Showing papers on "Electromagnetic coil published in 2004"

An electromagnetic, vibration-powered generator for intelligent sensor systems

Abstract: This paper describes the design of miniature generators capable of converting ambient vibration energy into electrical energy for use in powering intelligent sensor systems. Such a device acts as the power supply of a microsystem which can be used in inaccessible areas where wires can not be practically attached to provide power or transmit sensor data. Two prototypes of miniature generator are described and experimental results presented. Prototype A is based around two magnets coupled to a coil attached to a cantilever; prototype B is based around four magnets. For prototype A, experimental results are given for its resonant frequency and its open circuit and loaded output as a function of vibration amplitude. For prototype B, experimental results are given for the generator's Q factor in air and vacuum, its output voltage as a function of vibration amplitude as well as its magnetic field strength. This generator has been tested on a car engine and shown to produce a peak power of 3.9 mW with an average power of 157 micro watts.

Digital wireless position sensor

Abstract: A method is provided for tracking an object, including positioning a radio frequency (RF) driver to radiate an RF driving field toward the object, and fixing to the object a wireless transponder that includes a power coil and at least one sensor coil. The method also includes receiving the RF driving field using the power coil and storing electrical energy derived therefrom. A plurality of field generators are driven to generate electromagnetic fields at respective frequencies in a vicinity of the object that induce a voltage drop across the at least one sensor coil. A digital output signal is generated at the wireless transponder indicative of the voltage drop across the sensor coil, and the generation of the digital output signal is powered using the stored electrical energy. The digital output signal is transmitted from the wireless transponder using the power coil, and the transmission of the digital output signal is powered using the stored electrical energy. The digital output signal is received and processed to determine coordinates of the object.

Generation of electrical energy for portable devices: Comparative study of an electromagnetic and a piezoelectric system

Abstract: This paper presents the comparative study of two different electromechanical systems, in order to conceive autonomous portable generators capable of harvesting human mechanical energy. The first one is an electromagnetic system, made of a magnet in translation within a coil. The second one is a piezoelectric system, which is a PZT ceramic bar, polarised longitudinally, embedded at one end and constrained at the other end. The analytical models described in this paper present a high similarity and a duality in signal levels, adapted load and optimal working frequency, the two latters corresponding to the maximal electrical power generated.

Temperature and SAR calculations for a human head within volume and surface coils at 64 and 300 MHz

Abstract: Purpose: To examine relationships between specific energy absorption rate (SAR) and temperature distributions in the human head during radio frequency energy deposition in MRI. Materials and Methods: A multi-tissue numerical model of the head was developed that considered thermal conductivity, heat capacity, perfusion, heat of metabolism, electrical properties, and density. Calculations of SAR and the resulting temperature increase were performed for different coils at different frequencies. Results: Because of tissue-dependant perfusion rates and thermal conduction, there is not a good overall spatial correlation between SAR and temperature increase. When a volume coil is driven to induce a head average SAR level of either 3.0 or 3.2 W/kg, it is unlikely that a significant temperature increase in the brain will occur due to its high rate of perfusion, although limits on SAR in an y1go ftissue in the head may be exceeded. Conclusion: Attempts to ensure RF safety in MRI often rely on assumptions about local temperature from local SAR levels. The relationship between local SAR and local temperature is not, however, straightforward. In cases where high SAR levels are required due to pulse sequence demands, calculations of temperature may be preferable to calculations of SAR because of the more direct relationship between temperature and safety.

Improved analytical modelling of rotor eddy current loss in brushless machines equipped with surface-mounted permanent magnets

Abstract: An improved analytical model for predicting the rotor eddy current loss in brushless machines equipped with surface-mounted permanent magnets is presented. It is formulated in polar co-ordinates and based on the calculation of the two-dimensional electromagnetic field in the airgap/magnet regions, with due account of the eddy current reaction field. It enables the eddy current loss in the permanent magnets and the retaining sleeve, if fitted, to be calculated, and caters for motors having either overlapping or non-overlapping stator windings, as well as any specified load condition. The analysis accounts for both time and space mmf harmonics, but neglects the influence of stator slotting. The model is applied to a brushless DC traction machine in which the rotor loss is due predominantly to time harmonics in the armature reaction field which result from commutation events. The predicted rotor loss is compared with the loss deduced from thermometric measurements and from an analytical magnetostatic model which neglects the eddy current reaction field. Good agreement between predictions and measurements is achieved over the complete operating speed range.

Permanent magnet brushless machines with unequal tooth widths and similar slot and pole numbers

Abstract: This paper presents a comparative study of three-phase permanent-magnet brushless machines in which the slot and pole numbers are similar, with reference to conventional brushless dc machines in which the ratio of the slot number to pole number is usually 3 : 2. Three different motor designs are considered. Two have equal tooth widths, with one having a coil wound on every tooth and the other only having a coil wound on alternate teeth, while the third machine also has coils wound on alternate teeth but these are wider than the unwound teeth while the width of their tooth tips is almost equal to the rotor pole pitch in order to maximize the flux linkage and torque. Analytical and finite-element methods are employed to predict the flux-linkage and back-electromotive-force waveforms, and the self- and mutual-inductances, and these are shown to be in good agreement with measured results. It is also shown that the third machine is eminently appropriate for brushless dc operation.

External power source for an implantable medical device having an adjustable carrier frequency and system and method related therefore

Abstract: A transcutaneous energy transfer system, transcutaneous charging system, external power source, external charger and methods of transcutaneous energy transfer and charging for an implantable medical device and an external power source/charger. The implantable medical device has a secondary coil adapted to be inductively energized by an external primary coil at a carrier frequency. The external power source/charger has a primary coil and circuitry capable of inductively energizing the secondary coil by driving the primary coil at a carrier frequency adjusted to the resonant frequency to match a resonant frequency of the tuned inductive charging circuit, to minimize the impedance of the tuned inductive charging circuit or to increase the efficiency of energy transfer.

Transcutaneous energy transfer primary coil with a high aspect ferrite core

Abstract: Adjustable gastric band implants contain a hollow elastomeric balloon with fixed end points encircling a patient's stomach just inferior to the esophago-gastric junction. These balloons can expand and contract through the introduction of saline solution into the balloon. In current bands, this saline solution must be injected into a subcutaneous port with a needle to reach the port located below the skin surface. The port communicates hydraulically with the band via a catheter. As an alternative to using a percutaneously accessed injection port, a system for regulating the flow of saline that is totally implanted may rely upon bi-directionally pumping fluid from an implant device. This system instead transfers AC magnetic flux energy from an external primary coil to a secondary coil that powers the pump in the implanted reservoir. A magnetically permeable rod centered within the primary coil increases power coupled to the secondary coil.

External power source, charger and system for an implantable medical device having thermal characteristics and method therefore

Abstract: External power source, charger, system and method for transcutaneous energy transfer. An implantable medical device has a first housing having operational componentry for providing the therapeutic output. A secondary housing is mechanically coupled to the first housing having a secondary coil operatively coupled to the componentry, the secondary coil capable of receiving energy from the external source. A magnetically shielding material is positioned between the secondary coil and the first housing. An external power source has an external housing. A primary coil carried in the external housing, the primary coil being capable of inductively energizing the secondary coil when the housing is externally placed in proximity of the secondary coil with a first surface of the housing positioned closest to the secondary coil, the first surface of the housing being thermally conductive surface. An energy absorptive material carried within the external housing.

Pulse frequency modulation for induction charge device

Abstract: The present invention is related to a pulse frequency modulation for induction charge device, which comprises a pulse frequency modulation for induction charge device being provided to charge a portable electronic device, wherein, the portable electronic device comprises a induction coil, which comprises: an electric magnetic field generate and the secondary coil react circuit; a detection and modulation generate circuit; and a control switch circuit; whereby, the detection and modulation generate circuit could generate pulse singles with various frequencies according to the load varying generated due to distance varying between the portable electronic device and the charged device, and charge to the portable electronic device according the pulse singles so as to reach the goal of effective management the power.

Efficient high-frequency body coil for high-field MRI.

Abstract: The use of body coils is favored for homogeneous excitation, and such coils are often paired with surface coils or arrays for sensitive reception in many MRI applications. While the body coil's physical size and resultant electrical length make this circuit difficult to design for any field strength, recent efforts to build efficient body coils for applications at 3T and above have been especially challenging. To meet this challenge, we developed an efficient new transverse electromagnetic (TEM) body coil and demonstrated its use in human studies at field strengths up to 4T. Head, body, and breast images were acquired within peak power constraints of <8 kW. Bench studies indicate that these body coils are feasible to 8T. RF shimming was used to remove a high-field-related cardiac imaging artifact in these preliminary studies. Magn Reson Med 52:851–859, 2004. © 2004 Wiley-Liss, Inc.

Opportunistic power supply charge system for portable unit

Abstract: Systems and methods for opportunistically charging a rechargeable power source of a portable electronic unit are provided. The system includes a primary inductance assembly energized by a main power source for inducing an electro-magnetic flux in a secondary coil assembly associated with a power source of the portable unit. Such electro-magnetic flux creates an electric current that is subsequently employed for charging the power source of the portable unit. A controller of the charging system can monitor state of charge, and notify a user when a recharge is required. Scavenging modes may also be employed for recharging the main power source and the rechargeable source of the portable unit.

Impedance matching network and multidimensional electromagnetic field coil for a transponder interrogator

Abstract: An improved interrogator for an inductively coupled identification system is disclosed. The interrogator provides a multidimensional electromagnetic field through a plurality of coils aligned relative to each other. The coils provide a rotating magnetic field having approximately constant amplitude regardless of orientation with respect to the transponder. An additional coil may be utilized to precess the multidimensional electromagnetic field. The interrogator may further provide an impedance matching network that includes a series drive capacitor to match the impedance of a capacitor in parallel with a coil to a driver load impedance.

Elevator control device

Abstract: When there is a breakdown in either one of first and second power converters supplying electrical power to a multi-winding motor comprising a wind-up mechanism, a rescue operation can be safely and reliably carried out by using the remaining power converter. A wind-up mechanism comprises a two-winding motor having first and second windings, and, during normal operation, power is supplied to the first and second windings from first and second inverters respectively. When the first inverter has broken down due to excessive current, first and second contactors are switched off, and a third contactor comprising a short-circuiting unit is switched on. Consequently, both windings receive power from the second inverter, enabling the rescue operation to be carried out without causing vibrations.

Thermal analysis of multibarrier interior PM synchronous Machine using lumped parameter model

Abstract: This paper presents a lumped-parameter thermal model for a multi-barrier interior PM synchronous machine. The model consists of a network of 12 thermal resistances that make it possible to estimate temperatures at 9 critical points inside the machine including the stator end windings, rotor magnets, and the bearings. The details of the model are presented and two machines are analyzed, including a 6 kW 12-pole automotive starter/alternator and a 0.5 kW 4-pole electric water pump machine. The lumped-parameter model results for both machines demonstrate good agreement with results obtained using detailed thermal finite element analysis.

On the modeling and design of dual-stator windings to minimize circulating harmonic currents for VSI fed AC machines

Abstract: The major drawback of usual dual-stator ac machines, when supplied by a voltage-source inverter (VSI), is the occurrence of extra harmonic currents. These extra currents circulate only in the stator windings and cause additional losses. This paper deals with the modeling and design of dual-stator winding ac machines for safe operation with a VSI. A new reference frame model for a dual-stator induction machine (DSIM), including mutual leakage coupling, is proposed. This model allows us to highlight the previously mentioned circulating harmonic currents. The leakage inductance associated with these harmonics is shown to have quite a small value, highly depending on the coil pitch. It is also shown that full pitch is required, and that special slot shape designs should be investigated, to limit the magnitude of circulating currents. Experimental results on a prototype of a DSIM are presented and they show a very good correlation with theoretical curves.

Procedures for detecting winding displacements in power transformers by the transfer function method

Abstract: The paper investigates three different ways of using the transfer function method for detecting mechanical winding displacements in power transformers. The most reliable approach is time-based comparison , which requires finger print data from a previous measurement. Such information is, however, usually not available. For multilegged transformers without zigzag-connected windings the results of separately tested legs can be used as mutual references (construction-based comparison ). A third approach is to compare the transfer functions with those obtained from an identically constructed transformer ( type-based comparison). However, for a transformer with given nominal specification data, the winding design may over time undergo changes which causes changes to the transfer function. It is proposed to solve this problem by calculating tolerance bands using transfer functions from a big group of the same-type transformers. A novel statistical algorithm for this purpose is presented. The approach is demonstrated for a set of 28 specified identically 200-MVA power transformers.

System and method for transcutaneous energy transfer achieving high efficiency

Abstract: A system and method for transcutaneous energy transfer and/or charging in a transverse direction. An external power source having a primary coil being driven at a frequency selectable in the range between eight and twelve kiloHertz contained in a housing. An implantable medical device has componentry for providing a therapeutic output and a secondary coil operatively coupled to the componentry. The external power source is capable of providing energy to the implantable medical device when the primary coil of the external power source is placed in proximity of the secondary coil of the implantable medical device. The external power source has a lateral positional adjustment for the primary coil. The frequency of the external power source is frequency adjustable providing a frequency adjustment. The positional adjustment and the frequency adjustment allows, at least in part, the system to attain an efficiency of energy transfer from the external power source to the implantable medical device of at least thirty percent.

Magnetic field concentrator for electromagnetic forming

Abstract: A magnetic forming system ( 10 ) for creating a fluid circuit joint between a tube and a fitting includes an induction coil ( 12 ). The induction coil ( 12 ) may form a first stage electromagnetic current. A field concentrator ( 132 ) may focus the first stage electromagnetic current to form a second stage electromagnetic current. An insert ( 136 ) may focus the second stage electromagnetic current to form an electromagnetic field. The electromagnetic field forms the fluid circuit joint. The induction coil ( 12 ) may be insertable within the tube, generate an electromagnetic field, and impose the electromagnetic field on and to expand a portion of the tube within the fitting to form the fluid circuit joint. The system ( 10 ) may include a receptacle ( 54 ) that is external to the tube and the fitting. An insert ( 56 ) may be mechanically coupled within the receptacle ( 54 ) and limit the outward expansion of the tube and the fitting.

Non-contact power transmission system

Abstract: PROBLEM TO BE SOLVED: To conduct the efficient stabilization control of a secondary output voltage and a current in a noncontact power transmission system. SOLUTION: This non-contact power transmissions system can perform secondary stabilization control at high efficiency, in a small size, and at low cost, by transmitting a signal related to a secondary voltage and a current to a primary unit using a noncontact electromagnetic coupling coil, receiving a signal transmitted from the secondary side, and varying the drive frequency of a primary inverter. This reduces ineffective power consumption on the primary side by providing it with a means which controls the secondary output voltage and the current by shifting the drive frequency to a higher side at a light load or no-load and reducing the current of the primary coil of a coupling transformer thereby controlling the stabilization of the secondary output voltage and the current. COPYRIGHT: (C)2006,JPO&NCIPI

Method and apparatus for efficient power/data transmission

Abstract: A system, method and power/data transmission device comprising a coil having a high Q, a low-voltage driver and a high-voltage driver switchably coupled to the coil. The low-voltage driver and the high-voltage driver are controlled by a microcontroller and switch at about the same time thereby providing a modulated data signal for transmission. Furthermore, the system includes at least one implantable microstimulator coupled to the transmission device.

Method and system for providing dynamic actuation of a write head using a strain element

Abstract: A method and system for actuating a pole tip of a write head is disclosed. The write head includes a first pole and a second pole. The method and system include providing a strain element and providing a coil. The strain element is electrically insulated from the first pole and the second pole. The strain element is further configured to produce a strain for actuating the pole tip in response to a magnetic field. The coil carries a current capable of producing the magnetic field at the strain element.

Noncontact power transmitter

Abstract: PROBLEM TO BE SOLVED: To provide a noncontact power transmitter which can eliminate inconvenience that occurs when the user uses an object composed of two plane coils as a transformer for power transmission and can perform the communication for check of the other party of power transmission, using the transformer for power transmission. SOLUTION: This power transmitter detects the foreign matter to a primary coil 12 which constitutes the transformer 3 for power transmission and detects the improper positioning of the primary coil 12 and a secondary coil 21, and informs the user of that effect by an indicator when there is detection of it. Moreover, this checks (certifies) by communication whether a transmitter 1 and a receiver 2 are regular ones or not, and the transmitter 1 does not start full-scale power transmission to the receiver 2 not until finish of its check. COPYRIGHT: (C)2006,JPO&NCIPI

Composite magnetic core for switch-mode power converters

Abstract: A composite magnetic core formed of a high permeability material and a lower permeability, high saturation flux density material prevents core saturation without an air gap and reduces eddy current losses and loss of inductance. The composite core is configured such that the low permeability, high saturation material is located where the flux accumulates from the high permeability sections. The presence of magnetic material having a relatively high permeability keeps the flux confined within the core thereby preventing fringing flux from spilling out into the winding arrangement. This composite core configuration balances the requirements of preventing core saturation and minimizing eddy current losses without increasing either the height or width of the core or the number of windings.

Devices and methods for crossing a chronic total occlusion

Abstract: A catheter (10) comprising an elongate tubular member having a proximal end and a distal end, and a deflectable tip (11) at the distal end of the elongate tubular member. The deflectable tip (11) comprises a first helical coil (14) having a first diameter and a second helical coil (15) having a second diameter, the first diameter being larger than the second diameter. The first and second helical coils (14, 15) are arranged in a manner of a double helix. When viewed in cross-section, the first helical coil (14) and the second helical coil (15) are aligned at a first point on a circumference of each coil and misaligned at a second point on the circumference of each coil, where the second point is approximately 180 degrees from the first point. In certain embodiments the catheter further includes a dilatation balloon. Methods of use for crossing a chronic total occlusion are also described.

The generation of 25.05 T using a 5.11 T Bi2Sr2CaCu2Ox superconducting insert magnet

Abstract: A 25.05 T magnetic field was generated by a 5.11 T superconducting Bi2Sr2CaCu2Ox insert magnet within a 19.94 T resistive magnet. The Bi2Sr2CaCu2Ox magnet is constructed using fully reacted powder-in-tube conductor and insulated stainless steel reinforcement. Three concentric sections are used to minimize the total stress in the Bi2Sr2CaCu2Ox conductor: two double pancake stacks and an outer layer-wound section. The insert coil operates at 4.2 K in a 0.168 m diameter cryostat fitted to the resistive magnet. Here we provide an overview of the design and construction of the insert and the results of self-field and in-field testing. Mechanical and electrical safety issues, related to testing in a large resistive magnet, are discussed.

Eddy current sensor

Abstract: An eddy current sensor (10) has a sensor coil (100) disposed near a conductive film (6) formed on a semiconductor wafer (W) and a signal source (124) configured to supply an AC signal to the sensor coil (100) to produce an eddy current in the conductive film (6). The eddy current sensor (10) includes a detection circuit operable to detect the eddy current produced in the conductive film (6). The detection circuit is connected to the sensor coil (100). The eddy current sensor (10) also includes a housing (200) made of a material having a high magnetic permeability. The housing (200) accommodates the sensor coil (100) therein. The housing (200) is configured so that the sensor coil (100) forms a path of a magnetic flux (MF) so as to effectively produce an eddy current in the conductive film (6).

Sensorless aquisition of the rotor position angle for induction motors with arbitrary stator windings

Abstract: The anisotropy of a cage rotor is utilized to determine the angular position of the rotor in an induction machine. The switching transients generated by a pulsewidth controlled inverter serve as test signals. The response of the three inverter terminal currents is exploited to derive a quasi-instantaneous rotor position signal. The position is sensed at the inverter through the 3-phase motor cable by measuring the current derivatives. The method does not require additional wire connections. It is applicable to induction motors having the stator windings connected either in wye or in delta. The results are supported by measurements from an experimental setup.