Power Wireless Applications Research Articles

Calculation of mutual inductance between arbitrarily positioned planar spiral coils for wireless power applications

Mutual inductance is one of the main parameters required to determine the power link’s performance (output voltage, efficiency) in wireless power transfer. The coils are often misaligned angularly in these applications, which affects the mutual inductance and thus the performance. Hence, an accurate calculation of mutual inductance is necessary to decide the working region of the coil. This paper presents an analytical calculation of mutual inductance between two planar spiral coils under angular misalignment conditions. By solving the Neumann integral formula, mutual inductance is derived for constant current-carrying coils, and the final mutual inductance value is calculated numerically. The influence of angular misalignment of the coil, which can be due to nutation and spin angles, on mutual inductance is studied in detail. The mutual inductance of the spiral coil is calculated for different misalignment cases. The accuracy of the calculation results is verified by comparing it with conventional formulas (mainly the Liu, the Babic formula, and the Poletkin formula) and by simulation using the finite element method. The proposed method is a more generalized and simpler one that can be used to calculate the mutual inductance of any size of coils, either spiral or circular, with any lateral and angular misalignments. Finally, a couple of spiral coils are fabricated to validate it experimentally. The comparison of the simulation and experiment results with the calculation result shows its accuracy. Thus, the proposed method can be applied to compute mutual inductance in any angularly misaligned coupling coils for the optimization of the wireless power transfer and their design.

Multilevel Switched-Capacitor AC–DC Step-Down Rectifier for Wireless Charging With Reduced Conduction Loss and Harmonic Content

In this article, a wireless charging architecture employing a multilevel switched-capacitor (MSC) ac–dc rectifier is investigated. The proposed MSC rectifier features a multilevel design that is scalable to accommodate different power ratings and load ranges. The topology showcases advantages for wireless power transfer (WPT) systems in terms of compactness, efficiency, impedance tunability, and harmonic attenuation. The single-stage active topology is capable of varying its low-distortion staircase input voltage to tune the WPT system for high system-wide efficiency. A seven-level, 20-W prototype is used to verify the WPT loading and loss analysis. The prototype operates at 150 kHz with up to 3:1 step-down conversion ratio to an output voltage of 5.0 V. The experimental peak dc-to-dc efficiency is 93.8% and the rectifier peak efficiency is 98.3%. The rectifier demonstrates low waveform distortion and high efficiency across many WPT loading conditions, solidifying its place as a strong candidate for wireless power applications.

Simplified Mutual Inductance Calculation of Planar Spiral Coil for Wireless Power Applications.

In this paper, a simplified method for the calculation of a mutual inductance of the planar spiral coil, motivated from the Archimedean spiral, is presented. This method is derived by solving Neumann’s integral formula in a cylindrical coordinate system, and a numerical tool is used to determine the value of mutual inductance. This approach can calculate the mutual inductances accurately at various coaxial and non-coaxial distances for different coil geometries. The calculation result is compared with the 3D finite element analyses to verify its accuracy, which shows good consistency. Furthermore, to confirm it experimentally, Litz wire is used to fabricate the sample spiral coils. Finally, the comparison of a simplified method is also studied relative to the coupling coefficient. The accuracy of the calculation results with the simulation and the measurement results makes it a good candidate to apply it in wireless power applications.

A 600 mV +20 dBm IIP<SUB align="right">3 CMOS LNA with <i>g<SUB align="right">m</i> smoothening auxiliary path for 2.4 GHz wireless applications

CMOS low noise amplifiers (LNA's) finds a large-scale of applications in biomedical applications and other mission sensors which include cordless telephones, wireless keyboards, and radio equipment. For radio-frequency (RF) applications where signal frequencies are high, consequences of intermodulation distortion results from the nonlinearities of the MOS transistors used in the LNA. As it is impracticable to eradicate nonlinearities completely, second-order nonlinearities were added in out of phase with the third-order nonlinearities in derivative and modified derivative methods which suppress the third-order nonlinearities up to an input intercept point (IIP3) of 8 dBm only. In this article, proposed LNA reduces the nonlinearity interaction increases the IIP3 performance up to 12 dBm using the common source differential architecture with PMOS loads in the auxiliary path. The proposed LNA offers gain (S21) of 12 dB operates at ultra-low voltage supply headroom of 600 mV with good stability deemed as a favourable requirement for low power wireless applications.

Quad-Band Rectenna for Ambient Radio Frequency (RF) Energy Harvesting.

RF power is broadly available in both urban and semi-urban areas and thus exhibits as a promising candidate for ambient energy scavenging sources. In this research, a high-efficiency quad-band rectenna is designed for ambient RF wireless energy scavenging over the frequency range from 0.8 to 2.5 GHz. Firstly, the detailed characteristics (i.e., available frequency bands and associated power density levels) of the ambient RF power are studied and analyzed. The data (i.e., RF survey results) are then applied to aid the design of a new quad-band RF harvester. A newly designed impedance matching network (IMN) with an additional L-network in a third-branch of dual-port rectifier circuit is familiarized to increase the performance and RF-to-DC conversion efficiency of the harvester with comparatively very low input RF power density levels. A dual-polarized multi-frequency bow-tie antenna is designed, which has a wide bandwidth (BW) and is miniature in size. The dual cross planer structure internal triangular shape and co-axial feeding are used to decrease the size and enhance the antenna performance. Consequently, the suggested RF harvester is designed to cover all available frequency bands, including part of most mobile phone and wireless local area network (WLAN) bands in Malaysia, while the optimum resistance value for maximum dc rectification efficiency (up to 48%) is from 1 to 10 kΩ. The measurement result in the ambient environment (i.e., both indoor and outdoor) depicts that the new harvester is able to harvest dc voltage of 124.3 and 191.0 mV, respectively, which can be used for low power sensors and wireless applications.

High Frequency MOSFET Charging Circuit Using Series Parallel DC-DC Resonant Converter for Wireless Power Application

This paper proposes a new circuit topology of high frequency switching DC-DC Series Parallel Loaded Resonant Converter (SPLRC). The circuit is proposed to be used for a wireless power transmission application that required fast-charging operation. Most of the components used here are low-cost and commercially available in the market. Then, the purpose circuit is transformed into a different equivalent circuit that can efficiently analyze AC and DC modes. For each model, the operation for the converter is first described and explained. A full detailed circuit simulation is then carried out to find out the workability of the purpose converter. From the simulation, optimization is carried out. Here the components value is obtained. MATLAB R2018A is used for simulation purposes rather than being tested again using PSIM software to further prove the validity of the model. All the finding is explained and discussed, here, from the simulation result, it is confirmed that a high-frequency switching circuit is operated as expected.

A sub-1V dual-path noise and distortion canceling CMOS LNA for low power wireless applications

This paper presents a 0.8 ​V supply voltage low noise amplifier (LNA) with high linearity for low power wireless applications. To reduce both second- and third-order intermodulation components (IM2 and IM3), the proposed structure creates equal common-mode (CM) currents with the opposite sign by cascading two differential pairs with a cross-connected output and improves linearity. Using resistive feedback together with noise and distortion canceling technique mutually cancel noise and nonlinearity of both main and auxiliary amplifiers. Combining transformer-based gm-boosting and current reuse techniques makes the presented LNA a superior candidate for low power radios. Detailed analysis and simulations are provided to show the effectiveness of the proposed LNA structure. Simulation results using 65 ​nm CMOS process reveal that the linearized low power LNA achieves over 25 ​dB voltage gain, 2.7 ​dB NF, +10.1 dBm IIP3, and average IIP2 of more than +57 dBm while consuming 870 ​μW.

Calculation model of mutual coupling between two ferrite-cored square coils in wireless power application for electric vehicles

Wireless power transfer (WPT) devices have been widely accepted by more and more industrial producers and consumers due to their safe, convenient, and high-efficient features. Square coils with ferrite cores are usually utilized as magnetic coupling devices by WPT systems for electric vehicles (EVs). However, the research on coupling coils often depends on three-dimensional finite element analysis (3-D FEA) tools such as ANSYS Maxwell or HFSS, which are troublesome and time-consuming. This paper explores a calculation model of mutual coupling between two square coils with ferrite cores based on magnetic mirror method. With this model, accurate results and fast operation speed can be obtained, and 3-D FEA tool is used to compare and verify the performance of this work.

Microtransfer Printing High‐Efficiency GaAs Photovoltaic Cells onto Silicon for Wireless Power Applications

AbstractHere, the development of high‐efficiency microscale gallium arsenide (GaAs) laser power converters, and their successful transfer printing onto silicon substrates is reported, presenting a unique, high power, low‐cost, and integrated power supply solution for implantable electronics, autonomous systems, and Internet of Things (IoT) applications. 300 µm diameter single‐junction GaAs laser power converters are presented and the transfer printing of these devices to silicon is successfully demonstrated using a polydimethylsiloxane stamp, achieving optical power conversion efficiencies of 49% and 48% under 35 and 71 W cm−2 808 nm laser illumination respectively. The transferred devices are coated with indium tin oxide (ITO) to increase current spreading and are shown to be capable of handling very high short‐circuit current densities up to 70 A cm−2 under 141 W cm−2 illumination intensity (≈1400 Suns), while their open circuit voltage reaches 1235 mV, exceeding the values of pretransfer devices indicating the presence of photon recycling. These optical power sources could deliver Watts of power to sensors and systems in locations where wired power is not an option, while using a massively parallel, scalable, and low‐cost fabrication method for the integration of dissimilar materials and devices.

An Improved Single Stage Phase Shifted Control Based AC–DC PFC Converter for Wireless Applications

Recently, many researchers has more attention in a single stage AC to DC converter features and DC to DC regulator are extensively used into low power applications. When compared with the two stage conventional method over the Single stage converter has a simple design and utilize only less components. Therefore, this task has been used in this paper as a prposed work of AC–DC single stage converters combine a converter front end with DC–DC back end converter. This proposed work has been improved single stage power factor correction (PFC) converter based on phase-shifted controller for wireless Power applications. The proposed technique employed to develop the improved converter for task of an extensive series of voltage outputs with rippleless outcomes in low frequency, that shows the high essential in battery application and the PFC duty ratio restriction is eradicated. Similarly, DC–DC stage operation are designed in a related way of conventional full bridge phase shifted converter. Accordingly, the proposed technique of improved converter of this paper will achieves better efficiency compared with other conventional techniques and it has been prove more efficient for many Industrial applications, it has been discussed in result section clearly. The experimental results of proposed improved converter proves that it is potential to extend high power single stage converter with good power factor, conversion characteristics and efficiency.

Analytical computation of mutual inductance between two rectangular spiral coils with misalignments for wireless power applications

AbstractMisalignments between the transmitter and receiver coils are unavoidable in practical wireless power applications. Therefore, the computation of mutual inductance (MI) of coils with misalignments is valuable in terms of its engineering aspects. In this article, an analytical model of MI between two rectangular spiral coils with misalignments is proposed. The MI calculation with all possible layout s of two parallel rectangular spiral coils, including coaxial misalignment, lateral misalignment, rotational misalignment, and combinations of them, can be addressed by the proposed formula. Another advantage of the new formula is that, by incorporating a multiplicative spiral factor, the MI of rectangular spiral coils can be simply calculated similar to single‐turn rectangular coils. A series of experiments were performed, and the measured results agree well with the theoretically predicted values from the formula.

Designing cantilever dimension for low power wireless applications

<span>This paper presents the effect of cantilever width on the displacement pattern for low power acoustic energy propagation. A single layer cantilever configuration is used to design the harvester with Lead Zirconate Titanate (PZT-5H). The device is designed with 10×(1 to 10)×0.62 mm dimension. The displacements of the cantilever are obtained through the simulation analysis. The maximum displacements are found of 9.80E-28 mm with the smallest width while minimum displacement is found from 5 mm width. From the results, it is obvious that, smaller width can result larger displacements, however, rectangular and square cantilever shape can be advantageous for low power applications.</span>

Resonant Configuration Topology Exploration for Inductive Link Power Transfer

This paper investigates the performance of circuit topology used in wireless power applications to optimize the level of maximum efficiency. We analyse the series and the parallel resonant topologies for use in an inductive coupling link to derive power transfer efficiency expressions verified using MATLAB. We look into the two topologies into the link under resonant conditions for selectively supplying the device with power. The results are obtained analytically which are verified subsequently by MATLAB simulation. We then analyse the links to see how maximum power transfer efficiency for a given pair of coils can be achieved. The topology at a given tuning frequency is used for powering a selected resistive load. The method is presented using a given pair of coils simulated and the results agree well with the theoretical explanation and derivations.

Calculation of self‐ and mutual inductances of rounded rectangular coils with rectangular cross‐sections and misalignments

Rounded rectangular coils are more common in wireless power applications. It is important in practical engineering to calculate the self- and mutual inductances of rounded rectangular coils. A new model of the self- and mutual inductances of rounded rectangular coils with rectangular cross-sections is derived in this study. The proposed formulae are applicable not only to the rounded rectangular coils, but also to the extreme cases such as circular, rectangular, and race-track coils. The coil layouts including coaxial alignment and lateral misalignments are also discussed. Comparison of calculated self- and mutual inductances with experimental observations is provided and an excellent agreement between the two proves the feasibility of the proposed formulae.

Analytical model of mutual coupling between rectangular spiral coils with lateral misalignment for wireless power applications

Rectangular spiral coils are easier to implement in wireless power transfer (WPT) applications than circular spirals. Despite this fact, research into mutual coupling between rectangular spiral coils is insufficient. In this study, a new analytical model of mutual coupling is proposed, which converts a complex multi-turn rectangular spiral coil into a single-turn rectangular coil, simplifying calculation of the self- and mutual inductances. The mutual coupling between two different arbitrarily sized rectangular spiral coils with lateral misalignment and the rectangular cross-sections can be described accurately using this model. A series of experiments is carried out, the results of which agree well with the results of calculations. Finally, the effect of the number of turns in a coil on the coupling coefficient is discussed in order to determine the recommended number of turns. This research provides an effective tool for the design of a WPT system.

A Cross-Shape Coil Structure for Use in Wireless Power Applications

This paper presents a novel coil structure employing two parallel-connected subunit rectangular coils. The structure is based on the fact that the rectangular coils are less sensitive to misalignment along its longer side. Therefore, two identical subunit rectangular coils are vertically-oriented to one another and connected in parallel to form a cross-shape coil. The cross-shape coils have the advantage of better misalignment tolerance as compared to circular and square coils with similar footprints at the cost of an increased wire usage. Electromagnetic simulations and experiments on various small-sized coils are performed to verify the advantages of the proposed coil structure. Based on the simulation and measurement results, cross-shape coils exhibit not only better tolerance to misalignment, but also smaller self-inductance values resulting in larger coupling coefficients as compared to square and circular coils. A large cross-shape coil pair consisting of 100 × 70 cm subunit rectangles are fabricated with copper tubes and utilized in a frequency-tuned wireless power transfer system. When coils are separated by 17 cm, a near constant efficiency of more than 89% up to 15 cm misalignment along x- or y-directions and 13 cm along diagonal direction is obtained in the frequency-tuned system.

Ambient Backscatterers Using FM Broadcasting for Low Cost and Low Power Wireless Applications

Nowadays, the explosive growth of Internet-of-Things-related applications has required the design of low-cost and low-power wireless sensors. Although backscatter radio communication is a mature technology used in radio frequency (RF) identification applications, ambient backscattering is a novel approach taking advantage of ambient signals to simplify wireless system topologies to just a sensor node and a receiver (RX) circuit eliminating the need for a dedicated carrier source. This paper introduces a novel wireless tag and RX system that utilizes broadcast frequency modulated (FM) signals for backscatter communication. The proposed proof-of-concept tag comprises of an ultralow-power microcontroller (MCU) and a RF front-end for wireless communication. The MCU can accumulate data from multiple sensors through an analog-to-digital converter, while it transmits the information back to the RX through the front-end by means of backscattering. The front-end uses ON–OFF keying modulation and FM0 encoding on ambient FM station signals. The RX consists of a commercial low-cost software-defined radio which downconverts the received signal to baseband and decodes it using a suitable signal processing algorithm. A theoretical analysis of the error rate performance of the system is provided and compared to bit-error-rate measurements on a fixed transmitter-tag-RX laboratory setup with good agreement. The prototype tag was also tested in a real-time indoor laboratory deployment. Operation over a 5-m tag-reader distance was demonstrated by backscattering information at 2.5 kb/s featuring an energy per packet of $36.9~\mu \text{J}$ .

Analytical calculation of mutual coupling between two misaligned rectangular coils with rectangular cross-section in wireless power applications

An analytic model to calculate the mutual coupling between two misaligned rectangular coils with a wide range of aspect ratios of rectangular cross-section is proposed. The model can analyze all possible layouts of two parallel rectangular coils including coaxial alignment, lateral misalignment, rotational misalignment, and combinations of them. The effects of misalignments, geometry, and cross-sections of rectangular coils are addressed by a single mathematical expression. An experimental setup has been built in order to validate the analytical calculation. Theoretical and experimental results are then compared to verify the effectiveness of the proposed model.

Nulls-Free Wireless Power Transfer With Straightforward Control of Magnetoinductive Waves

We present a straightforward and yet, effective method to modulate the termination impedance of 1-D $LC$ resonating arrays for wireless power applications. The modulation method is based on activating/deactivating the last two cells of the array allowing to remove the power nulls caused by standing waves inside this type of arrays. The modulation of the terminating impedances is done at a distinct frequency than the resonance frequency of the cells. We explain why and how this distinct frequency was chosen. We further demonstrate how the same modulation is applicable for a wide range of load resistances on the receiver device. Modulation is achieved by wirelessly sensing the voltage delivered by the power supply according to where above the array a receiver device is located. A microcontroller records these voltages and determines which terminating impedance will provide the highest possible efficiency to the receiver device. Changes in the terminating impedances are set by digitally controlled solid state relays. The proposed modulation method permitted to power up a receiver device with a system efficiency of up to 60% anywhere over the 30 cm length of the resonating array.

Bandwidth Enhancement of RF Resonators Using Duffing Nonlinear Resonance for Wireless Power Applications

This paper presents a nonlinear resonator circuit based on the Duffing equation to enhance the bandwidth of wireless power harvesting and wireless power transfer systems. The Duffing resonator circuit can be implemented with passive components. In this paper, analysis of an electrical Duffing resonator is presented. The detailed discussion of the Duffing resonator’s properties is provided. As a proof of principle, a wireless power harvester employing such a nonlinear resonator has been designed and tested. It is shown that the Duffing resonator circuit enhances the bandwidth of the harvester by 2.7 times compared with a harvester using a linear resonator with the same quality factor, while achieving a similar amplitude level near the resonance frequency. Furthermore, the bandwidth of the nonlinear resonator is independent of its quality factor ( $Q$ ).