Receiver Coil Research Articles

Inspection of Defects Depth for Stainless-Steel Sheets Using Four-Coil Excitation Sensor and Deep Learning

The detection of lift-off variation presents a significant challenge in many eddy current testing (ECT) applications, where it is often considered an undesirable signal. To address this issue, the paper proposes a novel 4-coil excitation sensor, which can effectively suppress the lift-off effect when detecting defects of varying depths in planar structures. The proposed sensor design leverages opposite excitation directions between any two arbitrary adjacent excitation coils, which can effectively cancel out the lift-off signal due to a defect-free plate. However, this 4-coil excitation design has an angular sensitivity – i.e., different signal response for different angles between the same defect and the sensor. This angular sensitivity will cause trouble to identify the depth of defects without knowing the angle in prior. To overcome this challenge, the current study introduces deep learning (DL) models as a potential solution. Signals representing different defect depths and angles between the sensor and the defect are acquired using an experimental platform in our lab. The real and imaginary parts of the induced voltage on the receiver coil labelled with depths and angles are utilized to train a 1-D convolutional neural network (1D CNN) model, in which different convolution kernel sizes are used to extract more information and speed up convergence. The high performance of the proposed structure of 1D CNN were compared with convolutional long-short term memory (LSTM) model, recurrent neural network (RNN) model, LSTM+RNN model and ResNet18 model. The proposed 1D CNN model not only achieves good performances with a higher accuracy of 99.8% but also requires a smaller model size and less computational time.

Maximizing Energy Harvesting in a Miniaturized Implant with an Integrated Coil Receiver

In this work, a fully integrated energy harvester employing an on-chip coil and a voltage multiplier rectifier is proposed. The differential, multi-stage rectifier is optimized recurring to a genetic algorithm with the objective of maximize the power delivered to the load (W power transfer level) while minimizing area and start-up voltage. The rectifier is one of the most critical components in wireless-powered systems, generating a stable DC supply voltage, its efficiency is the main limiting factor in the achievable power budget. When implemented inside an implant, the circuit should occupy the minimum possible area and present a low start-up power as in the context of most applications, the amount of energy that reaches the receiver is extremely small. Simulation results show that the proposed circuit performs with an efficiency of 38% delivering a stable 1.16 V DC voltage to a 100 kΩ load, providing an output power of 14.9 W and solely occupying an area of 8750 m. Post-fabrication experimental results are presented, where a small inductive link employing a fully integrated receiver coil is used with the rectifier. A maximum power transfer of 12.5 W is achieved, with the inductive link operating at 915 MHz.

Near-Field Coupling을 접목한 배터리 셀 밸런싱을 위한 송 · 수신기 코일 모델링

This paper proposes a novel cell balancing method with using near-field coupling, which produces higher efficiency than passive type and faster than active type, which is the conventional battery cell balancing approach. As the importance of cell balancing has increased due to the increase in the proportion of renewable energy generation and the recycling of waste batteries, this approach is designed to meet the demand for high-capacity and high-power system. This paper focus on transmitter and receiver coil simulation models required to implement the proposed approach. it is confirmed that the schematic simulation model was sufficiently applicable. the measurement and 3D EM model are similar to the schematic model with only one inductor at the frequency we use. The measurement result of 2 times faster cell balancing with the coil designed with the proposed schematic model is presented

Spiral Resonator Arrays for Misalignment Compensation in Wireless Power Transfer Systems

In this contribution, the authors focus on the use of a metasurface (physically implemented as a 2D array of spiral resonators) as an additional component of a two-coil Wireless Power Transfer (WPT) system, with the aim of increasing the robustness to misalignment between the transmitter and the receiver coils. Resonator arrays have been proven to have a positive effect on WPT systems’ performance since they produce a focusing effect on the magnetic field; at the same time, they contribute to the reduction of the electric near field. In addition, we herein demonstrate how proper control over the metasurface’s unit cells can contribute to making a WPT system more tolerant to misalignment. In particular, the comparison between metasurfaces of different sizes (keeping the same transmitting and receiving coils) and their optimization performed to improve misalignment robustness is proved by numerical simulations.

New Osia® OSI200 active transcutaneous bone-anchored hearing device: how I do it

IntroductionThe new Osia® OSI200 implant incorporates a receiver coil and Piezo Power™ Transducer into one monolithic unit. Appropriate planning and surgical approach is needed for suitable positioning of the device.MethodTo optimise the surgical field and provide tension-free wound closure our team have adopted a versatile ‘Sheffield-S’ post-auricular incision which remains hidden within the hairline.ConclusionThis incision provides adequate exposure for device placement and bone polishing/recessing. The soft tissue approach has resulted in improved operative efficacy particularly in those patients with irregular cortical bone or where pre-existing osseointegrated implants need to be removed or avoided.

Two‐port network compact representation of resonator arrays for wireless power transfer with variable receiver position

SummaryThis paper presents an equivalent circuit characterization of an array of resonators for wireless power transfer (WPT) applications. These apparatuses are composed of magnetically coupled resonant coils acting as a transmitter which feeds a receiver coil that can be placed over them at any position, allowing the tolerance of the system to the receiver misalignment to be dramatically enhanced. This advantage makes resonator arrays a suitable solution for both low‐ and high‐power applications. The latter usually involve battery charging, with the resonator array acting as a transformer stage, ensuring galvanic isolation. An equivalent two‐port network can be defined for any receiver position, allowing the array to be treated as a traditional transformer. Thereby, the simulation of the system can be simplified, as it is required in the design steps of a converter and control strategy. Analytical expressions of the two‐port network parameters are proposed for arrays of any size and length. The formulas have been numerically and experimentally validated.

A multi-institutional comparison of acceptance testing data for a 0.35 T MRI scanner

Objective. To present and quantify the variability in the acceptance testing data for the imaging component of the 0.35 T magnetic resonance-linear accelerator (MR-linac). Approach. The current acceptance testing protocol by the MR-linac vendor was described along with the equipment and scanner parameters utilized throughout the process. The Bo field homogeneity, SNR/uniformity of the combined and individual receiver coils, American College of Radiology (ACR) image quality testing, and spatial integrity of the imaging data were collected from twelve different institutions. The variability in the results was accentuated and the ramifications of the results were discussed in the context of MR-guided radiation therapy. Main Results. The Bo field homogeneity was found to have a large gantry dependence with the median values being <4 ppm for all gantry angles. The SNR and uniformity were found to be well above the vendor-specified thresholds with a relatively small institutional-dependence. All institutions passed the ACR image uniformity tests. The largest institutional variability was noted to be for the slice positional accuracy test. The spatial fidelity was calculated to be <1.0 and <2.1 mm within a 100 and a 175 mm radius from the isocenter. Significance. The results from this study can be used to set the tolerances and formal guidelines for MR-linacs imaging quality assurance. Additionally, the multi-institutional data reported in this work will aid in future MR-linac acceptance and commissioning.

A novel sensor system to detect cerebral hemorrhage in rabbits through MIPS.

Magnetic-induction phase shift (MIPS) was rarely used in vivo and clinically because of low sensitivity and nonquantitative detection. The conventional single excitation coil and single detection coil (single coil-coil) generates divergent excitation magnetic field, resulting in different sensitivity of different object positions. To improve the sensitivity and linearity of MIPS and object volume to realize quantitative detection, a novel sensor system was proposed. The novel sensor system adopted uniform rotating magnetic field replacing the divergent magnetic field for the first time integrated with primary field cancellation. The uniform rotating magnetic field was generated by a birdcage coil excited by two orthogonal current; the primary field cancellation was realized by a specially arranged solenoid receiver coil installed co-axially with the birdcage coil detecting the z, not x and y-component of the secondary magnetic field. The saltwater simulation experiment showed that MIPS changed high linearity with the injection volume of all four different conductivity solutions. The experimental results of rabbit cerebral hemorrhage (CH) revealed that with injected blood volume increased to 3ml, the MIPS linearly decreased to -1.916°, which was 5.5 times higher than that of the single coil-coil method. Compared with the single coil-coil method, this novel detection system was more sensitive and linearly correlated for the detection of bleeding volume. It provided the probability of quantitative detection of the CH volume and a series of brain-content diseases.

Study and Design of Ratiometric Inductive Position Sensors Using Area-of- Overlap Functions

This article presents a theoretical study of an absolute, ratiometric inductive position sensor (IPS) based on eddy currents. The aim is to describe the working principle of the sensor, having as key components a transmitting coil, the receiving coils, and the conductive target, by introducing area-of-overlap functions. We show that each target–receiver pair needs the adoption of a different reconstruction formula for the identification of the target position, whereas in the literature the usual inverse tangent function is applied for every possible pair. Then, we seek the target–receiver pair that maximizes the amplitude of the induced voltages on the receivers. The results show that to achieve the maximum value of the induced voltages, the best choice is to have a rectangular target and rectangular receivers. To verify the theory, a simulation and optimization method has been applied to the rectangular receiver coils on two rotary IPS realized with printed circuit board (PCB) technology. Measurements performed on the prototypes have shown an increment of the induced voltage of more than 57% with respect to the commonly used sinusoidal receivers. However, a linearity error of 1.5%FS is obtained by using the inverse tangent reconstruction formula. When using the formula provided by the theory, the linearity error becomes 0.6%FS for the nonoptimized prototype and below 0.15%FS for the optimized one.

A Tilted-Orthogonal Receiver Coil Antenna to Improve Misalignment Tolerance in WPT Systems

This article proposes a novel receiver (Rx) coil antenna to mitigate the lateral misalignment problem in resonant wireless power transfer (R-WPT) systems. The proposed design comprising two Rx coils is analytically optimized by parametric sweeping the tilt angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(\theta)$ </tex-math></inline-formula> . Consequently, the resultant structure is designated as a tilted-orthogonal Rx coil antenna with stable mutual inductance in the Rx active region. Therefore, regardless of the Rx misalignment, power transfer efficiency (PTE), realized using the circuit parameters, maintains its consistency. The analytical results of the proposed Rx coil antenna are experimentally verified. The misalignment tolerance of the proposed tilted-orthogonal Rx coil antenna is improved by 120.18% in terms of PTE compared with the conventional planar Rx coil antenna.

Rectifier Design for Highly Loaded Inductive Wireless Power Transfer Systems for Biomedical Applications

Power transfer efficiency (PTE) and harmonics are crucial performance parameters of the resonant rectifier design for low/medium coupling inductive wireless power transfer (WPT) systems used in wireless biomedical implants. The performance of a resonant rectifier degrades under higher loading and lower coupling conditions as the voltage available to the rectifier at the output of the receiver coil becomes low. As the diode turn-on impedance increases, diodes turn on incompletely, leading to non-linearities that reduce rectifier efficiency and output voltage. This work proposes a new rectifier design to increase efficiency and reduce harmonics by decreasing the diode turn-on impedance compared to traditional rectifier designs, such as resonant Half Wave Rectifier (HWR). The proposed rectifier design offers individual paths for RF and rectification signals, which reduces the non-linear loading on the receiver coil and improves diode turn-on performance. Measurement and SPICE simulation results show efficiency enhancement of 50% and reduction of harmonics by 6 dB for the proposed rectifier compared to HWR.

Large-Area Free-Positioning Wireless Power Transfer to Movable Receivers

This article introduces a method for efficient and robust free-positioning wireless power transfer (WPT) in a large area, which can be applied to many use cases, including wireless charging of industrial robots, drones, and electric scooters. In these large areas of WPT applications, multiple transmitters (Txs) are placed in a pad-like area, and the Tx coils are optimally excited to enable robust and efficient power transfer to movable receivers within the charging area. The proposed configuration enables almost continuous magnetic flux path from a set of Tx coil(s) to another set of Tx coil(s) through the receiver coil ferrite core. Therefore, efficient power transfer is ensured throughout the whole Tx coverage area. The article introduces a novel method to detect the position and orientation of the receiver only from the Tx-side measurements. The proposed solution is experimentally verified in a laboratory prototype, and the experimental results show dc-to-dc efficiency of 91% with only 1% variation in most of the Rx positions.

Concept for gradient-free MRI on twin natural slices.

The design of an MRI for use in space requires that the hardware be kept to an absolute minimum in terms of mass, complexity, and power. In addition, NASA requirements are that the external stray field needs to be less than 3.2 Gauss, 7 cm from the MRI enclosure. RF encoding designs with Halbach magnets offer the best chance of meeting those requirements. Spatially non-uniform magnetic fields with foliations of isomagnetic surfaces, or natural slices, may be used to provide slice selection, and to reduce further the hardware complexity, for TRansmit Array Spatial Encoding (TRASE) Magnetic Resonance Imaging (MRI) or potentially for other radio frequency (RF) encoding methods. The design of such non-uniform magnetic fields in a Halbach configuration with built-in axial gradients leads to pairs of isomagnetic surfaces centered on either side of a central maximum field strength slice. If TRASE images from slices other than the central isomagnetic surface are desired, then the Nuclear Magnetic Resonance (NMR) signals originating from the twin natural slices must be separated during image reconstruction. Here, a design for simultaneously imaging on twin slices in such an inhomogeneous magnetic field using multiple receiver coils with spatially varying RF profiles is described mathematically and numerical simulation examples are given. To achieve RF encoding on the natural slices, at least three TRASE transmit coils are required. Here a solution with twisted solenoid coils is given. To achieve the twin slice separation at least two receive coils are required. Here a solution with two solenoids is given. The MRI design presented here uses a combination of RF encoding (TRASE), a spatial encoding magnetic field (SEM, pairs of natural slices) and receive coil spatial profiles to encode enough information into the NMR signal for image slice reconstruction. The design presented here enables using Halbach magnets with a built-in axial gradient to be used for MRI. The result is a new gradient-free TRASE MRI design capable of imaging pairs of electronically selectable axial slices.

Coil optimization and power orientation strategy of wireless power transfer system based on array coils

Aiming at the problem of power reduction when the transmitter and receiver coils are misaligned in wireless power transfer (WPT) system, a strategy to improve power by controlling the current phase of the array coils is proposed in this paper. Taking the square coil as an example, the expression of the magnetic field strength at a certain point in the array coil is discussed, and the parameters affecting the magnetic field distribution are determined. In order to improve the uniformity of the magnetic field distribution, the non-equidistant coil structure of the array coil is designed. BP neural network is introduced to learn the variation law of the magnetic flux with the current phase of the array coil in the specified area, and the phase difference between the coils when the magnetic flux is maximum is determined. Finally, the above concepts are realized through simulations and experiments. The results show that the proposed non-equidistant coil has more advantages in the uniformity of magnetic field distribution than the equidistant coil. Under the optimal phase configuration, the magnetic flux in the planar area of the array coil can be effectively improved.

Position Estimation of Multiple Receiving Coils and Power Transmission Control for WPT without Feedback

It is important to determine the position of the receiver (Rx) coils in wireless power transfer (WPT) system, and to control the power transmitted to the Rx coil based on this result. In particular, in a situation where there is no feedback between the primary side and the secondary side, it is difficult to control the received power because the information is limited. In this paper, a method for determining the position of the Rx coils and controlling the received power using limited parameters in a feedback-free WPT system is proposed. The proposed method is verified by constructing a 4×2 WPT system, and it is validated that the simulation result and the experimental result are consistent well. Furthermore, arbitrary power can be transmitted to the Rx coil based on the result of the position of the Rx coil. The experiment is conducted by transmitting about 1W to Rx 1 and Rx 2, and the efficiency for Rx 1 is about 32.93%, Rx 2 is 25.03%, and the overall efficiency is confirmed to be 57.96%.

Star-Shaped Coils in the Transmitter Array for Receiver Rotation Tolerance in Free-Moving Wireless Power Transfer Applications

Wireless power is one of the new promising technologies for IoT applications. The use of arrays for power transfer to free-moving objects has revolutionized wireless power transmission (WPT) applications. Herein, we present an extendable platform for transmitting power to a moving object receiving power from an array. The transmitter (TX) consists of two overlapping layers of square planar coils rotated 45 degrees to each other to provide the best electromagnetic flux coverage. Each layer consists of four coils to further control the power supply to the small receiver (RX) coil. This overlapping star-shaped array is stimulated automatically by a power amplifier. This smart stimulation can deliver uniform power to the receiver regardless of rotation and misalignment inconsistencies by using the geometry of the transmitter array. Moreover, by changing the direction of the current of each small square component in each array using the flower-shaped current, a receiver coil perpendicular to the transmitter’s plate can obtain power comparable with conventional structures. We use ADS-HFSS simulation to verify the fabrication and measurement results. The proposed transmitter achieves an average of 18.2% power transfer efficiency (PTE) to RX and at 90° angular misalignment, 11.5% PTE, while the conventional structure transfers no power to the perpendicular RX coil. A future application of the transmitter can be the investigation of the neurobehavioral of free-moving animals and brain–machine interface studies in medicine.

MRI data quality assessment for the RIN - Neuroimaging Network using the ACR phantoms

PurposeGenerating big-data is becoming imperative with the advent of machine learning. RIN-Neuroimaging Network addresses this need by developing harmonized protocols for multisite studies to identify quantitative MRI (qMRI) biomarkers for neurological diseases. In this context, image quality control (QC) is essential. Here, we present methods and results of how the RIN performs intra- and inter-site reproducibility of geometrical and image contrast parameters, demonstrating the relevance of such QC practice. MethodsAmerican College of Radiology (ACR) large and small phantoms were selected. Eighteen sites were equipped with a 3T scanner that differed by vendor, hardware/software versions, and receiver coils. The standard ACR protocol was optimized (in-plane voxel, post-processing filters, receiver bandwidth) and repeated monthly. Uniformity, ghosting, geometric accuracy, ellipse’s ratio, slice thickness, and high-contrast detectability tests were performed using an automatic QC script. ResultsMeasures were mostly within the ACR tolerance ranges for both T1- and T2-weighted acquisitions, for all scanners, regardless of vendor, coil, and signal transmission chain type. All measurements showed good reproducibility over time. Uniformity and slice thickness failed at some sites. Scanners that upgraded the signal transmission chain showed a decrease in geometric distortion along the slice encoding direction. Inter-vendor differences were observed in uniformity and geometric measurements along the slice encoding direction (i.e. ellipse’s ratio). ConclusionsUse of the ACR phantoms highlighted issues that triggered interventions to correct performance at some sites and to improve the longitudinal stability of the scanners. This is relevant for establishing precision levels for future multisite studies of qMRI biomarkers.

Winding loss analysis of planar spiral coil and its structure optimization technique in wireless power transfer system

Circular planar spiral coils are wildly used for the magnetic coupling system in a high-frequency wireless power transfer system. The loss of the magnetic coupling system usually takes dominance in the whole system. This paper built the calculation model of magnetic field strength and coil loss, the proposed calculation model can effectively consider the mutual influence between the transmitter and receiver coil and accurately calculated the AC loss of WPT coils. Then, the effect of turn spacing on the AC resistance of coil is analyzed. It reveals that the proximity effect loss is greater when the coil is tightly wound, and the AC loss can be optimized by designing the turn spacing. Based on the above analysis, a double-layer coil method is proposed. This method can reduce the AC loss and improve the quality factor (Q) without changing the mutual inductance and footprint of coil at high frequency. The AC resistance of the double-layer coil method can be greatly reduced compared with the general method through simulation and experiment. The work efficiency of WPT system is increased by 4.3%, which verifies the accuracy and flexibility of theoretical analysis.

DESIGN AND SIMULATION OF A MULTI-RECEIVER WIRELESS POWER TRANSFER SYSTEM BASED ON TRANSMITTER CONTROL METHOD

As is usual in a multiple-receiver wireless power transfer (WPT) system based on s-s geometry, the power of load obtained and system efficiency are very sensitive to changes in the number of receivers. An improved multi-receivers WPT system is introduced that ensures the power given for each load remains stable while other receivers enter or exit the system. This study proposes a multiple-load WPT system operated by a class E amplifier. The equivalent system circuit model is analyzed of major parameters such as receiver power, transmitter power, transmission efficiency, and each load power allocation. A control circuit is proposed to obtain high transmission efficiency, power control for the transmitter, and arbitrary power distribution ratios of receivers for different loads. The cross-coupling between the receiver coils is prevented by adding compensating capacitors at the receiver side in series. This further increases the power stability obtained by loads. Finally, in order to verify the feasibility of the proposed process, simulation results are presented.

Minimizing Leakage Magnetic Field of Wireless Power Transfer Systems Using Phase Difference Control

In this paper, we propose a method to reduce the leakage magnetic field from wireless power transfer (WPT) systems with series–series compensation topology by adjusting the phase difference between the transmitter (TX) coil current and the receiver (RX) coil current without additional shielding coils or materials. A WPT system employing the proposed method adjusts the phase difference between the TX coil current and RX coil current by tuning a resonant capacitor of the RX coil. The conditions for minimizing the leakage magnetic field are derived, and the range of the resonant capacitor of RX, considering power transfer efficiency and the leakage magnetic field, is proposed. Through simulations and experiments, it is verified that the proposed method can reduce the leakage magnetic field level without any additional materials. For that reason, the proposed method can be suitable for size-limited, weight-limited or cost-limited WPT systems.