Showing papers on "Electromagnetic coil published in 2007"

A micro electromagnetic generator for vibration energy harvesting

Abstract: Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes This paper presents a small (component volume 01 cm3, practical volume 015 cm3) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field Magnet size and coil properties were optimized, with the final device producing 46 µW in a resistive load of 4 k? from just 059 m s-2 acceleration levels at its resonant frequency of 52 Hz A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry The generator delivers 30% of the power supplied from the environment to useful electrical power in the load This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency

Inductive power source and charging system

Abstract: A portable inductive power source, power device, or unit, for use in powering or charging electrical, electronic, battery-operated, mobile, and other devices is disclosed herein. In accordance with an embodiment the system comprises a pad or similar base unit that contains a primary, which creates an alternating magnetic field by means of applying an alternating current to a winding, coil, or any type of current carrying wire. A receiver comprises a means for receiving the energy from the alternating magnetic field from the pad and transferring it to a mobile or other device. In some embodiments the receiver can also comprise electronic components or logic to set the voltage and current to the appropriate levels required by the mobile device, or to communicate information or data to and from the pad. Embodiments may also incorporate efficiency measures that improve the efficiency of power transfer between the charger and receiver.

Induction coil sensors—a review

Abstract: This review describes induction coil sensors, which are also known as search coils, pickup coils or magnetic loop sensors. The design methods for coils with air and ferromagnetic cores are compared and summarized. The frequency properties of coil sensors are analysed and various methods for output signal processing are presented. Special kinds of induction sensors, such as Rogowski coil, gradiometer sensors, vibrating coil sensors, tangential field sensors and needle probes are described. The applications of coil sensors as magnetic antennae are also presented.

Feedback Analysis and Design of RF Power Links for Low-Power Bionic Systems

Abstract: This paper presents a feedback-loop technique for analyzing and designing RF power links for transcutaneous bionic systems, i.e., between an external RF coil and an internal RF coil implanted inside the body. The feedback techniques shed geometric insight into link design and minimize algebraic manipulations. We demonstrate that when the loop transmission of the link's feedback loop is -1, the link is critically coupled, i.e., the magnitude of the voltage transfer function across the link is maximal. We also derive an optimal loading condition that maximizes the energy efficiency of the link and use it as a basis for our link design. We present an example of a bionic implant system designed for load power consumptions in the 1-10-mW range, a low-power regime not significantly explored in prior designs. Such low power levels add to the challenge of link efficiency, because the overhead associated with switching losses in power amplifiers at the link input and with rectifiers at the link output significantly degrade link efficiency. We describe a novel integrated Class-E power amplifier design that uses a simple control strategy to minimize such losses. At 10-mW load power consumption, we measure overall link efficiencies of 74% and 54% at 1- and 10-mm coil separations, respectively, in good agreement with our theoretical predictions of the link's efficiency. At 1-mW load power consumption, we measure link efficiencies of 67% and 51% at 1- and 10-mm coil separations, respectively, also in good accord with our theoretical predictions. In both cases, the link's rectified output dc voltage varied by less than 16% over link distances that ranged from 2 to 10 mm

Motor drive circuit with short startup time

Abstract: An H-bridge circuit is connected to a coil of the vibration motor that is to be driven. A comparator receives Hall signals indicating position information of a rotor of the vibration motor, and converts to an FG signal. A pulse width modulator generates a pulse-modulated pulse signal specifying energization time of the coil of the vibration motor. The pulse width modulator, in a first mode, after commencing start-up of the vibration motor, sets a duty ratio of the pulse signal to 100%, and after that, switches the duty ratio to a predetermined value in accordance with rotational frequency of the motor. In a second mode, the duty ratio of the pulse signal continues to be set to 100%. In a third mode, frequency and the duty ratio of the pulse signal are set based on a control signal of a pulse form inputted from outside. The control signal is used also in switching mode.

Highly Sensitive and Easy-to-Use SQUID Sensors

Abstract: We have developed a novel family of low-noise superconducting quantum interference devices (SQUIDs) to cover a wide range of applications. These sensors are robust and easy to use without compromising noise performance. They are optimized for operation with our high-speed direct-coupled flux-locked loop (FLL) electronics XXF-1. For the readout of cryogenic detectors, series arrays of 16 SQUIDs with 3 nH input inductance were designed which can be cooled down and operated in the Earth's field without magnetic shield. A compact gradiometric design allows the chips to be mounted directly on a Cu block at the cold stage of a mK cryostat without degradation in noise. A current noise level of 9 or 5 is achieved at 4.2 K or 300 mK, respectively. Ultra-high-speed operation was demonstrated by using a cold FLL electronics prototype in close proximity to the SQUID array. An extremely high FLL bandwidth of 350 MHz was achieved which outperforms any flux-locked SQUID before by more than an order of magnitude. For applications requiring a larger input inductance of up to 2 , integrated two-stage sensors were developed consisting of a single front-end SQUID with double-transformer coupling read out by a 16-SQUID array. These sensors are very convenient to use as their voltage-flux characteristic is essentially single-SQUID-like. Devices optimized for 4.2 K operation have a coupled energy resolution around 50 times Planck's constant . Heavily shunted devices for low-temperature operation typically achieve 80 or 8 at 4.2 K or 300 mK, respectively. An optional current limiter (Q-spoiler) at the input reduces the input current in pulsed applications like nuclear magnetic resonance or magnetorelaxometry. Integrated rf filters and resistor-capacitor shunts across the input coil result in smooth, well-behaved voltage-flux characteristics even at low temperatures 4.2 K. For magnetic field sensing applications, integrated miniature multiloop magnetometers were designed with maximized field resolution. For a 3 mm 3 mm chip size, a noise level of 3.6 is obtained at 4.2 K.

Three-dimensional distribution of the electric field induced in the brain by transcranial magnetic stimulation using figure-8 and deep H-coils.

Abstract: The H-coils are a novel development in transcranial magnetic stimulation (TMS), designed to achieve effective stimulation of deep neuronal regions without inducing unbearable fields cortically, thus broadly expanding the potential feasibility of TMS for research and for treating various neurologic disorders. This study compared the field distribution of two H-coil versions, termed H1 and H2, and of a standard figure-of-eight coil. Three-dimensional electrical field distributions of the H1 and H2-coils, designed for effective stimulation of prefrontal regions, and of a standard figure-8 coil, were measured in a head model filled with physiologic saline solution. With stimulator output at 120% of the hand motor threshold, suprathreshold field is induced by the H1-coil at lateral and medial frontal regions at depths of up to 4 to 5 cm, and by the H2-coil at medial prefrontal regions up to 2 to 3 cm, and at lateral frontal regions up to 5 to 6 cm. The figure-8 coil induced suprathreshold field focally under the coil's central segment, at depths of up to 1.5 cm. The ability of the H-coils to stimulate effectively deeper neuronal structures is obtained at the cost of a wider electrical field distribution in the brain. However, the H-coils enable simultaneous stimulation of several brain regions, whereas the depth penetration in each region can be controlled either by adjusting the stimulator output, and/or by varying the distance between various coil elements and the skull.

Designing Efficient Inductive Power Links for Implantable Devices

Abstract: Due to limited battery life and size limitations, many implantable biomedical devices must be powered inductively. Because of weak coupling between implanted and external coils, obtaining high power efficiency is a challenge. Previous authors have addressed the issue of optimizing power efficiency in these systems. In this paper, we further this analysis for the case of planar spiral "pancake" coils at low RF frequencies (100 kHz -10 MHz). We consider practical design constraints such as component variation, power amplifier limitations, and coil voltage limits. We introduce a new, complete expression for total power link efficiency.

Array compression for MRI with large coil arrays.

Abstract: Arrays with large numbers of independent coil elements are becoming increasingly available as they provide increased signal-to-noise ratios (SNRs) and improved parallel imaging performance. Processing of data from a large set of independent receive channels is, however, associated with an increased memory and computational load in reconstruction. This work addresses this problem by introducing coil array compression. The method allows one to reduce the number of datasets from independent channels by combining all or partial sets in the time domain prior to image reconstruction. It is demonstrated that array compression can be very effective depending on the size of the region of interest (ROI). Based on 2D in vivo data obtained with a 32-element phased-array coil in the heart, it is shown that the number of channels can be compressed to as few as four with only 0.3% SNR loss in an ROI encompassing the heart. With twofold parallel imaging, only a 2% loss in SNR occurred using the same compression factor.

Self-Capacitance of High-Voltage Transformers

Abstract: The calculation of a transformer's parasitics, such as its self capacitance, is fundamental for predicting the frequency behavior of the device, reducing this capacitance value and moreover for more advanced aims of capacitance integration and cancellation. This paper presents a comprehensive procedure for calculating all contributions to the self-capacitance of high-voltage transformers and provides a detailed analysis of the problem, based on a physical approach. The advantages of the analytical formulation of the problem rather than a finite element method analysis are discussed. The approach and formulas presented in this paper can also be used for other wound components rather than just step-up transformers. Finally, analytical and experimental results are presented for three different high-voltage transformer architectures.

Apparatus and method for controlling hybrid motor

Abstract: The present invention relates to an apparatus and method for controlling a hybrid motor, and more particularly, to an apparatus and method for controlling a hybrid motor, which uses a permanent magnet instead of a field coil for a rotor, winds a coil round a stator in a multi-phase independent parallel manner, fixes a rectifying type encoder to the rotor and connects a sensor to a driving circuit to smoothly start and rotate the hybrid motor, simplifies the configuration of the hybrid motor and reduce the manufacturing cost of the hybrid motor. The apparatus for controlling a hybrid motor having a multi-phase independent parallel stator coil comprises: an encoder attached to a rotor of the hybrid motor and operated in cooperation with a sensor in order to sense the pole of the rotor; the sensor for outputting a sensor signal indicating the polo of the rotor, sensed by the encoder; a speed input unit for generating a speed instruction signal for driving the motor; a power switching circuit for generating signals for driving the motor; a drive module for receiving the speed instruction signal and the sensor signal and outputting the speed instruction signal synchronized with the sensor signal as a signal for driving the motor; a power supply for applying a DC voltage to the power switching circuit; and a logic power supply for converting the DC voltage received from the power supply into a logic voltage and applying the converted logic voltage to the drive module. When the motor has n phases, the motor includes n power switching circuits and n drive modules.

A Wide-Band Power-Efficient Inductive Wireless Link for Implantable Microelectronic Devices Using Multiple Carriers

Abstract: This paper presents a novel inductive link for wireless transmission of power and data to biomedical implantable microelectronic devices using multiple carrier signals. Achieving higher data bandwidth without compromising the power efficiency is the driving force behind using multiple separate carriers. Two separate pairs of coils have been utilized for inductive power and forward data transmission, plus a pair of miniature antennas for back telemetry. One major challenge, however, is to minimize the interference among these carriers especially on the implantable side, where size and power are highly limited. Planar power coils with spiral shape are optimized in geometry to provide maximum coupling coefficient k. The data coils are designed rectangular in shape and wound across the power coils diameter to be oriented perpendicular to the power coil planes. The goal is to maximize data coils direct coupling, while minimize their cross-coupling with the power coils. The effects of coils geometry, orientation, relative distance, and misalignments on the coupling coefficients have been modeled and experimentally evaluated.

Contact-less power supply, contact-less charger systems and method for charging rechargeable battery cell

Abstract: The present invention relates to a contact-less power supply magnetically coupled to a battery device having a receiving coil therein, for contact-less charging the battery device, the contact-less power supply having a sending coil array including a plurality of sending coils for inducing a charging power to the receiving coil; and a driving means for detecting a sending coil magnetically coupled to the receiving coil and selectively driving only the detected sending coil.

High field magnetic resonance

Abstract: This document discloses, among other things, multi-channel magnetic resonance using a TEM coil.

Radio frequency coil technology for small-animal MRI.

Abstract: A review of the theory, technology, and use of radio frequency (RF) coils for small-animal MRI is presented. It includes a brief overview of MR signal-to-noise (S/N) analysis and discussions of the various coils commonly used in small-animal MR: surface coils, linear volume coils, birdcages, and their derivatives. The scope is limited to mid-range coils, i.e. coils where the product (fd) of the frequency f and the coil diameter d is in the range 2-30 MHz-m. Common applications include mouse brain and body coils from 125 to 750 MHz, rat body coils up to 500 MHz, and small surface coils at all fields. In this regime, all the sources of loss (coil, capacitor, sample, shield, and transmission lines) are important. All such losses may be accurately captured in some modern full-wave 3D electromagnetics software, and new simulation results are presented for a selection of surface coils using Microwave Studio 2006 by Computer Simulation Technology, showing the dramatic importance of the "lift-off effect". Standard linear circuit simulators have been shown to be useful in optimization of complex coil tuning and matching circuits. There appears to be considerable potential for trading S/N for speed using phased arrays, especially for a larger field of view. Circuit simulators are shown to be useful for optimal mismatching of ultra-low-noise preamps based on the enhancement-mode pseudomorphic high-electron-mobility transistor for optimal coil decoupling in phased arrays. Cryogenically cooled RF coils are shown to offer considerable opportunity for future gains in S/N in smaller samples.

Inductor Modeling in Wireless Links for Implantable Electronics

Abstract: This paper describes the ac power dissipation of coils as well as their self-capacitance, self-resonant frequency, and quality factor Q. In the past, self-resonant frequency was rarely calculated during design because of the lack of suitable closed-form design equations. However, coils are widely used in biomedical applications as inductive links for both power and data, and the power transfer capacity and the data rate of inductive links are determined by the operating frequency of the coils. The maximum operating frequency is limited by the self-resonant frequency of the coil. We present here an analytical express for the optimal frequency of a coil in terms of the design parameters. By varying the design parameters, we can move the optimal frequency close to the operating frequency, thereby boosting the efficiency of the inductive link. We have verified the derivation experimentally and shown it to be useful in optimizing coil Index performance.

Review Article Radio frequency coil technology for small-animal MRI

Abstract: A review of the theory, technology, and use of radio frequency (RF) coils for small-animal MRI is presented. It includes a brief overview of MR signal-to-noise (S/N) analysis and discussions of the various coils commonly used in small-animal MR: surface coils, linear volume coils, birdcages, and their derivatives. The scope is limited to mid-range coils, i.e. coils where the product (fd) of the frequency f and the coil diameterd is in the range 2-30MHz-m. Common applications include mouse brain and body coils from 125 to 750MHz, rat body coils up to 500MHz, and small surface coils at all fields. In this regime, all the sources of loss (coil, capacitor, sample, shield, and transmission lines) are important. All such losses may be accurately captured in some modern full-wave 3D electromagnetics software, and new simulation results are presented for a selection of surface coils using Microwave Studio 2006 by Computer Simulation Technology, showing the dramatic importance of the 'lift-off effect'. Standard linear circuit simulators have been shown to be useful in optimization of complex coil tuning and matching circuits. There appears to be considerable potential for trading S/N for speed using phased arrays, especially for a larger field of view. Circuit simulators are shown to be useful for optimal mismatching of ultra-low-noise preamps based on the enhancement-mode pseudomorphic high-electron-mobility transistor for optimal coil decoupling in phased arrays. Cryogenically cooled RF coils are shown to offer considerable opportunity for future gains in S/N in smaller samples. Copyright # 2007 John Wiley & Sons, Ltd.

Thickness measurement of non-magnetic plates using multi-frequency eddy current sensors

Abstract: A robust feature in multi-frequency eddy current (MEC) testing has been found that can be directly linked to the thickness of the plate under test. It is shown mathematically that the peak frequency of the imaginary part of the inductance change when an air-cored coil is placed next to a non-magnetic metallic plate is inversely proportional to the thickness of the plate for a given material. Experimental results indicate that this relationship also holds for a ferrite-cored U-shaped coil. In addition, this peak frequency has been shown to be relatively independent of lift-off variations. Use of this new feature provides a fast and accurate method to gauge the thickness of plates. Measurements made for a sample air-cored and ferrite U-cored coil next to copper and aluminium plates of various thicknesses verified the proposed method.

Novel gradient coils designed using a boundary element method

Abstract: Boundary element methods offer a powerful approach for designing gradient coils, allowing the generation of coils wounds on arbitrarily shaped surface so as to produce any form of field variation that is consistent with Maxwell's equations. These methods are based on meshing the current carrying surface into an array of boundary elements. In this work, we have extended boundary element methods that have previously been used used for coil design and integrated a powerful mesh generating program so as to produce coils with totally arbitrary geometry. Four examples are used to illustrate how the modified method provides a single versatile coil design protocol. These relate to the design of: i) shielded head gradients with highly asymmetric surface geometry that give the highest possible gradient field strengths; ii) very short, shielded gradient coils to allow improved access to the subject; iii) bi-planar coils generating highly asymmetric, stepped magnetic fields for use in fast imaging by multiple acquisition with micro-B0 arrays (MAMBA); iv) an insertable set of head gradient coils with shoulder cut-outs

System and method for inductively charging a battery

Abstract: An inductive charging system for recharging a battery. The system includes a charger circuit and a secondary circuit. The secondary circuit includes a feedback mechanism to provide feedback to the charger circuit through the inductive coupling of the primary coil and the secondary coil. The charger circuit includes a frequency control mechanism for controlling the frequency of the power applied to the primary coil at least partly in response to the feedback from the feedback mechanism.

Electric vehicle and power feeding device for vehicle

Abstract: PROBLEM TO BE SOLVED: To provide an electric vehicle which receives charging power wirelessly from a power supply outside the vehicle by a resonating method and can charge a vehicle-mounted electric storage device. SOLUTION: An electric vehicle 100 has a secondary self-resonant coil 110, a second coil 120, a rectifier 130, and an electric storage device 140. The secondary self-resonant coil 110 is combined with a primary self-resonant coil 240 of a power feeding device 200 magnetically by resonance of a magnetic field and is capable of receiving a high frequency power from the first self-resonant coil 240. The secondary coil 120 is capable of receiving power from the secondary self-resonant coil 110 by electromagnetic induction. The rectifier 130 rectifies the power received by the secondary coil 120. The electric storage device 140 stores the power rectified by the rectifier 130. COPYRIGHT: (C)2009,JPO&INPIT

Liquid dispensing system

Abstract: Dispensers for dispensing liquid from a concentrate/extract cartridge for a number of applications are also provided. The dispensers each include an actuating coil into which a dispensing tube is inserted. The concentrate/extract cartridge allows for dispensing a liquid in an accurate and repeatable manner. The cartridge includes an electromagnetically actuated piston connected to a valve. The piston includes an exterior ring supported by a hollow interior web that is configured to permit a flow of fluid into the dispensing tube when the valve body is in contact with the valve seat. A membrane is located below the web and is in sealing contact with the internal ring when the piston is activated. This allows a precise and repeatable amount of the liquid to be dispensed with each stroke. A controller is connected to the coil for controlling the actuation of the piston/valve assembly for dispensing the fluid in the cartridge.

Wave energy conversion system

Abstract: A wave energy conversion system converts wave energy within a wave medium into electrical energy. The wave energy conversion system includes a base substantially connected to a wave-medium floor, a tidal platform connected to the base and a tidal float connected to the tidal platform. An axle is connected to the tidal platform with an inductive coil positioned within the axle, such that an axis of the inductive coil is parallel to the axle. A magnetic sleeve includes a magnetic sleeve opening, such that the axle passes through the magnetic sleeve opening. A float member is connected to the magnetic sleeve. A wave moving through the wave causes displacement of the float member, causing the magnetic sleeve to move relative to the inductive coil and generate electrical energy within the inductive coil.

Material Formability and Coil Design in Electromagnetic Forming

Abstract: Pulsed electromagnetic forming is based on high-voltage discharge of capacitors through a coil. An intense transient magnetic field is generated in the coil and through interaction with the metal work-piece; pressure in the form of a magnetic pulse is built up to do the work. Data on formability of two aluminum alloys employed for exterior (6111-T4) and interior (5754) automotive body panels will be shown. Comparison of traditional Forming Limit Diagrams obtained by stretching of aluminum sheet with hemispherical punch to the results on formability, where hemispherical punch is replaced by a coil will be provided. It will be shown that material formability in high-rate forming conditions can significantly depend upon interaction with the forming die: electromagnetic forming into an open round window provides only slight improvement in formability, while forming in a V-shape die or into a conical die indicates a significant improvement. An important part of the electromagnetic forming technology is the design of the coil. The coil failure modes and measures preventing them are discussed.

Scanning system for lidar

Abstract: The present invention relates to a scanning system optimized for lidar that includes a nodding mirror, a rotary electromagnetic drive, a rotary optical encoder, and control circuitry The rotary electromagnetic drive includes a yoke incorporating a permanent magnet, and an arm having a coil at one end of the arm The coil is enclosed within the yoke, and an opposite end of the arm is coupled to the nodding mirror, such that movement of the coil within the yoke in response to a current causes the nodding mirror to rotate The rotary optical encoder produces an output signal in response to rotation of the nodding mirror, which serves as feedback to the control circuitry The control circuitry adjusts the current provided to the rotary electromagnetic drive in response to the output signal, such that the nodding mirror rotates in a reference scan pattern

Battery charging cradle and mobile electronic device

Abstract: A battery charging cradle and mobile electronic device include a battery charging cradle incorporating a primary coil which induces an AC magnetic flux to a specific portion of a planar, top plate of the cradle, and a rechargeable battery incorporated inside a bottom plate and charged by electric power which is induced to a secondary coil being electromagnetically coupled to the primary coil. The battery charging cradle has a positioning portion, so that the mobile electronic device is placed in a predetermined position by means of the positioning portion, the primary coil is electromagnetically coupled to the secondary coil, and thus the rechargeable battery incorporated in the mobile electronic device is charged.

Development of magnesium diboride (MgB2) wires and magnets using in situ strand fabrication method

Abstract: Since 2001 when magnesium diboride (MgB2) was first reported to have a transition temperature of 39 K, conductor development has progressed to where MgB2 superconductor wire in kilometer-long piece-lengths has been demonstrated in magnets and coils. Work has started on demonstrating MgB2 wire in superconducting devices now that the wire is available commercially. MgB2 superconductors and coils have the potential to be integrated in a variety of commercial applications such as magnetic resonance imaging, fault current limiters, transformers, motors, generators, adiabatic demagnetization refrigerators, magnetic separation, magnetic levitation, energy storage, and high energy physics applications. This paper discusses the progress on MgB2 conductor and coil development in the last several years at Hyper Tech Research, Inc.

System for inductive power transfer

Abstract: An inductive power transfer system including a synchronous drive system having a resonance control module. The resonance control module includes a primary coil module with a primary LC circuit. The resonance control module seeks and detects the resonant frequency of the primary LC circuit. The synchronous drive system further includes a switching coil amplifier for selectively energizing the primary coil to keep the primary LC circuit operating at or as close as possible to its natural resonant frequency. The inductive power transfer system may further include a secondary receiving unit. The secondary receiving unit includes a secondary LC circuit coupled with the primary LC circuit for inductively receiving power. The secondary LC circuit includes an LC filter and a rectifier unit for operating the secondary LC circuit at a mutual resonance with the primary LC circuit.

An Airborne Radar Power Supply With Contactless Transfer of Energy—Part I: Rotating Transformer

Abstract: Reliability and precision are key requirements for electronic systems in aerospace applications. Transferring electrical energy from a stationary to a moving device involves wearable parts such as slip rings and brushes. This paper examines the possibility of using a rotating transformer for contactless transfer of energy from the base to the revolving platform of an airborne radar system. The first part of the series focuses on the magnetic interface, investigating its electrical properties and their association with the core and windings geometry. The reader will gain an understanding of the merits and limitations of this technology and will be able to assess its suitability for other applications. The effects of the increased leakage and reduced magnetizing inductances of the transformer are investigated, and two winding layouts are proposed and characterized by measurements and finite-element analysis. Some equations are presented along with practical guidelines on designing a rotating transformer with a 0.25-2-mm air gap. The transformer voltage gain and efficiency plots are introduced as performance-assessment tools. The impact of the air-gap stray flux on the winding conduction losses is shown, and some electromagnetic-compatibility considerations are presented. Finally, a mechanical layout for a 1-kW rotating transformer is proposed.