Coil Driver Research Articles

Performance Analysis of Single Inductive Coil Driver

The performance of a single inductive coil driver with six different turns of drive coils is analyzed and emulated with the emulation program in this paper. Under the condition that the integral projectile mass is 1.125 kg and the armature length is 300.0 mm, the maximum velocities of the projectile are 130.1, 134.1, and 132.8 m/s when the drive coil axial lengths are 50.0, 100.0, and 150.0 mm, respectively, and the drive coil radial thickness is 20.0 mm. By changing the drive coil radial thickness to 30.0 mm, the maximum velocities of the projectile are 112.5, 110.2, and 116.3 m/s when the drive coil axial lengths are 50.0, 100.0, and 150.0 mm, respectively. The result shows that only when the structural parameters of the drive coil and the armature are matched suitably that the maximum velocity of the projectile can be reached. This conclusion provides a reference for the engineering practice of the inductive coil driver.

Development and Fabrication of the Micro Eddy Current Sensor by Using UV-LIGA Process

An analytical model of an eddy current sensor designed for noncontact distance measurement is presented. The device consists of two planar coil (driver coil and pickup coil) stacked on the magnetic core. The planar coil fabricated by UV-LIGA technology with SU-8 photoresist is illustrated, and the permalloy magnetic core electroforming process is presented also. Tested with 10-50 KHz sine signal, the output voltage of the sensing coil reached 30mv with a Ni target placed at a distance of 20μm. And the experimental showed a linear relation between the distance and output voltage within 60μm distance. The amplitude trend increases with the increasing of the frequency and amplitude of excited signal, which is according with the theory analytics. The whole size of the device is: Φ5mm×1.5mm. The results demonstrated that the device could nondestructive evaluate the distance and be easily integrated on chip, and the UV-LIGA Process could be used as a new method to fabricate the micro eddy current sensor massly.

System Design for High Energy Rate Electromagnetic Powder Compaction Devices

In this paper, the main element is constructed high energy electromagnetic compaction system on the high-energy flat coil. Physical model for analyzing dynamic response of high pulse current was reviewed. Design loading device using high energy electromagnetic technology to suppress powder, consider the exhaust, stripping, loading, positioning and other issues,propose a more reasonable program.The device includes various components of the installation. such as coil, the coil plate, driver, amplifiers, punching first, die, upper and lower fixing plate. The model of device based on Pro/E to facilitate manufacturing.Pressure embryo along the suppression direction has more uniform density distribution.The technology possesses advantagesof the single side forming and directional loading.

Magnetic propulsion of a magnetic device using three square-Helmholtz coils and a square-Maxwell coil

We introduce a square coil system for remote magnetic navigation of a magnetic device without any physical movements of the coils. We used three square-Helmholtz coils and a square-Maxwell coil for magnetic propulsion of a small magnet along the desired path. All the square coils are mountable on a cubic frame that has an opening to accommodate a living subject. The square-Helmholtz coils control the magnetic propulsion direction by generating uniform magnetic field along the desired direction while the square-Maxwell coil controls the propulsion force by generating magnetic gradient field. We performed magnetic propulsion experiments with a down-scaled coil set and a three-channel coil driver. Experimental results demonstrate that we can use the square coil set for magnetic navigation of a magnetic device without any physical movements of the coils.

3-D Eddy-Current Imaging of Metal Tubes by Gradient-Based, Controlled Evolution of Level Sets

Eddy-current nondestructive testing is widely used to detect defects within a metal structure. It is also useful to characterize their location and shape provided that proper maps of variations of impedance that the defects induce are available. Imaging of void defects in the wall of a hollow, nonmagnetic metal tube, is performed herein by controlled evolution of level sets. Such data are variations of impedance data collected by a circular probe array close to the inner surface of the tube when a coil source operated at one single frequency is set along its axis at some distance from the array, both receiver and coil source being moved simultaneously. The defect zone is represented in implicit fashion as a zero level set, which is amenable to topological changes via a nonlinear iterative method that minimizes a least-square cost functional made of the difference between the measured (computer simulated) and model data. The procedure requires the rigorous calculation of the gradient of the variations of impedance, in the case of a multistatic configuration (different driver and receiver coils), a vector domain integral field formulation being used for that purpose. Numerical examples developed by a dedicated extension of the general-purpose CIVA platform show pros and cons of the approach for inner, outer, and through-wall void defects. Further comparisons present results provided by an independently developed binary-specialized method.

Development of a virtual keyboard based on button tracking using magnetic induction

In this paper, we present the development of a virtual keyboard based on button tracking, which consists of fingertip sensors, keyboard panels, keyboard layouts, and a control unit. The fingertip sensor is composed of a small generator coil attached on the fingertip and two sensor coils installed on the keyboard panel. This keyboard panel functions as sensor amplifiers, generator coil drivers, and as a hand coaster while a user is typing. The keyboard layout which is only a picture describing the arrangement of keys on the keyboard is used for guiding the user during the training, and the control unit is used for coordinating the keyboard system and transmitting sensors’ data to the host computer. The theoretical formulation of the fingertip sensor and the realization of the virtual keyboard are also presented. To prevent interference among the generator coils, we adopt a time division method to scan the generator and sensor coils. To obtain high flexibility in the system, training and recognition methods for identifying the keyboard keys are also proposed. At the training stage, a simple and robust vector‐quantization‐based training algorithm is developed, so that trained models of an acceptable quality can be obtained even though 25% of outliers exist in the training data. At the recognition stage, an efficient recognition algorithm based on distance measurement is also presented. Additionally, in online typing, we propose a visual feedback technique to display the corresponding keys pressed by the fingers. So far, the experimental results of the virtual keyboard as well as both the training and recognition algorithms are very satisfactory. Results reveal that our virtual keyboard is currently usable for a man‐machine interface.

Surround sound speaker system

The present invention uses multivoice coil drivers in conjunction with the small satellite speakers of multichannel surround sound systems to achieve an overall linear response between 100 Hz to above 15 KHz. The multivoice coil drivers are designed to respond only to frequencies that fall between conventional upper base and lower midrange crossover frequencies which typically extend between 75 Hz and 225 Hz. The invention relies on the characteristics of human hearing which limits the listener's ability to localize the source of sound approximately to the wavelength of the sound being heard. The system may be incorporated in existing front and rear center speakers or separate enclosures to supplement the overall surround sound system.

Broadband calibration of radio-frequency magnetic induction probes

We describe broadband calibration of a magnetic induction probe using a network analyzer. Our procedure uses a small driver coil and the scattering matrix associated with the coil-probe pair. This allows rapid, high-resolution measurements of the amplitude and phase of the probe’s response to oscillating magnetic fields. Our setup gives high accuracy between 100kHz and 100MHz and less accuracy outside this range. We present over 1800 sensitivity measurements between 30kHz and 1GHz. The ideal probe response is compared to calibrations done with two different driver coils. We discuss several hurdles in probe design and calibration, as well as several high-frequency effects.

Transient Eddy-Current Driver Pickup Probe Response Due to a Conductive Plate

In this paper, we calculate the transient eddy-current response of a driver pickup probe due to a conducting plate by means of series expansions. We consider an excitation current in the driver coil that rises exponentially with time toward a constant value, the step function current being a special case with zero time constant. We find the transient response from the frequency domain expressions for the induced electromotive force in the pickup coil by using the inverse Laplace transform. Usually, the field of the excitation coil is expressed in the form of a Bessel integral with respect to the radial spatial frequency. Here, however, to improve computational efficiency, we approximate the integral as a series expansion by truncating the solution domain at a large but finite radius and setting the field on the truncation boundary to zero. The series is a sum of terms containing discrete spatial frequencies defined by the zeros of the first-order Bessel function of the first kind. We then form an inner summation from the temporal frequency-dependent terms in order to facilitate an analytical inverse Laplace transformation to the time domain. We present two alternative expansions for the inner sum. One is constructed with reference to the short time regime and the other with respect to the long time limit. Numerical results show good agreement between the alternative series approximations at a wide range of intermediate times.

Simple, compact source for low-temperature air plasmas

A simple, compact source of low-temperature, spatially and temporally uniform air plasma using a Telsa induction coil driver is described. The low-power ionization discharge plasma is localized (2 cm×0.5 cm×0.1 cm) and essentially free of arc channels. A Teflon coated rolling cylindrical electrode and dielectric coated ground plate are essential to the source’s operation and allow flat test samples to be readily exposed to the plasma. The plasma is a copious source of ozone and nitrogen oxides. Its effects on various microbes are discussed.

Designing electrodynamic loudspeakers by using a new computer modeling scheme

A new technique for the computer modeling of fluid-loaded magnetomechanical transducers is presented. This numerical technique is based on a finite-element method (FEM) and allows the precise calculation of the magnetic, mechanical, and acoustic fields, including their couplings. Further on, nonlinear effects in the mechanical and magnetic behavior are considered. Therewith, the complex dynamic behavior of electrodynamic loudspeakers was studied and, furthermore, an appropriate computer-aided engineering (CAE) environment has been established. This CAE tool allows an optimization of critical parameters, for example: The validity of the computer simulations is verified with the help of appropriate measurements. The calculated and measured values for eigenfrequencies, axial pressure responses, and electrical input impedances are in excellent agreement. The applicability of the presented calculation scheme with respect to the computer-aided design of moving coil drivers is demonstrated by reporting several practical applications, which are of great interest for loudspeaker manufacturers. In the present paper, the elimination of response dips at intermediate frequencies, the calculation of polar responses, and the examination of the so-called jump-out excursion, are presented.

Measurements of the performance of a thermoacoustic refrigerator prototype

The performance of a thermoacoustic prototype designed for a cooling capacity of 140 W and operating stack end temperatures of 282 and 306 K was measured. The device was operated using a 55%–45% helium–argon mixture at a mean pressure lower than or equal to 20 bars. The electrodynamic moving coil driver coupled to the half-wavelength resonator was tuned such that the system resonance frequency (i.e., the operating frequency) was around 180 Hz. The stack was made of a coiled polyester film and nylon filament spacers. The secondary system included finned-tube heat exchangers with water as the operating fluid. The power delivered to the driver coil was measured using a power meter. The cooling power was estimated from the water-side temperature drop across the heat exchangers measured using thermopiles, and from the water flow rate. Acoustic pressure, piston acceleration, and temperature measurements were also made at various locations inside the resonator. The measured values were compared with predictions obtained using DeltaE.

Sound-speed determination in a fluid-filled elastic waveguide

Theory and test methods are presented for determining the longitudinal sound speed inside a fluid-filled elastic waveguide. The waveguide is a vertically oriented open-ended column of water equipped with a moving coil driver. The elastic properties of the waveguide reduce the sound speed to the point where a passive anechoic termination can be used effectively. This facilitates a compact device that exhibits plane progressive waves for sensor calibration at low frequencies. Once the sound speed is determined, then the size of the device and usable bandwidth are known. The sound speed is determined through measurement of the longitudinal resonance frequencies associated with the free vibration case of a duct having ideal rigid and pressure-release boundary conditions. In practice, however, the moving coil driver presents an impedance boundary condition (e.g., not ideally rigid) that inadvertently couples the mechanical system of the driver to the acoustic system of the waveguide. To circumvent this issue, frequency response measurements are made between a neutrally buoyant velocity sensor suspended in the fluid and an accelerometer mounted to the active face of the driver. In effect, the measurement decouples the two systems and provides the standing wave resonance frequencies of the duct having ideal boundary conditions.

The test and analysis of a 3-stage reconnection coilgun

For the principle test a 3-stage reconnection coilgun was built. It has a 64 mm bore, length of 330 mm and a projectile weight of 1 kg. The muzzle velocity is about 100 m/s. The value of the capacitors of the driver coils are 4480, 3000 and 715 /spl mu/F with initial voltages 3.3, 3.6 and 6.0 kV respectively. The agreement of the results between the test and the analysis is good. The performances of AC and DC work modes are compared. DC mode means that a shunt circuit is inserted into each driver coil circuit to prevent current reversal. In the test, visible plastic deformations of the armature occur and it was confirmed by computer simulation.

Facility for chronic exposure of rats to ELF magnetic fields.

The facility consists of a 12 x 11.5 x 2.4 m high room containing six sets of exposure apparatus and the other equipment necessary to maintain a pathogen-free system. The apparatus sets produced 5 mT (rms), 0.5 mT, or a sham exposure. The apparatus was arranged in the room to minimize the fringing field of the 5 mT set at the sham position. Each set was 3.85 x 1.80 x 0.66 m in outside dimension, containing 24 cages in the magnetically homogeneous region. The apparatus was designed using Harvey's figure-eight-configuration and generated a horizontal sinusoidal alternating field. In order to save electric power, the coil of the apparatus constituted a 50 Hz LC resonance circuit with a condensor bank to which electric power was supplied to compensate losses. Magnetic flux density was kept constant by controlling the coil current. Although mild steel was used in the skeleton of the building, the fringing flux at the sham was as low as 0.1 to 1 microT. Stainless steel was used for ventilating ducts, racks for the cages, cage covers, feeder baskets, and watering nozzles. The homogeneity of the field was measured to be +/- 10% in the animal residence area, and food and water consumption was found to be unaffected by the field. At 5 mT, the coil current was 370 A, and the hollow coil was cooled by a stream of 20 degrees C water to prevent both heat and dew on the coil surface. Vibration and acoustic noise was prevented by fiber reinforced plastic framework of the coil. High harmonic distortion was not observed at the output terminal of the coil driver. The facility has operated without trouble for 2 years.

Closed-loop class E transcutaneous power and data link for microimplants.

Magnetic transcutaneous coupling is frequently used for power and data transfer to implanted electronic devices. The proposed development of MicroImplants, small enough to be injected through a hypodermic needle suggest the need for a high-efficiency magnetic transcutaneous link. This paper describes the use of a multifrequency transmitter coil driver based upon the Class E topology. The development of a "high-Q approximation" which simplifies the design procedure is presented. A closed-loop controller to compensate for transmitter and receiver variations, and a method of data modulation, using synchronous frequency shifting are described. The closed-loop Class E circuit shows great promise, especially for circuits with unusually low coefficients of coupling. Currents of several amperes, at radio frequencies, can easily and efficiently be obtained.

Constricted Liquid Metal Curtain for Inertial Confinement Fusion Reactors

Considerations are presented on the wall protection of inertial confinement fusion reactors by means of a falling cylindrical curtain of liquid metal that is intermittently contricted into a string of closed envelopes by the action of a series of cusped fields generated around the falling liquid cylinder. The formation of a liquid metal envelope in free space is discussed and the motion of the liquid curtain during constriction is numerically analyzed under the assumption of infinitesimally small curtain thickness and infinitely large conductivity. The single-turn cusp-field driver coils are assumed to have a circular cross section. The calculations indicate that the energy required for the driving field is quite small compared with the thermonuclear energy produced per pulse, and that an adequate electromagnetic force is generated by the coils for a 1 m radius cylindrical curtain of liquid lithium if it is constricted into closed envelopes within an interval of 30 ms.

Compensated crossover network

The signal from the crossover network of an audio output circuit is applied to certain of the audio system's low, middle and high frequency speakers through particular compensation circuits that are associated with the crossover network and the speaker driver coils. These compensation networks include: a resistor-inductor-capacitor sequence of selected values connected across the terminals of a high frequency or other driver whose resonant impedance peak must be compensated to a resistive impedance for optimum crossover; a resistor-capacitor sequence of selected values connected across the terminals of a low frequency or other driver whose inductance must be compensated to a resistive impedance for optimum crossover; and a variable inductor connected in series with one or more of the terminals of any driver where a "roll off" at higher frequency may be desired. The result is more faithful audio reproduction.

A whole-body NMR imaging machine

A nuclear magnetic resonance (NMR) machine capable of producing tomographic sections of the whole human body in vivo has been constructed. This system is based on a four coil, air-core electromagnet producing a field of 0.04 T which corresponds to a proton NMR frequency of 1.7 MHz. The images are produced line by line using a selective excitation technique. Magnetic field gradients up to about 5 mT/m are employed. Electronic subsystems are described here including a radiofrequency (RF) amplitude feedback circuit, an RF power amplifier, a transmit/receive switch, a receiver pre-amplifier and gradient coil drivers. For a single scan through a 103 mm3 sample of human muscle tissue in vivo, the measured proton density uncertainty is 24% and the spin-lattice relaxation time (T1) uncertainty is 74%. Phantom images using CuSO4 solution and in vivo sections through human chest, thighs and head are presented. T1 measurements of human muscle, liver and brain tissue in vivo give results which agree well with T1 values for corresponding rabbit tissues measured in vitro.

A one million bit bubble memory solution

Intel Magnetics is offering for sale a one million bit magnetic bubble memory package plus the LSI support circuits to build a complete memory subsystem compatible with the standard Intel microcomputer bus structures [1]. A manufacturable 2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . one megabit chip was realized with an 11.2 × 11.2 square micrometer storage cell and with block replicate and swap gates for control functions. A binary organization was chosen so that useable data storage is organized as 2048 bit blocks of 512 bits each. A minimum system of 128k Bytes can be contained in 14 square inches of board space and requires only +12 volt and +5 voH power supplies and maximum power of 5 watts. The system is easily expandable to 1 M Byte. Product features offered include error correction on each 256 bit block segment and a leadless bubble memory package with a matching socket. The LSI support devices include a Current Pulse Generator, a Coil Driver, A Coil Predriver, a Formatter/Sense Amplifier and a Bubble Memory Controller.