Resonant System Research Articles

Piezo stack energy harvesters with protection components for railway applications

Piezo stack energy harvesting from railway vibrations shows substantial potential for powering wireless sensor networks responsible for monitoring railway infrastructure. Nevertheless, assuring the safety and durability of these energy harvesters in the condition of the dynamically fluctuating railway vibrations remains a considerable challenge. In this paper, we present two innovative protection methods designed for piezo stack energy harvesters with a frequency up-conversion mechanism. These methods involve the incorporation of ring-type and circular stoppers within the resonant system and the utilisation of proposed impact protection components within the impact system. Two distinct harvesters incorporating the proposed protection components, Harvester Types I and II, are designed to align with their respective operating acceleration targets, which are determined based on the amplitudes of railway vibration acceleration. Finite element modelling is used to guide the design process, involving the evaluation and selection of various design parameters aligned with the acceleration target and stress limits. The protection mechanisms’ effectiveness and impact on energy harvesting performance have been validated through experimental testing under measured rail vibration signals, and their performance has been further assessed through stress analyses. Harvester Type I operates seamlessly within a 5 g threshold, effectively mitigating the increase in maximum output acceleration and stress beyond this limit. In contrast, Harvester Type II efficiently dissipates excess energy, enabling the harvester to operate at a 15 g acceleration while reducing the rate of acceleration and stress growth. The results demonstrate that both proposed harvesters provide effective protection from unexpected railway vibration overloads. This research makes a significant impact on the practical, real-world implementation of piezo stack energy harvesters operating within the dynamic environment of railway vibrations.

Multi-mechanical frequency locking mechanism and robustness analysis of MDOF coupled resonator

Mechanical frequency locking can overcome the dependence of peak frequency on the driving amplitude and improve the frequency stability in nonlinear resonant systems. Most research focuses on the single mechanical frequency locking phenomenon, but few studies focus on multi-mechanical frequency locking phenomenon. In this study, the multi-mechanical frequency locking mechanism and robustness analysis of the peak frequency is proposed through multi-mode coupled vibration. Firstly, a multi-degree-of-freedom (MDOF) coupled resonator consisting of a low-frequency resonant element and multiple high-frequency resonant elements is designed, and the vibration energy of the resonant system can be transferred from the low-frequency resonant element driven by a harmonic excitation to the high-frequency resonant elements via the 1:3 internal resonance. Through perturbation and bifurcation analysis, the nonlinear dynamic behaviors of MDOF coupled resonator are analyzed in detail. It is found that the peak frequency of the low-frequency resonant element can remain stable in multiple drive intervals, leading to multi-mechanical frequency locking phenomenon. Then, a 3-DOF magnetic coupled resonant system is experimentally designed to demonstrate the physical conditions and influencing factors of the double mechanical frequency locking phenomenon. Typically, introducing external disturbances, the frequency locking is experimentally demonstrated to improve the robustness of peak frequency. The experimental results show that when the mechanical frequency locking phenomenon occurs, the influence of small external noise disturbance on the peak frequency can be ignored, which greatly improves the frequency stability of nonlinear resonant systems.

Dynamic analysis of multi-DOF acoustic resonant system involving highly viscous fluids based on fluid-structure interaction

This paper investigates the dynamic characteristics of a multi-degree-of-freedom (multi-DOF) acoustic resonant system involving highly viscous fluids. First, a fluid-structure interaction (FSI) model is established to describe the interaction between the multi-DOF acoustic resonant system and the two-phase fluids, and then the effects of various excitation parameters on the dynamic response of the coupled system are studied. Under the influence of vertical acoustic vibration, the fluid in the container undergoes violent and irregular motions, which leads to a decrease and fluctuation in the equivalent mass of the fluid. The reduction in fluid equivalent mass causes the excitation frequency to deviate from the natural frequency of the multi-DOF acoustic resonant system, thus significantly reducing the dynamic response of the coupled system. Furthermore, the fluctuation of the fluid equivalent mass induces a quasi-periodic motion pattern of the acoustic resonant system. Although increasing the excitation amplitude can effectively increase the dynamic response of the coupled system, it can also increase the fluctuation level of the dynamic response to a certain extent. By appropriately increasing the excitation frequency, the coupled system can operate at a new resonant frequency, thereby reducing the influence of fluid motion on the dynamic response of the system.

Enhancing rational approximation of wideband resonant MIMO systems with frequency-domain data

Vector Fitting (VF) is a successful methodology for both time and frequency domain estimation of dynamic systems. These algorithms have gained popularity as a system identification tool due to their ability to provide a practical procedure for accurately approximating the measured frequency response behavior of complex and highly resonant dynamic systems using rational models. Instrumental Variable (IV) techniques can also be added to the VF algorithm to enhance the optimality of the solutions in the presence of measurement noise. In this context, this paper presents a multiple-input multiple-output (MIMO) generalization of instrumental variable (IV-)VF. The proposed algorithm can be applied to accurately estimating models formed by either continuous- or discrete-time rational basis functions (RBFs). We show that such a generalization preserves the main implementation features observed in Standard VF, but with improved optimality property for its solutions. Additionally, in order to alleviate convergence problems that may arise from the fixed high-frequency normalization, we also present in this paper how to incorporate in the proposed IV-VF method the relaxed formulation found in standard VF for both the continuous and discrete-time cases. The resulting MIMO IV-VF algorithm can be easily understood by VF users, and its applicability is discussed by using an estimation case study with two power system pieces of equipment (an 88 kV Transformer and a 550 kV Instrument Transformer) for which actual frequency domain measurements were collected in the field. It is shown that the proposed algorithm significantly improves the modeling accuracy when compared to standard VF algorithms.

The investigation of the interaction between fluorescent carbon dots labeling silk fibroin using a fluorescence microscope–surface plasmon resonance system

The use of fluorescent carbon dots (CDs) as highly precise biolabeling probes has been widespread in the fields of live cell imaging and protein labeling due to their small size and excellent photoluminescence ability to accurately target specific molecules with surface chemical properties. However, there was a lack of research on the interaction between CDs and labeled molecules. In this work, we presented a novel investigation strategy, the fluorescence microscopy-surface plasmon resonance (FM-SPR) system, which combined the use of fluorescence microscopy and wavelength modulation surface plasmon resonance to study the interaction between CDs and labeled molecules in real-time. Using this system, simultaneously recorded the SPR signals and the fluorescence images on the surface of the FM-SPR sensor chip. We observed the dynamic curve and fluorescence images of the interaction between green emissive nitrogen-doped carbon dots (N-CDs) and silk fibroin (SF) in real-time. The kinetic parameters, the quantitative analysis, and the investigation of the binding could be achieved. The results showed a strong linear relationship between the change in SPR signals and the concentration of N-CDs, with a linear coefficient of 0.99913. The linear detection range was 2.5 μg/mL–100 μg/mL, and the real lowest detection limit reached 0.5 μg/mL. Additionally, the green fluorescence points in the imaging region on the FM-SPR sensor chip increased with the concentration of N-CDs, which was consistent with the change in SPR signals. Using this system we also acquired the association rate and dissociation rate of N-CDs to SF which were 2.65 × 10−5/s and 1.52 × 10−5/s, respectively. This demonstrated the effectiveness of our method in quantitatively analyzing SF labeled with N-CDs.

INVESTIGATION OF THE CYLINDRICAL RESONATING CAVITY EFFECT ON A JET’S NEAR ACOUSTIC FIELD IN THE TWO-CHANNEL SYSTEM

Numerical gas flow modeling in the two-channel resonance system path of ITAM SB RAS is carried out. Numerical simulation of a nonstationary acoustic-convective flow was carried out using the Ansys Fluent software package in a three-dimensional formulation. As a result of the simulation, the gas-dynamic characteristics of the flow in the system central part, where a supersonic under-expanded jet is formed, are obtained. The analysis of pressure distributions in the first barrel of the jet near field, as well as inside its structure under the conditions of a two-channel system, is carried out. Six points in the near field of the jet were selected for the study. Taking into account the unsteadiness of the flow in the resonant system path, the studied points record the fluctuations of the formed flow and the change in the jet structure. The spectral composition is estimated near and inside the jet undisturbed by the resonator and a comparison with the spectrum of the resonant system is presented. The possibility of influencing the jet structure and acoustic characteristics near the jet using a resonator is shown.

Secular evolution of resonant planets in the coplanar case

Aims. We study the secular evolution of two planets in mutual deep mean-motion resonance (MMR) in the planar elliptic three-body problem framework for different mass ratios. We do not consider any restriction in the eccentricity of the inner planet e1 or in the eccentricity of the outer planet e2. Methods. The method we used is based on a semi-analytical model that consists of calculating the averaged resonant disturbing function numerically. It is assumed for this that all the orbital elements (except for the mean longitudes) of both planets are constant on the resonant timescale. In order to obtain the secular evolution inside the MMR, we make use of the adiabatic invariance principle, assuming a zero-amplitude resonant libration. We constructed two phase portraits, called the ℋ1 and ℋ2 surfaces, in the three-dimensional spaces (e1, Δϖ, σ) and (e2, Δϖ, σ), where Δϖ is the difference between the planetary longitude of perihelia and σ is the critical angle. These surfaces, which are related through the angular moment conservation, allow us to find the apsidal corotation resonances (ACRs) and to predict the secular evolution of e1, e2, Δϖ, and σ (libration center). Results. While studying the 1:1, 2:1, 3:1, and 3:2 MMR, we found that large excursions in eccentricity can exist in some particular cases. We compared the secular variations of e1, e2, Δϖ, and σ predicted by the model with a numerical integration of the exact equations of motion for different mass ratios. We obtained good matches. Finally, the model was applied to study the secular evolution of the resonant exoplanet systems HD 73526 and HD 31527. They both have a pair of planets and are very close to the deep MMR condition. In the first system, we found that the pair of planets that constitutes the system evolves in a symmetrical ACR, whereas in the second system, we found that planets c and d, which are in an unusual 16:3 MMR, are close to an ACR, but outside its dynamical region, where Δϖ circulates.

Modeling and analysis of magnetic resonance wireless transmission coil

Wireless transmission technology is a new type of power transmission technology with electric and magnetic fields as the medium. It has more advantages in transmission direction, transmission characteristics, security, and penetration. The model of a magnetically coupled resonant radio energy transmission system is designed. The main parameters such as resonance frequency and mutual inductance are considered comprehensively. The model is designed using the equivalent topological circuit structure of mutual inductance coupling. The equivalent parameters in the circuit topology can be affected by setting the size of the coil, the distance between the coils, the excitation size, and the high frequency. The structure parameters of the whole system are modeled and calculated by the Ansoft Maxwell software. At the same time, the influence on the power and efficiency of wireless power transmission is explored by several factors such as the coil diameter, the distance between the transmitting end and the receiving end, and the resonance frequency of the system, so as to achieve the purpose of verifying the technical characteristics of wireless power transmission. The key factors that may affect the transmission efficiency and power of the system are analyzed in detail by deriving the calculation model of transmission efficiency and power.

Development of a research cryostat for direct thermoacoustic cooling and conversion of hydrogen

Hydrogen thermoacoustics is a relatively unexplored but promising topic for development of new cryocoolers and hydrogen liquefaction. This paper describes a new research cryostat designed to investigate hydrogen as a working fluid in thermoacoustic systems. The cryostat is a modular, turbo-molecular pump driven, vacuum chamber with a 4.2 K pulse-tube cryocooler capable of 45 W of cooling at 50 K. Using this cryostat, a feasibility study of direct thermoacoustic cooling with ortho-parahydrogen conversion is initiated. An acoustic resonator system is designed to have the fundamental acoustic mode excited via imposed temperature gradient in a porous stack between the ambient environment and cold bar connected to the cryocooler. The generated acoustic waves transfer heat inside another porous stack to produce a refrigeration effect at cryogenic temperatures. In addition, the regenerator solid matrix will be catalyzed for ortho-parahydrogen conversion to demonstrate a novel combination of cooling and conversion of cryogenic hydrogen in a single device. Design, construction, and performance of the cryostat and modelling results for one thermoacoustic system are reported.

On the τf measurement of microwave dielectric ceramics

As a key parameter of microwave dielectric ceramics, the temperature coefficient of resonant frequency (τf) determines the temperature stability of microwave dielectric ceramics and relevant microwave devices. The τf of a microwave dielectric ceramic is typically calculated from the measured resonant frequencies of the system, consisting of the ceramic sample plus other dielectric elements, at two temperatures ∼60 – 70 °C apart. This measurement process assumes that τf is a constant; however, it is generally temperature-dependent based on both theoretical and experimental results. Furthermore, the as-measured τf is actually the τf of the dielectric resonator system, which is different from that of the sample itself. In this paper, these two overlooked problems during τf measurement are discussed in detail, and suggestions are given to avoid their possible misleading consequences and thus ensure the reliability of τf measurements.

Very high cycle fatigue assessment of thermoplastic-based hybrid fiber metal laminate by using a high-frequency resonant testing system

The prolonged fatigue lifetime of fiber metal laminates (FML) compared to monolithic metals is a key aspect for safety-relevant components, where detailed knowledge about the fatigue properties up to the very high cycle fatigue (VHCF) regime is necessary. For thermoplastic-based FMLs, offering formability, recyclability, and mass production due to short consolidation cycle times, this knowledge needs to be established.In this study, FML containing AA6082 sheets and unidirectional glass and carbon fiber-reinforced polyamide 6 was investigated. Fatigue tests up to max. 109 cycles were conducted on a servo-hydraulic and a high-frequency resonant fatigue testing system with frequencies of 10 Hz and 1,000 Hz. Frequency-induced self-heating was evaluated and limited using air-cooling to maintain the matrix properties. Fatigue progress was monitored through high-speed optical deformation analysis.Compared to HCF loads, VHCF loads lead to reduced crack and delamination occurrence. Changes in microstructure are dominated by singular crack initiation and propagation within the aluminum. The FML’s S-N curve shows a significant flattening from the HCF to the VHCF regime, simplifying the predictability of the fatigue life. By using post-stretching, the VHCF strength can be increased by over 60 %, making this thermoplastic-based FML a considerable competitor in the field of FML.

Design of a high sensitivity and wide range angular rate sensor based on exceptional surface

Abstract It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point, the sensitivity can in theory be significantly amplified at low angular rate. However, in fact, the exceptional point is easily disturbed by external environmental variables, which means that it depends on harsh experimental environment and strong control ability, so it is difficult to move towards practical application. Here, we propose a new angular rate sensor structure based on exceptional surface, which has the advantages of high sensitivity and high robustness. The system consists of two fiber-optic ring resonators and two optical loop mirrors, and one of the resonators contains a variable ratio coupler and a variable optical attenuator. We theoretically analyze the system response, and the effects of phase and coupling ratio on the system response. Finally, compared with the conventional resonant gyro, the sensitivity of this exceptional surface angular rate sensor can be improved by about 300 times at low speed. In addition, by changing the loss coefficient in the ring resonator, we can achieve a wide range of 600 rad/s. This scheme provides a new approach for the development of ultra-high sensitivity and wide range angular rate sensors in the future.

Research and Design of the RF Cavity for an 11 MeV Superconducting Cyclotron

In contrast to the room temperature cyclotron, the superconducting cyclotron’s high operational magnetic field and small extraction radius lead to a magnet design with a reduced radius. This limits the space available for the RF cavity in the 11 MeV superconducting cyclotron, necessitating a more compact RF cavity design. By using the transmission line theory, the complex structure of the quarter-wavelength coaxial cavity can be represented as a microwave circuit. Through relevant theoretical analytical formulas, equivalent circuit parameters can be derived. The resonant frequency of the RF cavity is then determined using the equivalent circuit method. The optimization of the RF cavity structure was achieved by creating a numerical model and conducting finite element numerical calculations on the high-frequency resonant system. The comparative results between the equivalent circuit and numerical calculations indicate that the frequency error remains within 0.1%, validating the compact RF cavity design. A multiple linear regression analysis facilitates the prediction of resonance frequency across various parameter variables. By analyzing the fitting formula, RF cavity machining error requirements are established, ensuring a prediction error within 1%, thus meeting engineering design criteria.

Temperature Self-Compensating Intelligent Wireless Measuring Contact Lens for Quantitative Intraocular Pressure Monitoring.

Flexible bioelectronic devices that can perform real-time and accurate intraocular pressure (IOP) monitoring in both clinical and home settings hold significant implications for the diagnosis and treatment of glaucoma, yet they face challenges due to the open physiological environment of the ocular. Herein, we develop an intelligent wireless measuring contact lens (WMCL) incorporating a dual inductor-capacitor-resistor (LCR) resonant system to achieve temperature self-compensation for quantitative IOP monitoring in different application environments. The WMCL utilizes a compact circuitry design, which enables the integration of low-frequency and high-frequency resonators within a single layer of a sensing circuit without causing visual impairment. Mechanically guided microscale 3D encapsulation strategy combined with flexible circuit printing techniques achieves the surface-adaptive fabrication of the WMCL. The specific design of frequency separation imparts distinct temperature response characteristics to the dual resonators, and the linear combination of the dual resonators can eliminate the impact of temperature variations on measurement accuracy. The WMCL demonstrates outstanding sensitivity and linearity in monitoring the IOP of porcine eyes in vitro while maintaining satisfactory measurement accuracy even with internal temperature variations exceeding 10 °C. Overcoming the impact of temperature variations on IOP monitoring from the system level, the WMCL showcases immense potential as the next generation of all-weather IOP monitoring devices.

On the reproducibility of electron-beam lithographic fabrication of photonic nanostructures.

Photonic nanostructures such as gratings and ring resonators have become ubiquitous building blocks in Photonics. For example, they are used in filters, they resonantly enhance signals and act as grating couplers. Much research effort is invested in using such structures to create novel functionalities, which often employs electron-beam lithography. An intrinsic issue in this field is the ability to accurately achieve a specific operating wavelength, especially for resonant systems, because nanometer-scale variations in feature size may easily detune the device. Here, we examine some of the key fabrication steps and show how to improve the reproducibility of fabricating wavelength scale photonic nanostructures. We use guided mode resonance grating sensors as our exemplar and find that the exposure condition and the development process significantly affect the consistency of the resonance wavelength, amplitude, and sensitivity of the sensor. By having careful control over these factors, we can achieve consistent performance for all the sensors studied, with less than 10% variation in their resonance behaviors. These investigations provide useful guidelines for fabricating nanostructures more reliably and to achieve a higher success rate in exploratory experiments.

Plasmonic nanosensor and pressure-induced transparency based on coupled resonator in a nanoscale system.

Plasmonic nanosensors and the dynamic control of light fields are of the utmost significance in the field of micro- and nano-optics. Here, our study successfully demonstrates a plasmonic nanosensor in a compact coupled resonator system and obtains the pressure-induced transparency phenomenon for the first time to our knowledge. The proposed structure consists of a groove and slot cavity coupled in the metal-insulator-metal waveguide, whose mechanical and optical characteristics are investigated in detail using the finite element method. Simulation results show that we construct a quantitative relationship among the resonator deformation quantity, the applied pressure variation, and the resonant wavelength offset by combining the mechanical and optical properties of the proposed system. The physical features contribute to highly efficient plasmonic nanosensors for refractive index and optical pressure sensing with sensitivity of 1800 nm/RIU and 7.4 nm/MPa, respectively. Furthermore, the light waves are coupled to each other in the resonators, which are detuned due to the presence of pressure, resulting in the pressure-induced transparency phenomenon. It is noteworthy to emphasize that, unlike previously published works, our numerical results take structural deformation-induced changes in optical properties into account, making them trustworthy and practical. The proposed structure introduces a novel, to the best of our knowledge, approach for the dynamic control of light fields and has special properties that can be utilized for the realization of various integrated components.

Pore Water Conversion Characteristics during Methane Hydrate Formation: Insights from Low-Field Nuclear Magnetic Resonance (NMR) Measurements

Understanding the conversion characteristics of pore water is crucial for investigating the mechanism of hydrate accumulation; however, research in this area remains limited. This study conducted methane hydrate formation experiments in unconsolidated sands using an in-house low-field nuclear magnetic resonance (NMR) system. It focused on pore water conversion characteristics and influencing factors such as initial water saturation and sand particle sizes. Results show that methane hydrate formation enhances the homogeneity of the effective pore structure within sand samples. The conversion rate of pore water is significantly influenced by differences in heat and mass transfer capacity, decreasing as initial water saturation and sand size increase. Pore water cannot be fully converted into hydrates in unconsolidated sands. The final conversion ratio of pore water in water-poor sand samples nears 97%, while in water-rich sand samples, it is only 65.80%. Sand particle size variation has a negligible impact on the final conversion ratio of pore water, with ratios exceeding 94% across different particle sizes, differing by less than 3%.

Development and possible applications of tunable elements based on composite materials

This work is devoted to the synthesis of nano-sized weakly agglomerated magnetic particles with different crystal structures, which were used in the development of nonlinear composite structures, in particular, nonlinear resonant microwave elements, left-handed media, and nonlinear magnetoelectric systems.

Parity-time symmetry enabled ultra-efficient nonlinear optical signal processing

Nonlinear optical signal processing (NOSP) has the potential to significantly improve the throughput, flexibility, and cost-efficiency of optical communication networks by exploiting the intrinsically ultrafast optical nonlinear wave mixing. It can support digital signal processing speeds of up to terabits per second, far exceeding the line rate of the electronic counterpart. In NOSP, high-intensity light fields are used to generate nonlinear optical responses, which can be used to process optical signals. Great efforts have been devoted to developing new materials and structures for NOSP. However, one of the challenges in implementing NOSP is the requirement of high-intensity light fields, which is difficult to generate and maintain. This has been a major roadblock to realize practical NOSP systems for high-speed, high-capacity optical communications. Here, we propose using a parity-time (PT) symmetric microresonator system to significantly enhance the light intensity and support high-speed operation by relieving the bandwidth-efficiency limit imposed on conventional single resonator systems. The design concept is the co-existence of a PT symmetry broken regime for a narrow-linewidth pump wave and near-exceptional point operation for broadband signal and idler waves. This enables us to achieve a new NOSP system with two orders of magnitude improvement in efficiency compared to a single resonator. With a highly nonlinear AlGaAs-on-Insulator platform, we demonstrate an NOSP at a data rate approaching 40 gigabits per second with a record low pump power of one milliwatt. These findings pave the way for the development of fully chip-scale NOSP devices with pump light sources integrated together, potentially leading to a wide range of applications in optical communication networks and classical or quantum computation. The combination of PT symmetry and NOSP may also open up opportunities for amplification, detection, and sensing, where response speed and efficiency are equally important.

A feature extraction method of rub-impact based on adaptive stochastic resonance and Hjorth parameter.

The characteristic frequency of a rub-impact fault is usually very complex and may contain higher harmonics and subharmonics. Due to the uncertainty of harmonic components and the complexity of signal-to-noise ratio (SNR) operation, the general scale transformation stochastic resonance (GSTSR) has certain limitations in the identification of rub-impact faults. To solve this problem, the paper starts with complexity and proposes a rub-impact fault identification method combining a swarm intelligence optimized algorithm (SIOA) with Hjorth parameters and GSTSR. The complexity of vibration signals will change greatly before and after rub-impact faults. The complexity parameter in Hjorth parameters can effectively embody the complexity of signals and is invulnerable to noise interference. Therefore, the complexity parameter in the Hjorth parameters is taken as the objective function of SIOA and combined with GSTSR. Vibration signals from cases are taken as input to adaptive stochastic resonant (ASR) systems, and the system parameters are adaptively and synchronously adjusted to realize the maximal resonant effect. Finally, the spectrum analysis of signals obtained from ASR is used to extract failure features and recognize faults in the rotor-stator rub-impact. The proposed method is verified by comparing it with other schemes under different SIOAs and different operating conditions. The result of the comparison shows that the complexity parameter of the Hjorth parameters can be taken as the objective function of SIOA to accurately identify the rub-impact fault. Meanwhile, the proposed method, compared with the method of taking SNR as an objective function, has a better effect on reducing time costs and strengthening fault characteristics.