Resonance Frequency Detection Research Articles

Online Mechanical Resonance Frequency Identification Method Based on an Improved Second-Order Generalized Integrator—Frequency-Locked Loop

To address the issue of mechanical resonance frequency detection in dual-inertia servo systems, this paper proposes an online identification method for mechanical resonance frequency using a low-pass filter and cascaded second-order generalized integrator—frequency-locked loop (LPF-CSOGI-FLL). Initially, the cascaded second-order generalized integrator—frequency-locked loop (CSOGI-FLL) is employed to eliminate the interference of direct current (DC) bias in resonance frequency identification. From a dual-stage structural perspective, the first second-order generalized integrator (SOGI-FLL) acts as a band-pass pre-filter to extract the mechanical resonance signal from the signal to be tested. The second SOGI-FLL generates a signal with equal amplitude and frequency to the mechanical resonance and obtains the frequency of the resonance signal through the frequency-locked loop. Subsequently, a low-pass filter (LPF) is applied to the frequency feedback loop of the second-stage SOGI-FLL, effectively reducing the oscillation of the estimated frequency. Finally, combining the CSOGI-FLL with an LPF forms a novel structure, namely, LPF-CSOGI-FLL. The results demonstrate that the proposed method significantly improves the detection accuracy of mechanical resonance frequency under various conditions. Compared to traditional offline techniques, this method overcomes the impact of resonance frequency drift and enhances system stability.

Automatic detection of field line resonance frequencies in the Earth’s plasmasphere

Automatic detection of field line resonance frequencies in the Earth’s plasmasphere

Validation of Photoplethysmography Using a Mobile Phone Application for the Assessment of Heart Rate Variability in the Context of Heart Rate Variability-Biofeedback.

Heart rate variability-biofeedback (HRV-BF) is an effective intervention to reduce stress and anxiety and requires accurate measures of real-time HRV. HRV can be measured through photoplethysmography (PPG) using the camera of a mobile phone. No studies have directly compared HRV-BF supported through PPG against classical electrocardiogram (ECG). The current study aimed to validate PPG HRV measurements during HRV-BF against ECG. Fifty-seven healthy participants (70% women) with a mean (standard deviation) age of 26.70 (9.86) years received HRV-BF in the laboratory. Participants filled out questionnaires and performed five times a 5-minute diaphragmatic breathing exercise at different paces (range, ~6.5 to ~4.5 breaths/min). Four HRV indices obtained through PPG, using the Happitech software development kit, and ECG, using the validated NeXus apparatus, were calculated and compared: RMSSD, pNN50, LFpower, and HFpower. Resonance frequency (i.e., optimal breathing pace) was also compared between methods. All intraclass correlation coefficient values of the five different breathing paces were "near perfect" (>0.90) for all HRV indices: lnRMSSD, lnpNN50, lnLFpower, and lnHFpower. All Bland-Altman analyses (with just three incidental exceptions) showed good interchangeability of PPG- and ECG-derived HRV indices. No systematic evidence for proportional bias was found for any of the HRV indices. In addition, correspondence in resonance frequency detection was good with 76.6% agreement between PPG and ECG. PPG is a potentially reliable and valid method for the assessment of HRV. PPG is a promising replacement of ECG assessment to measure resonance frequency during HRV-BF.

A Novel Microwave Humidity Sensor Based on Resonant Cavity Perturbation Method

This article proposes a novel humidity sensor using a microwave resonant cavity as the sensing device. This sensor comprises a high-quality factor resonant cavity and frequency detection circuits. The working frequency of the resonator is 9.6 GHz, it has the characteristics that the resonance frequency can be adjusted, and it is designed with embedded air guide holes to allow moist air to enter the interior of the resonant cavity. According to the perturbation theory, when humid air is distributed in the resonator’s sensing area, the resonator’s resonant frequency changes according to different relative humidity (RH) levels. Then, the frequency detection circuit is used to detect the resonance frequency change, and the RH level related to the shift in the resonance frequency can be obtained. In order to get more accurate measurement results, a temperature and atmospheric pressure compensation algorithm is introduced to correct the measurement results. Experiments show that the proposed humidity sensor effectively detects humidity in an RH environment of 20%-95%. It has the characteristics of fast detection speed and high stability, which avoids the need to use the conventional detection method of the vector network analyzer.

Passivity Enhancement Strategy of Grid-Connected Inverter System Based on the Adaptive Active Damper

The grid-connected inverter system may be unstable when connected to a weak grid, and installing an active damper as a virtual resistor at the PCC is convenient for stabilizing the system. This article proposes a passivity enhancement strategy for the grid-connected inverter system via the adaptive active damper. Furthermore, the admittances of the grid-connected inverter system with the active damper are derived, and the real parts of the admittances of the whole system have been calculated. And the admittance measurement results obtained by the frequency scanning method approximately match the theoretical results. Additionally, the virtual resistor’s stability region is discussed, the bandwidth of the phase-locked loop is recommended, ensuring the stabilizing effect of the active damper under the weak grid. And the online resonance frequency detection algorithm guarantees the passivity enhancement of the active damper when grid impedance changes. Finally, controller hardware-in-the-loop tests validate the theoretical analysis of passivity enhancement based on the active damper.

A Comparison of Adaptive Ultrasound Reflectometry Calibration Methods for Use in Lubrication Films

Adaptive calibration for ultrasound reflectometry methods used in the detection of lubrication film thickness is of great research interest. This is mainly due to the versatile non-destructive implementation of the technology in industrial applications, allowing for measurements of the lubrication film thickness, which directly relates to the friction, wear, and overall efficiency of the system. This study reviews and compares a curve fitting, extended Kalman filter, and resonance frequency detection adaptive calibration approach. Furthermore, the study compares two different regression models, used for the curve fitting and the extended Kalman filter approach. The study compares the methods and regression models based on both a theoretical and experimental analysis. The experimental analysis is based on data with varying lubrication film thickness. The lubrication film thickness is varied such that the resonance frequency is both detectable and non-detectable within the ultrasound transducer bandwidth. It is found that all three methods give results very similar to those achieved through manual calibration. However, since the extended Kalman filter approach is the only method that allows for continuous calibration, this method is found to have the greatest potential of the methods compared.

Structural Design and Optimization of a Resonant Micro-Accelerometer Based on Electrostatic Stiffness by an Improved Differential Evolution Algorithm.

This study designed an in-plane resonant micro-accelerometer based on electrostatic stiffness. The accelerometer adopts a one-piece proof mass structure; two double-folded beam resonators are symmetrically distributed inside the proof mass, and only one displacement is introduced under the action of acceleration, which reduces the influence of processing errors on the performance of the accelerometer. The two resonators form a differential structure that can diminish the impact of common-mode errors. This accelerometer realizes the separation of the introduction of electrostatic stiffness and the detection of resonant frequency, which is conducive to the decoupling of accelerometer signals. An improved differential evolution algorithm was developed to optimize the scale factor of the accelerometer. Through the final elimination principle, excellent individuals are preserved, and the most suitable parameters are allocated to the surviving individuals to stimulate the offspring to find the globally optimal ability. The algorithm not only maintains the global optimality but also reduces the computational complexity of the algorithm and deterministically realizes the optimization of the accelerometer scale factor. The electrostatic stiffness resonant micro-accelerometer was fabricated by deep dry silicon-on-glass (DDSOG) technology. The unloaded resonant frequency of the accelerometer resonant beam was between 24 and 26 kHz, and the scale factor of the packaged accelerometer was between 54 and 59 Hz/g. The average error between the optimization result and the actual scale factor was 7.03%. The experimental results verified the rationality of the structural design.

Reduction of the Fresnel Reflection Effect in the Hybrid PBF-PMF Resonator for RFOG

This paper proposes a fiber length matching method that reduces the influence of Fresnel reflection in a hybrid fiber resonator for the resonant fiber optic gyroscope (RFOG). A transfer model of the fused points inside and outside the fiber resonator is first built. Using the transfer model, we find that when the optical path ratio of the photonic bandgap fiber (PBF) is half of the entire fiber ring, the secondary resonant frequency points caused by Fresnel reflection coincide with the main resonant frequency points of the resonator, and the resonant depth becomes equal. The simulation result of the resonance curve demonstrates this theory. To validate our deduction, two hybrid resonators are obtained with PBF and polarization-maintaining fiber (PMF). The optical path ratio of one resonator is 0.5, and the other is approximately 0.2. The results show that after the fiber length matching, the resonance depth difference of the resonator is less than 1.8%, which is the best reported index of a fused PBF fiber resonator to our knowledge and 24.9% less than that of the other resonator. The experimental result also shows that the total loss of the two PBF-PMF fused points is less than 1.3 dB. Our scheme effectively reduces the effect of the Fresnel reflection at the fusing point in the PBF-PMF resonator, which is expected to achieve accurate resonance frequency detection of the RFOG.

A novel technique for online resonance frequencies monitoring based on wavelet transform for grid-connected solar inverters

Photovoltaic systems are often connected to the main grid through multiple paralleled inverters to support and to reinforce the power generation into the grid. This interconnection can be affected by resonance phenomena that may be introduced by the excitation of passive filters and lead either to small oscillations that can deteriorate the power quality or large oscillations that can affect the whole system reliability. Therefore, early detection of such oscillations is essential to keep a resilient operation. This paper proposes a novel algorithm for an online resonance frequency monitoring based on wavelet transform (RFM-WT) that can perform fast detection of undesired resonance frequencies. The RFM-WT is performed through two steps. The first step consists in decomposing each inverter output current into different signals using the wavelet transform. This allows separating the different frequencies that exist in the inverter output current. The second step allows estimating the frequencies from the signals obtained in the first step. Accordingly, a comprehensive approach describing the design of the proposed monitoring algorithm is presented. Its effectiveness is compared to the classical PLL algorithm. Unlike the PLL algorithm, the proposed technique is easy to implement and doesn't require regulators’ parameters design and configuration. The simulations and experiments proved that the algorithm can accurately locate the resonance frequencies in inverters output currents. Thus, its robustness was validated through load variation and transition from grid- connected to islanded mode.

Can HRV Biofeedback Improve Short-Term Effort Recovery? Implications for Intermittent Load Sports

As intensity and physical demands continue to rise in sport competition, faster and better recovery becomes essential. The aim of this study was to assess the effects of HRV biofeedback (HRVB) while recovering from a submaximal aerobic exercise. Ten physically-active graduate students participated in the study, which was conducted in four sessions: exercise with free-breathing recovery, first resonance frequency (RF) detection, second RF detection, and exercise applying HRVB during recovery. Measurements included time spent running and recovering, HRV parameters, and recovery/exertion perceptions. The results indicate that using HRVB during recovery improves cardiac variability (RRmean, SDNN, RMSSD and LF; p < 0.01). HRVB also lowers recovery time (p < 0.05) and seems to be improving the perception of recovery (p = 0.087). Moreover, time spent exercising (p < 0.01) and perceived physical exertion (p < 0.05) were higher when applying HRVB. The improvement in the psychophysiological adaptation after intensive aerobic exercise provided by the HRVB is a valuable benefit, not only for competition-driven athletes, but also for the general population.

Auto-Resonant Detection Method for Optimized ZVS Operation in IPT Systems With Wide Variation of Magnetic Coupling and Load

In wireless charging systems, the H-bridge converter's switching frequency is set close to the system's natural resonance for achieving optimized zero voltage switching (ZVS). Variations to the system's natural resonance are commonly tracked by following the changes in the resonant current's polarity, i.e., current zero-crossings. The main implementation challenge is accounting for the time delay between the real monitored current and the final resulting switches’ commutations. This becomes critical at high switching frequencies, particularly when the magnetic coupling and loading vary widely. This paper proposes an auto-resonant detection method that continuously ensures optimized ZVS turn-on with the minimal circulating current over the operable range of magnetic coupling and load. The suggested implementation provides two split variable references for the resonant frequency detection, which adaptatively compensate for the propagation delay based on the resonant current slope. The auto-resonant scheme is benchmarked against the commonly employed method with fixed current detection references. The results highlight the auto-resonant strategy's advantages, namely extended operable range, wider ZVS turn-on region, ease start-up, and improved DC-to-DC efficiency. The auto-resonant features and functionality are verified experimentally with a 200 W low-voltage e-bike wireless charger. Finally, the benefits of the presented method are analytically explored for high-power applications by considering the H-bridge semiconductor losses of a state-of-art 50 kW wireless charging system.

Detection of mechanical resonance frequencies for interior permanent magnet synchronous motor servo drives based on wavelet multiresolution filter

To realise the resonant characteristics of motor drive system, a wavelet multiresolution filter (WMF)-based scheme is proposed in this study to perform the detection of the mechanical resonant frequencies for interior permanent magnet synchronous motor servo drives. In a conventional motor drive system, the compliance in the coupling between motor and load may cause resonance. Moreover, the parasitic torque ripples resulting from the harmonics of a pulse-width modulation inverter may excite mechanical vibrations. In the proposed scheme, the localisation analysis of signal can be completed with the WMF at any time and frequency domains for the extraction of resonant frequencies. Then, a band-pass filter is applied to perform the frequency sweeping for the detection of resonant frequencies. In the final stage, the signal smoothing is implemented with the calculation of absolute and average values. To verify the effectiveness of the proposed resonant-frequency detection scheme using the WMF, some experimental results at different rotor speed and load conditions are provided. In addition, a two-channel dynamic signal analyser is also adopted in the experimentation for the comparison of resonant-frequency detection.

Applicability of impulse excitation technique as a tool to characterize the elastic properties of pharmaceutical tablets: Experimental and numerical study.

Elastic properties are of particular interest during the development of tablets especially for the definition of the formulation and of the process parameters. Impulse excitation, which is used in several industrial fields to determine elastic properties of materials, is presented in this article as a new fast and relatively cheap technology for the determination of elastic constants of pharmaceutical tablets. This technique is based on the detection of the natural resonance frequencies of solids. It was found in the present work that, for tablets obtained using different products under different compaction pressures, it was possible to detect clearly at least 3 resonance frequencies. Moreover, the shape of the resonance peaks obtained in the spectrum could be a sign of the viscoelastic nature of the tablet. With the two first resonance frequencies, it was possible, under the assumption of isotropy, to calculate Young's modulus and Poisson's ratio for each tablet using the methodology presented in the norm ASTM E1876-01. The values obtained were found independent of the tablet size as expected, and were consistent with those presented in the literature using other methodologies. Moreover, using FEM simulation, it was found that the difference between the experimental value of the third resonance frequency and the value obtained numerically was well correlated with the expected anisotropy of the tablet. Impulse excitation could thus be an interesting methodology to study tablet anisotropy.

Application of principal component analysis method for micro-resonator weak resonant signal detection.

The characteristic of weak resonant signal output by an electrothermally excited microresonator is analyzed, and the principal component analysis (PCA) method is proposed and applied in the resonant frequency detection of the output weak signal by separating the noises. Simulation on weak resonant signals under different levels of noises and different quality factors of the resonator was conducted after the influence of the data selection window width and the principal component number on detection results was analyzed. Finally, the experiment platform was built, and the output signal of the sensor sample was used to verify the detection effect of the proposed PCA method. Simulation and experiment results show that the proposed PCA method could accurately obtain the resonant frequency compared with the resonant frequency obtained by the smoothing filter and Lorentzian fitting method.

Improvement of shale gas reservoir based on plasma pulse shock and frequency resonance technology

A shale gas reservoir improvement equipment applied to shale gas stimulation was developed. The device mainly includes ground control system, energy storage charging system, resonance frequency detection system, discharge switch and discharge electrode. The shale gas reservoir is improved by plasma pulse shock and frequency resonance technology. The electron density distribution at different time of the switch was simulated, and the waveform of single discharge and repetitive pulse discharge of the electrode were measured. It is shown that the electron density distribution at different time is consistent with Townsend discharge and streamer theory. And the frequency range of discharge electrode is about 0–60 Hz, meanwhile the stable discharge time is about 1 h. Furthermore, the resonance excitation can significantly improve the crack percentage and volume of shale samples calculated from porosity curve which is obtained through CT-Scan technology, also the permeability reveals an increasing trend in different directions. The results indicate that the present research might have potential application in the field of shale gas reservoir.

Measurements of Density and Sound Speed in Mixtures Relevant to Supercritical CO2 Cycles

Abstract The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO2) power cycles. Direct-fired sCO2 cycles are a promising technology for the future power generation systems. The working fluid of sCO2 cycles will be near and above critical point of CO2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 °C. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixture properties in the literature are limited which is necessary to develop high-fidelity design tools for sCO2 power cycles. We measured the density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell was used for the density measurements. Sound speed was measured by resonant frequency detection using an external speaker and a piezoelectric pressure sensor. Mixtures studied in this work include carbon dioxide, methane, oxygen, and water vapor. Properties of pure CO2 were measured to show the validity of our technique. Compositions were selected to be close to frozen mixtures at the inlet, mid-progress, and exhaust conditions of a model sCO2 combustor in the previous numerical simulation work. Corresponding reaction progress variables (RPV) were RPV = 0, 0.5, and 1. Temperature and pressure conditions of experiments are 310–450 K and 0–150 bar. In our study, density and sound speed from the NIST REFPROP database agree with experimental measurements within the range of our measurement uncertainties.

Differential Ground-Based Radar Interferometry for Slope and Civil Structures Monitoring: Two Case Studies of Landslide and Bridge

Ground-based radar interferometry, which can be specifically classified as ground-based synthetic aperture radar (GB-SAR) and ground-based real aperture radar (GB-RAR), was applied to monitor the Liusha Peninsula landslide and Baishazhou Yangtze River Bridge. The GB-SAR technique enabled us to obtain the daily displacement evolution of the landslide, with a maximum cumulative displacement of 20 mm in the 13-day observation period. The virtual reality-based panoramic technology (VRP) was introduced to illustrate the displacement evolutions intuitively and facilitate the following web-based panoramic image browsing. We applied GB-RAR to extract the operational modes of the large bridge and compared them with the global positioning system (GPS) measurement. Through full-scale test and time-frequency result analysis from two totally different monitoring methods, this paper emphasized the 3-D display potentiality by combining the GB-SAR results with VRP, and focused on the detection of multi-order resonance frequencies, as well as the configure improvement of ground-based radars in bridge health monitoring.

Detection of resonance frequency of both the internal defects of concrete and the laser head of a laser Doppler vibrometer by spatial spectral entropy for noncontact acoustic inspection

In order to detect internal defects of concrete, we have studied noncontact non-destructive acoustic inspection and have detected and visualized internal defects using acoustic vibration excitation on the target surface by aerial sound waves and two-dimensional vibration velocity distribution by a laser Doppler vibrometer. Because a high sensitive scanning laser Doppler vibrometer (SLDV) is used, as the sound pressure increases, the reverberation of sound waves from the surroundings may cause resonance in the galvano mirror system of the laser head of the SLDV. For real concrete structures, for example a tunnel inner wall (distance about 5–10 m), there was no problem because the sound pressure was not so large. In the case of a viaduct, it was measured remotely (about 30 m), but because it is surrounded released space, the influence was not so large. However, in a closed space surrounded by concrete, the sound pressure needs to be increased as the distance increases, and the influence of the reverberation from the surroundings on a laser head cannot be ignored. Therefore, we propose a method to solve them, and at the same time, detect the resonance frequency of internal defects and improve the visualization of the defect.

Site-Specific Relationships between Bedrock Depth and HVSR Fundamental Resonance Frequency Using KiK-NET Data from Japan

It is commonly accepted that the horizontal-to-vertical spectral ratio (HVSR) technique enables the detection of the fundamental resonance frequency ($$f_{\text{HVSR}}$$) of a given site. The utility of this $$f_{\text{HVSR}}$$ is analyzed using the nonlinear regression relationships between $$f_{\text{HVSR}}$$ and bedrock depth ($$h$$). The derived relationships are mostly site-specific, so that the present paper consists of two main parts. The first is a literature review for the available empirical relationships between $$f_{\text{HVSR}}$$ and $$h$$. The aim of this part is to highlight the practical limitations of these established relationships and to make fair comparisons. The second is to generate new relationships, taking advantage of the very wide range of available lithological, geophysical, and geotechnical borehole drilling data of the 697 KiK-NET seismic stations in Japan. For this purpose, HVSR are calculated using 10,000 weak earthquakes or linear events recorded at KiK-NET stations to determine the $$f_{\text{HVSR}}$$ and correlate it with the corresponding $$h$$. The overlying layers/bedrock interface falling within sedimentary, igneous, or metamorphic layers significantly affect the derived frequency–depth relationships. In addition, these relationships are strongly reproduced by the $$V_{\text{p}} /V_{\text{s}}$$ ratio of the bedrock in the range of 1.6–2.2. Interestingly, it is found that $$f_{\text{HVSR}}$$ less than 1 Hz corresponding to $$h$$ more than 100 m leads the trend of the overall frequency–depth relationship.

Fracture Network Imaging on Rock Slope Instabilities Using Resonance Mode Analysis

AbstractWe performed modal analysis using frequency domain decomposition of ambient seismic vibration data collected on large rock slope instabilities. This technique enables a robust detection of resonance frequencies and provides the corresponding mode shape vectors. We applied the technique to synthetic and field data sets acquired by seismometer arrays on two rock instabilities in Switzerland. We found that, at the fundamental mode, the entire instability vibrates in‐phase with the dominant mode shape vector oriented perpendicular to dominant fracture systems. At higher frequencies, different compartments of the instability resonate antiphase. Therefore, delineating the zero crossings between the phases allows dominant fractures to be efficiently mapped. Approximately 1 hr of ambient vibration data suffices to apply the method successfully. The method also potentially detects hidden fractures that cannot be observed by geological field mapping. In addition, this approach combines classic amplification and polarization analysis into one technique, simplifying data processing efforts.