Specific Frequency Range Research Articles

Analysis of hyperbolic crystals with non-square lattice for improving acoustic energy harvesting

Abstract With the increase in the production of small and low-power electrical devices, there has been an increased focus on creating a useful power source to replace the battery. The energy contained in acoustic waves is one of the attractive energy sources for powering low-power devices. The design and fabrication of metamaterials is one of the effective methods of harvesting acoustic energy that has recently attracted the attention of many researchers. As is presented in this article, the aim is to design and fabricate a novel metamaterial structure with optimal dimensions to improve acoustic energy harvesting in a specific frequency range using a piezoelectric patch. In this metamaterial, hyperbolic crystals with non-square lattice have been used for the first time. This analysis is simulated using the 3D version of Comsol software 6.0. In addition, artificial neural networks and genetic algorithms were used to select the optimal parameters. The results showed that using the non-square lattice of the hyperbolic crystal, more average energy can be harvested in the frequency range of 3310-4325 Hz than in the metamaterial with the cylindrical crystal. Furthermore, the maximum amount of voltage and power extraction with an optimal electrical resistance of 10 kΩ in the metamaterial with the hyperbolic crystals at a frequency of 3374.71 Hz is equal to 27.26 mV and 74.33 nW, respectively, which is much larger compared to the metamaterial with the cylindrical crystals under the same mass and conditions. The simulation results are compared and validated with the experimental results by fabricating the present metamaterial and conducting laboratory tests.

Analytical study on the flexural wave band gaps of arbitrary periodic stiffened plates by using beam-plate coupling theory

In this paper, the flexural wave band gap characteristics of periodic stiffened plates are studied by using beam-plate coupling theory. A theoretical model of arbitrary periodic stiffened plate is established considering the coupling effect of Timoshenko beam and Kirchhoff plate. The flexural wave band structures of periodic stiffened plate are calculated by using plane wave expansion method and Bloch theorem. Numerical calculation and experimental tests were conducted to verify the proposed theoretical model. In addition, the parametric studies were performed to examine the effects of geometric parameters on both bandgap and vibration reduction characteristics of periodic stiffened plate. Results show that periodic stiffened plate can yield significant flexural wave band gaps and vibration isolation performance in a specific frequency range, which shows a good agreement with numerical simulation and experimental results. The geometrical parameters of stiffened plates have a significant influence on adjusting low-frequency flexural wave band gaps. These research findings offer a new technical approach for low frequency vibration and sound optimization of stiffened structures.

Frequency-dependent breakdown of backward volume spin-wave soliton formation

This study investigates the propagation characteristics of spin waves in an yttrium iron garnet waveguide using a vector network analyzer and a real-time oscilloscope. We confirm the propagation of backward volume magnetostatic spin waves in the linear regime. Solitary spin-wave formation was observed, and the transition from linear to nonlinear response was verified by establishing a threshold power. In the nonlinear regime, collision experiments between two spin waves were conducted, revealing a dependence of attenuation on the input carrier frequency. A comparison with the transmission loss curve confirms the correlation between attenuation and the position of “frequency regions with strong dispersion.” Notably, only within a specific frequency range among these regions do the colliding spin waves maintain their shapes and momenta, passing through each other without dissipation. This remarkable phenomenon is crucial for dissipation-free information transfer. Our findings offer valuable insights into spin-wave behavior, particularly for developing spin-wave-based logic and long-distance magnonic soliton information transfer.

Simultaneous acoustic and vibration isolation metamaterials based on triply periodic minimal surface

Metamaterials have attracted widespread attention because they exhibit novel physical behaviors not found in nature. In recent years, due to the excellent properties of triply periodic minimal surface (TPMS) structures, TPMS-based architected materials have played an increasingly important role in many fields. However, most TPMS-based research has focused on single functionality. This study introduces novel TPMS-based metamaterials designed for simultaneous vibration isolation and sound insulation, providing a multifunctional solution. We constructed TPMS structures and analyzed their mechanical properties, exploring how their topology and geometric parameters influence the attenuation of vibration and sound. Through simulations and experimental validations, we demonstrate that these metamaterials can effectively attenuate sound and elastic waves within a specific frequency range. This provides an innovative design approach for materials requiring combined acoustic and vibration control. The work demonstrates the ability to dynamically tune band gaps for multiple wave types by modifying structural parameters. This paves the way for developing advanced multifunctional materials with tailored acoustic and mechanical properties. Additionally, building on this work, future research could focus on refining fabrication processes and investigating different TPMS configurations. Expanding the frequency range could further enhance the robustness and practical applicability of these multifunctional materials.

High-Resolution Phase-Based Ranging Using Inverse Fourier Transform in an Iterative Bayesian Approach.

This article proposes an algorithm that determines the distance between two transceivers based on phase information collected in a specific frequency range. Even though we have focused on BLE technology, we do not necessarily adhere strictly to this standard regarding the procedures used to obtain phased samples. We assume that phase samples are given and propose an algorithm using a Bayesian approach to find delays in a multi-path environment. Analyzing these delays allows for determining the distance between both transceivers. We show several examples confirming the high accuracy and resolution of the proposed algorithm. Finally, we conclude with some pros and cons of the proposed solution, suggesting its use in such applications as, for example, virtual acoustics.

Numerical Analyses of Ultrasonic Atomization Utilizing Acoustic Effects of a Beam Diaphragm

To study mechanisms of jet atomization, a novel method of experimentation utilizing the resonation of diaphragms made from thin steel plates has been previously developed. In the experiments, a diaphragm covered by a film of water emitted acoustic sounds, and jet atomization from the water film was observed. Experiments using diaphragms composed of different materials and fast Fourier transformation analysis of the acoustic sound revealed that jet atomization occurred under limited surface conditions of the diaphragm and a specific range of frequency. In this article, the dynamics of a resonating body composed of the diaphragm and water film were analyzed using the finite element method with a combination of theoretical analyses of surface waves of water, such as the well-known Lang’s equation. The present FEA results, from harmonic response analyses with consideration of viscous damping effect due to interaction between the diaphragm and water film, precisely confirmed the results of FFT analysis previously obtained by the experiment. Specifically, the peak frequency of the frequency response agreed well with the FFT results, and the shift of the peak frequency and attenuation due to the interaction in the analyses corresponded with the difference in surface conditions between the hydrophilic and hydrophobic materials of the diaphragm in the experiments. Our interpretation of the mechanism of jet atomization is expanded by the present numerical results.

Upgrading Sustainable Pipeline Monitoring with Piezoelectric Energy Harvesting

This study presents the design and implementation of a piezoelectric power harvesting device to capture vibrational energy from pipelines to self-powered IoT devices. The device utilizes key components along with the PPA-1001 piezoelectric sensor, the STM32F103C8T6 microcontroller, and LTC-3588 energy harvesting power supply. Experimental results verified the system’s performance in harvesting power within a specific frequency range of 10 Hz to 50 Hz, with the foremost overall performance at 30 Hz. The device generated the highest voltage of 3.3 V, delivering a power output of 2.18 mW, which is sufficient to power low-power electronic devices. The device maintained solid performance across a temperature range of 40 °C to 50 °C, underscoring its robustness in various environmental situations. The findings highlight the capacity of this form of generation to offer a sustainable power source for remote pipeline tracking, contributing to stronger protection and operational efficiency.

Electromechanical coupling optimization for a sandwich beam activation using piezoceramics

Sandwich beams composed of two stiff carbon fiber skins and a viscoelastic core are often used to passively dissipate energy through the activation of shearing in a specific frequency range. Semi-active or active energy dissipation can be made possible on those structures adding piezoelectric patches, coupling mechanical vibration energy and electrical energy. J.L. Guyader et al. [jsv, 1978] theorized a frequency dependent equivalent dynamic model of a sandwich structure, recently extended to the homogenization of anisotropic multi-layers by F.Marchetti et al. [jsv, 2020]. This frequency-dependent stiffness of the beam has to be taken into account in the piezoceramic thickness definition in order to optimize the global electromechanical coupling coefficient. An analytical model is derived from the works of F.Marchetti et al. and adapted to predict the first vibration mode of a finite cantilever beam instrumented with a piezoelectric patch. The electromechanical coupling evolution is then calculated with the proper boundary conditions and for different PZT ceramic thicknesses. This model is furtherly used to define the best transducer configuration for a given sandwich structure beam.

Estimation of viscoelastic properties in ribbon-shaped homogeneous waveguides by wavenumber analysis and model reduction

Wavenumber based procedures applied to 1D waveguides provide a rigorous framework with an exact signal model that allows for a proper identification of both storage and loss properties independently from the boundary conditions. However, the associated inverse problem is either computationally intense if using a reference solution (e.g. SAFE) or limited to a specific frequency range that depends on the reduced beam model. We propose here to apply the wavenumber-based estimation of isotropic viscoelastic properties to ribbon-shaped homogeneous waveguides, characterized by a rectangular section with slender height-to-width aspect ratio. We show theoretically that considering the ribbon as a thick plate by assuming a model reduction in the height dimension, drastically reduces the wave propagation problem (hence its inverse counterpart) while providing a sufficiently good approximation on the low height-to-wavelength regime. In addition, full-field measurements are performed on an Aluminium and a PVC homogeneous ribbon-shaped waveguide. The experimental dispersive branches (bending and torsion modes) are identified on an ultra-wide frequency range (1 kHz - 1 MHz) using High Resolution Wave Analysis. For both materials, an excellent agreement is observed with the thick plate reduced model, paving the way for wide-band viscoelastic properties identification of ribbon-shaped waveguide.

Deep learning neural networks for monitoring early-age concrete strength through a surface-bonded PZT sensor configuration

Monitoring the immediate evolution of concrete’s strength is essential to ensure structural integrity and construction efficiency, requiring Forecasting to avoid unforeseen and severe failures during construction. The present investigation introduces an Equivalent structural parametric (ESP) study using a surface-bonded piezo sensor and electromechanical impedance (EMI) methodology to monitor and forecast the strength of concrete by implementing machine learning and deep learning methods. The concrete hydration processes are simulated using COMSOL™ 5.5. The concrete cube’s hydration is represented by altering Young’s modulus and damping ratio to show the rate of curing. Concrete strength development is examined in terms of conductance resonant frequency (CRF) and Conductance resonant peak (CRP). Continuous conductance signature monitoring and data analysis show that CRF and CRP increase with compressive strength. The system’s mechanical impedance is measured, and EMI signatures vs. frequency plots within a specific frequency range are compared to healthy impedance graphs. A mass-spring-damper system with identical properties is identified, and relevant structural parameters are computed. Modern ML algorithms include linear regression (LR), interaction LR, fine, medium, and coarse Gaussian SVM, etc. reliably predict strength with an error rate of less than 2%. Convolutional neural networks (CNN) have advanced image-based recognition, but their usage in EMI-based structural strength assessment is still being studied. A unique strategy using 2D CNN, 2D CNN– Long short-term memory (LSTM), and 2D CNN Bidirectional-LSTM to forecast concrete structure compressive strength shows the potential of deep learning. The proposed 2D CNN-Bi-LSTM model excels in compressive strength prediction, obtaining an R2 value of 0.99 and stabilizing loss error over a few epochs.

A robust proportional filtered integral controller based on backpropagation neural network

This paper introduces a novel design of a proportional filtered-integral (P-FI) controller whose parameters are auto-tuned using the backpropagation neural networks (BPNN) algorithm. The proposed controller is designed to address the main challenges posed by a class of complex systems characterized by uncertain high-gain and pure integrator dynamics, including high-frequency noise amplification and poor robustness against parameter variations. Designing such a controller involves three main steps: First, a proportional–integral–derivative (PID) controller is designed, with its parameters auto-tuned online using the BPNN algorithm, resulting in the primary (BPNN-PID) controller. Second, the obtained parameters of the previous controller are utilized to compute those of a low-pass filter offline. This filter is then cascaded with the integral parts of a PID controller, forming a P-FI controller structure. This configuration introduces a phase lead within a specific frequency range without amplifying high-frequency noise, overcoming the primary disadvantage of the derivative term. Finally, the parameters of the resulting P-FI controller are again auto-tuned online using the BPNN algorithm, resulting in the final robust (BPNN-P-FI) controller. This novel controller structure and its parameters tuning procedure, based on a two-stage BPNN learning approach, constitute the main contributions of this paper. Simulation results demonstrate the superiority of the proposed controller in terms of time-domain performance, sensor noise attenuation, and closed-loop robustness compared to those obtained with the BPNN-PID and optimally tuned PID controllers.

Bandwidth enhancement of piezoelectric MEMS microspeaker via central diaphragm actuation and filter integration

Abstract This study presents the piezoelectric microspeaker design consisted of the central-diaphragm, connecting-spring, and cantilever-plate actuators to create two resonances in the desired frequency range. In addition to the cantilever-plate actuator, the electrical routing and piezoelectric film are designed to drive the central-diaphragm independently. According to the stress distributions on the microspeaker structure for both lower and higher modes, the all-pass filter circuit is designed and implemented to manage the phase of input signals to the central-diaphragm, thereby changing the motion of the proposed design. Thus, the sound pressure level (SPL) beyond 1 kHz is improved and the SPL zero at specific frequency range is avoided. As a result, the bandwidth enhancement is achieved by the proposed microspeaker. Measurements are conducted under 0.707 Vrms with 9 VDC driving voltage in standard ear simulator to evaluate the performances of the proposed design. A reference design without a piezoelectric film on the central-diaphragm is also implemented for comparison. Measurements indicate, in the low frequency range (before 4 kHz), the proposed designs have over 3 dB SPL enhancement due to the excitation of central-diaphragm. Moreover, compared to the reference design, proposed designs prevent the occurrence of an SPL zero near 10 kHz (between lower and higher modes) and achieve over 15 dB SPL enhancement. When the driving frequency exceeds the higher mode (14 kHz), the proposed design with the all-pass filter eliminates the SPL zero (at 16.8 kHz) with nearly 8 dB enhancement in the 15–18 kHz frequency range. Thus, this study demonstrates the bandwidth enhancement by the proposed microspeaker design with central-diaphragm actuation and all-pass filter integration.

Multi-Variable Optimization to Enhance the Performance of a Cantilevered Piezoelectric Harvester

Over the past decade, various researchers have shown the practicality of extracting electrical energy from vibrating structures. The primary objective of this research was to optimize the parameters of a basic cantilever harvester to maximize the energy production of electricity from surrounding mechanical energy. A distributed parameter model and its modal solution were utilized to determine the design variables via a parametric investigation. It is important to ensure sufficient power generation when there is a wide range of frequencies being excited, without any specific frequency being emphasized. The cost function for the optimization problem was defined as the average power within a specific frequency range, considering geometric and physical restrictions. It was discovered that different parameters’ values can be utilized to generate varying maximum power levels for different frequency ranges. Furthermore, a comparative analysis was performed between the finite element method (FEM) using ANSYS and the current harvesting model. The comparison demonstrated a high level of concordance, enabling the utilization of the finite element method (FEM) for subsequent investigation.

Optimization of Desired Multiple Resonant Modes of Compliant Parallel Mechanism Using Specific Frequency Range and Targeted Ratios

In this paper, a dynamic optimization method capable of optimizing the dynamic responses of a compliant parallel mechanism (CPM), in terms of its multiple primary resonant modes, is presented. A novel two-term objective function is formulated based on the specific frequency range and targeted ratios. The first term of the function is used to optimize the first resonant mode of the CPM, within a specific frequency range. The obtained frequency value of the first mode is used in the second term to define the remaining resonant modes to be optimized in terms of targeted ratios. Using the proposed objective function, the resonant modes of a CPM can be customized for a specific purpose, overcoming the limitations of existing methods. A 6-degree-of-freedom (DoF) CPM with decoupled motion is synthesized, monolithically prototyped, and investigated experimentally to demonstrate the effectiveness of the proposed function. The experimental results showed that the objective function is capable of optimizing the six resonant modes within the desired frequency range and the targeted ratios. The highest deviation between the experimental results and the predictions among the six resonant modes is found to be 9.42%, while the highest deviation in the compliances is 10.77%. The ranges of motions are found to be 10.0 mm in the translations, and 10.8° in the rotations.

Enhanced damping and bandwidth in roton-like dispersion of a beyond nearest neighbor periodic chain

This paper investigates the intriguing roton-like phenomenon occurring in systems with non-local interactions, wherein a single dispersion curve exhibits positive and negative group velocities. Previous research has predominantly concentrated on investigating the roton dispersion in undamped metamaterials through steady-state vibration and driven wave methodologies. However, exploring transient wave propagation in damped metamaterials, employing a free wave approach to study damping enhancement (metadamping), has received comparatively little attention. Addressing this research gap, the damping of the system is quantified as the rate of decay of transient vibrations. Results show a significant increase in damping and attenuation bandwidth, coinciding with the presence of the roton-like phenomenon. Unlike previous studies on metadamping, the proposed beyond nearest neighbor (BNN) chain simultaneously enhances both damping and reduction in acoustic bandwidth without sacrificing either property. Spatiotemporal domain simulation evidenced the existence of backward propagating wave packets due to a roton-like phenomenon in the specific frequency range.

Electrically activated ferroelectric nematic microrobots

Ferroelectric nematic liquid crystals are fluids exhibiting spontaneous electric polarization, which is coupled to their long range orientational order. Due to their inherent property of making bound and surface charges, the free surface of ferroelectric nematics becomes unstable in electric fields. Here we show that ferroelectric liquid bridges between two electrode plates undergo distinct interfacial instabilities. In a specific range of frequency and voltage, the ferroelectric fluid bridges move as active interacting particles resembling living organisms like swarming insects, microbes or microrobots. The motion is accompanied by sound emission, as a consequence of piezoelectricity and electrostriction. Statistical analysis of the active particles reveals that the movement can be controlled by the applied voltage, which implies the possible application of the system in new types of microfluidic devices.

Novel small-size seismic metamaterial with ultra-low frequency bandgap for Lamb waves

Seismic metamaterials (SMs) possess bandgap characteristics, enabling effective attenuation of seismic waves within a specific frequency range. However, small-sized SMs typically struggle to achieve a wide low-frequency bandgap. This paper proposes four types of SMs. The dispersion curves of these models were analyzed, and their vibration modes were studied to elucidate the bandgap mechanism. To investigate the influence of structural parameters on the bandgap, geometric variables are analyzed. Subsequently, the spectrum and acceleration time history curves of Lamb waves in a finite SM system are analyzed to verify the bandgap's authenticity. The designed structure exhibits a bandgap ranging from 1.24 Hz to 16.86 Hz, with a relative bandwidth as high as 172.6% and over 96% maximum vibration displacement attenuation of the El Centro seismic wave. The designed SMs effectively cover the 2 Hz seismic peak spectrum that leads to structural damage. They possess ideal relative bandwidth and excellent isolation performance, further advancing the engineering application of SMs.

Data-driven hybrid modelling of waves at mid-frequencies range: Application to forward and inverse Helmholtz problems

In this paper, we introduce a novel hybrid approach that leverages both data and numerical simulations to address the challenges of solving forward and inverse wave problems, particularly in the mid-frequency range. Our method is tailored for efficiency and accuracy, considering the computationally intensive nature of these problems, which arise from the need for refined mesh grids and a high number of degrees of freedom. Our approach unfolds in multiple stages, each targeting a specific frequency range. Initially, we decompose the wave field into a grid of finely resolved points, designed to capture the intricate details at various wavenumbers within the frequency range of interest. Importantly, the distribution of these grid points remains consistent across different wavenumbers. Subsequently, we generate a substantial dataset comprising 1,000 maps covering the entire frequency range. Creating such a dataset, especially at higher frequencies, can pose a significant computational challenge. To tackle this, we employ a highly efficient enrichment-based finite element method, ensuring the dataset’s creation is computationally manageable. The dataset which encompasses 1000 different values of the wavenumbers with their corresponding wave simulation will be the basis to train a fully connected neural network. In the forward problem the neural network is trained such that a wave pattern is predicted for each value of the wavenumber. To address the inverse problem while upholding stability, we introduce latent variables to reduce the number of physical parameters. Our trained deep network undergoes rigorous testing for both forward and inverse problems, enabling a direct comparison between predicted solutions and their original counterparts. Once the network is trained, it becomes a powerful tool for accurately solving wave problems in a fraction of the CPU time required by alternative methods. Notably, our approach is supervised, as it relies on a dataset generated through the enriched finite element method, and hyperparameter tuning is carried out for both the forward and inverse networks.

Evaluation of bone integrity around the acetabular cup using noninvasive laser resonance frequency analysis.

Resonance frequency analysis (RFA) is valuable for assessing implant status. In a previous investigation, acetabular cup fixation was assessed using laser RFA and the pull-down force was predicted in an in vitro setting. While the pull-down force alone is sufficient for initial fixation evaluation, it is desirable to evaluate the bone strength of the foundation for subsequent fixation. Diminished bone quality causes micromotion, migration, and protracted osseointegration, consequently elevating susceptibility to periprosthetic fractures and failure of ingrained trabecular bone. Limited research exists on the evaluation of bone mineral density (BMD) around the cup using RFA. For in vivo application of laser RFA, we implemented the sweep pulse excitation method and engineered an innovative laser RFA device having low laser energy and small dimensions. We focused on a specific frequency range (2500-4500 Hz), where the peak frequency was presumed to be influenced by foundational density. Quantitative computed tomography with a phantom was employed to assess periprosthetic BMD. Correlation between the resonance frequency within the designated range and the density around the cup was evaluated both in the laboratory and in vivo using the novel laser RFA device. The Kruskal-Wallis test showed robust correlations in both experiments (laboratory study: R = 0.728, p < 0.001; in vivo study: R = 0.619, p < 0.001). Our laser RFA system can assess the quality of bone surrounding the cup. Laser RFA holds promise in predicting the risk of loosening and might aid in the decision-making process for additional fixation through screw insertion.

The development of cloaking techniques based on phase-modulated metasurfaces

Abstract More and more attention has been paid to explore the application background of cloaking techniques based on phase-modulated metasurfaces, which play an important role in modern engineering and military applications. Phase-modulated metasurfaces are an emerging field of research that explores how the propagation of electromagnetic waves can be manipulated by precisely controlling the phase on tiny elements. These tiny elements, usually nanoscale structures, are arranged on the metasurface to precisely control the propagation and scattering of electromagnetic waves in a specific frequency range. The thesis first reviews the development of metamaterial cloaking technology, introduces the realization of several mainstream metamaterial cloaking technologies, and points out the benefits of cloaking techniques based on phase-modulated metasurfaces compared with other cloaking technologies. Then the development history of cloaking techniques based on phase-modulated metasurfaces is introduced through four key time nodes. We can find that phase-modulated metasurfaces are not only getting thinner and thinner, but in addition to the stealth effect, i.e., the reduction of the RCS (Radar Cross Section), phase-modulated metasurfaces can also simulate different virtual shapes. Finally, the development and research progress of cloaking techniques based on phase-modulated metasurfaces are summarized, and personal opinions on its future development are put forward. This paper summarizes the advances in the field of phase-modulated metasurfaces over the last decade and presents some representative approaches to phase-modulated metasurfaces at various points in time, which can help readers better understand the field of metasurfaces and metamaterials.