Low Working Frequency Research Articles

Design and Analysis of Multi-layer Resistive Ink Film Based Metamaterial Ultra-thin Broadband Absorber

Purpose: In order to achieve an excellent electromagnetic absorption response for radar applications, this work proposes a design of an ultra-thin, super broadband, high efficiency meta-material that is insensitive to incidence angle. Methodology: a metamaterial based on multilayer resistive ink unit cell is selected, designed and optimized for minimum electromagnetic absorption and widest bandwidth. The equivalent circuit is derived and analyzed and compered using matlab to results from electromagnetic simulator CST. Findings: Calculating approval requires impedance matching in the structure, which makes it challenging to absorb at high frequencies. In this instance, the proposed structure achieves more than 0.98 absorptivity between 4 and 400 GHz, resulting in a broad absorption bandwidth. When exposed to oblique incidences, the proposed structure behaves in the same way for both transverse electric (TE) and transverse magnetic (TM) modes up to 45°. The total thickness of the planned absorber is 2.105 mm, or 0.028 λ0 at the lowest working frequency. Additionally, find and compare previous radar band reports with the proposed absorber. It is reported to offer more practical feasibility and to be a viable choice for S, C, X, Ku, K, Ka, V, and W bands in addition to millimeter-band radar applications. Unique contribution to theory, practice and policy: Increasing the band width compared to previous studies while increasing the absorption efficiency and reducing the thickness of the metamaterial.

Research on the electromagnetic characteristics of metasurfaces based on air dielectric substrates

Electromagnetic metasurfaces can achieve effective control of electromagnetic waves and achieve effects such as blocking, enhancing, reflecting, transmitting, or deflecting electromagnetic waves, possessing electromagnetic properties that go beyond traditional materials. Existing research indicates that the dielectric substrate of metasurfaces has a significant impact on their electromagnetic properties. Increasing the substrate thickness will be beneficial for expanding the impedance bandwidth of the metasurface, and changes in dielectric constant will also have some impact on the operating frequency and bandwidth of the metasurface. A metasurface based on an air substrate was proposed through the research of dielectric materials. In addition, an ultrawideband, miniaturized, and high-gain metasurface antenna based on an air substrate is designed. The overall size of the designed antenna is 0.5λL × 0.5λL (where λL represents the wavelength at the lowest working frequency in free space). The measured results indicate that the proposed antenna exhibits a −10 dB impedance bandwidth of 74.3% (2.53–5.52 GHz) and a peak boresight gain of 10.1 dBi.

Causal optimal and optically transparent ultra-wideband microwave metamaterials absorber with high angular stability.

Wideband microwave absorbers, especially those with high optical transparency, are significantly used in civil and military fields. This paper proposes an ultra-wideband optically transparent metamaterial absorber (MMA) with causal optimal thickness and high angular stability. Based on the equivalent circuits model of the MMA, a genetic algorithm is adopted to identify the best circuit parameters that can realize broadband microwave absorption. High transparent indium tin oxide and poly-methyl methacrylate are utilized to realize the absorber. Optimization and simulation results show that the designed MMA presents a high microwave absorption above 90%, covering a wide frequency of 2.05-15.5 GHz with an impressive FBW of 153.3%. The proposed MMA exhibits extraordinary angular stability. For TM polarization, it can still maintain a fractional bandwidth (FBW) over 114.5% at an incidence angle of 70° and over 142% at an incidence angle of 60°, while the FBW of both TE polarization and TM polarization exceeds 150% when the incidence angle is below 45°. Furthermore, the proposed absorber has the advantages of high transparency and polarization insensitiveness. A prototype of the proposed MMA is fabricated and experimentally tested. The measured results are in excellent agreement with the optimized design and the full-wave simulation results, demonstrating its excellent performance. Most significantly, the overall thickness of the absorber is 0.102 λ at the lowest working frequency and only 1.08 times the causality-dictated minimum sample thickness. The MMA proposed herein provides methods to achieve high compatibility with wideband microwave absorption, optical transparency, and wide-angle incidence, thus enabling a wide range of applications in stealth, electromagnetic pollution reduction, and electromagnetic compatible facilities.

Free-Standing Electrode and Fixed Surface Tiny Electrode Implemented Triboelectric Nanogenerator with High Instantaneous Current.

Conventional triboelectric nanogenerators (TENGs) face challenges pertaining to low output current density at low working frequencies and high internal impedance. While strategies, such as surface modification to enhance surface charge density, permittivity regulation of materials, and circuit management, have partially mitigated these issues. However, they have also resulted in increased complexity in the fabrication process. Therefore, there is an urgent demand for a universal and simplified approach to address these challenges. To fulfill this need, this work presents a free-standing electrode and fixed surface tiny electrode implemented triboelectric nanogenerator (FFI-TENG). It is fabricated by a straightforward yet effective method: introducing a tiny electrode onto the surface of the tribo-negative material. This approach yields substantial enhancements in performance, notably a more than tenfold increase in output current density, a reduction in effective working frequencies, and a decrease in matching resistance as compared to vertical contact-separation TENGs (CS-TENGs) or single-electrode TENGs (SE-TENGs). Simultaneously, a comprehensive examination and proposition regarding the operational mechanism of FFI-TENG, highlighting its extensive applicability are also offered. Significantly, FFI-TENG excels in mechanical energy harvesting even under ultra-low working frequencies (0.1Hz), outperforming similar contact-separation models. This innovation positions it as a practical and efficient solution for the development of low-entropy energy harvesters.

Miniaturized 3‐bit frequency‐reconfigurable monopole antenna with a meander line

AbstractA novel 3‐bit frequency‐reconfigurable antenna (FRA) with miniaturized dimensions is realized with a meander line. The frequency reconfiguration of the antenna is achieved by introducing N Radio Frequency (RF) PIN diodes into the meander line. The related parts of the meander line with different lengths are bypassed or included into the antenna by switching on or off the diodes, resulting in 2N switchable size lengths of the antenna and equally spaced operating frequencies. A 3‐bit reconfigurable meander‐line antenna (N = 3) is designed, and the simulated and measured results agree well. The antenna provides 8 (23) independent and switchable states, with the operating frequencies covering a wide switchable frequency range from 1.04 to 1.51 GHz and the working bandwidths varying from 80 to 150 MHz. The number of working bandwidth states is maximized, considering the number of switches used. Moreover, the results reveal an acceptable peak gain of 1.59 dBi in terms of the miniaturized total dimension of 0.17 λg × 0.07 λg (λg is the guided wavelength at the lowest working frequency), which is more compact than several published FRAs.

Design and Analysis of Pattern Reconfigurable Antenna Based on RF MEMS Switches

The research on reconfigurable antennas has some disadvantages such as low working frequency and large size. This paper presents a Ka-band patch antenna with pattern reconfigurability using RF MEMS switches. The antenna contains one main patch, two sub-patches, two parasitic patches, and two RF MEMS switches. By controlling the states of the RF MEMS switches, the antenna can achieve three different radiation patterns (−8°, 0°, and +8°) at 35 GHz. The pattern analysis was based on the electric field vector addition method. The analytical, simulated, and measured results agree well with each other. Due to its compact and thin structure of 3.7 mm × 5.2 mm × 0.4 mm, this antenna can be applied in fields such as satellites, smartphones, etc.

High-Speed Hardware Architecture Based on Error Detection for KECCAK.

The hash function KECCAK integrity algorithm is implemented in cryptographic systems to provide high security for any circuit requiring integrity and protect the transmitted data. Fault attacks, which can extricate confidential data, are one of the most effective physical attacks against KECCAK hardware. Several KECCAK fault detection systems have been proposed to counteract fault attacks. The present research proposes a modified KECCAK architecture and scrambling algorithm to protect against fault injection attacks. Thus, the KECCAK round is modified so that it consists of two parts with input and pipeline registers. The scheme is independent of the KECCAK design. Iterative and pipeline designs are both protected by it. To test the resilience of the suggested detection system approach fault attacks, we conduct permanent as well as transient fault attacks, and we evaluate the fault detection capabilities (99.9999% for transient faults and 99.999905% for permanent faults). The KECCAK fault detection scheme is modeled using VHDL language and implemented on an FPGA hardware board. The experimental results show that our technique effectively secures the KECCAK design. It can be carried out with little difficulty. In addition, the experimental FPGA results demonstrate the proposed KECCAK detection scheme's low area burden, high efficiency and working frequency.

Development of a novel fast tool servo using topology optimization

Micro/nanostructured surfaces have wide applications in optics, electronics, and aerospace. However, the current fast tool servo (FTS) cannot satisfy the large demand for micro/nanostructured surfaces in the industry, because their low working frequency influences the machining efficiency. To solve this problem, this paper develops a novel FTS with the high working frequency. To improve the working frequency, a topology optimization algorithm is proposed to design its mechanical structure. Then, the numerical models of the FTS, including the input stiffness, amplification ratio, natural frequency, and maximum stress, are established to analyze its specifications. Performance tests show that the stroke and maximal working frequency of the developed FTS are 15 μm and 1250 Hz, demonstrating superior performance. Besides, to improve motion accuracy, a closed-loop control system is designed based on the proportional-integral controller and feed-forward compensation methods. Experimental results show that errors of motion trajectories in three cases are lower than ± 50 nm, demonstrating the ultrahigh motion accuracy of the developed FTS. Therefore, this research develops a new FTS, which not only has a high working frequency but also has an ultrahigh motion accuracy.

A New Online Monitoring Method for Water-in-Oil Droplet Based Microfluidic Devices

The online water-in-oil (w/o) droplet monitoring is essential for the uniformity of the droplet based microfluidic devices. In this work, a contactless impedance detection (CID) method for online w/o droplet monitoring in microfluidic devices is proposed. In the proposed method, a new CID sensor, which can work at low working frequency and overcome the unfavorable influence of coupling capacitance, is developed to obtain the impedance information of the w/o droplet. Based on the obtained impedance information, measurement models are established to realize online measurement of drop length and dispersed phase holdup. Then the coefficients of variation (CVs) of the two measured parameters are calculated to evaluate the uniformity of the droplets for online monitoring. Online monitoring experiments of w/o droplet were carried out in a microfluidic device with a 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times $ </tex-math></inline-formula> 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> microchannel. The experimental results verify the effectiveness of the proposed droplet monitoring method. The developed CID sensor can realize impedance measurement at a working frequency lower than 50kHz. The drop length and dispersed phase holdup are useful parameters for online monitoring of droplets. With the established measurement models, the maximum relative error of droplet length measurement is less than 10% in the droplet length range of 1.5mm-3.5mm. And the maximum error of dispersed phase holdup measurement is less than 5% in the dispersed phase holdup range of 0.20-0.67.

An audio-tactile interface based on dielectric elastomer actuators

This paper presents a concept of a dielectric elastomer actuator (DEA) user interface (smart button) that can sense a user’s touch and provide multi-sensory tactile and acoustic feedbacks through a single electrical input signal. The DEA relies on a multi-layer layout, in which a layer detects user-driven deformations (touches) via custom-built capacitance sensing electronics, and the remaining layers are used to provide actuation (audio-tactile feedbacks). Building upon a recently presented principle, combined tactile and acoustic feedbacks are produced by concurrently exciting different vibration modes of the same active membrane over different frequency ranges. An integrated demonstrator setup is presented, which includes a DEA, an acoustic enclosure, compact sensing and driving electronics. A characterization of the prototype is conducted, including an analysis of the sound pressure level, the force/stroke output at lower working frequencies, the ability to sense deformations with different profiles and produce combined audio-tactile outputs. Compared to previous works on multi-function DEAs, the system presented in this paper provides largely improved sensing performance (with lower working voltage) and features a deeper level of integration (with small-scale custom sensing electronics, and logics embedded onto scalable microcontrollers) and is thus specifically optimised for user-interaction applications. On this end, tests with users are presented here for the first time, which allowed evaluating the subjective perception of the interface’s feedbacks. By means of further optimisation and miniaturisation of the power/sensing electronics and structural components, the layout and multifunction DEA principle presented here might lead, in the future, to the development of DEA-based smart buttons for active surfaces, or portable/wearable user interfaces and communicators.

Tapered Graded Index Lens Antenna With Enhanced Penetration for Near-Field Torso Imaging

A tapered graded index (GRIN) lens antenna that aims at enhancing electromagnetic penetration into human torso by generating focused planar near-field radiation is presented. The antenna is composed of a four-layer lens excited by a modified slot antenna. Each layer of the lens case is filled with fabricated mixtures of engineered materials that have specific relative permittivity values. The exciting antenna is made compact by utilizing meandered feed lines and substrate folded technique. The number of layers of the lens and the specification of each layer are determined by minimizing the generalized reflection coefficient of the antenna. A focused plan-wave radiation is achieved by tapering the lens based on the theory of total internal reflection. The study of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field quality inside the torso demonstrates that the proposed lens successfully converts spherical wave radiation into a local plane-wave radiation, resulting in 11 dB improvement in wave penetration inside the torso compared to the body-matched antenna (without lens). The measured results show that the antenna operates over a wide band from 0.43 to 1.85 GHz (125% fractional bandwidth), which is a merit for the torso imaging application. Furthermore, the antenna has the physical size of 110 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 110\times48$ </tex-math></inline-formula> mm3, corresponding to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15\times 0.15\times 0.06\lambda _{0}^{3}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength at the lowest working frequency. The results indicate that the antenna accomplishes 4.9 dB (209% improvement) stronger wave penetration inside the torso compared to other existing GRIN lens antennas.

Realizing the perfect sound absorption and broadening effective band using porous material and micro-perforated plate

The noise attenuation ability of a single material or structure, especially for low-frequency noise, is limited by its thickness. Aiming to achieve high-efficiency noise attenuation at low frequencies, this paper proposes the methods of porous material filling and micro-perforated plate (MPP) embedding to design a perfect sound absorber at different frequencies using the under-loss Helmholtz resonator (HR). Based on the transfer matrix method, the theoretical calculation models of the sound absorption coefficients of the HR, Helmholtz resonator with porous material (HRP), and Helmholtz resonator with micro-perforated plates (HRM) are constructed. Based on the theoretical models, the under-loss absorber HR1 with the peak absorption at 243 Hz, and the HRP and HRM with perfect absorption at 212 Hz and 157 Hz are designed, respectively. The impedance analysis and complex frequency plane method are used to analyze the sound absorption mechanisms of the HR1, HRP, and HRM. The accuracy of the theoretical model is verified by the finite element method. Finally, the three acoustic absorbers are manufactured using 3D printing technology, and the absorption coefficients are evaluated experimentally. The experimental results show that the HR1 has a high working frequency at 245 Hz and a narrow bandwidth of high-efficiency sound absorption ([Formula: see text]), which is only 12 Hz. The working frequency of the HRP is 214 Hz, and its high-efficiency sound absorption bandwidth is 54 Hz. The HRP has the lowest working frequency at 157 Hz and the widest high-efficiency sound absorption bandwidth of 58 Hz among the three absorbers. The research results presented in this paper provide a reference for the realization of low-frequency broadband noise attenuation designs and have certain application potential in noise control.

An optimized quadrature RF receive coil for very-low-field (50.4 mT) magnetic resonance brain imaging

The radiofrequency (RF) receive coil is a direct probe for magnetic resonance imaging (MRI), and its performance determines the quality of MRI results. The RF coil employed for low-field MRI has a low working frequency, which makes its characteristic different from the RF coil exploited for conventional clinic MRI and may result in a different optimum RF coil configuration. To design and optimize a head RF receive coil for a very-low-field (50.4 mT) MRI system, we investigated the relationship between the structure and performance of the RF coil. Specifically, we focused on a quadrature RF coil consisting of a saddle coil and a modified Helmholtz coil wound around the surface of an elliptical cylinder. First, we evaluated the efficiency and RF magnetic field inhomogeneity of one-loop RF coil and determined the optimum dimension for saddle coil and modified Helmholtz RF coil. Then, we further studied the performance of the optimum-dimension RF coil from the perspective of the number of RF coil loops and revealed that the number of loops of RF coil for very-low-field MRI was a remarkable feature influencing the alternative current (AC) resistance of the RF coil and therefore make the SNR increase first and then decrease with the number of RF coil loops. We finally obtained the optimum number of loops for the saddle coil, modified Helmholtz coil, and fabricated a quadrature RF coil. The performance of the quadrature coil was evaluated through CuSO4 phantom imaging and in vivo human brain imaging. In phantom imaging, the SNR of quadrature RF coil increased by about 40% compared with that of single-channel RF coil.

Measuring the Gradient of Sound Pressure Directly Via Flexoelectricity

In this work, we propose the design of a flexoelectric sensor, which can measure sound-pressure gradient directly. It is found that the sensitivity of sound-pressure gradient of the flexoelectric sensor has a wide band for low working frequencies. Our theoretical and experimental results indicate that the position of sound sources can be predicted based on the measured sound-pressure gradients of three flexoelectric sensors, which are perpendicular to each other. Moreover, different from the previous design for a piezoelectric sensor array, only three flexoelectric sensors are needed to determine the orientation of sound sources. The flexoelectric sensor proposed here may provide an alternative way for the pressure-gradient measurement.

A MEMS-Based Co-Oscillating Electrochemical Vector Hydrophone.

Aiming at the development needs of low-frequency and high-sensitivity vector hydrophones, this paper has developed a micro-electro-mechanical system (MEMS) based co-oscillating electrochemical vector hydrophone. We obtained the optimized geometric parameters through simulation analysis of the diameter of the rubber membrane, the length of the flow channel and the diameter of the flow holes. Based on the simulation results, electrodes were fabricated using MEMS technology, and were then assembled and tested. Device characterization was conducted, where the sensitivity and bandwidth were quantified as 0.5–150 Hz, −187 dB ref. 1 V/μPa, respectively. Compared with a previously reported co-oscillating vector hydrophone, the co-oscillating vector hydrophone developed in this article featured a lower working frequency band.

Study on Dual-Frequency Imaging of Capacitively Coupled Electrical Impedance Tomography: Frequency Optimization

In this work, a new dual-frequency imaging framework of capacitively coupled electrical impedance tomography (CCEIT) is presented. Unlike conventional single-frequency imaging and recently emerged multi-frequency imaging, the dual-frequency imaging adopts two different working frequencies to obtain the real part and the imaginary part of the impedance, respectively. With the real part image and the imaginary part image reconstructed at the two frequencies, the framework further introduces image fusion to obtain the fused image. To achieve the optimal selection of the two frequencies, data collection in a wide frequency range is carried out with a 12-electrode CCEIT sensor, an impedance analyzer, and a computer to obtain the real part and the imaginary part measurements. The multi-frequency data is then analyzed in depth and other two aspects, including the sensitivity distribution and the imaging quality at different frequencies, are also investigated. Research results show that a low working frequency is recommended for the real part, while a relatively high working frequency is recommended for the imaginary part. Within the investigated frequency range of 200 kHz - 20 MHz, the working frequencies for the real part and the imaginary part are optimized respectively under the investigated distribution setups. Results of verification experiment show that the proposed framework is effective. Compared with single-frequency CCEIT, dual-frequency CCEIT with the two optimized frequencies has much better imaging performance.

A Compact, Band-Notched Ultra-Wideband Fully-Recessed Antenna With Pattern Diversity for V2X Communications

In this paper, a compact, band-notched ultra-wideband (UWB) fully-recessed antenna with pattern diversity is proposed and demonstrated for vehicle-to-X communications. The antenna is composed of a multi-port central radiator fully embedded inside a bowl-shaped ground structure with a flush top. The multi-port central radiator consists of a top circular plate, four split-quarter conical monopoles, four vertically-and horizontally-orientated strips, a central metallic cylinder, and a bottom cylinder. Moreover, four F-shaped monopoles are loaded to the multi-port central radiator for producing two narrow notched bands. The integrated antenna achieves a form factor of 0.23λL3, where λL is the free space wavelength at the lowest working frequency. The proposed antenna was fabricated and characterized, achieving a measured S11 < -10 dB band ranging from 1.7 to 6 GHz with two stopbands at around 2.5 and 5.15 GHz for all four ports. Moreover, the measured mutual coupling is smaller than -15 dB, while the envelope correlation coefficients (ECCs) are below 0.1 between different input ports. A vertically-polarized (VP) omni-directional pattern can be supported when all four ports are excited simultaneously, whereas four directional patterns pointing towards different directions in the azimuthal plane can be realized when the four ports are excited individually. The demonstrated antenna is a promising candidate in multiple-input multiple-output communication systems for a wide variety of platforms.

Doğal Melanin Nanopartikülleri Kullanarak Kuvars Ayar Çatalı Tabanlı Kütle Duyarlı Sensörlerin Modifikasyonu İçin Farklı Stratejilerin Karşılaştırması

Quartz tuning fork (QTF) is a measurement tool that is gaining attraction nowadays due to remarkable features like their low cost, stable resonance frequency, and considerably low working frequency. However how to functionalize a QTF as a chemical or a physical sensor is still an important problem that needs to be solved for a widespread usage. This paper describes approaches to functionalize QTFs by utilizing melanin nanoparticles (MNP) in order to create a recognition layer for the creation of a target specific mass sensitive biosensor. In order to achieve this aim, electroplating and dip coating methods are chosen for their relative ease of use and cheap operating costs for the purpose of being industry-friendly and reproducible as a product for field applications. Moreover a comparative study on chemical etching of QTFs was conducted with the goal of improving MNP attachment during dip coating process.

Broadband Polarization-Insensitive Inkjet-Printed Conformal Metamaterial Absorber

The objective of this article is to devise a cost-effective, conformal, polarization-insensitive, and broadband metamaterial absorber for X-band applications. A periodic subwavelength conducting grid pattern is printed over flexible papers in a multi-layered fashion to achieve the broadband behavior. A silver nanoparticle incorporated inkjet printing technique is employed that does not require any post-processing such as sintering. The absorber is eco-friendly and suitable for rapid mass production at a low-cost. Moreover, the printed patterns do not crack when bent or applied over curved surfaces. The characteristics, working principle, and equivalent circuit of the absorber are described. The absorber is designed on a 1.06 mm (0.03 $\mathbf {{\lambda} _{\it l}}$ at the lowest working frequency) ultrathin substrate. It exhibits more than 90% absorptivity from 8.43 to 10.38 GHz for all angles of polarization with wide angular stability up to 45 $\text{\boldmath $^\circ $}$ . The flexibility and broadband feature is also confirmed by the experimental measurement of the fabricated prototype.

Comprehensive Design Method of a High-Frequency-Response Fast Tool Servo System Based on a Full-Frequency Error Control Algorithm.

With the development of optoelectronic information technology, high-performance optical systems require an increasingly higher surface accuracy of optical mirrors. The fast tool servo (FTS) based on the piezoelectric actuator is widely used in the compensation machining of high-precision optical mirrors. However, with the low natural frequency of mechanical structures, hysteresis of the piezoelectric actuators, and phase delay of the control systems, conventional FTS systems face problems such as a low working frequency and a large tracking error. This study presents a method for the design of a high-performance FTS system. First, a flexure hinge servo turret with a high natural frequency was designed through multi-objective optimization and finite element simulations. Subsequently, a composite control algorithm was proposed, targeting the problems of hysteresis and phase delay. The modified Prandtl–Ishlinskii inverse hysteresis model was used to overcome the hysteresis effect and a zero-phase error tracker was designed to reduce the phase error. The experimental results reveal that the tracking error of the designed FTS system was <10% in the full frequency range (0–1000 Hz).