Capacitive Gap Research Articles

Active control of plasmon-induced transparency based on a GaAs/Si heterojunction in the terahertz range

Active control optical terahertz modulator based on incorporating n-type GaAs film as the active media into plasmon-induced transparency metasurface, was investigated theoretically and experimentally. From the experimental results it could be found that the resonances transmission of the plasmon-induced transparency was optically modulated and the transmission modulation depth of 87% was achieved at 0.56 THz. This may be due to the fact that when the pump excitation power was tuned from 0 mW to 1000 mW, larger numbers of excited carriers were excited in the electronic “p-n" junction and diffused across the heterojunction to the n-type GaAs film. It increased the conductivity of the n-type GaAs film from 2.29 × 103 S/m to 1.56 × 104 S/m. As a results, the capacitive split gaps of the PIT split-ring resonators were short-circuited and the coupling strength between the resonators was decreased owing to the screening effect caused by the photo-excited carriers.

Polarization-independent perfect metamaterial absorber for C, X and, Ku band applications

In this paper, a polarization-independent perfect absorber with near-zero index metamaterial (NZIM) property is proposed. Conventional FR4 substrate without any lumped or substrate-embedded elements has been used with a unique patch of the swastika-shaped capacitive gap along with inductive tails at 90-degree rotational symmetry. The simulation results for both the unit cell and the array for co-polarized waves at normal and oblique incidences up to 90° has shown near unity absorptions at 4.238, 7.836, 10.482, 11.014 and 13.352 GHz along with near zero values of permittivity, permeability, and refractive index. The cross-polarization analysis has proved its perfect absorption capability. The absorber has shown 14 GHz of near-zero refractive index at the entire operating frequency range. The equivalent circuit analysis and measurement of both the array and the unit cell were in good agreement with simulation results, which proved it as a perfect NZIM absorber to enhance antenna gain and directivity and other sensing applications at C, X and Ku band.

Composite Right-/Left-Handed-Based, Compact, Low-Profile, and Multifunctional Antennas for 5G Applications

Two small multifunctional antennas based on the negative order resonance (NOR) are proposed for the 5G new radio (N78 band) application in this article. A novel ring-type resonator (RTR) inspired by the mushroom-type metamaterial structure is first proposed and studied by the equivalent circuit models and dispersion diagrams. The RTR comprises small patches to enhance the aperture efficiency and gain. By loading the left-handed (LH) components (gap capacitors and metallic vias), the first NOR (−1st NOR) mode is successfully excited, which leads to significant antenna size reduction. The designs overcome the bandwidth limitation of the conventional miniaturized antennas. A dual-polarized antenna with a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.30\lambda _{0} \times 0.30\lambda _{0} \times 0.04\lambda _{0}$ </tex-math></inline-formula> and a multifunctional antenna with a low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.06\lambda _{0}$ </tex-math></inline-formula> are developed with a shared aperture configuration. Moreover, they achieve a good bandwidth that well covers the 3.3–3.8 GHz N78 band, a high radiation efficiency that is larger than 80%, and flexible multipolarized radiation. These features make them preferable candidates for microcells to meet the 5G communication demands.

A New Reconfigurable Filter Based on a Single Electromagnetic Bandgap Honey Comb Geometry Cell

This work presents a new unit cell electromagnetic bandgap (EBG) design based on HoneyComb geometry (HCPBG). The new HCPBG takes a uniplanar geometry (UCPBG—uniplanar compact PBG) as a reference and follows similar design methods for defining geometric parameters. The new structure’s advantages consist of reduced occupied printed circuit board area and flexible rejection band properties. In addition, rotation and slight geometry modification in the HCPBG cell allow changing the profile of the attenuation frequency range. This paper also presents a reconfigurable unit cell HCPBG filter strategy, for which the resonance center frequency is shifted by changing the gap capacitance with the assistance of varactor diodes. The HCPBG filter and reconfiguration behavior is demonstrated through electromagnetic (EM) simulations over the FR1 band of the 5G communication network. Intelligent communication systems can use the reconfiguration feature to select the optimal operating frequency for maximum attenuation of unwanted or interfering signals, such as harmonics or intermodulation products.

Designing flexible asymmetric supercapacitor with high energy density by electrode engineering and charge matching mechanism

Extensive exploratory works are dedicating to increase the energy density of aqueous asymmetric supercapacitors (AASCs), from the perspective of augmenting the specific capacitance and widening the operating voltage window. Herein, Mxene (V2C) derived unique accordion-like layered vanadium nitride coated by ultrathin amorphous carbon layer (L-VN@AC) is synthesized via a facile nitride strategy as negative electrode materials for AASC. Profiting from the distinctive layered structure inherited from V2C, the resultant L-VN@AC electrode exhibits a more remarkable areal capacitance (631.4 mF cm−2) and outstanding rate capability compared to the V2C precursor and commercial vanadium nitride (C-VN). Furthermore, a brand-new charge matching mechanism is proposed for the assembly of AASCs with capacitive-type (pseudocapacitance/electric double layer capacitance) electrode materials to soften the impact of energy density ascribed to the capacitance gap between the asymmetrical electrodes. Based on this charge matching mechanism, an optimized L-VN@AC//α-MnO2 AASC with 2.4 V operating voltage is assembled to achieve the enhancements in energy densities (597.5 μWh cm−2 at 2.4 mW cm−2 and 8.5 mWh cm−3 at 34.3 mW cm−3). It is believed that the design of high-performance L-VN@AC electrode materials and the proposal of balanced capacitance mechanism will provide new insights for the development of supercapacitors from two aspects of material synthesis and device assembly mechanism.

Theoretical approach to verify the resonance frequency of a square split ring resonator

An analytical model for a square split ring resonator (S-SRR) having a single split-gap is considered here to reliably estimate the fundamental resonance frequency of the ring. An S-SRR is assumed to be equivalent to a series-resonant LC loop. The approximate formulas for equivalent self-inductance and total capacitance of the ring are derived separately. The total capacitance of the ring is expressed as a sum of a gap capacitance and a surface capacitance (which is associated with charges on the SRR walls). Both the capacitances are influenced by not only the medium in split-gap but also the dielectric constant of substrate. These are taken care of by including appropriate weight factors in the expressions for the capacitances. Again, using the software CST Microwave Studio, the resonance frequencies are calculated for several values of split-gap and SRR side length. Then the results of simulation are compared with the results obtained from our formula. It is found that simulation results agree quite well with the analytical results. Also, the analytical result for resonance frequency of SRR shows good agreement with a previously published experimental result. This model can be used for studies of the resonant properties of split rings in the microwave and terahertz regions.

USE OF THE FINITE ELEMENTS METHOD FOR THE IMPLEMENTATION OF THE COPLANAR CAPACITIVE SENSOR MODEL

The article presents the results of using computer simulation tools to study the characteristics of air gap sensors for the purpose of their optimization. The model is used to study the characteristics of air gap sensors in for the purpose of their further optimization depending on the design parameters of diagnosing object, which mainly depends on the type of powerful hydro generator. Changes in the air gap between the rotor and the stator can occur for a number of reasons, which are due to: shortcomings in the design, manufacture, installation and auxiliary alignments when fitting machine elements during assembly, aging components during operation, subsidence of the foundation, the negative impact of temperature changes, as available centrifugal and magnetic forces that occur on the machine during its operation. Changing the unevenness of the air gap in hydrogenerators largely determines its technical and economic performance, behavior during commissioning and during the entire operating period, because it is in the air gap is the conversion of mechanical rotating energy into electricity. To control the parameters of the gap became wider use capacitive sensors. The study performed a coplanar capacitive air gap sensor with high-potential, lowpotential and grounded electrodes. The model is used to study the picture of the electric field in the specified sensor, as well as to determine the transformation function "air gap - electrical capacity of the sensor". The results of obtained patterns of equipotential field distribution and sensor response characteristic are presented.

Active terahertz metamaterials electrically modulated by InGaZnO Schottky diodes

Active metamaterials (MTMs) are artificially engineered structures with tunable and exceptional properties that are absent in natural materials. Recently, InGaZnO (IGZO), a widely used semiconductor for large-area and flexible display backplane drivers, has gained interest for active control of MTMs due to its large-area uniformity, ease of thin film deposition, and low cost. In this paper, IGZO Schottky barrier diodes (SBDs) are proposed to reconfigure electric-field-coupled inductor-capacitor (ELC) MTMs and actively control terahertz (THz) waves for the first time. The SBDs are designed to bridge the capacitors of the ELC resonators so that the average conductivity within the capacitor gap can be modulated by bias voltage while keeping the capacitance value almost unchanged. To precisely simulate this mechanism, two U-shaped resistive sheet models beside the gap are built for IGZO SBD in 3-D simulation for maintaining the same capacitance and resonant frequency. Furthermore, a device with 14400 MTM cells is fabricated and characterized using frequency-domain spectroscopy. The measured transmission shows a continuous modulation from -14.2 to -9.4 dB at 0.39 THz, which corresponds to a modulation depth of 14.3%. This work paves a new way for active THz MTMs using industrial compatible thin-film technology.

Nonlinear THz‐Nano Metasurfaces: Nonlinear THz‐Nano Metasurfaces (Adv. Funct. Mater. 24/2021)

In article number 2100463, Ranjan Singh, Weili Zhang, Xiaojun Wu, and co-workers successfully fabricate novel nonlinear THz metasurfaces with nanometer capacitive gaps and large size and experimentally realized with precise frequency tuning. The gigantic resonant electric field enhancement in nanogaps induces carrier multiplication in silicon substrates, resulting in conductivity increase in the capacitive gap regions of the metasurface, serving as the source for the nonlinear response.

A Low Impedance CMOS-MEMS Capacitive Resonator Based on Metal-Insulator-Metal (MIM) Capacitor Structure

This letter presents the first nano-gap microelectromechanical systems (MEMS) resonator based on a Metal-Insulator-Metal (MIM) capacitor structure in standard CMOS. We develop an improved mask-less post-CMOS process to chemically remove the thin aluminum copper (AlCu) of the Capacitor-Top-Metal (CTM) with high selectivity to the adjacent materials, yielding a well-defined capacitive transduction gap of only 160 nm. The proof-of-concept resonator is designed in a standard TSMC 180 nm RF CMOS process, with a center frequency of 5.9 MHz, a quality factor of 1,000, and a low motional impedance of 5.7 $\text{k}\Omega $ under a medium dc-bias of 25V. Upon further optimizations, nano-gap CMOS-MEMS resonators based on the proposed CTM-etching technique are promising candidates for fully integrated oscillator applications.

Miniaturized Circularly Polarized Periodically Structured Surface Antenna for RFID Application Inspired by SRR

This article presents a novel miniaturized circularly polarized (CP) antenna based on periodically structured surfaces inspired by the vertical split-ring resonator (VSRR). The VSRR is considered as a magnetic dipole placed above the ground, which could excite strong boresight radiation with a reduced size. To enhance the aperture gain, multicapacitors and inductors (Multi-C&L) are loaded on the loop, which replace the single capacitive gap of the conventional split-ring resonator (SRR). Here an SRR-inspired periodic structure with a relatively uniform field distribution is achieved. The stepped impedance resonator (SIR) structure, as the unit cell of the SRR-inspired surface, is analyzed and investigated using the circuit models derived from the SRR. By cascading multiple high-value capacitors, a larger aperture with a uniform field distribution is obtained. Linearly polarized (LP) and CP antennas are studied. The proposed CP antenna is made of thin substrates and metallic screws, resulting in a negligible dielectric loss. It offers attractive features including a compact size, a low profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.191\lambda _{0} \times 0.191\lambda _{0} \times 0.032\lambda _{0}$ </tex-math></inline-formula> ), good radiation efficiency, novel working principle, flexible performance control, and a bandwidth well covering the 902–928 MHz UHF band, which is well situated for radio frequency identification (RFID) application.

Mid-Range Wireless Power Transfer at 100 MHz Using Magnetically Coupled Loop-Gap Resonators

We describe efficient four-coil inductive power transfer (IPT) systems that operate at 100 MHz. The magnetically-coupled transmitter and receiver were made from electrically-small and high-Q loop-gap resonators (LGRs). In contrast to the commonly-used helical and spiral resonators, the LGR design has the distinct advantage that electric fields are strongly confined to the capacitive gap of the resonator. With negligible fringing electric fields in the surrounding space, the IPT system is immune to interference from nearby dielectric objects, even when they are in close proximity to the transmitter and/or receiver. We experimented with both cylindrical and split-toroidal LGR geometries. Although both systems performed well under laboratory conditions, the toroidal geometry has the additional advantage that the magnetic flux is weak everywhere except within the bore of the LGR and in the space directly between the transmitter and receiver. Furthermore, we show that the toroidal LGR system can be operated efficiently at a fixed frequency for a wide range of transmitter-receiver distances. The experimental results are complimented by 3-D finite-element simulations which were used to investigate the electromagnetic field profiles and surface current density distributions. Finally, we demonstrate the use of our IPT system at powers up to 32 W and discuss possible applications.

Metamaterial‐based, compact, wide beam‐width circularly polarized antenna for 5G indoor application

AbstractThis paper describes a metamaterial‐based miniaturized circularly polarized (CP) antenna with high radiation efficiency and wide beam‐width or coverage for 5G indoor application. A novel meta‐resonator is first proposed, which is investigated by transmission line and equivalent circuit models. By exploring a split‐ring resonator‐like meta‐resonator structure, a high‐Q LC resonator tank is formed. Substantial size reduction and a wide beam‐width are achieved. Owing to a uniform field on these multiple capacitive gaps incorporated on this meta‐resonator surface, enhanced aperture efficiency and gain are obtained. It is partly inspired by the classical metasurface‐based antenna. For validation, a miniaturized CP antenna with a size of 0.29 λ0 × 0.29 λ0 × 0.04 λ0 (where, λ0 is the free‐space wavelength at 3.55 GHz) is fabricated and measured. The fabricated antenna achieves a good bandwidth of 3.30–3.80 GHz that well covers 5G‐N78 band, a peak radiation gain of 5.4 dBic, a high radiation efficiency of 90% and a wide half‐power beam‐width of 91°. It exhibits the merits of compact size, good bandwidth and beam‐width, high efficiency, and low‐cost, demonstrating good potential in miniaturized 5G indoor systems demanding wide‐beam coverage.

Dynamically tunable single-layer VO2/metasurface based THz cross-polarization converter

We demonstrate a single-layer THz metadevice that exhibits cross polarization transmission, a key factor to achieve optical activity. The device is comprised of a two-dimensional array of split ring resonators, each with a vanadium oxide (VO2) pad, integrated into one of the two capacitive gaps of the unit cell. Through numerical investigations we find that as the conductivity of VO2 increases the amplitude of the cross-polarization intensity decreases but maintains a wider broadband range than previously reported for single layered hybrid metamaterial (MM) devices as the VO2 transforms from the insulator to metallic phase. Also the asymmetric transmission, optically modulated by the device, is higher than that of multi-layered MM devices. Due to the materials properties of VO2, our results introduce a promising method that allows for an active sub-cycle dynamic tunability for THz polarization conversion with multiple modalities using optical, electrical or thermal switching. The study is an important step forward in developing compact, integrated, passive and active metadevices for polarization and wavefront control application in the THz.

Modeling of Active Gap Capacitance Electrical Discharge Machining

Abstract Active gap capacitance electrical discharge machining (AGC-EDM) is a high-speed EDM method for machining polycrystalline diamond tools utilizing the active capacitive effect and powder mixing effect formed by the kerosene dielectric added with graphene particles. The capacitive effect increases the discharge energy and explosive force, which in turn influences the material removal efficiency; the powder-mixed effect changes the states of dielectric and forms a non-fixed gap discharge process. Take into account these two aspects, a new discharge mechanism of AGC-EDM is proposed to describe the discharge process. Capacitance characteristics and chain stacking process of graphene-kerosene dielectrics are verified by experimental results. The material removal rate, relative electrode wear, and surface roughness are discussed with the pulse duration, peak current, and graphene concentration to study the theories of the new EDM process.

Investigation of plasma parameters of a single-gas ion engine using a single langmuir probe

This paper presents the results of an experimental study of the parameters of nitrogen, argon and helium plasma obtained in high-frequency capacitive ring discharge at a pressure of 35 Pa. The parameters were determined by a single Langmuir probe. Work is being carried out as part of a project to develop a backlash ion microwave plasma generator. The object of study is ionized gas formed in the ring capacitance gap of a microwave solid-state generator emitter on the MOSFET transistor MRF284. The power consumed by the microwave generator in the study is no more than 5 W. The work resulted in getting the volt-ampere characteristics of a high-frequency discharge in low-pressure gas and determining the main plasma parameters.

Highly Sensitive ELC Resonator Based Differential Sensor

A highly sensitive electric LC resonator-derived differential sensor is proposed in this work, with the major focus on detecting the purity of any reference dielectric material. The proposed sensor is designed with two identical electric-LC (ELC) resonators being loaded on either side of a 50- $\Omega $ microstrip line such that the magnetic wall of the microstrip line is perfectly aligned with that of the resonators. The fabricated unloaded sensor is operating at a resonance frequency of 3.385 GHz, falling between the two ISM bands, exhibiting a peak electric field intensity at the capacitive gap. The working principle of the sensor is analyzed through a lumped element equivalent circuit model. Experimental validation is performed via the fabricated prototype of the developed sensor on Taconic TLY-5 substrate for various standard and unknown dielectric samples. For the accurate testing of various samples using the proposed sensor, an empirical relationship is developed relating the difference in the resonance frequencies of the unloaded and loaded resonators, and the sample thickness. Furthermore, a novel error modeling technique is also incorporated to take into consideration the effect of fabrication tolerance and any possible air gap between the sensor region and the test specimen. The proposed differential sensor possess a substantially higher normalized sensitivity of 4.915% (165 MHz in terms of absolute sensitivity), which is quite useful for applications requiring detection of purity of a product. Its applicability is validated here by detecting the presence of termite infestation in wood sample.

Second Harmonic Exploitation for High-Efficiency Wireless Power Transfer Using Duplexing Rectenna

In this article, a novel duplexing rectenna with harmonic feedback capability is proposed for efficient wireless power transfer (WPT) applications. The proposed duplexing rectenna can harvest the incoming radio frequency (RF) energy efficiently and also make use of an inherent harmonic signal, which is sent back to the RF transmitter (Tx) for positioning in order to guide the radiation patterns from Tx antenna array for optimum WPT. A novel duplexing dipole antenna is designed based on the top loading and capacitive gap effects. It is used to receive RF power at fundamental frequency 0.915 GHz and transmit the second harmonic signals at 1.83 GHz as a feedback. Experimental validation of a complete WPT system with beam-scanning capability has been carried out. It is shown that the fabricated rectifier has realized a maximum RF-dc conversion efficiency of 71% (at 15-dBm input power) and a measured peak second harmonic power of −1 dBm. Thus, the proposed duplexing rectenna can form a closed-loop system by providing its location information for efficient WPT applications.

Compact Flexible Wideband Antenna for On-Body Electromagnetic Medical Diagnostic Systems

A flexible on-body antenna that is compact, unidirectional, and wideband is presented for electromagnetic (EM) biomedical diagnostic systems. To achieve a low operating-frequency band with compact size, an annular ring antenna is loaded with a capacitive gap, a shorting post at its end, and a shorted circular parasitic element. The antenna is designed and fabricated on a purposely built, highly flexible, low-loss, low-cost room-temperature-vulcanizing silicone (RTV) substrate with a tremendously compact size of $0.055\lambda _{0}\times 0.055\lambda _{0}\times 0.009\lambda _{0}$ , where $\lambda _{0}$ is the free-space wavelength at the lowest frequency of 0.55 GHz. The antenna exhibits a measured bandwidth of 0.55–3 GHz at different locations of the human body. The measured near-field radiation patterns demonstrate that the antenna attains unidirectional near-field radiations with more than 10 dB front-to-back-ratio. The received dominant signals of the antenna also exhibit a low distortion level with more than 90% fidelity factor. The achieved features of the proposed antenna confirm its merits for EM biomedical diagnosis applications.

Eigenmode operation of piezoelectric resonant gyroscopes

The theory of eigenmode operation of Coriolis vibratory gyroscopes and its implementation on a thin-film piezoelectric gyroscope is presented. It is shown analytically that the modal alignment of resonant gyroscopes can be achieved by applying a rotation transformation to the actuation and sensing directions regardless of the transduction mechanism. This technique is especially suitable for mode matching of piezoelectric gyroscopes, obviating the need for narrow capacitive gaps or DC polarization voltages. It can also be applied for mode matching of devices that require sophisticated electrode arrangements for modal alignment, such as electrostatic pitch and roll gyroscopes with slanted electrodes utilized for out-of-plane quadrature cancellation. Gyroscopic operation of a 3.15 MHz AlN-on-Si annulus resonator that utilizes a pair of high-Q degenerate in-plane vibration modes is demonstrated. Modal alignment of the piezoelectric gyroscope is accomplished through virtual alignment of the excitation and readout electrodes to the natural direction of vibration mode shapes in the presence of fabrication nonidealities. Controlled displacement feedback of the gyroscope drive signal is implemented to achieve frequency matching of the two gyroscopic modes. The piezoelectric gyroscope shows a mode-matched operation bandwidth of ~250 Hz, which is one of the largest open-loop bandwidth values reported for a mode-matched MEMS gyroscope, a small motional resistance of ~1300 Ω owing to efficient piezoelectric transduction, and a scale factor of 1.57 nA/°/s for operation at atmospheric pressure, which greatly relaxes packaging requirements. Eigenmode operation results in an ~35 dB reduction in the quadrature error at the resonance frequency. The measured angle random walk of the device is 0.86°/√h with a bias instability of 125°/h limited by the excess noise of the discrete electronics.