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Fachzeitschrift für Hochfrequenz- und Mikrowellentechnik

Messtechnik Shielding

Messtechnik Shielding Effectiveness and Shielded Enclosure Leakage Detector System Figure 1: AR Model CL-105A/CL-106A Shielding Effectiveness Leakage Detector System This application note will focus on the SELDS (Shielded Enclosure Leakage Detector System) approach. Today both commercial and military industries are more reliant than ever on electronics. In addition, the need to protect those electronics from potential threats has become even more vital. Threats like electromagnetic interference (EMI) and High-Altitude Electromagnetic Pulse (HEMP) have the ability to interrupt or even destroy the functionality of unprotected electronics. The military has long been aware of the effects of electromagnetic interference and has taken proper precautions to shield electronics, but in some cases, additional measures are required to ensure proper operation. Therefore, the military has, for a long time, often used shielded rooms to house their network and other equipment. have become more stringent and time-critical in testing the shielding effectiveness of facilities. The AR Model CL-105A/CL- 106A, Shielded Enclosure Leak Detection System (SELDS), is an instrument for verifying the integrity of shielded enclosures. The SELDS method can be used at almost any stage of enclosure construction, but it is most accurate and efficient when used after facility electromagnetic barrier is fully complete. SELDS can also be used to evaluate the shielding effectiveness of non-military and commercial applications— Banks and Financial Institutes, Data Centers, Research and Medical hospitals, Nuclear power plants, Subways, Submarine pipelines, Telecomm base stations, etc. Basics Any closed box could be considered “shielded” to some extent – even a lunch box – but to achieve the level of shielding needed to meet the stringent requirements of standards such as MIL-STD-188/125-1 and MIL-STD- 461G, an enclosure must be sealed to the extent that signal leakage is minimal. The main purpose of the MIL- STD- 188-125 Shielding Effectiveness Source: App Note #80, Shielding Effectiveness and Shielded Enclosure Leakage Detector System (SELDS), AR, rf/ microwave instrumentation Furthermore, as the entire world is moving towards innovations backed by emerging technologies such as IoT (Internet of Things), Blockchain, Automation, AI (Artificial Intelligence), etc., the need for storing and protecting the proprietary information has become extremely critical. With the increased amount of electromagnetic pulse (EMP) and EMI threats, the shielding requirements Figure 2: Enclosure Feed-Wire Connection Diagram View 8 hf-praxis 6/2019

Messtechnik ® (SE) test is to demonstrate the SE integrity of a shielded room/facility, conduit, and apertures Point-of-Entry (POE) as noted in Appendix C and SELDS survey IAW MIL- HDBK-423. The shielding effectiveness of the shielded barrier required for high-risk HEMP application is necessary for the protection of ground-based electronics with time-critical missions. Part-1 of MIL-STD 188-125 “High-Altitude Electromagnetic Pulse Protection for Ground-Based Facilities Performing Critical, Time-Urgent Missions Part 1 Fixed Facilities” reference the military handbook (MIL- HDBK-423) for Shielding Effectiveness (SE) integrity test methods. SELDS test method is an electromagnetic method for locating leaks in welded and brazed joints, including seams,patches, etc. The final SELDS test during construction is accomplished when the barrier is complete, prior to the final acceptance test. Furthermore, the SELDS technique is frequently the basis of the built-in shield monitoring capability required by MIlL-STD-188-125. So, the ideal EMI shielded room would be a metal box with no seams, openings, or ingress from cables, but unfortunately, that’s not possible due to the need for access to the equipment and military personnel inside. SE testing often identifies weaknesses in the shield, which are not visually detectable. There are two characteristics that determine the electromagnetic shielding effectiveness of an enclosure: • the ability of the enclosure wall material to reflect or dissipate the EM wave energy, and • the integrity of the wall; i.e., the tightness of the contact between panels, doors, and POE. This application note will focus on the SELDS approach defined in the military handbook (MIL-HDBK-423), to determine SE, using the AR rf/microwave instrumentation (AR) CL-105A/CL-106A, shown in Figure 1. The AR SELDS AR RF/Microwave Instrumentation has unveiled a Shielded Enclosure Leak Detection System (SELDS) for testing the electromagnetic shielding effectiveness of EMI enclosures. The new CL-105A/CL-106A detection system allows detection at the most likely points of degradation – the seams, doors and filters connections, in a convenient and hassle-free method. Discontinuities permitting RF leakage at welds, seams, corners, etc., can be detected and remedied to ensure that the finished enclosure is properly assembled. The system consists of a Model CL-105A Transmitter, Model CL-106A Receiver, headphones and a rugged carrying case. The incredible sensitivity of the model CL-105A Receiver allows it to meet the most rigid MIL standards (e.g. MIL-STD-188/125) for shielded room acceptance. The system is designed to make relative shielding effectiveness measurements by passing a current along the surface of an EMI enclosure in order to sense the small magnetic fields formed where breaks in the EMI enclosure may occur. The Model CL-105A Transmitter is used to generate an output signal (96kHz) which is connected to the EMI enclosure under test. This device has an auto-adjusting output that works with small, medium, and large EMI enclosures. The 96 kHz signal is low enough in amplitude to ensure that a relatively uniform RF current flow occurs on all sides of the enclosure. An LED indicator illuminates green when the Transmitter has adjusted the output to the optimum level for the connected EMI enclosure. The Model CL-106A Receiver has high sensitivity (dynamic range: 120 dB) to detect the smallest of magnetic fields produced at breaks/discontinuities in the EMI enclosure under test. This unit auto-zeros and features an auditory output with a varying amplitude related to the shielding effectiveness. The auditory output is available through the built-in speaker or included headphones. A 4-digit seven segment display is provided to indicate relative shielding effectiveness measurement values in dB. In addition, a built-in LED light source provides illumination when used in dark environments. Principle operation The Model CL-105A/CL-106A system is comprised of two main parts; a Transmitter and a Receiver. The Transmitter is designed to drive a current through the skin of a shielded enclosure. The CW output signal has a frequency of 96kHz. The system is designed to drive very low impedances; thus, the Transmitter is operating as a current source. The output current is nominally 800mA RMS. For normal tests, the Transmitter will be connected via feed wires to opposite corners of the enclosure exterior and will transmit an AC current across the metallic surface of the enclosure. The Receiver cannot detect the signal except at the points where the enclosure has openings or metallic discontinuities which cause a small magnetic field to form. The unit is designed to allow detec- WWW.AARONIA.DE HIGH RANGE DRONE DETECTION SYSTEM 270 90 RF Detection System with 24/7 recording and automatic signal-classification in real-time High Range, 15km and more Detects the UAV & Operator Passive & Fully Automatic Optional Countermeasures Telefon: +49 6556 9019 350 Mail: mail@aaronia.de Web: www.aaronia.de MADE IN GERMANY hf-praxis 6/2019 9 9

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