Planar Spiral Coil Research Articles

Self-Aligning Capability of IPT Pads for High-Power Wireless EV Charging Stations

This article studies magnetic forces between transmitter (Tx) and receiver (Rx) coils in an inductive power transfer (IPT) system aiming to use those forces to align the coils and, consequently, improve power transfer. Due to its popularity, the analysis is conducted on a series–series compensated IPT system with planar spiral coils. The proposed method utilizes the bifurcation operation mode of the system and unloaded resonating receiver to maximize attractive force between magnetic couplers. Three-dimensional finite-element method simulations indicate that high-power IPT systems can develop enough attractive force to align coils even under nominal current. Regardless of the coil shape, e.g., spiral or Double-D (DD), the attractive forces tend to align the coils. Hence, a smart charging station can be devised based on self-aligning capability. Furthermore, this article proposes a mechanical structure to facilitate the attractive lateral force for the alignment of high power applications, i.e., wireless fast-charging stations. The forces are analyzed, modeled, and simulated for a 100-kW IPT system with an operating frequency of 20 kHz, while the self-aligning capability is experimentally verified on a downscale 11-kW prototype.

Geometrical Optimization of Medium-Frequency Air-Core Transformers for DCX Applications

This article analyzes the potential of air-core transformers (ACTs) for realizing medium-voltage high-power isolated dc–dc converters. ACTs, i.e., transformers without magnetic cores, are particularly interesting for their simple construction and reduced weight. However, the reduced magnetizing inductance, the reduced magnetic coupling, and the stray fields are challenging aspects for the design of ACTs. A comprehensive model of the ACT (e.g., magnetic field patterns, skin and proximity losses, shield’s eddy currents, harmonics, insulation constraints, and thermal limit) is proposed and verified with measurements obtained with a prototype. Afterward, a complete multiobjective optimization of a series resonant converter (SRC) operating as a dc transformer (DCX) between two 7 kV buses with a rated power of 166 kW is conducted. Two different geometries are considered for the ACT: concentric cylindrical coils and planar spiral coils. As a result, the optimal ACT (operated at 162 kHz) features extreme power densities of 7.5 kW/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 31 kW/kg, which confirms the superiority of ACTs regarding the gravimetric power density. The calculated efficiencies are 99.5% and 98.7% for the ACT and the complete dc–dc converter, respectively. Finally, the different tradeoffs are highlighted and analyzed, e.g., mass, volume, efficiency, switching frequency, part-load behavior, and insulation distance.

A New Analytical Study on Mutual Inductance Calculations for Wireless Power Transfer Using Magnetic Vector Potential

This article presents a new analytical approach for the calculation of mutual inductance based on magnetic vector potential (MVP). To demonstrate the proposed mutual inductance calculation method, planar spiral coils of polygonal shape with an arbitrary number of sides are discussed. The coils considered in this work are coaxial and assumed to be composed of concentric filaments. The flux produced by the primary and linking the secondary is calculated by the line integral of the MVP. In order to simplify the calculation strategy, the MVP contribution of only one side of each single-turn filament of the primary is considered due to the symmetry of the coils’ shapes. Accordingly, coupling flux across the surface surrounded by each turn of the secondary is calculated by the line integral of the MVP over half path of the filament’s turn. The accuracy of the new analytical approach is confirmed by examining coil systems with a different primary and secondary in terms of the number of sides, the number of turns, and size. Results of the new approach are compared with those obtained from Ansys Maxwell, analytical studies in the literature, and experimental to demonstrate the validity of the proposed method. Results from this work are in good agreement with those obtained from simulation, studies in the literature, and experiment that proves the feasibility of formulas used in this work.

Dual-Mode Flexible Capacitive Sensor for Proximity-Tactile Interface and Wireless Perception

Flexible sensors with proximity and tactile sensing have attracted great interest in electronic skins (E-skin), human-machine interfaces (HMI), and soft robotics. However, it remains challenging to have both proximity and haptic sensing ability in one flexible device, yet enable wireless sensing. Here, based on the edge electric field and piezo-capacitive effect, we successfully present a combination of approaching non-contact sensation with pressure perception in one flexible dual-mode capacitive sensor (FDCS) which possesses both proximity-tactile interface interaction and wireless sensing. Large scale and low-cost methods of the screen printing and the laser engraving are selectively used to fabricate flexible electrodes and cone-pattern mold, respectively. Thanks to the stable conductivity of the electrodes and the micro-cone-like dielectric structure, the FDCS exhibits a detection distance of up to 20 cm in proximity mode and an extended operating range of 200 kPa, a low detection limit (10.2 Pa), fast response time (90 ms), and long endurance (>10,000 cycles) in pressure mode. A 64-unit pressure matrix successfully interacted with the coupling of the proximity finger and the actual pressure in two different modes. In addition, by assembling the FDCS with a planar spiral coil to form an LC (inductance-capacitance) resonator, rather than connecting directly to an LCR device, the device was able to detect external pressure wirelessly. The development of this dual-mode sensor and its demonstration paves the way for potential flexible sensors for applications in HMI and soft robots.

Metal detecting robotic vehicle

Today’s need for workers in mines is to detect the metals in the path. The previously used metal detector uses BFO (Beat Frequency Oscillation) and RFO (Resonant Frequency Oscillation) techniques which has a drawback of frequency instability. The depth further can be increased by Pulse Induction Method. It uses a single coil as both transmitter and receiver. When current is sent through the coil each pulse generates a magnetic field. When the pulse ends it reflects and it is called the reflected pulse. An electrical spark is generated when both the pulses collapse. Now when a metal comes in the range of the magnetic field, there is a change in the amplitude and phase of the pulse in the received coil. Planar square spiral coil is the geometry best suited for increasing depth sensitivity. It depends on the parameters such as fill ratio and spacing to width ratio. A coil with a higher fill ratio is shown to have higher size sensitivity and a coil with a smaller wire spacing-to-width ratio is shown to have higher depth sensitivity. Using this Pulse Induction Metal Detector we build a robotic vehicle.

Frequency splitting suppression in wireless power transfer using hemispherical spiral coils

In wireless power transfer (WPT) systems, frequency splitting phenomena always occur when the transfer distance is too small to obtain the maximum output efficiency in the working frequency. In this paper, a hemispherical spiral coil structure is proposed to suppress frequency splitting phenomena by containing the coupling the system without changing the original system size and transfer distance. Meanwhile, compared with the planar system, the hemispherical system can maintain high power and transfer efficiency and has better angular misalignment tolerance. A WPT system consisting of a hemispherical spiral coil and a planar spiral coil resonating at 110 kHz called the single hemispherical spiral coil WPT (SHWPT) system and another with two hemispherical spiral coils called the double hemispheric spiral coils WPT (DHWPT) system are suggested. Analytic models of these two structures are established to analyze the influence of the coil height on the frequency splitting. The critical coil height is closely related to the critical coupling that provides a reference for the design of the coil. Finally, the experimental results show that the hemispherical coil structure can suppress the frequency splitting to ensure the transmission stability of the WPT system. In the SHWPT system with a 1 cm inner diameter and a 13 cm outer diameter, the critical height of the coil is 5.2 cm, which can suppress frequency splitting when the transmission distance is 0 cm. In the DHWPT system, the critical height of the coil is 4.3 cm.

A 4 × 4 array multichannel magnetic stimulation system using submillimeter sized planar square spiral coils: The spatial distribution of electromagnetic field

Multi-coil magnetic stimulation has advantages over single-coil magnetic stimulation, such as more accurate targeting and larger stimulation range. In this paper, a 4 × 4 array multichannel magnetic stimulation system based on a submillimeter planar square spiral coil is proposed. The effects of multiple currents with different directions on the electromagnetic field strength and the focusing zone of the array-structured magnetic stimulation system are studied. The spatial distribution characteristics of the electromagnetic field are discussed. In addition, a method is proposed that can predict the spatial distributions of the electric and magnetic fields when currents in different directions are applied to the array-structured magnetic stimulation system. The study results show that in the section of z = 2 μm, the maximum and average magnetic field strengths of the array-structured magnetic stimulation system are 6.39 mT and 2.68 mT, respectively. The maximum and average electric field strengths are 614.7 mV/m and 122.82 mV/m, respectively, where 84.39% of the measured electric field values are greater than 73 mV/m. The average magnetic field strength of the focusing zone, i.e., the zone in between the two coils, is 3.38 mT with a mean square deviation of 0.18. Therefore, the array-structured multi-channel magnetic stimulation system based on a planar square spiral coil can have a small size of 412 μm × 412 μm × 1.7 μm, which helps improving the spatial distribution of electromagnetic field and increase the effectiveness of magnetic stimulation. The main contribution of this paper is a method for designing multichannel micro-magnetic stimulation devices.

Inductance Calculation of Single-Layer Planar Spiral Coil

In this paper, an analytical calculation of the inductance of an air-core planar spiral coil is presented. The inner and outer radius of the planar spiral coil is determined from the general equation of the filament of the wire. Using the Neumann integral formula, the expression of inductance is obtained. The double integral of Neumann’s formula is computed numerically to evaluate the inductance. The accuracy of the calculation results is verified by comparing it with the conventional and the simulation results. Different geometry of spiral coils is fabricated to validate it experimentally. Finally, the comparison is performed with the experiment results, which show good agreement. Thus, the accuracy of the calculation result paves the way for designing and optimizing the spiral coil for electromagnetic 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.

Wireless Humidity Sensor for Smart Packaging via One‐step Laser‐Induced Patterning and Nanoparticle Formation on Metallized Paper

AbstractIn this work, a scalable and rapid process is developed for creating a low‐cost humidity sensor for wireless monitoring of moisture levels within packaged goods. The sensor comprises a moisture‐sensitive interdigitated capacitor connected to a planar spiral coil, forming an LC circuit whose resonant frequency is a function of environmental humidity. The sensor is fabricated on a commercially available metallized parchment paper through selective laser ablation of the laminated aluminum (Al) film on the parchment paper substrate. The laser ablation process provides a unique one‐step patterning of the conductive Al layer on the paper while simultaneously creating high surface area Al2O3nanoparticles within the laser‐ablated regions. The intrinsic humidity‐responsive characteristics of the laser‐induced Al2O3nanostructures provide the wireless sensor with a tenfold higher sensitivity to humidity than a similar LC resonant sensor prepared by conventional photolithography‐based processes on FR‐4 substrates. The frequency change of the sensor is observed to be a linear function within the range of 0−85% RH, providing an average sensitivity of −87 kHz RH−1with good repeatability and stable performance. Furthermore, the employment of scalable laser fabrication processes using commercially available inexpensive materials renders these technologies viable for roll‐to‐roll manufacturing of low‐cost wireless sensors for smart packaging applications.

Misalignment Insensitive Wireless Power Transfer System Using a Hybrid Transmitter for Autonomous Underwater Vehicles

Compared to air surroundings, the marine environment is not stable due to the influence of ocean currents and other factors. Misalignments always occur inevitably when autonomous underwater vehicles are charging wirelessly in the docking station. Therefore, misalignment insensitive underwater wireless power transfer system need to be investigated. In this article, a novel hybrid transmitter composed of conical and planar spiral coils is proposed that greatly improves the misalignment tolerance and transfer performance. First, the coil tilt angle theory (CTAT) is presented and verified to determine the optimum tilt angle of conical coil. Then, based on the CTAT, a circular uniform magnetic field zone with a diameter of 30 cm in charging plane can be achieved by flexibly designing the hybrid transmitter. Moreover, a three-dimensional finite-element simulation software is employed to study the eddy current loss under different circumstances. Finally, experimental results show that the proposed transmitter has better performance in output power and power transfer efficiency (PTE) stability within the possible working region compared with conventional transmitters. It has demonstrated that the output power changes only within 5.7&#x0025; and the PTEs maintain at approximately 86&#x0025; in excessive misalignment area with transfer distance of 2 cm.

Compact Hybrid Metasurface-Inspired Resonator With Uniform Magnetic Field Distribution for Wireless Power Transfer

Compact and safe charging platforms have been one of the main goals in wireless power transfer (WPT) research and development. Here, we propose a compact hybrid metasurface-inspired resonator with a uniform magnetic field distribution for WPT. It consists of two orthogonally oriented layers of parallel printed wires with high-permittivity dielectric pads between them. This design allows us to spatially separate electric and magnetic fields, which provide high WPT efficiency and electromagnetic safety simultaneously. The prototype with 28 cm × 28 cm working area with uniform magnetic field was fabricated and experimentally studied. The measured coefficient of variation of the magnetic field in the working area of the resonator is 6.8%. The maximum achievable WPT efficiency reaches 70% over the working area. The numerically assessed specific absorption rate in human tissues placed on the proposed structure is 11 mW/kg, which is 30 times lower than on a conventional planar spiral coil. Our results pave the way to compact and safe WPT platforms for one-to-many charging.

Efficiency of the Wireless Power Transfer System with Planar Coils in the Periodic and Aperiodic Systems

This article presents the results of the proposed numerical and analytical analysis of the Wireless Power Transfer System (WPT). The system consists of a transmitting surface and a receiving surface, where each of them is composed of planar spiral coils. Two WPT systems were analysed (periodic and aperiodic) considering two types of coils (circular and square). In the aperiodic system, the adjacent coils were wound in the opposite direction. The influence of the type of coils, the winding direction, the number of turns, and the distance between the coils on the efficiency of the WPT system was compared. In periodic models, higher efficiency was obtained with circular rather than square coils. The results obtained with both proposed methods were consistent, which confirmed the correctness of the adopted assumptions. In aperiodic models, for a smaller radius of the coil, the efficiency of the system was higher in the square coil models than in the circular coil models. On the other hand, with a larger radius of the coil, the efficiency of the system was comparable regardless of the coil type. When comparing both systems (periodic and aperiodic), for both circular and square coils, aperiodic models show higher efficiency values (the difference is even 57%). The proposed system can be used for simultaneous charging of many sensors (located in, e.g., walls, floors).

A Hybrid Self‐Powered Arbitrary Wave Motion Sensing System for Real‐Time Wireless Marine Environment Monitoring Application

AbstractSelf‐powered arbitrary wave monitoring is a hot research topic which aims to remove of the trouble associated with managing conventional power for continuous and real‐time acquisition of wave information from the marine environment. Herein, an effective approach is presented that simultaneously generates power from arbitrary motion waves and can sense and wirelessly transmit the wave information without requiring an external supply. The hybridized ellipsoidal device inspired from an elliptical trajectory of objects over shallow water waves, consists of six planar spiral coils arranged to cover the arbitrary direction of waves for power generation. Four magnetic force‐actuated triboelectric nanogenerators (TENGs) pairs along four sides as the arbitrary direction self‐powered wave motion sensors are integrated. Furthermore, all the required circuitry for signal processing and wireless transmission are integrally powered by the generated electricity to realize a self‐sustained wireless marine environment monitoring system. The generator can deliver peak power of 106 and 44.8 mW (at 3Hz) along with major and minor axis motion directions. The self‐powered sensors have excellent motion sensitivity thus the signals obtained from these sensors are utilized to acquire useful information related to the water waves which are very crucial parameters for real‐time monitoring of the marine environment.

Printed Split-Ring Loops with High Q-Factor for Wireless Power Transmission

The use of printed spiral coils (PSCs) as inductors in the construction of Wireless Power Transmission (WPT) circuits can save space and be integrated with other circuit boards. The challenges and issues of PSCs present for WPT mainly relate to maintaining an inductive characteristic at frequencies in Ultra High Frequency (UHF) band and to maximising the power transfer efficiency (PTE) between primary and secondary circuits. A new technique is proposed to increase the Q-factor relative to that offered by the PSC, which is shown to enhance WPT performance. This paper provides four-turn planar split-ring loops with high Q-factor for wireless power transmission at UHF bands. This design enhances the power transfer efficiency more than 12 times and allows for a greater transfer distance from 5 mm to 20 mm, compared with a conventional planar rectangular spiral coil.

Electromagnetic Force Distribution of Planar Coils: Analytical Model and Optimization

The electromagnetic force (EMF) generated by planar spiral coils has been broadly applied as actuators in electromagnetic forming, launching, and driving. The distribution of the EMF strongly affects the performance of these actuators, especially in conditions with the allowable stress limits. But its optimization mainly depends on finite element analysis (FEA). Because there is no analytical model to describe the relationship between the distribution and parameters of the coils, optimization is normally highly time-consuming. To solve this problem, we established a model of two coupled coils based on the principle of virtual work, and then a procedure to optimize the distribution of the EMF by using the established model and a proposed genetic algorithm that adjusts the spacing intervals of the coils. Compared to traditional optimization based on FEA, this optimization method can find the desired parameters of the coils much faster.

Optimization and Analysis of Multilayer Planar Spiral Coils for the Application of Magnetic Resonance Wireless Power Transfer to Wearable Devices

In this study, small multilayer planar spiral coils were analyzed and optimized to wirelessly charge an in-ear wearable bio-signal monitoring device in a wine-glass-shaped transmitter (Tx) based on magnetic resonance wireless power transfer (MR-WPT). For analysis of these coils, a volume filament model (VFM) was used, and an equivalent circuit formulation for the VFM was proposed. The proposed method was applied to design effective multilayer coils with a diameter and height of 6 and 3.8 mm, respectively, in the wearable device. For the coils, a printed circuit board having a 0.6 mm thick dielectric substrate and a 2 oz thick copper metal was used. Moreover, the coils on each layer were connected in series. The dimensions of the double-, four-, and eight-layer coils were optimized for the maximum quality factor (Q-factor) and coupling efficiency. The operating frequency was 6.78 MHz. The optimal dimensions for the maximum Q-factor varied depending on the number of coil layers, pattern width, and turn number. For verification, the designed coils were fabricated and measured. For the four-layer coil, the coupling efficiency and Q-factor using the measured resistance and mutual inductance were 58.1% and 32.19, respectively. Calculations showed that the maximum Q-factor for the four-layer coil was 40.8 and the maximum coupling efficiency was 60.1%. The calculations and measurement were in good agreement. Finally, the entire system of the in-ear wearable bio-signal monitoring device, comprising a wine-glass-shaped transmitter, the designed receiving coil, and a monitoring circuit, was fabricated. The measured dc-dc efficiency of the MR-WPT system was 16.08%.

Improving Sensitivity and Resolution of Planar Magnetic Inductive Sensors by Optimizing Gap Between Magnetic Films

The sensitivity and resolution of the planar magnetic inductive sensors are enhanced by optimizing the gap between the upper and lower magnetic films. The tradeoff between the effect of the effective magnetic permeability and magnetic leakage of the magnetic films on the inductance of the sensor produces a gap that optimizes the sensor performance. This conclusion is verified theoretically and experimentally with the fabrication and testing of planar magnetic inductive sensors with given dimensions of magnetic films and planar spiral coil. From the analysis, the optimal gap ( g) for our manufactured sensors with given dimensions is four times the magnetic film thickness ( t). Experimentally, when g/t=4, the inductance value, inductance ratio, and voltage sensitivity of sensors are all the largest. The sensitivity and resolution of the sensor with g/t=4 are 1.81 mV/Oe and 50.23 nT at 500 kHz. Compared with the prototype whose magnetic films and planar coil are stacked tightly together, the sensitivity is increased by 43.72% and the resolution is improved by 33.51%. It is universally applicable that there is a gap that optimizes the performance of the planar magnetic inductive sensor.

Performance evaluation of three latent heat storage designs for cogeneration applications

Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A one-dimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46–72 °C and a HTF supplying flowrate range of 4.2–8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spiral coil design (1830 kWh). The ellipsoid capsule design shows a slightly lower accumulated storage capacity (700 kWh) than the slab design for 3-hr charge and an equivalent accumulated storage capacity/depth of discharge (250 kWh/14%) as the latter. Furthermore, the storage power cost of the slab capsule design is the lowest, by 6–12% lower than the spiral coil design and by 2–3% lower than the ellipsoid capsule design. However, with the highest design flowrate of 8.4 m3/h, the low state of charge (below 40%) after three hours and the low depth of discharge (below 14%) after one hour indicate that redesigning the heat transfer boundary conditions and the configurations of the three units are necessary to meet desirable storage performance in cogeneration applications.

Design of filamentary planar spiral coils with enhanced channel model for magnetic induction based underground communication

AbstractEarlier researches have proved that the magnetic induction (MI) communication has better performance compared to the electromagnetic (EM) wave propagation in underground (UG) medium as it provides low signal attenuation using small MI coils. In general, non‐planar coils are employed as transceivers in the MI UG communication and their performance is dependent on coil parameters. The disadvantages of non‐planar coils are their bulkiness and limited transmission distance. In this article, a novel idea of using compact filamentary planar spiral coils for MI UG communication is proposed to achieve higher received power at greater transmission distance. An enhanced MI channel model is also proposed to study the medium's influence on MI performance accurately by considering different soil characteristics. Performances of the circular and square coils in the MI system are evaluated based on mutual inductance, path loss, received power, and signal‐to‐noise ratio. The performance comparison suggests that the filamentary planar spiral square coil MI system achieves 9.22% higher received power than the filamentary planar spiral circular coil MI system. Moreover, the lateral and angular misalignment study shows that square coils are more tolerant to misalignments. For the proposed filamentary planar square spiral coil (FPSSC) MI system, the influence of coil parameters, channel parameters, and coil misalignment on the received power was carried out and its least sensitive and most sensitive parameters were identified for further optimization. The performance comparison between the proposed FPSSC MI system and the traditional non‐planar MI coil system suggests that the received power of the proposed system is improved by 47‐49 dBm thus extending the achievable transmission distance.