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Feb 2000

Volume 71, Issue 2, pp. 335-1239

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back to top ELECTRONICS; ELECTROMAGNETIC TECHNOLOGY; MICROWAVES

Extraction of radio frequency from electromagnetic surface waves guided by metallic strips

M. Friedman

Rev. Sci. Instrum. 71, 551 (2000); http://dx.doi.org/10.1063/1.1150239 (3 pages)

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Pulses of rf radiation with power in the megawatt range was extracted from electromagnetic surface waves. These nonradiating waves propagated on a long and thin metallic strip with most of the wave energy confined to a distance of less than a half wavelength around the strip. The electromagnetic energy of the surface waves was first extracted into rectangular waveguides in a TE01 mode and then radiated into the atmosphere with an overall efficiency of 90%.
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84.40.Az Waveguides, transmission lines, striplines
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Compact THz-radiation source consisting of a bulk semiconductor, a mode-locked fiber laser, and a 2 T permanent magnet

Shingo Ono, Takeyo Tsukamoto, Masahiro Sakai, Zhenlin Liu, Hideyuki Ohtake, Nobuhiko Sarukura, Seizi Nishizawa, Akio Nakanishi, and Makoto Yoshida

Rev. Sci. Instrum. 71, 554 (2000); http://dx.doi.org/10.1063/1.1150240 (3 pages) | Cited 10 times

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A compact THz-radiation source using an InAs semiconductor is demonstrated with a turn-key femtosecond fiber laser as an excitation source and a newly designed 2 T permanent magnet. By using a newly designed magnetic circuit, a compact permanent magnet which can exceed the remanence magnetic field was obtained. This compact source is sufficiently intense for absorption spectroscopy. © 2000 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
42.62.Fi Laser spectroscopy

Very low frequency quadrature oscillator

J. Bayard

Rev. Sci. Instrum. 71, 557 (2000); http://dx.doi.org/10.1063/1.1150241 (6 pages) | Cited 3 times

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We propose a low-cost, practical, quadrature oscillator with a period, Tq, which may be very long (Tq ≥ 1 s). We illustrate this design with an oscillator that produces two quadrature sinusoidal waves with a 1 s period. This design can be modified to provide signals of any shape by adjusting the value of one or more resistors. This design uses digital integrated circuits (ICs) and analog multiplexers. Digital ICs and an analog multiplexer are used to generate a stair-step waveform approximation by switching between the four members of a set of constant voltages. The duration, Tc, of each constant voltage is held constant (Tc = Tq/16). Then, a set of linear ramps, each ramp with a period Tc, is generated and selectively added to the stair-step approximation with another analog multiplexer. The use of multiplexed linear ramps, together with the stair-step approximation to the desired waveform, results in a smooth analog wave. The period, Tc = Tq/16, of the necessary linear ramp can be reduced as needed by increasing the number, 16, of stair-step per period, Tq, of the desired overall waveform. In this way, the values and sizes of components needed to generate high-quality waves with extremely long periods are made small enough to be practical. Experimental results of a detailed study of waveform quality are included. © 2000 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
84.30.Sk Pulse and digital circuits

High voltage multichannel wave form generator for liquid crystal research

T. Matuszczyk and R. Beccherelli

Rev. Sci. Instrum. 71, 563 (2000); http://dx.doi.org/10.1063/1.1150242 (4 pages) | Cited 2 times

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The article describes a wave form generator designed primarily for experiments on addressing all kinds of liquid crystal displays. It can also be used in any application requiring several simultaneous sources of high-voltage arbitrary pulse trains. The instrument has eight channels capable of pulse amplitudes of ±100 V at a slew rate better than 300 V/μs. Its design differs significantly from a typical arbitrary wave form generator. First and foremost the wave forms are directly constructed from pulses with variable width as well as amplitude. Two interchangeable memory banks guarantee transient-free adjustments of generated wave forms. The generator is computer controlled with well integrated software and provides all functionality to assist in the creation of wave forms and experiments with liquid crystal addressing schemes in a straightforward and intuitive way. To point out its versatility we discuss a new mode of operation intended primarily for generation of analogue gray shades on a surface-stabilized ferroelectric liquid crystal display. The instrument creates conditions corresponding to driving a display of virtually any size with image frames changing at video rate. © 2000 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
84.30.Ng Oscillators, pulse generators, and function generators
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
84.30.Jc Power electronics; power supply circuits

Eddy current testing probe with dual half-cylindrical coils

Byung-Hoon Bae, Jung-Mi Choi, and Soo-Yong Kim

Rev. Sci. Instrum. 71, 567 (2000); http://dx.doi.org/10.1063/1.1150243 (4 pages)

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We have developed a new eddy current probe composed of a dual half-cylindrical (2HC) coil as an exciting coil and a sensing coil that is placed in the small gap of the 2HC coil. The 2HC coil induces a linear eddy current on the narrow region within the target medium. The magnitude of eddy current has a maximum peak with the narrow width, underneath the center of the exciting 2HC coil. Because of the linear eddy current, the probe can be used to detect not only the existence of a crack but also its direction in conducting materials. Using specimen with a machined crack, and varying the exciting frequency from 0.5 to 100 kHz, we investigated the relationships between the direction of crack and the output voltage of the sensing coil. © 2000 American Institute of Physics.
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81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
84.32.Hh Inductors and coils; wiring

Two-dimensional finite element model for a long rectangular eddy current surface coil

Andrei Ptchelintsev and Benoit de Halleux

Rev. Sci. Instrum. 71, 571 (2000); http://dx.doi.org/10.1063/1.1150244 (6 pages) | Cited 2 times

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An eddy current model for predicting the electrical impedance variation of a long rectangular surface coil due to a surface breaking defect in layered conductors is reported. The method is based on transforming a three-dimensional eddy current problem into the spatial frequency domain and solving the transformed diffusion problem for a limited number of the spatial spectrum components. The transformed problem has been assumed to be quasitwo dimensional (2D) for a long rectangular surface coil and formulated in terms of a two-component transformed vector magnetic potential Ā and scalar electric potential math. The 2D problems have been solved with the finite element method using triangle elements. The system of algebraic equations was obtained using the Galerkin weak formulation and solved with the Gaussian elimination method. A high accuracy solution with ten spatial frequency components takes around 4 min on a Pentium 200 MHz PC. The accuracy of the solution has been tested experimentally at 200 kHz on coated stainless steel samples using a rectangular surface coil with the length-to-width ratio around 6. Agreement between theory and experiment is excellent. Discrepancies between the theory and experiment are within 15% and typically less. The method is useful for eddy current nondestructive evaluation and modeling, and can be also applied for the case of buried defects and for general multilayer coatings’ problem. © 2000 American Institute of Physics.
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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
84.32.Hh Inductors and coils; wiring
02.70.Dh Finite-element and Galerkin methods
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