Showing papers on "Lamb waves published in 2010"

A sonic band gap based on the locally resonant phononic plates with stubs

Abstract: Using the finite element method, we have studied the acoustic properties of a novel phononic crystal (PC) structure constructed by periodically depositing single-layer or two-layer stubs on the surface of a thin homogeneous plate. Numerical results show that the extremely low frequency band gap (BG) of the Lamb waves can be opened by the local resonance (LR) mechanism. We found that the width of such a BG depends strongly on the height and the area of cross section of the stubs. The displacement field distribution of the oscillating modes is given to explain how the coupling of the modes induces the opening of the BG. The physics behind the opening of the LRBG in our phononic structures can be understood by using a simple 'spring-mass' model.

Basics of Biomedical Ultrasound for Engineers

Abstract: Preface. Acknowledgments. Introduction. Prelude and Basic Definitions. The Advantages of Using Ultrasound in Medicine. A General Statement on Safety. Some Common Applications of Ultrasound. What Is It that We Need to Know? References. 1 Waves A General Description. 1.1 General Definitions of Waves A QualitativeDescription. 1.2 General Properties of Waves A QualitativeDescription. 1.3 Mechanical One-Dimensional Waves. 1.4 The Wave Function. 1.5 The Wave Equation. 1.6 Harmonic Waves. 1.7 Group Waves. 1.8 Wave Velocity. 1.9 Standing Waves (a Mathematical Description). 1.10 Spherical Waves. 1.11 Cylindrical Waves. 1.12 The Wave Equation in a Nonhomogeneous Medium. References. 2 Waves In A One-Dimensional Medium. 2.1 The Propagation Speed of Transverse Waves in a String. 2.2 Vibration Frequencies for a Bounded String. 2.3 Wave Reflection (Echo) in a One-Dimensional Medium. 2.4 Special Cases. 2.5 Wave Energy in Strings. 2.6 Propagation of Longitudinal Waves in an Isotropic Rod orString. 2.7 A Clinical Application of Longitudinal Waves in aString. References. 3 Ultraspmoc Waves in Fluids. 3.1 Waves in Fluids. 3.2 Compressibility. 3.3. Longitudinal Waves in Fluids. 3.4 The Wave Energy. 3.5 Intensity. 3.6 Radiation Pressure. 3.7 A Perfect Reflector. References. 4 Propogation of Acoustic Waves in Solid Materials. 4.1 Introduction to the Mechanics of Solids. 4.2 The Elastic Strain. 4.3 Stress. 4.4 Hooke s Law and Elastic Coefficients. 4.5 The Wave Equation for an Elastic Solid Material. 4.6 Propagation of a Harmonic Planar Wave in a SolidMaterial. References. 5 Attenuation and Dispersion. 5.1 The Attenuation Phenomenon. 5.2 Explaining Attenuation with a Simple Model. 5.3 Attenuation Dependency on Frequency. 5.4 The Complex Wave Number. 5.5 Speed of Sound Dispersion. 5.6 The Nonlinear Parameter B/A. References. 6 Reflection and Transmission. 6.1 The Acoustic Impedance. 6.2 Snell s Law. 6.3 Reflection and Transmission from Boundaries Separating TwoFluids (or Solids with No Shear Waves). 6.4 Reflection from a Free Surface in Solids (ModeConversion). 6.5 Reflection and Transmission from a Liquid SolidBoundary. References. 7 ACOUSTIC LENSES AND MIRRORS. 7.1 Optics. 7.2 Optics and Acoustics. 7.3 An Ellipsoidal Lens. 7.4 Spherical Lenses. 7.5 Zone Lenses. 7.6 Acoustic Mirrors (Focusing Reflectors). References. 8 Transducers and Acoustic Fields. 8.1 Piezoelectric Transducers. 8.2 The Acoustic Field. 8.3 The Field of a Point Source. 8.4 The Field of a Disc Source. 8.5 The Field of Various Transducers. 8.6 Phased-Array Transducers. 8.7 Annular Phased Arrays. References. 9 Ultrasonic Imaging Using the Pulse-Echo Technique. 9.1 Basic Definitions in Imaging. 9.2 The A-Line . 9.3 Scatter Model for Soft Tissues. 9.4 Time Gain Compensation. 9.5 Basic Pulse-Echo Imaging (B-Scan). 9.6 Advanced Methods for Pulse-Echo Imaging. References. 10 Special Imaging Techniques. 10.1 Acoustic Impedance Imaging Impediography. 10.2 Elastography. 10.3 Tissue Speckle Tracking. 10.4 Through-Transmission Imaging. 10.5 Vibro-acoustic Imaging. 10.6 Time Reversal. 10.7 Ultrasonic Computed Tomography. 10.8 Contrast Materials. 10.9 Coded Excitations. References. 11 Doppler Imaging Techniques. 11.1 The Doppler Effect. 11.2 Velocity Estimation. 11.3 Frequency Shift Estimation. 11.4 Duplex Imaging (Combined B-Scan and Color FlowMapping). References. 12 Safety and Therapuetic Applications. 12.1 Effects Induced by Ultrasound and Safety. 12.2 Ultrasonic Physiotherapy. 12.3 Lithotripsy. 12.4 Hyperthermia HIFU and Ablation. 12.5 Drug Delivery. 12.6 Gene Therapy. 12.7 Cosmetic Applications. References. Appenidx A: Typical Acoustic Properties of Tissues. Appendix B: Exemplary Problems. Appendix C: Answers to Exemplary Problems. Index.

A new algorithm for acoustic emission localization and flexural group velocity determination in anisotropic structures

Abstract: This paper presents a new in situ Structural Health Monitoring (SHM) system able to identify the location of acoustic emission (AE) sources due to low-velocity impacts and to determine the group velocity in complex composite structures with unknown lay-up and thickness. The proposed algorithm is based on the differences of stress waves measured by six piezoelectric sensors surface bonded. The magnitude of the Continuous Wavelet Transform (CWT) squared modulus was employed for the identification of the time of arrivals (TOA) of the flexural Lamb mode ( A 0 ). Then, the coordinates of the impact location and the flexural wave velocity were obtained by solving a set of non-linear equations through a combination of global Line Search and backtracking techniques associated to a local Newton’s iterative method. To validate this algorithm, experimental tests were conducted on two different composite structures, a quasi-isotropic CFRP and a sandwich panel. The results showed that the impact source location and the group speed were predicted with reasonable accuracy (maximum error in estimation of the impact location was approximately 2% for quasi-isotropic CFRP panel and nearly 1% for sandwich plate), requiring little computational time (less than 2 s).

Temperature-compensated aluminum nitride lamb wave resonators

Abstract: In this paper, the temperature compensation of AlN Lamb wave resonators using edge-type reflectors is theoretically studied and experimentally demonstrated. By adding a compensating layer of SiO2 with an appropriate thickness, a Lamb wave resonator based on a stack of AlN and SiO2 layers can achieve a zero first-order temperature coefficient of frequency (TCF). Using a composite membrane consisting of 1 ?m AlN and 0.83 ?m SiO2, a Lamb wave resonator operating at 711 MHz exhibits a first-order TCF of -0.31 ppm/°C and a second-order TCF of -22.3 ppb/°C2 at room temperature. The temperature-dependent fractional frequency variation is less than 250 ppm over a wide temperature range from -55°C to 125°C. This temperature-compensated AlN Lamb wave resonator is promising for future applications including thermally stable oscillators, filters, and sensors.

Characteristics of second harmonic generation of Lamb waves in nonlinear elastic plates

Abstract: This paper investigates the characteristics of the second harmonic generation of Lamb waves in a plate with quadratic nonlinearity. Analytical asymptotic solutions to Lamb waves are first obtained through the use of a perturbation method. Then, based on a careful analysis of these asymptotic solutions, it is shown that the cross-modal generation of a symmetric second harmonic mode by an antisymmetric primary mode is possible. These solutions also demonstrate that modes showing internal resonance-nonzero power flux to the second harmonic mode, plus phase velocity matching-are most useful for measurements. In addition, when using finite wave packets, which is the case in most experimental measurements, group velocity matching is required for a cumulative increase in the second harmonic amplitude with propagation distance. Finally, five mode types (which are independent of material properties) that satisfy all three requirements for this cumulative increase in second harmonic amplitude-nonzero power flux, plus phase and group velocity matching-are identified. These results are important for the development of an experimental procedure to measure material nonlinearity with Lamb waves.

Propagation of acoustic waves and waveguiding in a two-dimensional locally resonant phononic crystal plate

Abstract: We demonstrate the waveguiding of Lamb waves in a locally resonant phononic crystal (LRPC) and we present an analysis of the guiding of elastic waves in straight and bent waveguides. The finite element method combined with the supercell technique was used to analyze the band gap and the dispersion relation of LRPC waveguides. Unlike the traditional phononic crystals, we show the possibility of guiding only one confined mode inside a LRPC waveguide. We discuss the confinement and the transmission of the guided mode as a function of the width of the waveguide based on both the band structure and the displacement field.

Acoustic surface evanescent wave and its dominant contribution to extraordinary acoustic transmission and collimation of sound.

Abstract: We demonstrate both theoretically and experimentally the physical mechanism that underlies extraordinary acoustic transmission and collimation of sound through a one-dimensional decorated plate. A microscopic theory considers the total field as the sum of the scattered waves by every periodically aligned groove on the plate, which divides the total field into far-field radiative cylindrical waves and acoustic surface evanescent waves (ASEWs). Different from the well-known acoustic surface waves like Rayleigh waves and Lamb waves, ASEW is closely analogous to a surface plasmon polariton in the optical case. By mapping the total field, the experiments well confirm the theoretical calculations with ASEWs excited. The establishment of the concept of ASEW provides a new route for the integration of subwavelength acoustic devices with a structured solid surface.

Thermally compensated aluminum nitride Lamb wave resonators for high temperature applications

Abstract: In this letter, temperature compensation for aluminum nitride (AlN) Lamb wave resonators operating at high temperature is presented. By adding a compensating layer of silicon dioxide (SiO2), the turnover temperature can be designed for high temperature operation by varying the normalized AlN film thickness (hAlN/λ) and the normalized SiO2 film thickness (hSiO2/λ). With different designs of hAlN/λ and hSiO2/λ, the Lamb wave resonators were well temperature-compensated at 214 °C, 430 °C, and 542 °C, respectively. The experimental results demonstrate that the thermally compensated AlN Lamb wave resonators are promising for frequency control and sensing applications at high temperature.

One-way mode transmission in one-dimensional phononic crystal plates

Abstract: We investigate theoretically the band structures of one-dimensional phononic crystal (PC) plates with both antisymmetric and symmetric structures, and show how unidirectional transmission behavior can be obtained for either antisymmetric waves (A modes) or symmetric waves (S modes) by exploiting mode conversion and selection in the linear plate systems. The theoretical approach is illustrated for one PC plate example where unidirectional transmission behavior is obtained in certain frequency bands. Employing harmonic frequency analysis, we numerically demonstrate the one-way mode transmission for the PC plate with finite superlattice by calculating the steady-state displacement fields under A modes source (or S modes source) in forward and backward direction, respectively. The results show that the incident waves from A modes source (or S modes source) are transformed into S modes waves (or A modes waves) after passing through the superlattice in the forward direction and the Lamb wave rejections in the backward direction are striking with a power extinction ratio of more than 1000. The present structure can be easily extended to two-dimensional PC plate and efficiently encourage practical studies of experimental realization which is believed to have much significance for one-way Lamb wave mode transmission.

Probabilistic damage identification based on correlation analysis using guided wave signals in aluminum plates

Abstract: An algorithm based on correlation analysis was adopted to estimate the probability of the presence of damage in aluminum plates using Lamb wave signals from an active sensor network. Both finite element analysis and experimental evaluations were presented. The Shannon entropy optimization criterion was applied to calibrate the optimal mother wavelet and the most appropriate continuous wavelet transform scale for signal processing. The correlation coefficients for individual sensing paths between the present state (with damage) and the reference state (without damage) were calculated, and the probability of the presence of damage in the monitoring area enclosed by the active sensor network was estimated to identify the damage. A concept of virtual sensing paths (VSPs) was proposed to enhance the performance of the algorithm by increasing the number of sensing paths in data fusion. The results identified using both simulation and experimental Lamb wave signals from different groups of sensing paths at diffe...

Characterization of a large-area PVDF thin film for electro-mechanical and ultrasonic sensing applications

Abstract: Large-area PVDF thin films have been prepared and characterized for quasi-static and high frequency dynamic strain sensing applications. These films are prepared using hot press method and the piezoelectric phase (beta-phase) has been achieved by thermo-mechanical treatment and poling under DC field. The fabricated films have been characterized for quasi-static strain sensing and the linear strain-voltage relationship obtained is promising. In order to evaluate the ultrasonic sensing properties, a PZT wafer has been used to launch Lamb waves in a metal beam on which the PVDF film sensor is bonded at a distance. The voltage signals obtained from the PVDF films have been compared with another PZT wafer sensor placed on the opposite surface of the beam as a reference signal. Due to higher stiffness and higher thickness of the PZT wafer sensors, certain resonance patterns significantly degrade the sensor sensitivity curves. Whereas, the present results show that the large-area PVDF sensors can be superior with the signal amplitude comparable to that of PZT sensors and with no resonance-induced effect, which is due to low mechanical impedance, smaller thickness and larger area of the PVDF film. Moreover, the developed PVDF sensors are able to capture both A(0) and S-0 modes of Lamb wave, whereas the PZT sensors captures only A(0) mode in the same scale of voltage output. This shows promises in using large-area PVDF films with various surface patterns on structures for distributed sensing and structural health monitoring under quasi-static, vibration and ultrasonic situations. (C) 2010 Elsevier B.V. All rights reserved.

Damage Detection in Thin Composite Laminates Using Piezoelectric Phased Sensor Arrays and Guided Lamb Wave Interrogation

Abstract: Damage detection in composite laminated panels using Lamb waves is demonstrated with an innovative use of a sensor array and processing algorithm. Two models were developed to characterize the Lamb wave propagation properties of orthotropic panels. Predictions of the dispersion relations were made for a fiber-reinforced composite laminate. Experiments were conducted to empirically characterize the wave propagation behavior in a manufactured laminate. Piezoelectric patches were used as sensors and actuators in the experiments. Comparisons were made between analytical predictions and experimental results, which demonstrate that the higher order model captured essential wave propagation behavior at frequencies of interest. Sensor arrays and associated processing were used for wavenumber decomposition and filtering of the Lamb wave modes. Composite laminates were manufactured with an embedded defect to simulate inter-ply delamination. Experiments were conducted to detect the presence of delamination damage in...

Interaction of guided Lamb waves with an asymmetrically located delamination in a laminated composite plate

Abstract: Propagation of the primary anti-symmetric Lamb mode (Ao) in an asymmetrically delaminated cross-ply laminate has been studied through both numerical simulations and experiments employing the air coupled ultrasonic technique. When the Ao mode interacts with the entrance and the exit of an asymmetrically located delamination, in addition to Ao, a mode converted to the primary symmetric Lamb mode (So) also propagates in each of the two sub-laminates as well as the main laminate. These Lamb modes propagate independently in each of the sub-laminates. In addition, turning modes (i.e. the mode propagating in one sub-laminate interacts with delamination edge and starts propagating in the other sub-laminate) and a mode converted turning mode (a new mode is generated during the interaction of turning mode with delamination edge) were also observed in the numerical simulation. The presence of the 'mode converted turning modes' was also validated through the experiments in this study.

High-frequency lamb wave device composed of MEMS structure using LiNbO 3 thin film and air gap

Abstract: High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO3 thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO3 single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO3 film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14 000 and 12 500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH0) and symmetric (S0) modes.

A Linear Mapping Technique for Dispersion Removal of Lamb Waves

Abstract: A robust signal processing technique using linear mapping for removing dispersion of Lamb waves is presented in this article. Based on the assumption that the dispersion relation characteristic can...

Optimizing a spectral element for modeling PZT-induced Lamb wave propagation in thin plates

Abstract: Use of surface-mounted piezoelectric actuators to generate acoustic ultrasound has been demonstrated to be a key component of built-in nondestructive detection evaluation (NDE) techniques, which can automatically inspect and interrogate damage in hard-to-access areas in real time without disassembly of the structural parts. However, piezoelectric actuators create complex waves, which propagate through the structure. Having the capability to model piezoelectric actuator-induced wave propagation and understanding its physics are essential to developing advanced algorithms for the built-in NDE techniques. Therefore, the objective of this investigation was to develop an efficient hybrid spectral element for modeling piezoelectric actuator-induced high-frequency wave propagation in thin plates. With the hybrid element we take advantage of both a high-order spectral element in the in-plane direction and a linear finite element in the thickness direction in order to efficiently analyze Lamb wave propagation in thin plates. The hybrid spectral element out-performs other elements in terms of leading to significantly faster computation and smaller memory requirements. Use of the hybrid spectral element is proven to be an efficient technique for modeling PZT-induced (PZT: lead zirconate titanate) wave propagation in thin plates. The element enables fundamental understanding of PZT-induced wave propagation.

Piezoelectric-paint-based two-dimensional phased sensor arrays for structural health monitoring of thin panels

Abstract: A damage detection method based on an innovative 2D phased sensor array made of piezoelectric paint is proposed for in situ damage detection of a thin isotropic panel using guided Lamb waves A design analysis of candidate 2D arrays based on spiral, cruciform and circular element layouts is performed In this study, a 2D phased sensor array with a spiral configuration is fabricated using a piezoelectric composite (piezopaint) patch and used for detecting damages in an aluminum panel Steered array responses are generated from the raw sensor signals using a directional filtering algorithm based on phased array signal processing The fundamental flexural (or transverse), A0 mode, of the guided Lamb waves is used though the sensing and analysis technique is not limited to the mode used in this work To enhance the proposed analysis technique, empirical mode decomposition (EMD) and a Hilbert–Huang transform (HHT) are applied A new damage detection algorithm including threshold setting and damage index (DI) calculation is developed and implemented for detecting damages in the form of holes and a simulated crack The characteristic damage indices consistently increase as damage size grows

Lamb wave tuning curve calibration for surface-bonded piezoelectric transducers

Abstract: Surface-bonded lead zirconate titanate (PZT) transducers have been widely used for guided wave generation and measurement. For selective actuation and sensing of Lamb wave modes, the sizes of the transducers and the driving frequency of the input waveform should be tuned. For this purpose, a theoretical Lamb wave tuning curve (LWTC) of a specific transducer size is generally obtained. Here, the LWTC plots each Lamb wave mode' amplitude as a function of the driving frequency. However, a discrepancy between experimental and existing theoretical LWTCs has been observed due to little consideration of the bonding layer and the energy distribution between Lamb wave modes. In this study, calibration techniques for theoretical LWTCs are proposed. First, a theoretical LWTC is developed when circular PZT transducers are used for both Lamb wave excitation and sensing. Then, the LWTC is calibrated by estimating the effective PZT size with PZT admittance measurement. Finally, the energy distributions among symmetric and antisymmetric modes are taken into account for better prediction of the relative amplitudes between Lamb wave modes. The effectiveness of the proposed calibration techniques is examined through numerical simulations and experimental estimation of the LWTC using the circular PZT transducers instrumented on an aluminum plate.

Delamination detection in composite laminates using dispersion change based on mode conversion of Lamb waves

Abstract: A new ultrasonic propagation system has been constructed using macrofiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. The MFCs and FBGs can be integrated into composite laminates because of their small size and high fracture strain. The developed system can send and receive broadband Lamb waves. In this research, this system was used to detect delamination damage in composite laminates. First, the multiple modes of Lamb waves in a carbon-fiber-reinforced plastic (CFRP) quasi-isotropic laminate were identified by transmitting and receiving the symmetric and antisymmetric modes separately. Then, the mode conversions at both tips of a delamination were investigated through an experiment and a two-dimensional finite element analysis (FEA). A new delamination detection method was proposed on the basis of the mode conversions, and experiments were carried out on laminates with an artificial delamination. When antisymmetric modes were excited, the frequency dispersion of the received A1 mode changed, depending on the delamination length owing to the mode conversion between the A1 mode and the S0 mode. This phenomenon was confirmed through the FEA and these results prove that this new method is effective in detecting a delamination in CFRP laminates.

Phononic plate waves

Abstract: In the past two decades, phononic crystals (PCs) which consist of periodically arranged media have attracted a lot of interests due to the existence of complete frequency band gaps and maneuverable band structures. Recently, Lamb waves in thin plates with PC structures started to receive increasing attention for their potential applications in filters, resonators, and waveguides. This paper presents a review of recent works conducted by the authors and co-workers on this topic. Both theoretical and experimental studies of Lamb waves in two-dimensional (2D) PC plate structures are covered. On the theoretical side, analyses of Lamb waves in 2D phononic plates using the plane wave expansion (PWE) method, finite-difference time-domain (FDTD) method, and finite-element (FE) method are briefly addressed. These methods were applied to determine the frequency ranges of the complete band gaps of Lamb waves, characteristics of the propagating and localized eigenmodes that can exist in the PC plate structures, and behavior of anomalous refraction called negative refraction. The theoretical analyses demonstrated the effects of PC based negative refraction, lens, waveguides, and resonant cavities. We also discuss the influences of geometrical parameters on the guiding and resonance efficiency and the frequencies of waveguide and cavity modes. On the experimental side, we present design and fabrication of a silicon based Lamb wave resonator which utilizes PC plates as reflective gratings to form the resonant cavity of Lamb waves. The measured results showed significant improvement of the insertion losses and quality factors of the resonators when the PCs are applied.

Identification of corrosion damage in submerged structures using fundamental anti-symmetric Lamb waves

Abstract: Corrosion is a representative modality of damage in metallic structures serving in humid or corrosive environments, and examples include petroleum pipelines immersed underwater or buried underground. To facilitate awareness of corrosion at its initial stage is a key measure to prevent further deterioration and failure of these structures. A damage identification approach capitalizing on the fundamental anti-symmetric Lamb wave mode (A0) and in terms of a pulse-echo measurement scheme was developed for evaluating corrosion in submerged structures. However the presence of a coupled fluid medium and changes in its properties exert influence on the propagation characteristics of the A0 mode in the structures at a phenomenal level, leading to erroneous identification without appropriate rectification. Allowing for this, the effect arising from fluid coupling on the A0 mode was investigated and calibrated quantitatively, whereby rectification and compensation were applied to the identification. The proposed approach was numerically and experimentally validated by evaluating through-thickness hole and chemical corrosion in submerged aluminium plates, with the assistance of a probability-based diagnostic imaging approach. Identification results have demonstrated the necessity of rectification and compensation for the medium coupling effect when applying Lamb-wave-based damage identification to structures with coupled media.

Negative refraction of zero order flexural Lamb waves through a two-dimensional phononic crystal

Abstract: We investigate experimentally the refraction of antisymmetric Lamb waves at frequencies in the second band of a two-dimensional phononic crystal. The heterostructure is made of a square lattice of air inclusions in a silicon plate. Our experimental scheme is based on the selective generation of narrow band elastic waves at a few megahertz. Both positive and negative refractions are observed. The comparison of our data with computed dispersion curves shows very good agreement.

Adhesive Layer Effects on PZT-induced Lamb Waves at Elevated Temperatures

Abstract: The role of the adhesive layer on PZT-induced Lamb wave propagation in structures exposed to elevated temperatures is presented in this article. Both experiments and numerical simulations were performed to study the effects of the adhesive layer on sensor signal at elevated temperatures. Experimentally, signals from PZT transducers with different adhesive thicknesses (40 and 120 μm) were investigated up to 500 kHz. In model simulations, the spectral element package (PESEA), which was developed previously, was adopted to simulate the test results. The simulations agreed with the experimental data quite well. Parametric studies were was then performed using PESEA to evaluate the effect of adhesive layer on PZT-induced Lamb wave propagation at elevated temperatures as compared to other mechanical properties of the host structure and PZT materials; these studies revealed that the stiffness change of adhesive layer due to temperature is the most influential parameter for the change in sensor signals as compare...

A two-port ZnO/silicon Lamb wave resonator using phononic crystals

Abstract: We present numerical and experimental studies on a two-port ZnO/silicon Lamb wave resonator using two-dimensional phononic-crystal (PC) gratings. Band gaps and reflections of Lamb waves in PC structures were analyzed using the finite element method. Constructive interference was obtained with suitable reflective distance between wave sources and the PC. The simulated result was utilized to optimize the design of Lamb wave resonators. On the experimental side, a layered ZnO/Si Lamb wave resonator with square-lattice PC reflective gratings was fabricated. The measurement showed that with 15-row PCs, the resonator Q factor can be up to 2269 at 158.15 MHz resonant frequency.

Adhesive interface layer effects in PZT-induced Lamb wave propagation

Abstract: In PZT-induced acousto-ultrasound techniques, the adhesive layer between a PZT and a host structure significantly affects sensor signals. However, its effects have been barely studied so far. A numerical model is essential to fundamentally understand the role of the adhesive interface. Using the hybrid spectral element, the effects of the adhesive bond-line layer on the Lamb wave generation and reception were modeled and compared with available test data for validation of the hybrid spectral element. The validations were conducted with different adhesive layer thicknesses. The trends in simulation results agreed well with the experiments. Parametric studies are presented to understand the adhesive layer effects. In these studies, adhesive thickness and stiffness, and PZT diameter and thickness, are selected as parameters. The physics of the adhesive layer are then discussed.