Spurious Response Research Articles

Band edge modulation for high-performance LL-SAW resonators on LiNbO3/SiC by introducing an ultra-thin intermediate oxide layer

With the exploding demand of rapid information transmission, high-frequency acoustic filtering devices are becoming an immediate need. Longitudinal leaky surface acoustic wave (LL-SAW) devices with unique advantages can be a promising platform. In this paper, we introduce a 100 nm intermediate oxide layer into the X-cut lithium niobate on silicon carbide (LiNbO3/SiC) to improve the in-band performance of LL-SAW resonators. First, the dispersion curves of the structures are analyzed by finite element method. In this part, we successfully interpret the intrinsic low quality factor (Q) of LL-SAW on LiNbO3/SiC in general design, and predict the enhancement of Q by introducing an intermediate oxide layer without degradation on spurious response. Then, one port resonators considered in the simulation are fabricated and measured. As a result, enhancements in Bode Q among the whole passband are confirmed. Compared with devices state of art, resonators with leading performances are demonstrated. The fabricated resonators have peak-valley admittance ratio of 63.87 dB, Bode Q of ∼300 at fr and ∼530 at far, keff2of 15.66 % and phase velocity of 6187.3 m/s. Additionally, the resonant frequency of SH1 mode shifts to higher frequency. This work enables the design of next generation high frequency mobile communication filters.

High-selectivity wideband bandpass filter based on quintuple-mode stub-loaded resonator and defected ground structures

Abstract A high-selectivity wideband bandpass filter (BPF) based on a quintuple-mode stub-loaded resonator and defected ground structures (DGSs) is presented. Thanks to the symmetrical topology, the even/odd theory is adopted for analyses. By properly adjusting the stub dimensions, the resonant frequencies of the transmission poles and zeros can be controlled to obtain wide passband and sharp out-of-band rejection performances. The bandwidth of the upper stopband is further extended by introducing a pair of DGSs under the interdigital coupled line feeding structures, and the spurious response rejection is improved by 18.9 dB. A BPF prototype that operates at 6 GHz with a fractional bandwidth (RBW) of 70 % is manufactured for validation. The measured insertion loss and return loss are 1.3 and 17 dB, respectively. The measured out-of-band rejection over DC-2 GHz and 8.8–21 GHz are better than −30 dB.

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.

Assessing the Spurious Impacts of Ice-Constraining Methods on the Climate Response to Sea-Ice Loss using an Idealised Aquaplanet GCM

Abstract Coupled climate model simulations designed to isolate the effects of Arctic sea-ice loss often apply artificial heating, either directly to the ice or through modification of the surface albedo, to constrain sea ice in the absence of other forcings. Recent work has shown that this approach may lead to an overestimation of the climate response to sea-ice loss. In this study, we assess the spurious impacts of ice-constraining methods on the climate of an idealised aquaplanet general circulation model (GCM) with thermodynamic sea ice. The true effect of sea-ice loss in this model is isolated by inducing ice loss through reduction of the freezing point of water, which does not require additional energy input. We compare results from freezing point modification experiments with experiments where sea-ice loss is induced using traditional ice-constraining methods, and confirm the result of previous work that traditional methods induce spurious additional warming. Furthermore, additional warming leads to an overestimation of the circulation response to sea-ice loss, which involves a weakening of the zonal wind and storm track activity in midlatitudes. Our results suggest that coupled model simulations with constrained sea ice should be treated with caution, especially in boreal summer, where the true effect of sea-ice loss is weakest but we find the largest spurious response. Given that our results may be sensitive to the simplicity of the model we use, we suggest that devising methods to quantify the spurious effects of ice-constraining methods in more sophisticated models should be an urgent priority for future work.

Enhancement in performance of SAW resonator on LN/SiC substrate by take slowness asymmetry into account

Abstract Layered structures comprising high-coupling lithium niobate (LiNbO3, LN) piezoelectric thin plates bonded to high-velocity SiC substrates have attracted much attention of high-performance surface acoustic wave (SAW) devices. However, such these layered structures exhibit severe Rayleigh mode spurious responses that degrade the performances of SAW devices. This paper explores the generation mechanism of spurious modes on LN/SiC layered structure, and proposes an optimized layered structure with suppressed Rayleigh spurious modes. The investigation involves deriving the Euler angle range of LN by analysing the slowness surface of both LN and SiC. In addition, it is worth noting that slowness surface overlaps at some Euler angle ranges, which will cause coupling between different modes, thus generating spurious mode. Simulation result shows the frequency characteristics of SAW resonator at resonant and anti-resonant frequencies of 4.3 GHz and 4.88 GHz of SH mode, achieving a K 2 of up to 26.5% and a quality factor Q of 828. It is proved that the optimization structure offering larger K 2, higher velocity and improved Q values and Rayleigh spurious mode suppression, which is favourable for wideband and high frequency SAW devices applications.

Ultra-subwavelength rect-particles for wideband phase velocity equalization in coupled lines

This paper presents a procedural approach for utilizing ultra-subwavelength rectangular chiral particles embedded in the substrate to eliminate the spurious response of the coupled transmission lines by equalizing the even and odd mode phase velocities in a large bandwidth, making it applicable to wideband coupled-line based structures. Even and odd mode phase velocities, is equalized with the BW of 4 GHz, spanning the range 0.5–4.5 GHz, the normalized phase velocity Root Mean Square Error is less than 0.005.

Spurious Response Due to Linear Interpolation of Input Load and Some Remedies

ABSTRACT This study focuses on the analytical identification and quantification of one type of spurious responses in the context of response history analysis. The spurious response is caused by linear interpolation of input loads. Through analytical derivations and numerical simulations, it is shown that the identified spurious response is fully caused by the interpolation and can significantly affect both damping and inertial forces. Furthermore, the spurious response is not bounded, thus, resistance-based designs could potentially be non-conservative. The findings are applicable to (non-)linear MDOF systems. To address this issue and improve the quality of numerical results, remedies and recommendations are proposed.

Wide-Band Unambiguous Quantum Sensing via Geodesic Evolution.

We present a quantum sensing technique that utilizes a sequence of π pulses to cyclically drive the qubit dynamics along a geodesic path of adiabatic evolution. This approach effectively suppresses the effects of both decoherence noise and control errors while simultaneously removing unwanted resonance terms, such as higher harmonics and spurious responses commonly encountered in dynamical decoupling control. As a result, our technique offers robust, wide-band, unambiguous, and high-resolution quantum sensing capabilities for signal detection and individual addressing of quantum systems, including spins. To demonstrate its versatility, we showcase successful applications of our method in both low-frequency and high-frequency sensing scenarios. The significance of this quantum sensing technique extends to the detection of complex signals and the control of intricate quantum environments. By enhancing detection accuracy and enabling precise manipulation of quantum systems, our method holds considerable promise for a variety of practical applications.

Analysis of propagation and resonance properties of longitudinal leaky surface acoustic wave on LiNbO3/SiC bonded structure

Abstract The propagation and resonance properties of longitudinal leaky surface acoustic waves (LLSAW) on a bonded structure comprising an X-cut LiNbO3 (LN) thin plate and a 4H-SiC support substrate are theoretically investigated. The strong LLSAW responses with high Q factors were obtained at the LN thin-plate thickness h where the LLSAW phase velocity was slower than the bulk shear wave of 4H-SiC of 7126 m/s, and a fractional bandwidth (FBW) of 9–10% was obtained for the normalized Al film thickness by wavelength h Al/λ = 0.06–0.07 and h/λ = 0.30–0.40. Moreover, even at h/λ with a faster phase velocity than the bulk shear wave of 4H-SiC, the strong LLSAW responses without spurious response owing to the LLSAW higher-order mode were obtained. Finally, h Al/λ = 0.031 and h/λ = 0.19 were extracted to obtain a phase velocity of 7800 m/s, high Q factors, and FBW of 7.6%.

Performance of GPT-4 on the American College of Radiology In-training Examination: Evaluating Accuracy, Model Drift, and Fine-tuning

Rationale and ObjectivesIn our study we evaluate GPT-4’s performance on the American College of Radiology (ACR) 2022 Diagnostic Radiology In-Training Examination (DXIT). We perform multiple experiments across time points to assess for model drift, as well as after fine-tuning to assess for differences in accuracy. Materials and MethodsQuestions were sequentially input into GPT-4 with a standardized prompt. Each answer was recorded and overall accuracy was calculated, as was logic-adjusted accuracy, and accuracy on image-based questions. This experiment was repeated several months later to assess for model drift, then again after the performance of fine-tuning to assess for changes in GPT’s performance. ResultsGPT-4 achieved 58.5% overall accuracy, lower than the PGY-3 average (61.9%) but higher than the PGY-2 average (52.8%). Adjusted accuracy was 52.8%. GPT-4 showed significantly higher (p = 0.012) confidence for correct answers (87.1%) compared to incorrect (84.0%). Performance on image-based questions was significantly poorer (p < 0.001) at 45.4% compared to text-only questions (80.0%), with adjusted accuracy for image questions of 36.4%. When the questions were repeated, GPT-4 chose a different answer 25.5% of the time and there was no change in accuracy. Fine-tuning did not improve accuracy. ConclusionGPT-4 performed between PGY-2 and PGY-3 levels on the 2022 DXIT, but significantly poorer on image-based questions, and with large variability in answer choices across time points, but without improvement with fine-tuning. This study underscores the potential and risks of using minimally-prompted general AI models in interpreting radiologic images as a diagnostic tool. Implementers of general AI radiology systems should exercise caution given the possibility of spurious yet confident responses.

Data-driven dimensionality reduction and causal inference for spatiotemporal climate fields.

We propose a data-driven framework to describe spatiotemporal climate variability in terms of a few entities and their causal linkages. Given a high-dimensional climate field, the methodology first reduces its dimensionality into a set of regionally constrained patterns. Causal relations among such patterns are then inferred in the interventional sense through the fluctuation-response formalism. To distinguish between true and spurious responses, we propose an analytical null model for the fluctuation-dissipation relation, therefore allowing us for uncertainty estimation at a given confidence level. We showcase the methodology on the sea surface temperature field from a state-of-the-art climate model. The usefulness of the proposed framework for spatiotemporal climate data is demonstrated in several ways. First, we focus on the correct identification of known causal relations across tropical basins. Second, we show how the methodology allows us to visualize the cumulative response of the whole system to climate variability in a few selected regions. Finally, each pattern is ranked in terms of its causal strength, quantifying its relative ability to influence the system's dynamics. We argue that the methodology allows us to explore and characterize causal relations in spatiotemporal fields in a rigorous and interpretable way.

An extended modal approach for modal parameter identification of structure under the existence of harmonic excitations

The existing operational modal analysis (OMA) methods for the structure subjected to white noise and harmonic combined excitations have some limitations such as easy misjudgment of true and spurious modes and slow identification speed. Through expressing the system response with the extended modal matrix (EMM) and the extended modal response (EMR) vector, a novel operational modal parameter identification approach called the extended modal approach is proposed to obtain structural true modes under the existence of multiple harmonic excitations. The EMRs consist of the true modal responses and the spurious modal responses, and each of the former is random while each of the latter is harmonic. It is also proved theoretically that the EMM can be identified using the power spectrum density transmissibility (PSDT) method. Therefore, the extended modal approach includes three steps: (1) Using the PSDT to identify the EMM; (2) Utilizing the least squares reconstruction method to obtain the EMRs from the underdetermined extended modal equation; (3) Judging each of the EMRs to be true or spurious according to its empirical density function. Structural true modes can be ultimately obtained by removing all spurious modes from the identified results. The new approach is numerically verified through the OMA of two multiple-degree-of-freedom systems and then experimentally verified through the OMA of a test beam. The results in numerical simulation and experiments all show that the extended modal approach can identify accurately and quickly structural true modes under multiple harmonic excitations. Besides, the approach has good robustness against noise contamination.

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.

Retaining Short‐Term Variability Reduces Mean State Biases in Wind Stress Overriding Simulations

AbstractPositive feedbacks in climate processes can make it difficult to identify the primary drivers of climate phenomena. Some recent global climate model (GCM) studies address this issue by controlling the wind stress felt by the surface ocean such that the atmosphere and ocean become mechanically decoupled. Most mechanical decoupling studies have chosen to override wind stress with an annual climatology. In this study we introduce an alternative method of interannually varying overriding which maintains higher frequency momentum forcing of the surface ocean. Using a GCM (NCAR CESM1), we then assess the size of the biases associated with these two methods of overriding by comparing with a freely evolving control integration. We find that overriding with a climatology creates sea surface temperature (SST) biases throughout the global oceans on the order of ±1°C. This is substantially larger than the biases introduced by interannually varying overriding, especially in the tropical Pacific. We attribute the climatological overriding SST biases to a lack of synoptic and subseasonal variability, which causes the mixed layer to be too shallow throughout the global surface ocean. This shoaling of the mixed layer reduces the effective heat capacity of the surface ocean such that SST biases excite atmospheric feedbacks. These results have implications for the reinterpretation of past climatological wind stress overriding studies: past climate signals attributed to momentum coupling may in fact be spurious responses to SST biases.

A New Compact Wideband Filter Based on a Coupled Stepped Impedance Resonator.

A new compact wideband filter is introduced to address the requirements of recent communication and radar systems. The filter is based on a quarter-wavelength short-circuit coupled stepped impedance resonator (SIR). The analytical solution shows that the suggested SIR resonator provides a compact size and a wide stopband response, which are essential features in many wireless communication systems. The analytical results also reveal that increasing the impedance ratio of the SIR extends the stopband by increasing the first spurious response and reducing its total length. A compact two-coupled short-circuit SIR filter is designed at 1.23 GHz. The design approach is validated using an ideal transmission line modeling analysis and electromagnetic simulation using CST Microwave Studio 2021. The proposed structure is shown to be flexible, allowing the achievement of a relative bandwidth as low as 5% and as high as 50%. A four-resonator filter is designed by cascading two stages of the designed two-coupled short-circuit SIR filter, which are coupled through a quarter-wavelength line. The simulation results illustrate that the suggested structure can be used to design a filter with any number of resonators. The filter is implemented using a high-resolution LPKF laser machine on Rogers RT/duroid 6010.2LM material with a thickness of 0.635 mm. From the measurements, the bandwidth is found to be 390 MHz and centered at 1325 MHz (29.4% relative bandwidth) and the insertion loss is 1.3 dB. The simulation and experimental results verify the proposed approach and indicate the potential of this component in meeting the design requirements of next-generation microwave circuits related to flexibility and size-compactness.

Modeling for High-Frequency Spurious Responses in Incredible High-Performance Surface Acoustic Wave Devices.

To ensure that surface acoustic wave (SAW) filters fulfill the requirements of Carrier Aggregation (CA) applications, the development of modeling tools that can forecast and simulate high-frequency spurious responses has been necessary. This paper presents an advanced methodology for extending the coupling-of-modes (COM) model to obtain precise modeling of the high-frequency spurious responses of incredible high-performance surface acoustic wave (I.H.P. SAW) devices. The extended COM (ECOM) model is derived by modifying the conventional COM model and extending it accordingly. The parameters used in this model are determined through numerical fitting. For validation, firstly, the ECOM model is applied to a one-port synchronous I.H.P. SAW resonator, and the simulation and measurement results match. Then, the structural parameters of the ECOM model are varied, and the accuracy of the model after the structural parameters are varied is verified. It is demonstrated that this model can be applied to the design work of SAW filters. Finally, the ECOM model is applied to the design of the I.H.P. SAW filter based on a 42°YX-LiTaO3 (LT)/SiO2/AlN/Si structure. By using this method, the I.H.P. SAW filter's high-frequency spurious response can be predicted more accurately.

Serially connected strip-type acoustic wave resonator using X-40°Y LiNbO3 (XSAR)—feasibility study using macro model

This work presents a new serially connected strip-type acoustic resonator using X40°Y-LiNbO3 (LN) (XSAR). The proposed design is composed of a serial of strip-type bulk acoustic wave resonators connected together. The volume between two strips is penetrated through to eliminate the spurious response and enhance quality (Q) factor. The Euler angle (90°, 90°, 40°) of LN is optimized to obtain the maximal piezoelectric constant e 34, which determines the coupling factor of shear mode of the resonator. Simulation results show that the new design is superior in terms of impedance ratio (Z-ratio) and bandwidth (BW) and exhibits the largest BW of 32% ever reported. The slow shear mode spurious response is successfully removed by the proposed penetrated structure combined with narrow strip. Furthermore, the device was prototyped in macro scale using 350 μm thick LN, by which the ultra-wide BW and potentially good performance in HF were confirmed.

Effectiveness of Homeopathic Medicine in Canine Urinary Incontinence: Outcomes of Owner Response Survey

With advances in data collection via electronic surveys, they have become a popular tool for researchers especially with the changes in normalcy caused by the Coronavirus pandemic. During this pandemic period, previously collected traditional format paper data on Homeopet ™ ‘Leaks No More’ was collated, analysed, written up, reviewed, and published Farrington TJ and Smith . The current study was again an owner response survey like the previous studies but done electronically. In the case of this Homeopet™ 'Leaks No More' survey, the selection criteria used to identify eligible participants who had purchased the product directly from the manufacturer's website helped to ensure that the responses collected were from genuine product users including first time and repeat users. This helped to eliminate potential bias in the responses and ensured that the data collected was of high quality. It ensured elimination of spurious responses and replies from unverified users. The use of gratuities only to those who agreed to provide fully completed surveys containing a true assessment of their pets' responses with an email and other contact details including agreement to be contacted helped to improve the response rate and quality of data collected. In fact the normal verifying of email addresses and names of respondents was turned off for data protection requirements after collection before sending data to analyst and authors removing only from them ability to cross-reference to an original mail shot offering the survey to people who had joined the mailing list on Homeopets own sales site, the researchers were after completion of the paper able to ensure that the data collected was authentic and reliable without exposing any personal data for the participants from the survey collection while still ensuring it was verifiable. Despite striving to write the survey questionnaire in a balanced inclusive way so that it would resonate with a wide range of perspectives and viewpoints across a broad range of views, one can assume that those who filled it out were more likely to have been open to complementary medicine or to have a pet who had failed to respond or responded poorly to conventional therapy. It also meant that emails and names could be verified and if necessary, through the email DNS, and thus could be contacted to complete any missing data needed, which thanks to response numbers was not necessary so the data remained completely confidential. As Homeopet ™ ‘Leaks No More’ is an OTC (Over the Counter) retail product which during the pandemic sold primarily online through various online retailers due to the restricted access to bricks and mortar retailers, shops, and stores there was little or no direct access to or contact with the end users and thus the electronic survey proved highly effective in that environment. Overall, electronic surveys have proven to be a more successful and time-efficient way of collecting data compared to traditional methods as shown in this research paper. The high-quality data collected in this study will be valuable for future research and product development in the field of complementary medicine for pets. Methods and Outcomes: An online questionnaire template was developed using questionnaires from the previous studies and he decision was to use SurveyMonkey® as the mode of delivery to participants. Homeopet™ LLC employed an independent consultant to design and develop the front end for owner response input and the back end for data collection. Ms Jenny Doran Halcyon Days Ltd. worked with Dr Farrington and his team, some external individuals unfamiliar with the project (to ensure the public would understand the questionnaire fully), including staff at Homeopet familiar with the process, to test prototype versions of the SurveyMonkey® and tailor them to the projects requirements till the entire team came to a consensus acceptable to Homeopet™ in the time constraints available. The survey was then made available online with an invitation to participate added to the purchase process on the manufacturer’s website. Other online outlets were considered but were not open to the authors having access to their customer information even for verification purposes. This outlet area is being worked on for future surveys.

Spurious response suppression in wideband bandpass filters using chirality

A simple chiral medium is used to enhance the response of a conventional microstrip coupled line bandpass filter (BPF). The approach is applicable to both narrowband and wideband BPFs using the presented chiral topology. The topology is based on an ultra-subwavelength planar chiral particle that is utilized in the interface between two slabs of substrate. More specifically the medium realizes the suppression of the second spurious response of the filter at a large bandwidth, which enables its practical application in wideband coupled-line based BPFs. The effect of the chiral particles on the substrate's effective permittivity and on the phase velocities of the even and odd mode of two coupled transmission lines on top of the substrate structure is explicitly used in the design of the filter. The methodology is applicable to any coupled-line BPF order. Two wideband microstrip coupled-line prototype filters are designed, fabricated, and measured, one involving a substrate without particles and one involving the chiral substrate. Measurement results are in good agreement with the simulations. The chiral medium based filter results in a wide fractional bandwidth (FBW) of 81% for a 1 GHz center frequency and a measured suppression level of −60 dB.

The explicit β1/β2-Bathe time integration method

In this paper we introduce the explicit β1/β2-Bathe method for solving dynamic problems, in particular wave propagations. Like for the implicit β1/β2-Bathe method, the proposed explicit scheme uses two sub-steps per time step and can be used directly as a first-order and a second-order method with the capability to suppress high spurious frequency response. In both sub-steps, standard Taylor series are employed resulting in an explicit solution scheme. The novelty is that we calculate the final displacements and velocities in each sub-step by applying correction terms using the generalized trapezoidal rule with control parameters β1 and β2. This approach makes the method a quite simple scheme. We consider the stability, accuracy and numerical dispersion and give recommendations on the parameter values β1 and β2 to be used in practice. We give the solutions of four problems, three of which are wave propagation problems, and compare the results with those obtained using other methods. While more experience in the use of the procedure is needed to understand its full solution capabilities, we can already conclude that the proposed method is effective in some wave propagation analyses.