Get our free email newsletter

Banana Skins – May 2024 (#445-451)

445. Electronic Articles Surveillance (EAS) systems interfere with disabled aid

My work includes the installation of induction loops for hearing aid users. The availability of these is almost the only way of complying with the Disability Discrimination Act in public buildings which have an amplification system.. Many hearing aid users will not, for example, attend a Church which does not have a working loop system. These generate an audio magnetic field which is received by a special pick-up coil in the hearing aid.

One of the more widespread sources of interference to induction loops is the security system used in larger shops and libraries. The library building in Halesowen has a small theatre on the top floor. Tests reveal a 1kHz audio signal throughout the whole building including the whole of the theatre. The source of this is the security system to stop theft of books. These consist of a pair of coils which form a “gateway” through which all books have to be carried.

The flagship library in Bournemouth town centre has this security system. The necessary induction loops fitted to the desks where the Library Staff issue books for borrowing have to be at least 5 metres away from these. Otherwise the background whistle is intolerable. On one visit there, I happened to have an induction loop monitor with me. Out of curiosity, I tried the desk loop and found that the background whistle was intrusive even at the furthest point on the counter.

- Partner Content -

How To Work Safely with High‑Voltage Test & Measurement Equipment

This white paper describes an alternative approach to calibrating high-voltage systems and provides meter and probe safety considerations and general guidance for safely operating high-voltage equipment.

On another occasion, I happened to need a new bulb for my car, and visited one of Birmingham’s car parts shops on my way home from a service job. Seeing a similar security coil system in the shop, I went back in with a loop monitor and found that the whistle was audible out in the car park as well as at the cash desks where shops are now having loops fitted.

Getting cynical in my old age, I think that the audio spectrum falls off the bottom end of the 9kHz or 150kHz lower limit of a lot of EMC specifications, and so does not enter people’s thinking. On the other hand, specifications that limit noise emissions into mains supplies seem irrelevant when someone is designing an audio magnetic radiator such as is used in these security gateways.

(Sent in by Robert Higginson of AREAC, 2nd August 2007)

446. Some more examples of medical interference

  • A video system used for endoscopy experienced random episodes of interference during electrocautery.
  • Cardiopulmonary bypass blood pumps stopped unexpectedly during surgery.
  • An infusion pump changed rate when a cellular phone was placed on the instrument stand.
  • A fetal hearth monitor located in a nursery experienced incorrect readings. A wireless base station had been placed on a wall outside the nursery.

(Taken from the PowerPoint presentation “Medical Equipment Immunity Assessment by Time Domain Analysis,” Mireya Fernández-Chimeno, Miguel Ángel García-González and Ferran Silva, 2007 IEEE International Symposium on Electromagnetic Compatibility, 8-13 July 2007, Honolulu, Hawaii, ISBN: 1-4244-1350-8, IEEE EMC Society: These examples were previously reported by Silberberg J.L, in: “What Can/Should We learn from Reports of Medical Device Electromagnetic Interference?” Proceedings on Electromagnetics, Health Care & Health, Paper, Montreal, Quebec, Canada. 1995.)

447.  Fibre-optics used in ‘EMI-Immune’ Aircraft Program

Maryland-based Optelecom-NKF, Inc. has announced that its Electro-Optics Systems Group has received a contract from Parker Aerospace for optical fiber control system architecture design in support of the Electromagnetic Interference (EMI) immune aircraft program, designated AVE3I. The Parker Aerospace contract is part of an Air Force Research Laboratories (AFLR) program to develop EMI-immune aircraft. Parker Aerospace is under contract to GE Aviation, the prime contractor in the Air Force contract. The AVE3I program is scheduled to advance in several stages through design, laboratory demonstration, and, potentially, flight demonstration.

- From Our Sponsors -

According to Bill Ziegler, the Electro-Optics Group’s Program Manager, “This contract continues our long-standing emphasis on developing optical fiber-based systems to protect aircraft from the threats associated with EMI.”

(Extracted from “Optelecom-NKF Wins Contract in Support of EMI-Immune Aircraft Program,” EMC News, Interference Technology’s Online Guide to EMC, August 5th 2007.)

448. EMP could threaten existence of civil society in the US

Over the past seven years, a substantial number of articles have been written by this author and others identifying the threat and importance of intentional electromagnetic interference (IEMI). The major conference for this topical area was the AMEREM Conference in July 2006 in Albuquerque, New Mexico. This is the major conference in the world dealing directly with high power electromagnetic environments, effects, and protection, including IEMI and all types of nuclear EMP.

A second area to be discussed in this article is the work of the Congressional EMP Commission in the United States. As part of their study, they examined the historical record of information including data from high‑altitude nuclear tests performed by the United States and the Soviet Union in 1962, and they directed research to evaluate the susceptibility of today’s critical architecture. They completed their work in 2004 by describing the HEMP threat to the U.S. infrastructure, and they took up their work again in May 2006 to review the response to their initial report and to encourage those responsible for the critical infrastructure to develop mitigation methods to deal with the threat.

The terminology of the electromagnetic pulse has evolved over the years, but today the generic term for all types of nuclear generated electromagnetic transients is EMP. Of interest here is the EMP caused by a high-altitude burst, generally defined as one occurring at a burst height greater than 30km. At this altitude, the radiation produced by the nuclear burst would not reach the earth’s surface, but several types of electromagnetic signals would. Because the burst is at high altitude (in space), this type of EMP is usually referred to as HEMP. The concern is that these high-level electromagnetic fields will create serious problems for computers and other electronic systems on the earth’s surface, including the critical infrastructure (power, telecommunications, transportation, finance, water, food, etc.). This is the focus of the EMP Commission in the United States and the IEC subcommittee 77C in Geneva.

While the EMP Commission studied all major aspects of the critical infrastructure, they determined that the power system was the most critical because of its connection to all of the other major infrastructures such as communications, transportation, emergency services, energy distribution, water/food, etc. After considerable study, the commission concluded:

  1. HEMP-induced functional collapse of the electrical power grid risks the continuing existence of U.S. civil society.
  2. Early-time HEMP transients are likely to exceed the capabilities of protective safety relays.
  3. Late-time HEMP could induce currents that create significant damage throughout the grid.
  4. The national electrical grid is not designed to withstand near simultaneous functional collapse
  5. Procedures do not exist to perform “black start” after and EMP attack as restart would depend on telecom and energy transport, which depend on power.
  6. Restoration of the national power grid could take months to years.
  7. HEMP-induced destruction of power grid components could substantially delay recovery.

The HEMP threat is one of a few potentially catastrophic threats to the United States.

(Extracted from: “2007 Update on intentional electromagnetic interference (IEMI) and high-altitude electromagnetic pulse (HEMP),” by Dr William A Radasky, Ph.D., P.E., Interference Technology’s EMC Directory & Design Guide 2007, pages 143-148. For the Congressional Report itself, visit,, and

449. Explosive material probe and implantable medical devices

An ‘In Vitro’ study was made of the electromagnetic interactions between a hand-held probe used for detecting explosive materials, and implantable medical devices such as pacemakers. The probe uses a quadrapole nuclear resonance technique, and was tested with fifteen devices from three major manufacturers. Testing has been completed and a number of interactions were found. The severity of the interactions has yet to be determined.

(Adapted from “Wireless EMC in the Medical Industry” by Hank Grant et al., speaking in the “Current EMC Issues in Healthcare” workshop session of the IEEE 2002 International EMC Symposium, Minneapolis, August 19-23 2002.)

450. Wireless phone and medical devices

  • Specific recommendations for cellular telephones:
    • Designate locations where they can be used without concern of interference;
    • Prohibit patients and visitors from using cell phones and similar devices within highly-instrumented clinical areas;
    • Consider whether or not cellphones and similar devices should be permitted in general patient care areas;
    • Consider allowing wider use of cell phones and similar devices by clinical staff;
    • Instruct staff to maintain a minimum distance of 1 meter (3 ft) – but preferably greater;
    • Consider cordless phone use.
  • Specific recommendations for walkie-talkie and FRS (family radio service) devices:
    • Prohibit use by patients and visitors;
    • Allow use by necessary staff:
    • Do not allow use in ‘talk’ mode within 6 to 8 meters (20 to 25 ft) of highly instrumented areas;
    • Ensure that staff are aware that walkie-talkie transmissions can penetrate walls, floors, and ceilings, which may affect medical devices in adjacent rooms or floors.

(Adapted from “ECRI’s Updated EMC-Healthcare Recommendations & Utility of Ad-Hoc Testing” by Art Augustine, speaking in the “Current EMC Issues in Healthcare” workshop session of the IEEE 2002 International EMC Symposium, Minneapolis, August 19-23 2002.)

451. Value of Ad-Hoc EMC testing in hospitals

Ad-Hoc testing is important in healthcare because many older medical devices that are still in use in hospitals were not designed or tested for EMC and even newer medical devices that meet EMC standards can experience electromagnetic interference in use.

For example:

  • Wireless PDA interfered with 42% of tested critical care medical devices (Juett, S. “Healthcare EMI war stories/due diligence,” AAMI 2001 Conference and Expo, June 2001,
  • Critical function of four of 33 medical devices disrupted by cell phone at 25cm or greater (Morrisey et al., “Characterisation of electromagnetic interference of medical devices in hospital due to cell phones”, Health Physics, vol. 82, no. 1, pp. 45-51, Jan 2002.)
  • RF wireless LAN interfered with three of 44 medical devices tested (Rice, W.P. “2.4 GHz RF WLAN EMI in medical devices,” J. Clkin. Eng., vol 25, no. 5, pp 260-264,
    Sep/Oct 2000.)

(Adapted from “Status of the Second Edition of the ANSI C.63.18 Ad-Hoc Test Method” by Jeffrey L Silberberg, speaking in the “Current EMC Issues in Healthcare” workshop session of the IEEE 2002 International EMC Symposium, Minneapolis, August 19-23 2002.)

Related Articles

Digital Sponsors

Become a Sponsor

Discover new products, review technical whitepapers, read the latest compliance news, trending engineering news, and weekly recall alerts.

Get our email updates

What's New

- From Our Sponsors -

Sign up for the In Compliance Email Newsletter

Discover new products, review technical whitepapers, read the latest compliance news, trending engineering news, and weekly recall alerts.