Planar Rectangular Coil Research Articles

Wearable Inductive Sensing of the Arm Joint: Comparison of Three Sensing Configurations

Currently, there is a rapidly growing interest and demand for wearable textile sensors that can monitor human motions in a naturalistic environment. Some potential applications for this technology include research on measuring the motor skill performance of patients with motor disabilities such as autism spectrum disorder, Parkinson’s disease, cerebral palsy, and stroke and evaluating the efficacy of applied treatments. Among wearable sensors, inductive sensors that are made from highly conductive threads are attractive due to their easy development process, high reliability, and low cost. In this study, we analyzed and compared the performance of three inductive wearable sensor configurations—(1) single planar rectangular coil, (2) two separated coils connected in series, and (3) two helical coils connected in series—in terms of the change in the resonant frequency of the tank circuit they comprised as a result of the change in elbow joint angle through simulations. Three parameters of length, width, and the number of turns were considered to calculate sensor sensitivity to the joint angle. The coil with the highest sensitivity was then fabricated and measured, and its performance was compared with the simulation results. The proposed methodology can be extended to sensing other joints in the body such as the shoulders, fingers, and knees.

Quantifying Hole-Edge Crack of Bolt Joints by Using an Embedding Triangle Eddy Current Sensing Film

Hole-edge crack quantification of bolt joints is critical for monitoring and estimating structural integrity of aircraft. The paper proposes a new triangle eddy current sensor array for the purpose of increasing the level of quantifying hole-edge crack parameters, especially, the crack angle. The new senor array consists of triangular coils instead of planar rectangular coils. The configuration of the novel sensor array, including the excitation current directions and the excitation winding shape, is optimized by simulation. The ability of the proposed sensing film to identify the crack parameters has been verified by finite element simulations and experiments. Results shows that triangular coils with same current directions in circumferentially adjacent coils and opposite current directions in axially adjacent coils achieve better performance in sensor linearity and resolution compared to rectangular coils. In addition, it has also been proved that the sensing film has a good potential to identify the crack depth and length.

A Low Complexity Design Framework for NFC-RFID Inductive Coupled Antennas

Inductive Wireless Power and Data Transfer (WPDT) technology has become a vital enabler to the globalisation of Internet of Things. Driven by an increasing demand for data within applications and by the need to reduce the devices footprint by transmitting data and power with the same antenna, power transfer efficiency has become a barrier to WPDT systems' performance. To overcome the limitations of power transfer efficiency, current research focuses on the design of efficient integrated circuits and does not consider the challenges of inductive antennas' design and system integration. Hence, current system integration methods used in industry to design receivers for WPDT applications still require expensive experimental benchmarking of antennas. This paper introduces a new framework for inductive WPDT systems integration that focuses on the design of inductive coils and tuning capacitances. First, this framework proposes a new planar rectangular coil inductance formula that achieves an average error of 11% based on the testing of one hundred of coils, which out performs the current state of the art. Then, based on a detailed electrical model of both transmitter and receiver of WPDT systems, our design framework computes the coils geometric parameters and tuning capacitances that will optimize the overall efficiency of the WPDT system. Unlike state of the art design approaches, the main advantage of this framework is that it does not require expensive benchmarking of inductive antennas to find the optimal antenna. Verification of our design framework was achieved through a comparative analysis for Very High Bit Rate 13.56 MHz RFID applications. Results indicate an improvement of more than 15% in overall system power transfer efficiency compared to current state of the art methods within a comparatively more cost effective framework. A sensitivity analysis provides an insight and practical guide to implications of manufacturing variances in component parameters.

Optimisation of planar rectangular coil achieving uniform magnetic field distribution for EV wireless charging based on genetic algorithm

Inductive power transfer is a method that can be used to transfer power to electric vehicles. The output power and the transmission efficiency drop significantly when there is a misalignment between receiver on the vehicle and transmitter on the parking spot. This can be resolved by designing the transmitter coil that produces uniform magnetic fields for wireless charging. Here, a planar rectangular coil with unevenly spaced turns is proposed for improving the uniform magnetic field distribution over the charging zone, together with the genetic algorithm for determining the geometric parameters of the coil structure. An analysis that is divided into four design variables is presented. The magnetic characteristic of the optimal unevenly spaced transmitter coil using genetic algorithm and optimal evenly spaced transmitter coil using conventional method are compared and analysed. The uniform magnetic field distribution of the designed prototype is measured by an electric and magnetic field probe and by a receiver coil. The measured results agree well with the theoretical values and validate the improved uniform magnetic field distribution.

Integral and series solutions for inductance of rectangular coils with parallel end faces

A detailed analysis is presented for the inductance calculations of rectangular coils with parallel end faces, with the coils of parallel sides as the special case. Integral solutions are given by the theory of second-order scalar potential. The authors further provide the series solutions for the inductance, which are based on the truncated region eigenfunction expansion method. These series are quite concise and accurate, and with higher computational efficiency by comparison with the integrals. The integral and series solutions are also obtained for the planar rectangular coils. The numerical results of both methods are compared with those of the experimental data, and the proposed methods prove to be accurate and efficient enough for practical applications.

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.

Simplified Calculation Method of Impedance of a Planar Coil in Consideration of the Influence Depending on Eddy Current

An eddy current sensors have various uses, for example metal detection and determination, nondestructive inspection, and position detection. However, there are few studies which show the influence of a conductor on the impedance of a detector coil using a theoretical formula. This paper shows the simplified calculation method on impedance of a planar coil that can be found from an equivalent circuit by considering that a conductor plate is one turn of coil which form changes according to displacement. The impedance corresponding to the overlap length of a conductor plate was calculated about the planar rectangular coil and the planar triangular coil. The calculated value was compared with the measured value and the calculated value of finite element method. The calculated value of impedance of rectangular coil and triangular coil agreed with the measured value within an error of ± 5.98%. Mutual inductance between the planar coil and conductor plate was calculated from the area ratio of planar coil and overlap.

Passive Wireless Resonant Galfenol Sensor for Osteosynthesis Plate Bending Measurement

The healing process of bone fractures can be monitored by a measurement of the osteosynthesis plate bending. For this purpose a wireless magnetostrictive bending sensor is proposed. A planar rectangular coil on top of a magnetostrictive Galfenol ( alloy) layer forms an electrical resonant circuit. The sensor is manufactured in thin film technology. Coil turns were electrodeposited by pattern plating. Sensors with overall dimensions of (13 2 0.5) mm were manufactured with varied turn numbers showing self-resonance frequencies from 5 to 50 MHz. Examined sensors possess linear frequency-force characteristic up to 6 N with frequency shifts of 6 kHz . In order to obtain the sensor resonance frequency wirelessly, several measurement techniques were employed using inductively coupled coils. Frequency domain measurements have been carried out by employing a network analyzer with a single detection coil and a lock-in amplifier with separate coils for excitation and detection. In time domain measurements, two coils for transmission and reception are used. In the transmit case a short sine pulse excites the sensor and afterwards its decaying response signal is received. To determine the resonance frequency, a frequency counting, Fourier or wavelet technique can be used. By integrating additional cores of high permeability into sensor and detection coil, measurement ranges can be increased.

Multilayer planar rectangular coils for eddy current testing: Design considerations

Planar rectangular coils provide some interesting features different from those of pancake coils, such as good performance in conductivity measurement at high frequencies, high sensitivity to scratches and other shallow imperfections and the possibility of inspecting complex surfaces. The impedance of these coils has been modeled by different authors. A brief discussion of some analytical approaches in the literature is presented and calculations using the second-order vector potential approximation are introduced, aimed at the study of the influence of coil shape and size on the sensitivity to electrical conductivity of the substrate. Three cases were modeled, (A) coil in free space—inductance L 0 as a function of number of turns ( n) and width of the spiral conductive lanes ( c) for different coil inner shape factor ( rr i ); (B) coil on a conductive substrate (Zircaloy-4)—impedance change, Δ Z, as a function of f· σ, the product of the test frequency ( f) and the substrate electrical conductivity ( σ) for different rr i and (C) coil sensitivity to small changes in σ(Δ σ). L 0= L 0( c, n) increased as expected with n and/or coil area and decreased with shape factor. Normalized Δ Z depends strongly on inner rr i , the curves (or surfaces) for smaller values of rr i enclosing those for larger values. Another shape factor, the outer shape factor ( rr o ), was introduced. Strong dependence of the sensitivity to Δ σ on n was observed, as well as the existence of an optimal theoretical frequency. Because the sensitivity to surface conditions also increases with coil size, it could be established that for conductivity assessment it is better to use coils with the smallest n and c, compatible with the particular application, and that the resolving power for this type of measurements is not greatly affected by the shape factor.

Planar rectangular spiral coils in eddy-current non-destructive inspection

The results of a theoretical and experimental study of planar rectangular coils in eddy-current NDE are presented. Three fundamental cases are examined: a planar coil (i) in free space, (ii) above a defect-free conductive half-space and (iii) centered above a long, uniform crack. Closed-form expressions for the coil impedance are presented for these three cases and the theoretical predictions are validated against experiment using a series of coils with different aspect ratios and both non-magnetic and magnetic plates. While the change in normalized coil impedance due to the half-space depends only weakly on the coil aspect ratio, the change in normalized impedance due to the crack depends strongly on coil aspect ratio with the maximum normalized response observed for an aspect ratio of 1:1, i.e. for square coils. In contrast to planar circular coils, the response of planar rectangular coils depends on their orientation with respect to the crack. This orientation dependence is investigated in detail.