IMPORTANCE OF ELECTROMAGNETIC COMPLIANCE FOR BOMB SUITS AND HELMETS


By Doug Wong1, Jean-Philippe Dionne1, Aris Makris1, Alex Leask2, Trevor Yensen2

1 Med-Eng, 2400 St. Laurent Blvd., Ottawa, Canada, K1G 6C4
2 Allen-Vanguard, 2405 St. Laurent Blvd., Ottawa, Canada, K1G 5B4

Insurgents’ activities over the last two decades in Iraq and Afghanistan have shown an alarming trend towards command-initiated Radio Controlled Improvised Explosive Devices (RCIEDs). These devices are easy to make, inexpensive, and can be easily acquired in almost any country. With an estimated 70% of terror attacks globally involving remotely detonated IEDs, technological adaptations of equipment and operating procedures are required to ensure all-hazard protection to bomb technicians against the evolving threat of Radio-Frequency (RF) initiated IEDs.

The primary means of mitigating this threat to bomb technicians is through the use of high-energy Electronic Counter-Measures (ECM), often called “jammers”. ECM equipment can be mounted inside a vehicle or hand-carried (Figure 1) by the technician. It has the effect of jamming or blocking Radio-Frequency (RF) signals in a localized area to prevent terrorists from using a remote transmitter to activate the RCIED. This is accomplished by radiating various electromagnetic frequency patterns at high energy in the area near the jammer. The radiated power will disrupt RF signals in the jamming “bubble”, including lawful communication frequencies that may be used by the bomb technicians. In addition to the active effects of transmission blocking, the ECM equipment may induce unwanted electric signals in any electrical component carried by bomb technicians that has inadequate shielding. These spuriously induced signals can interfere with electronic operations and degrade performance in any unprotected electronic system such as communications systems and microcontrollers. Such unprotected electronic systems also risk permanent damage from high RF energy.

The level of RF interference in a jamming “bubble” may be higher than what US Federal Communications Commission (FCC) compliance testing would experience, so passing more stringent military standards tests is needed to minimize issues due to Electromagnetic Interference (EMI).

Figure 1: a) Bomb technician hand-carrying an ECM device (RF jammer) while approaching a suspected device.  b) Bomb technician next to a vehicle equipped with mounted RF jammers.

Certain Explosive Ordnance Disposal (EOD) helmet designs available on the market today were not intentionally designed to provide sufficient RF shielding in order to permit full electronic functionality of the various on-board subsystems, e.g., speakers, ventilation, communications, under an active jammer environment. In particular, RF compliance was not included in the development of the NIJ 0117.01 standard for Public Safety Bomb Suit from the US National Institute of Justice, the only currently existing standard specific to EOD personal protective equipment. Moreover, irrespective of the use of ECM equipment, it is possible that the electronic functions (i.e. communication, ventilation, lighting, power) of the existing EOD helmets allow for short-range induction into other electrical components. This induction could potentially cause an inadvertent detonation of an IED that may contain an overly sensitive electrically-driven initiation system.

As such, it is necessary to reconfigure the conventional design of EOD helmets to permit them to be operational and safe in close proximity to IEDs and/or in conjunction with ECM equipment being deployed, from both a susceptibility and emissions perspective.

DESIGN CONSIDERATIONS
The first RF/ECM compatible EOD helmet was launched in 2007, developed through funding from the CBRN Research and Technology Initiative from Defence R&D Canada, the research branch of the Canadian Army. The improved design that resulted from this initiative allowed bomb technicians to work in harsh RF environments using state-of-the-art ECM equipment while maintaining the required and expected functionality currently used as a standard by most First Responders in North America, Europe, Middle East, Africa and Asia. This helmet also accommodated combined Chemical/Biological Blast protection to EOD technicians already available with conventional EOD helmets at the time.

Electromagnetic compatibility is an essential feature of any specification for military and law enforcement electrical equipment (not just EOD) and is defined as the ability of electrical and electronic equipment, subsystems and systems to share the electromagnetic spectrum and perform their desired functions without unacceptable degradation for or to the specified electromagnetic environment.

The EOD helmet (and interface) design changes necessary to ensure electromagnetic compatibility that permit close-up and safe operation in harsh RF environments included redesign of problematic components and systems to address the RF shielding and emission challenges. The electronics systems had to be redesigned, the mechanical enclosure revamped and the entire system tested to ensure compatibility with RF/ECM standards (namely MIL-STD-461 and Def-Stan-59-411, discussed in the next section). All cabling and interfaces, including connectors, had to be redesigned and “hardened” to resist leakage (entry or emissions) of RF spectrum within the frequency range of interest, as defined by the particular standards adhered to for ECM design compatibility.

To meet the most stringent Electromagnetic Interference (EMI) and EMC tests, all systems and wiring designs must pay careful attention to high performance shielding, and maintaining shielding integrity, as well as rigorous filtering of all signals and power wiring. For instance, audio circuits, both microphone and speakers, are particularly susceptible to EMI ingress, causing a buzzing sound, especially from an ECM jammer.

Manufacturing methods are also important as RF hardening introduces a higher level of complexity in component selection and assembly methods, and consequently higher costs. For example, it is uncommon for small wearable connectors to be waterproof and still offer a full 360-degree braided shield connection capability. Likewise, it is problematic to make a high-quality EMI gasket on a small electronic enclosure that is also fully waterproof. The connectors on enclosures are also critical in allowing or preventing noise from crossing the enclosure wall. Even shielded connectors are insufficient in this regard and special techniques are needed to achieve high performance. Another example is designing good EMI filters on a printed circuit board (PCB), which requires special methods to ensure noise gets properly attenuated without bypassing the filters.

STANDARD ELECTROMAGNETIC TESTS
To ensure optimal functionality and safety in the view of RF threats, bomb suits and helmets, in a first step, should be tested against relevant electromagnetic military standards. Such standards establish limits for both radiated electromagnetic emissions and susceptibility to electromagnetic radiation with respect to electronic, electrical and electromechanical equipment and subsystems.

Figure 2: a) EOD helmet tested for electromagnetic compliance (MIL-STD-461 and Def-Stan59-411)in an anechoic chamber (David Florida Laboratory, Canadian Space Agency, Ottawa, Ontario, Canada)   b) RF jammer (Allen-Vanguard) subjected to the same tests.

While there exist commercial electromagnetic compliance standards (e.g. FCC, EC), more stringent military standards are deemed more suitable in the context of EOD environments and the use of life-saving equipment such as bomb suits, often used in military settings. Two military standards are commonly used for this purpose: the MIL-STD-461 standard from the United States Department of Defense and the Def-Stan 59-411 from the UK.

The MIL-STD-461 standard document declares that “the stated interface requirements are considered necessary to provide reasonable confidence that a particular subsystem or equipment complying with these requirements will function within their designated design tolerances when operating in their intended electromagnetic environment (EME)”. This standard was first released in 1967, and multiple revisions have since been generated (Revision G dates back to 2015). The UK-based Def-Stan 59-411 Part 3 document “provides requirements for Ministry of Defence (MOD) Project Officers and Defence Contractors to assist them in the specification and selection of Electromagnetic Compatibility (EMC) Test Methods and Limits for Subsystems to limit the propagation and coupling of unintentional electromagnetic energy whether conducted or radiated.” The original version of that document was first released in 1999, and the latest revision dates back to 2008.

Both sets of tests are to be conducted in an anechoic chamber (Figure 2), with representative and fully functional test samples with associated accessories.

Two main types of tests are conducted for each standard: radiated emissions, and susceptibility, at frequencies up to 20 GHz.

RF JAMMER DEVICES
RF jammers are engineered to ensure interoperability with various vehicle and manpack systems. The jammers include the ability to customize the waveform technique to minimize interference with friendly collocated systems as well to share reference oscillators, timing indicators, triggers and data communications to allow for constructive synchronization between systems that compete for electromagnetic spectrum resources.

Multiple jammers are often required to target the threat profile. In particular, the ability to collocate multiple jammers in close proximity is a prime consideration in EOD carry forward scenarios (Figure 3). The potential for self-interference between the jamming units themselves, through radiated susceptibility, must be addressed similar to the interoperability scenario between the jammer and EOD helmet. The close proximity of RF jammers necessitates the need for proper RF shielding, validated through MIL-STD-461 radiated susceptibility testing. Without a suitably RF hardened enclosure, jammers may interfere with each other.

Figure 3: RF jammers in close proximity (SCORPION, Allen-Vanguard) on a “Dual Carrier” to maximize the jamming response for enhanced operator safety.

Currently, to comply with the MIL-STD-461 Radiated Standard requires a field strength of 50 Volts/meter with no impact to the device. As an added safety measure, the most advanced jammers are routinely qualified to 200 Volts/meter field strength in the majority of the frequency bands to ensure that the probability of adverse effects are significantly further reduced.

MIL-STD-461 standards, in particular the RS103, are just one in a suite of MIL-STD tests that jammer manufacturers utilize to ensure product robustness in harsh operating environments. Other applicable standards include MIL-STD-810, featuring operational hot & cold, storage hot & cold, humidity, thermal shock, shock and vibration as well a commercial IEC/EN 60529 for IP ratings water and dust ingress rating.

REPRESENTATIVE TESTS AGAINST AN ACTUAL JAMMER DEVICE
While compliance to the requirements of the above standards ensures that EOD Personal Protective Equipment (PPE) is well shielded against RF/ECM threats, it offers no guarantee that an EOD helmet’s full functionality would be preserved when exposed to a specific jammer since jammer specifications are secret. However, compliance to the MIL-STD-461 and Def-Stan 59-411 truly minimizes the chances of interferences between EOD PPE and jammers.

Figure 4: Volunteers testing the functionality of different Med-Eng legacy EOD helmets at varying distances from an ECM device.

This being said, compliance of EOD equipment with a specific jammer device can be verified through functionality tests representing actual threat environments to ensure that bomb technicians have the required electronic functionality to accomplish their mission safely. For instance, through the development of the first RF shielded EOD helmet, volunteers tested four different legacy EOD helmets (Figure 4), among which only one was designed towards RF/ECM compliance. A representative radio communication system and a wired system were both tested in combination with the helmets. Two ECM jammer devices were situated at one end of the test site and the radios and hard-wired system were situated 100 meters away. Pylons were set up at 10-meter intervals from the ECM devices until a distance of 50 meters from the ECM device was reached (Figure 5).

Figure 5: Test setup for the EOD helmet tests against actual jammers. Pylons positioned at 10-meter intervals from two SCORPION ECM devices (Allen-Vanguard jammers).

The ECM devices were then activated. Each volunteer was asked to operate their helmets’ different functions (searchlights, ventilation fans, communications) to determine whether the helmet was being affected by the ECM device and, if so, in which way (i.e. buzzing noise, searchlights would not turn on, etc.). Once each helmet had been tested for its functionality, the volunteers then walked towards the ECM device stopping at each 10-meter interval to repeat the functionality test. If the helmet was determined to be too painful to wear, or its functions were no longer operating, it was removed from the trial. The trial was then repeated for each ECM frequency band.

The results highlighted the benefits associated with RF shielding of the helmet, since all helmets, except the shielded one, introduced loud interference noises when exposed to the jammer, which in some cases became unbearable to the operator. In addition, some helmet functions were negatively affected (e.g. fans and communications) for all helmets, except the intentionally shielded helmet design version. Additional tests were then conducted with the operators hand- carrying the ECM devices. Even in this harsh scenario, only faint sounds were noticed for the shielded helmet, while none of the non-shielded helmets were found to be operable.

These tests thus confirmed the appropriateness of designing EOD helmets, connections, and accessories around the requirements of military electromagnetic compliance standards, to ensure full helmet functionality in the presence of a particular functioning jammer device. While the tests described above involved only one single jammer type, it is suspected that the shielded helmet’s performance would remain satisfactory in the presence of other jammers, given its shielding level, so long as frequencies and power emitted were in an acceptable range consistent with the standards.

CONCLUSION / DISCUSSION
As bomb technicians are increasingly exposed to the threat of Radio-Controlled Improvised Explosive Devices, the deployment of advanced Electronic Counter Measure tools has become critical to minimizing the chances of explosive devices being triggered during render-safe missions.

As such, intentional design for shielding the electronic systems of the bomb technician, including their PPE and accessories, against electromagnetic threats is essential to ensure that operator safety and operational functionality of the equipment are not compromised. The tests highlighted above clearly demonstrated the difference between “hardened” systems and ordinary commercial electronics on bomb suit ensembles.

While there is no guarantee that a bomb suit ensemble designed to specific standards, such as MIL- STD-461 and Def-Stan 59-411, will remain fully operational in the presence of all current and future ECM jammer tools, meeting these stringent military requirements provides some safeguarding that a protective system will be functional and safe within an ECM and RCIED environment. To ensure full equipment compatibility, further validation trials should be conducted with the actual jammer ECM equipment of interest and specific PPE worn by the bomb technician, alongside any electronic accessories.

Irrespective of such further validation trials, meeting stringent military requirements for electromagnetic compliance (as opposed to less stringent commercial variants such as FCC and CE) represents a significant enhancement in capability against the most prevalent IED threat being faced by deployed militaries against the most prominent terrorist organizations. The use of electronic equipment that is not suitably shielded and validated in an RCIED render safe mission and/or within the range of ECM radiation may place the bomb technician at undue risk through the possibility of accidental detonation or malfunction of the equipment being used. ■

ABOUT THE AUTHORS

Alex Leask holds an Industrial C.E.T for Robotics, Automated Controls, RAB Certified Lead Quality Auditor with over 25 years expertise in compliance testing to Mil-461,810, 1275 as well as UL, CSA, EN, CE, FCC, STANAG, Def- Std., for complex high frequency RF systems, mechanical systems & safety equipment. He is currently the Engineering System Verification and Test Manager at Allen Vanguard.

 

Dr. Trevor Yensen holds a Ph.D and M.Eng in Electrical Engineering. His 17 years of work with Allen- Vanguard, most recently as its Chief Scientist, has established a world- class electronic warfare (EW) program with a focus on jamming systems for radio controlled improvised explosive devices (RCIEDs).

 

Dr. Aris Makris holds Masters and Ph.D. degrees in Mechanical Engineering, specializing in explosions and protection against blast effects, with over 30 years of related experience. He is VP of Research, Development & Engineering and Chief Technology Officer at Med-Eng, and has led numerous programs to design and develop personal protective systems to protect against IEDs, landmines, and explosive threats.

 

Dr. Jean-Philippe Dionne holds a Ph.D. in Mechanical Engineering and has over 20 years expertise in the fields of numerical simulations of detonations, blast waves and combustion. As the Director of Engineering at Med-Eng, he has directed numerous blast test programs and significantly contributed to the National Institute of Justice NIJ 0117.01 standard for Public Safety Bomb Suits.

 

Douglas Wong holds a B. Eng. and has over 30 years of experience in mobile data acquisition systems, robotics, spectrometer development, and optics. As the Med-Eng Director of Electronics Engineering, he holds EOD-related expertise in advanced sensors and signal conditioning methods used to monitor and measure blast events and their effects.


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