Frequency Response Properties Research Articles

The Effect of Soil-Structure Interaction (SSI) on Structural Stability and Sustainability of RC Structures

The issue of SSI involves how the ground or soil reacts to a building built on top of it. Both the character of the structure and the nature of the soil have an impact on the stresses that exist between them, which in turn affects how the structure and soil beneath it move. The issue is crucial, particularly in earthquake regions. The interaction between soil and structure is an extremely intriguing factor in increasing or reducing structural damage or movement. Structures sitting on deformable soil as opposed to strong soil will experience an increase in static settlement and a decrease in seismic harm. The engineer must take into account that the soil liquefaction problem occurs for soft ground in seismic areas. A reinforced concrete wall-frame dual framework's dynamic reaction to SSI has not been sufficiently studied and is infrequently taken into consideration in engineering practice. The structures’ seismic performance when SSI effects are taken into account is still unknown, and there are still some misconceptions about the SSI idea, especially regarding RC wall-frame dual systems. The simulation study of the soil beneath the foundations significantly impacts the framework's frequency response and dynamic properties. Therefore, the overall significance of SSI in the structural aspect and sustainability aspects will be reviewed in this research.

Frequency and temperature-dependence ZnO based fractional order capacitor using machine learning

This paper investigates the fractional order behavior of ZnO ceramics at different frequencies. ZnO ceramic was prepared by high energy ball milling technique (HEBM) sintered at 1300 °C to study the frequency response properties. The frequency response properties (impedance and phase angles) were examined by analyzing through impedance analyzer (100 Hz - 1 MHz). Constant phase angles (84 °-88 °) were obtained at low temperature ranges (25 °C-125 °C). The structural and morphological composition of the ZnO ceramic was investigated using X-ray diffraction techniques and FESEM. Raman spectrum was studied to understand the different modes of ZnO ceramics. Machine learning (polynomial regression) models were trained on a dataset of 1280 experimental values to accurately predict the relationship between frequency and temperature with respect to impedance and phase values of the ZnO ceramic FOC. The predicted impedance values were found to be in good agreement (R2 ∼ 0.98, MSE ∼ 0.0711) with the experimental results. Impedance values were also predicted beyond the experimental frequency range (at 50 Hz and 2 MHz) for different temperatures (25°C - 500°C) and for low temperatures (10 °C, 15 °C and 20 °C) within the frequency range (100 Hz - 1 MHz).

Identification of Dynamic Parameters and Frequency Response Properties of Active Hydraulic Mount with Oscillating Coil Actuator: Theory and Experiment

Active hydraulic mounts (AHMs) provide an effective solution for refining ride comfort noise and vibration in passenger cars. AHMs with inertia tracks, decoupler membranes, and oscillating coil actuators (AHM-IT-DM-OCAs) have been extensively studied owing to their compact structures and strong damping characteristics in the low-frequency band. This study focuses on the full parameter identification based on the distinct features of external dynamics, which can be used to obtain an accurate and reliable estimate of the transfer functions required for active control algorithms. A lumped parameter model was established for the AHM-IT-DM-OCAs, and the analytical frequency bands were defined by the two resonance frequencies of the fluid channel and actuator mover. Methods for nonlinear model simplification were proposed in different bands and verified theoretically. Based on the simplified models, the distinct features of the active and passive dynamics are successively revealed, which include three resonances and seven horizontal segments. Subsequently, a series of experimental studies on the distinct features were carried out, which agreed well with the theoretical results. However, owing to the limitations of the test equipment and fixture modalities, only the distinct features of one fixed point, two resonance peaks, and three horizontal segments can be used for parameter identification. Based on the validated distinct features, a procedure for full parameter identification is proposed, and all six key parameters are identified. The obtained results showed good consistency and rationality, indicating that this approach can be used for the transfer function estimation of the primary and secondary paths of the AHM-IT-DM-OCAs.

Multiplexing of RF-assisted fiber ring resonators based on phase-shift amplification.

The multiplexing of fiber ring resonators (FRRs) for no crosstalk loss sensing is proposed and demonstrated experimentally. The difference between the parallel and series FRRs is theoretically elaborated to determine the multiplexing scheme. The frequency response properties of the cascaded FRRs at distinct radio frequency (RF) working points are compared and analyzed. The optical carrier-based microwave interferometry system is implemented to verify the numerical investigation and exhibit the multiplexing of phase-shift based demodulation at diverse RF working points. Enhanced by the phase-shift amplification and the series configuration, each FRR can be independently demodulated by recording the phase of frequency response at the specific RF working point. The experimental results indicate that the sensitivity of transmittance reaches -0.341 rad with the advantage of robustness and immunity to power fluctuation. Owing to the prominent contribution of insensitive points and the series strategy, the crosstalk of multiplexing for loss sensing between two FRRs is eliminated virtually, which matches well with the theory. The proposed scheme provides an innovative approach for multiplexing the phase-based FRRs sensors without additional expenditure.

Damping and Frequency Response Characteristics of Functionally Graded Fiber-Reinforced Composite Cylindrical Shells

This paper presents research on the modal damping and frequency response of functionally graded fiber-reinforced composite cylindrical shells considering the internal damping. Based on the Love shell theory and energy approach, the dynamical equations of cylindrical shells are established. In the process of variable separation, the Haar wavelet series and trigonometric functions are respectively to represent the axial and circumferential modes. Based on the microscopic damping prediction method and multi-cell model of hybrid materials, the equivalent damping and elastic characteristics of composite materials are determined. Then the damping and frequency response characteristics are solved by the complex modulus method. The present analysis is validated by comparing the results with those in the literature and finite element simulation. The effects of fiber content and distribution, lamination and geometry configuration on damping and frequency response properties are further analyzed. The analysis show that the damping decreases monotonically with the increase of fiber volume fraction. The damping behaviors may be improved by changing the fiber distribution type and stacking sequence. Increasing the internal damping of composites can obviously reduce the vibration amplitude in the resonance region, especially in the high frequency range.

Highly sensitive and fast response strain sensor based on evanescently coupled micro/nanofibers

Flexible strain sensors play an important role in electronic skins, wearable medical devices, and advanced robots. Herein, a highly sensitive and fast response optical strain sensor with two evanescently coupled optical micro/nanofibers (MNFs) embedded in a polydimethylsiloxane (PDMS) film is proposed. The strain sensor exhibits a gauge factor as high as 64.5 for strain ≤ 0.5% and a strain resolution of 0.0012% which corresponds to elongation of 120 nm on a 1 cm long device. As a proof-of-concept, highly sensitive fingertip pulse measurement is realized. The properties of fast temporal frequency response up to 30 kHz and a pressure sensitivity of 102 kPa⁻¹ enable the sensor for sound detection. Such versatile sensor could be of great use in physiological signal monitoring, voice recognition and micro-displacement detection.

Frequency Response Properties of the B-Dot Sensors Employed on a High Current Pulsed Power Facility

B-dot sensor, as an important device, is extensively employed to measure the current flowing in the magnetically insulated transmission line (MITL). To shield the output signal of the B-dot sensor from electron flow and high electrical field in the MITL anode-cathode (A-K) gap and also avoid the electrical breakdown in the A-K gap, the sensor is often covered with the metallic film and located in a conductor cavity penetrating the MITL electrode hole simultaneously. The frequency response properties of such kind of sensor are investigated. The experiment results indicate that the upper limited response frequencies of the sensors with and without the attached 5-μ m-thick Ni-Chrome foil are 50 MHz and 148 MHz, respectively. Moreover, as a result of penetration of magnetic flux into the cavity's wall and the wire loops wound to form the sensor, the low-frequency components of the B-dot sensor output signal are amplified, consequently the falling edge of the waveform given by the B-dot probe will be distorted. We have proposed a method to make a first-order correction for such effect by using a passive resistor-capacitor integrator instead of the numerical process suggested previously. The integrator combines the behaviors of integration and compensation of the B-dot sensor output. The actual measured current waveform can be directly obtained by multiplying the output signal of the integrator by the sensitivity of the B-dot monitor. The B-dot sensors and this post-processing method have been successfully used on a pulsed power accelerator.

FREQUENCY RESPONSE AND DISTORTION PROPERTIES OF RECONSTRUCTION ALGORITHMS IN COMPUTED TOMOGRAPHY

Denoising reconstruction techniques can introduce nonlinear properties into computed tomography (CT) systems. These nonlinear algorithms introduce distortion which affects the assessment of the resolution of the system. The purpose of the present study was to decouple and investigate amplitude modulation and waveform distortion in reconstruction algorithms in CT. The methodology developed by Wells, J. R. and Dobbins, J. T. III [Frequency response and distortion properties of nonlinear image processing algorithms and the importance of imaging context. Med. Phys. 40, 091906 (2013)] was adapted to CT reconstruction algorithms. The CT simulating program ASTRA Toolbox© for MATLAB™ was used for the reconstruction of the sinusoidal wave functions. Filtered back projection and the simultaneous iterative reconstruction technique were investigated with simple nonlinear mechanisms: a median filter and a non-negative constraint, respectively. The native reconstruction algorithms were not free from nonlinear waveform distortion, however, none of the metrics showed any dependence on the contrast-to-noise ratio (CNR). Furthermore, the algorithms including nonlinear mechanisms showed a clear and specific CNR dependence, indicating the necessity for distortion analysis in nonlinear CT reconstruction.

Design and electromechanical properties of three-layer fabric-based pressure sensor

In this study, we developed a three-layer fabric-based pressure sensor and analyzed the structural factors and design parameters that affect its electromechanical properties. The sensor has a three-layer fabric and angle interlocking structure, which enhance its structural stability, sensing capability, and durability. Based on the factors that affect the sensing properties of the fabric sensor, 12 fabric sensors were designed. The electromechanical properties of these sensors were analyzed by adjusting the warp density and material of the three-layer fabric structure, as well as the weft yarn type of the dielectric layer. The curve showing the efficiency of the fabric sensor was divided into three zones, namely, elastic, yield, and crush, to investigate the frequency-response properties, linear variation range, sensitivity, and stability of the fabric sensor. The results indicated that the warp density and warp and weft yarn types of the dielectric layer of the sensor affected the capacitance change rate and sensitivity. The effects of the weft yarn type of the dielectric layer on the electromechanical properties of the fabric sensor were complex. Additionally, the woven and angle interlocking structures of the three-layer fabric sensor contributed to the electrical stability and durability of the sensor. In the design of a multilayer flexible fabric sensor, the appropriate warp density, as well as the warp and weft materials, should be considered to ensure its linearity, sensitivity, and repeatability.

Investigating Gelatine Based Head Phantoms for Electroencephalography Compared to Electrical and Ex Vivo Porcine Skin Models

Gelatine based phantoms for electrophysiology are becoming widely used as they allow the controlled validation of new electrode and new instrumentation designs. The phantoms mimic the electrical properties of the human body and allow a pre-recorded electrophysiology signal to be played-out, giving a known signal for the novel electrode or instrumentation to collect. Such controlled testing is not possible with on-person experiments where the signal to be recorded is intrinsically unknown. However, despite the rising interest in gelatine based phantoms there is relatively little public information about their electrical properties and accuracy, how these vary with phantom formulation, and across both frequency and duration of use. This paper investigates ten different phantom configurations, characterising the impedance of the gelatine and electrodes, comparing this to both previously reported electrical models of Ag/AgCl electrodes placed on human skin and to a model made from ex vivo porcine skin. This article shows how the electrical properties of the phantoms can be tuned using different concentrations of gelatine and of sodium chloride (NaCl) added to the mixture, and how these properties vary over the course of seven days for a.c. frequencies in the range 20-1000 Hz. The results demonstrate that gelatine phantoms can accurately mimic the frequency response properties of the body-electrode system to allow for the controlled testing of new electrode and instrumentation designs.

Control Strategies For DFIG Based Wind Turbine Systems Frequency Regulating

As the energy crisis worsens and global problems intensify, wind power generation has emerged as one of the most successful and fastest-growing alternatives among some of the different mechanisms. The running of a power plant is continually jeopardized by irregular and malfunctioning circumstances. A conceptual implementation of an innovative solution is suggested for the proper output of a wind turbine power system in a wind-solar hybrid microgrid to track frequency fluctuations caused by various load factors and environmental conditions (MG). As a standard PI controller is used to track frequency, it is coupled with a sophisticated fuzzy logic controller to enhance frequency regulation. The frequency response properties of traditional WTs are tested and distinguished with varying loads and wind speeds. It is claimed that as the wind power speed rises, the power output of the device would deteriorate. The simulation shows that frequency modulation is accomplished in the time allocated. Furthermore, the proposed solution can be implemented into day-to-day applications without making any external modifications.

Epitaxial Aluminum Scandium Nitride Super High Frequency Acoustic Resonators

This paper demonstrates super high frequency (SHF) Lamb and surface acoustic wave resonators based on single-crystal orientation Aluminum Scandium Nitride (AlScN) thin films grown on silicon substrates by molecular beam epitaxy (MBE). We report on the experimental frequency response and electromechanical properties of 400 nm-thick crystalline AlScN acoustic resonators with up to 12% Sc/(Sc+Al) ratio. The film thickness is optimized for operation at the SHF range, targeting emerging wireless communication standards, such as 4G LTE/5G. We report on high-performance acoustic devices that take advantage of the crystallinity, and high piezoelectric properties of 400 nm-thick epitaxial AlScN films. Our work presents enhanced effective electromechanical coupling coefficients (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) up to 5.3% and unloaded quality factors (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) of ~192 at 3-10 GHz. However, fabrication challenges due to the high-stress levels of sub-micron AlScN epi-layers grown on Si substrates remain challenging and will be discussed in this paper. [2019-0231].

Inverse Shaper Based Active Vibration Control of Flexible Structures with a Collocated Sensor-Actuator Pair

We propose a new control design for active vibration suppression of flexible structures with a collocated sensor-actuator pair. The proposed controller is based on the inverse form of a well-known input zero vibration (ZV) shaper. The inverse ZV shaper is utilized with a serially interconnected all-pass filter. This way, the appropriate controller frequency response properties for vibration suppression of collocated flexible systems is achieved, when the controller is applied in the positive feedback path. We propose two different cost functions to optimize the parameters of the proposed controller for efficient vibration suppression. The performance of the controller is investigated in both frequency and time domains through the vibration control of a cantilever beam model with a collocated piezoelectric sensor-actuator pair. Furthermore, its performance is compared with a recently improved version of the positive position feedback controller, which is a state-of-the-art work. It is shown via the simulations that the proposed controller suppresses vibrations more efficiently.

Effect of Sintering Temperature on Low Frequency Response Properties of Ba0.6Sr0.4TiO3 Ceramic

Ba0.6Sr0.4TiO3 ceramic was synthesized by the sol-gel method combined with the solidstate reaction. Phase composition and microstructure analyses indicate that pure BST phase with aggregated nanograins can be achieved. The dielectric properties change with sintering temperature, and reach the maximum at suitable temperatures. The highest dielectric constant of 4351 is obtained at 100 Hz for 1 275 ℃ sintered sample that is 2 times greater than that of the original sample, which indicates the dielectric properties can be modulated by grain size and density. The results show that Ba0.6Sr0.4TiO3 is a promising candidate for microwave applications.

A Novel LMMSE-EM Channel Estimator for High Mobility STBC-OFDM System

In time-selective fading channel, the Alamouti orthogonality principle is lost due to the variation of channel from symbol-to-symbol in space–time block-coded orthogonal frequency division multiplexing (STBC-OFDM) system and causes co-channel interference (CCI) effects. To combat the CCI effects, various signal detection schemes have been proposed earlier by assuming that a priori channel state information (CSI) is known to the receiver. However, in practice, the CSI is unknown and therefore accurate estimation of channel is required for efficient signal detection. In this paper, by exploiting circulant properties of the channel frequency response (CFR) autocorrelation matrix [Formula: see text], we propose an efficient low complexity linear-minimum-mean-square-error (LMMSE) estimator. This estimator applies an expectation–maximization (EM) iterative process to reduce the computational complexity significantly. Finally, we compare the proposed LMMSE-EM estimator with conventional least square (LS) and LMMSE estimator in terms of performance and computational complexity. The simulation results show that the proposed LMMSE-EM estimator achieves exactly the same performance as the optimal LMMSE estimator with much lower computational complexity.

카메라 캘리브레이션을 위한 영상의 주파수 특성 기반 스테레오 카메라의 상대적인 회전값 추정

카메라 캘리브레이션을 위한 영상의 주파수 특성 기반 스테레오 카메라의 상대적인 회전값 추정

Lamb Wave Directional Sensing with Piezoelectric Fiber Rosette in Structure Health Monitoring

Directional piezoelectric sensors can detect the Lamb wave propagation direction to locate damage in structural health monitoring (SHM). The directivity of the round piezoelectric fiber is exploited with a 0°/45°/90° rosette configuration to acquire flexural Lamb wave signals. The directional response of the piezoelectric fiber under narrowband tone‐burst excitation is theoretically deduced. Experimental tests are conducted to demonstrate the directivity and the frequency response property of the piezoelectric fiber under different excitation central frequencies in comparison with the MFC, rectangular piezoelectric sheet, and circular piezoelectric disc. Continuous wavelet transform (CWT) is applied to extract the maximum response amplitude information of the acquired Lamb wave signal at a central frequency. Experimental test results indicate that the piezoelectric fiber is capable to be used as a Lamb wave directional sensor than other piezoelectric sensors. A numerical estimation method for the Lamb wave propagation direction is proposed by defining an error function between the theoretical and experimental normalized response amplitude. The proposed method is generally applicable for different rosette configurations. Experimental results validate the accuracy of the proposed estimation method. The research results are significant to design or select the piezoelectric sensor to measure Lamb wave signals.

A Low-Profile Dual-Layer Patch Antenna with a Circular Polarizer Consisting of Dual Semicircular Resonators

In this paper, a circular polarizer comprising dual semicircular split-rings (DSSRs) is presented. By placing it above an elliptical radiator that radiates linearly polarized (LP) waves, dual-layer patch antennas capable of radiating right-hand (RH) or left-hand (LH) circularly polarized (CP) waves are achieved in terms of the different offset direction of the bottom splits of the DSSRs. Because of both the capacitive coupling to the radiator and the degenerate modes existing in the excited DSSRs, the DSSRs collaboratively result in a circularly polarized radiation, successfully converting incident LP waves into CP ones. Simulated results show that the impedance, axial ratio (AR), and gain frequency response of both proposed CP antennas are identical, with a simulated 3-dB AR bandwidth of 72 MHz covering 2.402–2.474 GHz and a gain enhanced by 3.9 dB. The proposed antennas were fabricated and measured, revealing an operational bandwidth of 65 MHz (2.345–2.41 GHz) and a peak gain up to 9 dBi. Moreover, a low profile of 0.063λ0 is maintained. The proposed CP antennas could be as a candidate for wireless target detection applications in terms of their identical frequency response property.

Dynamic evolution of a primary resonance MEMS resonator under prebuckling pattern

This paper analytically investigates the dynamic evolution of the primary frequency response of a prebuckling microbeam-based resonator with $$\hbox {Z}_{2}$$ symmetry. A doubly clamped straight microbeam actuated by two symmetric stationary electrodes is simplified as a time-varying capacitor model for qualitative analysis purpose. Nonlinearities induced by the midplane stretching of the microbeam and the electrostatic force are considered. During solution procedure, electrostatic force holds its original form without any Taylor series expansion, and only one assumption with a small ratio of AC to DC voltage is introduced. The average equation, frequency response, backbone curve and stability condition are determined, respectively, based on the method of multiple scales combined with homotopy concept. Results demonstrate for the first time that the frequency response includes two types of branches, namely low- energy branch and high-energy branch. As the increase ion AC excitation amplitude, both branches close to each other along the backbone curve until they intersect. Further analyses are then performed to investigate the details of the backbone curve and the frequency response equation. Analytical formulas to determine the hardening and softening switches of the frequency response and the intersection condition of the low- and high-energy branches are both deduced and examined in depth. Primary frequency response properties in pull-in and secondary pull-in case are classified and depicted through theoretical predictions via the method of multiple scales and then verified through numerical results via the finite difference method combined with Floquet theory. Finally, a specific case study based on equivalent lumped parameters via Galerkin method is presented. Excellent agreements between theoretical predictions and simulation results illustrate the effectiveness of the whole analyses.

A QCM humidity sensor based on fullerene/graphene oxide nanocomposites with high quality factor

This paper described a quartz crystal microbalance (QCM) humidity sensor based on fullerene (C60)/graphene oxide (GO) nanocomposites. Humidity sensing properties such as the quality factor, frequency response property, response/recovery time, and humidity hysteresis were measured and quantitatively compared with a GO based QCM humidity sensor. The experiments provided evidences that the GO film was viscous even at low relative humidity, which had a large impact on the measurable result of a GO coated QCM humidity sensor. As a result, the proposed sensor showed better performances at quality factor and dynamic response/recovery behavior than the GO based QCM humidity sensor. Based on the admittance analysis and frequency response analysis of the sensors, it was speculated that the introduction of C60 molecules into GO reduced the aggregation of the GO sheets and formed some hydrophobic isolation layers between the GO sheets, which could inhibit the water molecules permeation and maintain the mechanical stiffness of the C60/GO film.