Coil Pattern Research Articles

Design and construction of gradient coils for an MRI-guided small animal radiation platform

Small animal radiation experiments use a dedicated hardware platform to deliver radiation to small animals to support pre-clinical radiobiological studies. Image guidance is critical to achieve experiment accuracy. MR-based image guidance became recently available in human radiation therapy by integrating an MR scanner with a medical linear accelerator. Our group is developing a small animal MR-guidance system for pre-clinical radiation studies using a unique low-field unilateral magnet design. In this paper, we reported our design, construction, and characterization of split gradient coils for the MRI scanner. The coils were designed to have a 4 cm gap to allow the radiation beam to pass through for radiation experiments. We designed the coil patterns by solving an optimization problem. We constructed the coils by printing molds for the designed coil patterns using 3D printing technology and wiring the coils following the pattern. We measured parameters of the coils to characterize their performance. The coils achieved a linear magnetic field throughout a 4 cm spherical region of interest. The slew rates were 8640 and 1970 T/m⋅s, and the efficiencies were 1.2 and 0.21 mT/m⋅A for the Y-coil and X-coil, respectively. Preliminary imaging with the coils on our proposed system validates spatial encoding functions of the developed coils.

High-performance shim coil design and engineering optimization for use in an extremely high field superconducting magnet

The extremely high field has significant advantages in imaging quality and analyzing the fine structure of substances. However, its excellent performance requires the support of a higher-performance shim technique. In this paper, a novel structural design pattern of the shim coil for a 27 T extremely high field superconducting magnet is proposed. According to the contours of the stream function, we designed and optimized the shim coil pattern and engineering processing. The novel design was realized by using the contours as the centerline, and the wire spacing was controlled at 1 mm. The performance of the novel pattern was compared with those of alternative winding schemes. The results indicate that the novel design can improve coil performance, achieving higher fidelity and lower power dissipation.

Modeling for silicone foam material extrusion with liquid rope coiling

This research demonstrates a Modeling idea using parametric Modeling and considering the process to predict coiling patterns effectively in open-cell foams material extrusion (MEX) with liquid rope coiling (LRC) effect. The model consists of three sub-models, including pneumatic extrusion model, liquid rope coiling model, and geometric model, considering material properties, material extrusion, falling, LRC, pattern formation process and device structure. The model uses four MEX process parameters (back pressure, moving speed, inner nozzle diameter, and nozzle height) to predict three geometric parameters of the coiling pattern. The capability to predict pattern shape (period length, width, and loop length) accurately is validated by comparing the fit of predicted and experimental values when adjusting the process parameters, with R-squared coefficients up to 0.957. Then, application value is demonstrated by printing silicone open-cell foams under the guidance of the proposed model and studying the compression properties of these foams. The obtained three-region stress-strain curves indicate the feasibility of variable stiffness foam fabrication by adjusting the process parameters according to the proposed model during the printing process. Based on the results, the proposed model demonstrates accuracy in predicting geometric parameters of translational coiling pattern, makes predictable manufacturing of complex cellular structures available, and provides a foundation for design and fabrication of load-based variable stiffness silicone open-cell foam.

Thermally Degradable Inductors with Water-Resistant Metal Leaf/Oleogel Wires and Gelatin/Chitosan Hydrogel Films.

Ingestible electronics monitor biometric information from outside the body. Making them with harmless or digestible materials will contribute to further reducing the burden on the patient's oral intake. Here, considering that the inductive part plays an important role in communications, we demonstrate a degradable inductor fabricated with harmless substances. Such a transient component must meet conflicting requirements for both operation and disassembly. Therefore, we integrated a substrate made of gelatin, a thermally degradable material, and a precision coil pattern made of edible gold or silver leaf. However, gelatin itself lost its initial shape easily due to quick sol-gel changes in physiological conditions. Thus, we managed the gelatin's thermal responsiveness by using a tangle of gelatin/chitosan gel networks and genipin, an organic cross-linking agent, and gained insights into the criteria for developing transient devices with thermo-degradability. In addition, to compensate for the lack of water resistance and low conductivity of thin metal foils, we propose a laminated structure with oleogel (beeswax/olive oil). LCR resonance circuits, by connecting a commercial capacitor to the coil, worked wirelessly in the megahertz band and gradually degraded in a warm-water environment. The presented organic electronics will contribute to the future development of transient wireless communications for implantable and ingestible medical devices or environmental sensors with natural and harmless ingredients.

Hybrid Mechanism of Electromagnetic and Piezoresistive Sensing Using a Soft Microfluidic Coil

Soft magnetic sensors for tactile and pressure sensing based on the intensity change of the magnetic field has been drawing attentions recently due to the simplicity in manufacturing using commercial Hall effect sensors with high linearity and sensitivity. However, these sensors usually show relatively narrow sensing ranges due to fast saturation of the output signals from the magnetic field. In addition, rigid components for creating the magnetic field often limit the structural compliance. In this study, we propose a soft pressure sensor not only sensitive in a small pressure range but also has a large dynamic range using a hybrid mechanism of two different sensing modes: electromagnetic and piezoresistive sensing. By directly printing eutectic gallium-indium (EGaIn) to form a double-layered pancake coil pattern on a silicone elastomer, we fabricate a microfluidic soft coil that can be used as either an electromagnet or a variable resistor. Parameters, such as the sensor height, the stiffness of the material, and the resistance of the soft coil are configured for an enhanced sensitivity, a short recovery time from deformation, and reduction in electrical failures during operation. In this letter, we introduce the design and fabrication of the proposed sensor and characterizes a single sensor prototype. An array of the proposed sensors is also demonstrated as an application.

Surface Heater Fabrication Using Micro-Lithography for Transpiration Cooling Heat Transfer Coefficient Measurements

Abstract Transpiration cooling is able to provide more uniform coolant coverage than film cooling to effectively protect the component surface from contacting the hot gas. Due to numerous coolant ejection outlets within a small area at the target surface, the experimental thermo-fluid investigation on transpiration cooling becomes a significant challenge. Two classic methods to investigate film cooling, the steady-state foil heater method and the transient thermography technique, fail for transpiration cooling because the foil heater would block numerous coolant outlets, and the semi-infinite solid conduction model no longer holds for porous plates. In this study, a micro-lithography method to fabricate a silver coil pattern on top of the additively manufactured polymer porous media as the surface heater was proposed. The circuit was deliberately designed to cover the solid surface in a combination of series connection, and parallel connection to ensure the power in each unit cell area at the target surface was identical. With uniform heat flux generation, the steady-state tests were conducted to obtain distributions of a pair of parameters, adiabatic cooling effectiveness, and heat transfer coefficient (HTC). The results showed that the adiabatic cooling effectiveness could reach 0.65 with a blowing ratio lower than 0.5. Meanwhile, the heat transfer coefficient ratio (hf/h0) of transpiration cooling was close to 1 with a small blowing ratio at 0.125. A higher HTC ratio was observed for smaller pitch-to-diameter cases due to more turbulence intensity generated at the target surface.

An Inverter Topology for MultiTransmitter Wireless Power Transfer Systems

This paper presents an inverter topology for a static wireless power transfer (SWPT) system that is intended to reduce the component counts and complexity of the conventional excitation circuit for multiple transmitter coils. The proposed inverter topology requires only (n+1) power switches, where “n” is the number of transmitter coils. The currents in the transmitter coils can be independently controlled. The output voltage is regulated through the transmitter-side control by adjusting the duty cycle of the inverter switches. A detection method of the receiver coil position is developed by comparing the transmitter currents to the predetermined transmitter coil patterns. The proposed detection method helps decide the proper transmitter selection, which improves the transfer efficiency throughout the operation. An experimental study is performed on the created 500-watt WPT multi-coil system. As the receiver coil is placed in the designated area, the proper transmitter coil pattern can be automatically selected and energized. The output voltage can be regulated to the desired values throughout the operation, regardless of the load condition.

Gradient Coil Design Method Specifically for Permanent-magnet-type Low Field Portable MRI Brain Scanner

ferromagnetic structures, particularly the anti-eddy plate, in a bi-planar permanent-magnet-type low-field (0.05 T) magnetic resonance imaging (MRI) brain scanner can distort the gradient field in the target region. This study aims to provide a new gradient coil design method that reduces ferromagnetic influences on gradient field linearity. Thus, a simplified model of electromagnetic (EM) structures of the permanent-magnet-type MRI scanners was established. By using precise analytical proof, the anti-eddy plate was reduced to a homogeneous magnetic plate. The overall effects of the EM structures, which can be represented by bi-planar magnetic plates, were evaluated. In sequence, the image magnetic dipole was first introduced to show the effects of anti-eddy plates were added to the conventional equivalent magnetic dipole (EMD) approach. A novel equivalent image magnetic dipole (EIMD) method was proposed to build the gradient coil pattern. The effect of ferromagnetic materials was predicted throughout the gradient coil design phase using the proposed method, and a high-linear gradient field was generated under real working conditions. The computational and experimental results showed that the gradient coil was linear when ferromagnetic structures were present. The effectiveness of the proposed method was demonstrated by comparing T1-weighted images of the conventional method to those of the proposed method. The proposed method reduced image distortion caused by nearby EM structures in bi-planar permanent-magnet-type low-field MRI systems and provided an effective and concise solution for gradient coil designs.

Actively-shielded ultrahigh field MRI/NMR superconducting magnet design

Active shielding technology has been widely applied to the superconducting magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) magnets design, revealing excellent performance on the stray field control. For such a highly homogeneous field superconducting magnet design, an appropriate optimization strategy is essential to guarantee the magnetic field homogeneity in the central region and the expected 5 Gauss line range, especially for the ultrahigh field superconducting magnet. Based on the compensating field optimization method, an actively-shielded whole-body 14 T MRI magnet and an actively-shielded 1.3 GHz NMR magnet were presented, and detailed analyses were conducted to evaluate the feasibility of the designs. The developed magnet design method, coil pattern, wire arrangement, and stress/strain adjustment will be used to guide the corresponding project implementation.

Optimization and Analysis of Multilayer Planar Spiral Coils for the Application of Magnetic Resonance Wireless Power Transfer to Wearable Devices

In this study, small multilayer planar spiral coils were analyzed and optimized to wirelessly charge an in-ear wearable bio-signal monitoring device in a wine-glass-shaped transmitter (Tx) based on magnetic resonance wireless power transfer (MR-WPT). For analysis of these coils, a volume filament model (VFM) was used, and an equivalent circuit formulation for the VFM was proposed. The proposed method was applied to design effective multilayer coils with a diameter and height of 6 and 3.8 mm, respectively, in the wearable device. For the coils, a printed circuit board having a 0.6 mm thick dielectric substrate and a 2 oz thick copper metal was used. Moreover, the coils on each layer were connected in series. The dimensions of the double-, four-, and eight-layer coils were optimized for the maximum quality factor (Q-factor) and coupling efficiency. The operating frequency was 6.78 MHz. The optimal dimensions for the maximum Q-factor varied depending on the number of coil layers, pattern width, and turn number. For verification, the designed coils were fabricated and measured. For the four-layer coil, the coupling efficiency and Q-factor using the measured resistance and mutual inductance were 58.1% and 32.19, respectively. Calculations showed that the maximum Q-factor for the four-layer coil was 40.8 and the maximum coupling efficiency was 60.1%. The calculations and measurement were in good agreement. Finally, the entire system of the in-ear wearable bio-signal monitoring device, comprising a wine-glass-shaped transmitter, the designed receiving coil, and a monitoring circuit, was fabricated. The measured dc-dc efficiency of the MR-WPT system was 16.08%.

A volumetric finite-difference method for the design of three-dimensional, arbitrary-structured MRI gradient coil.

A volumetric finite-difference based method is presented in this paper for the design of three-dimensional (3D), arbitrarily structured gradient coils in magnetic resonance imaging. In the proposed method, the coil space is discretized with quasi-rectangular elements, and the current density of each element is expressed by a finite-difference based numerical approximation of stream functions. The magnetic flux density at target field points can be calculated by those stream function values at all grids of the coil space. The optimization problem is constructed and solved to determine the stream function and coil patterns. This proposed method has been tested on several designs that include a shielded, ultra-short cylindrical coil, a partially shielded biplanar coil, and an asymmetric head coil with 3D geometries. The numerical results show that the proposed method is straightforward to implement and is versatile and suitable for designing complex structured gradient coils with high electromagnetic performance.

Development of Ingestible Thermometer With Built-in Coil Antenna Charged by Gastric Acid Battery and Demonstration of Long-Time in Vivo Telemetry

A safe and affordable ingestible thermometer measuring core body temperature has the potential to become a future healthcare device for versatile applications in daily life. In this study, we developed an ingestible thermometer charged by a gastric acid battery. The device can operate in bowels by using the charged energy in multilayer ceramic capacitors as a storage capacitor. Adopting this strategy for energy storage solves the issues related to a conventional button battery: risk of injury to the digestive tract, bad disposability, and degradation. Additionally, to make it easy to assemble a coil antenna and electrical circuits in the device automatically, we developed a fabrication process based on a vertical stacking process of printed circuit boards with coil patterns. The dimensions of the prototyped device were smaller than those of existing ingestible thermometers. In an experiment involving a dog, we successfully recorded the temperature in the digestive tract for 24 h in cycles of approximately 10 or 20 min, using a rectal thermometer and an existing ingestible thermometer as references. The temperature variations in time among our device, rectal thermometer, and existing ingestible thermometer were almost parallel. The recording ability of the core body temperature using our device has the potential to measure basal body temperature during sleep, the circadian rhythm, and fever type easily and robustly in daily life. Our ingestible thermometer is a step toward the development of sensors that can be swallowed for preventive medicine and health promotion.

Feasibility analysis of a modular uniform magnetic field coil.

In this paper, a feasibility analysis of a modular uniform magnetic field coil is provided. The modular uniform magnetic field coil consists of n2 square coil units. By adjusting the number of coil units or the current in the coil units, different sizes and patterns of uniform magnetic field coils can be easily formed to meet different experimental requirements. An analytical model of the modular uniform magnetic field coil considering the gap between coil units is first developed based on the Biot-Savart law and the superposition principle, and the analytical model is verified by the 3D finite element method. Then, the characteristics of the modular uniform magnetic field coil are analyzed and compared with the traditional Helmholtz coil, demonstrating the advantages of the proposed magnetic field coil. These advantages precisely verify the original intention of the modular uniform magnetic field coil proposed in this paper. Finally, a robustness analysis of the modular magnetic field coil is performed, including the effects of gap between coil units and assembly misalignment on the performance of the modular uniform magnetic field coil.

Experimental Study on Quench Protection of HTS Magnet Composed of Multiple Pancake-Coils by Use of Auxiliary Resistive Shunt Loop Method

In the authors' previous work, a new quench protection method to reduce hot-spot temperature and increase quench detection voltage was proposed to protect an HTS magnet composed of multiple pancake sub-coils from quench damages (Toriyama et al., 2019). In the method, a current of a quenching sub-pancake coil is transferred to the other sub-coils of the magnet forming auxiliary resistive shunt loop (ARSL) by resistively shorting the other sub-coils. In this work quench behaviors of the pancake sub-coils of a model magnet was investigated by a simulation experiment using small scale test pancake coils wound of YBCO wire. Current patterns of the sub-pancake coils of a model magnet at a quench event were calculated for the case that ARSL method was applied, and in the experiment, the same patterns of the calculated currents were applied to the quenching test coils by a controllable current supply. Experimental results show effectiveness of the new method.

Single-Layer Transmitter Array Coil Pattern Evaluation toward a Uniform Vertical Magnetic Field Distribution

A uniform magnetic field distribution is a critical aspect in the transmitter array coil design process for achieving a homogenous vertical magnetic field distribution. The free position and orientation features can thus be implemented in the wireless power charging system. This paper presents vertical magnetic field distribution generated by a single-layer circular flat spiral air core transmitter array coil model analysis and evaluation using a numerical analysis method. This method is developed based on the off-symmetry axis magnetic field distribution due to a circular current loop derived from the Biot-Savart law. The proposed evaluation criteria are used to obtain the vertical magnetic field distribution characteristic of the evaluated array coil model. The vertical magnetic field distribution of several circular flat spiral air core coils, in both single and array coil models with different coil geometries were investigated to obtain the relation between the coil parameters and the distance between the adjoining coil centers to generate uniform vertical magnetic field distribution. A case study was also conducted to analyze and evaluate several array coil model patterns (1 × 2 array coil, 1 × 3 array coil, 2 × 2 array coil, 2 × 3 array coil) to meet uniform vertical magnetic field distribution. The array coil model is composed of an identical single circular flat spiral air-core coil. Every single coil has inner coil diameter (Di), outer coil diameter (Do), wire diameter (W), pitch (P) and a number of turns (N) at 25 mm, 47.8 mm, 0.643 mm, 0.03 mm, 17 respectively. The study and evaluation of several array coil pattern models show that the distance between the adjoining coil centers should be defined close to the half of coil outer diameter (1/2Do) to generate close to uniform vertical magnetic field distribution. The vertical magnetic field distribution average and magnetic field effective transmitting areas array coil model with the given coil parameters changing as the effect in variation in distances between the adjoining coil centers.

Triangular coil pattern of local radius of gyration face for heterogeneous face recognition

This paper puts forward a novel methodology for Heterogeneous Face Recognition (HFR), where we present a new-fangled image representation technique called the Local Radius of Gyration Face (LRGF), which has been theoretically proved to be invariant to changes in illumination, rotation and noise. Finally, a novel Local Triangular Coil Binary Pattern (LTCBP) is presented so as to apprehend the local variations of the LRGF attributes, and the method has been entitled as the Triangular Coil Pattern of Local Radius of Gyration Face (TCPLRGF). The proposed algorithm has been tested on a number of challenging databases to study the precision of the TCPLRGF method under varying condition of illumination, rotation, noise and also the recognition accuracy of sketch-photo and NIR-VIS image. The Rank-1 recognition accuracy of 98.27% on CMU-PIE Database, 98.09% on Extended Yale B Database, 96.35% on AR Face Database, 100% on CUHK Face Sketch (CUFS) Database, 89.01% on LFW Database and 98.74% on the CASIA-HFB NIR-VIS Database exhibits the supremacy of the proposed strategy in Heterogeneous Face Recognition (HFR) under various conditions, compared to other recent state-of-the-art methods. For reckoning the similarity measure between images, a hybridized approach amalgamating the Jaccard Similarity method and the standardized L1 norm approach has been taken into account.

An Inverter Topology for Wireless Power Transfer System with Multiple Transmitter Coils

This paper presents an inverter topology for a wireless power transfer (WPT) system that is intended to reduce the component counts and complexity of the conventional excitation circuit for multiple transmitter coils. The proposed inverter topology requires only (n+2) power switches, where “n” is the number of transmitter coils. An excitation of a proper transmitter coil pattern with regard to the receiver coil position is determined. The output voltage can be regulated through the primary-side control by adjusting the duty cycles of the inverter switches. A detection method of the receiver coil position is presented using the detection switches on the secondary side. The detection algorithm is based on the reflected impedance knowledge and requires only a current sensor on the primary side. A proper transmitter coil pattern is energized to ensure maximum transfer efficiency throughout the operation. The proposed system is experimentally validated on the created 500-watt WPT multi-coil system. After the receiver coil is placed in a designated area, the proper transmitter coil pattern can be automatically selected and energized. The output voltage can be regulated to a desired value under the typical operation conditions, including load change.

Sinistral, Dextral, and Mixed Coiling Patterns Observed in Heligmonellid Nematodes (Trichostrongyloidea)

Coiling patterns of heligmonellid nematodes were examined for 520, 208, and 33 individuals of Nippostrongylus brasiliensis, Orientostrongylus tenorai, and Sabanema sp., respectively, collected from murine rodents of Indonesia. Besides typical sinistral coiling, complete dextral coiling was found in 3.3% of N. brasiliensis and 12.1% of Sabanema sp. Mixed coiling with partial sinistral and dextral patterns was also observed in 38.8% of N. brasiliensis, 60.7% of Sabanema sp., and 3.4% of O. tenorai. In dextral coils, the left ventral area with large ridges was located inside as in sinistral coils, keeping the ability to cling to intestinal villi. The cuticular dilatation at left to left dorsal area was located caudally in sinistral coils but rostrally in dextral coils. Presence of mixed coiling indicates that the coiling patterns can change. As the transition of coiling pattern accompanies a change in direction of coil axis, it is surmised that the dextral coiling may be chosen when a worm leaves a villus to move to another villus.

Magnetic Analysis of Copper Coil Power Pad with Ferrite Core for Wireless Charging Application

Wireless charging can automate the charging of electrical devices, very quickly connected with IoT based smart systems. The efficiency of wireless charging collectively depends on the design of the power pad, the frequency level of power transfer, the distance between the transmitter and receiver, alignment between the coils. Coils design comprehend the shape of the coil, material of the coil used, the thickness of the wire used and core shape and material used in the core. The manuscript compares the power pad coil shapes, with the introduction of ferrite material core across the coils to design an extremely efficient power pad for the wireless charging of electric vehicle. A 3D finite element method was used for analysis, due to the unconventional distribution of the flux. Only three types of coils, D, DD, and DDQ, are taken for analysis of magnetic core introduction. The comparison is made based on simulation results, magnetic flux pattern as well as data imported from the results. Ansys 3D Maxwell simulation software is used to simulate the magnetic pattern of the power pad coils. Finally, the results show the DD type coil shows the best magnetic fields and the maximum coupling coefficient with the maximum misalignment tolerance and the ferrite core across the coils have aligned the magnetic flux pattern and slightly improved the coupling coefficient.

To coil or not to coil: application practices, perception and efficacy of mosquito coils in a malaria-endemic community in Ghana.

Although evidence of mosquito coils' impact on disease epidemiology is limited, they are popularized as mosquito-borne disease prevention devices. Their usage affects the environment, human and mosquito health. This study investigated the perception, usage pattern and efficacy of coils in a predominantly poor malaria-endemic Ghanaian peri-urban area. Information on protection methods, perception and usage pattern was garnered using questionnaires. The efficacy of commonly used coils in the area was then assessed on the malaria vector, Anopheles gambiae, in a glass chamber. Sole or co-application of mosquito control methods and risky usage practices were reported. Coils were deemed harmful to humans and mosquitoes, and their perceived effectiveness varied, with several factors influencing their purchase. High d-allethrin concentration coils induced quicker mosquito knockdown; however, mortality was less than 85%. The coil usage pattern compromises users' health and can enhance mosquito tolerance to d-allethrin. The coils were ineffective against the vector, outlining a dichotomy between the users' perception of efficacy and the observed efficacy. Hence, the usage of other safer and more effective vector control methods should be encouraged to protect households.