Search

This paper presents a novel hierarchical cooperative control strategy to solve the problems of unbalanced State of Charge (SoC), unreasonable load current sharing, and unstable bus voltage for battery storage system (BSS) in islanded DC microgrid. In the communication layer, a neighbor-to-neighbor communication network architecture is constructed in which each battery storage unit (BSU) only communicates information with neighboring nodes, and a multi-agent consensus algorithm is used to iteratively estimate the relevant average global variables. In the main control layer, the droop coefficient is dynamically adjusted by constructing a fast SoC convergence function to ensure that the load current is reasonably distributed based on the rated capacity of each BSU. In the secondary control layer, a virtual voltage drop equalization controller and an average bus voltage compensation controller are designed to eliminate the impact of line impedance mismatch and compensate the average bus voltage. Furthermore, an optimized factor is designed to accelerate the later stage of SoC convergence. Finally, a DC microgrid experimental platform based on StarSim HIL is built, and the results demonstrate that the proposed strategy can achieve the control objectives of fast SoC balance, proportional load current sharing, and bus voltage stability.

This letter presents a bondwire model in the form of a lumped-element network, which is based on the geometry of the bondwire and landing pads. For the interconnection between a chip and the feedline on a printed circuit board (PCB) substrate, the associated parasitics are calculated, which are responsible for the performance degradation caused by the bondwire at millimeter-wave (mmWave) frequencies. A matching network is realized with planar-lumped elements on the PCB and integrated for impedance mismatch compensation at a center frequency of 60 GHz. Simulations show an operating bandwidth of 50–70 GHz. The proposed solution is first verified by the measurements of PCB-to-PCB bondwire interconnects. Then, as an application example, an antenna-switch chip is placed at the PCB feedline. Remarkable improvements in terms of input matching and insertion loss are observed compared with an unmatched bondwire interconnect.

Rotary ultrasonic machining (RUM) is a superior technology to machine hard and brittle materials. Traditionally, the compensation optimization for the RUM system is limited to a single resonant frequency. This article presents a novel double compensation approach for the impedance and frequency regulations of RUM via multiobjective genetic algorithm (MOGA) aiming to achieve the system resonance and monitor the machining process in real time. For this, we first establish the impedance model of the rotary ultrasonic holder (RUH) by adopting the T-type circuit that includes the comprehensive electromagnetic parameters. The obtained impedance model reveals that both frequency mismatch and impedance mismatch exist in the RUM system, causing the low voltage gain and low vibration transmission. To obtain the optimal compensation to match both the frequency and impedance, an optimization model-based MOGA is developed to intelligently search the accurate capacitance values, where the Pareto frontier is employed to visualize the capacitance solution distribution. Moreover, the response feature of the RUH system is attained by using the state-space equation. Detailed comparisons of four compensation topologies show that the series–series (SS) topology offers the optimal performance, which can match both of the frequency and the impedance well, improving the output active power 7.634 times compared to the conventional one. Finally, the validity of the proposed optimization method is confirmed by using both simulations and experiments. Note to Practitioners —This article was motivated by the transmission efficiency and the stability of ultrasonic vibration in the rotary ultrasonic machining (RUM). The matching issue is critical in RUM because the whole system is very complicated with multiple components such as electrical devices, piezoelectric rings, and mechanical horn. In the conventional RUM, the system matching is limited to a single resonant frequency between the piezoelectric transducer and the electrical driver. However, the impedance matching is also important to influence the ultrasonic vibration. The problem of the ultrasonic matching stems from empirical experiences of the engineers’ or simple heuristic rules instead of advanced approaches. On the other hand, optimization-based techniques are viewed as a great success in industrial and engineering applications. With the assistance of our proposed numerical model and the corresponding simulation, we found that the multiobjective genetic algorithm (MOGA) can intelligently search the optimal compensated parameters to achieve the double matching for both the resonant frequency and the impedance in the RUM system. Finally, our experiments prove that the MOGA optimization can attain optimal transmission efficiency for the electrical voltage and current compared with conventional approaches. This significantly benefits the application of the RUM technology in industry, especially for the precision machining of the hard and brittle materials.

This chapter presents the elements used to integrate payload units to form the payload. The most important ones are coaxial cable and waveguide. Coax is used at low frequencies and low power, while waveguide is used at the higher frequencies or when the power is high. Circular waveguide is of interest because its propagation modes are the basis of the resonance modes in some kinds of filters. The chapter presents the integration of impedance mismatch and S‐parameters. All payload units, integration elements, and partial integrations of the payload are characterized by their measured S‐parameters. The payload‐integration items are used in close conjunction with filters and are sometimes part of filter assemblies. Impedance mismatch or simply mismatch is a topic that must be mastered for proper accounting of the losses accrued during payload integration, which are not assignable to the units and integration elements themselves but to the fact that they are connected with each other.

Ti3C2TX MXene has been proven to be a material of high application potential in the field of electromagnetic (EM) protection. Considering the density, MXene/polymer films (MPFs) are fabricated by employing the simple tape casting process and exhibit excellent electromagnetic shielding performance with respect to the MXene content. However, the absorption properties of as-fabricated MPFs are not satisfactory due to the impedance mismatch. Herein, a multilayer impedance gradient absorber with MPFs arranged in order has been successfully designed and prepared. The developed absorber possesses excellent EM wave absorption properties owing to the well-matched impedance and adjustment of permittivity. Moreover, the effect of the thickness of MPFs on the EM wave absorbing properties has been investigated by theoretical calculations and experimental measurements. The HFSS calculation reveals that the effective absorption bandwidth is capable to cover the whole X-band (8.2–12.4 GHz) with only a micro-adjustment of the thickness, with the minimum reflection coefficient (RCmin) reaching up to −26.10 dB. In addition, the synergistic effect of the multiple loss mechanisms has been discussed in detail. This study not only proposes the effective design of a novel multilayer impedance gradient absorber, but also provides new fundamental basis for combining the simulation technology and material design.

In inductive power transfer (IPT) systems, load, and magnetic coupling variations cause an impedance mismatch. Impedance mismatch is one of the most serious problems in IPT systems for electric vehicles (EVs) because an EV is not always parked in the same location. Therefore, an impedance tuning control for semibridgeless active rectifiers (SBARs) is proposed in this article to compensate for this mismatch. The proposed impedance tuning control is achieved by adjusting the turn- on point and duty of the SBAR without using any additional component. Moreover, a technique for detecting the voltage-rising edge of the SBAR switch is proposed to extract the switching frequency and to synchronize the SBAR with the primary system. A 3.3-kW prototype of the IPT system with the SBAR is manufactured, and the proposed impedance tuning control is verified through experimental results according to the coupling coefficient. The proposed control can achieve an efficiency improvement of 6.4% under the impedance mismatch.

Modifications of the geometry of a folded dipole antenna operating in the infrared were studied with the objective to increase the antenna input impedance. These modified folded dipoles were designed and optimized using numerical simulations. Candidate antennas were fabricated, and input impedance was measured experimentally using scattering-scanning near-field optical microscopy. Numerical and experimental results confirm that the choice of an appropriate antenna geometry leads to an input impedance of 1 kΩ or above. With this impedance, the modified folded dipole antenna could be implemented as a solution for the impedance mismatch challenge that arises in antenna-coupled infrared detectors.

With microgrids gaining more popularity in effectively meeting the increasing power demand, the operational challenges keep on increasing hand-in-hand. Especially when the microgrid work in islanded mode, it has to supply its area loads and maintain the system parameters as per the standards. This requires systematic coordination among the distributed generators so that the real and reactive power sharing is proportional to their ratings, simultaneously maintaining the system voltage and frequency at the rated values. While a droop controller shares the real power accurately, it is ineffective for precise reactive power sharing. The errors in reactive power sharing are compensated by adding virtual impedance in series with the distributed generator. The key objective of the work is to estimate the virtual impedance value to nullify the reactive power sharing errors without the need for communication links. A fuzzy logic controller is proposed to estimate the value for virtual impedance based on the real and reactive power demand at that particular instant. The virtual impedance dynamically changes depending on the load demand in order to compensate for the feeder impedance mismatch and hence called adaptive virtual impedance. Thus with the proposed fuzzy logic controller, accurate reactive power sharing is made possible without the requirement of communication links and the knowledge of feeder impedance. A secondary controller is also included to restore the frequency and the voltage to the rated values. A microgrid with equally and unequally rated DGs has been simulated in Matlab Simulink with the proposed fuzzy controller and successfully validated.

Analytical models for passive linear structures, like metallic traces, vias, are proposed for simulations at the package and Printed circuit board (PCB) levels. In the proposed method, traces are modeled based on the transmission line theory, whereas the vias are described by the parallel-plate impedance and several equivalent circuits elements. The proposed models can be applied to efficiently simulate composed passive linear structures. Several scenarios are analyzed including traces with two or three width, traces routed into different layers and interconnects commonly used in PCBs. The results of the models are compared with those from the fullwave simulations and experiments. An improvement on the computation speed has been observed with respect to the full-wave simulations at the effective range of models. In our measurements, a compensation approach of impedance mismatch in parameter measurements is analyzed and calculated, which could significantly simplify the experimental process.

The communication distance of Radio Frequency Identification (RFID) system is affected by the environment. This study presents a compact ferrite-less frequency-tuned printed-coil (PC) resonator, which introduces the additional PC resonators as well as the tunable matching circuits to the coil-based antennas, to address the rear metallic effect and the impedance mismatch effect caused by the environment variation for RFID system. The tunable matching circuit using the proposed negative voltage generator achieves low power consumption of only 0.5 mW. The usefulness of the proposed technique is experimentally validated with the rear metallic plate and the interference of water. Measurements show that compared with the commercial PC resonator, the proposed technique reduces the gaps between the coil and the rear metallic plate from 2.9 mm to 1.1 mm when the detected distance is 4.1 mm and, furthermore, improves the detected distance of the system from 3 mm to 17 mm with the interference of water.

Carbon fiber (CF) is a significant multifunction material, which is extensively used in aircraft because of its superb performance. However, its microwave absorption properties (MAPs) are seriously restricted as a result of the impedance mismatch issue. To address this issue, an efficient strategy is conducted by a series of CF@MoS and CF@MoS@FeO composites that are fabricated by in-situ grown MoS nanosheets (MoS-NS) and FeO nanoparticles (FeO-NPs) on the surface of CF. The results of microwave absorption performance (MAP) reveal that the minimum reflection loss (RL) can reach -21.4 dB with a CF@MoS composite coating thickness of 3.8 mm; the effective attenuation bandwidth (RL < -10 dB, i.e., 90% microwave energy is attenuated) is up to 10.85 GHz (7.15-18.0 GHz). From a detailed analysis, it is observed impedance mismatch is the critical limiting factor for MAPs rather than attenuation. Furthermore, for CF@MoS@FeO, the MAP is strongly dependent on the level of coating of magnetic FeO-NPs on the surface of CF@MoS composites. The mechanisms underlying the superb MAP and related phenomena are investigated, opening new directions for fabricating CF-based microwave absorbers with high efficiency and wide-bandwidth. Finally, the occurrence of multi-reflection phenomena of EM waves in absorbers are critically analyzed.

A large circular transmitter (power pad) is often utilized for inductively wireless charging so that the power receiver can position itself freely within the power pad. However, the uneven magnetic field distribution leads to the impedance mismatch and the variable transferred power due to the misalignment between a receiving coil and a relatively large transmitter coil. In this paper, the effects of the turn numbers, trace spacing, and coil size on the uniformity of magnetic field distribution over a planar spiral coil (PSC) are investigated based on an analytical model. Then, the genetic algorithm is used to optimize the trace width and spacing of a ten-turn PSC with the fixed outer and inner diameters, whereas the magnetic field is numerically calculated by HFSS software. The geometrically optimal PSC is obtained with the trace width approximately equal to trace spacing for each turn by minimizing the coefficient of variation (COV) of magnetic field within an effective charging area over the coil. The results showed that the simulated and measured COVs of magnetic field were 0.130 and 0.121, respectively, which are obviously less than that of the uniformly spaced regular coil and show a little less than that of the optimally spaced coil with fixed trace width. Therefore, the trace spacing is a major consideration to achieve the uniform magnetic field, whereas the trace width variation is applied to refine the evenness of field. It is also expected that the proposed GA-based optimization is well applied to design other Txs with conformable shape in inductively WPT systems for stable power delivery regardless of the receiver positions.

The application of carbon-based materials in microwave absorption (MA) field are limited due to the impedance mismatch caused by high permittivity and low permeability. In this work, Cu2O@nanoporous carbon (Cu2O@NPC) composites derived from Cu-based MOFs are synthesized using a simple method. Variation of C and Cu2O contents in Cu2O@NPC allows the regulation of permittivity and permeability, resulting in superior ultrabroad-bandwidth absorptivity. The maximum reflection loss (RL) of Cu2O@NPC-4 is up to −31.1 dB at 5.6 GHz, while the effective bandwidth (RL ≤ −10 dB) can reach 7.3 GHz (10.7–18 GHz) with a matching thickness of 1.85 mm. The results of this study open a new opportunity for solving the impedance mismatch of C-based materials and obtain ultrabroad effective bandwidth.

Rotational speed and temperature measurements of an engine blade surface play a vital role in the performance detection of an engine. We proposed a wireless passive LC sensor based on thick-film integration technology to integrate the sensor in situ on the surface of the rotating part, which can be used to monitor the rotational speed and temperature of the rotating part. The reflection signal generated by the impedance mismatch is output in the form of voltage through the detection circuit such that the synchronous online measurement of rotational speed and temperature is realized by analyzing the time slot of adjacent troughs and the amplitude of the output voltage. In addition, we used laser drilling, screen printing, high-temperature sintering, and other technologies to integrate the sensor in situ on the surface of the ceramic turntable, which is lightweight. Finally, the test was conducted by setting up a rotational speed-high-temperature composite experimental platform, and the results showed that the sensor can work normally in the range of 25–830°C, and the rotational speed measurement range was 50–400rpm. The consistency of the rotational speed measurement was suitable, the maximum error was less than 1%, and the work was stable within 180 min.

Many applications utilize flexible capacitive electrode implementations and analog front-end optimizations for improving noncontact electrocardiogram (ECG) measurements. However, the influence of the negative impedance in the circuit front end on noncontact measurements has not been investigated. The objective of this study was to develop negative impedance capacitive electrodes for improving the degraded noncontact ECG signals induced by the high-impedance interface between the skin and electrode. A capacitive electrode with a negative impedance of $-200\,\,\text{M}\Omega $ was designed to reduce the impedance mismatch between the body and measurement electrode. The proposed electrodes were applied on a subject’s chest to continuously measure the cardiac signals through a fabric layer and further evaluate the signal-to-noise (SNR) performance for noncontact ECG measurements. The negative impedance in the circuit front end reduced the coupling effect between the skin and the measurement electrodes, thus improved the SNR in theory and in practice. Importantly, our system produced a distinguishable heartbeat signal even with a maximum cloth thickness of 1.8 mm and skin–electrode capacitance exceeding 57 pF, which is suitable for wearable applications. This study is a pilot effort toward validating the efficacy of negative impedance capacitive electrodes for noncontact physiological measurements. This novel electrode design is expected to potentially address the limitations imposed by a fabric layer and its thickness in noncontact bioelectric sensing in the future.

Multi-channel biosignal recording systems that employ a shared-reference scheme and achieve high common-mode rejection ratio (i.e., CMRR > 80dB) have been reported in recent works. While it is well-understood that a shared-reference scheme causes impedance mismatch at the input terminals of bioamplifier, and thus limits the maximum achievable CMRR, a theoretical study that can provide quantitative assessment of this source of degradation is still lacking. This brief provides an equivalent electrical circuit model of the input interface consisting of an electrode array and bioamplifiers, followed by a complete analysis to formulate the CMRR degradation. Simulation results based on a previously designed and fabricated 32-channel neural recording front-end in a 180nm CMOS process are presented, exhibiting close agreement with the theory.

This paper presents a combination of the Vibration-based method and Non-destructive Ultrasonic C-scan method to identify, locate, and quantify the damage in impacted carbon composite fiber reinforced structure. The main objective of work consists of developing a new method to assessment of damage in carbon composite by using a different method to be applied to structural health monitoring. Experiments were carried out on laboratory specimens, which consists of carbon/epoxy laminates having three different stacking sequences ([0/0]s, [0/90]s, and [45/0–45/90]s) subjected to three different impact energies (7 J, 14 J, and 24 J) using conical shape impactor. Frequency Response Function (FRF) for intact and damaged specimens was obtained by using hammer and accelerometer sensors. FRFs are analysed using suitable metrics, including a new one, which is compared in terms of their capability for damage identification. Afterword, the ultrasonic C-scanning method is used to locate and quantify the damage in the specimen. The ultrasonic C-scanning works on the principle of ultrasonic reflection at the interface of impedance mismatch. In this method defects are based on the amplitude of ultrasonic high-speed waves; a qualitative approach is used to identifying the defects while measuring the amplitude of the signals. This technique has demonstrated great potential for damage localization and extension in carbon composites. Finally, the new method is proposed to identify and localization of damage in the impacted specimen using the Vibration-based method and Ultrasonic C-scanning methods.

Digital control delay is studied as one of the leading factors causing instability in grid-tied voltage source inverter (VSI) systems. However, how this delay affects the small-signal output impedance of the VSI and how the change in impedance shape further influences the system stability are still not clear. This article, for the first time, thoroughly analyzes the impact of delay on the dq -frame output impedance of the VSI operating in both the single current loop control mode and the dual-loop control mode. It is found that when delay is considered, a distinct magnitude drop and a phase rise always exist at the high-frequency area of the impedance, which is named the “impedance trough.” By studying the dq -frame output impedance of the VSI, the origin of the impedance trough, and its analytical relationships with the current loop dynamics, voltage loop dynamics, and delay values are unveiled. Meanwhile, the influence of the impedance trough on the stability of the grid-tied VSI system under these two control modes is evaluated through d–d channel impedance matching and generalized Nyquist criterion (GNC). It is demonstrated that the joint effects of delay and control parameters result in the impedance mismatch between the grid and the VSI, which is the root cause of high-frequency oscillations in the grid-tied system. Finally, experimental results verify the analysis.

The object-relational impedance mismatch (ORIM) problem characterises differences between the object-oriented and relational approaches to data access. Queries generated by object-relational mapping (ORM) frameworks are designed to overcome ORIM difficulties and can cause performance concerns in environments which use object-oriented paradigms. The aim of this paper is twofold, first presenting a survey of database practitioners on the effectiveness of ORM tools followed by an experimental investigation into the extent of operational concerns through the comparison of ORM-generated query performance and SQL query performance with a benchmark data set. The results show there are perceived difficulties in tuning ORM tools and distrust around their effectiveness. Through experimental testing, these views are validated by demonstrating that ORMs exhibit performance issues to the detriment of the query and the overall scalability of the ORM-led approach. Future work on establishing a system to support the query optimiser when parsing and preparing ORM-generated queries is outlined.

Line impedance mismatch and unregulated harmonic currents cause serious problems for an islanded microgrid, such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To overcome these issues, a coordinated virtual resistance and capacitance are introduced together with its control scheme for parallel distributed generation (DG) in an islanded microgrid. The proposed coordinated virtual impedance control scheme directly modifies the DG output impedance at the fundamental frequency to realise accurate current sharing among DG units. In addition, a variable harmonic impedance control loop is proposed for each DG to absorb the non-linear load harmonic current. Thanks to the proposed control scheme, the PCC harmonic voltage distortion is successfully compensated and power-sharing among DG units is accurately achieved. The stability of the microgrid system was analysed in detail to verify the feasibility of the coordinated virtual impedance control scheme. Experiments on a laboratory prototype microgrid are performed to validate the performance of the proposed control scheme.

The proposed 1D elastic metamaterial rod finds application in non-destructive evaluation, as a filter in the transduction side, where only the torsional and flexural modes need to be generated by isolating longitudinal modes. In this Letter, this is achieved by obtaining a wide bandgap in low-frequency ultrasound regime. The novelty of the proposed design arises from the use of a high impedance mismatch between the materials selected for the rod. The proposed concept is demonstrated and verified with numerical simulations. The effectiveness of the proposed technique is confirmed by comparing the results obtained from the rod made of a single material.

The addition of RF interferometers to vector network analyzer (VNA) test benches has allowed for realization of low-noise high-frequency measurements of extreme impedance devices. However, when employing correction techniques such as the short-open-load method, the RF response of the interferometer hardware introduces measurement inaccuracies due to unwanted load-dependent inconsistencies. This letter presents a novel VNA calibration method that enables both low-noise and accurate small-signal characterization of highly mismatched devices. The proposed solution is experimentally validated in the 10–18-GHz band, confirming a 23-fold improvement in measurement resolution with absolute accuracy across the entire $\Gamma $ range of the VNA. The accuracy of the new calibration process is verified via comparison with traceable reference standards supported by state-of-the-art uncertainties.

In this article, impedance mismatch effects on the characteristics of common-mode (CM) electromagnetic bandgap (EBG) filters are studied using three-dimensional (3-D) full-wave numerical simulations. The CM EBG filters considered herein are designed using standard printed circuit board technology and contain either microstrip (MS) differential pairs running above the EBG plane, or stripline (SL) differential pairs running on one of the layers next to the EBG plane. First, the terminations are fixed at 50 Ω, and the effects of the differential line impedance variations on the EBG filter parameters are studied. Overall, the considered variations in the widths of the traces and edge-to-edge separation distances in both the MS and SL structures do not drastically deteriorate the performance of the EBG CM filters. Then impedances of the ports are set different from 50 Ω, and the effects of this mismatch on the baseline SL and MS EBG structures are studied. It is shown that lower port impedances may have significant effect on the characteristics of filters. In addition, baseline EBG filters are cascaded with unmatched four-port load, and this may also deteriorate performance of filters.

This paper presents a theoretical and experimental analysis of the capabilities of the dual-input Doherty power amplifier (DPA) architecture to mitigate efficiency and output power degradations when used in a mismatched load environment. Following a simplified linear piecewise approach, an analytical demonstration is proposed to derive optimal radio frequency drives applied to the Auxiliary path of the DPA to restore power performances while avoiding large signal voltage clipping of active cells. The proposed analytical study is corroborated with harmonic balance simulated results of a C-band, 20-W GaN DPA prototype. The fabricated dual-input DPA prototype has been measured under 1.5-VSWR mismatch configurations to validate the proposed analysis.

The majority of electronic products today are built using no-clean soldering processes. However, the effect of no-clean flux residue on signal integrity is a concern for many high-frequency products, such as fifth-generation (5G) and other communication products. No-clean flux residue can create an alternative path to the signal and degrade the signal integrity performance, especially at high frequency. However, there are limited studies on the effect of no-clean residue on signal integrity. This work sets out to study the effects of no-clean flux residue on signal integrity at high frequency, including the frequency spectrum used for 5G technology. This study includes the analytical modeling of the dielectric loss and impedance mismatch loss at high frequency. In addition, the insertion loss is measured at different frequencies up to 50 GHz. The results show that the loss due to the presence of no-clean flux residue is statistically insignificant within the scope of this study.

Deeply buried inclusions such as pipes and cables cannot be detected when the air–ground interface suffers severe impedance mismatch, resulting in little electromagnetic (EM) signals penetrating the subsurface, even before the scattering and reflection from the buried inclusions occur. Therefore, increasing the penetration depth by effectively enhancing the EM transmission into the lossy subsurface domain is of great importance. In this article, we present our simulation and experimental results of a type of antireflection metasurfaces that can sufficiently enhance the transmission from the air to the subsurface for ground-penetrating radar (GPR) applications. The proposed metasurface design consists of an array of closed ring resonators (CRRs) and metallic mesh on each side of a dielectric spacer, showing near-perfect antireflection. The corresponding enhanced transmission is only limited by the material losses of the metasurface itself. Through the geometry optimizations, three metasurface designs have been numerically and experimentally demonstrated for the dry, medium moist, and wet scenarios. It is discovered that the transmission into the wet foam brick can be increased by up to 50% when the metasurface is in place. The metasurface-based transmission enhancement is also relatively insensitive to the deviation of the permittivity of the material under test (MUT). Our real-world GPR experiments demonstrate that an undetectable buried pipe can be distinguished if the metasurface is placed at the air–ground interface. The proposed metasurface approach provides a promising solution to the impedance matching problems for nondestructive testing applications.

Losses are often the impairing feature of metamaterial true time delay line devices. In this study, the authors analytically demonstrate that ohmics losses in this kind of structures as well as impedance mismatch depend on the bandwidth. These results allow to consider wide band application for radar systems. It is verified experimentally that metamaterial delay line devices are fitted for wide band delay line applications for they allow low insertion losses, low return loss and tunable delay.

Gluing an Antenna-on-Chip (AoC) directly on a ground plane or heat sink in the lead-frame is a standard process for commercial applications. To reduce the effect of losses in the silicon substrate and improve the antenna’s radiation efficiency, the wafer thickness is often drastically reduced. However, the close proximity of the antenna and ground plane can cause an impedance mismatch. Metal tiles, which are embedded in silicon dioxide layers, are designed as an Artificial Magnetic Conductor (AMC) to increase the radiation efficiency and tune the antenna impedance. A double-layer AMC is applied instead of a single-layer AMC to reduce the silicon dielectric loss. Additionally, the double-layer AMC has more capacitance to tune the impedance when integrating with a monopole on-chip antenna. The resulting -10 dB impedance bandwidth is increased to 5.8 GHz around the 60 GHz band, the simulated realized gain increases by 3.3 dB, and the simulated antenna radiation efficiency is increased from 11% to 21%. The measured input impedance of the AoC shows good agreement with the simulation results after probe calibration.

This study presents an adaptive analogue calibration method to compensate electrode-skin impedance mismatch during biopotential signal (electrocardiogram, electroencephalogram and electromyogram) acquisition with enhanced immunity to electromagnetic interference (EMI). The method continuously measures the variation of the impedance mismatch between the electrode-skin interfaces arising primarily due to motion artefacts, and thereafter compensate for the resulting distortions at the output. The compensation is done with the help a proportional-integral-derivative controller in the feedback loop, together with the acquisition of the biopotential signals. A common mode shunt feedback at the output attenuates the common mode EMI and reduces the common mode deviation. As compared to previously reported techniques, the proposed technique refutes any need for offline manual calibration and shows a significant improvement in EMI attenuation without interrupting the main system's operation. This study explains the proposed technique with the comprising blocks, illustrates the theoretical models and analyses, and evaluates the superior performances of the proposed method by comparing the responses with those obtained from the other EMI-Immune electrode mismatch compensating front-ends existing in the literature.

Electromagnetic pollution has become a serious concern with the immense utilization of wireless information technologies and this has aroused huge interest in the area of microwave absorption. To solve this issue, fabrication of advanced, novel and superior microwave absorbing materials (MAM) with high electromagnetic wave absorption, wide absorption bandwidth, lightweight and cost-efficient are highly required. To date, magnetite (Fe3O4) is being thoroughly investigated as MAM, due to its exceptional dual electromagnetic properties (permittivity and permeability), proper saturation magnetization and high Curie temperature. However, large density and impedance mismatch are some of the limiting factors that hinder its microwave absorption performance (MAP). To circumvent these challenges, reduction of size to the nanoscale, fabrication of hierarchical nanostructures and/or conjugation with other lossy materials have been extensively explored as viable solutions to optimize the MAP of Fe3O4. In this review, the progressive research in the fabrication of Fe3O4 based nanocomposites as MAM is discussed. The factors influencing the MAP of these absorptive materials are likewise discussed in detail. Conclusively, some challenges, limitations, and future prospects in the development of Fe3O4 based MAM are put forth.

Transient plasma generated by high-voltage nanosecond pulses in a pulsed corona configuration has proven to be an efficient medium for e.g., air purification applications. In this article, we present a study on boosting the energy efficiency of such a system by using a special type of plasma reactor: the multiple-wire plasma reactor. The basic principle of such a reactor is that it has a lower transmission-line impedance than a normal wire-cylinder reactor while at the same time still producing the required high electric fields necessary for plasma generation. The lower impedance of the reactor results in a smaller impedance mismatch between the high-voltage pulse source and the reactor, thereby minimizing pulse reflections on the source-reactor interface, increasing the energy efficiency of the system. We calculate the impedance of the multiple-wire reactor and assess both the electrical energy efficiency as well as the chemical efficiency of the plasma by measuring electrical energies and ozone concentrations generated by the plasma when energized by a fast solid-state nanosecond pulse source (with 7-ns rise time pulses of up to 20kV) for a range of multiple-wire plasma reactor parameters. We show that with the multiple-wire reactor we can almost double the energy efficiency of the reactor (from 45% to 85%), reduce the voltage stress in the system by 29%-31% and increase the system efficiency by 95%-98% when using a multiple-wire electrode geometry (as compared to a single-wire system).

The quality of the communication links in VPLC (vehicular power line communication) suffer from an impedance mismatch resulting from fluctuating VPLN (Vehicular Power Line Network) access impedance, which renders the fixed impedance matching circuit inefficient. In this paper, we designed a T-shaped adaptive impedance matching system on the basis of the resonance- and absorption-based T-shaped network complex impedance matching approach. We identified the load-Q (quality factor) for different matching situations to facilitate designing T-shaped networks with broad bandwidths. The designed T-shaped adaptive impedance matching system adjusts the component values of the T-shaped network to implement adaptive impedance matching between the VPLC modem and VPLN. A set of simulations are conducted for 1 MHz-100 MHz, which demonstrates that the designed adaptive matching system with a simple circuit structure and control logic is capable of significantly improving signal power transfer.

Rayleigh backscattering-based distributed fiber optic sensing technology is well known and widely used for large-scale structural health monitoring. Inspired by the Rayleigh backscattering-based sensing methodology on an optical fiber, in this paper, we present a sensing concept based on the random inhomogeneities on a coaxial cable. As an analogy of Rayleigh backscattering along an optical fiber length, “backscattering” also exists from a commercial coaxial cable due to its inherent defects along a cable length which induce a local variation (i.e., impedance mismatch). This is because of the irregular microscopic structures of the inner/outer conductors, and the inhomogeneous density or permittivity of the inner dielectrics after the cables are manufactured. The accumulated backscattered signals along the coaxial cable can be obtained using frequency-domain reflectometry. By analyzing the shift in the local backscattered signal, the local environmental perturbations (e.g., local strain or temperature) can be determined, so that truly distributed sensing capability using a coaxial cable can be achieved. To verify the proposed concept, an intact and commercial coaxial cable was demonstrated for distributed temperature sensing. Compared with the existing coaxial cable-based distributed sensing technologies, the proposed sensing concept does not need extra modifications to the coaxial cable and offers a truly distributed sensing capability.

Nowadays, one of the most challenging situations for software developers is the presence of a mismatch between relational database systems and programming codes. In the literature, this problem is defined as "impedance mismatch". This study is to develop a framework built on innovations based on the existing Object Relational Mapping technique to solve these problems. In the study, users can perform operations for three different database systems such as MsSQL, MySql and Oracle. In addition, these operations can be done within the framework of C# and Java programming languages. In this framework, while the developers can define database tables in the interface automatically, they can create relations between tables by defining a foreign key. When the system performs these operations, it creates tables, views, and stored procedures automatically. In addition, entity classes in C# and Java for tables and views, and operation classes for stored procedures are created automatically. The summary of the transactions can be taken as pdf file by the framework. In addition, the project can automatically create Windows Communication Foundation classes to facilitate the handling of database elements created and the interfacing operations, as well. This framework, which supports distributed systems, can be downloaded at this link.

Single-flux-quantum (SFQ) circuit technologies are promising digital circuit technologies with high-speed and extremely low-power characteristics. However, heavy wire routing tasks are finished either by considerable human effort or by commercial routing tools with few physical considerations for the SFQ circuits. In this paper, we present an integrated global and detailed router for the SFQ circuits, qGDR, which aims at reducing the impedance mismatch during signal transfer by minimizing the total number of used vias. The global router allocates routing resources while minimizing the via usage by a dynamic layer assignment algorithm. The detailed router follows the global routing results to complete the routing task by resorting to a maze routing algorithm. Following the MIT-LL SFQ5ee process technology, qGDR can use only two routing layers to route an 8-bit integer divider with more than 40 000 Josephson junctions in less than one hour.

Hyperthermia plays an important role in the treatment of cancer. A circular ring slot patch antenna for Hyperthermia applications is presented at 2.45 GHz. The proposed antenna shows return loss without significant detuning or impedance mismatch with different positions concerning a phantom muscle model. The simulation study is done by a Finite Element Method (FEM) based on Ansoft’s HFSS software. The antenna penetration depth, return loss, and the specific absorption rate (SAR) pattern are evaluated for various antenna orientations concerning the phantom muscle model.

The development of information transmission technology towards high-frequency microwaves and highly integrated and multi-functional electronic devices has been the mainstream direction of the current communication technology. During signal transmission, resistance-capacitance time delay, crosstalk, energy consumption increase and impedance mismatch restrict the high density and miniaturization of Printed circuit board (PCB). In order to achieve high fidelity and low delay characteristics of high-frequency signal transmission, the development of interlayer dielectric materials with low dielectric constant (Dk) and low dielectric loss factor (Df) has become the focus of researchers. This review introduces the dielectric loss mechanism of polymer composites and the resin matrix commonly used in several high-frequency copper-clad laminates, and mainly describes how to reduce the dielectric constant and dielectric loss of materials from the level of molecular structure design, as well as the effect of fillers on the dielectric properties of polymer substrates. As a kind of potential functional fillers for dielectric polymeric composites, the carbon nanofillers are used to tailor the dielectric properties of their composites via different dimensions and loadings, as well as their proper preparation methods. This review finally summarizes the interface bonding failure mechanism and a feasible idea to optimize the dielectric properties of polymer matrix composites is also proposed.

As one of the fundamental phenomena in optics, reflection always occurs for the refractive index contrast between different materials for the impedance mismatch. In many applications, such as solar cells or photodetectors, reflection is unwanted and the reduction of reflection is highly desirable. Metasurfaces have attracted intensive attention recently for their ability to efficiently reshape electromagnetic waves in desired manners on a flat and ultrathin platform. Numerous new concepts, effects, and applications have been intensely studied in recent years. As some of the most important applications, metasurfaces exhibit superior capabilities to enhance absorption, antireflection, and transmission. Here we demonstrate a silicon metasurface with significantly enhanced antireflection over a broad spectrum from 1 to 5 μm. Over the more than two-octaves bandwidth, the transmittance is all above 78% with an average value as high as 95%. The proposed metasurface is a silicon layer on top of an InAs layer on a GaSb substrate and exhibits polarization-insensitive transmission enhancement for the symmetry of the geometry. This structure can be potentially used for thermal targets detection, imaging, sensing, and biochemical analyses.

Flexible wearable wireless devices have found practical uses as their cost has fallen and Internet of Things applications have gained further acceptance. These devices are gaining further use and acceptance in the consumer and wearable space for applications such as logistical tracking and maintaining sensor information, including temperature, humidity, and location. In such applications, antennas are exposed to bending and crumbling. Therefore, flexible substrate antennas for use with polymer-based flexible devices are an important area of research that needs to be addressed. In this study, the bending capabilities of flexible polymer substrate antennas for general IoT applications were practically analyzed by fabricating flexible antennas on Polyethylene Terephthalate (PET), Polytetrafluoroethylene (PTFE) Teflon, and Polyvinylchloride (PVC) substrates operating at 2.45, 4.45, and 7.25 GHz frequencies. The basic premise was to investigate the flexibility and bending ability of polymer materials, and their tendency to withstand deformation. In the current paper, we start by providing an equivalent model for the flexible microstrip patch antenna under bent conditions, followed by outlining the process of designing flexible antennas on polymer substrates. Finally, the fabricated flexible antennas were tested in an anechoic chamber for various radiation characteristics such as reflection coefficients, operating frequency shifts, and impedance mismatch with the transmission line, under bending conditions up to 7 mm. The practical outcomes were then compared with our recent investigation on flexible polymer substrate antennas for wearable applications. This study provides a means to select a suitable polymer substrate for future wearable sensors and antennas with high bendability.

This paper focuses on the analysis of performance degradation of UHF-RFID tags considering the impact of objects and materials in its immediate proximity. Materials utilized as packaging and container material in logistics and production environments, combined with its contents frequently lead to a complex and inhomogeneous environment. Although it is well known that the surface material and tag positioning have a great impact on the tag antenna, a meaningful rating method for performance evaluation, taking into account the introduced impedance mismatch, as well as the altered radiation pattern is still lacking. Hence, this paper proposes a rating scheme enabling a convenient application-specific tag readability evaluation. The impact of materials, as well as tag positioning on the target object can be evaluated, taking into account the sensitivity of the tag-IC, antenna characteristics and polarization. By utilization of full-wave simulation techniques, the complex near-field effects are determined. Based on the simulation results, the tag readability for a selection of common use-cases is evaluated. Finally, measurements in an anechoic chamber confirm the validity and usefulness of the proposed evaluation.

Deep brain stimulation (DBS) represents an important treatment modality for movement disorders and other circuitopathies. Despite their miniaturization and increasing sophistication, DBS systems share a common set of components of which the implantable pulse generator (IPG) is the core power supply and programmable element. Here we provide an overview of key hardware and software specifications of commercially available IPG systems such as rechargeability, MRI compatibility, electrode configuration, pulse delivery, IPG case architecture, and local field potential sensing. We present evidence-based approaches to mitigate hardware complications, of which infection represents the most important factor. Strategies correlating positively with decreased complications include antibiotic impregnation and co-administration and other surgical considerations during IPG implantation such as the use of tack-up sutures and smaller profile devices.Strategies aimed at maximizing battery longevity include patient-related elements such as reliability of IPG recharging or consistency of nightly device shutoff, and device-specific such as parameter delivery, choice of lead configuration, implantation location, and careful selection of electrode materials to minimize impedance mismatch. Finally, experimental DBS systems such as ultrasound, magnetoelectric nanoparticles, and near-infrared that use extracorporeal powered neuromodulation strategies are described as potential future directions for minimally invasive treatment.

The current lightest available harmonic radar tags, with mass of a few milligrams, can only be carried by relatively large insects. However, small insects such as weevils and mosquitos are unable to sustain available tags. The former extensively infest food, and the latter kills nearly three million people and infects another 200 million or more every year. Two methods for reducing the tag’s mass and struggles of using these methods are presented here, followed by a review of the solutions. Retaining tag efficiency must be considered in every approach so as not to lose the detecting range because of impedance mismatch between the dipole and attached diode. These approaches include using a thinner wire and a short non-resonant dipole. The simulation was performed using Computer Simulation Technology (CST) software. Consequently, a wire tag lighter than 200-300 μg is expected, which has low mass for tracking smaller insects.

In this paper, a simple printed cross-dipole (PCD) antenna to achieve a right-hand circular polarization (RHCP) at the L/S-band for direction finding (DF) systems is presented. The radiating part of the antenna consists of two printed dipoles that interlock with each other and are mounted orthogonally on a dual-layer printed reflector. To connect the feedlines of the dipole elements to the antenna’s feed network, which is located on the backside of the reflector, a through-hole signal via (THSV) is employed as the signal interconnection instead of the mainstream approach of using coaxial bead conductor. This feeding technique provides a degree of freedom to control the impedance of the signal path between the feedlines and the feed network in the numerical simulation for improved matching conditions. The proposed THSV extending through the dual-layer printed reflector is more reliable, durable, and mechanically robust to stabilize the matching conditions of the fabricated antenna in contrast to the coaxial-based approach that is more susceptible to impedance mismatch due to solder fatigue. Thus, the proposed PCD antenna offers advantages of broadband, flexible impedance matching, and fabrication ease. The antenna exhibits an impedance bandwidth (IBW) of 59% (1.59–2.93 GHz), a 3-dB axial ratio bandwidth (ARBW) of 57% (1.5–2.7 GHz), and a peak of 7.5 dB within the operating frequency band.

In order to avoid grid oscillations caused by the frequency domain impedance mismatch of power electronic devices and power system, this paper studies and designs a controllable broadband power grid impedance measurement device to measure real-time parameters of low-voltage distribution network. The core circuit of this portable device adopts an improved “butterfly bridge” circuit, which reduces the size and weight of the device. The main control unit selects the DSP chip TMS320F28335 of Texas Instruments Semiconductor and one injection can realize wide-frequency harmonic excitation. In addition, users can directly generate modulation signals at specific frequency band through touching on the screen, and monitor the process and results of disturbance injection in real time. The final built device has a power of about 5 kV.A, has an AC voltage below 400V, and an AC current below 50A sampling capacity. Considering the measuring results, the designed device is efficient in measuring the wide-frequency band impedance for power grid within the set frequency range.

At present, the electromagnetic compatibility(EMC) high and low voltage coupling network test for automotive electrical sub-assembly(ESA) in the standard only requires the use of an adapter to connect the network and the test sample, in other words, the impedance matching is not considered. In practice, if the impedance does not match, accuracy and consistency of test results cannot be guaranteed. But it is difficult to achieve impedance matching in the whole frequency band.In view of the above problem, this paper proposes an impedance matching method for high-low voltage coupling test, by isolating indirectly contact between the test system and the sample, which reduces test errors and improves the accuracy of test data caused by impedance mismatch. The experimental results prove that this method can effectively solve the shortcomings of the existing high and low voltage coupling EMC test technology of electric vehicle ESA, and provide a reasonable test idea for accurately testing the electric vehicle ESA high and low voltage coupling network test method.

International audience; Triaxial measurement is an effective means to determine the transfer impedance of a shielded cable. It is based on coupled transmission line principle. In an ideal case, both transmission lines in the setup would be matched to guarantee the high frequency performance. In practice, matching is hard to achieve without compromising on usability and generality of the measurement setup. This paper discusses how triaxial cell diameter and the resulting impedance mismatch affects transfer impedance measurement results. In addition, the paper shows how impedance mismatches can be modeled, presents a simplified model to quickly understand the effects of impedance mismatch, and compares the model to results measured with different triaxial cell sizes. The simple model presented achieved similar accuracy to a more complex model defined in IEC 62153.

In this study, the analytical solution for the group delay of a high-speed system with large impedance mismatch is derived. The accuracy and applicability of the solution are validated by comparing the calculated results between the analytical formulation and commercial tool results. Causal frequency-dependent stripline model is used in the formulation, and the derivation of analytical formulation is based on the transmissions and reflections of wave components in the high-speed channel. Therefore, the causality of the system can be ensured, and the number of transmissions and reflections considered in the calculation can be specified in the formulation. The derived analytical results indicate that multiple reflections in a system with impedance mismatch will contribute to oscillations in the group delay curve, but the minimum group delay at the valleys of the oscillations does not appear to be the minimum propagation delay of the system. The benefits of having analytical results play a critical role in identifying channel impairments in high-speed designs.