Attenuation Of Surface Acoustic Waves Research Articles

The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe3O4 with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications.

Investigation of acoustoelastic surface acoustic waves in prestressed media

Dispersion of broadband surface acoustic waves (SAWs) is often used for the nondestructive evaluation of near-surface elastic properties of materials. The accurate forward model of SAW propagation is essential for inversion. In this paper, we present a combining semi-analytical finite element (SAFE) and perfectly matched layer method for accurately predicting the phase velocity dispersion, attenuation and polarization modes of SAWs in any prestressed anisotropic layered half-space. Equations of motion are formulated based on the Biot's theory of small deformations influenced by initial stress, so it does not matter whether the residual stress results from hyperelastic transformations. The simulated results are firstly validated by the solutions from the exact three-dimensional elasticity theory-based method. The SAFE method is then used to discuss the effect of material anisotropy and residual stress on the SAWs. Finally, the method is applied to two practical examples. The differences and similarities of two common types of acoustoelastic theories are also discussed.

Surface acoustic wave investigation of magnetic nanoparticle size and concentration effect on liquid crystal behavior.

The effect of spherical magnetic nanoparticles with different size (5, 10, 15, and 20 nm) and volume concentration (10-3, 5 × 10-4, and 10-4) on liquid crystal 4-cyano-4'-hexylbiphenyl (6CB) behavior was investigated using surface acoustic wave (SAW). The attenuation response of SAW propagating along with the substrate/liquid crystal interface was used to study the structural changes induced by an applied magnetic field. The obtained results showed the shift of the threshold magnetic field with an increase in the volume concentration of nanoparticles toward lower fields and also the decrease in the isotropic-nematic phase transition temperature depending on the nanoparticle size and the nanoparticle volume fraction. Results confirmed again that the bulk viscosity coefficients should dominate the SAW attenuation and that the SAW investigation in the presented configuration is applicable to monitoring of the role of magnetic dopants in structural changes under external fields. Some theoretical background of the presented SAW investigation is introduced as well. Obtained results are discussed within the context of previous ones.

Coexistence of two hole phases in high-quality p−GaAs/AlGaAs in the vicinity of Landau-level filling factors ν=1 and ν=(1/3)

We focused on the transverse AC magnetoconductance of a high-mobility $p$-GaAs/AlGaAs quantum well $(p=1.2\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}2})$ in the vicinity of two values of the Landau-level filling factor $\ensuremath{\nu}$: $\ensuremath{\nu}=1$ (integer quantum Hall effect) and $\ensuremath{\nu}=1/3$ (fractional quantum Hall effect). The complex transverse AC conductance ${\ensuremath{\sigma}}_{xx}^{\mathrm{AC}}(\ensuremath{\omega})$ was found from simultaneous measurements of attenuation and velocity of surface acoustic waves propagating along the interface between a piezoelectric crystal and the two-dimensional hole system under investigation. We analyzed both the real and imaginary parts of the hole conductance and compared the similarities and differences between the results for filling factor 1 and filling factor 1/3. Both to the left and to the right of these values maxima of a specific shape, ``wings,'' arose in the $\ensuremath{\sigma}(\ensuremath{\nu})$ dependences at those two $\ensuremath{\nu}$. Analysis of the results of our acoustic measurements at different temperatures and surface acoustic wave frequencies allowed us to attribute these wings to the formation of collective localized states, namely, the domains of a pinned Wigner crystal, i.e., a Wigner solid. While the Wigner solid has been observed in 2D hole systems previously, we were able to detect it at the highest hole density and, therefore, the lowest hole-hole interaction reported.

Influence of Goethite Nanorods on Structural Changes and Transitions in Nematic Liquid Crystal E7

A composite ferronematic system based on the nematic liquid crystal E7, doped with lath-like goethite magnetic nanoparticles of volume concentrations 10−3, 5 × 10−4, and 10−5, was investigated. Both surface acoustic waves (SAWs) and the magneto-optical effect were used to study the influence of magnetic nanoparticles on ferronematic liquid crystals’ structural changes, focused above all on structural transitions. The responses of SAW attenuation and light transmission to external magnetic fields were investigated experimentally under linearly increasing/decreasing or jumped (time influence) magnetic fields, respectively. An investigation of temperature on structural changes was performed, as well. The experimental results validated the decrease in the threshold field of the ferronematic composites in comparison with the pure E7, as well as an increase in the transition temperature with the increasing volume fraction of nanoparticles. The effect of the nanoparticles’ concentration on both total structural changes and residual attenuations at the vanishing magnetic field was also registered. The light transmission measurements confirmed the effect of the concentration of goethite nanoparticles on the resultant magneto-optical behavior, concerning both its stability and switching time.

Extraction of Attenuation Parameter in Periodic Shorted Reflectors of One-Port SAW Resonator Using Scattering Matrix Approach

In this work, the well-known scattering matrix approach to the design of one-port surface acoustic wave (SAW) resonators is adapted toward extraction of the coupling-of-modes (COM) attenuation parameter, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> for Rayleigh SAW propagation on a periodic shorted aluminum grating. The attenuation close to resonance inside the reflectors of the one-port SAW resonator is extracted by matching the measured conductance of the resonator to its version calculated from the experimentally measured interdigital transducer (IDT) scattering coefficients, intrinsic substrate parameters, and geometry of the resonator. Based on the extracted value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> , it was observed that the proposed method could predict the unloaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor of the resonator at a minor discrepancy of ~7.02%. At the same time, since the proposed method utilizes the measured IDT scattering coefficients to consider the effect of IDT losses on the measured conductance of the resonator, it offers a convenient scheme to directly extract the attenuation of SAW contributed by the reflectors of the device through numerical means while operating purely in the frequency domain. The proposed method could be applied to quantify the increase in attenuation caused by viscous damping of SAW inside sensing film-coated reflectors of one-port SAW resonator sensors, and thereby, aid to optimize the sensing film thickness to deploy these devices for high-resolution frequency-based sensing applications.

Creation and research of the SAW transducer with a single-phase grid and a piezoelectric zinc oxide film

A method for obtaining a new type of surface acoustic wave (SAW) transducer operating at double frequency with a single-phase closed-loop lattice and a piezoelectric zinc oxide film is developed and experimentally investigated. A method for calculating such a transducer has been developed, its equivalent circuit has been compiled, taking into account propagation losses, losses in the metal film and the inductance of the connecting wires. When the frequency is doubled, the SAW attenuation per unit length increases.

Study on dispersion and attenuation of laser-induced surface acoustic wave by grinding surface roughness

The dispersion and attenuation of surface acoustic wave (SAW) are important indicators for evaluating the damage of machined surface layer. However, the dispersion and attenuation of SAW is also affected by surface roughness. The finite element method can simulate the rough surface without surface damage. Based on the measured surface profiles of roughness profiler, a series of grinding surfaces of C45E steel with different surface roughness Ra are simulated by finite element method, and the dispersion and attenuation of laser-induced SAW are studied. It is found that with the increase of roughness Ra, the increase of dispersion is relatively uniform, while the increase of attenuation not. The possible reason is that the dispersion is mainly affected by the average amplitude of roughness, while the occasional deep valley profile has a great influence on the attenuation. Compared with the experimental data, it is found that the velocity variation of 10–40 MHz SAW caused by Ra 0.12–0.75 μm surface roughness accounts for 8%–19% of the total velocity variation, and the proportion increases with the increase of roughness. The attenuation of 15 MHz SAW caused by surface roughness accounts for 8%–13% of the total attenuation. For a rough surface, dispersion is approximately linear with the frequency of SAW, while the attenuation coefficient increases sharply with the increase of frequency. Therefore, it is necessary to first evaluate the influence of surface roughness, especially the influence on attenuation, when the dispersion and attenuation of SAW are used to evaluate the machined surface damage. The results of this paper can be used to evaluate the influence of roughness on the dispersion and attenuation of SAW, and reduce the deviation in the evaluation of machined surface damage.

Influence of the Core Pillar Height on the Bandgap Characteristics of Piezoelectric Phononic Crystals with Ring-Shaped Grooves

Dispersion profiles and surface acoustic wave attenuation characteristics of ring-shaped phononic crystals are investigated as a function of the core pillar height. Finite element method simulations are carried out for both band analyses and transmission spectra calculations. The results reveal that increasing core pillar height results in a decrement in the local resonance band frequency and the corresponding transmission peaks. The obtained dispersion profiles show that the phononic crystal bandgap also expands from 6 MHz to 11 MHz while the pillar height increases from 5 um to 7 um. Similar characteristics are also seen in the transmission spectra for the varying core pillar heights of the ring-shaped periodic grooves. In addition, surface acoustic wave attenuation competency depends on the core pillar height. The frequencies where the investigated phononic crystals are functional can be tuned by adjusting the core pillar height.

Study of electronic band structure in a 75-nm-wide n-GaAs/AlGaAs quantum well by surface acoustic waves

From measured magnetic field dependences of attenuation and velocity of surface acoustic waves (SAW), we calculated the real part of electron the conductivity in a 75-nm-wide n-GaAs/AlGaAs quantum well in magnetic fields of up to 18 T at frequencies of 30–300 MHz in the temperature range 20–500 mK. We observed slow magneto-oscillations of the conductivity depended on SAW intensity and occurred due to elastic intersubband scattering between the symmetric (S) and antisymmetric (AS) subbands formed by Coulomb repulsion between the electrons. Our theoretical description of the magneto-oscillations allowed estimating the quantum and the intersubband scattering times. The experimentally obtained subband splitting value 0.42 meV was close to the theoretically found 0.57 meV. Additionally, in tilted magnetic fields of 0.5–1.5, T we observed crossings of the Landau levels between the S and AS subbands. According to the developed theory, the crossings at the in-plane field below 1.5 T occur due to different dependences of cyclotron energies in the subbands on the in-plane field. Namely, the cyclotron energy in the S (AS) subband decreases (increases) with the rising of the in-plane field. Work supported by “BASIS,” NSF DMR-1644779 and DMR-1420541, GBMF4420, and State of Florida.]

Evaluation of the surface damage of brittle materials based on the attenuation of laser-induced surface acoustic wave

In this paper, the surface damage of machined surface of brittle material is evaluated by using the attenuation of laser-induced surface acoustic wave (SAW) in propagation. Taking the typical brittle material single crystal silicon as an example, the feasibility of evaluating surface layer damage based on the attenuation of SAW is demonstrated theoretically and experimentally. Theoretical analysis shows that the micro-cracks produced in the processing of brittle materials can cause significant changes in the attenuation coefficient of SAW. After the lapped silicon wafer is etched, the surface roughness Ra is almost unchanged, while the attenuation coefficient of SAW decreases from 4.3 dB/cm to 2.0 dB/cm, which indicates that the surface layer damage of the silicon can still significantly change the attenuation coefficient after removing the influence of the surface roughness. After measuring the attenuation coefficients of SAW of silicon wafers in different processing steps, it is found that with the improvement of processing accuracy, the attenuation coefficient of SAW decreases, and the attenuation coefficient of SAW reflects the changes in surface damage. Experiments show that surface scratches can also significantly change the attenuation coefficient of SAW. Therefore, the wave attenuation coefficient of the laser-induced SAW can be used to evaluate the surface damage of the brittle material machined surface.

Nondestructive Evaluation of Electroplating-Induced Hydrogen Embrittlement in Cadmium-Coated High-Strength Steel Using Ultrasonic Surface Waves

Development of a nondestructive evaluation (NDE) method to detect nascent hydrogen embrittlement (HE) in electroplated high-strength steel parts is becoming important for the aerospace industry. This research investigates the feasibility of surface acoustic waves (SAWs) measurements to distinguish between cadmium (Cd) plated SAE 4340 steel samples with low and high HE susceptibilities. SAWs were generated with a 10 MHz piezoelectric transducer and detected by line scans via a laser Doppler vibrometer setup. Using signal processing algorithms in MATLAB, SAW velocities as well as attenuation coefficients were estimated. Depth profiles of steel hardness near coatings were also evaluated using Vickers microindentation tests. Average steel hardness in not-baked samples was slightly increased. Cd coatings were characterized by laser and optical microscopy methods. Small variations found in thickness and surface roughness of the Cd coatings among the samples did not significantly affect the NDE results. On average, samples in the not-baked condition (high HE risk) exhibited lower SAW attenuation coefficients compared to immediately baked and late-baked conditions (low HE risk). However, it was not possible to distinguish between the manufacturing conditions of individual samples due to overlaps in attenuation measurement results. SAW velocities as estimated by the cross-correlation method were found to be not sensitive to manufacturing conditions.

Effect of Liquid Crystalline Host on Structural Changes in Magnetosomes Based Ferronematics.

The effect of the liquid crystalline host on structural changes in magnetosomes based on ferronematics is studied using the surface acoustic wave (SAW) technique supported by some capacitance and light transmission measurements. The measurement of the attenuation response of SAW propagating along the interface between LC and the piezoelectric substrate is used to study processes of structural changes under magnetic field. The magnetosome nanoparticles of the same volume concentration were added to three different nematic LCs, 5CB, 6CB, and E7. Unlike to undoped LCs, the different responses of SAW attenuation under the influence of magnetic and electric fields in LCs doped with magnetosomes were observed due to characteristic structural changes. The decrease of the threshold field for doped LCs as compared with pure LCs and slight effects on structural changes were registered. The threshold magnetic fields of LCs and composites were determined from capacitance measurements, and the slight shift to lower values was registered for doped LCs. The shift of nematic-isotropic transition was registered from dependencies of SAW attenuation on temperature. The acoustic anisotropy measurement approved the previous supposition about the role of bulk viscosity in used SAW measurements. In addition, capacitance and light transmition investigations supported SAW results and pointed out conclusions about their magnetic field behavior. Obtained results are discussed and confronted with previous ones and coincide well with those observed using acoustic, optical, or dielectric techniques.

Structural changes in liquid crystals doped with spindle magnetic particles

A new composite ferronematic system based on the nematic liquid crystal 6CB doped with hematite spindle-like magnetic particles characterized with magnetic moments oriented perpendicularly to their main axes was prepared. The surface acoustic waves (SAWs) were used to study the effect of magnetic particles on liquid crystals' structural changes in a magnetic field using measurements of the attenuation of SAW propagating along the ferronematic liquid crystal surface. For a study of new composite materials' orientational properties, the ferronematic samples were prepared with three different lengths of the particles and with the volume concentrations of particles φ1 = 10−3, φ2 = 10−4, and φ3 = 10−5. SAW attenuation response to the external magnetic field was investigated experimentally for two different directions of the magnetic field regarding the cell position, perpendicular and/or parallel to the LC cell. Experimental results validated a decrease of the threshold field in the ferronematic samples in comparison with the pure 6CB for the field in a perpendicular direction and an increase of the threshold shift with a growth of both the volume fraction of solid impurity and the length of particles for magnetic field applied perpendicularly to the cell plane. The effect of particle concentration on the magnitude of structural changes and also on the large residual attenuation at decreasing the magnetic field was observed in this arrangement. The parallel magnetic field direction led to the similar behavior of investigated ferronematic systems in early studied magnetic particles and provided switching processes.

Surface acoustic wave attenuation in polycrystals: Numerical modeling using a statistical digital twin of an actual sample

Grain boundary scattering-induced attenuation and phase-velocity dispersion of Rayleigh-type surface acoustic waves are studied with a time-domain finite-element method (FEM). The FEM simulation incorporates a realistic material model based on matching the spatial two-point correlation function of a Laguerre tessellation with that obtained from optical micrographs of a previously studied aluminum sample. Plane surface acoustic waves are excited in a multitude of statistically equivalent virtual polycrystals, and their surface displacement fields are averaged for subsequent extraction of the coherent-wave attenuation coefficient and phase velocity. Comparisons to previous laser-ultrasonic experiments, an analytical mean-field model, and the FEM results show good agreement in a broad frequency range from about 10 to 130MHz. Observed discrepancies between models and measurement reveal the importance of spatial averaging in the context of mean-field approaches and suggest improvement strategies for future experimental studies and advanced analytical models. A different attenuation power law for Rayleigh waves is found in the stochastic scattering regime compared to bulk acoustic waves.

Generation and detection of 50 GHz surface acoustic waves by extreme ultraviolet pulses

We use femtosecond extreme ultraviolet pulses derived from a free electron laser to excite and probe surface acoustic waves (SAWs) on the (001) surface of single crystal SrTiO3. SAWs are generated by a pair of 39.9 nm pulses crossed at the sample with the crossing angle defining the SAW wavelength at 84 nm. Detection of SAWs is performed via diffraction of a time-delayed 13.3 nm probe pulse by SAW-induced surface ripples. Despite the low reflectivity of the sample in the extreme ultraviolet range, the reflection mode detection is found to be efficient because of an increase in the diffraction efficiency for shorter wavelengths. We describe a methodology for extracting the SAW attenuation in the presence of a thermal grating, which is based on measuring the decay of oscillations at twice the SAW frequency. The proposed approach can be used to study ultrahigh frequency SAWs in a broad range of materials and will bridge the wave vector gap in surface phonon spectroscopy between Brillouin scattering and He atom scattering.

Acoustoelectronic interaction in metal island films

The interaction of surface acoustic waves with conduction electrons of island films of various metals was investigated. Island films were formed on the surface of piezoelectric crystalline substrates: Lithium Niobate, Bismuth Germanate, and Piezoquartz. It is experimentally obtained that the surface acoustic wave attenuation as a function of film resistance has a characteristic maximum, and that the velocity changes from the velocity at the free surface of the substrate to that at the metallized surface.

Influence of X7GeS5I (X = Ag, Cu) Superionic Nanoparticles on Structural Changes in Nematic Liquid Crystal

The effect of two types of superionic nanoparticles; Cu7GeS5I and Ag7GeS5I, respectively on nematic liquid crystal (6CB) behavior under an external electric field is investigated. The response of both attenuation of surface acoustic waves propagating along with the substrate/liquid crystal interface and light transmission are used to study the structural changes induced by applied electric field. The increasing/decreasing regime as well as jumped change of applied field were used. The light transmission was investigated using linearly polarized laser beam (532 nm) propagating through the liquid crystal. Results obtained from both measurements for three different concentrations (0.01, 0.05 and 0.10 wt%) and in addition two different sizes of nanoparticles are compared and results, relying on structural changes, suspension stability and switching behavior are evaluated.

Detection of x rays by a surface acoustic delay line in contact with a diamond crystal

In this study, we present proof of concept for an x-ray detector. The hybrid device consists of a synthetic single crystal diamond in mechanical contact with a piezoelectric lithium niobate surface acoustic wave (SAW) delay line. Upon x-ray irradiation, the diamond crystal experiences a change in conductivity, which, in turn, very sensitively influences the SAW transmission on the delay line. This change in SAW attenuation is directly used to monitor the x-ray beam intensity. The SAW attenuation shows a monotonic variation with dose rate D in the studied range between 100 and 1800 μGy/s. While the response time leaves room for further improvement, the SAW detection principle offers the unique possibility for wireless remote powering and sensing.

Analysis of amplitude and frequency detection error of surface acoustic wave generated by laser line source

Laser-generated surface acoustic wave (SAW) is widely used in damage detection, elastic constant evaluation, film thickness determination and so on. Among them, the amplitude attenuation and frequency components of SAW are important index parameters in data analysis. In this paper, the diffuse attenuations of SAW generated by laser line source in non-contact and contact detection methods are analyzed respectively, and the calculation formulas are given. Contact SAW detector is widely used because of its high sensitivity and high stability, but it will produce frequency error. In this paper, the relationship between the detection line length of the contact detector and the signal amplitude, signal noise ratio (SNR) and frequency error is analyzed. It is found that for a certain detection line length, the higher the SAW center frequency, the greater the frequency error.