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Electromagnetic Fields in Biological Systems
to RF EMF exposure or impose a risk due to EMI from other intentional and unintentional transmitters, resulting in the disruption of medical device function or network
service.
Communication with medical electronic implants is possible via an interface placed
on the body surface. Currently, special mobile phones or telephone modems are available for remote transmission of data that are stored in the implants. Depending on the
system, remote transmission can be carried out automatically without requiring patient
action or with manual help from the patient responding to an individual call from the
health service. Remote patient monitoring is based on existing mobile phone networks.
The use of WLAN technology enables even bidirectional data transmission that allows
for interrogating and programming including transmission of parameters and electrocardiograms in real time without the use of the traditional programming head.
Communication via electromagnetic information transfer includes the following:
• Continuous transmission of signals (e.g., acoustic signals received by the beltworn master device to the in-the-ear hearing aid)
• Recurrent transmission to read out stored data (e.g., episodes of cardiac dysfunction)
Communication is usually restricted to specific frequencies allocated for industrial,
scientific, and/or medical use (ISM frequencies) such as 6.8 MHz, 13.6 MHz, 27 MHz,
41  MHz, 433 MHz, 2.45 GHz, and 5.8 GHz. For application in telemedicine and in
mobile telecommunication, short-range communication bluetooth or WLAN could be
used or general telecommunication services such as global system of mobile communication (GSM), universal system of mobile communication (UMTS), or long-term evolution (LTE).
Usually output power for such short-range transmission is low, and the exposure is
several orders of magnitudes below the basic restrictions (Figure 6.8).
Figure 6.8 Intracorporal SAR distribution in a cross-section through an in-the-ear hearing
aid, caused by the telecommunication link to a belt-worn transmitter. Voxel SAR values are in the
nanowatt per kilogram range.