.9 MHz, respectively. The proposed dual-frequency transducer has potential applications in vivo thrombolytic therapy and ultrasound-guide of pedicle screws.

A Contribution to the Study of Grounding Systems Based on Circuit Synthesis

This work presents an unprecedented technique capable of representing grounding grids directly in the time domain using an association of passive and discrete circuit elements (RLC circuits: resistors, inductors and capacitors). It is based on the frequency response of RLC circuits and ensures that all elements will be positive (physically implementable), solving situations that other techniques, such as vector fitting, generally presented in the literature are not able to solve using only passive circuits (feasible). The proposed technique is applied from the harmonic impedance previously provided, and therefore this impedance can be obtained using any model. It is accurate; it presents excellent results and was validated by comparing the harmonic admittance and transient voltage curves to those obtained with the hybrid electromagnetic model. The advantage of this technique is that it allows that several components in power systems, such as grounding systems and transmission towers, to be represented by a feasible circuit. Once this circuit is implemented in the laboratory, analysis and comparisons with conventional software (e.g. ATP) can be made and accurate transient electromagnetic responses can be obtained.

Quantitative evaluation method for nonlinear characteristics of piezoelectric transducers under high stress with complex nonlinear elastic constant

The high power properties of piezoelectric transducers were evaluated considering a complex nonlinear elastic constant. The piezoelectric LCR equivalent circuit with nonlinear circuit parameters was utilized to measure them. The deformed admittance curve of piezoelectric transducers was measured under a high stress and the complex nonlinear elastic constant was calculated by curve fitting. Transducers with various piezoelectric materials, Pb(Zr,Ti)O3, (K,Na)NbO3, and Ba(Zr,Ti)O3–(Ba,Ca)TiO3, were investigated by the proposed method. The measured complex nonlinear elastic constant strongly depends on the linear elastic and piezoelectric constants. This relationship indicates that piezoelectric high power properties can be controlled by modifying the linear elastic and piezoelectric constants.

A new analytical model to study the influence of weld on the vertical dynamic response of prestressed pipe pile

SummaryThis investigation is concerned with the mathematical analysis of a viscoelastic prestressed pipe pile embedded in multilayered soil under vertical dynamic excitation. The pile surrounding soil is governed by the plane strain model, and the soil plug is assumed to be an additional mass connected to the pipe pile shaft by applying the distributed Voigt model. Meanwhile, the prestressed pipe pile is assumed to be a vertical, viscoelastic, and hollow cylinder governed by the one‐dimensional wave equation. Then, analytical solutions of the dynamic response of the pipe pile in the frequency domain are derived by means of the Laplace transform and impedance function transfer method. Subsequently, the corresponding quasi‐analytical solution in the time domain for the case of the prestressed pipe pile undergoing a vertical semi‐sinusoidal exciting force applied at the pile top is obtained by employing the inverse Fourier transform. Utilizing these solutions, selected results for the velocity admittance curve and the reflected wave curve are presented for different heights of the soil plug to examine the influence of weld properties on the vertical dynamic response of prestressed pipe pile. The reasonableness of the theoretical model is verified by comparing the calculated results based on the presented solutions with measured results. Copyright © 2017 John Wiley & Sons, Ltd.

Simplified determination of nonlinear coefficients in piezoelectric transducers

Hard-type piezoelectric materials usually need to be driven under high power operation. However, in this occasion the piezoelectrics show significant nonlinear behavior, which affects various properties and should be taken as one extra criterion. In previous studies, the nonlinear phenomena in piezoelectric transducers were investigated and a nonlinear model was proposed to describe the nonlinear phenomena. Curve fitting of admittance curves yielded the nonlinear level of the piezoelectric transducers. In this study, on the basis of the nonlinear model a simplified method was proposed to replace the curve fitting; for hard-type piezoelectric transducers the results obtained from two methods show consistence with each other. With the determined nonlinear coefficients, we analyzed the high power properties of hard-type piezoelectric transducers. The conventional method for calculating quality factor was improved and demonstrated to be efficient. The energy density of high power piezoelectrics was also discussed.