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Regulations

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Safety requirements for limiting exposure to time-varying electric, magnetic and electromagnetic fields are enforced by national commissions, e.g., EU directives [1996, 1999] and FCC [1985].

These regulations are based on international guidelines by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and IEEE Standard for Safety Levels [2005] combined with national considerations, e.g. [NRP 2004,ARPNSA 2002]. Table 1 summarizes threshold currents for indirect effects. In general, it has been shown that threshold currents, which produce perception and pain, vary little over the frequency range of 100 kHz and 1MHz. Below 100 kHz the primary effect of alternating current is nerve and muscle stimulation perceived as a primary sensation of nerve tingling. At increased frequencies from 100 kHz to 10MHz, the dominant effect changes towards heating, while above 10MHz the limits are defined in terms of the specific absorption rate (SAR). Temperature rises of less than 1 degree are considered to be safe, i.e. not resulting in any adverse heating effects.

Table 1: Ranges for threshold currents for indirect effects, including children, women and men [ICNIRP 1997].

Indirect Effect Threshold current [mA]
50/60 Hz
1 kHz
100 kHz
1MHz
Touch Perception
0.2-0.4
0.4-0.8
25-40
24-40
Pain on finger contact
0.9-1.8
1.6-3.3
33-55
28-50
Painful shock
8-16
12-24
112-224
n/a
Severe shock difficulty
12-23
21-41
160-320
n/a

 

Derived from the guidelines, intra-body communication is restricted by the limits of contact currents [ICNIRP 2003]. Depending on the frequency range, the allowed contact current increases up to 20 mA at 100 kHz and remains constant above according to Tab. 2.

Threshold currents for indirect effects is a term used in the standard to express current limits triggering particular physical sensations of the subjects

INTRA-BODY COMMUNICATION TECHNOLOGY

Table 2: Reference levels for time varying contact currents from conductive objects [ICNIRP 1997]

Exposure Characteristics
Frequency Range Max.
Contact Current [mA]
Occupational Exposure
2.5 kHz - 100 kHz
0:4x.f [kHz]
100 kHz - 110MHz
40
General Public Exposure
2.5 kHz - 100 kHz
0:2 x f [kHz]
100 kHz - 110MHz
20

 

The occupationally exposed population consists of professionals who are exposed under known conditions. These people are trained to be aware of potential risks and to take appropriate precautions. In contrast, the general public comprises individuals of all ages and of varying states of health, and may include particularly susceptible groups or individuals. Since the threshold currents that elicit biological responses in children and adult women are approximately one-half and two-thirds, respectively, of those in adult men, the reference levels for contact currents for the general public are set to half the values for occupational exposure.

 

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