Rectangular Spiral Coil Research Articles

A Novel Folding Wireless Charging Station Design for Drones

Unmanned aerial vehicles (UAV) have been used in many fields nowadays. In long-term applications, batteries need to be constantly changed by someone due to short battery life. This problem is eliminated with wireless power transfer (WPT). A reliable, effective, and autonomous solution is offered using wireless charging. The most suitable wireless charging technique for UAVs is inductive power transfer (IPT). In this paper, a novel foldable coil and charge station design is proposed for the wireless charging of UAVs. IPT is provided by receiver and transmitter coils placed on the drone legs and the charging station, respectively. Receiver coils are placed on both legs of the UAV in a light and balanced manner to avoid creating imbalance and weight on the UAV. Receiver coils are designed as vertical rectangular planar spirals. A transmitter coil consists of three rectangular planar spiral coils with two movable edge windings and a fixed middle winding. The transmitter’s folding windings provide both alignments for the UAV during landing and increase the magnetic coupling. A folding wireless charge system of the UAV is designed for 100 W output power at a 138.1 kHz frequency. The misalignment tolerance of the proposed design in the vertical axis is examined. The design’s magnetic flux density distribution is analysed. As an experimental result of the study, 97.66% efficiency was reached in the aligned condition. Also, over 85.48% efficiency was achieved for up to 10 cm of vertical alignment misalignment.

A Novel Antenna Design of Compact HF and UHF Passive RFID Tags with Interconnected Structure for Energy Harvesting and Tracking Systems

We propose a new dual-band passive RFID tag antenna design by combining a rectangular spiral coil and patch-meander-line dipole with an interconnected structure. This design enables operation in high-frequency (HF) and ultra-high-frequency (UHF) RFID systems, suitable for energy harvesting and tracking applications. The simulations by the CST full-wave software demonstrate conjugate impedance matching between the tag antenna and two RFID tag chips. At 13.56 MHz (HF), the tag antenna exhibits an inductive reactance of 422.79 Ω, while at 922.5 MHz (UHF), it presents an impedance of 9.41+j174.96 Ω. The antenna generates a maximum magnetic field intensity of 0.5 A/m and omnidirectional electromagnetic fields with an antenna realized gain of -4.26 dBi at 922.5 MHz. We also analyze the impact of the tag antenna combination using numerical software. Furthermore, we fabricate a prototype tag antenna and validate its performance with RFID readers. The proposed tag antenna achieves the maximum read ranges of 11 cm and 6.9 m for the HF (13.56 MHz) and UHF (920-925 MHz) bands, respectively, accompanied by the energy harvesting of 1.48 volts at the HF band by the coupling magnetic field received by the HF antenna to the chip ST25DV04K at the output voltage pin.

Numerical simulation of intracerebral hemorrhage detection using magnetic induction spectroscopy

Magnetic Induction Spectroscopy (MIS) is an emerging technique for contactless measurement of bioimpedance with promising application in intracerebral hemorrhage (ICH) detection. Here, we report numerical simulations of ICH detection based on the MIS. A novel MIS sensor using two planar rectangular spiral coils (TPRSC) as the exciter with frequency range 120 kHz-9 MHz is proposed for the first time. The exciter can generate an antisymmetric normal magnetic field at the detection sensor, and hence the primary voltage can be canceled theoretically. We construct symmetry-based and asymmetry-based ICH models with realistic anatomic structure and hexahedral discretization feature for numerical simulations. The numerical simulations based on the finite integration technique are conducted in the three-dimensional electromagnetic analysis software CST. The voltage phase spectrum, the phase change spectrum and the relative conductivity change spectrum at different hemorrhage volumes are calculated. We compare sensitivities between the TPRSC-based MIS sensor and the conventional type (CC MIS sensor) which uses the single planar rectangular spiral coil as the exciter. Using the constructed ICH models, the specific absorption rate (SAR) and the internal electric field strength are computed to evaluate the electromagnetic safety of the TPRSC-based MIS sensor. Results show that compared with the CC MIS sensor, the sensitivity of the TPRSC-based MIS sensor for measuring the voltage phase is improved by two orders of magnitude, and for measuring the phase change is improved by more than ten times. The phase change and relative conductivity change spectra for the TPRSC-based MIS sensor demonstrate good separability between different small-volume hemorrhages. In addition, the electromagnetic safety of the TPRSC-based MIS is also superior to that of the CC MIS sensor, which conforms to the IEEE standard and the ICNRP guidelines over a wide range of the amplitude of the excitation current.

Optimal Design with Generalized Inductance Calculation for IPTs Using a Spiral Rectangular Coil Pair

It is important to analytically and accurately calculate the self-inductance of the primary and secondary coils and the mutual inductance between them, in order for the optimization algorithm of the Inductive Power Transmission (IPT) system. In this paper, the inductance calculation methods used in the IPT designs at different power levels are examined. The performances of these methods have been evaluated according to the experimental results of these IPTs using rectangular coil pairs. Inductance results were obtained with Finite Element Analysis (FEA) for IPTs without experimental results. Accordingly, a 120 W IPT has been designed to be used for wireless charging of the Electric bicycle (e-bike). Rectangular spiral coil pair with 75 mm distance between them was fabricated according to the design result. Analytical and experimental inductance values are compatible with each other for the optimal IPT design. The efficiency between the DC power supply to the load has been achieved as 92.1672% in approximate load conditions.

Examination of the arrangement and shape of coils for permittivity measurement of dielectric sandwiched between carbon fiber reinforced plastics using electromagnetic induction testing

The arrangement and shape of coils for permittivity measurement of a dielectric sandwiched between carbon fiber reinforced plastics (CFRPs) using electromagnetic induction testing (EIT) is investigated here. First, the influence of the electromagnetic shielding effectiveness of the CFRPs on the permittivity measurement using EIT was examined by finite element analysis (FEA). The effectiveness was lower than that of general metals, indicating that EIT can be used for permittivity measurement. Next, the coil arrangement and shape suitable for permittivity measurement were investigated by FEA. The use of two rectangular spiral coils, one as a driver coil and the other as a pickup coil, was adopted. Finally, the permittivity was measured experimentally using the coil arrangement, geometry, and test conditions determined based on the FEA results. The experimental results showed that the output voltage increased as the permittivity increased, demonstrating the effectiveness of the proposed method.

Mutual inductance model of double printed circuit board‐based coplanar rectangular spiral coils for eddy‐current testing

AbstractIn the field of eddy‐current testing (ECT), most studies on detection probes are primarily based on circular solenoid coils; related research on rectangular spiral coils is rare. In this study, an analytical model of the mutual inductance (MI) between two coplanar rectangular spiral coils was developed in which the two coplanar rectangular spiral coils were placed above a conductive plate. The MI calculation does not need to consider the thickness of the coils, which is consistent with the actual situation of the printed circuit boards (PCB)‐based spiral coils, and simplifies the multi‐turn rectangular spiral coil into a set of concentric single‐turn coils. Two experimental setups were constructed to verify the analytical model and they were used to detect defects in the aluminium plate. The experimental results indicate that the analytical model can be used to evaluate the performance of ECT probes using PCB‐based spiral coils, through the geometrical dimensions of the coils, centre distance and lift‐off, and so forth. Compared with traditional methods, this method can still obtain satisfactory calculation accuracy after ignoring thickness parameters. The analytical model is also an effective tool to aid in the design of detection probes and optimisation of related parameters.

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.

Development of dynamic wireless power transfer coils for 3rd generation wireless in‐wheel motor

AbstractShort cruise range is a major issues in electric vehicles, and dynamic wireless power transfer (WPT) has been proposed to solve this problem. In this study, a new dynamic power transfer system is introduced, called the hird generation wireless in‐wheel motor, that integrates the drive circuit and motor. Additionally, a methodology of the transmitter and receiver coil design that can calculate inductance and resistance of the rectangular spiral coils in a fast manner is proposed. It considers the theoretical efficiency of coils, current of coils, and voltage of resonance capacitor as constraints. Inductance calculation models only use coordinates of coil edge and the distance between coil and ferrite core. The coils designed by the proposed method were manufactured and evaluated using an LCR meter. The calculation error of the self‐inductance and mutual inductance was found to be ± 9%. With the transmitter coil and receiver coil, an output and DC to DC efficiency of is 18 kW and 95.2%, respectively, were obtained by actual WPT test.

Mutual Inductance Analysis of Rectangular Spiral Coils with Angle and Position Variations for Wireless Power Transfer

For wireless charging, a misalignment between a receiver (Rx) coil in the devices (EV, drone and IMD) and a transmitter (Tx) coil often occurs. In this case, a mutual inductance between the coils changes, and consequently a power transfer efficiency (PTE) of the wireless power transfer (WPT) system also changes. To analyze the WPT system in such a situation, this paper presents an analytical method using Neumann formula to derive mutual inductance considering angular and position variations of two rectangular spiral coils. To verify the proposed method, magnetic resonant WPT systems of 85 kHz and 6.78 MHz are implemented, and the PTE values derived from the analyzed mutual inductance and the measured S-parameters are compared for the cases of angle and position variations. For each case, the two PTE values agree well with each other, and it is verified using the normalized root mean square error (NRMSE) values.

Inductance Formula for Rectangular Planar Spiral Inductors with Rectangular Conductor Cross Section

In modern technology, inductors are often shaped in the form of planar spiral coils, as in radio frequency integrated circuits (RFIC’s), 13.56 MHz radio frequency identification (RFID), near field communication (NFC), telemetry, and wireless charging devices, where the coils must be designed to a specified inductance. In many cases, the direct current (DC) inductance is a good approximation. Some approximate formulae for the DC inductance of planar spiral coils with rectangular conductor cross section are known from the literature. They can simplify coil design considerably. But they are almost exclusively limited to square coils.
 This paper derives a formula for rectangular planar spiral coils with an aspect ratio not exceeding a value between 2.5 and 4.0, depending on the number of turns, and having a cross-sectional aspect ratio of height to width not exceeding unity. It is valid for any dimension and inductance range.
 The formula lowers the overall maximum error from hitherto 28 % down to 5.6 %. For specific application areas like RFIC’s and RFID antennas, it is possible to reduce the domain of definition, with the result that the formula lowers the maximum error from so far 18 % down to 2.6 %. This was tested systematically on close to 140000 coil designs of exactly known inductance. To reduce the number of dimensions of the parameter space, dimensionless parameters are introduced. The formula was also tested against measurements taken on 16 RFID antennas manufactured as PCB’s.
 The derivation is based on the idea of treating the conductor segments of all turns as if they were parallel conductors of a single-turn coil. It allows the inductance to be calculated with the help of mean distances between two arbitrary points anywhere within the total cross section of the coil. This leads to compound mean distances that are composed of two types of elementary ones, firstly, between a single rectangle and itself, and secondly, between two displaced congruent rectangles. For these elementary mean distances, exact expressions are derived. Those for the arithmetic mean distance (AMD) and one for the arithmetic mean square distance (AMSD) seem to be new.
 The paper lists the source code of a MATLAB® function to implement the formula on a computer, together with numerical examples. Further, the code for solving a coil design problem with constraints as it arises in practical engineering is presented, and an example problem is solved.

Design and Fabrication of Wireless Multilayer Tracking Marker for Intraoperative MRI-Guided Interventions

This article presents the design, fabrication, and evaluation of miniature magnetic resonance (MR) compatible wireless markers, which can provide three-dimensional (3-D) positional tracking under magnetic resonance imaging (MRI). To achieve the small size of such markers, rectangular spiral planar coils were stacked in multiple layers, which can be fabricated on a flexible printed circuit board. Finite-element-based simulations and analytical modeling were applied to ensure the proper adjustment of the MRI scanner resonant frequency while maintaining a high circuit quality factor. A four-layer planar tracking coil was prototyped with a size of 6.7 × 1.5 × 0.3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and a quality factor of 28.5. This design and fabrication approach is reportedly the first design to initiate wireless markers in such a small size, enabling straightforward integration with interventional tools. When validated under MRI, the tracking marker appeared as a very high contrast spot on the MR images. For a 48 mm distance from the isocenter, the estimated maximum errors in 3-D position was 0.48 mm. And the inherent standard deviation of marker localization was 0.12 mm. With the high MR contrast signal generated, the presented markers enable automatic and real-time tracking in 3-D but without MR image construction. In combination with the small form factor, this marker would facilitate the MRI-guided navigation of interventional tools, in particular for those assisted by teleoperated robots.

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.

Application of ECT technology with a miniature PCB-based spiral coil in the visualization of CFRP laminates

ABSTRACTAn eddy-current testing (ECT) method with miniature-printed circuit board (PCB)-based planar spiral coils for carbon fibre-reinforced plastics (CFRP) is proposed in this paper. First, the electromagnetic model of the rectangular spiral coil is discussed, thus the analytical expressions of the impedance in free-space, and impedance change due to the eddy-current are provided. Next, the intensity areas of impedance change of a certain PCB-based planar spiral coil for metal and CFRP are theoretically given with different frequencies. Then, an ECT system for CFRP is established, and a resonant probe with a PCB-coil is designed by coupling to the parasitic capacitance of the cables. Finally, a series of ECT experiments for unidirectional, four-directional angle-ply, and orthogonal woven CFRP laminates are conducted. The results show that the minimum defect depth that can be detected on the unidirectional CFRP laminate reaches 0.1 mm. This study is an effective attempt for CFRP ECT based on planar spiral coils fabricated by PCB technology and lays the foundation for further ECT large-scale array scanners manufactured by PCB technology.

Analysis of Misalignment Effect on Wireless Charging System for Inspection Robots

To solve the issues including the inflexibility, connector wear, and electric shock risk in contact charging system for inspection robots, the wireless charging system for inspection robots is introduced in this paper. The circuit model of this paper is developed based on the mutual inductance theory. The expressions of the receiving power and the efficiency are derived. The coordinate calculation method for mutual inductance between non-coaxial rectangular spiral coils according to the movement characteristics of inspection robot is presented. According to the calculation method, the characteristics of the receiving power and the efficiency varying with the position change of the receiving coil are investigated. The location of the positioning device for starting the wireless charging system can be selected based on the system characteristics. The theoretical analysis is verified by experiments.

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.

Design and Optimization of Load-Independent Magnetic Resonant Wireless Charging System for Electric Vehicles

A load-independent wireless power transfer system with constant current and constant voltage output for electric vehicles charging is designed and optimized in this paper. Wireless charging system based on $LCL$ -S or $LCL$ – $LCL$ compensation topology is systematically analyzed. And dynamic $LCL$ -S/ $LCL$ switching topology is designed and simplified to achieve constant current in the transmitting coil and load-independent constant current and constant voltage output, which can be controlled easily. Moreover, the coupling structures composed of different coil shapes and shielding structures are comparatively studied to improve the coupling stability under misalignment. Figure-of-merit and coupling change rate $\Delta k_{t}$ defined in this paper are the key parameters in the process of coupling structure design and optimization. The combination of rounded rectangular spiral coil and splicing magnet core units is optimized as the coupling structure of the wireless charging system. Finally, the resonant wireless charging system prototype is being built and tested. The experimental results show that the load-independent and other characteristics of the implemented system are well correlated with the theoretical analysis and design.

Calculation of the inductance and AC resistance of planar rectangular coils

An effective calculation method for AC resistance and the inductance of planar rectangular spiral coils is proposed. For the calculation, a volume filament model and its equivalent circuit are provided. By using the method, AC resistance and inductance are calculated accurately in megahertz frequency range by including both skin and proximity effects. The method is verified with experiments and used to optimise rectangular spiral coils for the maximum quality factor (Q-factor) at 6.78 MHz. A small planar rectangular coil is shown to have the maximum Q-factor when the width of the innermost coil loop is about a half of that of the outermost coil loop.

High-Efficiency PCB- and Package-Level Wireless Power Transfer Interconnection Scheme Using Magnetic Field Resonance Coupling

As technology develops, the number of chips increases while the thickness of mobile products continuously decreases, which leads to the need for high-density packaging techniques with high numbers of power and signal lines. By applying wireless power transfer technology at the printed circuit board (PCB) and package levels, the number of power pins can be greatly reduced to produce more space for signal pins and other components in the system. For the first time, in this paper, we propose and demonstrate a high-efficiency PCB- and package-level wireless power transfer interconnection scheme. We enhance the efficiency by applying magnetic field resonance coupling using a matching capacitor. The proposed scheme can replace a high number of power interconnections with rectangular spiral coils to wirelessly transfer power from the source to the receiver at the PCB and package levels. The equivalent circuit model is suggested with analytic equations, which is then analyzed to optimize the test vehicle design. For the experimental verification of the suggested model, the $Z$ -parameter results obtained from the model-based equation and measurement of the designed and fabricated test vehicles are compared at up to 1 GHz. The power transfer efficiency from the source coil to the receiver coil in this scheme is able to reach 85.6%. Finally, we designed and fabricated a CMOS full-bridge rectifier and mounted it on the receiver board to convert the transferred voltage from ac voltage to dc voltage. A measured dc voltage of 2.0 V is sufficient to operate the circuit, which generally consists of 1.5 V devices.

Micromachined rectangular-spiral-coil actuator for radio-controlled cantilever-like actuation

This paper reports of a micromachined shape-memory-alloy (SMA) actuator in the shape of a rectangular spiral coil that is designed to perform cantilever-like actuation. The SMA-coil actuator itself forms a passive resonant circuit that functions as a wireless heat source activated using external radio-frequency (RF) electromagnetic fields for frequency-selective control of the actuation. The SiO2 stress layers are selectively patterned on the actuator structure of nickel–titanium SMA, or Nitinol, to manipulate the cantilever profile at the nominal cold state. RF radiation with varying field frequencies shows strong frequency dependence of wireless heating, actuation displacement, and force generation by microfabricated actuators with resonant frequencies of 170–245MHz. The actuators excited at resonance exhibit maximum out-of-plane displacement and force of 215μm and 71mN, respectively. The developed wireless SMA actuator not only provides >2× the force and 2× more power-efficient response compared to the preceding design with similar self-heating mechanism but also offers broader potential applications brought by its commonly adopted cantilever-based actuation.

Formability of magnetic pulse uniaxial tension of AZ31magnesium alloy sheet

In this paper, the formability of magnetic pulse uniaxial tension of AZ31magnesium alloy sheet at room temperature were investigated by the numerical simulation and experimental method. The numerical simulation for the magnetic pulse uniaxial tension of AZ31 sheet is performed by means of the ANSYS FEA software. The changes in velocity and strain rate were analyzed by simulation. The approximate rectangular flat spiral coil was employed to carry out the magnetic pulse uniaxial tensile experiments. The forming process was recorded by the high-speed camera, and the simulation result was consistent with it. The experimental results indicate that the total elongation of AZ31 sheet improves about 37 % compared with the quasi-static case. The major and minor principal strains at most increase by approximately 112 and 96 % under 5.12 kJ energy, respectively.