Resonance Research Articles

Gold as a Promising Electrode Material for LiNbO3-on-Insulator (LNOI) SH-SAW Resonators: An Experimental Study.

The need for wideband radio frequency front ends (RFFEs) with next-generation wireless protocols highlights the importance of electromechanical coupling [Formula: see text]. The hetero acoustic layered (HAL) surface acoustic wave (SAW) resonator with aluminum (Al) electrodes has shown superior performance compared to conventional SAW devices. Despite gold (Au) having excellent conductivity and stable properties, its high acoustic absorption and low phase velocity have made it less favorable for electrodes. This work demonstrates that high-performance shear horizontal (SH)-SAW resonators can be fabricated on the lithium niobate-on-insulator (LNOI) platform using a setup specifically designed for an Au electrodes. Experimental validation shows that the device achieves a high quality factor (Q) over 870, excellent [Formula: see text] up to 40%, and operates around 765 MHz. Unwanted transverse spurious modes are suppressed through adequate electrode design, and the temperature stability of LNOI SH-SAW with Au electrodes is discussed. This study highlights gold's potential as an electrode material for high [Formula: see text], clean spectrum, and wideband applications.

Acoustic scattering by smooth and rough elastic cylinders insonified by directional sonars: Bistatic experiments.

Bistatic laboratory measurements are presented for acoustic scattering from both smooth and rough elastic cylinders insonified by directional spherical waves. A scattering model, accounting for incident directional spherical waves while assuming negligible end effects, was derived in a previous article [Mursaline, Stanton, Lavery, and Fischell, J. Acoust. Soc. Am. 154, 307-322 (2023)] but only evaluated for monostatic scattering by smooth cylinders. The evaluation is extended here to bistatic geometries for both smooth and rough cylinders. The effect of axi-symmetric Gaussian roughness (axi-symmetric random variations in cylinder radius) on the cylinder on overall scattering levels and resonances is investigated. Particular emphasis is given to the influence of roughness on the excitation of axially propagating guided wave resonances associated with oblique incident angles. Bistatic laboratory observations presented herein further substantiate the effects on scattering due to the properties of the incident field from practical sonars, such as spherical spreading, as observed in the above-mentioned article. For smooth cylinders, axially propagating guided wave resonances are seen to become more prominent during bistatic in-plane scattering compared to bistatic orthogonal-plane scattering and previously published monostatic data. For rough cylinders, both overall scattering levels and resonances are found to be diminished compared to the smooth case.

Design and fabrication of lithium niobate asymmetrical mode resonators toward C-band and Ku-band

Abstract This work presents a laterally excited bulk wave resonator (XBAR) based on the suspended Z-cut lithium niobate thin film. In order to systematically analyze the influence of geometric structure on the performance of resonators, including electromechanical coupling coefficient (kt 2) and quality factor (Q), the pitch of inter-digital transducers and lateral reflective boundary width (D) were optimized via finite element analysis simulation. Besides, the XBARs with the broadband piston mode structure (BPM-XBAR) were further studied, and the transverse displacement was weakened after optimization, hence enhancing the Q value of the targeted mode. Consequently, the fabricated devices exhibited first order asymmetrical (A1) mode resonance at 5.87 GHz with kt 2 of 12.98% and Q of 218, a nearly 70% increase in Q value. The third order asymmetrical (A3) mode resonance occurred at 17.18 GHz with kt 2 of 7.91%. The above devices have the potential to construct large bandwidth and low loss filters toward the C-band and Ku-band.

Mechanically forced meniscus water waves in a square container with functionalized wetting conditions

Capillary–gravity surface waves, called meniscus waves, are excited at the air–water interface near the lateral boundary of a mechanically forced square container. Experiments are conducted in two working containers: one is overall hydrophilic at four boundaries and the other is functionalized to have a hydrophobic boundary. The static meniscus structures and instantaneous wave topography are reconstructed at high resolution from the side-view and top-view high-speed camera recordings. Wave resonances arise from the interaction of four inward-traveling waves, with the frequency-response characteristics indicating the effect of wetting conditions on the selection of standing wave patterns. The most-resonant modes are identified as a superposition of dominant modes and higher-order components. An analytical model of the rest-state meniscus and resonant-state wave surface decomposes the wave responses into two groups of resonances along two transverse directions linked by a frequency-dependent parameter γ. Theoretical selection of the dominant wave components and the second-order harmonics is in close agreement with the spatiotemporal surface-fitting experimental results. Additionally, the wetting boundary conditions can be functionalized to excite specific standing wave patterns, which could provide a novel approach to precise pattern control in bioprinting technology for tissue engineering applications.

Study on the suppression of parasitic resonance of film bulk acoustic wave resonators

To suppress the parasitic resonance of a film bulk acoustic resonator (FBAR) and meet the high-frequency requirements of 5G communication, an FBAR model was established based on COMSOL Multiphysics simulation software. The effects of the piezoelectric materials, electrode lateral size, electrode shape (rectangle, circle, trapezoid, and regular pentagon), and apodization angle (30°, 36°, 40°, and 45°) on parasitic resonance were studied, and the suppression effect of the step-load structure on lateral acoustic wave leakage was discussed. The simulation results show that the best suppression effect on parasitic resonance is achieved when the piezoelectric material is AlN, the electrode shape is a non-regular pentagon, and the apodization angle is 40°; when the resonant area is 3600μm2, its non-circularity is 6.45 %, which is equivalent to the rectangular electrode when the resonant area is 10000μm2. The designed electrode step-load structure improved the quality factor at the parallel resonance point. When the electrode lateral size is 60 μm, the quality factor of the second-order electrode load structure is 1378, which is 10.07 % higher than the quality factor of the electrode-free load structure.

Three-dimensional resonant sloshing in an upright cylindrical container with a ring baffle

The effect of ring baffles on suppressing the three-dimensional (3D) resonant sloshing in an upright cylindrical container is experimentally investigated. The main objectives of this work are to examine the effectiveness of various baffle configurations, to establish the stability boundaries of the stable steady-state waves in the unbaffled and baffled containers, to provide accurate experimental data for the verification of the analytical and numerical models, and to prompt future investigations. For this purpose, hundreds of sloshing experiments are conducted in a cylindrical container with or without a ring baffle. An analytical potential-flow solution and an asymptotic multimodal method are used to elucidate the experimental results. It is found that the vertical location of the ring baffle has small influence on the fundamental natural frequency of the system; however, it has a significant influence on the viscous damping and the damping rate increases gradually with the ascension of the baffle. When the distance between the baffle and the free liquid surface is sufficiently large, the system exhibits three types of resonant wave patterns, namely stable planar, stable swirling, and irregular chaotic. These wave patterns are qualitatively and quantitatively similar to those in the unbaffled container. When the baffle is near the free liquid surface, neither the chaotic waves nor the swirling waves take place, but a new wave pattern with the characteristic of multiple wave crests is observed. Probably, this is the first time that the 3D resonant sloshing in the baffled cylindrical container has been systematically investigated.

Electron acceleration by stochastic wave fields in a bounded plasma system

We investigate the electron acceleration dynamics in spatially stochastic wave fields. For a bounded system, the spectra (frequency and wave number) of the stochastic wave fields are discrete so that they can form spatiotemporal “singular” structures once their phases are in synchronization. As a consequence, the electrons will experience significant scattering by these singular structures, which is an in-phase effect of an ensemble of non-resonant wave–particle interactions. In the presence of parallel symmetry breaking, it is found that the governing Fokker–Planck equation has a structure similar to that of the resonant wave–particle interaction but with a broader parameter regime in the velocity/energy space of the electron distribution function.

Hamiltonian Birkhoff Normal Form for Gravity-Capillary Water Waves with Constant Vorticity: Almost Global Existence

We prove an almost global existence result for space periodic solutions of the 1D gravity-capillary water waves equations with constant vorticity. The result holds for any value of gravity, vorticity and depth, a full measure set of surface tensions, and any small and smooth enough initial datum. The proof demands a novel approach—that we call paradifferential Hamiltonian Birkhoff normal form for quasi-linear PDEs—in presence of resonant wave interactions: the normal form is not integrable but it preserves the Sobolev norms thanks to its Hamiltonian nature. A major difficulty is that paradifferential calculus used to prove local well posedness (as the celebrated Alinhac good unknown) breaks the Hamiltonian structure. A major achievement of this paper is to correct (possibly) unbounded paradifferential transformations to symplectic maps, up to an arbitrary degree of homogeneity. Thanks to a deep cancellation, our symplectic correctors are smoothing perturbations of the identity. Thus we are able to preserve both the paradifferential structure and the Hamiltonian nature of the equations. Such Darboux procedure is written in an abstract functional setting applicable also in other contexts.

6 GHz lamb wave acoustic filters based on A1-mode lithium niobate thin film resonators with checker-shaped electrodes

The first-order antisymmetric (A1) mode lamb wave resonator (LWR) based on Z-cut LiNbO3 thin films has attracted significant attention and is widely believed to be a candidate for next-generation reconfigurable filters with high frequency and large bandwidth (BW). However, it is challenging for traditional interdigitated electrodes (IDTs) based LWR filters to meet the requirement of a clean frequency spectrum response and enough out-of-band (OoB) rejection. To solve the problem, we propose LWRs with checker-shaped IDTs for the design of filters that meet the Wi-Fi 6E standard. By taking advantage of checker-shaped IDTs with unparalleled boundaries, the fabricated 6-GHz resonators successfully suppress higher-order A1 spurious modes, demonstrating a spurious-free impedance response and a high figure-of-merit (FOM) up to 104. Based on the demonstrated checker-shaped electrode design, the filter features a center frequency (f0) of more than 6 GHz, a 3 dB BW exceeding 620 MHz, and an excellent OoB rejection >25 dB, consistent with the acoustic-electric-electromagnetic (EM) multi-physics simulations. Furthermore, through the capacitance-inductance matching network technology, the filter’s voltage standing wave ratio (VSWR) is successfully reduced below 2, showing an excellent 50 Ω impedance matching. This study lays a foundation for ultra-high-frequency and ultra-wideband filters for the Wi-Fi 6/6E application.

Novel spectral methods for shock capturing and the removal of tygers in computational fluid dynamics

Spectral methods yield numerical solutions of the Galerkin-truncated versions of nonlinear partial differential equations (PDEs) involved especially in fluid dynamics. In the presence of discontinuities, such as shocks, spectral approximations develop Gibbs oscillations near the discontinuity. This causes the numerical solution to deviate quickly from the true solution. For spectral approximations of the inviscid Burgers equation in one-dimension (1D), nonlinear wave resonances lead to the formation of localised oscillatory structures called tygers in well-resolved areas of the flow, far from the shock. Recently, the author of [1] has proposed novel spectral relaxation (SR) and spectral purging (SP) schemes for the removal of tygers and Gibbs oscillations in spectral approximations of nonlinear conservation laws. For the 1D inviscid Burgers equation, it is shown in [1] that the novel SR and SP approximations of the solution converge strongly in L2 norm to the entropic weak solution, under an appropriate choice of kernels and related parameters. In this work, we carry out a detailed numerical investigation of SR and SP schemes when applied to the 1D inviscid Burgers equation and report the efficiency of shock capture and the removal of tygers. We then extend our study to systems of nonlinear hyperbolic conservation laws, such as the 2×2 system of the shallow water equations and the standard 3×3 system of 1D compressible Euler equations. For the latter, we generalise the implementation of SR methods to non-periodic problems using Chebyshev polynomials. We then turn to singular flow in the 1D wall approximation of the 3D-axisymmetric wall-bounded incompressible Euler equation [2]. Here, in order to determine the blowup time of the solution, we compare the decay of the width of the analyticity strip, obtained from the pure pseudospectral method (PPS), with the improved estimate obtained using the novel spectral relaxation scheme.

On the Absorption of γ-Radiation by Absorbers with a Thickness Equal to a Multiple of the Mean Free Path and Analogies with Standing Waves in a Sound Resonance Tube

This article addresses the phenomenon of the decreased absorption of γ-radiation when the thickness of the absorber equals a multiple of the mean free path, as observed in relevant laboratory experiments with various absorbing materials. This phenomenon can be compared with the periodic peaks in intensity in an open-ended sound tube that appear at multiples of half wavelength. This could suggest that there is analogy between the two physical systems that are the γ-ray absorber and the sound wave resonance tube. More similarities between the two systems are also presented.

Few-femtosecond soft X-ray transient absorption spectroscopy with tuneable DUV-Vis pump pulses

Achieving few-femtosecond resolution for a pump-probe experiment is crucial to measuring the fastest electron dynamics and for creating superpositions of valence states in quantum systems. However, traditional UV-Vis pump pulses cannot achieve few-fs durations and usually operate at fixed wavelengths. Here, we present, to our knowledge, an unprecedented temporal resolution and pump tuneability for UV-Vis-pumped soft X-ray transient absorption spectroscopy. We have combined few-fs deep-UV to visible tuneable pump pulses from resonant dispersive wave emission in hollow capillary fiber with attosecond soft X-ray probe pulses from high harmonic generation. We achieve sub-5-fs time resolution, sub-fs interferometric stability, and continuous tuneability of the pump pulses from 230 to 700 nm. We demonstrate that the pump can initiate an ultrafast photochemical reaction and that the dynamics at different atomic sites can be resolved simultaneously. These capabilities will allow studies of the fastest electronic dynamics in a large range of photochemical, photobiological and photovoltaic reactions.

Direct temporal characterization of sub-3-fs deep UV pulses generated by resonant dispersive wave emission: erratum

An erratum is presented to include the correct upper horizontal axis in Fig. 3 in our published manuscript [“Direct temporal characterization of sub-3-fs deep UV pulses generated by resonant dispersive wave emission” Opt. Express 31, 26854 (2023).10.1364/OE.494879

Wave resonances and the time-dependent capillary gravity wave motion

The interconnection of time and frequency domains for capillary gravity wave motion in the presence of current is discussed in this article. The general time-dependent problem is solved using Green’s function technique, and the asymptotic solution is derived using the method of stationary phase for large time and space. Also, the frequency domain solution is derived as a special case using the Cauchy Residue theorem. Different types of wave resonances like Trapping, Blocking and Bragg resonances are discussed. The existence of the trapped mode below the cutoff frequency is justified theoretically, and numerical results are obtained using the multipole expansion method. The blocking and Bragg resonances are analyzed above the cutoff frequency. It is found that in the presence of current, when the ripple wavenumber of the bottom undulation equals twice the cosine angle of incidence of wave times the wavenumber of the wave, Bragg resonance occurs. It is found that three propagating modes exist in the case of wave blocking, and the trapped modes exist only for the first propagating mode. Furthermore, because of the negative group velocity inside the blocking zone, the Bragg reflection increases while decreasing outside. The effect of current on the wave energy propagation in the form of group velocity is analyzed and the same is verified in the case of time-dependent problem.

AlN/ScAlN composite films-based spurious free A1 mode lamb wave resonator with adjustable effective electromechanical coupling coefficient

AlN/ScAlN composite films-based spurious free A1 mode lamb wave resonator with adjustable effective electromechanical coupling coefficient

Ultracoherent Gigahertz Diamond Spin-Mechanical Lamb Wave Resonators.

We report the development of an all-optical approach that excites the fundamental compression mode in a diamond Lamb wave resonator with an optical gradient force and detects the induced vibrations via strain coupling to a silicon vacancy center, specifically, via phonon sidebands in the optical excitation spectrum of the silicon vacancy. Sideband optical interferometry has also been used for the detection of in-plane mechanical vibrations, for which conventional optical interferometry is not effective. These experiments demonstrate a gigahertz fundamental compression mode with a Q factor of >107 at temperatures near 7 K, providing a promising platform for reaching the quantum regime of spin mechanics, especially phononic cavity quantum electrodynamics of electron spins.

Effects of interlayer SiO2 or Au on the performances of LNOS-SAW

Abstract Surface acoustic wave (SAW) resonators and filters based on lithium niobate (LN) or lithium tantalate crystals have been widely used in modern wireless communication systems. However, acoustic energy in these kinds of devices is lost in the substrate due to longitudinal attenuation. The enhancements of quality factor and coupling coefficient are still in demand for further applications. This work proposes a SAW based on LN thin film on a sapphire substrate (LNOS). Besides, we explored the effects of using different bonding materials on the LNOS-SAW performances. The presence of the interlayer not only plays a role in bonding but also has an impact on the performance of the resonator. Considering the compatibility of the process in this method, 2 μm-thick silicon dioxide (SiO2) or 1 μm-thick gold (Au) is designed as the interlayer. As the displacement diagrams show, the acoustic energy of the SAW with interlayer is reflected at the interface, and the energy leakage is suppressed. The simulation results show that the presence of SiO2 or Au causes a decrease in resonant frequencies of the resonators, and the effect is more pronounced with Au. Significantly, the presence of SiO2 enhances the coupling efficiency of the resonator while the Au interlayer brings a more obvious improvement in the quality factor.

Hydrodynamic analysis of an oscillating water column array in presence of variable bathymetry

In this study, hydrodynamic analysis of an oscillating water column (OWC) array in the presence of the variable bathymetry (seafloor depth) is performed by using a semi-analytical potential-flow solver. Within the framework of linear theory, the boundary-value problem associated with wave diffraction and radiation by an OWC array with variable bathymetry is formulated and the semi-analytical hydrodynamic model is developed using the matched eigenfunction expansion method. The fluid domain above variable bathymetry is mathematically discretized into multiple subdomains using the boundary approximation method. The Haskind relation and the energy flux conservation law are used to verify the semi-analytical model. The hydrodynamic performance of the OWC array in the presence of the ripple and coral reef bathymetries are investigated in further. Pronounced oscillations are observed for the curve of reflection coefficient Cr and hydrodynamic efficiency η for cases with ripple and coral reef bathymetries. Bragg resonance is identified as the triggering of the strong oscillations in Cr and η for case of ripple bathymetry. The primary frequency of Bragg resonance and the peaked value of Cr converge as the ripple number increases (i.e., Ns > 3). Particularly, for cases with coral reef bathymetry, the wave resonance modal in open-ended basins results in a significant wave amplification at the weather side of the OWC array.

A High Q Lamb Wave Resonator with Dummy Toes Based on 20% ScAlN Film

Abstract The lamb wave resonator (LWR) based on aluminum nitride (AlN) films are preferred strategy for high-frequency filters in 5G communication due to the tunable electromechanical coupling and high Q value. However, since the low electromechanical coupling and piezoelectric coefficient of AlN films, conventional lamb filters are difficult to meet the requirements of high bandwidth and low loss. This work proposes a lamb wave resonator with dummy toes (DT-LWR) based on scandium-doped aluminum nitride (ScAlN) film to improve the quality factor(Q) meanwhile suppress the spurious modes. The processed DT-LWR was tested using a vector network analyser (VNA, Keysight N5222B), and the MBVD model was used to fit the Z parameters. The Q value of DT-LWR is 1437.23, while that of LWR is 1250.09. It is increased by 14.97%. The enhancements make the DT-IWR as an ideal for filters with minimal insertion loss.

Maximum Bandwidth Analysis With a Universal AWLR‐Based Filter Structure

ABSTRACTThe bandwidth enhancement of the acoustic‐wave‐lumped‐element resonator (AWLR)‐based filter has been investigated for a long time. However, few researches are focused on the maximum bandwidth analysis. Based on a universal circuit structure of the AWLR‐based filter, we proposed the maximum bandwidth analysis of the hybrid filter. In the analysis process, the universal filter structure can be transformed into a novel AWLR‐based filter structure by incidentally excluding most of the other structures (including the reported hybrid filter structures) under the defined electrical characteristics. The novel hybrid filter obtains the maximum fractional bandwidth (FBW). Moreover, the proposed calculation results are better than the simulation results without artificial intervention. They are 2.12kt2 and 1.63kt2, respectively. kt2 is the electromechanical coupling coefficient of the acoustic wave resonator (AWR). Third‐order AWLR‐based bandpass filters with five‐type circuit structures have been manufactured and measured. They include the proposed novel AWLR‐based filter and the hybrid filter with the reported structure based on the universal AWLR‐based filter structure. The experimental results indicate that the proposed novel AWLR‐based filter has the maximum FBW.