Compatibility Measurements Research Articles

Fluxgate magnetometer for low-frequency magnetic electromagnetic compatibility measurements

A new fluxgate magnetometer has been developed for measuring magnetic fields with frequencies up to 2 kHz, based on a novel sensor design and readout electronics which ensure the stabilization of the premagnetizing field. The sensor is made from an amorphous core material, 25-/spl mu/m thick, and provides a closed path for the premagnetizing field. The magnetometer has been designed using a pulse-width modulator and has a resolution of 10 nT. Errors due to nonlinearity and frequency response are smaller than 0.1 mT/T over the specified frequency range.

Organic Materials Filled with Ferrite Powder for Electromagnetic Compatibility

Electromagnetic Compatibility (E.M.C.) measurements, that today becomes more and more important, requires materials having high attenuation level, typically -20 dB from 30 MHz to 20 GHz. Because of their low frequency range absorption, ferrite are only efficient up to 1 GHz. The use of dispersion techniques for development of granular materials as microwave absorbers is a convenient way to make coatings with good attenuation characteristics in the 1 - 20 GHz range. Especially, elastomer mixing is a very good technique for dispersion and individualization of each grain of ferromagnetic powder (iron, cobalt, permalloy,...) or ferrimagnetic powder up to 60% (volume) while maintaining electrical insulation [1]. Such materials are easy to process by classical processing polymer techniques and can be processed in various shapes. It has already been shown that combination of magnetic material properties and geometrical effect by molding under the form of conical or pyramidal shapes significantly broadens the absorber frequency range working [2]. These absorbers with conical or pyramidal pattern, are very efficient above 1 GHz due to creation of a geometrical gradient. The realization of an architecture by combining a ferrite tile with a conical shaped ferrimagnetic granular material leads to very braodband absorbers suitable for E.M.C. applications. Their high level of performances (typically -20 dB from 30 MHz to 20 GHz for a thickness less than 100 mm) makes them a new generation of absorbers for anechoic chambers compared to classical pyramidal dielectric foams.

Exact solution for the characteristic impedance of rectangular coaxial cone transmission line

The exact and approximate expressions for the characteristic impedance of a rectangular coaxial cone transmission line are obtained using the conformal mapping method. The formula is exact and simple, so, it enables the characteristic impedance of a broadband transverse electromagnetic (TEM) cell to be calculated accurately and easily. This broadband TEM wave cell, has increasing applications in both electromagnetic interference and electromagnetic compatibility measurements.

Simulating measurements for a cable radiation study

Accurate numerical simulations are needed for analyzing and developing better electrical interconnects and electromagnetic compatibility (EMC) measurement systems. Numerical simulations enable one to predict the field behavior and compute the voltages, currents, impedances and other parameters of interest for a given structure such as cable shielding. A numerical simulation is used to analyze measured data from a cable radiation study. The finite difference time domain (FDTD) and the method of moments based Numerical Electromagnetics Code (NEC) are used to compute the total radiated power from the cable, and the results are shown to be in agreement with measured data. A numerical study is carried out to demonstrate the usefulness of the method at aiding the design of a measurement system without much additional experimental work.

A low-frequency model for wedge or pyramid absorber arrays-I: theory

The interaction of electromagnetic waves with an array of absorbing wedges or pyramid cones is studied in the low-frequency limit; i.e., when the period of the array is small compared with wavelength. A theoretical model is obtained using the method of homogenization, which replaces the transversely periodic structure with a transversely uniform medium possessing a certain (generally anisotropic) effective permittivity and permeability. Plane-wave reflection from such structures can then be modeled using well-known techniques for one-dimensionally inhomogeneous media; a Riccati equation for the reflection coefficient is used in this work. This model is appropriate for use with absorbers found in anechoic chambers used for electromagnetic compatibility and electromagnetic interference (EMC/EMI) measurements over the frequency range of 30-1000 MHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A low-frequency model for wedge or pyramid absorber arrays-II: computed and measured results

Based on the theoretical model developed in Part I of this two-part paper, we present numerical results for the plane-wave reflection coefficient from arrays of pyramid-cone absorbers when the period of the array is smaller than half a wavelength. Comparison is made with results of a moment-method calculation, as well as with experimental measurements. The model is then used to modify the design of some existing types of commercially available absorbers for reduced reflection in the frequency range of 30-300 MHz. These improved absorbers have been installed in an anechoic chamber used for electromagnetic compatibility and electromagnetic interference (EMC/EMI) measurements. Site attenuation measurements from this chamber are presented which show closer correspondence to an ideal open-field test site. >

Recent developments in measurement techniques for use in screened rooms

Screened rooms have been used for many years to perform electromagnetic compatibility measurements in an electromagnetically isolated environment. It is only in recent years that measurement techniques have been developed that to some extent overcome many of the difficulties encountered when a measurement is performed in a totally or partially reflecting environment. The paper reviews these recent techniques and describes their application. The techniques are reviewed in ascending order of frequency range of applicability.

Thermodynamics of PVC—plasticizer interaction: A review

AbstractIn this review we evaluate many of the experimental techniques for measurement of polymer solvent interaction thermodynamics, placing special emphasis on the interaction between plasticizers and semicrystalline materials. Methods are reviewed for measurement of heat and volume of mixing, Flory‐Higgins interaction parameter (chi), virial coefficients, and empirical compatibility measurements.

Short axial length broad-band horns

Ever-increasing antenna frequency bandwidth requirements for countermeasures applications and electromagnetic compatibility measurements have provided the impetus for the development of a series of very broad-band horns. In addition to the broad bandwidth, a substantial reduction in axial length over that of earlier models has been achieved for the two designs discussed in this communication. The first horn described covers the frequency range from 1.0-12.0 GHz with the flared portion of the horn having an axial length of 6 in as compared with 12 in for an earlier model. Although horn antennas are not commonly considered for use at frequencies as low as 0.2 GHz, the short axial length design appeared to be an attractive approach in developing a very reasonably sized antenna operating in the 0.2-2.0 GHz range. The technique of fabricating the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> plane walls in the form of a grid was used in both designs as a means of maintaining the required <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> -plane half-power beamwidths. The grid for the 1.0-12.0 GHz horn is of printed circuit form while the grid elements of the lower frequency horn are made of aluminum tubing. Electrical characteristics of both designs are presented, as well as some additional data for recent advances which indicate that a further reduction in axial length or an increase in bandwidth can be achieved with only a moderate rise in VSWR in the lower portion of the frequency range.

Compatibility of plasticizers with poly(vinyl chloride)

AbstractThe tendency of a plasticizer to resist exudation from poly(vinyl chloride) (PVC) under compressive stress, known technologically as “compatibility,” is treated in terms of a network model, the plasticized composition being thought of as a rubber crosslinked by crystallites. Compatibility is increased by increased solvency (Flory‐Huggins χ) and decreased by increasing plasticizer molar volume. A large crosslink density and/or insufficient melting of crosslinks during processing (thermal history) also decreases compatibility. All commercial primary plasticizers are believed to be infinitely miscible with amorphous PVC. Phase separation which occurs is syneresis and not related to any phase diagram. Swelling tests for compatibility and swelling measurements on dilute PVC gels are described. Some general principles relating to gel formation and association in polymer solutions are also discussed.

Increased sensitivity of direct-detection microwave receivers for compatibility measurements

Increased sensitivity of direct-detection microwave receivers for compatibility measurements