John K. Daher

Electromagnetic shielding and corrosion protection for aerospace vehicles

Electromagnetic Shielding Effectiveness and Corrosion Prevention.- Fundamentals of Corrosion.- Fundamentals of Electromagnetic Shielding.- Investigation of the Relationship Between DC Resistance and Shielding Effectiveness.- Identification and Evaluation of Optimum Conductive Sealant Materials.- Field Test Evaluations on E-3A Aircraft.- Assessment of the Validity of the MIL-B-50878 Class R Bonding Requirements.- EMI Gaskets.

Measurement and modeling of near- and far-field antenna factor

This paper summarizes a recent investigation into the measurement and modeling of antenna factor as a function of separation distance. Measurements were made of coupling and antenna factor (AF) for a standard gain dipole as a function of distance from an identical source. Coupling and AF were also computed using two electromagnetic computer codes to compare the numerical results with each other and with the measurements. The coupling measurements were made in an anechoic chamber using two identical standard gain dipoles at 300 MHz, both with and without a ground plane. In the case with a ground plane, both horizontal and vertical polarizations were examined. Distances were varied to cover from the very near-field to the far-field of the antenna. Measured values of the AF at 300 MHz were frequency scaled to predict the AF at 30 MHz. In addition to the measurements, the Numerical Electromagnetics Code (NEC) Method of Moments and the General Electromagnetic Model for the Analysis of Complex Systems (GEMACS) were used to calculate coupling and AF values for direct comparison with the measured values.<<ETX>>

A radiated susceptibility test technique for PC boards implementing built-in-test or boundary scan designs

The authors describe a test technique and procedure for performing radiated susceptibility testing of printed circuit (PC) boards which implement built-in-test (BIT) or boundary scan designs. The measurement technique involves illumination of the circuit-under-test (CUT) with an electromagnetic plane wave generated in a TEM (transverse-electromagnetic) cell using a fiber-optic input/output (I/O) interface to the external test equipment. By isolating the CUT from the rest of the test environment, flaws in the EMI (electromagnetic interference) design/layout of PC boards can readily be identified and quickly retested using the recommended technique. Only a limited number of I/O pins must be interfaced to the digital test equipment when testing in BIT mode. A specific example of the use of these techniques and procedures as applied to a self-testing Am29034-bit microprocessor slice test circuit is also given.<<ETX>>

Test concept and experimental validation of the use of built-in-test to simplify conducted susceptibility testing of advanced technology integrated circuits and printed circuit boards

A description is given of the test concept and experimental validation of measurement techniques which exploit built-in-test (BIT) to simplify RF susceptibility measurements of complex digital integrated circuits (ICs) and printed circuit (PC) boards. The use of the BIT capability of VLSI devices and PC boards: (1) simplifies the hardware and software interfaces to the device-under-test; and (2) reduces the external test equipment requirements. A specific example is given as to how these techniques and procedures were applied to a self-testing Am2903 4-bit microprocessor slice test circuit. Test data are presented which demonstrate the feasibility of using BIT techniques to obtain susceptibility thresholds with a significant reduction in test complexity and external test equipment requirements. The limitations associated with using BIT techniques for susceptibility characterizations of ICs and PC boards are also addressed.<<ETX>>

Commercial GPS receiver susceptibility evaluation

The radio frequency (RF) susceptibility characteristics of two commercial Global Positioning System (GPS) receivers were evaluated. A first-order analysis was performed to predict the receiver susceptibility thresholds based on the receiver sensitivity and processing gain. The receiver susceptibility thresholds in the post-acquisition mode were then measured for various interference signal frequencies and modulations. Both receivers exhibited very low susceptibility thresholds to in-band continuous wave (CW) signals. In addition, both receivers could be overdriven with an out-of-band signal. In this state the receivers indicated acceptable figures of merit despite loss of satellite signal lock.<<ETX>>

Fundamentals of Electromagnetic Shielding

The shielding effectiveness (SE) is typically defined as the ratio of the magnitude of the incident electric field, E i , to the magnitude of the transmitted electric field, E t :

Electromagnetic Shielding Effectiveness and Corrosion Prevention

SE = \left| {\frac{{\vec E_i }} {{\vec E_t }}} \right| SE\left( {dB} \right) = 20 \cdot \log _{10} \left( {\frac{{E_i }} {{E_t }}} \right)

Fundamentals of Corrosion

(3.1)