Planar Spiral Coil Research Articles

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.

Reconfigurable transmitter coil structure for highly efficient and misalignment-insensitive wireless power transfer systems in megahertz range

The structural optimization of coils is a key issue in wireless power transfer (WPT) applications owing to size limitations. In this study, a novel planar-spiral transmitter coil (TX-coil) with an outer-tight and inner-sparse configuration is proposed to achieve a high quality factor (Q-factor) and uniform magnetic field, which ensures high efficiency and improves the misalignment tolerance for several-megahertz WPT systems. Furthermore, a closed-form expression for the Q-factor is provided and analyzed for coil optimization. By using this method, a TX-coil with an outer diameter of 100 mm and a wire diameter of 1.5 mm is designed and tested at 1 MHz. Finite element method simulations and experimental results demonstrate that the Q-factor is increased by about 8% in comparison with evenly spaced planar spiral coils, which is achieved while ensuring a relatively uniform magnetic field.

A novel structured spiral planar embedded inductor: Electroless-plating NiCoP alloy on copper coil as magnetic core

Abstract In this work, electroless-plating of magnetic film directly on planar spiral copper coil to fabricate embedded inductor was designed and realized by introducing NiCoP alloys as its cladding magnetic core. This method with novel structure was achieved with significant increasing of inductance L and Q factor. The optimized alloy of Ni41Co58P1 results in enhanced inductance L around 32%@10 MHz and Q factor of 18. Cp experimental demonstrates its typical ignorable parasitic capacitance. Finally, HFSS simulation revealed the magnetic film constrained the magnetic line transmitted flowing the magnetic film, leading to effective inductance L increasing, which is in good agree with the experimental results.

Radio Frequency Planar Coil-Based On-Chip Probe for Portable Nuclear Magnetic Resonance

Miniaturization of nuclear magnetic resonance (NMR) systems has seen a tremendous development during the last two decades. However, it has not gained popularity particularly, for biological investigations due to high manufacturing cost, sophisticated tools requirement, and mismatching problems arising due to connecting wire between radio frequency (RF) coil and transmission line. The aim of the research work presented in this paper is to develop cost effective, portable, and benchtop NMR system for biological investigation related to healthcare. In this paper, RF planar spiral coil is developed on double sided printed circuit board (PCB) using conventional PCB technology having high-quality factor of 29.265 at 21.287 MHz. Then, the same coil is used to develop on-chip NMR probe by extending the transmission line. This developed probe is a novel design, which improves the coupling between RF coil and transmission line; and hence, improves the sensitivity of NMR. A pair of permanent magnets having 0.5 T magnetic field strength with rectangular iron yoke has been used in the NMR system. Finally, the efficiency of this portable NMR was tested by recording the NMR spectrum of human blood cells. The spectrum obtained was compared to the commercial NMR (Bruker, ULTRASHIELD −500 PLUS) and found to be similar with remarkably small sample volume requirement. Moreover, in this research, we report a very low-cost coil and probe with novel probe design using CST tool, for the first time to the best of our knowledge.

Mutual inductance calculation between two coaxial planar spiral coils with an arbitrary number of sides

In this paper, we present a full derivation of a new model based on the partial inductance method to calculate the mutual inductance between two planar spiral coils with an arbitrary number of sides. The planar spiral coils are approximated by regular concentric polygons and then each polygon is decomposed to its sides. The mutual inductance between each side of the primary and secondary polygons is analyzed considering geometrical properties of the sides with respect to each other. The method developed in the present study is general and straightforward in comparison with those available in the literature as it includes only required sequential steps to calculate the mutual inductance between the independent segments of the coils. We validated the results of the proposed method with those available in the literature, simulation and measurement results. Moreover, the developed method was implemented for the percent error analysis to assess the error of the approximation of the circular coils with n-sided polygons.

Comparative Study of the Accuracy of Analytical Inductance Formulae for Square Planar Spiral Inductors

In the design of radio frequency (RF) microelectronic integrated circuits (IC’s) and of antennas for short-wave radio frequency identification (RFID) and telemetry systems, planar spiral coils are important components. Many approximate analytical formulae for calculating the inductance of such coils can be found in the literature. They can simplify the problem of designing inductors to a predefined inductance considerably. But the error statistics given by different authors cannot be compared because they are based on different or unknown domains of definition. Hence, it is not possible to decide which formula is best in a given case by merely studying the literature. This paper compares the maximum relative errors of six of some of the most cited formulae in the literature. To all formulae, the same domains of definition are applied. Each of them spans all four dimensions of the parameter space. Precise inductances are obtained numerically with the help of the free scientific and industrial standard software FastHenry2 and used as reference values to calculate the errors of the formulae. It has been found that the alleged maximum errors reported by some authors are far too optimistic. Only two formulae feature small enough errors to be useful in circuit design. The method and the domains of definition applied in the present study may also prove useful for the assessment of future formulae.

Modeling of Open Square Bifilar Planar Spiral Coils

In this paper an electrical model for square bifilar planar spiral coils (BPSC) is presented. Its main aim is the study of BPSC electrical parameters and behavior involving the frequency range where the first resonances (valley and peak) occur for bifilar coils in open-circuit configuration. A new approach to determine mutual capacitances of BPSCs based on coplanar waveguide (CPW) lines is presented. This study can be applied for modeling of passive self-resonant (PSR) sensors and wireless power transfer (WPT) systems. In order to validate the proposed model, three BPSCs were manufactured, tested by means of an impedance analyzer and also submitted to electromagnetic (EM) simulations. The results obtained, presented by means of tables and graphs, show that the present study is feasible and promising for the modeling of open square BPSCs.

Evaluation of AC Resistance in Litz Wire Planar Spiral Coils for Wireless Power Transfer

Evaluation of AC Resistance in Litz Wire Planar Spiral Coils for Wireless Power Transfer

Magnetic Detection Structure for Lab-on-Chip Applications Based on the Frequency Mixing Technique.

A magnetic frequency mixing technique with a set of miniaturized planar coils was investigated for use with a completely integrated Lab-on-Chip (LoC) pathogen sensing system. The system allows the detection and quantification of superparamagnetic beads. Additionally, in terms of magnetic nanoparticle characterization ability, the system can be used for immunoassays using the beads as markers. Analytical calculations and simulations for both excitation and pick-up coils are presented; the goal was to investigate the miniaturization of simple and cost-effective planar spiral coils. Following these calculations, a Printed Circuit Board (PCB) prototype was designed, manufactured, and tested for limit of detection, linear response, and validation of theoretical concepts. Using the magnetic frequency mixing technique, a limit of detection of 15 µg/mL of 20 nm core-sized nanoparticles was achieved without any shielding.

Failure mode analysis of MEMS suspended inductors under mechanical shock

Micro-electromechanical system (MEMS) suspended inductors have been widely studied in recent decades because of their excellent radio frequency performance. However, few studies have been performed on the failure analysis of MEMS suspended inductors under mechanical shock. In this study, the failure of MEMS suspended inductors with a planar spiral coil is investigated through analytical and experimental methods. We present a stress and deformation analysis to study the failure mode of the suspended inductors under shock. To verify the theoretical analysis, MEMS inductors are designed and fabricated, and shock tests are carried out. The shock tests show that the failure mode of the MEMS suspended inductors is a fracture that occurs at the ends of the inductor coil, and the test results agree with the theoretical analysis.

Theoretical Analysis of Planar Spiral Coils between Two Multilayer Media for Electric Vehicle Wireless Charging

Square and circular coils are two typical topologies for coupling coils and are applied to wireless charging. However, most of the research on coupling coils is based on the finite element model (FEM), which is a time-consuming process for 3-D structure coils. In this paper, on the basis of Fourier–Bessel transformation and Dual Fourier transformation, two theoretical models of square and circular coils between two multilayer media are proposed. With the proposed models, we consider several important parameters such as the size of the coils, thickness, and permeability of each layer. Thus, both the self-inductance and mutual inductance of two planar coils can be calculated without much computational time. Additionally, these theoretical models can help designers figure out the different trends of self-inductance and mutual inductance, which has plenty of benefits for the preliminary pad design. Lastly, a prototype with a size of 600 mm × 600 mm and a 200 mm air gap was built in order to verify the proposed models.

Enhancing Coil Design for Micromagnetic Brain Stimulation.

This work further advances the micromagnetic stimulation (μMS) technology, which has shown the capability of stimulating the nervous system using magnetic induction in a focal region of tissue by discharging a time-varying current through a sub-millimeter size coil. However, μMS was originally based on commercial off the shelf (COTS) inductors, which are designed to maximize efficiency and minimize its losses albeit shielding off the magnetic field from reaching the neural tissue. In this work, we study and fabricate microscale coil structures for next-generation μMS devices. The coil was designed to optimize the flux injected into the tissue by using a planar square spiral coil geometry, which was previously shown to be optimal for neuronal stimulation. The results of the electromagnetic Finite Elements Method (FEM) simulations of the proposed μMS device show that even though the spiral has a fully symmetric design, it nonetheless exhibits an asymmetry in the induced electric field in the tissue that can potentially be used for activating neurons with a specific axonal orientation. Such devices could become the brain and heart stimulators of the future with their contactless ability to deliver the neuronal stimulation needed for therapeutic efficacy in patients in need of implantable cardioverter-defibrillators or pace-makers, or patients with Parkinson's disease, epilepsy.

Analysis of Square and Circular Planar Spiral Coils in Wireless Power Transfer System for Electric Vehicles

Nowadays, wireless power transfer (WPT) has attracted great attention from researchers because it is a safe, convenient, and reliable way to recharge electric vehicles. Square and circular coils are most commonly used in WPT systems. However, there are few analyses of comparing these two geometry windings in detail. In this paper, two analytical models of both square and circular planar spiral coils between two semi-infinite substrates are developed based on Fourier–Bessel transformation and dual Fourier transformation. An analytical calculation of the self- and mutual inductance can be carried out with respect to the main parameters of the WPT systems such as the line spacing, the number of turns of the coils and the properties of the substrate. The analytical models can be used to investigate the different tendencies of self- and mutual inductance of square and circular coils, which is helpful for speeding up the design process. Finally, to compare the lateral misalignment tolerance between square and circular coils, a ${{\text{600}}\,\text{mm}\,\times \,{\text{600}}\,\text{mm}}$ with a nominal 200-mm-gap prototype has been built and tested.

Annex Wireless Charging Coil Design Parameters UAV Introduction

Based on the coupling coefficient, quality factor and structure of the planar spiral coil better than that of the cylindrical spiral tube, a magnetic resonance resonant wireless charging system is established. The effects of coil transmission efficiency, coil turns, coil inner diameter, coil outer diameter and coil spacing on coil transmission efficiency are calculated. The influence of mutual inductance, M and coil equivalent internal resistance is analyzed deeply.

A Novel Dual Modality Sensor With Sensitivities to Permittivity, Conductivity, and Permeability

In this paper, an electromagnetic sensor which can operate simultaneously in capacitive and inductive modalities with sensitivities to permittivity, conductivity, and permeability is developed, and a novel measurement strategy is proposed accordingly. The sensor is composed of two planar spiral coils with a track width of 4 mm, which promotes its capacitive mode. The capacitive coupling is measured in common mode, while the inductive coupling is measured in differential mode. In capacitive mode, the sensor is sensitive to changes in permittivity, i.e., the dielectric material distribution; while in inductive mode, it is sensitive to magnetically permeable material and electrically conductive material. Furthermore, it is demonstrated that the sensor can simultaneously measure dielectric and conductive materials. This novel sensing element has been designed and implemented. Experimental results verified its effectiveness in dual modality measurement.

Study on Load Impedance Matching Characteristics of Magnetic Coupled Resonant Wireless Power Transfer System

The impedance matching problem of magnetic coupled resonant wireless power transfer system based on planar spiral coils is studied in this paper. Taken the coupling factors into account, the relationships between impedance matching, resonant frequency and transfer distance are analyzed. Supported by the simulation analyses and experimental evidences, it is indicated that the optimum matching resistances for transfer power and transfer efficiency are different. In details, the optimal matching resistance for output power decreases with the transfer distance, while that for the transfer efficiency does not vary with transfer distance. Thus, this research provides a valuable reference for the further research on adaptive impedance matching of magnetic coupled resonant wireless power transfer system.

Flow of Microencapsulated Phase Change Material Slurry through Planar Spiral Coil

ABSTRACTForced convection cooling is an effective method in thermal management that relies mainly on dissipating heat by pumping heat transfer fluid (HTF) through the heat source. In this paper, we investigate the thermal properties enhancement of dielectric water as the HTF. To enhance the properties of the HTF, microencapsulated phase change materials (MPCM) will be added to the base fluid. The MPCMs are composed of phase change material (PCM) encapsulated with shell materials. The PCM inside the capsules may undergo a phase change. This leads to a significant heat gain and release. The numerical model is developed to solve for continuity, momentum, and heat transfer equations using the finite volume method. The behavior of the MPCM slurry in curved channels, generates unique patterns due to different viscosity values and the centrifugal forces. Our preliminary numerical data on MPCM slurry through planar spiral coil heat exchangers show the new patterns of velocity and heat transfer curves. The current paper studies the steady condition of laminar flow at different boundary conditions. The velocity and temperature profiles, heat transfer data with different mass fractions of MPCM additives to the base fluid, and their heat removal capabilities are quantified and discussed in detail.

Phosphorous Detection In Water Using Electromagnetic Sensor

This paper introduces the phosphorous detection by means of electromagnetic planar hexagonal spiral coil sensor. To determine the sensor characteristics successions of experiments were performed. The reference set of readings with milli-Q water, and then phosphate was dissolved with milli-Q water in a number of different ratios. The results illustrate the detection capability of the sensor. The hexagonal sensors characteristics were compared and the phosphorous in water is tested successfully.

Application of 2-Dimensional Coil Detector for the Sensitive Direct Salmonella Detection on Plastic Board

To avoid food contaminated by pathogens such as Salmonella, magnetoelastic biosensors were used for rapid, wireless, and on-field detection. This paper demonstrates a series of measurements from low to high concentration of Salmonella typhimurium on a polyethylene (PE) chopping board by using a highly sensitive surface-scanning system. In this research, two-dimensional planar spiral coils were fabricated and utilized as the surface scanning detectors in the measurement system for the rapid and sensitive detection of Salmonella. ME biosensors, which was made by metallic glass (Metglas alloy 2826MB) with great magnetoelastic properties were applied on the sample surface for the real-time and in-situ measurement process. The resonant frequency changes of different measurement sensors (coated with E2 phage) change with the various of the Salmonella concentration. At the same time, the stability of control sensors (coated with blocking only) confirmed the specific binding of Salmonella typhimurium by the E2 phage.

Modeling circular inductors coupled to a semi-infinite magnetic medium considering the proximity effect

This paper presents a simple 2D electromagnetic model that solves the high-frequency current distribution, considering the proximity effect, in a planar spiral coil above a linear conductive or non-conductive semi-infinite magnetic medium. The conductive regions are divided into axisymmetric elements in which the current is assumed constant. The current flowing in each element depends on its complex impedance and is computed by Kirchhoff’s circuit law. To take the effect of the magnetic medium into account, a new set of mutual inductance formulas are presented. Those formulas are expressed in terms of elliptic integrals and the fast-converging arithmetic–geometric mean iteration of Gauss. The geometric mean distance method is used to deal with elements of arbitrarily shaped cross-section. Elliptic integrals are also used to express the magnetic flux density. The current distribution, the magnetic field and the equivalent impedance computed with the multifilament model agree well with the results obtained using commercial finite element software.