Coil Displacement Research Articles

Evaluation of Characteristics of Transcutaneous Thin Transformer Utilizing Amorphous Magnetic Fiber for Implantable Artificial Heart

This paper deals with the characteristics of a thin disk-shaped transformer utilizing amorphous magnetic fiber, designed for an artificial heart system. The transformer can be applied to the patient with the primary coil placed on the surface of the body and the secondary coil implanted subcutaneously. There was little leakage flux behind the coils and relatively small change in output power with relative coil displacement. The system could transmit over 100 W of electric power. When transmitting 20 W, the temperature rise of the secondary coil was about 7.5°C, and efficiency was about 90%.

Depletion flocculation in dispersions of sterically-stabilised particles 2. Modifications to theory and further studies

An earlier (pragmatic) theory for calculating the interparticle interaction energy between two sterically-stabilised particles, in the presence of free polymer and solvent, is extended to take account of the possible compression of the attached polymer chains by the free polymer chains, as observed in neutron scattering experiments. This theory is compared with a recent approach based on the Scheutjens-Fleer model of polymers at interfaces. Both theories account well for the depletion flocculation observed when the added free polymer is of the same type as the attached polymer, that is, in this case when polystyrene (PS) is added to dispersions of silica particles, carrying terminally-anchored polystyrene chains, in toluene. However, subtle deficiencies are revealed in the pragmatic theory when the added polymer is different from the attached polymer. For example, when polydimethylsiloxane (PDMS) is added to the same dispersions, a type of incipient flocculation occurs at high PDMS volume fractions. This is related to the basic incompatibility of PS and PDMS. It is shown that an additional term, namely a displacement interaction term, must be included in the pragmatic theory this accounts for the free energy change associated with displacement of free coils, from overlap with the attached chains, into bulk solution. Similarly, when polyvinylmethylether (PVME) is added to the dispersions, bridging flocculation, is observed at very low PVME volume fractions. The pragmatic theory does not account for this. Depletion flocculation occurs in the same systems at much higher PVME volume fractions.

Cryogenic Servo-Controlled Infrared Fabry-Perot Spectrometer

High resolution infrared spectroscopy obtains fundamental information about the kinematics, composition, and energetics of astronomical infrared sources because it can sort out typical Doppler velocity components and separate adjacent lines from various species. In important cases the instrument having the maximum possible sensitivity for detection is a cryogenic Fabry-Perot spectrometer because it rejects noise from the bright and often flickering background without injecting any radiation. Such an instrument need only be limited by the performance of the best detectors. Coupled to a two-dimensional array, a cryogenic Fabry-Perot can produce spectroscopic infrared images of high quality. We have developed a prototype cryogenic infrared Fabry-Perot spectrometer and have operated it successfully on-site. The system uses a unique optical servo control for reliable sensing of the interferometric surfaces, and electromagnetic voice coil displacement drivers for the large motions needed for flexible operation. The present etalons and detector are optimized for the 4 to 5 Am band. We present a description of the instrument, recent astro-physical results obtained at a telescope, and a summary of development plans. Such a system can be operated from space out to submillimeter wavelengths.

Short Circuit Vibration Analysis of a Shell Form Power Transformer

The short-circuit axial vibration of a 250 Mva 500 kV single phase shell form transformer is calculated. The displacements of the coils and the stresses on the pressboard insulation between the coils are found for various design and operating conditions. Three different lumped mass models with nonlinear press-board representation are used for calculating the vibration in various parts of the coils because the frame which backs up the coils during short circuit is nonuniform. In shell form transformers manufactured by the authors' company the frame consists of both the core and the tank which have considerably different mechanical impedances. These impedances are shown to be quite important and methods for evaluating them are given. The impedance of the tank is determined from the results of tests of a 1/7 scale model. The results show that dynamic effects are not large. The maximum calculated pressboard stress is 2290 psi (15790 kPa), which is only 27% higher than the statically calculated stress; and the maximum calculated coil displacement is .87 inch (2.21 cm). It is also found that friction in the interleaved core joints is sufficient to prevent core separation.

Signal flow graphs for electroacoustic transducers (or modeling made easy)

The simulation of an electroacoustic transducer such as a loudspeaker system requires a mathematical model that can serve as the basis for building a computer model. We have three kinds of elements in a loud speaker : electrical, mechanical, and acoustical. Understanding the model and the results of the simu lation suggests that we not follow the traditional path of converting the mechanical and acoustical eZe ments to equivalent electrical elements to form an electrical network as the model to study. Instead, we have found it easier to follow a scheme originally suggested by Larrowe1,3 and form a model based on stating all physical laws in an integral formulation. In modern notation, this is simply accomplished by drawing a signal flow graph as a mathematical model of the system. The resulting signal flow graph (if we use the "right" technique) has an optimum set of state variables in the sense that all quantities are of clear physical significance in the system. For a loudspeaker system, the state variables turn out to be voice-coiz current, voice-coil velocity, voice- coil displacement, cabinet pressure, and volume velocity at the vent. Once this signal flow graph has been drawn, an analog computer model can be formed by proper insertion of minus signs and scale factors. The state-variable differential equation read from the signal flow graph can be converted to a phasor equation and then solved by complex matrix inversion. A time-shared computer terminal or a minicomputer programmed in BASIC is a convenient way to implement a digital simulation of an electro acoustic transducer.

The Shading Coil Displacement Transducer

The shading coil displacement transducer is unique among the family of variable inductance displacement transducers in that no motion of an iron core is necessary. The moving element is a small, one-turn winding which functions as a shading coil. This means that this device is characterized by an extremely light armature.