Working Frequency Bandwidth Research Articles

Theoretical and experiment optimization research of a frequency up-converted piezoelectric energy harvester based on impact and magnetic force

Harvesting environmental vibrations to power electronic components is an essential approach for addressing the power supply challenge in MEMS. However, conventional vibration energy harvesting systems frequently suffer from limited frequency bandwidth and high-frequency deficiencies. This paper proposes a novel up-frequency structure for piezoelectric vibration energy harvesting (VEH) that relies on both nonlinear magnetic force and piecewise linear force. The proposed VEH’s nonlinear dynamic characteristics are analyzed theoretically, and an experimental prototype machining and vibration test platform are constructed. Theoretical and experimental results are compared and analyzed by conducting basic experiments and key parameter optimization experiments. The research results demonstrate that the proposed VEH can efficiently harvest vibration energy in low-frequency and wide-band environments. Regarding the system parameters, higher vibration acceleration results in increased output voltage and wider working frequency bandwidth. Reducing the gap distance enhances piecewise linear vibration, which broadens the working frequency bandwidth. Furthermore, the proposed VEH’s ability to harvest low-frequency vibrations can be enhanced by reducing the magnet distance, thereby reducing the linear resonance frequency of the system. The findings of this study offer valuable insights for advancing the engineering application of MEMS self-power supply technology.

Design and experimental validation of a broadband multi-modal coupled capsule-shaped transducer for underwater acoustics

This paper introduces a novel approach to expand the working frequency band of underwater acoustic transducers through multi-modal coupling. We designed a broadband multi-modal coupled piezoelectric capsule-shaped transducer structure by leveraging the advantages of conventional piezoelectric spherical-shell and piezoelectric cylindrical-tube transducers. First, the finite element method (FEM) was employed to scrutinize the influence of key structural parameters on the acoustic performance of the capsule-shaped transducer, thereby establishing the foundation for the final transducer design. Subsequently, the designed transducer was characterized through modal analysis and harmonic response analysis of electrical-mechanical-acoustical multiphysics field coupling. Finally, a prototype of the capsule-shaped transducer was fabricated and measured, with the results compared with those of a spherical-shell transducer. A comparative analysis of the measured outcomes revealed that the capsule-shaped transducer exhibits coupling among three modes within the frequency range of 10 kHz to 30 kHz. The transmitting voltage response (TVR) values exceeded 143.5 dB, reaching a maximum of 151.9 dB, and the working frequency bandwidth achieved 18 kHz. Compared with the spherical-shell transducer, the average TVR value demonstrates a 3.7 dB improvement, and the bandwidth exhibited an 8.4 % increase. According to the experimental findings, the proposed capsule-shaped piezoelectric transducer offers advantages such as high voltage response, a broad working frequency band, compact size, low weight, and easy installation. This technology can be further applied to small underwater platforms, enhancing their acoustic detection range and spatial coverage performance.

A broadband multi-frequency microwave combined biological exposure setup.

With the rapid popularization of wireless electronic devices, there has been an increasing concern about the impacts of the electromagnetic environment on health. However, most research reports on the biological effects of microwaves have focused on a single frequency point. In reality, people are exposed to complex electromagnetic environments that consist of multiple frequency microwave signals in their daily lives. It is important to investigate whether multi-frequency combined microwave energies have different biological effects compared with single frequency microwave energy. Unfortunately, there are limited reports on this topic due to the lack of suitable platforms for research on multi-frequency microwave energy combined with biological exposure. To address this issue, this study presents a setup that has a very wide working frequency bandwidth and can be compatible with single frequency and multi-frequency microwave combined exposure. Moreover, it can achieve relatively equal exposure to multiple biological samples at any frequency point in the working frequency range, which is crucial for electromagnetic biology research. The experimental results are in good agreement with the simulation results, confirming its capability to facilitate the study of complex electromagnetic environment effects on organisms.

A rigid–soft hybrid paper-based flexible pressure sensor with an ultrawide working range and frequency bandwidth

A rigid–soft hybrid design strategy to fabricate paper-based pressure sensor with ultrawide working range and frequency bandwidth.

Electromagnetic interference from automobile passive keyless entry in cardiovascular implantable electronic devices

ABSTRACT Introduction The automobile passive keyless entry (PKE) system is a potential source of electromagnetic interference (EMI). We aim to determine the incidence and significance of EMI from automobile PKE system in cardiovascular implantable electronic device (CIED) patients. Methods This was a single-center cross-sectional study conducted at Maharaj Nakorn Chiang Mai hospital, Thailand. Patients with CIED were instructed to lock and unlock two automobiles using the PKE system. Any EMI or arrhythmias were detected by CIED interrogation and single-lead electrocardiogram event recorder. We also used a spectrum analyzer to identify the automobiles working frequency bandwidth. Results There was a total of 102 CIED patients. Device types included 48.0% defibrillators, 37.3% permanent pacemakers, and 14.7% cardiac resynchronization therapy device. Both interrogated data from device and event monitor revealed no incidence of EMI during the PKE activation. We failed to identify the working frequency bandwidth of the two studied cars due to very low signal strength, thus blended in with the background noise. Conclusions Automobile PKE systems transmitted very low power signals. Therefore, under normal circumstances, CIED patients can use automobile PKE system safely without any EMI regardless of key fob positions in relation to the CIED pulse generator. Trial Registration The study was registered at ClinicalTrials.gov (https://clinicaltrials.gov), and the identification number is NCT03016390.

A petal–cylindrical seismic metamaterial occupying low-frequency wide bandgaps in horizontally stratified soils

Earthquake prevention is of fundamental interest in seismic research area. Seismic metamaterials proved very useful for this purpose, but because they are mainly based on resonant structures, the working frequency bandwidth of these metamaterials is narrow. This work aims to increase the bandwidth by improving cylindrical resonant structure. Two types of cylindrical structures with four petals attached to the four sides of hollow and solid cylinders are proposed. Their bandgap properties have been investigated by using the finite element method. Particularly, considering more realistic site conditions for seismic surface wave propagation, we explored the properties of the proposed structures for horizontally stratified soils, besides homogeneous soil. The results show that a low-frequency wide bandgap is provided in case of homogeneous soil. Excitedly, in case of a stratified substrate, an additional bandgap is obtained in lower frequency region. Moreover, to confirm the feasibility of the proposed structures, the transmission coefficients for the finite unit cells are calculated for both homogeneous and horizontally stratified soils along with the different directions. The finding substantiates that the finite system for stratified soils can effectively attenuate seismic surface waves within the two low-frequency bandgaps occupying the relative bandwidths of 154% and 81%.

Harvesting vibration energy by novel piezoelectric structure with arc-shaped branches

In this study, we proposed a novel energy harvester that consists of a piezoelectric inverted beam and two arc-shaped branches. The harvester owns the characteristics of super-harmonic and sub-harmonic vibrations, so its working frequency bandwidth can be significantly extended. Then, for broadband excitation, the harvester can keep a fairly large electric output. The theoretical model is established at first, and the simulations for frequency-sweeping and harmonic excitations are carried out. The results show that there exist the super-harmonic and sub-harmonic vibrations in response. Then, the validation experiments are conducted, and the results prove the theoretical analyses. Furthermore, in the experiments there occurs the transition from the synchronization vibration to sub-harmonic resonance, which results in a dramatic increase in amplitude and output. Finally, the experiment for stochastic excitation is carried out. The results show the harvester could give a large electric output under weak stochastic excitations. For the excitation of PSD = 0.07 g2/Hz, the output power can reach 21.2 μW.

Extended topological interface modes with tunable frequency in the piezoelectric phononic crystal

Acoustic metamaterials have provided a versatile platform to explore more degrees of freedom for tunable topological wave manipulation. Recently, extended topological interface modes (ETIMs) with heterostructure have been proposed to extend the spatial degree of freedom. However, the absence of frequency tunability still restricts the application of the wave transports of ETIMs. Here, we propose a one-dimensional piezoelectric topological phononic crystal (PTPC) with electrically tunable working frequency by introducing external capacitor circuit. With the bandgap frequency actively controlled by appropriately tuning the capacitances, we construct the heterostructured PTPCs possessing high-energy-capacity ETIMs with electrically tunable working frequency range and bandwidth. This work paves the way to wide engineering applications on acoustic sensing enhancement, nondestructive testing, energy harvesting, information processing, and reconfigurable topological wave transports.

Origami-based acoustic metamaterial for tunable and broadband sound attenuation

Noise reduction is of critical importance in many engineering applications. One way to achieve noise reduction is using acoustic metamaterials. However, traditional acoustic metamaterials have long been criticized for the fixed and narrow frequency band in low- and medium-frequency sound attenuation. In this study, by incorporating the accordion origami into Helmholtz resonators as the side cavity, a novel origami-based acoustic metamaterial (OBAM) with tunable and broad bandwidth sound-eliminating capacities is developed. The sound attenuation properties of the proposed OBAM, quantified by transmission loss (TL), are extensively investigated by theoretical, numerical, and experimental methods. The sound attenuation of the OBAM can be readily tuned by air pressure via capitalizing on the single-degree-of-freedom property of accordion origami. The transfer matrix method is used to compute the TL of the OBAM analytically, compared with those obtained from the finite element and acoustic impedance methods. Results show that the theoretical, numerical, and experimental methods have good consistency, and the TL can be easily and quantitatively tuned by pressure in the low-medium frequency band. The working frequency bandwidth (TL larger than 10 dB), achieving an effective attenuation of more than 90% of the sound energy, can reach 500 Hz in the range of 271–790 Hz, in which the thickness of the OBAM is only 1/18–1/6 λ with λ being the working wavelength, demonstrating the powerful and broadband low-frequency sound elimination capacity of the OBAM at sub-wavelength. Moreover, the proposed OBAM allows airflow-permeating, possesses high design flexibility and programmability, and remains scale-independent, real-time tuning, and free of the complex control algorithm. This study paves the way for effective tunable and broadband sound insulation attenuation equipment with efficient ventilation.

High-Temperature-Resistant Fiber Laser Vector Accelerometer Based on a Self-Compensated Multicore Fiber Bragg Grating.

We propose and demonstrate a novel high-temperature-resistant vector accelerometer, consisting of a ring cavity laser and sensing probe (i.e., fiber Bragg gratings (FBGs)) inscribed in a seven-core fiber (SCF) by using the femtosecond laser direct writing technique. A ring cavity laser serves as a light source. Three FBGs in the outer cores of SCF, which are not aligned in a straight line, are employed to test the vibration. These three FBGs have 120° angular separation in the SCF, and hence, vibration orientation and acceleration can be measured simultaneously. Moreover, the FBG in the central core was used as a reflector in the ring cavity laser, benefiting to resist external interference factors, such as temperature and strain fluctuation. Such a proposed accelerometer exhibits a working frequency bandwidth ranging from 4 to 68 Hz, a maximum sensitivity of 54.2 mV/g, and the best azimuthal angle accuracy of 0.21° over a range of 0–360°. Furthermore, we investigated the effect of strain and temperature on the performance of this sensor. The signal-to-noise ratio (SNR) only exhibits a fluctuation of ~1 dB in the range (0, 2289 με) and (50 °C, 1050 °C). Hence, such a vector accelerometer can operate in harsh environments, such as in aerospace and a nuclear reactor.

Theoretical and experimental studies on bistable vibration energy harvester with levitation magnet couple

To improve the efficiency of vibration energy harvesting, a levitation magnet couple is introduced to the bi-stable energy harvester (BEH) to create a desired potential energy, by which the harvester’s response and output can be increased greatly. Compared to the classical BEH, the novel harvester has a lower potential barrier and a flatter bottom of its potential well, which can help increase the response and outputs. The experimental results show that the introduction of levitation magnet couple effectively extends the working frequency bandwidth of the harvester. The inter-well jump can be executed easily under weak stochastic excitations and the amplitude is larger than the classical one, even in the case of executing the same kind of intra-well oscillation. The experiments prove that the output voltage of the novel harvester outperforms the classical BEH over the whole intensity range. This study may provide a good guidance to improving the performance of bistable energy harvester.

Increasing the efficiency of a bistable cantilever beam energy harvester exploiting vibro-impact effects

In this paper, a novel energy harvester is proposed by adding a barrier to a typical bistable energy harvester, which is modeled exploiting an equivalent single degree of freedom. By using Euler-Lagrange equations, mass, structural stiffness, magnetic force and electromechanical coupling coefficient of the harvester, are converted to an equivalent SDOF model. The frequency bandwidth of the system and the level of harvested power in impacting and non-impacting conditions are obtained. According to the numerical results, it is found by adding a barrier to a typical bistable energy harvester, the working frequency bandwidth of the system is increased tangibly. In fact, by vibro-impact phenomenon, the working frequency bandwidth and extracted power of the system are increased about 42.95% and more than 7 times, respectively. Additionally, the effects of stiffness and initial gap of the barrier are shown on frequency bandwidth of the harvester. It is observed that the gap distance has more effect on widening frequency bandwidth of the system against barrier stiffness. Finally, the effect of the electrical load resistance on the harvested power is discussed at various barrier stiffnesses and initial gap distances and finally the optimum values of the electrical load are provided for each condition.

Antenna Systems in Medical Masks: Applications for 5G FR1 and Wi-Fi 7 Wireless Systems

This paper proposes a small antenna system (47 mm × 8 mm × 0.2 mm) to be used in a medical mask. The medical mask is composed of a frame and shield. The frame is made of polycarbonate (PC), and the shield is made of polyethylene terephthalate (PET). The author sets two groups of antennas on the upper side of the frame and sets two other groups of antennas on the sides facing away from the face of the shield. The substrates of the four antennas are all FR4 (εr = 4.4, tanδ = 0.02), so the first antenna type is a combination of PC and FR4, and the second antenna type is a combination of PET and FR4. The antenna system has three working frequency bands, in which the reflection coefficient is lower than −10 dB after actual measurement, and its working frequency bandwidth is 2.38–2.62 GHz, 3.38–3.74 GHz, and 5.14–8 GHz, respectively. It can be effectively used in 5G FR1 and Wi-Fi 7 frequency bands and can easily be combined with medical masks of different materials. This antenna system can use Wi-Fi 7 for wireless transmission indoors and use the 5G FR1 frequency band for wireless transmission outdoors, achieving seamless transmission capabilities.

A flexible hinge accelerometer based on dual short fiber Bragg grating

Fiber Bragg gratings (FBGs) are a type of optical element with several advantages. In this study, we propose a vibration monitoring system consisting of a flexible hinge and a dual FBG. The novel design enables the dual short FBG to be tensile and compressed separately during vibration, while achieving sensitivity enhancement and self-temperature compensation. Through theoretical analysis and experiments, the resonant frequency was 150 Hz. The working frequency bandwidth of the accelerometer ranged from 10 to 100 Hz with a sensitivity of 1711 pm/g. The minimum resolution and detectable acceleration of the proposed system were 0.584 mg and 3 mg, respectively, which are significantly better than similar systems with a single FBG.

Knitting integral conformal all-textile strain sensor with commercial apparel characteristics for smart textiles

Combining traditional textile methods with electronic devices accelerates the development of wearable textiles in health and movement monitoring. Generally, using manufacturing methods of knitting yarns with heavy coatings or overlaying multi-layer fabrics rigidly do improve the performance of textile devices but trade off their characteristics of comfort and aesthetics, which hinders the practical and commercial promotion of wearable textiles. Using commercial knitting technology, we developed an all-yarn-based all-textile sensor (AATS) with good textile characteristics and electrical performance, which was presented in an innovative alternating high elastic structure for human health and motion monitoring. Taking full advantage of the knitted structure and special covered yarns, the AATS exhibited ultra-stretchability (up to 133%), wide working frequency bandwidth (0.5 Hz to 8 Hz), and high stability (over 10,000 times), satisfying the need for sensitivity to capture the large range of deformation signals caused by human motion and respiration. It also fully meets the commercial apparel requirements of comfort, aesthetics and washability (50 cycles). Furthermore, AATSs can be seamlessly integrated into different parts of knitwear using mature seamless knitting technique. Such smart knitwear can accurately obtain and real-time monitor continuous human physiological activity signals and multi-dimensional sleeping status. This study investigated the potential of using commercial knitting technology to achieve smart textiles for comfort and personalization.

Modeling and analysis of a three-degree-of-freedom piezoelectric vibration energy harvester for broadening bandwidth

This study proposes a multi-frequency response piecewise-linear piezoelectric vibration energy harvester (MFRPLP-VEH) by combining the linear multi-frequency resonance and nonlinear vibration bandwidth broadening methods to improve the working frequency bandwidth and environmental robustness of the piezoelectric vibration energy harvester. A theoretical model is established based on the electromechanical coupling and the dynamic response of the MFRPLP-VEH. The energy harvesting performance and broadening width efficiency of the MFRPLP-VEH were obtained through an experimental verification platform, where the resonant frequencies of the three beam are 28.9, 33.6, and 38.6 Hz, respectively. Furthermore, the operating frequency range is widened by 90.9% at an external excitation acceleration of 10 m/s2. The energy generated by the MFRPLP-VEH is 194% of the energy generated by its linear counterpart under the same excitation conditions. The numerical and experimental results verify the accuracy of the theoretical model and the broadband working frequency range of the MFRPLP-VEH.

A three-dimensional broadband underwater acoustic concentrator

We propose a three-dimensional (3D) omnidirectional underwater acoustic concentrator based on the concept of an acoustic prison, which can realize a substantial enhancement of underwater sound signals in broadband ranges. This device mainly employs the non-resonant multiple reflection characteristics of the semi-enclosed geometric space, so it has a wide working frequency bandwidth. Compared with previously reported concentrators based on transform acoustic mechanisms, the structure is more simple and, most importantly, it can realize omnidirectional signal enhancement in a 3D space. Moreover, the working frequency band of this acoustic concentrator depends on the size of the concentrator, so it can be changed directly through size scaling, which is convenient for engineering applications. In general, the designed underwater acoustic concentrator has the advantages of a simple structure, scalability, large bandwidth of working frequency, and high signal gain. It has potential applications in underwater target detection and other aspects.

Sensitivity Enhancement of Fiber Bragg Grating Accelerometer Based on Short Grating

We propose and develop a high-sensitivity fiber Bragg grating (FBG) accelerometer based on a flexible hinge for vibration sensing. The proposed method employs a 1-mm FBG that is inscribed pointwise using a femtosecond laser such that the resultant stress concentration at the FBG is improved significantly by reducing the distance between the two bonding points of the FBG structure. Through theoretical calculations and finite element simulations, the relationship between sensitivity and distance was found to be inversely proportional. Using this structure, the sensitivity was enhanced to 804 pm/g at 15 and 30 Hz. The resonant frequency of the proposed accelerometer is 102 Hz, and the working frequency bandwidth is from 10 to 50 Hz. The performance of the accelerometer allows the detection of vibrations in seismic explorations with high reliability.

Modeling of spatial correlation characteristics of broadband ocean ambient noise vector field

The signal-to-noise ratio gain of the array is closely related to the spatial characteristics of the noise field. The modeling of the spatial characteristics of marine environmental noise is always a hot spot. For sonar with different functions, the working frequency band and bandwidth are usually different. Therefore, the spatial correlation coefficient of the noise field in arbitrary frequency band has important reference value for designing sonar systems. According to the process of generating the marine environmental noise field under the high frequency approximation condition, a noise field time-domain modeling method is proposed, and the integral expression of the time-domain sound pressure and particle vibration velocity of marine environmental noise in a horizontally layered medium is given. This lays the foundation for establishing a broadband model of the noise vector field. In particular, the analytical expression of the spatial correlation coefficient of the broadband white noise vector field in the vertical direction under specific condition is also given. Following the spectral structure of wind-generated noise, the spatial correlation coefficients of noise fields with different frequency bands and different spectral slopes are numerically calculated, revealing the influence of bandwidth and spectral structure on the spatial characteristics of marine environmental noise, and the principle behind the result is explained through theoretical derivation. With the increase of the array element spacing and bandwidth, the number of oscillation periods and the oscillation amplitude of the spatial correlation coefficient of each component of the noise vector field gradually decrease, which is caused by the frequency domain average of the noise field correlation coefficient. When the spectral slope is less than zero, the low-frequency noise plays a major role, causing the spatial correlation radius of the broadband noise field to be larger than that of the narrowband noise field. The result of the experiment conducted in South China Sea shows that the measured vertical spatial correlation coefficient of the sound pressure field of marine environmental noise is in good agreement with the theoretical result. The model has potential application prospects for the research of transducer array technology and the inversion of environmental parameters.

Performance of a dual piezoceramic cantilever for low frequency energy harvesting applications: modeling and experiment verification

Vibration-based energy harvesting is a growing field for generating low-power electricity to use in wireless electronic devices. These applications are usually in an environment of abundant low frequency vibration, which can be collected through an appropriate energy conversion structure. However, traditional energy conversion architectures such as cantilever-cantilever type or spring-mass type have the problem of high working frequency and narrow bandwidth (limiting its use and far from the frequency found in the surrounding environment). To overcome these challenges, this work proposes a study of a piezoelectric vibration energy harvester based on a dual cantilever structure. The energy harvesting system is designed, analyzed and verified with the finite element analysis method and an experimental study. The results show that the bandwidth is enlarged of 30 Hz and a power is generated and equals to the sum of the power generated by each cantilever (190 nW) with an output voltage supplying a resistive load of 110 KΏ.