Electromagnetic Compatibility Research

The Institute tests small satellites and subsystems for electromagnetic compatibility in accordance with military and government specifications such as MIL-STD-461 and MSFC-521B.

Computer-controlled testing
SwRI has developed software to automate most routine EMC tests. Computer-assisted calibration ensures reproducible and repeatable test results, which are important during the development of preproduction equipment. Test data are available for each test point, allowing detailed study of equipment performance during the test.

Vehicle design evaluation
The Institute performs automotive component and whole-vehicle tests for compliance with SAE, U.S., and international EMC vehicular industry standards. These services can be performed at any stage in development - from initial concept to final production. After analyses and investigation, SwRI can offer modification suggestions and services to the client.

Medical devices
SwRI tests electronic medical implants, monitoring equipment, and diagnostic equipment to European Union standards and to the Federal Drug Administration (FDA) Reviewer Guidance for Premarket Notification Submissions. These guidelines include those that govern cardiovascular, respiratory, and neurological devices.

Telecommunication devices
SwRI tests central office shelf-level telecommunications equipment for EMC, earthquake resistance, and fire in accordance with the Telcordia GR-1089-CORE test standard. The Institute also tests cell phones and other intentional radiators to FCC regulations.

EMC Test Facilities

Stirred mode chamber

SwRI designed this facility to accommodate testing of the whole vehicle as well as smaller components and subsystems. The stirred mode facility provides highly efficient immunity testing because the device being tested is immersed in a quasi-homogeneous electric field. This method minimizes test time and costs.

Using a ceiling-mounted aluminum stirrer turned by a pneumatic motor, the SwRI stirred mode facility efficiently tests whole vehicles and smaller systems. The position of the stirrer is monitored through a fiber-optic link.

Shielded enclosures

Institute EMC facilities include eight shielded enclosures, ranging in size from 10 by 20 by 10 feet to 20 by 30 by 12 feet. All enclosures have filtered 120/208 three-phase 60 Hz power, with 50 and 400 Hz power available, and can be configured with RF absorptive material. Two sets of enclosures share a common wall, which makes it possible to isolate the EUT and instrumentation from the ambient RF fields. Each enclosure provides:

• 100 dB of attenuation to electric fields from 1 kHz to 25 MHz
• 100 dB of attenuation to plane waves 25 MHz to 10 GHz
• 20 dB H-Field attenuation at 1 kHz increasing to 100 dB at 150 kHz

RF anechoic chambers

SwRI's RF anechoic chamber measures 28 by 16 by 16 feet and provides RF attenuation in excess of 100 dB in the 30 MHz to 40 GHz range. This facility can be fully configured with anechoic material or used without the material on the floor to expose the ground plane.

Open area test site

The Institute maintains an open area test site (OATS) to measure radiated emissions from electronic and electrical equipment. The level test site is clear of electromagnetic reflecting surfaces for a minimum radius of 32 meters. Three-phase 60 and 400 Hz, single-phase 50 Hz, and DC power are available to test systems. This site has a large, continuous metal ground plane (20 by 40 meters) and a four-meter diameter flush-mounted turntable capable of supporting 15,000 pounds to conduct tests in accordance with:

• ANSI C63.4
• CISPR
• IEC
• ISO standards

Tri-plate-line fixture

SwRI's extensive facilities include a Tri-plate-line (TPL) test fixture, designed and built by SwRI in accordance with Society of Automotive Engineers (SAE) specification J1113-25. Using the TPL fixture, engineers conduct radiated immunity testing of various automotive modules, sensors, subsystems, and their associated wire harnesses. Within the TPL, electromagnetic fields in excess of 200 volts/meter from 10 kHz to 1 GHz can be produced.

The Tri-Plate-Line test fixture is used to assess radiated immunity of automotive electronic modules. SwRI subjects small assemblies to very high levels of radiated electromagnetic fields.

Transverse electromagnetic (TEM) cells

The Institute's three TEM cells are ideal for EMC testing small modules and brass board prototypes. The largest cell operates over frequencies from DC to 250 MHz. SwRI built the two additional cells to the Crawford cell design. One operates from DC to 500 MHz and the other, from DC to 1 Ghz.

EMC Development Activities

EMC engineers and technicians, certified by the National Association of Radio and Telecommunications Engineers, Inc., perform tests on electronic devices to detect and measure electomagnetic emissions and to identify susceptibility/ immunity problems associated with radiated radio frequency energy. Based on an analysis of these data, SwRI engineers can suggest electronic design modifications to remedy EMC noncompliance.

To understand complex electromagnetic compatibility interactions, engineers use sophisticated modeling algorithms. This planewave simulation at the interface of two media shows that the incident and reflected fields on the left side interfere with the surface wave on the right (plot of magnitude versus position).

Using internal funding, the Institute develops improved EMC test equipment, special-purpose test systems, and novel testing techniques. SwRI staff members have developed direct RF injection techniques and performed studies to develop stirred-mode technology.

SwRI engineers used custom-designed pneumatic controls (left) to remotely control this vehicle without interference from the radiated electric field.

EMC simulation and numerical analyses

SwRI performs EMC simulation and modeling of systems interactions that are difficult to characterize using standard EMC test procedures. To perform these analyses, engineers use a wide range of theoretical analytical techniques, including:

• Finite difference time domain modeling
• Method of moments
• Partial element equivalent circuit
• Pade Via Lanczos algorithms
• Statistical methods

Using state-of-the art simulation and modeling techniques, SwRI analyzes

• Circuit boards
• Transmission-line interconnects
• Wire harness cross-talk
• Shielding effectiveness
• Waveguides and transmission lines
• Antenna cosite and collocation issues

Additional Services

Electrical properties

SwRI evaluates the electrical properties, shielding effectiveness, transmission loss, and reflection coefficients of materials for frequencies up to 20 GHz. Active and passive circuits — in whole buildings, enclosures, and systems — are tested according to:

• MIL-STD-285
• NSA 65-6
• MIL-R-770B
• ASTM D 3380
• ASTM D 1531

On-site consultation

The Institute provides rapid response consultation and technical support for specific, on-site evaluations ranging from short tests to long-term projects requiring more extensive testing. SwRI has the diagnostic test equipment needed for fast, accurate, and cost-effective solutions to a variety of EMC-related problems. With this expertise, Institute engineers can identify and remedy noncompliant conditions while on-site.

Training

SwRI offers classroom and laboratory training covering many aspects of EMC technology, either at SwRI or at a client's facility. Subjects include design, analyses, maintenance, test methodology, and standards interpretation. Assistance is also available to architects and engineers in developing appropriate shielding, SCIFs, and RED/BLACK installations.

Systems support

Complex systems and subsystems often require a multidisciplinary approach to testing. The Institute tests and evaluates systems for EMC, environmental, and other performance parameters, including MIL-STD-810, MIL-STD-461/462, and FAA/RTCA DO-160. Additional multidisciplinary guidance is available from the Institute's 12 technical divisions.

Antenna calibration

SwRI provides reproducible and repeatable antenna calibration, using various techniques, such as two-antenna signal substitution and the ANSI three-antenna method. The Institute also performs directivity pattern measurements as required by FCC regulations.

Environmental services

In addition to providing EMC services, the Institute simulates environments to pinpoint and solve operational problems. Environmental conditions that are impossible to otherwise recreate, such as earthquakes, can be simulated to determine their effects on systems and components. SwRI's range of environmental simulation services includes:

• Simulation of in-service vibration loading
• Seismic simulations using SwRI- or client-defined earthquake inputs
• Simulation of natural environments
• System dynamic response characterization
• Vibroacoustic system simulation services
• Validation of analysis scenarios from model data
• Validation of telecommunications equipment according to specific standards, for example, Telcordia TR-NWT-000063, Issue 4 NEBS.

The Electromagnetic Compatibility Research Section of SwRI has achieved accreditation to ISO/IEC 17025, "General Requirements for the Competence of Calibration and Testing Laboratories."

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