Broad Frequency Bandwidth Research Articles

Hierarchical engineering of CoNi@Air@C/SiO2@Polypyrrole multicomponent nanocubes to improve the dielectric loss capability and magnetic-dielectric synergy

Impedance matching characteristics and loss capabilities including magnetic loss, polarization loss and conduction loss are critical factors to improve microwave absorption performances (MAPs). To elevate these aspects, herein, yolk-shell structured CoNi@Air@C/SiO2@Polypyrrole (PPy) magnetic multicomponent nanocubes (MCNCs) were designed and successfully fabricated in high efficiency through a continuous co-precipitation route, classical Stöber method, thermal treatment and polymerization reaction. The obtained results indicated that the formation of SiO2 effectively stabilized the cubic geometrical morphology and yolk-shell structure during the high-temperature pyrolysis process. The introduction of PPy greatly boosted their polarization loss and conductive loss capabilities. Therefore, the as-prepared yolk-shell structured CoNi@Air@C/SiO2@PPy MCNCs presented superior MAPs compared to CoNi@Air@C/SiO2 MCNCs. Furthermore, by regulating the content of PPy, the obtained CoNi@Air@C/SiO2@PPy MCNCs displayed tunable and excellent comprehensive MAPs in terms of strong absorption capabilities, broad frequency bandwidths and thin matching thicknesses, which could be ascribed to the unique structure and excellent magnetic-dielectric synergistic effect. Therefore, our findings provided an alternative pathway to effectively utilize the magnetic-dielectric synergy and loss capabilities for the developing yolk-shell structured magnetic MCNCs as the strong wideband microwave absorbers.

From core@shell ZnSe/FeSe2@MoSe2 to core@shell@shell magnetic ZnFe2O4@C@MoSe2 flower-like nanocomposites: An effective strategy to boost microwave absorption performance of MoSe2-based nanocomposites

The selenylation/sulfuration of magnetic precursor brings about the great challenges to construct magnetic transition metal dichalcogenides (TMDs)-based multicomponent nanocomposites (MCNCs), which greatly hinders the improvements in magnetic loss ability and impedance matching characteristic. Theoretically speaking, the addition of carbon layer is conducive to protect the magnetic nanoparticles, optimize the impedance matching, strengthen the interfacial polarization and magnetic loss abilities, and so on. In order to verify these ideas, herein, we elaborately designed and produced core@shell ZnSe/FeSe2@MoSe2 and core@shell@shell ZnFe2O4@C@MoSe2 flower-like MCNCs. The results of comparative study indicated that the as-prepared ZnSe/FeSe2@MoSe2 and ZnFe2O4@C@MoSe2 with the different MoSe2 contents and flower-like geometrical morphologies could be synthesized by regulating the amounts of Mo and Se sources. And the introduction of carbon layer not only effectively inhibited the selenylation of ZnFe2O4 precursor, but also greatly improved the impedance matching characteristic, dielectric and magnetic loss capabilities. The obtained ZnFe2O4@C@MoSe2 MCNCs presented the excellent comprehensive microwave absorption properties (MAPs) including strong absorption capability, broad frequency bandwidth and thin matching thickness. Therefore, our findings not only presented a simple and viable route to produce magnetic TMDs-based MCNCs, but also provided an effective strategy to boost their comprehensive MAPs.

Broadband microwave antenna for uniform manipulation of millimeter-scale volumes of diamond quantum sensors

Quantum sensors based on nitrogen-vacancy (NV) centers in diamond are expected to demonstrate a wide variety of applications. For high-sensitivity quantum sensors with NV center ensembles, uniform manipulation of the electron spins of the NV centers in large volumes is required. In addition, a broad microwave frequency bandwidth for manipulating the NV centers' electron spin is necessary for vector magnetometry and measurement under a finite static magnetic field. Here, we demonstrate a broadband microwave antenna for uniform manipulation of millimeter-scale volumes of diamond quantum sensors. The simulation shows that the current is distributed at both edges of the loop coil of a single copper plate due to the skin effect. The loop coil acts like a Helmholtz coil, which realizes uniformity in the z-direction of the microwave magnetic field (B1). The plate structure has a higher mechanical stability, durability, and a larger heat capacity than the Helmholtz coil, due to its large volume. The antenna achieves a higher performance than previously reported antennae, with a maximal B1 of 4.5 G, a broad bandwidth of 287 ± 6 MHz, and a peak-to-peak variation of 9.2% over a 3.1 mm3 cylinder volume. These performances show that the presented antenna is suitable for manipulating solid-state spin ensembles for high-sensitivity quantum sensors.

Tool-tip dynamics in micromachining with arbitrary tool geometries and the effect of spindle speed

Mechanical micromachining has become a leading approach to fabricating complex three-dimensional microscale features and miniature devices on a broad range of materials. To satisfy the accuracy and productivity demands of various micromachining applications, the tool-tip dynamics, i.e., the dynamic behavior of the tool-ultra high-speed spindle assembly as reflected at the cutting edges of a microtool, should be well-understood. However, existing techniques for predicting tool-tip dynamics pose strict limitations in frequency bandwidth and do not capture the effect of the spindle speed on tool-tip dynamics. In addition, those techniques cannot be applied broadly to predict tool tip dynamics for a myriad of microtool geometries. This paper presents a systematic approach to predicting the tool-tip dynamics accurately in micromachining when using ultra-high-speed (UHS) spindles and for arbitrary microtool geometries. The speed-dependent dynamics of the UHS spindle are obtained using an experimental approach. The dynamics of microtools are obtained analytically using the spectral Tchebychev technique, such that any microtool geometry can be modeled accurately and does not require new testing. The tool-tip dynamics are then predicted by combining (coupling) the spindle and microtool dynamics using a novel modal-Tchebychev domain coupling technique. This technique enabled accurate coupling/decoupling of substructure dynamics within a broad frequency bandwidth (up to 15 kHz) and at different spindle speeds (up to 120,000 rpm). Furthermore, an empirical model for the mode-splitting effect is derived to capture the effect of spindle speeds on tool-tip dynamics. The overall approach is demonstrated and experimentally validated on a UHS spindle with microtool blanks and micro endmills at operational speeds. We conclude that the presented methodology can be used to determine the tool-tip dynamics accurately.

Principle and Control of Active Engine Mount Based on Magnetostrictive Actuator

Engine mount system affects the automobile NVH performance. Active mounts would achieve excellent vibration isolation and relative displacement control performance in a broad frequency bandwidth by outputting controlled force to the mounting system. The actuator and control method of the active mounts determine the system performance. In this paper, an active mount based on the smart material, i.e., Terfenol-D rod, is proposed, which mainly includes three parts: rubber spring, magnetostrictive actuator (MA), and hydraulic amplification mechanism (HAM). Dynamic model of the active mount is correspondingly established. A state feedback control method based on x-LMS (Least-Mean-Square) algorithm is proposed as well. Specifically, with the consideration of the unmeasurable state parameters in the active mounting system, an x-LMS state feedback controller with the system state as the reference signal is constructed by employing Sage-Husa Kalman filter to realize the state estimation of the active mounting system. Then a detailed analysis of the proposed control method is conducted, with deriving iterative formula of tap-weight vector. Sequentially, the problem of the dependence on the excitation signal in the x-LMS algorithm is addressed. The feasibility and capability of the proposed control method are verified and evaluated by simulation of a two-degree-of-freedom active mounting system.

Highly electro-responsive ionic soft actuator based on graphene nanoplatelets-mediated functional carboxylated cellulose nanofibers

Electro-responsive ionic soft actuators have attracted increasing interest owing to the promising applications for soft robots, biomimetic robots, active medical devices, flexible electronics, and wearable devices. However, existing ionic actuators still need a technology breakthrough for larger bending strain, faster response, and excellent actuation durability. Herein, we report a novel highly electro-responsive ionic actuator based on functional carboxylated cellulose nanofibers (CCNF) by doping with ionic liquid (IL) and graphene nanoplatelets (GN). The proposed CCNF-IL-GN actuator demonstrated a large tip displacement of 15.71 mm (peak-to-peak) at 2.0 V with 0.1 Hz, faster rise time (2.9s), broad frequency bandwidth (0.1–3.0 Hz), markedly reduced phase delay, and long actuation durability (98.6% retention for 3 h) without actuation response distortion, all of which were due to the fast-easy ion migration and massive charge transport ability of the designed ionically crosslinked electrolyte membrane, resulting from the strong ionic interactions and crosslinking of CCNF nanofibers with IL and GN. Furthermore, we investigated the actuator's bionic applications such as the bionic flower, bionic finger, and bionic window. These results elucidate the great potential of the designed CCNF-IL-GN actuators for bionic robots, soft robots, wearable electronics, and biomedical active devices.

Metasurface Radome to Achieve a Wideband High Gain, Low RCS, and Low SLL Antenna

A Phase- and amplitude-adjustable metasurface radome (PAMR) is proposed to achieve a wideband high gain and low radar cross-section (RCS) antenna with arbitrary sidelobe levels (AS-PGMA) at a 9.8 GHz operating frequency. The proposed PAMR is a special multilayer phase gradient metasurface lens whose amplitude distribution is modified based on the Dolph-Tschebyscheff technique. The AS-PGMA simulation results indicate that a high gain, low RCS, and low sidelobe level (SLL) antenna can be achieved over a broad impedance frequency bandwidth of 9.25–10.1 GHz with in-band average values of 17 dB, −7.5dBsm, −20 dB/−27 dB for gain, RCS, and E-/H-plane SLL, which are measured at 9.8 GHz as 17.4 dB, −9dBsm, and −23.02 dB/−27.91 dB, respectively. Additionally, a novel analytical method for calculating the RCS of the proposed PAMR and AS-PGMA is described and verified by measurement and simulation findings. Measurement results show that the E-/H-plane SLL of the AS-PGMA is improved by 12.2 dB/5.1 dB at the operating frequency, respectively, while its gain and RCS reduction are reduced by 1.6 and 2.1 dB, respectively. Moreover, RCS of the AS-PGMA is reduced over an ultrawide bandwidth of 1–20 GHz for orthogonal polarizations. The analysis, simulations, and measurements are all in good agreement.

Fast time-domain current measurement for quantum dot charge sensing using a homemade cryogenic transimpedance amplifier

We developed a high-speed and low-noise time-domain current measurement scheme using a homemade GaAs high-electron-mobility-transistor-based cryogenic transimpedance amplifier (TIA). The scheme is versatile for broad cryogenic current measurements, including semiconductor spin-qubit readout, owing to the TIA's having low input impedance comparable to that of commercial room-temperature TIAs. The TIA has a broad frequency bandwidth and a low noise floor, with a trade-off between them governed by the feedback resistance RFB. A lower RFB of 50 kΩ enables high-speed current measurement with a −3 dB cutoff frequency f−3dB = 28 MHz and noise-floor NF = 8.5 × 10−27 A2/Hz, while a larger RFB of 400 kΩ provides low-noise measurement with NF = 1.0 × 10−27 A2/Hz and f−3dB = 4.5 MHz. Time-domain measurement of a 2-nA peak-to-peak square wave, which mimics the output of the standard spin-qubit readout technique via charge sensing, demonstrates a signal-to-noise ratio (SNR) of 12.7, with the time resolution of 48 ns, for RFB = 200 kΩ, which compares favorably with the best-reported values for the radio frequency reflectometry technique. The time resolution can be further improved at the cost of the SNR (or vice versa) by using an even smaller (larger) RFB, with a further reduction in the noise figure possible by limiting the frequency band with a low-pass filter. Our scheme is best suited for readout electronics for cryogenic sensors that require a high time resolution and current sensitivity and, thus, provides a solution for various fundamental research and industrial applications.

Bistable enhanced passive absorber based on integration of nonlinear energy sink with acoustic black hole beam

The nonlinear energy sink (NES) has a broader frequency bandwidth than the linear tuned-mass-damper (TMD), making it more robust. However, the NES is only efficient in a narrow energy range. The mitigation property of NES may deteriorate when input energy is too small or large. To overcome this shortage, a novel NES named ABH-BNES is proposed in this paper, by combining a bistable nonlinear energy sink (BNES, which has negative linear stiffness, cubic nonlinear stiffness, and linear damping) and acoustic black hole (ABH) beam. The negative linear stiffness and cubic nonlinear stiffness elements can generate a large cross-well motion to improve the performance of vibration mitigation for low input energy. By replacing the attached mass in traditional NES as an ABH beam, multiple high-damping modes can be introduced into the vibration absorber. So that the performance of ABH-BNES is also enhanced for large input energy. First, the Gaussian Expansion Method and Modal Approach are employed to establish the dynamic model of a single-dof linear oscillator coupling with an ABH-BNES. Such a modeling approach is verified by comparing it with the models in the existing literature and established by the finite element method (FEM). The slow invariant flow (SIM) theory and time-domain integration are employed to analyze the novel NES's vibration mitigation mechanism. In addition, a multi-solution boundary related to the existence of targeted energy transfer is derived for optimizing the nonlinear absorber. Then, the energy method is used to verify the superiority of the novel NES by comparing it with TMD, NES, and the Linear ABH absorber. The results show that the ABH-BNES can behave with an excellent mitigation effect and an extensive energy bandwidth when the parameters are appropriately selected. Finally, an experiment is carried out to verify the new NES's superiority and the correctness of the theoretical model.

Hydroacoustic High Absorption with Broadband and Wide-Angle Impedance Matching

We numerically demonstrate a general method to achieve acoustic high absorption in water with a wide range of incident angles and a broad frequency bandwidth. Different from previous studies considering local resonances with a narrow bandwidth or porous materials with a gradient design, we show that flat multilayer solid composites can be engineered to be perfectly impedance matched with water over a wide range of angles and a broad spectrum. By adding a proper loss factor to the composites, sound waves can be gradually dissipated and high absorption can be realized. Such a method is robust and adaptive to a broad range of material parameters. Our work could promise broad underwater applications.

Two new broadband and tunable terahertz pyramid patch/disk absorbers based on graphene metasurface

In this work, an efficient circuit model of functional thin-film graphene-assisted metamaterial devices with exploiting transmission line theory is presented. The design is done by the usage of a MATLAB code analytically and the numerical results are obtained by the Finite Element Method (FEM) to verify the accuracy and validity of the circuit model approach. This paper proposes two new broadband graphene metasurface absorbers at terahertz frequencies. At first, a metasurface absorber consisting of pyramid graphene patches separated by dielectric layers is introduced. For most absorber applications, the bandwidth of the absorber is one of the most remarkable metrics. The obtained normalized absorption bandwidth for this absorber is 83.85 % for 90 % absorption with a bandwidth of 4.57 THz. To attain broad frequency bandwidth, we design the metasurface absorber consisting of disk graphene and extract its circuit model. There is good agreement between the results of the circuit model and those of the full-wave simulations. Also, the obtained normalized absorption bandwidth is 82.57 % for 90 % absorption with a bandwidth of 4.74 THz. The suggested method is easy and general, so we can apply it to the design and the simulation of other subwavelength structures in the wide frequency range from terahertz (THz) to visible regions.

Bio-inspired, bimetal ZIF-derived hollow carbon/MXene microstructure aim for superior microwave absorption

Electromagnetic pollution has become an increasingly important problem which has drawbacks to both the accurate operation of the electronic facilities and the safety of human beings. To alleviate and eliminate electromagnetic irradiation, it is inevitable to design microwave absorption materials with desirable absorption intensity and broad effective frequency bandwidth. The combination of carbon-based materials and magnetic materials is an adoptable strategy to perform remarkable microwave absorption performance, while the microstructure should not be ignored. Inspired by the electromagnetic response behaviors of the microstructure from the leafhopper, the hetero-microstructure with hollow void is constructed by adopting bimetal ZIF as the precursor, followed by an interfacial tailoring strategy through electrostatic assembling and calcinating process, which enhances the microwave absorption performance by integrating the merits between the components and the micro-structure. The minimum value of reflection loss achieved -76.40 dB at 7.50 GHz under filler loading of 20% with the thickness of 2.92 mm. Besides, the effective absorption bandwidth could be tailored from 3.55 to 18 GHz among different thicknesses as required. The bio-inspired strategy is validated as a promising method, exhibiting great potential in the designing of the next-generation microwave absorber.

A universal method based on fractional derivatives for modeling magnetic losses under alternating and rotational magnetization conditions

The performance of electromagnetic devices like motors and transformers is dictated by their efficiency of magnetic energy conversion, and the adequate modeling of this efficiency is essential in device design processes. However, a universal model that yields satisfactory results for this process under both alternating and rotating magnetic fields has yet to be developed. The present work addresses this issue by extending a previously proposed vector dry-friction modeling method to include frequency dependence using fractional derivative operators. The resulting vector model relies on eight parameters that can be adjusted to fit a wide range of experimental data, and thereby provides accurate estimations of magnetic losses over broad frequency bandwidths under both alternating and rotating magnetic fields. The model provides excellent agreement with the commonly observed reduction in magnetic losses when approaching saturation under low frequency rotating excitations, and further includes overshadowing with eddy current loss as the frequency increases. The accuracy and universality of the model are demonstrated under both alternating and rotational magnetization conditions based on comparisons with experimental results.

Analysis of Imageless Ground Scene Classification Using a Millimeter-Wave Dynamic Antenna Array

We present an analysis of the capability for imageless ground scene classification using a subset of the Fourier domain information obtained with a rotationally dynamic millimeter-wave antenna array. The concept is based on the detection of signal artifacts generated by artificial objects in a scene, which manifests in the Fourier, or spatial frequency, domain. Man-made, artificial structures, such as buildings and roads, are generally characterized by sharp edges, which generate spatial frequency responses that are confined to a narrow angular range but extend over a broad spatial frequency bandwidth. These artifacts can be detected by generating a ring-shaped filter in the Fourier domain, which can be obtained through the novel design of a linear antenna array with rotational dynamics. We discuss the design of a millimeter-wave linear dynamic array for generating ring-filters and analyze the ability of such an array to classify ground scenes containing artificial structures from those without when mounted on an aerial platform, such as a drone. We compare ring filter designs and explore the use of a heuristic classifier and the K-nearest neighbor (K-NN) classifier on a large dataset of microwave ground scenes obtained from a database. Using a single ring filter that can be implemented with a two-element antenna array, small classification errors of 0.6%–3.2% were observed. Implementing multiple filters in a linear array consisting of four elements reduced the error to 0.3%.

Perfect, broadband, and sub-wavelength absorption with asymmetric absorbers: Realization for duct acoustics with 3D printed porous resonators

This article explores, theoretically and experimentally, asymmetric absorbers made of detuned and folded quarter wavelength resonators filled with air or porous materials. When used as acoustic lining in ducts, their thickness can be sub-wavelength and they can be designed for perfect absorption in broad target frequency bandwidth. The considered filling porous material can be easily 3D printed and is formed of a structured micro-lattice with variable lattice constant, allowing precise control of its acoustic properties. The underlying physics of asymmetric absorbers is discussed through a simplified analysis by means of the transfer matrix method. The behavior of the porous absorbers is also predicted by a mode-matching technique accounting for the possible couplings between the resonators. An absorber made of folded quarter-wavelength resonators is optimized, 3D printed and experimentally tested. The experimental results are in good agreement with the theory and show a mean absorption coefficient of 99% over almost an octave and below the quarter-wavelength frequency corresponding to the height of the absorber.

Enhanced electromagnetic wave absorption properties integrating diverse loss mechanism of 3D porous Ni/NiO microspheres

The research and development of electromagnetic wave absorbing materials with light weight, thin thickness, powerful absorption, and wide frequency bandwidth is a long-term pursuing. Here, Ni/NiO microspheres were synthesized through hydrothermal reaction followed by thermal reduction process. The experimental results indicated that the electromagnetic parameters and electromagnetic wave absorption performance were seriously affected by the morphology, composition and loading of Ni/NiO microspheres. When the reduction temperature rose to 550 °C, Ni/NiO550 showed a special porous-microsphere structure which assembled by irregular Ni/NiO core-shell nanorods. The micro-size combination of porous and core-shell structures, the affluent surface area, sufficient NiO-Ni interface, high-concentration active sites were conducive to the impedance matching and diverse loss mechanism including conductive loss, interfacial polarization, dipole polarization, natural/exchange resonance and multiple scattering. Finally, 45 wt% porous Ni/NiO/paraffin composite exhibited high reflection loss (− 52.15 dB) and broad effective frequency bandwidth (3.22 GHz) at a thickness of 2.17 mm.

On the use of nonlinear impact oscillators in vibrating electromagnetic based energy harvesters

This work investigates the use of impact-oscillators in nonlinear electro-magnetic cantilever based broad bandwidth frequency energy harvester. The electro-mechanical model includes the dynamical equations of the nonlinear impact-oscillators, the nonlinear frequency resonant cantilever beam equation of the harvester, and the Lorenz magnetic force resulting from the surrounding nonlinear magnetic field. The simulated results of the harvested power show a band of resonant frequencies of the vibrating cantilever beam extended beyond its fundamental natural frequency. Due to the strong nonlinearity of both the impact oscillators’ forces and the magnetic flux, the harvested power of the enhanced system shows wider bands in its respective frequency response. Moreover, the harvested power of the cantilever beam shows that considering two magnets in repulsion generates higher values mainly due to the strong nonlinear transient magnetic flux, resulting into few times more power as compared to the case of considering only one magnet in the system.

Design of Ultra-Compact On-Chip Discrete Phase Filters for Broadband Dispersion Management

This paper provides an in-depth theoretical and numerical analysis of a group-velocity dispersion (GVD) management scheme for broadband waveforms using ultra-compact on-chip discrete spectral phase filters based upon waveguide Bragg gratings (WBGs) in a silicon-on-insulator (SOI) platform. Through this technique, mm-long discrete phase filters can be designed to impart a target arbitrary GVD profile on a high-rate (typically, $\geq\!10$ GHz) periodic pulsed waveform, including fully customized and extremely large second and higher-order dispersion terms (e.g., equivalent to 10,000 km of a standard single-mode fiber), over a broad frequency bandwidth (up to $\sim\!3$ THz, demonstrated here). The capabilities and limitations of this technique to impart a target GVD profile over an arbitrary (generally, non-periodic) broadband signal are also studied. We show that customized GVD lines can be efficiently implemented offering a net group-delay excursion in the hundreds-of-ps range using mm-long integrated discrete phase filters. Additionally, we suggest and numerically demonstrate a simple and practical strategy to improve significantly the performance of the discrete phase filtering approach for application on non-periodic waveforms, by combining the discrete phase filter with a suitable periodic resonance (frequency-comb) amplitude filter. An extensive tolerance analysis is conducted, and we conclude that the proposed SOI design framework is well within practical fabrication requirements as well as robust to the expected variability in the main WBG device design parameters.

One pot synthesis and electromagnetic interference shielding behavior of reduced graphene oxide nanocomposites decorated with Ni0.5Co0.5Fe2O4 nanoparticles

With the rapid evolution of wireless communication technology, microwave absorbing materials having broad frequency bandwidth has been at center stage. Present article reports the direct facile method for synthesis of Ni0.5Co0.5Fe2O4 nanoparticles decorated reduced graphene oxide (RGO) nanocomposites (NG) by insitu genesis of Ni0.5Co0.5Fe2O4 nanoparticles in graphene oxide heterogeneous mixture, preceded by hydrazine reduction and calcination. Because of magnetic Ni0.5Co0.5Fe2O4 and dielectric reduced graphene oxide, the intercalated microstructure of NG nanocomposites shows increased shielding effectiveness due to absorption with major contribution from strong conduction loss, polarization effects, enhanced attenuation ability, eddy current losses and multiple scattering. Consequently, the shielding effectiveness of 36.3 dB (~99.98% attenuation of the electromagnetic wave) has been attained in 12.4–18 GHz for a corresponding thickness of 2 mm. The results indicates that the interface linkages and synergy among Ni0.5Co0.5Fe2O4 and RGO plays an important role in improvement of microwave absorbing properties and hence in designing of lightweight microwave absorbers.

Bilateral multi-impact oscillators for cantilever energy harvesting enhancement

ABSTRACT This paper presents an enhancement energy harvesting in a cantilever system using bilateral multi-impact oscillators with nonlinear magnetic flux for a broad bandwidth frequency. Two nonlinear oscillators with low resonant frequency provided bilateral multi-impacts onto a cantilever beam in different positions. The nonlinear electromagnetic distribution around the coil placing the tip of the cantilever beam produced the Lorenz force along with the motion during the system in operation. The response frequencies of the cantilever beam were no longer near its resonance frequency due to the bilateral multi-impact oscillators. The strong impacts and nonlinear Lorenz force affected the entire system, which reduced power harvesting enhancement with a large response frequency range from the oscillator’s natural frequency (12 Hz) to several times its frequency (39 Hz). It was also observed that the numerical simulations of the obtained power of the cantilever beam were a good agreement with the experimental results. Moreover, the two magnets placing the top and bottom of the tip cantilever beam in repulsion had a much higher voltage response due to the strong nonlinear transient magnetic flux, which resulted in ~4 times more power in the bilateral multiple impacts system.