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RADIO FREQUENCY (RF) EMISSIONS & RF INTERFERENCE (RFI):
In an increasingly wireless world, RFI is becoming a bigger issue every day. More and more devices rely on RF signals, and more and more signals are being packed into limited RF Spectrum. Product value chains rely on RFID for inventory control, medical facilities rely on RF systems for security, pharmaceuticals tracking, patient monitoring, diagnostic systems and instrumentation, and many medical systems are sensitive to their RF environment.
Research facilities often have requirements for RF systems that are part of sensitive research instrument specifications. Transportation systems rely heavily on wireless systems, from air traffic controllers and dispatch radios to aircraft landing and guidance systems. Transportation systems cannot tolerate poor performance or system-degrading interference because it can increase risk to human life and safety.
Interference among multiple systems is part of the growth of wireless systems. This interference can be caused by simple devices that worked fine in the lab but when deployed cause interference with wireless networks we all depend on every day; Public Safety Dispatch radio communications sometimes can’t be effectively used because of interference such as receiver saturation which garbles the communications. In high-intensity, high-density RF environments, interference is a constant worry and electromagnetic shielding can be required to ensure systems function properly.
During 9/11, first responder, police and fire fighter networks not only didn’t effectively interoperate, they often didn’t operate at all. RFI, under the right conditions, can disrupt virtually any electrical or electronically controlled device, with potentially harmful or even disastrous results.
Military systems not only areheavy users of RF Spectrum, but governments must be aware of the risk of offensive use of the RF Spectrum from threats like EMP, which, theoretically, could disrupt or destroy virtually all electronics and communications systems over a large area and also cause considerable harm to electrical and transportation systems.
FMS has deep expertise and extensive experience in RF systems, and the complex causes of RFI and effective solutions to RFI problems. Our consulting services help clients deploy effective RF-dependent systems through the analysis of existing environments for potential interference, providing design guidance to avoid problems, and designing/deploying electromagnetic shielding when necessary. RFI can present itself in environments where other EMI is a primary issue or RFI can be the entire problem. No company is better prepared to help with the full range of problem/solution areas related to RF/RFI than FMS.
STANDARDS, LEGAL, REGULATORY:
There are generally clear standards for wireless systems, and clear definition for most RFI. Contrary to low frequency electric and magnetic fields, there are clear standards and regulations for RF/RFI in the North America and international standards that are applied throughout other parts of the world. In the U.S. OET65, which is the FCC policy on human exposure to radio frequency electromagnetic fields must be followed, Canada has similar standards (Safety Code 6). The FCC in 1996 also adopted the ICNIRP’s recommended Maximum Permissible Exposure limits for field strength and power density for transmitters operating at frequencies of 300 kHz to 100 GHz, and the SAR (specific absorption rate) limits for devices operating within close proximity to the body as specified within the ANSI/IEEEE C95.1-1992 guidelines. These standards are focused on human health and safety (http://transition.fcc.gov/oet/rfsafety/sar.html).
In office areas human exposure to RF fields will be predominately caused by two-way radio, mobile phones, Wi-Fi and unintentional RF signals from nearby equipment. Depending on the type of equipment, radio frequency fields are normally considered to present a threat of malfunction to standard office electronic equipment when the field strength exceeds 50 to 100 V/m although certain IT equipment is much more sensitive – in the range of 1 – 3 V/m.
Electronic equipment often will produce low level narrow and broadband signals at frequencies up to and above 1 GHz. The U.S. Federal Communications Commission (FCC) specifies the maximum level of radio frequency interference (RFI) that computer equipment is permitted to generate in Part 15 the FCC Rules and Regulations. These limits are set in order to prevent computer equipment from interfering with the operation of licensed RF communications and commercial broadcast systems.
RF networks are generally assigned a power and a frequency for their use; often interference is a result of non-compliance with intended RF signal emanations. FMS is deeply familiar with FCC and more informal guidelines such as industry standards and “rules of thumb.” for effective operation of RF devices in complex environments. Our measurement and analysis equipment and personnel have decades of experience in the field and at the design table helping solve these problems.
FMS was the EMI/RFI consultant for the US Army’s Medical Research Institute for chemical Defense (USAMRICD).
FMS provided the project team with an extensive EMI threat assessment of plans for the new fourteen-story Yawkey Center for Cancer Care in Boston, Ma.
Over its 20 years, FMS has successfully completed hundreds of EMI projects which included a diverse range of consulting and mitigation services.