Spurious Resonances Research Articles

Application of Deconvolution in Path Integral Simulations.

In path integral molecular dynamics (PIMD) simulations, atoms are represented by several replicas connected with harmonic springs, so additional vibrations appear beyond the physical vibrations because of the normal mode frequencies coming from the springs of the ring polymer. In harmonic approximation, the frequencies of these internal modes can be determined exactly from the physical frequencies. We show that this formal effect of the path integral simulations on the vibrations can be considered as a convolution if we use the square of the frequency as an independent variable. This convolution can be represented as a matrix multiplication. The potential of the formalism is demonstrated in two applications. We present an alternative method to determine the power spectrum of thermostats used in PIMD simulations. We also show that in simple anharmonic model systems, the physical frequencies can be obtained from ring polymer molecular dynamics simulations by deconvolution, even in cases where spurious resonances appear.

Edge treatment for spurious mode suppression in thin-film lithium niobate resonators

Thin-film lithium niobate is an attractive material for RF acoustic devices because of its high electromechanical coupling. However, due to the large coupling and the high anisotropy, thin-film lithium niobate resonators are prone to accidental resonances called spurious modes. These modes compromise the frequency response of the resonators, limiting their use in filter and oscillator applications. In this work, we present a novel method of spurious mode suppression through a special edge treatment etch process. Two thin-film lithium niobate resonators were fabricated, one with smooth sidewalls and one with the edge treatment. It was found that the edge-treated resonators show a weaker spurious mode response. This is potentially a new way to mitigate spurious resonances, a major issue in lithium niobate Lamb wave devices.

Suppression of spurious responses near anti-resonance of TC-SAW resonators by selective thinning of SiO2

This paper discusses the generation mechanism and suppression of spurious resonances near the anti-resonance in temperature compensated surface acoustic wave devices using the SiO2/128°YX-LiNbO3 structure. Detailed field analysis is performed for the spurious resonances, and the result indicates that the spurious modes are caused by excitation and/or scattering near the electrode finger edges, and can be suppressed well by thinning of the SiO2 layer selectively in the gap region. It is also shown that most of spurious responses can be suppressed for the piston design using the Cu dots with the SiO2 selective thinning. In contrast, this selective SiO2 thinning does not work well for the piston design using the Cu stripes.

SAW velocity reduction and spurious modes suppression on the layer structure

This paper discusses the use of the layered structure for the SAW velocity reduction. First, it is shown that the insertion of SiO2 is crucial between the piezoelectric layer and the base substrate to keep a large electromechanical coupling factor even when the SAW velocity is reduced. It is also shown that the use of a high-velocity substrate such as Si is also crucial for bringing spurious resonances much higher than the main resonance. The impact of Si orientation is also discussed. Next, suppression of transverse mode resonances and lateral leakage is studied. It is shown that the double busbar structure offers Q enhancement through good lateral energy confinement, and its combination with the piston design also gives good transverse mode suppression. Furthermore, discussions are extended to a strong spurious resonance that appears near the anti-resonance.

Application of an overlay for spurious suppression of multi-layered surface acoustic wave resonators with double busbar configuration

Abstract This paper discusses the suppression of a spurious resonance called the gap mode which appears when the double busbar configuration is applied to multi-layered surface acoustic wave resonators. Two kinds of overlay structures are proposed for the gap mode mitigation. First, the use of lossy ones is studied. The results indicate that the lossy overlay can effectively mitigate the gap mode response when the viscosity is adequate. The layer thickness has a negligible impact on the mitigation. Then, the discussion is extended to the application of high-acoustic-velocity materials as the overlay. The resonance frequency of the gap mode can be moved to the upper-frequency side without affecting the main resonance by simply depositing a high-velocity overlay to the gap region. Finally, the comparison and choice of overlay materials are also studied. The results point out that Si3N4 is the optimum choice for industrial use.

S0-like SAW mode resonator on LiNbO3/SiO2/SiC structure

Abstract This paper discusses the basic properties of a surface acoustic wave (SAW) mode like the zeroth-order symmetric (S0) Lamb mode in the LiNbO3/SiO2/SiC configuration in detail. At first, the influence of the SiO2 insertion is discussed, and it is shown that SiO2 insertion offers significant enhancement of the electromechanical coupling coefficient K 2 for the S0-like SAW mode without significant reduction of the phase velocity. Then, the discussion is extended to spurious resonance characteristics. It is shown that the dummy electrodes are not necessary in this case. Then, two kinds of piston design are applied for the transverse suppression, and their effectiveness is discussed.

Use of periodically slotted SiO2 in a layered surface acoustic wave structure for transverse mode suppression

This work demonstrates the applicability of periodically slotted SiO2 (PSS) structures (PSSs) for controlling the urface acoustic wave (SAW) slowness shape and eliminating the transverse modes in layered SAW structures represented by the Incredible High Performance SAW. The use of PSS comprising SiO2 blocks and air gaps provides larger acoustic anisotropy for slowness shape manipulation. The effect of PSSs on transverse mode suppression is revealed. The slowness curves and frequency responses with different structural parameters of PSS are calculated by FEM analysis. Then, an electrode is designed for further spurious resonance suppression. A hammer-head configuration and Si3N4 overlay are applied. It is shown that higher-order transverse modes in the passband were well suppressed without reduction of the electromechanical coupling factor.

Semi-empirical calibration of remote microphone probes using Bayesian inference

The empirical calibration of remote microphone probes (RMP), used to acquire wall-pressure fluctuations, can introduce spurious resonance into the sensor transfer function due to the difference in the pressure field inside the calibrator geometry over multiple calibration steps. Such spurious resonance subsequently propagates into the unsteady-pressure data at which the calibration is applied, hindering the accuracy of the measurements. Current post-processing methods for tackling these issues are often manual and strongly dependent on the operator’s expertise. In this study, we propose an original semi-empirical calibration method to remove spurious resonance in a less operator-reliant manner. The approach is based on fitting an existing analytical fluid-dynamical model for the propagation of pressure waves in the probe to the empirical calibration data using Bayesian inference. The proposed method is successfully applied to three datasets, from a simple probe recessed behind a pinhole to a more complex branching RMP. For all the configurations, spurious resonance is eliminated from the transfer function with a strongly reduced impact of the operator intervention while retaining the resonant features that are characteristic of the RMP. The affected frequency bands are then replaced using the underlying physical model. In this way, the detrimental impact of spurious resonance is removed from the measured wall-pressure spectra. Furthermore, the RMP parameters retrieved by the fit can also be used as inputs to corrective models, specifically to account for averaging effects due to the probe sensing area or for the impact of grazing flow or temperature variations on the transfer function.

Perturbation analysis of nonlinear responses caused by transverse modes in AlN FBAR based on 2D scalar wave model

This paper describes perturbation analysis of nonlinear signal generation in apodized film bulk acoustic resonators using a multi-branch LCR equivalent circuit where all necessary simulation parameters are derived by the two-dimensional (2D) scalar wave model. Nonlinear signals are evaluated by adding two voltage sources representing nonlinear strain and electric flux, and their amplitude is determined by currents in the circuit for linear analysis. Simulated second and third harmonic responses agree well with experimental ones. The magnification mechanism of spurious resonances is also discussed.

Quasi-3D Model for Lateral Resonances on Homogeneous BAW Resonators.

Lateral modes are responsible for the in-band spurious resonances that appear on BAW resonators, degrading the in-band filter response. In this work, a fast computational method based on the transmission line matrix (TLM) method is employed to model the lateral resonances of BAW resonators. Using the precomputed dispersion curves of Lamb waves and an equivalent characteristic impedance for the TE1 mode, a network of transmission lines is used to calculate the magnitude of field distributions on the electrodes. These characteristics are specific to the stack layer configuration. The model's implementation is based on nodal Y matrices, from which particle displacement profiles are coupled to the electric domain via piezoelectric constitutive relations. Consequently, the input impedance of the resonator is obtained. The model exhibits strong agreement with FEM simulations of FBARs and SMRs, and with measurements of several SMRs. The proposed model can provide accurate predictions of resonator input impedance, which is around 200 times faster than conventional FEM.

MmWave Zero Order Resonant Antenna with Patch-Like Radiation Fed by a Butler Matrix for Passive Beamforming.

A small zero-order resonant antenna based on the composite right-left-handed (CRLH) principle is designed and fabricated without metallic vias at 30 GHz to have patch-like radiation. The mirror images of two CRLH structures are connected to design the antenna without via holes. The equivalent circuit, parameter extraction, and dispersion diagram are studied to analyze the characteristics of the CRLH antenna. The antenna was fabricated and experimentally verified. The measured realized gain of the antenna is 5.35 dBi at 30 GHz. The designed antenna is free of spurious resonance over a band width of 10 GHz. A passive beamforming array is designed using the proposed CRLH antenna and the Butler matrix. A substrate integrated waveguide is used to implement the Butler matrix. The CRLH antennas are connected to four outputs of a 4×4 Butler matrix. The scanning angles are 12∘, -68∘, 64∘, and -11∘ for excitations from port 1 to port 4 of the 4×4 Butler matrix feeding the CRLH antenna.

Spurious Mitigation of Layered Surface Acoustic Wave Resonators With Double-Busbar Configuration Using 42°YX-Lithium Tantalate Thin Plate

This article investigates a spurious resonance appearing near the antiresonance when the double-busbar configuration is applied to layered surface acoustic wave (SAW) resonators using 42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> YX-LiTaO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula> thin plates, and possible mitigation methods are studied both theoretically and experimentally. First, the origin of the spurious resonance is revealed, and the influence of structural parameters is studied using the periodic 3-D finite-element method (FEM) powered by the hierarchical cascading technique (HCT). Then, possible methods are discussed for spurious mitigation. Finally, experimental data are provided for validation of the present analysis.

Dual‐band inkjet printed coplanar waveguide‐fed stepped‐impedance slot dipole antenna for ISM application

AbstractIn this work, a dual‐industrial, scientific, and medical (ISM)‐band flexible slot dipole antenna is investigated. It is based on quarter‐guided‐wavelength () stepped impedance resonator (SIR) slots fed by coplanar waveguide. Compared to the mostly used SIR, the use of the type SIR not only enables compact size but also leads to broadside radiation without gain decline at the first harmonic. The analysis of fundamental and spurious resonance conditions was also elaborated to reveal the theory behind compact size and harmonics suppression. Planar measurements show the impedance bandwidths are 500 MHz (20.4%) for 2.2–2.7 GHz, and 1200 MHz (21.4%) for 5–6.2 GHz, with peak gain of 3.7 and 5.8 dBi at 2.4 and 5.5 GHz, respectively. Furthermore, in curving measurement, both the reflection coefficient and radiation pattern remain stable during bending. Our proposed antenna will benefit a bunch of flexible and compact applications operating in dual‐ISM‐band.

Spurious Resonance of the QCM Sensor: Load Analysis Based on Impedance Spectroscopy

A research topic of equal importance to technological and application fields related to quartz crystal is the presence of unwanted responses known as spurious resonances. Spurious resonances are influenced by the surface finish of the quartz crystal, its diameter and thickness, and the mounting technique. In this paper, spurious resonances associated with fundamental resonance are studied by impedance spectroscopy to determine their evolution under load conditions. Investigation of the response of these spurious resonances provides new insights into the dissipation process at the QCM sensor surface. The significant increase of the motional resistance for spurious resonances at the transition from air to pure water is a specific situation revealed experimentally in this study. It has been shown experimentally that in the range between the air and water media, spurious resonances are much more attenuated than the fundamental resonance, thus providing support for investigating the dissipation process in detail. In this range, there are many applications in the field of chemical sensors or biosensors, such as VOC sensors, humidity sensors, or dew point sensors. The evolution of D factor with increasing medium viscosity is significantly different for spurious resonances compared to fundamental resonance, suggesting the usefulness of monitoring them in liquid media.

Attenuating pseudo S‐wave splitting caused by vector infidelity

AbstractShear wave (S‐wave) splitting analysis can provide knowledge about, among other properties, principal stress directions and fracture orientation. It is an essential step in multi‐component, converted wave processing. Caution must be taken, however, when performing such analysis on ocean bottom cable seismic data, which is highly susceptible to different coupling of the two horizontal components with the seafloor. Receiver coupling correction methods attempt to balance the seismic response on all components and seek to minimize spurious resonance effects. We show on field data from an ocean bottom cable seismic dataset how these coupling effects that simulate S‐wave splitting behaviour can be attenuated to significantly improve PS‐wave stack images of the shallow seabed. Furthermore, corrected pre‐stack data of all azimuths may reveal true splitting effects for stress and fracture information.

Spurious Self-Suppression Method: Application to TM Cavity Filters

This article presents a new approach for improving spurious free bands in filters. The main idea is to control the coupling coefficients of the spurious resonances, in order to force them to cancel each other. This approach is completely different from the classical one where all couplings are minimized in order to excite spurious resonances as less as possible. In fact, in this approach, all spurious couplings are maximized except the central coupling that is instead minimized. This method is first explained in terms of equivalent circuits. Then, in order to show its applicability to real microwave filters, it is applied to the TM cavity filters and used to remove both spurious resonances due to higher order cavity modes and to TE10 mode of coupling irises. Design examples of fourth- and sixth-order TM cavity filters are presented. With respect to the classical TM cavity filter, where the first spurious appears around 11.4 GHz, the TM filters designed by exploiting the self-suppression method present spurious free bands up to 20.2 GHz (20 GHz for sixth-order filter), improving the filter response up to 2.2 times the center frequency of 9.2 GHz. Another advantage is that, in contrast to the classical spurious suppression method that does not allow responses with TZs in TM filters, the self-suppression method allows for a number of TZs equal to N-2 (N being the filter order) and it also allows a certain control of their position.

Analysis of spurious peaks at series resonance in solidly mounted resonators by combined BVD-Mason modelling

Solidly Mounted Resonators (SMRs) for high frequency RF filters and sensing applications often display spurious resonances that distort their frequency response. In this work, we try to identify the origin of spurious resonances accompanying the main series resonances in AlN-based SMRs with the help of modified Butterworth Van Dyke (BVD) and Mason’s models. By manufacturing SMRs of different sizes and shapes and studying the influence of the position of the electrical probing spot, we have demonstrated both theoretically and experimentally that devices with larger areas are more likely to display these additional peaks. Our updated models accurately simulate the frequency response of the SMRs, revealing that spurious peaks are mostly related to the resistance of the electrodes. Our study clarifies the origin of the spurious resonances and offers solutions for both, the optimal design and measurement method of SMRs.

Substrate-Integrated Waveguide Band-Pass Filter and Diplexer With Controllable Transmission Zeros and Wide-Stopband

In this brief, a substrate integrated waveguide (SIW) bandpass filter (BPF) with wide out-of-band rejection is researched and fabricated with the center frequency of 45.8 GHz and 3-dB FBW of 2.18%. Due to the exploitation of electronic excitation, higher order modes mismatch and orthogonal transmission, the simulated and measured out-of-band rejection is better than 20 dB with frequencies up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.6f_{0}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.4f_{0}$ </tex-math></inline-formula> , respectively. Diplexer with stopband suppression better than 30 dB up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.87f_{0}$ </tex-math></inline-formula> is proposed based on the theory of the proposed filter. Dual-mode resonator operating with TE301 mode (43.8 GHz) and TE103 mode (45.8 GHz) has been designed to provide the transition of two filter channels. High isolation better than 27 dB over the whole band can be achieved. Transmission zeros (TZs) are generated by spurious resonances under electrical excitation, resulting in high selectively of the passbands. Good agreements between simulations and measurements can be observed.

Wideband Surface Acoustic Wave Filter at 3.7 GHz With Spurious Mode Mitigation

As an essential functional block in radio frequency (RF) front-ends, surface acoustic wave (SAW) filters with large fractional bandwidth (FBW), high center frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> ), and low loss are highly sought-after in 5G new radio (NR). To address this end, 32°Y-X LiNbO3/SiO2/Si heterostructure with high electromechanical coupling coefficient of 23% was constructed, while the propagation characteristics as well as spurious resonance were analyzed through finite element method (FEM) and one-port resonators measurement. It is revealed that by using thin electrodes in the series resonator and thick electrodes in the parallel resonator, spurious modes are successfully eliminated out of the passband. As a result, the SAW filters formed by the above resonators are capable of several superb RF performances: a large bandwidth of 730 MHz (FBW of 19.5%) at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> of 3.74 GHz, a small insertion loss (IL) of 3.03 dB, and a flat passband. Furthermore, since our devices were fabricated by standard photolithography process, this work advances commercial implementation of SAW filter in 5G NR.

Compact 1.75–2.7 GHz Tunable BPF With Wide Stopband Up to 9.5 GHz Using Harmonic-Controlled SIDGS Resonators

In this brief, a harmonic-controlled substrate-integrated defected ground structure (SIDGS) resonator with tuning capacitor is proposed for the design of tunable filter. Such resonator exhibits a harmonic-controlled characteristic. The fundamental resonant frequency can be properly tuned, while the spurious resonance is controlled at much higher frequency to achieve a wide stopband. To verify the principle, a tunable bandpass filter (BPF) is designed and fabricated based on the resonator. The center frequency can be tuned from 1.75 to 2.7 GHz. Meanwhile, the stopband can extend up to 9.5 GHz with a rejection level of 20 dB for all tuning cases. The BPF also exhibits low insertion loss (i.e., 1.1–1.9 dB) and compact size (i.e., 0.07 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda _{g}}\,\,{\times }\,\,0.08\,\,{\lambda _{g}}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda _{g}}$ </tex-math></inline-formula> is the microstrip guided wavelength at the 1.75 GHz).