Impedance Of Transducer Research Articles

Model-Based Analysis and Regulating Approach of Air-Coupled Transducers with Spurious Resonance.

As an essential characteristic of air-coupled transducers, electrical impedance can provide valuable information for quality control during manufacturing of transducers. It is also found feasible to directly read the optimal operating frequency from the impedance plots when the resonance is independent of the others. However, the spurious resonance emerges when two neighboring resonances are closely spaced, resulting in distorted impedance and ambiguous optimal operating frequency. In this paper, the electrical impedance of air-coupled transducers with spurious resonance is modeled using the Butterworth–Van Dyke (BVD) equivalent circuit. Then model-based sensitivity analysis is performed to evaluate the mutual interference between adjacent resonances. Based on the analysis results, the prestress method is proposed to regulate and suppress the spurious resonance by adjusting the equivalent parameters of the BVD model. Experimental study was carried out on the response of the electrical impedance and the vibration velocity of the transducer with spurious resonance to pre-tightening force. The results show that the spurious resonance disappeared when the pre-tightening force was initially loaded. Moreover, the vibration velocity of two main resonance peaks increases about 45.6% and 33.9% as the pre-tightening torque increases to 0.25 N∙m. Hence it is validated that the proposed prestress method is efficient to suppress the spurious resonance and improve the transducers performance.

Electrical tuning for sensitivity enhancement of a piezo-electric ultrasonic transducer: Simulation and fabrication

In this study, two simple electrical impedance tuning methods derived from Krimholtz, Leedom, and Matthaei (KLM) modeling were proposed for increasing the sensitivity of a piezo-electric material-based ultrasonic transducer. In the first method, the reactance components of the ultrasonic transducer were removed, and in the other method, the electrical impedance of an ultrasonic transducer was matched to that of the ultrasonic system. To these ends, electrical circuits composed of inductors and capacitors were de-signed and KLM simulations of the two methods were performed. To verify the simulation results, ultrasonic transducers were fabricated and operated under the same conditions as in the simulations, and the experimental results were compared with the simulated results. In conclusion, the electrical tuning method (elimination of the reactance compo-nents) was more effective and the transducer circuit structure was simpler. The experi-mental results showed good agreement with the KLM simulation results.

A structural impedance measurement method by using polyvinylidene fluoride as actuator and sensor.

Polyvinylidene fluoride (PVDF) patches have extremely small Young's modulus and piezoelectric coefficients. They are usually chosen as sensors in the structural impedance measurement for health monitoring. In this paper, a novel method is demonstrated for structural impedance measurement using PVDF patches as actuators and sensors. The impedance of the host structure is decoupled from the capacitance impedance of the piezoelectric transducer by using one of the patches as the actuator and the other as the sensor. Phase sensitive detection is then adopted to recover weak impedance signals in the experimental studies. This technique enables measurement of the resonant frequencies and further identification of the health condition of the host structure. The superiority of this method is illustrated theoretically comparing to the conventional impedance-base method. A prototype consisting of a metal cantilever with two PVDF patches is fabricated and tested. Experimental results demonstrate the effectiveness of the proposed method in the detection of the resonance of the substrate precisely with respect to FEM simulation and the results under base-movement excitations. Moreover, mass change induced impedance shifting can be obtained.

Method for removing temperature effect in impedance-based structural health monitoring systems using polynomial regression

Structural health monitoring systems are employed to evaluate the state of structures to detect damage, bringing economical and safety benefits. The electromechanical impedance technique is a promising damage detection tool since it evaluates structural integrity by only measuring the electrical impedance of piezoelectric transducers bonded to structures. However, in real-world applications, impedance-based damage detection systems exhibit strong temperature dependence; therefore, variations associated with temperature changes may be confused as damage. In this article, the temperature effect on the electrical impedance of piezoelectric ceramics attached to structures is analyzed. Besides, a new methodology to compensate for the temperature effect in the electromechanical impedance technique is proposed. The method is very general since it can be applied to nonlinear (polynomial) temperature and/or frequency dependences observed on the horizontal and vertical shifts of the impedance signatures. A computer algorithm that performs the compensation was developed, which can be easily incorporated into real-time damage detection systems. This compensation technique is applied successfully to two aluminum beams and one steel pipe, minimizing the effect of temperature variations on damage detection structural health monitoring systems in the temperature range from −40°C to 80°C and the frequency range from 10 to 90 kHz.

A novel method to monitor soft soil strength development in artificial ground freezing projects based on electromechanical impedance technique: Theoretical modeling and experimental validation

The artificial ground freezing is an important technique for soft soil reinforcement and underground water sealing carried out by continuously refrigerating ground. It is of great significance to monitor the soil strength development in artificial ground freezing projects not only for better evaluation of the soil freeze–thaw status but also for predicting and controlling the concurrent adverse effects which may cause serious engineering accidents. In this study, the electromechanical impedance method was explored in monitoring the soil strength development in the freeze–thaw process. The lead zirconate titanate transducer was embedded inside the soil specimen, and changes in the conductance signatures were monitored throughout the soil freeze–thaw process. The experimental results indicate that the resonant frequency of the embedded lead zirconate titanate transducer can serve as a reliable index for assessment of the soil’s dynamic elastic modulus in the freeze–thaw process. More importantly, an analytical model was developed based on the piezo-elasticity theory to characterize the correlation between the electromechanical impedance of the lead zirconate titanate transducer and the soil’s mechanical properties, and its validity was further confirmed by the experimental research. Based on the proposed model, the development of the soil’s strength can be well predicted from the measured conductance signatures. As a nondestructive testing method, the proposed soil testing technique will help save considerable time and resources by avoiding the conventional sampling, specimen preparation, and testing of soil. The theoretical and experimental research will contribute to the future application of the electromechanical impedance method in real-life artificial ground freezing engineering projects.

Influence of a delamination on Lamb wave excitation by a nearby piezoelectric transducer

This article presents the results of theoretical and experimental investigations of characteristic changes of Lamb wave excitation and scattering by a strip-like horizontal delamination in a layered elastic waveguide for Lamb waves induced by a piezoelectric wafer active sensor. The boundary integral equation method is used to describe wave propagation in an infinite layered waveguide with a delamination, while the frequency domain spectral element method is employed to model the dynamic behaviour of the piezoelectric wafer active sensor, which allows to simulate debonding between the piezoelectric wafer active sensor and the waveguide. Experimental investigations of the dynamic interaction of the piezoelectric wafer active sensor with a layered plate containing a horizontal delamination is conducted for several damage scenarios, showing a good agreement with the results obtained using the developed mathematical model. The obtained mathematical model is employed to analyse alteration of the piezo-induced Lamb waves including modes’ decomposition due to delamination. The conversion and/or conservation of the Lamb waves on account of a delamination is investigated. The electro-mechanical impedance of the piezoelectric transducer and the stress intensity factors of a delamination are analysed in dependence on the delamination location.

Effect of Terfenol-D rod structure on vibration performance of giant magnetostrictive ultrasonic transducer

In this study, a giant magnetostrictive ultrasonic transducer was designed with Terfenol-D as the active material. The influence of different Terfenol-D rod structures on the performance of the giant magnetostrictive transducer was investigated. Finite element analysis was used to analyze the dynamics of the theoretical giant magnetostrictive transducer and to validate the design. Eddy current losses were simulated for Terfenol-D rods of various structures using finite element analysis in ANSYS Maxwell. Two different Terfenol-D rods were then fabricated with either slices along the axial direction or slit along the radial direction, then the impedance and amplitude of the magnetostrictive ultrasonic transducer composed of the two Terfenol-D rods were measured. The results suggest that sliced Terfenol-D rods can suppress eddy currents more effectively, resulting in higher energy conversion efficiency; therefore, the Terfenol-D rods of small giant magnetostrictive transducers should be sliced along the axial direction to suppress eddy currents, whereas radial slits should be adopted for the rods of large giant magnetostrictive transducers to ensure integrity of the Terfenol-D rod and avoid adverse effects on the vibration performance of the giant magnetostrictive transducer that are caused by cutting the rods.

Influence of scandium concentration on parameters of piezoelectric transducer based on aluminum scandium nitride

An analytical approach is presented that allows one to determine the influence of the scandium concentration on the input electrical impedance of piezoelectric transducer based on aluminum scandium nitride. The scandium concentration dependences of the properties aluminum scandium nitride affecting on the transducer impedance were determined by means of the approximation of the dependences obtained from their experimental values for various Sc concentration. Based on the frequency dependences of the impedance the influence of Sc concentration in Al1-xScxN piezoelectric layer on the frequencies of the serious and parallel resonance of the unloaded and loaded transducer has been established.

RESULTS OF STUDIES OF OPERATION OF SPECIAL IMPEDANCE TRANSDUCERS ON THE RIGID METAL STRUCTURES OF REAL PRODUCED OBJECTS

The paper presents the studies of capabilities of special impedance transducers with mechanical filter of oscillation frequencies at the input (output) as a tool of non-destructive testing of real produced objects. Objects under test were elements of a power reactor, which are exposed to high temperature aggressive medium and which are inaccessible for direct contact because of the cooling system. The use of special transducers allowed the development of a new method, which used natural oscillations of the object under test and, thus, provided a mean for monitoring of inaccessible elements of the structure. The method is based on fixation of energy redistribution by the modes of natural oscillations of the object under test, when exposed to damping factors caused by cracks, erosion and other defects. It is shown, how this method operates, when using an artificial damper and in presence of real defects. The use of the artificial damper made it possible to determine that this method allowed the non-destructive testing over the entire surface of the monitored element of the structure.

Differential impedance spectra analysis reveals optimal actuation frequency in bulk mode acoustophoresis

This work reports a method to select the optimal working frequency in transversal bulk resonator acoustophoretic devices by electrical impedance measurements. The impedance spectra of acoustophoretic devices are rich in spurious resonance peaks originating from different resonance modes in the system not directly related to the channel resonance, why direct measurement of the piezoelectric transducer impedance spectra is not a viable strategy. This work presents, for the first time, that the resonance modes of microchip integrated acoustophoresis channels can be identified by sequentially measuring the impedance spectra of the acoustophoretic device when the channel is filled with two different fluids and subsequently calculate the Normalized Differential Spectrum (NDS). Seven transversal bulk resonator acoustophoretic devices of different materials and designs were tested with successful results. The developed method enables a rapid, reproducible and precise determination of the optimal working frequency.

A High-Tolerance Matching Method Against Load Fluctuation for Ultrasonic Transducers

Fluctuation of acoustic load significantly weakens the performance of ultrasonic system. To address this problem in a simple way, we consider the main input and output variables related to the ultrasonic transducer's performance and propose a detailed mathematical model based on the simplest LC matching network containing only one capacitor and one inductor. In this model, a new resonance frequency ${\boldsymbol{f}_{\bf 0}}$ brought by matching components was found and defined. The optimum analysis method is used to solve the model, and a high-tolerance matching method against load fluctuation is obtained. Analysis indicates that when activated at the mechanical resonance frequency, the impedance and apparent power of the piezoelectric transducer (PT) matched by the proposed method are constant no matter how the load changes, and thereby can significantly increase the stability and robustness of ultrasonic systems. For its simple structure and high performance, the proposed matching method can be widely applied in most ultrasonic systems. The tolerance of the proposed method against other environmental factors and high-order LC matching networks were also discussed. In addition, the feasibility and advantage of the proposed matching method are also verified by experiments.

Monitoring of Fiber-Reinforced Composite Single-Lap Joint with Electromechanical Impedance of Piezoelectric Transducer.

The single-lap joint of fiber-reinforced composites is a common structure in the field of structure repair, which has excellent mechanical properties. To study and monitor its quasi-static response behavior under external load, two methodologies called effective structural mechanical impedance (ESMI) and reduced-ESMI (R-ESMI) are presented in this article. A two-dimensional electromechanical impedance (EMI) model for a surface-bonded square piezoelectric transducer (PZT) is adopted to extract more sensitive signatures from the measured raw signatures. There are two major advantages of the monitoring scheme based on ESMI and R-ESMI signatures: (1) excellent monitoring results with less signatures to process, (2) the ability to monitor the quasi-static behavior of a single-lap joint with previously ignored susceptance signatures. Combining the extracted ESMI signatures with the index of root-mean-square deviation, the quasi-static behavior of single-lap joints can be effectively quantified. To test the effectiveness of ESMI methodology, verifying experiments were conducted. The experimental results convincingly demonstrated that the presented ESMI and R-ESMI methodologies have good feasibility in monitoring the quasi-static behavior of a fiber-reinforced composite single-lap joint. The proposed method has potential application in the field of structural health monitoring (SHM).

Measurement of impedance and sensitivity of electroacoustic transducers

In the paper a methodology is presented for electroacoustic transducer impedance and transmitting sensitivity measurement. Loaded transducer electrical impedance is measured in water test tank. The methodology for measurement of transmitting sensitivity is based on the pulse method. Experimental results are presented for measured impedance and sensitivity of piezoceramic disc transducer in water filled test tank.

Study and simulation with VHDL-AMS of the electrical impedance of a piezoelectric ultrasonic transducer

<span>Ultrasonic transducers are a key element that governs the performances of both generating and receiving ultrasound in an ultrasonic measurement system. Electrical impedance is a parameter sensitive to the environment of the transducer; it contains information about the transducer but also on the medium in which it is immersed. Several practical applications exploit this property. For this study, the model is implemented with the VHDL-AMS behavioral language. The simulations approaches presented in this work are based on the electrical Redwood model and its parameters are deduced from the transducer electroacoustic characteristics.</span>

Theory of Series Inductance Matching to Transducer at Premechanical Resonance Zone in Ultrasonic Vibration Cutting

In order to obtain large vibration amplitude in ultrasonic vibration cutting, the transducer demands an additional inductance to match its native capacitance. The objective of this paper is to determine the optimum oscillation frequency of the resonant tank constructed using additional inductance and the transducer's native capacitance. By analyzing the transducer impedance matching on the impedance circle deduced from the transducer equivalent circuit model, the optimum oscillation frequency is found to be not equal to the transducer mechanical resonance frequency, but below it. Frequencies near the optimum oscillation frequency are referred to as the optimum premechanical resonance zone. Consequently, the Theory of Ultrasonic Transducer Impedance Matching at Premechanical Resonance Zone is proposed. Comparative experiments are conducted at different frequency zones. The results reveal that when the transducer is excited at the premechanical resonance zone, the vibration amplitude increases and the excitation voltage signal is the desired sine wave, compared to that when excited at the mechanical resonance frequency and the postmechanical resonance zone. The experimental results confirm the feasibility of this proposed theory.

Ultrasonic Air Coupled Transducer Output Impedance Measurement Technique

Estimation of the output impedance of ultrasonic transducers is required for electrical matching circuits design and for receiving amplifiers noise optimization. This paper presents a simple technique for transducer output impedance estimation using the same data acquisition system and signals that are conventionally used in non-destructive testing. A pair of ultrasonic transducers is used: one for transmission, one for reception. Received signal is recorded under low and high resistance load and transducer output impedance is then obtained from these two signals. Hence, this technique requires only one measurement channel and bias errors are low (no need for calibration). In addition, it is ground referenced and does not require the transducer to be removed from the positioning fixture. Experimental results obtained using different probing signals have been compared against conventional measurements obtained by an impedance analyser.DOI: 10.5755/j01.eie.25.1.22731

A Review of Electric Impedance Matching Techniques for Piezoelectric Sensors, Actuators and Transducers

Any electric transmission lines involving the transfer of power or electric signal requires the matching of electric parameters with the driver, source, cable, or the receiver electronics. Proceeding with the design of electric impedance matching circuit for piezoelectric sensors, actuators, and transducers require careful consideration of the frequencies of operation, transmitter or receiver impedance, power supply or driver impedance and the impedance of the receiver electronics. This paper reviews the techniques available for matching the electric impedance of piezoelectric sensors, actuators, and transducers with their accessories like amplifiers, cables, power supply, receiver electronics and power storage. The techniques related to the design of power supply, preamplifier, cable, matching circuits for electric impedance matching with sensors, actuators, and transducers have been presented. The paper begins with the common tools, models, and material properties used for the design of electric impedance matching. Common analytical and numerical methods used to develop electric impedance matching networks have been reviewed. The role and importance of electrical impedance matching on the overall performance of the transducer system have been emphasized throughout. The paper reviews the common methods and new methods reported for electrical impedance matching for specific applications. The paper concludes with special applications and future perspectives considering the recent advancements in materials and electronics.

Investigation of the Use of Collagen-Gelatin-Gold Nanoparticle Nanocomposite System as an Aptasensor Matrix

In this study, a collagen-gelatin-gold nanoparticles (AuNPs) matrix, a material widely used in biosensor applications, controlled release systems, tissue engineering and many other biotechnology fields, was applied to the apta-sensor technology. The matrix was characterized using techniques like scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and fourier-transform infrared spectroscopy (FTIR). Immobilization conditions were optimized through immobilization of thrombin binding aptamers (TBA) on to the collagen-gelatin-AuNPs surface. Polymer, cross-linker, AuNPs and aptamer concentrations in addition to pH were optimized in the developed aptasensor systems. In addition, re-usability and reproducibility were examined for validation purposes. Thrombin levels as low as 1.97 nM were detected using screen printed carbon electrodes as transducer and Electrochemical Impedance Spectroscopy (EIS) as the electrochemical method.

An Online Viscosity Measurement Method Based on the Electromechanical Impedance of a Piezoelectric Torsional Transducer

In this paper, we proposed an online viscosity measurement method based on the electromechanical impedance (EMI) of a piezoelectric torsional transducer. During testing, the contact torsional resonance of the cylindrical rod or host structure system is actuated and sensed by the ring array of shear mode piezoelectric patches. According to the quantitative electromechanical equivalent model we derived, the viscous damping from the contact fluid can be obtained by tracking the change of the piezoelectric impedance. A series of viscosity measurements was conducted on glycerol–water solutions of various concentrations, and the measurement results agree well with that given by standard laboratory viscometers. As the torsional vibration is a pure in-plane shear mode, which is more sensitive to the viscous damping and features a high quality factor, the proposed EMI-based measurement method is effective and promising for online viscosity measurement, especially for medium to high viscosity fluids.

Effect of static axial loads on the lateral vibration attenuation of a beam with piezo-elastic supports

In this paper, vibration attenuation of a beam with circular cross-section by resonantly shunted piezo-elastic supports is experimentally investigated for varying axial tensile and compressive beam loads. The beam's first mode resonance frequency, the general electromechanical coupling coefficient and static transducer capacitance are analyzed for varying axial loads. All three parameter values are obtained from transducer impedance measurements on an experimental test setup. Varying axial beam loads manipulate the beam's lateral bending stiffness and, thus, lead to a detuning of the resonance frequencies. Furthermore, they affect the general electromechanical coupling coefficient of transducer and beam, an important modal quantity for shunt-damping, whereas the static transducer capacitance is nearly unaffected. Frequency transfer functions of the beam with one piezoe-elastic support either shunted to an RL-shunt or to an RL-shunt with negative capacitance, the RLC-shunt, are compared for varying axial loads. It is shown that the beam vibration attenuation with the RLC-shunt is less influenced by varying axial beam loads and, therefore, is more robust against detuning.