Changes In Input Impedance Research Articles

Determination of Compensation Capacitor Considering the Dead-Time Characteristics for ZVS in Wireless Power Transfer System

In the Wireless Power Transfer (WPT) system, the input impedance characteristics change depending on the load and the air-gap between the coils. Changes in input impedance affect zero voltage switching (ZVS) and dead-time related to stability, efficiency, and electromagnetic interference. Existing studies lack the dead-time analysis according to operating conditions. In addition, this resulted in unnecessary power dissipation as it cannot determine an appropriate compensation capacitance. Thus, it is important to analyze dead-time and determine the compensation capacitance accordingly for ZVS. This paper presents a compensation capacitor selection method for ZVS in a WPT system with various operating conditions based on dead-time analysis. The compensation capacitor that should be adjusted is identified, and its value is calculated considering dead-time, output power, and efficiency. Therefore, the proposed method can stably implement the WPT system and improve the power and overall system efficiency. A 500W WPT system is designed to validate the theoretical analysis. The designed WPT system is measured under various coupling coefficients and load conditions. It is confirmed that the proposed method implements ZVS under various conditions of the WPT system. Experiments show that the proposed method improves overall system efficiency by up to 3.75% and reduces dead-time by 77%.

Echo TEMPEST: EM Information Leakage Induced by IEMI for Electronic Devices

Electromagnetic (EM) information leakage encourages attacks, wherein the attackers passively capture and analyze EM waves that are unintentionally generated by devices. Generally, devices with weak EM emission intensities are not targeted. However, even these devices would be subject to attacks if it becomes possible to actively sense the electrical changes that occur within them when information is processed. This article demonstrates the feasibility of the information leakage threat induced by the active sensing of input impedance changes in the input/output (I/O) circuit of an integrated circuit (IC). Specifically, the changes in the input impedance when information was transmitted from the IC, were measured by irradiating the EM waves from outside the target device. This article labels the threat as Echo TEMPEST. The experiment validated Echo TEMPEST with an evaluation board that simulated the I/O circuit of the IC, UART modules, and USB keyboards. It was also demonstrated that attackers could control the distance (obtained information from the target device), depending on the intensity of the irradiated EM waves. Furthermore, we discussed countermeasure methods focusing on the conditions for executing Echo TEMPEST.

Estimation of the electrodynamics parameters of the multilayer strip-slot transition based on the approximation of its equivalent circuit by the chebyshev filter of the first kind

The basic structural element of volume-modular microwave devices is a multilayer strip-slot transition, which provides electromagnetic coupling between its layers in a wide frequency range. The mathematical model of the multilayer strip-slot transition is known. It is based on the use of circuit analogies of its design elements. However, in the papers related to the study of its equivalent circuit only the amplitude-frequency dependences are reflected without analyzing other electrodynamics parameters, such as: phase-frequency characteristics and dependences of the input impedance on frequency. The purpose of this paper is to estimate the electrodynamics parameters of the multilayer strip-slot transition based on its equivalent circuit, approximated by the Chebyshev filter of the first kind and to conduct a comparative analysis of the results of its circuit and electrodynamics simulations. At the same time, the following simulation results are compared: 1) amplitude-phase characteristics of the functions of the reflection coefficient and transmission coefficient; 2) change in input impedance in the frequency range. As a result of the study it has been established that the equivalent circuit of the multilayer strip-slot transition can be approximated by the Chebyshev filter of the first kind. It allows to determine the necessary characteristic impedances of strip and slot resonators by given return/insertion losses in the pass band and their cutoff frequencies, while reflecting all electrodynamics characteristics correctly.

Design of Continuous Class-B/J Power Amplifier Based on Mirrored Lowpass Filter Matching Structure

This paper proposes a methodology for designing broadband class B/J power amplifier based on a mirrored lowpass filter matching structure. According to this filter theory, the impedance of this design method is mainly related to the cutoff frequency. Series inductors and shunt capacitors filter out high frequencies. The change of input impedance with frequency is small in the passband. Which can suppress higher harmonics and expand bandwidth. In order to confirm the validity of the design method, a broadband high-efficiency power amplifier in the 1.3 - 3.9GHz band is designed and fabricated. Measurement results show that the output power is greater than 40.5dBm, drain efficiency is 61.2% - 70.8% and the gain is greater than 10dB.

Wireless Monitoring of Displacement Using Spiral Resonators

A distance sensor based on a spiral resonator (SR) label printed on a dielectric substrate and remotely interrogated through a small loop antenna acting as reader is presented. The proposed system is working at a single frequency (856.5 MHz) and could be compliant with conventional RFID readers. The measurement of distance is carried out by observing the magnitude variation of the response at resonance, namely the real part of the input impedance of the probing loop. Indeed, the latter response changes as a function of the distance between the tag and the loop due to the variation of mutual coupling between the pair. The proposed sensor is capable of providing estimates of the distance with high resolution within the specified range of operation. The results also show that the sensitivity of the sensor, which is quantified by the change of input impedance over distance, decreases at large displacements, eventually reaching a saturation point which defines the maximum detectable distance. The sensing principle is verified using simulations and measurements. It is also demonstrated that the maximum readable distance is comparable to the size of the SR. Finally, the effect of lateral displacement was investigated experimentally to demonstrate how the sensor performs in conditions where perfect axial alignment cannot be guaranteed. Thanks to its scalability potential, the proposed sensor is suitable for various practical scenarios.

An Impedance Matching Strategy for Micro-Scale RF Energy Harvesting Systems

Radio frequency (RF) energy harvesting is widely adopted as an alternative source of energy to power a wireless sensor node or an Internet of Things (IoT) node. In order to extract maximum power from an RF energy source, variations in an RF to DC converter (RDC) input impedance with input power should be taken into account. This brief demonstrates that a tunable impedance matching strategy is essential to track the changes in input impedance to ensure maximum power transfer across the desired input power levels. A two-state tunable matching network is proposed to track variations in input impedance with the input power of an RDC with a load of 10 kΩ, and at an operating frequency of 953 MHz. The proposed impedance matching network and the RDC are designed using 0.18-μm CMOS technology node. Circuit simulations demonstrate that the proposed matching strategy extends the input power range over which maximum power transfer occurs by 5 dBm and 13 dBm in comparison to a fixed matching network designed at -24 and -18 dBm, respectively.

Near‐field reconstruction for portable wireless devices by deconvolution from input impedance changes

The near-field validation of computational electromagnetic models of personal wireless communication devices is becoming indispensable, especially, when assessing specific absorption rate (SAR) compliance to regulatory limits by computer simulation. A possible practice for such validation is to compare measured and simulated electromagnetic field distributions in a standard flat phantom designed for SAR compliance measurements. The authors recently presented an input impedance measurement-based validation method. They extend their scheme with a deconvolution procedure. This enables near field validation based on the reconstructed E 2 field obtained by the deconvolved measurement of the impedance change compared to the calculated E 2 . However, the reconstruction problem is inherently ill conditioned and requires numerical treatment. They demonstrate that the regularisation of the convolution matrix makes the reconstruction of the E 2 field feasible with promising error. Through examples of a 1 GHz printed inverted F and a 1.8 GHz printed monopole antenna, they show that the mean-square error as low as 1% between the original and the reconstructed E 2 is achievable with the proposed method.

Fabricating patch antennas within complex dielectric structures through multi-process 3D printing

In this work, a 3D printed patch antenna is fabricated within a complex dielectric structure relevant to the construction of satellites – an isogrid panel. The antenna was fabricated via a multi-process, hybrid, additive manufacturing system that included polymer material extrusion enhanced with complementary manufacturing capabilities of foil placement and patterning, wire integration and component placement. The antenna design targeted the commercial frequency of Bluetooth communication at 2.4 GHz by introducing a rectangular conductor of precise width, height and thickness from ground plane for the specific resonance. The measured reflection and gain coefficients were reasonable, however, two challenges were identified with the fabrication related to (1) imperfections typical of material extrusion additive manufacturing processes including unintentional porosity and (2) the insecure mechanical bonding between the output connector and substrate. Porosity impacted the dielectric features (permittivity) of the substrate and consequently introduced error in final antenna resonance (2.13 GHz versus the target of 2.4 GHz). The bonding affected mechanical reliability and caused changes in input impedance which affected signal quality for some orientations depending on cable flexing. Several remediations were identified, all of which included reinforcing the connector during embedding with a bonding agent. In the end, the antenna was compared to a commercial dipole antenna and the signal-to-noise ratios were within 6%.

An Accurate CMOS Interface Small Capacitance Variation Sensing Circuit for Capacitive Sensor Applications

In this paper, an accurate front-end CMOS interface circuit for sensing very small capacitance changes in capacitive sensors is presented. The proposed structure scales capacitance variation to the sensible impedance changing. The scaling factor of the circuit can be easily tuned by adjusting bias points of the transistors. In order to cancel or decrease the parasitic components, the RC feedback and input transistor cascading techniques are employed in the design. To simulate the circuit, HSPICE simulator is utilized to verify the validity of the theoretical formulations in 0.18 $$\upmu \hbox {m}$$μm technology. According to schematic and post-layout simulation results, input impedance changes linearly versus capacitance variations up to 0.7 GHz, while the sensor capacitance changing is varied between 0 and 200 fF. According to the simulation results, total dc power consumption is obtained as low as 1 mW with 0.9 V power supply.

FDTD based Analysis of Input Impedance of a Wearable Patch Antenna with Milli Bends

Wearable antennas are prone to bending and crumpling. This work presents the analysis of input impedance of a wearable patch antenna with milli bends using Finite Difference Time Domain (FDTD) method. FDTD method using stair case scheme is used to model milli bends at different places along the length of a wearable patch antenna and the effect of milli bends on input impedance of the wearable patch antenna is presented developing a FDTD code for it. It is shown that presence of milli bends in a wearable patch antenna significantly changed the input impedance of the antenna under consideration. It is observed that milli bends closer to the feeding strip line provided better input impedance matching. Results concluded that change in input impedance leads to change in resonant frequency and reflection coefficient of the antenna. General Terms: RF and microwave communication, Antenna design and analysis.

Validation of Numerical Models of Portable Wireless Devices for Near-Field Simulation

The major contribution of the paper is a theoretical proof of the equivalence between two approaches of near-field validation techniques for the numerical models of personal wireless communication devices. The current validation practice is to compare measured and computed electromagnetic field or specific absorption rate distributions. A new validation technique introduced by the authors recently compared measured and computed antenna input-impedance changes while the near field is systematically perturbed by a dielectric control object. The proof of the equivalence is based on two novel formulas derived here: a reaction impedance-change formula, and an error formula that establishes a quantitative relationship between the errors of the impedance changes and the near-field values. The equivalence of the two validation techniques is verified experimentally too by comparing measurements and computations for a planar-inverted F antenna. By performing numerical experiments for two types of printed-circuit board antennas, it is also proved here the first time that the new validation technique is feasible even if the geometric and material properties of the control object are such that the Born approximation can be introduced in the impedance-change formula.

A Broadband Antenna Array Using Full-Wave Dipole

This work introduces a bandwidth broadening technique for full-wave dipole (FWD) antennas and arrays, which are realized by introducing gaps in both two arms of the dipole. Several parameters are analyzed to illustrate the change of input impedance of the proposed FWD and the moving of resonant modes. The proposed FWD array antenna shows advantages in terms of impedance bandwidth, 3-dB gain bandwidth and the complexity of the feeding network, when the four-unit FWD array antenna compares with the eight-unit half-wave dipole array antenna. The impedance bandwidth of the proposed FWD array antenna is up to 67.8% with the reflection coefficient <−10 dB from 3.9 to 7.9 GHz. The 3-dB gain bandwidth of the proposed antenna array is 51.4% with the maximum gain of 14.2 dBi and unidirectional radiation property across the entire operating bandwidth. The proposed methodology is good for a high-gain antenna array design through the reduction of antenna elements so as to minimize the complexity of power distributed network to the array. The ultimate goal of this work is to devote a low-cost and high-efficiency antenna array to broadband wireless communication systems.

On the sensitivity of matching network to load variation for passive RFID sensor

ABSTRACTA novel study on sensitivity of matching network to load variation is presented in this work. In passive RFID sensor tag, it is desired that a small change in input impedance of tag antenna should yield a significant response, which can be achieved by a matching network with high sensitivity. In this work, network sensitivity is defined and maximum sensitivity matching network is acquired for certain source and load impedances. Several LC and microstrip matching circuits are designed and fabricated to verify the network sensitivity theory. By inserting a sensitive matching network to a temperature sensor tag in literature, three times higher sensitivity is achieved, which proves the merit of the theory. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:232–236, 2017

An accurate CMOS interface small capacitance variation sensing circuit for capacitive MEMS sensor applications

ABSTRACTAn accurate front-end CMOS interface circuit for sensing very small capacitance changes in capacitive sensors is presented in this paper. The proposed structure scales capacitance variation to the sensible impedance changing. The scaling factor of the circuit can be easily tuned by adjusting bias points of the transistors. In order to cancel or decrease the parasitic components, the RC feedback and input transistor cascading techniques are used in the design. To simulate the circuit, HSPICE simulator is utilized to verify the validity of the theoretical formulations in 0.18 µm technology. According to schematic and post layout simulation results input impedance changes linearly versus capacitance variations up to 0.7 GHz while the sensor capacitance changing is varied between 0~200fF. Total dc power consumption is obtained as low as 1.2 mW with 1.8 V power supply.

Abstract P254: Hypertension: A proposed Mechanistic Pathway for Arterial System Remodeling

Arterial properties change during hypertension (HTN) development. The time course of the changes can be used as a marker of vascular remodeling in the development of HTN. Study Aim: To determine whether pressure induced changes in vascular properties result in alterations in pressure-flow patterns that impact the load for ventricular function: input &amp; characteristic impedance, A rterial C ompliance (AC)= SV/PP (stroke volume)/(pulse pressure), AC=Tau/peripheral resistance (PR), and PP were investigated. Methods: Pressure and flow relations were investigated in dogs during the development of renal-HTN over 4-weeks (Wks). The sensitivity of hemodynamic markers of vascular remodeling was evaluated by changes in AC= SV/PP, and by AC= Tau/PR and PP. Results: All BP components increased during the development of HTN. Changes in Input Impedance, increased through Wks 2 to 4. Increases in the steady component of the cardiac cycle were reflected by peripheral PR, and changes in the pulsatile component were reflected by changes in AC=SV/PP, and AC=Tau /RP; and changes in characteristic impedance. PP and PAP increased by Week 2, reflection of the cardiac and arterial workloads and vascular Tension RP that progressed through Wk 4 Conclusion: Reliable and accessible markers that indicate changes in arterial pressure, flow &amp; volume, are: PP and AC (SV/PP), and AC (Tau /TPR). These variables detected increases in the heart-load and alterations in pressure-flow patterns that impair cardiovascular-function resulting in HTN-CVD; input and characteristic impedance, also provides remodeling information about the arterial system but are not readily available to clinicians.

Research on input impedance of dipole antenna in GTEM cell

The formula of input impedance of dipole antenna in Gigahertz Transverse ElectroMagnetic (GTEM) cell based on the dyadic Green’s function is first obtained in this paper. The validation of the formula is verified by the results of theoretical derivation and simulation with well agreements. In comparison with the formula of input impedance in free space, the relationship between the change of input impedance with the length of antenna and the position of antenna in GTEM cell is obtained. In addition, some meaningful conclusions are presented, which not only can be referred by the further research of ElectroMagnetic Interference (EMI) measurements in GTEM cell, but also provide the theoretical basis for testing compensation and error analysis.

Effect of Transverse Acoustic Flow on the Input Impedance of Rapidly Flaring Horns

Abstract In slowly flaring horns the wave fronts can be considered approximately plane and the input impedance can be calculated with the transmission line method (short cones in series). In a rapidly flaring horn the kinetic energy of transverse flow adds to the local inertance, resulting in an effective increase in length when it is located in a pressure node. For low frequencies corrections are available. These fail at higher frequencies when cross-dimensions become comparable to the wavelength, causing resonances in the cross-direction. To investigate this, the pipe radiating in outer space is modelled with a finite difference method. The outer boundaries must be fully absorbing as the walls of an anechoic chamber. To achieve this, Berenger's perfectly matched layer technique is applied. Results are presented for conical horns, they are compared with earlier published investigations on flanges. The input impedance changes when the largest cross-dimension (outer diameter of flange or diameter of the horn end) becomes comparable to half a wavelength. This effect shifts the position of higher modes in the pipe, influencing the conditions for mode locking, important for ease of playing, dynamic range and sound quality.

Ivabradine: An hypothesis generating study – An important link between bench and bedside

Coronary artery disease (CAD) remains a major cause of mortality and morbidity. Flow in coronary circulation occurs predominantly in diastole, matching large input impedance changes imposed by ventricular contraction and relaxation on intra-myocardial vessels. Thus myocardial perfusion time decreases and myocardial oxygen consumption in turn increases with heart rate. Auto-regulation of coronary vessels maintains a marginal balance of oxygen supply and demand in physiologic conditions. A lower vascular resistance causes a nearly five-fold increase in instantaneous diastolic coronary flow [1].

伝送線路の入力インピーダンスの変化を用いた振幅変調型磁界センサの基礎特性

A new amplitude-modulation-type magnetic field sensor using a magnetic/dielectric hybrid transmission line is presented. The transmission characteristics of the transmission line are influenced by a permeability change due to application of on external magnetic field to the magnetic layer. This sensor uses the change in the input impedance of the transmission line. A big change in input impedance is provided when the transmission line is used as a stub that is short-circuited or opened with a trailing end.

Independent control of resonantfrequency and input impedanceof a microstrip patch byindividually biased varactor diodes

Individually biased varactor diodes fitted to the radiating edges of microstrip patch antennas enable independent control of the resonant frequency and input impedance. The technique has been successfully applied to polarisation-agile patch antennas and it affords a solution to the problem of the change in input impedance when switching between polarisations.