Capacitive Grid Research Articles

Body-Area Capacitive or Electric Field Sensing for Human Activity Recognition and Human-Computer Interaction

Due to the fact that roughly sixty percent of the human body is essentially composed of water, the human body is inherently a conductive object, being able to, firstly, form an inherent electric field from the body to the surroundings and secondly, deform the distribution of an existing electric field near the body. Body-area capacitive sensing, also called body-area electric field sensing, is becoming a promising alternative for wearable devices to accomplish certain tasks in human activity recognition (HAR) and human-computer interaction (HCI). Over the last decade, researchers have explored plentiful novel sensing systems backed by the body-area electric field, like the ring-form smart devices for sign language recognition, the room-size capacitive grid for indoor positioning, etc. On the other hand, despite the pervasive exploration of the body-area electric field, a comprehensive survey does not exist for an enlightening guideline. Moreover, the various hardware implementations, applied algorithms, and targeted applications result in a challenging task to achieve a systematic overview of the subject. This paper aims to fill in the gap by comprehensively summarizing the existing works on body-area capacitive sensing so that researchers can have a better view of the current exploration status. To this end, we first sorted the explorations into three domains according to the involved body forms: body-part electric field, whole-body electric field, and body-to-body electric field, and enumerated the state-of-art works in the domains with a detailed survey of the backed sensing tricks and targeted applications. We then summarized the three types of sensing frontends in circuit design, which is the most critical part in body-area capacitive sensing, and analyzed the data processing pipeline categorized into three kinds of approaches. The outcome will benefit researchers for further body-area electric field explorations. Finally, we described the challenges and outlooks of body-area electric sensing, followed by a conclusion, aiming to encourage researchers to further investigations considering the pervasive and promising usage scenarios backed by body-area capacitive sensing.

Design of a sensor structure for linear displacement measurement based on a capacitive grid sensor

Design of a sensor structure for linear displacement measurement based on a capacitive grid sensor

Reversible capacitive Frisch grid TlBr detectors

A reversible capacitive Frisch grid detector was fabricated using a thallium bromide (TlBr) crystal with a symmetrical electrode design. The device operates by switching the polarity of the applied voltage, which is necessary for a stable TlBr detector operation. A 2 mm × 2 mm × 5 mm bar-shaped TlBr crystal was used to construct the detector, which exhibited an (full width at half maximum) energy resolution of 1.9% for 662 keV γ-rays measured using a depth correction method at RT. The TlBr detector also showed a stable operation for 8 h of with hourly bias switching.

Thin flexible multi-octave metamaterial absorber for millimeter wavelengths.

The development of radiation-absorbent materials and devices for millimeter and submillimeter astronomy instruments is a research area of significant interest that has substantial engineering challenges. Alongside a low-profile structure and ultra-wideband performance in a wide range of angles of incidence, advanced absorbers in cosmic microwave background (CMB) instruments are aimed at reducing optical systematics, notably instrument polarization, far beyond previously achievable specifications. This paper presents a metamaterial-inspired flat conformable absorber design operating in a wide frequency range of 80-400GHz. The structure comprises a combination of subwavelength metal-mesh capacitive and inductive grids and dielectric layers, using the magnetic mirror concept for a large bandwidth. The overall stack thickness is a quarter of the longest operating wavelength and is close to the theoretical limit stipulated by Rozanov's criterion. The test device is designed to operate at a 22.5° incidence. The iterative numerical-experimental design procedure of the new metamaterial absorber is discussed in detail, as well as the practical challenges of its manufacture. A well-established mesh-filter fabrication process has been successfully employed for prototype fabrication, which ensures cryogenic operation of the hot-pressed quasi-optical devices. The final prototype, extensively tested in quasi-optical testbeds using a Fourier transform spectrometer and a vector network analyzer, demonstrated performance closely matching the finite-element analysis simulations; that is, greater than 99% absorbance for both polarizations, with only a 0.2% difference, across the frequency band of 80-400GHz. The angular stability for up to ±10∘ has been confirmed by simulations. To the best of our knowledge, this is the first successful implementation of a low-profile, ultra-wideband metamaterial absorber for this frequency range and operating conditions.

Modified Passivity-Based Control for LCL-Filtered Grid-Tied Inverter with Output Admittance Reshaping

As a nonlinear control method, the Euler–Lagrange- (EL-) based passivity-based control (PBC) has been studied for grid-tied converters based on energy function to achieve better performance. However, the EL-based PBC method is dependent on an accurate mathematical model. In the traditional EL-based PBC research for LCL-filtered grid-tied inverter, the effect of the digital control delay is rarely considered and the stability under the grid impedance uncertainties is not discussed, especially in the capacitive grid or complex weak grid. To address these concerns, this study proposes a modified EL-based PBC method based on the output admittance reshaping for LCL-filtered grid-tied inverters. The system’ passive region is expanded by adding capacitor current feedback loop up to the Nyquist frequency. The potential resonance is thus eliminated irrespective of the grid impedance. Additionally, the stable region and control parameters design methods of the modified EL-based PBC method with inverter-side control are also carried out. To verify the correctness of the theoretical analysis, both simulation and experimental results are investigated from a 3 kW grid-tied inverter prototype.

Control Strategy for Power Generation from a Capacitive Mixing Cell and Grid Injection

In this work, the possibility of extracting energy from a capacitive mixing cell based on the potential that exists as a result of the salinity gradient between fresh and salt water passing through the electrodes of a deionization cell is studied. For this, a two-stage process is defined. The first step uses a dual buckboost converter for the positive and negative cycles of the input voltage. This topology acts as a current source and is chosen due to its ability to provide high power factor and to work with extremely low voltage levels. The second stage consists of an Hbridge inverter synchronized with the AC grid to feed power into the grid. A hysteresis control system has been designed for the current flowing through the coil. With this, it has been analyzed how the efficiency of the total system (cell + power converter) varies with the changes in the series resistance of the CapMix cell or with the discharge current selected in the power converter. Simulations are carried out to characterize the energy extraction and some experimental results confirm the possibility of using this new renewable energy source.

An Improved Three-Level Cascaded Control for LCL-Filtered Grid-Connected Inverter in Complex Grid Impedance Condition

The passivity-based control (PBC) with Euler–Lagrange (EL) model has been used for LCL-filtered grid-connected converter. However, the impacts of the control delay and the interaction resonances under capacitive grid impedance are rarely considered for PBC method. Nonlinear Lyapunov’s stability theory is hard to estimate the stability of the system and accurately design the controller parameters considering the control delay. This paper derived the impedance model of LCL-filtered grid-connected inverter with grid current control based on PBC method. The passive theory and the zero-pole maps are applied to reveal the influence of the digital delay and differential item of inverter current loop. A new three-level cascaded control method is then proposed based on traditional PBC method to achieve stability and high robustness in complex grid. Furthermore, controller parameters are designed accurately to maintain passivity within switching frequency ranges and parameter variations of the LCL filter are investigated. Final validation of the effectiveness and performance of the proposed control structure is performed by simulation and experimentation.

Design and Control of A Novel Dual Function Grid-Connected Solar Inverter

In this paper, a novel dual-function grid-connected solar inverter is developed for better utility interaction applications. The proposed topology is able to inject active power, reactive power, and mitigate harmonic problems caused by non-linear loads. The proposed configuration consists of switched LC-connected inverter (SLC-CI) in parallel with static VAR compensator (SVC) to achieve the design requirements. The system description, mathematical model, control algorithm, and parameter design of the proposed system is systematically developed to ensure acceptable performance. The system performance is evaluated with both linear and non-linear loads and compared to two conventional topologies; inductive and capacitive grid connected inverters. The results demonstrate that the proposed topology have better performance, comparing to other topologies, in terms of using lower DC-bus voltage (25% less) and using around half the power rating of inverter. Moreover, the proposed double switched LC filter-connected inverter (DSLC-CI) shows its ability to work as active power filter and mitigate harmonics to acceptable level.

Passivity-based stability analysis of parallel single-phase inverters with hybrid reference frame control considering PLL effect

The passivity-based stability criterion (PBSC) is an effective tool to analyze the interactive stability issues between the multi-parallel inverters and the grid. However, when using the passivity theory to evaluate the interactive stability, the influences of grid synchronization and multisampling on the passivity of inverter output admittance are overlooked in previous studies. To fill this gap, the impact factors in the grid-connected control, such as multisampling, capacitor current feedback active damping (CCF-AD) and various phase-locked loops (PLLs), on the passivity of inverter output admittance is investigated in this paper. Moreover, the stability of the interconnected system in the inductive and capacitive grid scenarios are also assessed. Since the effective control delay are determined by the multisampling coefficient, the passivity of inverter output admittance in the high-frequency range is mainly affected by multisampling and CCF-AD, whereas the passivity in the low-frequency range is related to the bandwidth of PLLs. In case of an identical PLL bandwidth, the non-passive region of admittance when using SOGI-PLL appears in a lower frequency band, and thus the non-passive region is the smallest in comparison, which provides stronger robustness. Finally, simulation studies and experimental results are presented to verify the effectiveness of the theoretical analysis.

An artificial dielectric slab for ultra high-field MRI: Proof of concept

High-permittivity dielectric pads, i.e., thin, flexible slabs, usually consisting of mixed ceramic powders and liquids, have been previously shown to increase the magnetic field at high and ultra high-fields in regions of low efficiency of transmit coils, thus improving the homogeneity of images. However, their material parameters can change with time, and some materials they contain are bio incompatible. This article presents an alternative approach replacing ceramic mixtures with a low-cost and stable artificial dielectric slab. The latter comprises a stack of capacitive grids realized using multiple printed-circuit boards. Results in this article show that the proposed artificial dielectric structure can obtain the same increase in the local transmit radiofrequency magnetic field distribution in a head phantom at 7 T as the conventional dielectric pad.

Passivity-Based Design of Grid-Side Current-Controlled $LCL$-Type Grid-Connected Inverters

The frequency-domain passivity theory offers an effective way to assess the stability of inverters connecting to complex grid conditions, e.g., inductive grid, capacitive grid, and system comprising multiple inverters. In this article, an admittance model for the grid-side current-controlled $LCL$ -type inverter with capacitor voltage feedforward active damping (CVF-AD) is built to facilitate the passivity-based stability assessment and controller parameter design. Especially, it is found that if the antiresonance frequency of the inverter-side inductor and the filter capacitor is designed in a certain region, i.e., $(\text{0.66}f_c + \text{0.034}f_s, \text{0.22}f_s)$ , all frequencies’ passive output admittance of the inverter can be achieved via a modified CVF-AD scheme with simple digital implementation. Thanks to the proposed methods, the inverter can be connected to the grid regardless of the grid impedance, which means a robust plug-and-play functionality suitable for microgrid applications. In addition, the controller parameters are analytically designed; time-consuming iterations are, hence, avoided. The allowable tolerance of power circuit parameters for a valid controller parameter design is as high as 64% or more. The validity of the theoretical analysis and effectiveness of the proposed method are verified by using experimental results on a laboratory prototype.

Mesh low-pass filters for millimeter-wave applications: is the square capacitive shape optimal?

The use of mesh filters for millimeter-wave applications using capacitive and inductive grids is well known, and they are widely used in cosmic microwave background instrumentation. We report on an investigation into whether the capacitive square shape typically used in low-pass filter designs could be improved. The microgenetic algorithm and the finite-difference time-domain, and electromagnetic modeling method were used to look for shape variations to the standard square shape. Any shape changes discovered were then analyzed to establish which variations had the most effect. We show that improvements found using pixelated patterns evolved by the genetic algorithm were somewhat mixed.

Analysis and verification of harmonic interaction between DDWTs based on αβ stationary coordinate system

This study presents an analysis method of harmonic interaction characteristics between direct-drive wind turbines (DDWTs) based on αβ coordinates and the relative gain array (RGA). First, considering the digital delay of inverters, the capacitive current feedback active damping is applied to suppress the resonance of LCL filter, and the output current of DDWT is regulated by quasi-proportional resonant controller in the αβ coordinates and then combined with the topology of the direct-drive wind farm (DDWF), the transfer function matrix of the DDWF is established. Second, based on the RGA principle, the relationship between parameters and harmonic interaction characteristics is quantitatively analysed. The results show that with the proportional coefficient increasing, the degree of negative interaction between DDWTs is strengthened, which increases the harmonic content in the negative interaction frequency band. However, the increase of resonance coefficient and number of DDWTs will weaken the degree of negative interaction. In addition, with the increase of capacitive current feedback coefficient and grid inductance, the interaction frequency gradually decreases. Finally, the DDWF model is built both on Matlab/Simulink and StarSim + PXI hardware-in-the-loop platform to verify the analytical results. The harmonic interaction characteristics can be used to guide the parameter design of DDWTs, so as to optimise power quality of the wind farm.

Principle and Robust Impedance-Based Design of Grid-tied Inverter with LLCL-Filter under Wide Variation of Grid-Reactance

Currently, how the inductive grid impedance variation affects the stability of digitally controlled grid-tied inverters with a high-order ( LCL or LLCL ) filter has been numerously studied. Note that a distributed power system may contain the capacitive load, the power factor correction (PFC) capacitor, and the long cable. During the design of grid-tied inverters, we should address the effects of the equivalent grid reactance, including both the inductive and the capacitive impedances, on the stability of system. Nevertheless, up to now, to the best knowledge of authors, the detailed parameter design method of the LCL - or LLCL -filter-based grid-tied inverter has not yet been introduced, when the capacitive grid impedance is addressed. In this paper, by using the passivity-based analysis, the detailed stability study on the LLCL -filter-based grid-tied inverter is carried out, when the grid reactance varies in a wide range. Based on the analysis, an exact and robust parameter design of system is proposed. Simulations and experimental results on a 220 V/2 kW prototype confirm that by using the proposed parameter design method, a high-performance grid-tied inverter system can be achieved under the rigid grid condition.

3D‐printed index‐modulated substrate for beam in Fabry‐Perot cavity antennas

AbstractThe design of a beam steerable Fabry‐Perot cavity antenna based on the use of a phase modulated partially reflective surface is reported. The latter partially reflective surface makes use of a 3D‐printed index‐modulated dielectric substrate so as to incorporate the phase modulation. The engineered substrate is combined with uniform inductive and capacitive grids in order to design the phase‐modulated metal‐dielectric‐metal metasurface acting as a partially reflecting surface in the cavity antenna. Thanks to the phase modulation, the radiated beam of the antenna is steered to an off‐normal direction.

Gradient phase partially reflecting surfaces for beam steering in microwave antennas.

A metal-dielectric-metal gradient phase partially reflecting surface based on the combination of a gradient index dielectric substrate with an inductive and a capacitive grids, is designed at microwave frequencies for antenna applications. The gradient index is obtained by realizing air holes of different dimensions in a dielectric host material. A prototype of the gradient index dielectric substrate is fabricated through three-dimensional printing, an additive fabrication technology. It is then associated to two patterned metallic grids to realize a partially reflecting surface with a gradient phase behavior. For experimental validation, the partially reflective surface is used as reflector in a low-profile Fabry-Perot cavity antenna. An angular enhancement of the emitted beam in a desired direction is reported by further engineering the phase introduced by the inductive and the capacitive grids. Far-field measurements are performed on fabricated antenna prototypes to validate the concept. Such gradient phase reflective surface paves the way to low-cost easy-made microwave metal-dielectric surfaces incorporating functionalities such as beam control, forming and collimation.

Tunable Terahertz Hybrid Metal–Graphene Plasmons

We report here a new type of plasmon resonance that occurs when graphene is connected to a metal. These new plasmon modes offer the potential to incorporate a tunable plasmonic channel into a device with electrical contacts, a critical step toward practical graphene terahertz optoelectronics. Through theory and experiments, we demonstrate, for example, anomalously high resonant absorption or transmission when subwavelength graphene-filled apertures are introduced into an otherwise conductive layer. These tunable plasmon resonances are essential yet missing ingredients needed for terahertz filters, oscillators, detectors, and modulators.

Capacitive Frisch grid型TlBr検出器出力波形のデジタル信号処理

Capacitive Frisch grid型TlBr検出器出力波形のデジタル信号処理

Inductive‐varying grid for highly beam‐steerable cavity antennas

The design of a locally one-dimensional inductive-varying metamaterial operating near 10 GHz is reported. This is combined with a fixed capacitive grid to design a phase-varying metasurface. This composite metasurface is then used as a partially reflecting surface (PRS) together with a perfect electric conductor surface to form a resonant Fabry-Perot type cavity. A patch antenna acting as a primary source is embedded in the cavity to constitute a highly beam-steerable directive antenna. A 56° deflection of the antenna beam is experimentally observed.

CdZnTe detectors with parallel capacitive Frisch grid

The crystal size and energy resolution of CdZnTe(CZT) detectors are limited by crystal growth technology.In this paper,capacitive Frisch grid detector structure was used to reduce the leakage current and overcome the charge carriers' recombination by the geometric of unipolar charge.The electrode contact of the detector was made of Schottky contact which can further compress the weight of potential and reduce the leakage current noise.A large volume multi-element parallel detector was made by capacitive Frisch grid structure and Schottky contact electrode(In-p/CZT-AuCl3).The energy resolution of multi-element detectors is not limited to the worst energy resolution unit and the detection efficiency is 2.45 ~ 7.31 times more than that of the single unit.