Quality Factor Of Coil Research Articles

Improved Design of PCB Coil for Magnetically Coupled Wireless Power Transfer

In recent years, wireless power transfer (WPT) has progressed rapidly in both theory and commercialization. However, existing research into WPT coil design for low-power devices to mitigate the coil offset is limited. A dual-layer printed circuit board (PCB) structure is proposed in this paper to mitigate the coil offset while retaining manufacturing simplicity for practical uses. Specifically, the impacts of key geometric parameters on the coil quality factor and coupling coefficient are analyzed through models and simulations. Equivalent PCB coils were formed for mutual inductance models, and four basic compensation circuits were analyzed. The impacts of changes in coil thickness, line width, turn spacing, and number of turns on the quality factor of PCB coils were analyzed with a fixed outer diameter of the coil. Eleven types of PCB coils were manufactured to verify the simulation results. The offset transmission efficiency can reach 46.6% with an output power of 14.4 W. The PCB coil with improved design could offer remarkable improvements in the WPT system for low-power electronic devices.

Detunable wireless Litzcage coil for human head MRI at 1.5 T.

Inductively coupled radiofrequency (RF) coils are an inexpensive and simple method to realize wireless RF coils in magnetic resonance imaging (MRI), which can significantly ease the MRI scan setup and improve patient comfort because they do not require bulky components such as cables, baluns, preamplifiers, and connectors. However, volume-type wireless coils are typically operated in transmit/receive mode because detuning such coils is much more challenging due to their complex structure and multiple resonant modes. Meanwhile, adding too many detuning circuits to a wireless coil would decrease the coil's quality factor, impair the signal-to-noise ratio, and increase the cost. In this work, we proposed, constructed, and tested a novel wireless volume coil based on the Litzcage design for 1.5-T head imaging. Being an inductively coupled coil, it has a much simpler structure, resulting in a lighter weight and less bulky design. Despite its simpler structure, it exhibits comparable imaging performance with a commercial receive array, providing an alternative to conventional wired coils with a high cost and complex structure. The unique figure-of-8 conductor pattern within the rungs ensures that the proposed wireless Litzcage can be efficiently detuned with minimal detuning circuits.

Model-Based Optimization of Spiral Coils for Improving Wireless Power Transfer

Inductive wireless power transfer is a promising technology for powering smart wearable devices. The spiral coil shape is widely used in wireless power transfer applications. Nevertheless, during the coil design process, there are many challenges to overcome considering all the design constraints. The most important is to determine the optimal coil parameters (internal radius, external radius, spacing, wire width, and conductive wire) with the aim of obtaining the highest coil quality factor. Coil modeling is very important for the wireless power transfer system’s efficiency. Indeed, it is challenging because it requires a high computational effort and has convergence problems. In this paper, we propose a new approach for the approximation of spiral coils through concentric circular turns to reduce the computational effort. The mathematical model determines the optimal coil parameters to obtain the highest coil quality factor. We have chosen the smart textile as an application. The system operates at a frequency of 100 Khz considering the Qi guidelines. To validate this approach, we compared the approximated circular coil model with the spiral coil model through a finite element method simulation using the COMSOL software. The obtained results show that the proposed approximation reduces the complexity of the coil design process and performs well compared to the model corresponding to the spiral shape, without significantly modifying the coil inductance. For a wire width smaller than 1 mm, the total deviation is around 4% in terms of the coil quality factor in a predetermined domain of its parameters.

Experimentally verified numerical model for asymmetric ferrite core wireless power transfer with on-chip interfacing circuits

This paper presents a novel numerical model for asymmetric ferrite core wireless power transfer, which has been experimentally verified. The research focuses on addressing the challenge of reducing the resonance frequency in wireless power transfer technology, particularly for cost reduction in power transfer systems. To achieve this, a toroidal ferrite core is utilized to decrease the self-resonant frequency, and the transmission parameter is measured using a vector network analyzer. Inductive wireless power transfer designs operating at MHz frequencies often suffer from low current efficiency due to the quality factor of the resonant coils. To overcome this limitation, finite element analysis is employed to optimize the cross-sectional area of the inductors, specifically for high-frequency wireless power transfer. The results demonstrate the effectiveness of the optimized coils, achieving an impressive transfer efficiency of nearly 98% at 5 cm, with an operating frequency of 21.6 MHz. Furthermore, the system is enhanced with a CMOS-based interfacing circuit, designed to enable system-on-chip power transfer for Internet of Things (IoT) applications. This integrated system design contributes to the advancement of wireless power transfer technology by not only addressing resonance frequency reduction but also proposing a cost-effective and efficient solution for power transfer in IoT applications.

Investigation of HTS Coil Structure Robustness Against Misalignment Between Coils in a Wireless Power Transmission System for Railway Vehicles

A wireless power transmission (WPT) system using high-temperature superconducting (HTS) coils has been investigated. However, it is difficult to precisely match the positions of the primary and secondary coils. Thus, the HTS coil structure with high misalignment tolerance is required. In this paper, we investigated the non-circular HTS coil structure with a high quality factor for the WPT system, such as a rectangular coil and a racetrack coil. Also, we evaluated the power transmission characteristics of the WPT system using the non-circular HTS coils. As a result, the quality factor of the non-circular HTS coils was maximum when the radial gap between turns was almost the same as the HTS wire width, and increased with increasing coil length in a rail longitudinal direction. Also, the receiving power and the system efficiency using the non-circular HTS coils were more robust against misalignment between coils than those using the circular HTS coils. On the other hand, the receiving power decreased with increasing the coil length of the non-circular HTS coils in the rail longitudinal direction due to thermal radiation from normal temperature. From the above, the receiving power of the WPT system with small lateral misalignments can be improved by using the rectangular coils with a short coil length in the rail longitudinal direction in parallel. Moreover, the system efficiency of the WPT system with large lateral misalignments can be improved by using the rectangular coils or the racetrack coils with a long coil length in the rail longitudinal direction.

Resonant Mechanism for a Long-Distance Wireless Power Transfer Using Class E PA and GaN HEMT

This paper presents a study on long-distance wireless power transfer (WPT), which formulates the voltage gain in terms of the coupling coefficient between the power transmitting unit (PTU) and the power receiving unit (PRU) coils. It is proposed that maximum power transfer efficiency (PTE) can be reached when maximum voltage gain is achieved under a matching condition between the coil quality factor and the coupling coefficient. In order to achieve maximum power delivered to load (PDL), we need to elevate the input voltage as high as the high breakdown-voltage of gallium nitride (GaN) high-electron mobility transistors (HEMT) along with class E amplifier circuit topology. In order to promote voltage gain, knowledge of the coupling coefficient between two coils including the factors of the coil diameter, wire diameter, coil turns, and the coil resistance are derived. It was observed that a lower coil resistance leads to a reduced parallel quality, which facilitates long-distance wireless power transfer. Experimental results support the findings that the maximum PTE occurred at the maximum voltage gain existing at a specific distance matches the coupling coefficient between coils. A maximum power point tracking (MPPT) method is also developed to achieve maximum PDL. At a distance of 35 cm, experiments with more than 100 W successfully receive a PTE of 57% at the PRU when the received voltage reached 1.4 kV. This is used to verify the concepts and analysis that are proposed in this paper.

Novel coil design and analysis for high-power wireless power transfer with enhanced Q-factor

The power transfer efficiency (PTE) is a crucial aspect for effective wireless power transfer (WPT) applications. The quality factor (Q) of the WPT coil plays a critical role in ensuring higher PTE. In this paper, a novel method of improving the Q of a WPT coil is proposed. Resistance reduction techniques are presented which involves variation of the trace pitch, width, and thickness. This approach targets the high AC losses centered in the inner turns, which subsequently results in an increased Q. Numerical analysis with respect to the inductance and resistance models are presented, analyzed, and compared to that of the EM simulation results. To verify the efficacy of the proposed coil structure, a prototype is fabricated where good agreement is achieved between the measured and simulated results. The proposed coil attained a quality factor increment of about 19.24% at 85 kHz in comparison to the conventional one. The proposed technique can be used to optimize planar spiral coils to attain higher Q.

High power transmission efficiency of wireless power transfer system using high-quality factor superconducting bulk coil

We developed a high-quality-factor high-temperature superconducting (HTS) bulk coil to increase the power transfer efficiency (PTE) of wireless power transfer (WPT) systems. We proposed the resonant frequency tuning by using the two sapphire substrates thickness of coil support. The configuration of a 65 mm diameter HTS bulk coil was optimized to a resonant frequency of 64 MHz. The measured quality factor of the HTS bulk coil was 9,431, which is 12 times that of the copper coil. At the transfer distance of 20 cm, the measured PTE of the WPT system using HTS bulk coils and one using copper coils were 74.8% and 20.6%, respectively.

Analysis of Coil-Thickness-Variation Technique for Q-Factor Enhancement of Rectangular Planar Coils

For wireless power transfer (WPT) applications, such as battery charging, the attainment of a high coil quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) becomes prudent to ensure a high-power transfer efficiency (PTE). In this article, we demonstrate an effective method to enhance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> by employing different thicknesses for each trace of the coil. The thickness of the inner turns of the coil, where high alternating current (ac) losses are concentrated, is relatively smaller compared to the outer coil turns. This technique realizes a reduction in the ohmic resistance, thereby increasing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of the coil. Furthermore, we present the analysis on the performance of the conventional coils with the same turn thicknesses compared to the proposed coil. To validate this technique, the prototypes of both the proposed and conventional coil structures are fabricated, where good agreement is achieved between the simulation and measurement results. The proposed coil realizes an increment of about 11.54% in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> compared to the conventional coil.

A Shared Method of Metal Object Detection and Living Object Detection Based on the Quality Factor of Detection Coils for Electric Vehicle Wireless Charging

High power alternating magnetic fields can cause lesions and pathological changes in living object bodies entering the wireless charging area. Also, as for metal objects, the eddy effect can cause the security risks such as fire and ignition hazards. Hence, metal object detection (MOD) and living object detection (LOD) are the necessary functions for a wireless power transfer (WPT) system. A shared method of MOD and LOD based on the quality factor of detection coils for electric vehicle wireless charging was proposed in this paper to realize the dual functions by the same detection coil array. Firstly, the effect of metal objects and living objects on the detection coil quality factor was analyzed in detail. Secondly, a method of real-time calculation of quality factor was proposed to detect whether the foreign object exists. Then, a distinction algorithm based on the phase variation trend of resonant capacitor voltage was designed to classify the type of foreign objects. Finally, a 3.3 kW experimental prototype, including a foreign object detection (FOD) system, was established to verify the validity. The advantage of the quality factor as the core indicator for FOD was analyzed in detail. Under the condition of an iron wafer, aluminum wafer, and beef chunk placed on the detection coil, the quality factor calculation results of the detection coil in contrast to those without foreign objects decreased by 80.8%, 50.5%, and 69.9%, respectively. Meanwhile, the phase difference of the excitation relative to the resonant capacitor voltage changed -61.3°, -74.6°, and 49.4°, respectively.

Analysis and Optimization of Planar Excitation Coil for EPS Torque Senor Based on GWO

Planar coil is usually used as a basic element in various research fields. This paper models a sensor equivalent circuit by taking the planar spiral excitation coil as an optimization object according to the electromagnetic coupling principle. The influence of coil electrical parameters on the coupling efficiency is analysed. The present result shows that the excitation coil should be small size, large inductance and high-quality factor. A two-dimensional planar spiral coil is modelled using ANSYS Maxwell software. The coil structure parameters with significant influence on the coil quality factor are chosen by the single factor experiment. The two-factor, five-level central composite deign principle is selected to establish a multivariate quadratic model by Response Surface Methodology (RSM). Then the paper implemented Grey Wolf Optimizer (GWO) to optimize response surface model, and obtained the optimal coil structure parameters. The conclusion was drawn that the inductance and quality factor of the optimized coil increase from 27.031 μH and 161.293 to 43.171 μH and 175.537, respectively. Compared to the control coil, the inductance is 1.597 times as the original coil and the quality factor is increased by 8.8%.

High Efficiency Wireless Power Transmission System That Uses HTS Transmitting and Copper Receiving Coils With a Large Difference in Quality Factor

We developed an efficient wireless power transmission (WPT) system using a high-temperature superconductor (HTS) spiral coil with a high quality factor as the transmitting coil and a copper coil as the receiving coil. The HTS spiral coil was fabricated using double-sided HTS wire which we developed previously. The double-sided HTS wire consists of two conventional HTS coated conductor wires. The measured quality factor of the HTS spiral coil containing modified coil support was about 14 times higher than that of the copper coil. We designed the WPT system using the filter design theory. We measured the design parameters for a coupling coefficient and an external quality factor. We measured the power transmission efficiency (PTE) of the WPT in the facing direction, position misalignment, and angular misalignment. The PTE of the WPT system with the high quality factor HTS spiral coil showed significant improvements in all measurements compared to the system with copper coils.

Optimization of Transfer Quality Factor of Limited-Size Coils for Series-Series Compensated Inductive Power Transfer System

For an inductive power transfer system, high transfer quality factor means that the system can obtain large theoretical transmission efficiency. In this paper, a method of coil optimization in a limited space to improve the transfer quality factor for a series-series compensated inductive power transfer system is presented. High transfer quality factor in a limited space can be achieved by determining the optimal number of turns with equal turn spacing coil, and then optimizing the distance between adjacent turn. The results of finite element simulation and experimental measurement show that the method proposed in this paper can obtain a higher transfer quality factor than the conventional method of winding coil with equal turn spacing. The method proposed in this paper can be used to guide the optimal design of coils in a limited space.

Investigation of correlation of design parameters in wireless power transfer system

Achieving higher power transfer efficiency with permissible output load power is a formidable challenge in designing a magnetically coupled resonant wireless power transfer system. Consequently, to instigate the power transfer characteristics, the theoretical models based on reflected load theory as well as lumped circuit models have been employed, which have been substantiated with the experimental measurements. It has been apprehended that maximum efficiency as well as the power delivered to the load can be enriched from the depreciated value through appropriate deliberation of coil's quality factor (coil design dependent) and coupling coefficient with acceptable operating frequency under different electric load conditions. The obtained results illuminate the correlation between the maximum power transfer ability and the quality factor of the coils, as well as the coupling coefficient, under different electric load conditions.

MRI Coils Optimized for Detection of 1H and 23Na at 0.5 T

Experiments on proton and sodium MRI at 0.5 T are described to assess the sensitivity of various types of coils, namely solenoidal, surface, volumetric, and with specific complex geometry. Each type of coil, characterized by its geometric specificity, was built to record MR signal of protons (1H) and sodium (23Na) at 21.1 MHz and 5.6 MHz, respectively. Sodium coils were initially built for 1H MRI and modified for 23Na MRI. Measurements in a container phantom filled with a 12% salt solution showed that the quality factor and sensitivity of various type coils approximately coincide at both sodium and proton resonance frequencies. The possibility of using data on SNR for a highly concentrated sample and Q-factor measurements to predict MRI results for a weakly concentrated sample is considered. These measurements represent a guide for extension to multinuclear whole body low field MRI clinical platform that is usually designed to operate in proton mode only.

A Millimeter-Wave Receiver Using a Wideband Low-Noise Amplifier With One-Port Coupled Resonator Loads

This article presents design techniques to facilitate the use of the driving point impedance (Z 11 ) of one-port transformer-coupled resonators as wideband loads of millimeter-wave amplifier stages for a 28-GHz receiver front end. While the use of both the Z 11 of a one-port and the transimpedance (Z 21 ) of a two-port coupled resonator is considered to achieve a wideband response, it is shown that under conditions of low magnetic coupling and constrained network quality factor, the use of Z 11 can result in a higher gain-bandwidth product of low-noise amplifier (LNA) amplifier stages. The effect of the complex zero in the Z 11 response on the in-band gain ripple is shown to be alleviated merely by lowering the quality factor of the transformer's secondary coil; this strongly motivates the use of compact, nested-inductor transformer layouts. Implemented in a 65-nm CMOS process, a three-stage LNA (with Z 11 wideband loads in two stages) achieves a 24.4-32.3-GHz bandwidth (27.9 % fractional bandwidth), a peak S 21 of 24.4 dB (20.4 dB), a minimum noise figure (NF) of 4 dB (4.6 dB), and an input-referred P1dB of -23 dBm (-22 dBm) while consuming 22-mW (9.9 mW) power from a 1.1-V (0.85 V) supply. The use of compact transformers limits the LNA's footprint to only 0.12 mm2. A 26.5-32.5-GHz quadrature receiver prototype employing the LNA achieves a 29.5-dB peak conversion gain, a 5.3-dB minimum NF, and a -26-dBm inputreferred P1dB while consuming 33 mW from a 1.1-V supply.

A temperature-controlled cryogen free cryostat integrated with transceiver-mode superconducting coil for high-resolution magnetic resonance imaging.

Small-sized High Temperature Superconducting (HTS) radiofrequency coils are used in a number of micro-magnetic resonance imaging applications and demonstrate a high detection sensitivity that improves the signal-to-noise ratio. However, the use of HTS coils could be limited by the rarity of cryostats that are suitable for the MR environment. This study presents a magnetic resonance (MR)-compatible and easily operated cryogen-free cryostat based on the pulse tube cryocooler technology for the cooling and monitoring of HTS coils below the temperature of liquid nitrogen. This cryostat features a real-time temperature control function that allows the precise frequency adjustment of the HTS coil. The influence of the temperature on the electrical properties, resonance frequency (f0), and quality factor (Q) of the HTS coil was investigated. Temperature control is obtained with an accuracy of over 0.55 K from 60 K to 86 K, and the sensitivity of the system, extracted from the frequency measurement from 60 K to 75 K, is of about 2 kHz/K, allowing a fine retuning (within few Hz, compared to 10 kHz bandwidth) in good agreement with experimental requirements. We demonstrated that the cryostat, which is mainly composed of non-magnetic materials, does not perturb the electromagnetic field in any way. MR images of a 10 × 10 × 15 mm3 liquid phantom were acquired using the HTS coil as a transceiver with a spatial resolution of 100 × 100 × 300 µm3 in less than 20 min under experimental conditions at 1.5 T.

Knitted coils as breathing sensors

A new implementation of a wearable respiratory inductive plethysmography garment is obtained by knitting a 250 μm thin insulted Cu wire simultaneously with yarn in the round. This was used to integrate a knitted coil in the body of a baby romper suit. During simulated breathing the diameter of knitted coil changes by stretching the knit circularly, causing a variation of the self-inductance of the coil. Coils with 5 rows of integrated metal wire with different stitch types and patterns were investigated to determine their influence on inductance, series resistance and sensitivity. We observed that knit styles that reduce the resistance of the coil, such as lace and jacquard also reduce the inductance and flexibility of the garment. Jacquard with three colours and one metal wire for each colour, gave the highest coil quality factor but also the poorest flexibility. We found that 1/1 rib stitch has the highest self-inductance for all yarn types. Its sensitivity of 0.5 – 0.6 μH/cm is similar to stockinette stitch except when elastic viscose yarn is used. Coils in stockinette stitch and elastic viscose yarn have the highest sensitivity of 0.84 μH/cm. No hysteresis in self-inductance was observed for circumference variations between 44 and 53 cm of the body of the baby romper in 1/1 rib stitch due to the elasticity of knitted garments.

Electromagnetic Characteristics of Shape Memory Spring

Electric impedance is widely used in imaging and detection techniques. The applications range from non-destructive testing, structural health monitoring, and geophysical imaging to medical imaging. The frequency of the signal used for the measurement ranges from less than 1 Hz to about 1 GHz. This paper addresses the measurement and evaluation of the phase dependent electrical resistance, inductance, capacitance, and impedance of a shape memory alloy (SMA) spring (BMX 150, Toki Corporation). The material characteristics can be obtained by means of their electromechanical impedance. Experimental procedures are implemented and the electrical characteristics are obtained for a wide range of frequency. The electrical resistance, inductance, impedances of the austenite and martensite phase are determined, also the quality factor of the Bio Metal coil to be (9.465 – 9.95) Ω and (10.358 – 10.8) Ω, (0.458 – 0.38) μH and (0.458 – 0.36) μH and, (9.47 – 10.24) Ω and (10.36 – 11.11) Ω respectively for the frequency range of 100 kHz - 1MHz. The quality factor of the Bio Metal ranges between 0.03 and 0.2 during heating and, 0.028 and 0.022 during the cooling phase. The experimental results herein show that an equivalent circuit of the SMA spring is a series resistor-inductor circuit with a parasitic capacitance effect. The electromagnetic behaviour of SMA is determined using a finite element tool.

Maximizing Transfer Distance for WPT via Coupled Magnetic Resonances by Coupling Coils Design and Optimization

The technology of wireless power transfer via coupled magnetic resonances (CMR-WPT) has a good transfer performance in the “middle range”, but it is far from satisfying the application requirements in practice. To achieve a longer transfer distance, coils are usually complicatedly designed, making the system unwieldy and costly. Based on the intuitive and easily adjustable coil parameters, a design and optimization method was proposed in this paper, which can realize the minimum size coil that meets the requirements at 6.78 MHz. First, an equivalent model of the CMR-WPT system was developed, and the influences of coil parameters on the effective transfer distance and power transfer efficiency (PTE) were analyzed, indicating that the effective transfer distance and PTE were not always proportional to the coil radius, the number of turns or the pitch. Then, the coil impedance and the quality factor of different coils were calculated. In addition, the influence degree of coil parameters on the transfer performance was also compared using variable control. Finally, an experimental platform was built, and experimental results agreed well with the simulation results.