Coil Distance Research Articles

A Low-Frequency Versatile Wireless Power Transfer Technology for Biomedical Implants

Implantable biomedical sensors and actuators are highly desired in modern medicine. In many cases, the implant's electrical power source profoundly determines its overall size and performance . The inductively coupled coil pair operating at the radio-frequency (RF) has been the primary method for wirelessly delivering electrical power to implants for the last three decades . Recent designs significantly improve the power delivery efficiency by optimizing the operating frequency, coil size and coil distance . However, RF radiation hazard and tissue absorption are the concerns in the RF wireless power transfer technology (RF-WPTT) , . Also, it requires an accurate impedance matching network that is sensitive to operating environments between the receiving coil and the load for efficient power delivery . In this paper, a novel low-frequency wireless power transfer technology (LF-WPTT) using rotating rare-earth permanent magnets is demonstrated. The LF-WPTT is able to deliver 2.967 W power at ∼180 Hz to an 117.1 Ω resistor over 1 cm distance with 50% overall efficiency. Because of the low operating frequency, RF radiation hazard and tissue absorption are largely avoided, and the power delivery efficiency from the receiving coil to the load is independent of the operating environment. Also, there is little power loss observed in the LF-WPTT when the receiving coil is enclosed by non-magnetic implant-grade stainless steel.

Modeling, fabrication and characterization of micro-coils as magnetic inductors for wireless power transfer

This work presents modeling, fabrication and characterization of planar microcoils for wireless power transfer in medical implanted devices, proposing integrated technology as a way to reduce the dimensions and achieve higher efficiency. The wireless power transfer (WPT) architecture is composed by: a primary coil carrying the alternating current signal to generate a magnetic field and the receiving coil to convert magnetic field in current, that is located parallel to the primary one with a gap between the two inductors.In the proposed design the two microcoils are circular with short-circuited turns to minimize electrical resistance. The electrical measurements on the fabricated test structures with different pitch sizes show a dramatic reduction of coil resistance to few ohms with respect to classic coil design. The experimental values of the resistance and inductance (from 24 to 45nH) are in good agreement with the analytical model.The efficiency of fabricated microcoils for wireless power transfer is predicted by Finite element method (FEM) at 10kHz modeling in terms of coupling factor ranging the distance of the inductors from 0 to 1mm. FEM results show that the transfer efficiency can be further enhanced by the introduction of a ferromagnetic material on the back side of each coil in order to confine the magnetic field. High coupling factor above 65% can be achieved with this shielding layer, even with lowest pitch value and high coil distances.

Optimization of Induction Brazing Parameters for Stellite Strip of Steam Turbine Blade Using Taguchi-Neural Network

To repair the damaged of steam turbine blades, the method of increasing wear resistance of the blade leading edge with brazing of stellite plates by induction heating has been addressed in this work. Induction brazing of a Cobalt-based alloy to SUS410Cb steam turbine blades in an electrical power plant has been carried out. Ag-Cu-Zn based material was chosen to be the filler metal sandwiched between the stellite strip and the turbine blade. In order to cope with the large size of blades, an automatic brazing process which used moving induction coils has been developed. In the proposed brazing process, there are three parameters that significantly affect the quality of the brazing joints including coil distance, moving coil speed, and power of induction heating. In this work, the optimum choice of brazing parameters is obtained by using a Taguchi-neural network technique. According to the results of our previous work, it is recommended to attain the temperature distribution at around 750°C for maximum strength and good quality brazing in the brazed components. The objective for the evaluation of brazing quality is therefore a function of this temperature and defined as the temperature deviation from the best brazing temperature. The design is verified and confirmed by the manufacturing of brazed joint applying suggested parameters. The experimental results showed that the Taguchi-Neural network method resulted in a better brazed quality than when using only the Taguchi method.

A systematic review of mosquito coils and passive emanators: defining recommendations for spatial repellency testing methodologies

Mosquito coils, vaporizer mats and emanators confer protection against mosquito bites through the spatial action of emanated vapor or airborne pyrethroid particles. These products dominate the pest control market; therefore, it is vital to characterize mosquito responses elicited by the chemical actives and their potential for disease prevention. The aim of this review was to determine effects of mosquito coils and emanators on mosquito responses that reduce human-vector contact and to propose scientific consensus on terminologies and methodologies used for evaluation of product formats that could contain spatial chemical actives, including indoor residual spraying (IRS), long lasting insecticide treated nets (LLINs) and insecticide treated materials (ITMs). PubMed, (National Centre for Biotechnology Information (NCBI), U.S. National Library of Medicine, NIH), MEDLINE, LILAC, Cochrane library, IBECS and Armed Forces Pest Management Board Literature Retrieval System search engines were used to identify studies of pyrethroid based coils and emanators with key-words “Mosquito coils” “Mosquito emanators” and “Spatial repellents”. It was concluded that there is need to improve statistical reporting of studies, and reach consensus in the methodologies and terminologies used through standardized testing guidelines. Despite differing evaluation methodologies, data showed that coils and emanators induce mortality, deterrence, repellency as well as reduce the ability of mosquitoes to feed on humans. Available data on efficacy outdoors, dose–response relationships and effective distance of coils and emanators is inadequate for developing a target product profile (TPP), which will be required for such chemicals before optimized implementation can occur for maximum benefits in disease control.

Numerical simulation of effects of cusp magnetic field on oxygen concentration of 300 mm CZ-Si

In magnetic Czochralski (MCZ) silicon growth, the distance and diameter of the electrified coils may affect the magnetic field intensity and melt flow. By changing the above parameters, the optimum geometric configuration of the coils was attempted. Through analyses of the oxygen concentration distribution of the crystal/melt interface, axial and radial velocity distribution of melt and the magnetic field intensity in the melt, it is found that smaller diameter of coils contributes to reducing the needed current intensity and production costs. For a given current intensity, there is a best distance of coils when the oxygen concentration at crystal/melt interface reaches the lowest.

Variation of stimulation intensity in transcranial magnetic stimulation with depth

The quantification of stimulation intensity in transcranial magnetic stimulation (TMS) as a function of depth is of interest in order to adjust stimulator output when non-motor regions are stimulated. Currently, a linear increase of stimulator output to correct for depth has been suggested. This is contrary to the physical properties of the electric field that is induced by the stimulation coil as measured in vitro.For two stimulation coils, we determined the characteristics of their field in air. We then measured motor thresholds for the abductor hallucis muscle of 10 healthy subjects. Coil position, distance from the scalp, and orientation were controlled with a head tracking robotic system that corrected for head movements.In both coils an approximately exponential increase, rather than a linear increase, of the threshold with the scalp–coil distance was measured. The slope of the increase was slightly smaller than expected from the field characteristic, but overall in good agreement.With respect to the depth of the TMS target, different results were obtained from the threshold ratios of the coils and from the slopes of the threshold increase with distance.For the adjustment of stimulator output to scalp-to-cortex distances exponential functions with parameters motivated by physical properties of the coils should be used. Estimation of the target depth from the thresholds, with different coils, is not reliable. Our results resolve a conflict between physiological data and physical properties of TMS coils. They provide a more reliable base for depth dependent corrections for TMS stimulator output.

Evaluation of SAR in a human body model due to wireless power transmission in the 10 MHz band

This study discusses a computational method for calculating the specific absorption rate (SAR) due to a wireless power transmission system in the 10 MHz frequency band. A two-step quasi-static method comprised of the method of moments and the scalar potential finite-difference method are proposed. The applicability of the quasi-static approximation for localized exposure in this frequency band is discussed by comparing the SAR in a lossy dielectric cylinder computed with a full-wave electromagnetic analysis and the quasi-static approximation. From the computational results, the input impedance of the resonant coils was affected by the existence of the cylinder. On the other hand, the magnetic field distribution in free space and considering the cylinder and an impedance matching circuit were in good agreement; the maximum difference in the amplitude of the magnetic field was 4.8%. For a cylinder–coil distance of 10 mm, the difference between the peak 10 g averaged SAR in the cylinder computed with the full-wave electromagnetic method and our quasi-static method was 7.8%. These results suggest that the quasi-static approach is applicable for conducting the dosimetry of wireless power transmission in the 10 MHz band. With our two-step quasi-static method, the SAR in the anatomically based model was computed for different exposure scenarios. From those computations, the allowable input power satisfying the limit of a peak 10 g averaged SAR of 2.0 W kg−1 was 830 W in the worst case exposure scenario with a coil positioned at a distance of 30 mm from the chest.

Evaluation of Wireless Resonant Power Transfer Systems With Human Electromagnetic Exposure Limits

This study provides recommendations for scientifically sound methods of evaluating compliance of wireless power transfer systems with respect to human electromagnetic exposure limits. Methods for both numerical analysis and measurements are discussed. An exposure assessment of a representative wireless power transfer system, under a limited set of operating conditions, is provided in order to estimate the maximum SAR levels. The system operates at low MHz frequencies and it achieves power transfer via near field coupling between two resonant coils located within a few meters of each other. Numerical modeling of the system next to each of four high-resolution anatomical models shows that the local and whole-body SAR limits are generally reached when the transmit coil currents are 0.5 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RMS</sub> - 1.2 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RMS</sub> at 8 MHz for the maximal-exposure orientation of the coil and 10-mm distance to the body. For the same coil configurations, the exposure can vary by more than 3 dB for different human models. A simplified experimental setup for the exposure evaluation of wireless power transfer systems is also described.

Stray Capacitance of a Magneto Cumulative Generator Including $N$-Turn, Single-Layer, Solid, and Round Conductor With Insulating Coating

This paper presents a new method to calculate stray capacitance of coil turns of magneto flux cumulative generator. The proposed method depends on the coil geometrical properties. The presented analysis in this paper is based on the calculation of capacitance between two adjacent turns and capacitance between the coil turns and the central cylindrical liner of the generator for a single-layer coil with N series turns having an integrated round cross section. Moreover, the effects of the insulating coating of winding, winding pitch, distance of coil turns to the central cylindrical liner on the stray capacitance, and the sensitivity analysis of effective parameters in the creation of stray capacitance between coil turns and also between coil turns and the central cylindrical liner are considered in this paper. Simulation results show that the proposed method is very useful for the designing geometrical structure of the magneto cumulative generator coil.

Fault-Tolerant Permanent Magnet Synchronous Linear Motor

The principle and characteristics of Fault-tolerant Permanent Magnet Synchronous Linear Motor are introduced. The design or computational method of the polar distance of concentrated winding coil, the armature parameters, the armature winding parameters, the coil diameter, the distance from the adjacent armature windings are given. The magnetic thrust equation is derived, and the core issues are analyzed. It provided theoretical basis for structural optimization of the Fault-tolerant Permanent Magnet Synchronous Linear Motor.

Design and Optimization of Resonance-Based Efficient Wireless Power Delivery Systems for Biomedical Implants

Resonance-based wireless power delivery is an efficient technique to transfer power over a relatively long distance. This technique typically uses four coils as opposed to two coils used in conventional inductive links. In the four-coil system, the adverse effects of a low coupling coefficient between primary and secondary coils are compensated by using high-quality (Q) factor coils, and the efficiency of the system is improved. Unlike its two-coil counterpart, the efficiency profile of the power transfer is not a monotonically decreasing function of the operating distance and is less sensitive to changes in the distance between the primary and secondary coils. A four-coil energy transfer system can be optimized to provide maximum efficiency at a given operating distance. We have analyzed the four-coil energy transfer systems and outlined the effect of design parameters on power-transfer efficiency. Design steps to obtain the efficient power-transfer system are presented and a design example is provided. A proof-of-concept prototype system is implemented and confirms the validity of the proposed analysis and design techniques. In the prototype system, for a power-link frequency of 700 kHz and a coil distance range of 10 to 20 mm, using a 22-mm diameter implantable coil resonance-based system shows a power-transfer efficiency of more than 80% with an enhanced operating range compared to ~40% efficiency achieved by a conventional two-coil system.

Combining multiple signals of an electromagnetic induction sensor to prospect land for metal objects

ABSTRACTBuried unexploded ammunition is a major problem on arable land in former battle areas. Many battlefields of the First World War (WWI) still contain a lot of unexploded shells just below the plough layer, posing serious threats to soil editors and trenchers. Electromagnetic induction (EMI) sensors have been used for a variety of agricultural and archaeological purposes to map the natural soil variability and to locate buried archaeological remains. Besides its sensitivity to variations in soil texture and anthropogenic disturbances, EMI proves to respond strongly to metal objects in the soil. Most EMI sensors rely on a single signal, with magnitude and sign of the metal anomalies differing according to the instruments coil distance and separation. The multi‐coil EMI sensor, the DUALEM‐21S, provides four simultaneous apparent electrical conductivity (ECa) signals enhancing significantly the possibilities for signal processing. To calibrate our instrument, we buried different masses of metal at different depths. The four ECa measurements showed a response to the metal objects down to 1.2 m. The measurements were subtracted by their gradual trend to obtain the local anomalies (ΔECa). A combination of these four ΔECa’s was used to amplify the signal response to metal, influenced by both depth and mass of the buried objects. At an intensively shelled former WWI battle field near Ypres (Belgium), a detailed prospection was conducted with the DUALEM‐21S. Based on our multi‐signal procedure, we located 40 positions, 20 where we predicted buried metal and 20 where we expected that no metal was present within 1.2 m depth. There were no false negative predictions and at the 20 locations where we expected metal, shells up to 90 kg were excavated. As a final outcome we produced a map with predictions of the mass of metal objects in the soil assuming a fixed depth and alternatively a map with predictions of the depth of metal objects assuming a given mass.Apart from their potential for agricultural and archaeological investigations, multi‐ECa signals were shown to be useful for locating metal objects, like unexploded WWI shells, in the top 1.2 m of soil.

Assessment of standard coil positioning in transcranial magnetic stimulation in depression

Transcranial magnetic stimulation (TMS) is a non-invasive technique used in the treatment of major depression. Meta-analyses have shown that it is more efficient than a placebo and that its efficacy is enhanced by the optimum tuning of stimulation parameters. However, the stimulation target, the dorsolateral prefrontal cortex (DLPFC), is still located using an inaccurate method. In this study, a neuronavigation system was used to perform a comprehensive quantification of target localization errors. We identified and quantified 3 sources of error in the standard method: cap repositioning, interexpert variability in coil positioning and distance between the stimulated point and the expected target. For cap repositioning, the standard deviation was lower than 5mm in the 3 axes. For interexpert variability in coil positioning, the spatial dispersion of the points was higher than 10mm in 2 of the 3 axes. For interindividual anatomical variability, the distance between the actual “reference” DLPFC and its standard determination was greater than 20mm for 54% of the subjects, while one subject out of eleven was correctly targeted which means 10mm or less from the reference. Results showed that interindividual anatomical variability and interexpert variability were the two main sources of error using the standard method. Results demonstrate that a neuronavigation system is mandatory to conduct reproducible and reliable studies.

Novel architecture and algorithm for remote interrogation of battery-free sensors

This paper presents an inductive telemetry platform system for the continuous, real-time and simultaneous remote measurement in harsh environment. First, a SOL (self-oscillating loop) topology for the remote interrogation of wireless battery-less passive sensors is described. This system uses a capacitive sensor configured as an LC-tank whose resonant frequency shifts with the physical measurement. Such a system is generally based on an impedance analyzer in order to measure this frequency shift. In fact, if you increase the distance between the sensor and the reader, the sensibility is not sufficient to use the SOL technique. To overcome this issue, an anti-resonance cancellation, realized with a simple RC cell, is implemented. However, this architecture is dedicated only for a single capacitive sensor. Second, based on an efficient algorithm used for system identification purpose, a readout unit for multiple sensors is proposed. The overall performances of these architectures are analyzed with respect to coupling factor and sensor parameters. Using these two approaches, tests show promising results at mutual coil distances up to 5 cm.

Using Increased Structural Detail of the Cortex to Improve the Accuracy of Modeling the Effects of Transcranial Magnetic Stimulation on Neocortical Activation

Transcranial magnetic stimulation (TMS) is a noninvasive technique that can alter brain activation by inducing electrical current in neurons using dynamic magnetic fields. Because of its painless nature, clinical usage has expanded to diagnostic purposes and therapeutic treatments. However, several issues and challenges still exist for TMS. A very limited understanding of the interaction between magnetic fields, cortical structure, and consequent brain excitation is currently available. Most previously published models lack key anatomical details that are essential elements in calculating induced electric fields critical to brain activation. In this study, gross human brain and head structures were derived using multiple modality images and a finite-element model was constructed. Furthermore, microstructural detail was incorporated using neocortical columnar structures. Using this detailed model, we investigated the influence of TMS coil position, distance and orientation on induced electric fields, and neocortical activation. Several activation standards and conductivity values were tested for their impact on the distribution of neocortical activation. Optimized activation patterns agreed well with published clinical experiments, under similar coil configurations. A structurally detailed finite-element model capable of accurately predicting neocortical activation for a given coil/magnetic field profile may provide a critical resource for understanding the electrophysiological consequences of TMS and for further refinement of this important technique.

Rotational speed measurement using induction coil sensor inserted in the magnetic field of the rotational permanent magnet

In this paper the application of induction coil sensor, inserted into a mechanical rotational magnetic field of the rotational permanent magnet for the rotational speed measurements has been proposed and described. The sensor is simple, low-cost, and applicable for machine shafts speed measurements (spatially available and unavailable). On the shaft, whose rotational speed is measured, the rotational permanent magnet is fixed. From measured frequency value of induced voltage in the coil sensor the rotational speed value is given using PC with adequate software, interface for the analogue signal conditioning and AD converter. The rotational speed dependence on the induction coil sensor distance from the rotational permanent magnet has been given. The induced voltage dependence on the coil distance from the magnet has been obtained as well. The maximum distance for precise measurements of rotational speed has been determined from those relations.

Engineering challenges in designing an attractive compact stellarator power plant

This paper summarizes the key engineering outcomes from the ARIES-CS study. The most promising power plant concept is described. The engineering design of the fusion power-core components (including the blanket and divertor) and the coil structural design are briefly described along with a summary of the key results from the detailed neutronics, stress, thermal-hydraulic and power cycle analyses performed in support of the design. The preferred port-based maintenance scheme is summarized. The key stellarator-specific challenges affecting the design are highlighted, including the impact of the minimum plasma–coil distance, the coil design requirements and the need for alpha power accommodation.

A hybrid optimization method for biplanar transverse gradient coil design

The optimization of transverse gradient coils is one of the fundamental problems in designing magnetic resonance imaging gradient systems. A new approach is presented in this paper to optimize the transverse gradient coils' performance. First, in the traditional spherical harmonic target field method, high order coefficients, which are commonly ignored, are used in the first stage of the optimization process to give better homogeneity. Then, some cosine terms are introduced into the series expansion of stream function. These new terms provide simulated annealing optimization with new freedoms. Comparison between the traditional method and the optimized method shows that the inhomogeneity in the region of interest can be reduced from 5.03% to 1.39%, the coil efficiency increased from 3.83 to 6.31 mT m−1 A−1 and the minimum distance of these discrete coils raised from 1.54 to 3.16 mm.

A synchronous rectification using a digital PLL technique for contactless power supplies

Transcutaneous energy transmission systems for the artificial heart with synchronous rectifiers were developed. The input voltage is 24 V and the output voltage is 9 to 18 V. This paper shows the efficiency of the system with synchronous rectifier using a digital PLL technique achieved 92% DC-DC efficiency at 5 mm coil distance. Using the ferrite core and a digital PLL technique, inductor and capacitor were eliminated from the rectifier circuit. And the circuit was mounted to the back of the secondary coil. And we developed the control systems for stable output voltage and apply this result to other contact power supply system.

P12.12: Relationship between single umbilical artery in twin pregnancies and pregnancy outcome

manifestations of the underlying hemodynamic imbalance may be present as early as the first trimester of gestation and may have a profound impact on the development of the UC angioarchitecture. Methods: Twenty four consecutive monochorionic twins with TTTS were included into the study. The length of one complete umbilical vascular coil (distance between the right outer surface of consecutive arterial coils) was measured in a longitudinal section of the UC. The coiling index (CI), defined as the reciprocal value of that measurement, was calculated. The UC coiling pattern was classified as normal or abnormal [uncoiled, hypocoiled (CI 90th centile)] according to local reference ranges. Atypical (uncoordinated, supercoiling) coiling was classified according to Raio et al. (ISUOG 2003, OC 205). Results: Nine (37.5%) and 8 (33.3%) cases were treated with endoscopic laser coagulation and amnionreduction, respectively. In the remaining 7 (29.2%) cases, no treatment was undertaken. The surviving rate was 72.2%, 56.3%, and 21.4% in the laser, amnioreduction and no treatment group, respectively. The donor twin showed in 22 (91.7%) cases a less twisted UC than the recipient twin. Of these, 12 (54.5%) were uncoiled and 5 (22.7%) hypocoiled. On the other hand, the UCs of recipient twins were characterized by a high percentage of atypical [4 (16.7%) with supercoiling, and 8 (33.3%) with uncoordinated coiling], and abnormal coiling patterns [4 (16.7%) with hypercoiling, 2 (8.3%) hypocoiling]. Only 13 (27.1%) cases had a CI within normal ranges for gestational age. In one case informations on UC angioarchitecture was available from the first trimester and the UCs were uncoiled and atypical, respectively. Conclusions: Monochorionic twins with TTTS have different UC coiling patterns.