studies have involved analysis of sleep responses, and a study by Borbely et al.39 indicated that sleep to a certain extent was affected in that the electroencephalogram (EEG) was somewhat more active, which could be interpreted as a degree of arousal occurring during RF exposure. That study involved exposure during sleep. Another group has found a similar effect, but from exposure before sleep.40 The indication is that exposure effects last for up to 30 min after the end of a call. The obvious importance of this kind of study is in trying to analyze the possible effects of cell phone antennas or other antennas placed on buildings where the subjects are sleeping. Alteration in sleep patterns lead to other psychological effects such as depression and anxiety. Direct provocation studies on humans during cognitive testing have been conducted by Preece et al.41 and Koivisto et al.42 Both these studies indicated that RF exposure to the brain resulted in enhanced cognitive performance related to changes in reaction time. The sum total of the sleep, cognitive, and electrophysiological studies suggests indeed that there is an effect of RF on the brain, whether it is analog or pulsed. The mechanism for these is important. If indeed it is simply heating, then this is probably of very little physiological significance, and very likely it is unrelated to any health effects and therefore really has few implications for safety. It has been pointed out, however, that most of the exposures to handset antennas result in a very minimal degree of temperature elevation, probably not more than 0.1 of a degree, as clearly shown by both calculation and experiment by Van Leeuwen et al.43

Therefore, the mechanism may be somewhat more complex and there are two other possible candidates. One of these is the direct effect on the synapses in the brain, which is in the reaction time determining processes, a glutamate response. This requires the release of a neurotransmitter in response to an electrical signal. The electrical signal in the neuron that leads to the neurotransmitter release area is held at a particular potential until triggered. The supposition is that the superposition of a RF alternating signal on this potential means that the threshold for the triggering can be achieved more easily, thus leading to a speeding up of response. This is exactly the kind of reaction seen both in the Preece41 (15 ms speeding up) and the Koivisto42 study (19 ms speeding up) in reaction time. The third possibility, which may have more serious implications because of the possible long-term effects, is that these changes could be mediated by protein alterations. One candidate is the change in heat shock protein (in particular, HSP70) that has been demonstrated to be altered in some simple animal models. A study by de Pomerai et al.44 shows that nonthermal levels of RF lead to the alteration in the production of HSP series of compounds. This effect has been seen in other in vitro systems and in cellular systems, also at electromagnetic frequencies from 50 Hz to 2.5 GHz.

There is obviously much more research needed but the existence of these effects has led to the suggestion that the intervention levels should be lowered for the general public (see the Stewart report in Section 26.6).

26.4 Other Safety Issues

26.4.1 Interaction with Safety Critical Equipment

The levels of radiation likely to cause problems for electronic devices are probably lower than for people. The EN60601-1-2, the EMC standard for medical devices, specifies an immunity of at least 3 V/m to radiation frequencies from 26 MHz to 1 GHz. This is in contrast to the recommendation for personal exposure of 50/70 V/m at these mobile phone frequencies. The Food and Drug Administration (FDA) of the United States, which licenses medical devices and reports adverse incidents, has recorded over 100 incidents in a 15-year period, some of which involve devices other than mobile phones. In particular, some medical equipment can cause problems because emission of RF energy is part of its normal function. Examples are electro-surgery and short-wave diathermy devices, both of which can produce fields of 30 to 40 V/m at short distances and are well-known sources of interference. Devices particularly at risk are ventilators, infusion pumps, hearing aids, and powered wheelchairs. There have also been reported cases of interference with physiological monitors of the kind used in intensive care units. The question of interference with pacemakers is a serious one but fortunately the risk to an implanted pacemaker is very small indeed. Many of these devices do show interference when on the bench but once implanted the

© 2002 by CRC Press LLC

conductivity of the tissue that surrounds them is a highly protective device. The field strength in air at any distance d from an antenna is approximately

E = (30PG) d V m−1

(26.3)

where P is power in Watts, and G the antenna gain.

For a typical device (mobile phone) with a dipole antenna configuration giving a gain of 1.6

E =	7 P	V m−1	(26.4)
	d

A survey was conducted by the Medical Devices Agency (MDA) in the United Kingdom that has shown it is necessary to have a safety clearance area between safety critical devices and the use of mobile phones or handheld communicators. This is fully reported in a bulletin45 that suggests a minimum clearance of 1.5 m is necessary to protect some devices. In practice, most hospitals now have a clearance zone of 3 m that take into account the higher powered mobile communicators occasionally used by security, fire, and ambulance staff (Fig. 26.2).

There is a particular problem with antennas mounted on mobile vehicles that may carry safety critical equipment (e.g., an ambulance). For the purposes of providing adequate light to attend to patients,

FIGURE 26.2 Probability of interaction of typical hospital critical care equipment with different communication devices at different distances.

© 2002 by CRC Press LLC