Equivalent Input Impedance Research Articles

Accurate Modeling, Design, and Load Estimation of LCC-S Based WPT System With a Wide Range of Load

Modeling of the wireless power transfer (WPT) system is the premise to design and control it. First-harmonic-analysis (FHA) is a simple and effective method to model the WPT system, but its accuracy may decrease with the variation of load in a wide range. In this paper, harmonics are analyzed in the primary side of an LCC-S compensation network based WPT system, depicting a waveform of the output current of the inverter much closer to the real one compared with FHA based model. In the secondary side, the time-domain analysis is conducted both in CCM&DCM of the rectifier, deriving an equivalent input impedance featuring the non-linear characteristics of the system. Based on the proposed model, the parameters of the LCC network are designed, proving to tune the ZVS condition better than the FHA based method. Finally, the load of the system is estimated, achieving a high accuracy (with the estimating error less than 5%) in a wide range with a simple sampling method.

Double-Sandwich Magnetic Coupling Structure Design for Dual-LCL Wireless Charging System in EV Applications

In the wireless charging system of EVs, the traditional single-stage LC resonance network has the issues of narrower of parameter design and small equivalent input impedance. While the composite resonant network will introduce additional resonant capacitors and inductors, which increases the system volume, cost, and reduces the efficiency. This paper proposes a design scheme of double-sandwich magnetic coupling structure with a low cross-coupling coefficient, which integrates the resonant inductors into the power transmitter and receiver, and it is designed taking the magnetic leakage and loss as constraints. A 500W prototype is built, and the comparison of experimental efficiencies between the double-sandwich and the separate magnetic coupling structures is performed. Finally, the effectiveness of the integrated design scheme is validated.

Design Space Exploration of Antenna Impedance and On-Chip Rectifier for Microwave Wireless Power Transfer

This paper discusses a design methodology to efficiently determine the best combination of rectenna (rectifier and antenna) to minimize the input power under a given output condition for microwave wireless power transfer (MWPT) without any other external components, such as a matching network, for cost reduction. A linearized equivalent circuit model is expanded upon to include the microstrip line connecting the antenna and rectifier. Based on the model, the design flow is presented that has mainly three steps: (1) Determination of the equivalent rectifier input impedance and the amplitude of input voltage by running SPICE simulation, (2) Drawing contour plots of input power by rectifier candidate on the antenna impedance plane by conducting model calculation and impedance loci of antenna candidates on the contour plots, and (3) Selecting the combination of antenna and rectifier which gives the minimum input power for all the combinations. To validate the equivalent circuit model and design flow, a single-diode (SD) rectifier and a voltage-doubler (VD) rectifier were fabricated in 65 nm CMOS. The input power to generate 100 μA at 1 Vdc was measured and compared. The model, SPICE and measurement are in good agreement with each other that VD has 30–50% lower input power than SD does. In addition, the sensitivity of the parasitic elements, such as the microstrip line and the bonding wires and pads on the input power, are investigated to explore the design space for rectenna.

Analysis and Design of a High-Frequency Low-Profile Converter for Bendable Equipment

In this article, a 10-MHz low-profile converter for bendable equipment based on aircore inductor is proposed. The mathematical model and inductance calculation method of the bendable planar circular spiral coil under different bending situations is analyzed. An optimal design method of the T type matching network is depicted in detail which helps to guarantee soft-switching characteristics and high efficiency within the whole bending range by realizing weak inductive equivalent input impedance. A 32 V input, 9V/6.3 W output prototype is proposed in the laboratory and the experimental results verify the feasibility of the proposed optimal design methodology, the system efficiency can be improved by 4% than the traditional method.

A wireless power transfer system based on impedance matching network

In this paper, we design a wireless power transfer (WPT) system based on the impedance matching network to achieve highly efficient wireless power transmission from a power source of 220 V/50 Hz to a 50 kHz transmission power to a 25 kHz alternating current (AC) output power. The proposed WPT system is composed of primary rectifier-filter module, DC-DC buck module, primary inverter module, primary impedance matching module, WPT module, secondary impedance matching module, secondary rectifier-filter module, and secondary inverter module. With the used of the secondary impedance matching module, the WPT module with the optimal transfer efficiency can be achieved. By introducing the primary matching module, the efficiencies of the primary inverter module and the DC-DC buck module are improved and meanwhile the equivalent input impedance of the WPT module is increased to suppress the excessive primary-side current caused by the removal of the receiving coil. The proposed prototype system has been fabricated, and the measurement results demonstrate that the system efficiency of 57% can be obtained with a distance of 30 mm at the 42 W input power.

An Impedance Matching Network Tuning Method for Constant Current Output Under Mutual Inductance and Load Variation of IPT System

This article proposes a double-sided inductor–capacitor–capacitor–capacitor matrix (D-LC-CCM) impedance matching network to eliminate the impact of the load and the mutual inductance variation on inductive power transfer system. A thorough mathematical analysis is conducted and a control strategy is proposed to obtain a constant current output when the load and the mutual inductance vary. When the load changes, the equivalent impedance of the secondary side can be kept unchanged by adjusting the capacitor matrix in the receiver, then adjusting the input voltage can achieve constant current output simultaneously. The equivalent input impedance of the primary side and the output current can remain stable by adjusting the capacitor matrix in the transmitter when the mutual inductance changes. The experimental prototype was built, and the system constant current output was achieved when the load changes from 40 to 80 Ω and the mutual inductance varies from 13 to 17 μ H, which has validated the effectiveness of the D-LC-CCM impedance matching network.

On the Design of Ultrawideband Circuit Analog Absorber Based on Quasi-Single-Layer FSS

In this letter, an ultrawideband and single-layer circuit analog absorber with a low profile and small unit size is proposed. The absorber is composed of a Rogers 4003 dielectric with two square loop arrays, respectively, printed on the top and bottom, and a metal ground below. Lumped resistors are embedded on the four edges of the square-loop arrays to introduce resistance loss. Equivalent circuit, input impedance, and current distribution are then presented to provide great insight into the existence of three resonances and wideband. The absorber offers a fractional absorption bandwidth of 132.3% (4.91:1) with at least 10 dB reflection reduction. The thickness and the unit size are, respectively, reduced to $0.075\lambda _{L}$ (wavelength at the lowest frequency) and $0.13\lambda _{L}$ , leading to a good performance under oblique incidence. A good agreement between the calculated, simulated, and measured results validates the proposed design.

Efficiency Improvement of Wireless Power Transfer Based on Multitransmitter System

Multitransmitter wireless power transfer system gets more and more applications as it can maintain high efficiency in a large space range. This article focuses on modeling the multitransmitter system, and proposes an impedance matching method to improve efficiency under lateral-misalignment conditions. The theoretical analysis shows that the maximum transfer efficiency can be achieved as long as the equivalent input impedance of the transmitters is regulated to be the same under misalignment condition. Hence, a double closed-loop control strategy is proposed to realize maximum efficiency point tracking, where the primary control loop adjusts the input impedance of the transmitters through pulsewidth modulation, while the second control loop maintains constant output power by a dc–dc converter. A 500-W prototype is built to validate the feasibility of the proposed method. The efficiency is always higher than 90% with an improvement of up to 20.3% compared to that without such a method when the lateral misalignment increases from 0 to 10 cm (0%–41% of maximum coil size).

Analysis, Modeling, and Design of a 2.45-GHz RF Energy Harvester for SWIPT IoT Smart Sensors

Simultaneous wireless information and power transfer (SWIPT) is a flexible and cheap way to supply Internet-of-Things (IoT) smart sensors avoiding battery replacement. In this paper, we analyze, model, and design a 2.45-GHz RF energy harvesting (RFEH) system based on a discrete-component matching network (MN), a custom 65-nm CMOS cross-coupled rectifier, and an off-the-shelf storage-charging power management unit (PMU), which regulates the rectifier output voltage with maximum power point tracking (MPPT). We propose a reverse global analysis to model the RFEH. It allows an accurate prediction of the power harvesting efficiency (PHE) to directly size the MN and select the RFEH MPPT regulation ratio, at different incident RF power levels. We perform parasitic-aware RFEH design to take advantage of printed circuit board (PCB)/package capacitive parasitics at the rectifier input for optimizing the $\pi $ -MN with the help of the proposed RFEH modeling results. We show that this parasitic capacitance introduces a maximum bound on the real impedance at the rectifier input to ensure good impedance matching in practice. MPPT is used to help reach this target real impedance at given incident RF power, as the rectifier equivalent input impedance is a function of both its input and output voltages. Measurement results show a sensitivity as low as −17.1 dBm with a peak PHE of 48.3% at −3-dBm incident RF power. Global modeling, simulation, and measurement results demonstrate that the PHE is limited by PCB/package parasitic capacitance and that PCB/packaging technology improvement to reduce parasitic capacitance by 150 fF could boost the PHE up to 45% for a low incident RF power level of −10 dBm.

Evaluation of an optical energy harvester for SHM application

In this paper a preliminary study on an array configuration of rectified optical nanoantennas for energy harvesting application is proposed. Currently, the major impediments for the use of the rectified optical nanoantenna known as rectenna are the relatively low conversion efficiency and low power transfer to the load, both of them caused mainly by the mismatch between the impedance of the rectifier (several kilo ohms) and that of the antenna (hundreds of ohm). For this reason, the design of the array represents a crucial point to obtain the maximum energy transfer from the rectenna to the load, represented as a typical DC/DC boost power converter, and modeled by an equivalent input impedance. The novelty of this study confirms that it is possible to obtain dynamically an impedance matching between the array of optical rectennas and the load. According to this method, in the proposed rectenna array, N elements can be serially connected so to allow to the open circuit voltage to be increased and M elements can be parallel connected to give the degree of freedom needed to achieve the impedance matching with the load. Finally, a case study for Structural Health Monitoring (SHM) application is presented.

Analysis of the input impedance of the rectifier and design of LCC compensation network of the dynamic wireless power transfer system

A design method of line commutated converter (LCC) compensation network for the dynamic wireless power transfer (DWPT) system based on a complex impedance model (Z-model) of the input impedance of the rectifier is proposed in this study. The continuous conduction mode and discontinuous conduction mode (DCM) of the rectifier are analysed to calculate the equivalent input impedance of the rectifier. Based on the proposed model of the input impedance of the rectifier, a design method of LCC compensation network for the DWPT system is presented. Simulation results prove that the Z-model of the rectifier is more accurate than the prevailing resistive model. Experiments show that the DWPT system with the designed LCC network meets the requirement of the average output power with an average DC–DC efficiency over 93%.

Analysis and Design of Three-Coil Structure WPT System With Constant Output Current and Voltage for Battery Charging Applications

Compared with the traditional plug-in charging system, the wireless charging system for battery charging has broad application prospects due to its significant advantages, such as security, convenience, and aesthetics. In practical applications, in order to prolong the battery lifecycles, it is preferred to charge the battery with constant current (CC) and constant voltage (CV) modes. However, since the battery equivalent resistance varies greatly during charging, it is not easy to design a complete charging system owning CC and CV output characteristics. Besides, the equivalent input impedance of the system is preferably resistive to improve efficiency and enhance power transfer capability; therefore, achieving the zero phase angle (ZPA) operation is extremely important. Hence, a novel three-coil structure WPT system is proposed in this paper to solve the above issues. A comprehensive theoretical analysis for the three-coil system to realize the CC and CV charging modes with perfect ZPA operation at two fixed operating frequencies is presented. Furthermore, due to the parasitic losses of passive components and the instability of the dc input voltage, it is unrealistic to achieve accurate and stable CC and CV outputs through the inherent properties of the circuit itself. Consequently, a simple closed-loop controller is introduced into the system to enable the desired CC and CV charging characteristics with zero voltage switching (ZVS) operation by slightly adjusting the operating frequency. Finally, a confirmatory experimental prototype with 4.6-A charging current and 56-V charging voltage is fabricated to confirm the feasibility and validity of the proposed method. The experimental results agree well with the theoretical analysis.

Rectifier Load Analysis for Electric Vehicle Wireless Charging System

This paper presents the analysis of a rectifier load used for an electric vehicle (EV) wireless charging system, as well as its applications on compensation network design and system load estimation. First, a rectifier load model is established to get its equivalent input impedance, which contains both resistance and inductance components, and can be independently calculated through the parameters of the rectifier circuit. Then, a compensation network design method is proposed, based on the rectifier load analysis. Furthermore, a secondary side load estimation method and a primary side load estimation method are put forward, which adopt only measured voltages and consider the influence of the rectifier load. Finally, an EV wireless charging prototype is developed, and experimental results prove that the rectifier equivalent load can be correctly calculated on conditions of different system load resistances, rectifier input inductances, dc voltages, and mutual-inductances. The experiments also show that rectifier load equivalent inductance will impact system performances, and the proposed methods have good accuracy and robustness in the cases of system parameter variations.

Effect of added resonators in RFID system at 13.56 MHz

In this study, a reader antenna including resonators is proposed to improve detection of a small moving tag in the case of tracking a radiofrequency identification (RFID) system. The near-field RFID technology is based on load modulation, the input impedance on the reader coil and the mutual inductance between the reader and tag coils are the main parameters for performing detection. They are calculated from the impedance matrix parameters. The added resonators change all the parameters of the impedance matrix consequently the input impedance and mutual inductance are also changed. In this study, analytical formulation defining the equivalent impedance matrix parameters is developed. These formulae are used to evaluate the performance of the proposed design according to the tag misalignment (lateral and angular). From the calculation and simulation results, a frequency shift in the equivalent input impedance is found. To avoid this problem, optimising the positioning of the resonators on the reader coil is performed. This study is confirmed by measures of RFID detection for a reader prototype (with and without resonators) and a small commercial tag. Both the surface and volume of detection of the small moving tag (lateral and angular misalignment) are improved by the principle of added resonators.

An Active-Rectifier-Based Maximum Efficiency Tracking Method Using an Additional Measurement Coil for Wireless Power Transfer

The efficiency of wireless power transfer (WPT) systems is highly dependent on the load, which may change in a wide range in field applications. Besides, the detuning of WPT systems caused by the component tolerance and aging of inductors and capacitors can also decrease the system efficiency. In order to track the maximum system efficiency under varied loads and detuning conditions in real time, an active single-phase rectifier (ASPR) with an auxiliary measurement coil (AMC) and its corresponding control method are proposed in this paper. Both the equivalent load impedance and the output voltage can be regulated by the ASPR and the inverter, separately. First, the fundamental harmonic analysis model is established to analyze the influence of the load and the detuning on the system efficiency. Second, the soft-switching conditions and the equivalent input impedance of ASPR with different phase shifts and pulse widths are investigated in detail. Then, the analysis of the AMC and the maximum efficiency control strategy are provided in detail. Finally, an 800-W prototype is set up to validate the performance of the proposed method. The experimental results show that with 10% tolerance of the resonant capacitor in the receiver side, the system efficiency with the proposed approach reaches 91.7% at rated 800-W load and 91.1% at 300-W light load, which has an improvement by 2% and 10% separately compared with the traditional diode rectifier.

Eddy Current Probe Identification and Analysis

This paper presents a new approach to the classical method for failure detection with eddy currents. In contrast to traditional methods of measuring reflected impedance on the probe circuit, this paper uses concepts of identification theory to find a transfer function that characterizes the dynamics of the measuring system by eddy currents. The transfer function represents the admittance of the input equivalent circuit. The estimated parameters of the transfer function were used to compute the inductive time constant of equivalent circuit of the metal specimen. The results of the time constant variation of the equivalent circuit of the sample were compared with the equivalent input impedance variation. A preliminary analysis is done in a simple case study, which has shown that the inductive time constant is more sensitive than the reflected impedance on the probe circuit, especially at low frequencies. Moreover, the estimated time constant is independent of the excitation frequency and mutual inductance.

Human middle-ear model with compound eardrum and airway branching in mastoid air cells.

An acoustical/mechanical model of normal adult human middle-ear function is described for forward and reverse transmission. The eardrum model included one component bound along the manubrium and another bound by the tympanic cleft. Eardrum components were coupled by a time-delayed impedance. The acoustics of the middle-ear cleft was represented by an acoustical transmission-line model for the tympanic cavity, aditus, antrum, and mastoid air cell system with variable amounts of excess viscothermal loss. Model parameters were fitted to published measurements of energy reflectance (0.25-13 kHz), equivalent input impedance at the eardrum (0.25-11 kHz), temporal-bone pressure in scala vestibuli and scala tympani (0.1-11 kHz), and reverse middle-ear impedance (0.25-8 kHz). Inner-ear fluid motion included cochlear and physiological third-window pathways. The two-component eardrum with time delay helped fit intracochlear pressure responses. A multi-modal representation of the eardrum and high-frequency modeling of the middle-ear cleft helped fit ear-canal responses. Input reactance at the eardrum was small at high frequencies due to multiple modal resonances. The model predicted the middle-ear efficiency between ear canal and cochlea, and the cochlear pressures at threshold.

On the equivalent circuit, input impedance, reflection coefficient, and bandwidth of printed monopole antenna

ABSTRACTThis article presents the derivation of a closed form expression for input admittance of horizontal electric dipole over an ungrounded substrate using transmission line analogy. The derived expression is then used to calculate reflection coefficient of rectangular and circular printed monopole antenna (PMA) fed by a microstrip line. Analytical result for the reflection coefficient of both rectangular and circular PMA is verified using high frequency structure simulator (HFSS). For circular PMA, analytical, and simulated results are also compared with the measured results available in literature. Effect of the dimension and dielectric material on the antenna bandwidth is also studied and verified by HFSS. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1535–1538, 2015

On the Concept of Grounding Impedance of Multipoint Grounding Systems

An N -port equivalent circuit approach is adopted to model a multipoint grounding system, N being the number of injection points. A methodology is proposed to determine the parameters of the N -port equivalent circuit from either numerical simulations or experimental measurements. For the case of a symmetrical grounding system, analytical closed-form expressions are derived for the equivalent parameters of the N -port circuit. We show that the concept of the equivalent input impedance (harmonic impedance) could be used in the case of a symmetrical multipoint grounding system. We show also that the experimental evaluation of the impedance of a grounding system using a single injection point is a conservative engineering practice, since the obtained impedance might be overestimated at high frequencies.

Influence of space-charge on hysteresis loop characteristics of ferroelectric thin films

Hysteresis loops of Pb(Zr, Ti)O3 (PZT) thin films obtained by using a Sawyer-Tower (ST) circuit are affected by many factors. This paper investigated the influence of space charge on the hysteresis loop of thin-film ferroelectrics, based on the model that polarization consists of two parts: linear and switching polarization. It is found that the space charge affects both the shape and offset of the ideal hysteresis loop. Further investigation shows that the practical hysteresis loop has a close relationship with the equivalent ST circuit parameters: the leakage resistance of the FE film, the equivalent input impedance of the measurement equipment, the signal source, and other similar parameters. The normally assumed symmetric hysteresis loop without any offset is obtained with an ST circuit when the output becomes stable. The hysteresis loop obtained at the initial stage of applied signal depends on the initial status of the FE film, and remnant polarization causes an initial offset that gradually disappears.