Operating Frequency Bandwidth Research Articles

Decoupling Algorithm and Maximum Operation Frequency of a Novel Parallel Type Six-Axis Accelerometer

This paper presents a novel non-gyro six-axis accelerometer based on a derivative of Stewart parallel mechanism (SPM). To reduce the impact of interference noise, a set of geometric constraint equations are presented to compensate the errors of redundant outputs. A decoupling algorithm is introduced for easy modelling of this multiple-axis vibration problem. An auxiliary angular velocity is adopted so that the system dynamic equations can be directly solved by traditional explicit recursive formulas (ERFs) for real-time applications. Both an eigenvalue analytical algorithm and a matrix iteration approach are used to compute the fundamental frequency (FF) of the accelerometer for comparison. At the end, a four-step method is summarized in order to obtain an appropriate operation frequency range of this sensor. The analysis results reveal that the maximum operation frequency (MOF) of a parallel type six-axis accelerometer is always proportional to its FF in a ratio between 1/35~1/32. The predicted numerical results of the established decoupling algorithm are verified within the identified operation frequency bandwidth by comparing with virtual and actual experiment data, showing a maximum relative error of 0.47% and 8.87%, respectively.

Design and simulation of a frequency self-tuning vibration energy harvester for rotational applications

In order to broaden the operating frequency bandwidth of the vibration energy harvester (VEH), a novel frequency self-tuning VEH is proposed for rotating applications. Under the rotating excitation, the proposed VEH can simultaneously adjust two parameters that affect the resonant frequency by centrifugal force, which is the key to realize frequency self-matching of the VEH in a certain frequency range. The two parameters are the axial force and effective length of the piezoelectric beam. A frequency tuning mass was designed to effectively adjust the axial force of the piezoelectric beam, and a nonlinear spring was designed to accurately control the effective length of the piezoelectric beam. The proposed VEH was simulated with ANSYS. The simulation results show that there is only one frequency matching point in a certain rotation frequency range when the centrifugal force only changes the axial force of the piezoelectric beam, which is the reason why the reported self-tuning VEH can not achieve frequency self-matching within a certain frequency range. When the centrifugal force simultaneously changes the axial force and the effective length of the piezoelectric beam, the frequency self-matching can be realized in a certain frequency range instead of only one frequency point. Simulation data analysis shows that the proposed VEH can achieve frequency self-matching in the range of 10–20 Hz through easy spring design.

A dual-core fiber for tunable polarization splitters in the terahertz regime

We present a new scheme of dual-core THz fiber for tunable polarization splitter based on the mode coupling theory. Each elliptical polymer core is modified with two elliptical air holes, which is helpful for high modal birefringence and low transmission loss. Due to different coupling lengths for x and y polarizations, the two orthogonal polarizations can be easily separated in an appropriate transmission length. Characteristics of the proposed fiber are discussed numerically in detail, including modal birefringence, effective material absorption loss, coupling and splitting length, transmission loss, extinction ratio, tunability. For the THz polarization splitters, 0.865 cm splitting length is numerically demonstrated at the operation frequency of 1 THz. An efficient tuning method is provided that the operation frequency can be tuned by the applied pressure. This tuning method extends the operation frequency bandwidth from 0.9 to 1 THz in the fixed splitting length. This proposed pressure-tuning THz fiber polarization splitter has potential applications in the field of on-chip integrated THz polarization devices and in-fiber integrated optical devices.

Hybrid absorber with carbon black composite and metamaterial structure

This study introduces a new broadband hybrid perfect absorber (HA) that includes metamaterial absorber (MA) and a lossy composite. The unit cell of the MA is in the form of two concentric ring-based structures fabricated on an FR4 substrate, which provides a broadband absorption band because of two neighbouring resonance frequencies. The composite layer is built by mixing the carbon black powder and epoxy resin in an optimised weight percentage. By modelling the structure with multiple transmission line sections, a closed-form procedure has been proposed to optimise the HA parameters. The final tuning of the HA parameters is performed using HFSS. A prototype of the HA is fabricated and measured. The results indicate that the proposed HA provides nearly perfect absorption (absorption ratio over 99%) in the frequency range of 2–2.8 GHz. It is, also, polarisation-insensitive due to its symmetrical design. The total thickness of the proposed structure is 12.5 mm, which is acceptable concerning the absorption rate and the operational frequency bandwidth.

Design and Analysis of a TEM Mode Rectangular Coaxial Waveguide for Mobile 5G Millimeter Wave Antenna Module Applications

In this paper, design and analysis of a transverse electromagnetic (TEM) mode rectangular coaxial waveguide for a mobile 5G millimeter wave (mmWave) antenna module are presented. General structures of 5G radio frequency (RF) module for mobile sub-6 GHz and mmWave applications are also discussed in this paper. Thorough analysis of transmission line and waveguide structures at mmWave frequency band is essential and fundamental information to design highly integrated RF front-end modules. Theoretical design equations of the waveguide, such as impedance, loss, and radiation are presented, and the equations are verified by a full wave 3D FEM electromagnetic simulator. Impedance value of the rectangular waveguide structure was calculated using the conformal mapping method. Theoretical operation frequency bandwidth and design guide are also presented. The characteristics and analysis of the rectangular coaxial waveguide structure presented in this paper is easily scalable to other frequency bands. The proposed design equations are also applicable to various planar layer-by-layer integrated circuit (IC) or module manufacturing process.

A novel MEMS triboelectric energy harvester and sensor with a high vibrational operating frequency and wide bandwidth fabricated using UV-LIGA technique

A novel triboelectric energy harvesting (TEH) and sensing system scaled down to microelectromechanical systems (MEMS) size is presented. The design is structurally optimized for harvesting the highest average power and power density while ensuring the structural robustness. Unlike traditional triboelectric energy harvesters, this design results in a high operating frequency with a wide bandwidth. Adoption of MEMS fabrication techniques including the use of spin-coated Teflon AF rather than a Teflon sheet, adaptation of UV-LIGA (Ultra-Violet Lithographie, Galvanoformung, Abformung) with modifications and implementation of a thick polyimide sacrificial layer make the fabrication process unique. If excited by ±9.33 g external vibration with a frequency of 1.15 kHz, the TEH can generate 0.179 μW average power and 0.597 μW peak power at an optimum resistive load of 256 kΩ. The peak surface power density, volumetric power density and acceleration-normalized volumetric power density reach 3.98 μWcm−2, 2.64 mWcm-3 and 30.3 μWcm-3/g2, respectively. While the surface power density of the presented TEH is moderate, the volumetric power density and acceleration-normalized volumetric power density are quite competitive among the state-of-the-art designs. The TEH also demonstrates a wide operating frequency bandwidth of 920 Hz. If operated as an accelerometer, the device shows a linear sensitivity of 43 mV/g. Although the simulation predicts the optimum operating frequency and load resistance of the system to be at 800 Hz and 10 MΩ, respectively, the experimental results demonstrate these values to be at 1150 Hz and 256 KΩ. A few fabrication anomalies, most notably the notching in the Teflon layer and bowing of the proof-mass, are responsible for this deviation. In addition, a distortion is observed in the simulated output voltage profile which is not present in the experimental output voltage profile due to the presence of the parasitic capacitance in the experimental circuit. The aforementioned triboelectric energy harvester can have specific applications in the sensor and actuator systems in the aircraft industry as well as in the automobile industry, micro-robotic systems, prosthetic systems, and sensor nodes in the internet of things (IoT) due to its operating frequency and bandwidth range.

Enhanced nonlinear energy harvesting using combined primary and parametric resonances: Experiments with theoretical verifications

Presented in this paper is harvested nonlinear energy from a vibration energy harvester device; the device has been designed, manufactured, and tested successfully – the device performance is verified theoretically to some extent. The design concept is on the basis of merging the nonlinearities of the building block (i.e. a beam) and those induced by the motion limiters, which for some design parameters leads to the combination of parametric and primary resonances of the device; these two resonances increase the operational frequency bandwidth by 118%. By introducing motion limiters to the proposed system, the overall frequency bandwidth of the primary and parametric resonances is able to be broadened even more -- up to 178%. By varying the angle between the base (ambient) excitation and the length of the core element; the optimal angle for the largest possible frequency bandwidth is obtained. Theoretical investigations including the finite element method (FEM) using ANSYS and an averaging perturbation technique have been performed to verify the experimental results for few cases. An experimental parametric study on the performance of the device has also been conducted to highlight the limiter gap and type as well as orientation angle effects.

Broadband metamaterials and metasurfaces: a review from the perspectives of materials and devices

Abstract Metamaterials can possess extraordinary properties not readily available in nature. While most of the early metamaterials had narrow frequency bandwidth of operation, many recent works have focused on how to implement exotic properties and functions over broad bandwidth for practical applications. Here, we provide two definitions of broadband operation in terms of effective material properties and device functionality, suitable for describing materials and devices, respectively, and overview existing broadband metamaterial designs in such two categories. Broadband metamaterials with nearly constant effective material properties are discussed in the materials part, and broadband absorbers, lens, and hologram devices based on metamaterials and metasurfaces are discussed in the devices part.

Optimal Design of an X-Band, Fully-Coaxial, Easily-Tunable Broadband Power Equalizer for a Microwave Power Module

A microwave power module (MPM), which is a hybrid combination of a solid-state power amplifier (SSPA) as a driver and a traveling-wave tube amplifier (TWT) as the final high power stage, is a high-power device largely used for radar applications. A gain equalizer is often required to flatten the TWT output power gain owing to its big gain fluctuations over the operating frequency range. In this paper, the design of an X-band, fully-coaxial, easily-tunable broadband power equalizer for an MPM is presented. The structure is composed of a coaxial waveguide as the main transmission line and a coaxial cavity loaded with absorbing material as a resonant unit. Sensitivity analyses of the attenuation amplitude and resonant frequency of the equalizer in terms of coaxial cavity length, thickness of the absorbing disc, and insertion depth of the probe were carried out. The measured results were in good agreement with the simulated ones, showing that the equalization curve met the requirements well and proved that this optimal structure has the advantages of a large power capacity, a wide operating frequency band, is easily tunable, and good transmission performance.

A Compact Broadband Monolithic Sub-Harmonic Mixer Using Multi-Line Coupler

A compact broadband monolithic sub-harmonic mixer is presented in a 70 nm GaAs Technology for millimeter wave wireless communication application. The proposed mixer adopts a novel multi-line coupler structure; where the two-sided coupling energy of radio frequency (RF) and local oscillation (LO) signals are both collected and efficiently feed to anti-parallel diode pair (APDP) topology; resulting in broadband performance and compact chip size. As a comparison in the same circuit configuration; the five-line coupler can expand the bandwidth of the existing three-line coupler by 85% and reduce the area by 39.5% when the central frequency is 127 GHz. The measured conversion gain is −16.2 dB to −19.7 dB in a wide operation frequency band of 110–170 GHz. The whole chip size is 0.47 × 0.66 mm2 including test pads. The proposed mixer exhibits good figure-of-merits for D-band down-converter applications

Design of high-efficiency compact Doherty power amplifier with harmonics suppression and wide operation frequency band

A novel Doherty power amplifier (DPA) using a novel power divider with harmonics suppression and size reduction is proposed. The designed power divider suppresses eight unwanted harmonics. Moreover, the proposed divider reduces the circuit size and only occupies 41% in comparison with conventional divider. In the DPA structure two elliptical resonators are used instead of two long λ/4 transmission lines to size reduction. The AB and C classes power amplifiers are exploited as main and auxiliary amplifiers. The proposed DPA has good specifications such as wide bandwidth from 500 MHz to 1900 MHz with a fractional bandwidth of 116%. The DE, PAE and gain parameters of the designed DPA are 76%, 71%, and 19 dB, respectively.

A Compact Integrated Small Disk Monopole Antenna with DGS for Wireless Applications

The structure of a compact Micro strip feed circular monopole antenna working in the frequency range of (2.5GHz-4GHz) and wideband of frequency ranging from 4.9GHz to 19.93GHz is proposed in this paper. Using a circular radiating monopole with terrible ground wideband frequency operation is possible. Two frequency bands can be accomplished by separating the middle part of the patch and further engraving a circular arc r=4.4 and a loss tangent of 0.02 was utilized to realize and simulate this antenna. It can be operated in both the frequency bands 2.5-4GHz and 4.9-19.93GHz [wideband] possessing less than -10dB reflection coefficient. The whole WB and also in the low-frequency band as mentioned above shows a sturdy radiation pattern.

Dual-Active Bridge Series Resonant Electric Vehicle Charger: A Self-Tuning Method

This paper presents a new self-tuning loop for a bidirectional dual-active bridge (DAB) series resonant converter (SRC). For different loading conditions, the two active bridges can be controlled with a minimum time displacement between them to assure zero voltage switching (ZVS) and minimum circulation current conditions. The tuning loop can instantly reverse the power direction with a fast dynamics. Moreover, the tuning loop is not sensitive to series resonant tank tolerances and deviations, which makes it a robust solution for power tuning of the SRCs. For simplicity, the power is controlled based on the power-frequency control method with a fixed time displacement between the active bridges. The main design criteria of the bidirectional SRC are the time displacement, operating frequency bandwidth, and the minimum and maximum power, which are simply derived and formulated based on the self-tuning loop’s parameters. Based on the parameters of the tuning loop, a simplified power equation and power control method is proposed for DAB-SRCs. The proposed control method is simulated in static and dynamic conditions for different loadings. The analysis and simulation results show the effectiveness of the new tuning method.

Broadband vibration energy harvesting for wireless sensor node power supply in train container.

Wireless sensor nodes (WSNs) for temperature and humidity monitoring are commonly used in a cold chain logistics container. Energy harvesting technology is expected to realize the sustainable self-power supply for the WSN. Low amplitude and broadband vibration energy harvesting performance are the key points in train application. In this study, two piezoelectric vibration energy harvesters (PVEHs) are designed and simulated via COMSOL. Their low resonant frequencies and high electromechanical sensitivities are realized by big L-shaped mass blocks with different material densities. Their broadband vibration energy harvesting performance is achieved by the stopper and series connection. Experimental data are shown at an acceleration of 0.5 m/s2; PVEH-1 and PVEH-2 have maximum powers of 0.24 mW and 0.1 mW when excited at the resonant frequencies of 13.1 Hz and 18.8 Hz, respectively, and they both have the optimal load resistance of 40 kΩ. Two circuit design styles of two PVEHs, independent and series styles, are proposed for broadband vibration energy harvesting. Experimental results show that the series style has a wider operating frequency bandwidth and shorter charging time. Two PVEHs in series style can be effectively used for power supply of the temperature and humidity WSN in the broadband frequency range of 8.7-22.0 Hz above charging root mean square voltage of 5 V at the acceleration of 3.0 m/s2. This scheme is promised to be applied to the cold chain logistics train container.

Low-frequency and broadband vibration energy harvester driven by mechanical impact based on layer-separated piezoelectric beam

Vibration energy harvesting is to transform the ambient mechanical energy to electricity. How to reduce the resonance frequency and improve the conversion efficiency is very important. In this paper, a layer-separated piezoelectric cantilever beam is proposed for the vibration energy harvester (VEH) for low-frequency and wide-bandwidth operation, which can transform the mechanical impact energy to electric energy. First, the electromechanical coupling equation is obtained by the Euler-Bernoulli beam theory. Based on the average method, the approximate analytical solution is derived and the voltage response is obtained. Furthermore, the physical prototype is fabricated, and the vibration experiment is conducted to validate the theoretical principle. The experimental results show that the maximum power of 0.445 □W of the layer-separated VEH is about 3.11 times higher than that of the non-impact harvester when the excitation acceleration is 0.2 g. The operating frequency bandwidth can be widened by increasing the stiffness of the fundamental layer and decreasing the gap distance of the system. But the increasing of operating frequency bandwidth comes at the cost of reducing peak voltage. The theoretical simulation and the experimental results demonstrate good agreement which indicates that the proposed impact-driving VEH device has advantages for low-frequency and wide-bandwidth. The high performance provides great prospect to scavenge the vibration energy in environment.

An Improved Design Methodology of the Double-Sided LC-Compensated CPT System Considering the Inductance Detuning

This paper proposes an improved design methodology of the double-sided LC -compensated capacitive power transfer (CPT) system considering the inductance detuning. Compared to the perfect-resonant scenario, this paper shows that the inductance detuning has the benefit to achieve the soft-switching condition for the CPT system, and the output current and internal voltage stresses can also be maintained within the desired range. The contributions of this paper are summarized in three parts. First, it analyzes the impacts of the inductance variations on the system frequency property, including the input current, output current, and internal capacitor voltage stresses. Second, it proposes three principles to detune the inductances as the methodology to design a CPT system. Third, a prototype is implemented, which achieves 368.5 W power transfer across a 400 mm × 400 mm × 4 mm glass layer with 91.8% dc–dc efficiency. Experimental results validate that the proposed design principles are satisfied, showing that the output current is within the desired range, the input soft-switching condition is achieved, and the internal voltage stresses are within the safety limit. Moreover, the efficiency and frequency properties are also validated by the experimental results, showing a wide power range of the high-efficiency operation (higher than 90%) and a wide frequency bandwidth of the soft-switching operation (from 0.96 to 1.12 MHz).

A Low-Profile High-Gain and Wideband Log-Periodic Meandered Dipole Array Antenna with a Cascaded Multi-Section Artificial Magnetic Conductor Structure.

This paper presents a low-profile log-periodic meandered dipole array (LPMDA) antenna with wideband and high gain characteristics. The antenna consists of 14 dipole elements. For compactness, a meander line structure is applied to each dipole element to reduce its physical length. As a result, a compact and wideband LPMDA antenna is realized, exhibiting a wide impedance bandwidth of 1.04–5.22 GHz (ratio bandwidth of 5.02:1) for || < −10 dB. To enhance the antenna gain performance while maintaining the wideband behavior, the LPMDA antenna is integrated with a new design of an artificial magnetic conductor (AMC) structure. The designed AMC is realized by combining three AMC structures of different sizes to form a cascaded multi-section AMC structure, of which its overall operating bandwidth can continuously cover the entire impedance bandwidth of the LPMDA antenna. The proposed AMC-backed LPMDA antenna is experimentally verified and its measured −10 dB reflection bandwidth is found to be in the range of 0.84–5.15 GHz (6.13:1). At the main beam direction within the operating frequency bandwidth, the gain of the proposed AMC-backed LPMDA antenna ranges from 7.15–11.43 dBi, which is approximately 4 dBi higher than that of an LPMDA antenna without an AMC. Moreover, the proposed antenna has a low profile of only 0.138. ( is the free-space wavelength at the lowest operating frequency).

Two-Dimensional Pattern-Reconfigurable Cross-Slot Antenna With Inductive Reflector for Electromagnetic Torso Imaging

A wideband and low-profile cross-slot pattern reconfigurable antenna for electromagnetic imaging systems is proposed. The antenna is designed to cover the human chest area with steerable unidirectional radiation patterns at 0.7–0.9 GHz. The antenna is comprised of a corrugated cross-slot as the main radiator, and four parasitic slots with four p–i–n diodes operating as reflectors. An embedded feeding network with six p–i–n diodes is used to feed the main slot and switch the feeding path to modify the direction of the radiated beam (vertical/horizontal). In addition, an inductive mesh-grid surface is used to reduce the back lobe and enhance the operating frequency bandwidth. The antenna dimensions are ${0.8} {\lambda }_{0} {\times 0.} {8} {\lambda }_{0} {\times 0.18} {\lambda }_{0}$ (where ${\lambda }_{0}$ is the wavelength of the lowest frequency operation). By turning the parasitic slot p–i–n diodes to ON/OFF modes, the main beam can be steered along five distinctive positions at 0°, and at ±30° in two perpendicular planes. The antenna achieves a peak gain of 9 dBi at 0.8 GHz with 1 dB gain variations over the band of operation with a peak front-to-back ratio of 20 dB.

Radial Basis Functions Intended to Determine the Upper Bound of Absolute Dynamic Error at the Output of Voltage-Mode Accelerometers.

In this paper, we propose using the radial basis functions (RBF) to determine the upper bound of absolute dynamic error (UAE) at the output of a voltage-mode accelerometer. Such functions can be obtained as a result of approximating the error values determined for the assumed-in-advance parameter variability associated with the mathematical model of an accelerometer. This approximation was carried out using the radial basis function neural network (RBF-NN) procedure for a given number of the radial neurons. The Monte Carlo (MC) method was also applied to determine the related error when considering the uncertainties associated with the parameters of an accelerometer mathematical model. The upper bound of absolute dynamic error can be a quality ratio for comparing the errors produced by different types of voltage-mode accelerometers that have the same operational frequency bandwidth. Determination of the RBFs was performed by applying the Python-related scientific packages, while the calculations related both to the UAE and the MC method were carried out using the MathCad program. Application of the RBFs represent a new approach for determining the UAE. These functions allow for the easy and quick determination of the value of such errors.

Pattern Reconfigurable Metasurface Antenna for Electromagnetic Torso Imaging

A pattern reconfigurable metasurface antenna for an electromagnetic torso imaging system operating at the ultrahigh frequency (UHF) band is presented. To meet the requirements of electromagnetic torso imaging, the antenna can scan the human chest with steerable unidirectional radiation patterns. The designed antenna consists of three rectangular microstrip-fed slot radiators illuminating a metasurface layer with $7\times 5$ unit cells to cover the whole chest. Six p-i-n diodes are used to switch the radiating slots creating different beams. The unit cell dimensions are $0.125\lambda _{0}\times 0.125\lambda _{0}$ and the antenna has a low profile of $0.9\lambda _{0}\times 0.7\lambda _{0}\times 0.06\lambda _{0}$ ( $\lambda _{0}$ is the wavelength of the lowest operating frequency of the antenna). The antenna creates three distinct beams with a peak gain of 8 dBi at 1 GHz and 2 dBi gain variations across different beams over its measured wide operating frequency bandwidth of 27% at 0.8–1.05 GHz. A complete electromagnetic torso imaging system, which utilizes the designed antenna, is built and is successfully tested to detect 20 mL of fluid (water) inside the torso, thus differentiating between healthy and unhealthy cases.