Ronald M. Sega

Infrared Measurements of Scattering and Electromagnetic Penetration through Apertures

An infrared detection technique is used to measure the electromagnetic fields near apertures of planar and cylindrical structures. Qualitative and quantitative results are presented and compared with theoretical solutions where applicable.

An Infrared Measurement Technique for the Assessment of Electromagnetic Coupling

A non-destructive, non-perturbing infrared measurement technique is under development to observe the effects of electromagnetic coupling of energy to the interior of complicated geometrical structures. The applications, advantages, and disadvantages of this new infrared technology are discussed.

Phase Measurements of Electromagnetic Fields Using Infrared Imaging Techniques and Microwave Holography

Complex (magnitude and phase) measurements of the near field of a radiating antenna over a known surface (usually a plane, cylinder, or sphere) can be used to determine its far-field radiation pattern using near-field to far-field Fourier transformations. Standard gain horn antennas are often used to probe the near field. Experimental errors are introduced into the near-field measurements by mechanical probe position inaccuracies and electrical probe interactions with the antenna under test and probe correction errors. A minimally perturbing infrared (IR) imaging technique can be used to map the near fields of the antenna. This measurement technique is much simpler and easier to use than the probe method and eliminates probe position errors and probe correction errors. Current IR imaging techniques, which have been successfully used to rapidly map the relative magnitude of a radiating field at many locations (mXn camera pixels per image captured) over a surface, however, suffer from an inability to determine phase information. Absolute magnitude and relative phase data can be obtained by empirical or theoretical calibration of the IR detector screens (used to absorb the radiated energy over the measurement plane) and by using techniques from microwave holography. For example, magnitude only measurements of the radiating field of an antenna at two different locations (over two different surfaces) in the near field of the antenna can be used to determine its complex (magnitude and phase) far-field radiation pattern using plane-to- plane (PTP) iterative transformations. This paper discusses the progress made to data in determining both magnitude and phase information from IR imaging data (IR thermograms); thus, enabling near-field and far-field measurements of antenna patterns using IR thermal imaging techniques.

Correlation of infrared measurement results of coupled fields in long cylinders with a dual series solution

A theoretical code for determining electric field distributions in long cylinders is validated by an infrared experimental method. A summary of the theoretical approach using the generalized dual series (GDS) solution is presented. The theoretical solutions for selected geometries used for comparison are depicted as cross-sectional views of experimentally generated infrared (IR) images. The IR images are obtained from microwave interactions and are related to the field intensity at their locations. Qualitative comparisons are made between the field strengths measured using the thermal radiation experimental approach and a theoretical prediction for various frequencies. The experimental and theoretical results show reasonable correlation. >

Scattering effects of electric and magnetic field probes

Many electromagnetic measurements of electromagnetic pulse (EMP) interactions with electronic systems use B-dot and D-dot probes. The effects of the measurement probe on the field distribution being measured is considered. An infrared measurement technique is used to determine the field distributions with and without the presence of electric- or magnetic-field probes. Two-dimensional thermogram images of the scattered field patterns are measured. The scattering effects of various probes in the frequency range from 1 to 10 GHz are presented. This frequency range can be used to scale-model many EMP and high-power microwave (HPM) effects. It is shown that wide variations in the response of a probe can occur due to resonant frequency and mutual-coupling effects. These effects are due, in part, to the different measurement configurations of the probe relative to the direction of propagation and polarization of the incident electromagnetic wave to be measured. These differences can be significant at certain frequencies and separation distances for the various probe measurement configurations. >

Measured Internal Coupled Electromagnetic Fields Related to Cavity and Aperture Resonance

Preliminary internal coupling tests using an infrared (IR) measurement technique were conducted with a hollow metal cylinder having a thin slot aperture. Internal field mapping shows dramatically that the energy coupled through an aperture into a given structure is strongly dependent on frequency. In particular, frequencies corresponding to the resonance of the cavity and resonance of the aperture show significant coupling into the cylinder, while those frequencies slightly off a resonance frequency show a greatly reduced internal field confined to the immediate region of the aperture.

Infrared mapping of transient electromagnetic fields radiated by high power microwave pulsed sources

The intensity of the transient field radiated from a high-power microwave (HPM) pulsed source is measured using an infrared (IR) mapping technique. The electromagnetic (EM) waveguide mode generated in the interior source region of the HPM source is determined. The transverse electromagnetic (TEM) mode excited in the antenna feed structure is mapped in the cross section of the feed horn. The radiated EM field exterior to the HPM source in the main beam of the TEM horn is mapped to determine the near and far field structure of the HPM source. >

Infrared Application To The Detection Of Induced Surface Currents

It has been qualitatively demonstrated that the surface currents induced by incident electromagnetic radiation produce I2R heating detectable through thermographic techniques. This paper presents the progress to date toward obtaining quantitative comparisons of known surface current amplitude distributions with those obtained through infrared thermographic analysis. Data for correcting for the directional dependence of IR emission from various surfaces is given, a method of digital analysis of the thermographic data is discussed, and an actual thermographic determination of the surface currents on a square flat plate is presented. These experimental results represent a necessary step in the effort of infrared detection and measurement of the current amplitude distributions on complex shapes.

Microwave Fields Determined From Thermal Patterns

An infrared (IR) measurement technique is described which can be used to detect microwave fields, both continuous wave (CW) and pulsed. The technique involves placing a thin lossy detection screen material in the region over which the electromagnetic (EM) field is to be mapped. The fields are detected through the Joule heating that occurs when EM energy is absorbed by the screen material. When the surface temperature of the screen rises to 0.1 K or higher above the ambient temperature, the induced temperature distribution at the surface of the screen (which corresponds to the EM field intensities in the screen) can be detected by an IR scanning system via emitted thermal radiation. CW measurements by an IR measurement technique have been demonstrated and reported over the past several years. While the technique requires a minimum energy deposition for sufficient heating, the electrical parameters of the detection screen can be selected, such that the thermal mass of the screen is reduced, allowing a faster response. IR data acquisition to a high-speed memory has also been developed to store approximately 500,000 pixels of a two-dimensional IR image in less than three seconds. 5 This corresponds to thirty 128 x 128 frames of data with each pixel element represented as an 8-bit word, which correlates to the electric or magnetic field intensity at that location. As a diagnostic tool, this technique can be used to measure radiated fields and to support tests and evaluations of electronic systems in the presence of EM radiation, e.g., to determine the free-field environments around microwave sources, to determine the energy coupled into electronic circuits through partially shielded enclosures, and to verify hardening techniques. The near, far, and internal fields generated by a microwave horn can be mapped using a thin lossy screen. Apertures in enclosures can be identified by placing a resistive coating on the surface of the metal in the area suspected of containing an aperture. Examples of energy coupled into an electronic circuit and analysis of radiation from antennas are presented. The applications, advantages, and disadvantages of this new infrared technology are also discussed.

Expansion Of An Infrared Detection Technique Using Conductive Mesh In Microwave Shielding Applications

An IR transparent, but microwave opaque, conductive mesh structure is developed to shield an infrared (IR) system from intense electromagnetic (EM) interference in the microwave range . To prevent potentially damaging EM radiation from penetrating or coupling into the IR system, the IR scanner is enclosed in a Faraday cage. One implication of this IR camera shielding technique is an ability to acquire accurate IR data in any noisy EM environment. A second application of the conductive mesh involves the investigation of EM fields in a copper cylinder, closed at both ends, constructed with a copper mesh section incorporated at one end of the cylinder. Using several positions for the detection material, three-dimensional field profiles are obtained and the results are presented.