**2. Basic requirements for the exposure systems**

Since the early development of mobile telephony, concern aroused on the possibility of the exposure to EM signals in the RF range inducing hazardous effects on population health. Consequently, a number of experiments were carried out (Lin, 2004; Valberg et al., 2007) aiming at the evaluation of possible biological effects of RF EM fields. The obtained results were often conflicting and difficult to replicate, mostly due to inaccurate dosimetry and to a lack of well-characterized exposure conditions.

Since the 90s, the need of a common approach to the bioelectromagnetic research became evident, as pointed out by a number of workshops and publications yielded by the scientific community. In 1994, the Wireless Technology Research (WTR) held a workshop to highlight 294 Real-Time Systems, Architecture, Scheduling, and Application

In the past, several studies were carried out suggesting a possible interference of the EM fields with neurons, but with controversial results and unable to clearly state the molecular basis of this interaction (Sienkiewicz et al., 2000; Wang and Lai, 2000; Dubreuil et al., 2003; Preece et al., 2005). For a review on EM field effects on cognitive functions see (D'Andrea et al., 2003). This is not surprising: experimental investigation of the EM coupling with neurons, in fact, is rather complicated since it involves measurements of the electrical activity of neurons, i.e. the acquisition of electrophysiological recordings of the transmembrane voltage and of the ionic currents. Therefore, a prerequisite of well-posed experiments involving neuronal activity is the possibility to acquire the useful signals simultaneously with the exposure to the RF EM field. Hence, in the last years, there has been

Some of the most recent results achieved with the aid of ad hoc designed real-time systems state that there is no significant coupling between low intensity RF EM fields and specific membrane channels, i.e. biological membrane proteins which allow the passive movement of ions from the external to the internal of the cell and vice-versa (Marchionni et al., 2006; Platano et al., 2007). Other studies, investigating the effects of low intensity RF EM fields on electrical activity in rat hippocampus, one of the major component of brain, (Tattersall et al., 2001) described an effect on synaptic transmission; however the effect reported has been later explained by localised heating produced by interaction of the RF fields with the recording and stimulating electrodes. This contradiction emphasizes the fundamental issue

Although real-time investigations have been gaining increasing interest in the last ten years, a complete and systematic framework on specific requirements of RF exposure systems

Aim of this chapter is to merge the well-assessed design procedure of RF exposure systems (Kuster and Schönborn, 2000; Paffi et al., 2010) with the requirements emerging from real-

In the chapter, at first a description of what is an exposure system and which are the guidelines to optimally design it are given. Then, it is provided how to adapt the general rules for exposure system design to real-time systems ones, which, of course, have very specific requirements. Finally, a complete and updated review of the real-time systems

Since the early development of mobile telephony, concern aroused on the possibility of the exposure to EM signals in the RF range inducing hazardous effects on population health. Consequently, a number of experiments were carried out (Lin, 2004; Valberg et al., 2007) aiming at the evaluation of possible biological effects of RF EM fields. The obtained results were often conflicting and difficult to replicate, mostly due to inaccurate dosimetry and to a

Since the 90s, the need of a common approach to the bioelectromagnetic research became evident, as pointed out by a number of workshops and publications yielded by the scientific community. In 1994, the Wireless Technology Research (WTR) held a workshop to highlight

time investigations, thus providing a reference work on this segment of knowledge.

a pressing need to design real-time exposure systems.

related to the proper design of real-time systems.

available in literature is provided.

when applied to real-time data acquisition is still lacking.

**2. Basic requirements for the exposure systems** 

lack of well-characterized exposure conditions.

the appropriate directions for the development of exposure systems (Carlo, 1998). In 1996, the EMF Project of the World Health Organization (WHO) fixed these concepts and emphasized the importance of an accurate dosimetry in all scientific studies (WHO, 1996). Such items, together with a deep discussion on quality assurance, were the main arguments of two European Cooperation in Science and Technology (COST) workshops: "Exposure systems and their dosimetry", in Zurich, in February 1999 (Schönborn et al., 1999; Bitz et al., 1999) and "Forum on future European research on mobile communication and health", in Bordeaux, in April 1999 (Kuster and Schönborn, 1999).

In 2000, recommended minimal requirements for exposure systems, in order to obtain reproducible and scientifically valuable results, were synthesized in (Kuster and Schönborn, 2000). Basically, two classes of requirements can be identified: biological and EM ones. Biological requirements are dictated by the laboratory equipment, the experimental procedures, and the environment; the EM ones define the exposure parameters (frequency, amplitude, modulation scheme of the signal), the characteristics of the induced EM field (polarization, intensity and homogeneity), and the "dose" at the location of the biological sample.

More in detail, to meet the biological requirements, the exposure system must allow for the exposure of the required number of samples or animals; in the meantime, the environmental conditions required by the specific experiment must be guaranteed (Kuster and Schönborn, 2000). As for the EM requirements, (i) the delivered signal must be precisely defined in terms of frequency, amplitude, and modulation scheme; (ii) the electric and magnetic field strength and polarization must be known at the location of the exposed biological target; (iii) the fields inside the sample should be homogeneous; (iv) any electromagnetic interference (EMI) and/or electromagnetic compatibility (EMC) issue must be avoided (Kuster and Schönborn, 2000). Moreover, the system should guarantee the monitoring of relevant parameters, such as the temperature and the delivered power, during the experiment and the possibility of carrying out sham exposures and blind experiments. In the sham exposure, a number of cell cultures or animals are subjected to environmental conditions identical to those of the group of the exposed subjects, except for the exposure. Data collected by the sham group are thus used as negative control. This is an unavoidable procedure to prevent the incorrect attribution to the RF exposure of an observed effect, which might be due to other factors, e.g. to the stress of the animals (Samaras et al., 2005). In blind experiments the exposure setup provides an automated procedure to assign the real and the sham exposure to two different groups of samples. In this way, experimenter polarization errors are removed, since he/she does not know which samples are really exposed.

Finally, the exposure system should be easy to be handled even by non-engineering personnel and its cost should be reasonable (Kuster and Schönborn, 2000). To maintain low the cost of the whole exposure setup, in particular of the signal amplifier of the generation chain, the EM structure should be designed to have the power efficiency as high as possible. The power efficiency is defined as the mean EM power absorbed by the unitary mass of sample per unitary input power feeding the EM structure.

Biological requirements are usually the most limiting ones on the exposure setups. As example, the kind of experiment may dictate the equipment needed and the environment; the overall duration of the experiment and the number of samples or animals necessary for statistical significance may strongly influence the choice of the EM structure employed as

Real Time Radio Frequency Exposure for Bio-Physical Data Acquisition 297

The aim of an exposure system is to expose a biological target to a well-controlled and reproducible SAR, while maintaining appropriate environmental conditions and allowing the monitoring of some parameters during the exposure, such as temperature (Lin et al.,

An exposure system is a complex structure used for allocating the biological samples during

3. the system for maintaining the environmental parameters needed for the well-being of

Although the exposure system is the complex structure, consisting of several parts, guaranteeing the desired exposure conditions of the sample, in the following, with the term exposure system, we will refer to its main part: the EM structure emitting the field, which

Essentially it is possible to find exposure systems for *in vitro* and for *in vivo* biological experiments. In the first case, the biological target is constituted by cultured tissues or cells contained in sample holders such as flasks, tubes, Petri dishes, multiwells, and cuvettes. In

*In vitro* experiments are an accepted method for determining, at cellular level, the SAR threshold for the onset of biological effects and damage (Guy et al., 1999). One of the main limitations of *in vitro* experiments is that the effects observed in cell cultures do not necessary imply any impairment at physiological level. For this reason, *in vivo* experiments, carried out on living animals, such as mice, rats, and rabbits, are of great scientific interest. I*n vivo* exposure systems could be rather different from the *in vitro* ones (Lin et al., 2009). This is mainly due to the larger dimensions of animals with respect to the *in vitro* sample holders. Moreover, animals tend to move inside the exposure system, unless they are restrained inside special containers, as required in some experiments. Finally, requirements for the maintenance of the environment conditions depend on whether cells or animals have to be exposed. In the first case, generally an incubator is needed; in the second case,

can be an antenna, a waveguide, a resonator, as described in detail in Section 6.

the second case, the target is a specific animal or part of it, e.g. head, eyes, and ears.

ventilation, food and water should be provided, especially for long-term exposures.

2010; Voyvodic et al., 2011) suitable to be applied to living animals.

correlated event.

**4. The concept of real-time acquisitions in bioelectromagnetic investigations**  Real-time data acquisition in biomedicine is employed in a lot of different applications, both *in vitro* and *in vivo*. Real-time monitoring of chemical reactions (Shutes and Der, 2005), gene expression (Gubern et al., 2009), drug release from nanoparticles (Chouhan and Bajpai, 2009) are significant examples of *in vitro* applications. As for *in vivo* investigations, the real-time acquisition is usually based on non-invasive imaging techniques (Ohtani et al., 2010; Li et al.,

The common issue in both *in vitro* and *in vivo* real-time experiments for biomedicine is that the experimental acquisition of physiological data is performed simultaneously with the

the exposure phase in a biological experiment. It encompasses:

2. the chain for the generation and control of the EM signal;

1. the EM structure emitting the EM field;

4. the software for the system management.

the exposed samples;

2009).

exposure system. For this reason, a lot of different exposure systems have been published during the past ten years (Lovisolo et al., 2009; Paffi et al., 2010, 2011), according to the great variety of experimental endpoints and protocols.

Moreover, during the past years, several cooperative research programmes, e.g. the European projects: PERFORM A, PERFORM B, and RAMP2001 have been carried out. The necessity of conducting a coordinate research activity in laboratories of different countries has arisen the issue of whether standardized exposure systems and protocols should be used. This was one of the topics of the Workshop: "EMF health risk research lessons learned and recommendations for the future" held in Monte Verita in November 2005. The outcome of the work stated that, due to different endpoints and protocols used in bioelectromagnetic investigations, exposure setups could not be standardized. In the same time, strong quality control on dosimetry is mandatory to assure the repeatability and reproducibility of results even when different exposure systems are used (Samaras et al., 2005; Lovisolo et al., 2009). Although the concept of using a standardized exposure system for all types of studies is not possible, the choice, design, and characterization of the system can be standardized to obtain repeatable and reproducible results from biological experiments (Paffi et al., 2010).

## **3. Exposure systems for experimental investigations**

Well-dened and characterized exposure conditions are necessary for health-risk assessments (WHO, 1996). Unless the "dose" is accurately known, the results of bioelectromagnetics studies will have little value for determining exposure thresholds for health risk or for developing exposure limits in standards; therefore, great research effort has been devoted to reproduce well-defined exposure conditions in the last twenty years.

For the EM exposure in the RF range, the "dose" is considered the incremental absorbed EM energy per unit mass (ICNIRP, 1998), given in terms of Specific Absorption Rate (SAR), which is defined as follows:

$$\text{SAR} = \frac{\text{d}}{\text{dt}} \left( \frac{\text{dW}}{\text{dm}} \right) = \frac{\text{d}}{\text{dt}} \left( \frac{\text{dW}}{\rho \text{dV}} \right) \tag{1}$$

where *dW* is the incremental energy dissipated in an incremental mass *dm* included in an incremental volume *dV* and ρ is the mass density. SAR (measured in W/kg) can be calculated directly from the electrical loss, which is proportional, through the conductivity σ, to the mean square of the electric field strength E locally induced in the tissue (ICNIRP, 1998), as follows:

$$\text{SAR} = \frac{\sigma \text{E}^2}{\rho} \tag{2}$$

To have a precise and accurate knowledge of the SAR distribution inside the exposed sample during the experiments, exposure systems have to be designed, fabricated, and characterized, in order to meet all the requirements discussed in Section 2. In fact one cannot employ commonly used EM sources, such as phone cells or microwave ovens, as done in several cases, especially in studies published prior to 1990s, since in these cases the dose absorbed by the target will be completely unpredictable.

The aim of an exposure system is to expose a biological target to a well-controlled and reproducible SAR, while maintaining appropriate environmental conditions and allowing the monitoring of some parameters during the exposure, such as temperature (Lin et al., 2009).

An exposure system is a complex structure used for allocating the biological samples during the exposure phase in a biological experiment. It encompasses:

1. the EM structure emitting the EM field;

296 Real-Time Systems, Architecture, Scheduling, and Application

exposure system. For this reason, a lot of different exposure systems have been published during the past ten years (Lovisolo et al., 2009; Paffi et al., 2010, 2011), according to the great

Moreover, during the past years, several cooperative research programmes, e.g. the European projects: PERFORM A, PERFORM B, and RAMP2001 have been carried out. The necessity of conducting a coordinate research activity in laboratories of different countries has arisen the issue of whether standardized exposure systems and protocols should be used. This was one of the topics of the Workshop: "EMF health risk research lessons learned and recommendations for the future" held in Monte Verita in November 2005. The outcome of the work stated that, due to different endpoints and protocols used in bioelectromagnetic investigations, exposure setups could not be standardized. In the same time, strong quality control on dosimetry is mandatory to assure the repeatability and reproducibility of results even when different exposure systems are used (Samaras et al., 2005; Lovisolo et al., 2009). Although the concept of using a standardized exposure system for all types of studies is not possible, the choice, design, and characterization of the system can be standardized to obtain

repeatable and reproducible results from biological experiments (Paffi et al., 2010).

Well-dened and characterized exposure conditions are necessary for health-risk assessments (WHO, 1996). Unless the "dose" is accurately known, the results of bioelectromagnetics studies will have little value for determining exposure thresholds for health risk or for developing exposure limits in standards; therefore, great research effort has been devoted to

For the EM exposure in the RF range, the "dose" is considered the incremental absorbed EM energy per unit mass (ICNIRP, 1998), given in terms of Specific Absorption Rate (SAR),

> d dW d dW SAR dt dm dt dV

where *dW* is the incremental energy dissipated in an incremental mass *dm* included in an

calculated directly from the electrical loss, which is proportional, through the conductivity σ, to the mean square of the electric field strength E locally induced in the tissue (ICNIRP,

> <sup>2</sup> <sup>E</sup> SAR σ

To have a precise and accurate knowledge of the SAR distribution inside the exposed sample during the experiments, exposure systems have to be designed, fabricated, and characterized, in order to meet all the requirements discussed in Section 2. In fact one cannot employ commonly used EM sources, such as phone cells or microwave ovens, as done in several cases, especially in studies published prior to 1990s, since in these cases the dose

ρ

= =

ρ

is the mass density. SAR (measured in W/kg) can be

<sup>=</sup> (2)

(1)

**3. Exposure systems for experimental investigations** 

reproduce well-defined exposure conditions in the last twenty years.

ρ

absorbed by the target will be completely unpredictable.

which is defined as follows:

incremental volume *dV* and

1998), as follows:

variety of experimental endpoints and protocols.


Although the exposure system is the complex structure, consisting of several parts, guaranteeing the desired exposure conditions of the sample, in the following, with the term exposure system, we will refer to its main part: the EM structure emitting the field, which can be an antenna, a waveguide, a resonator, as described in detail in Section 6.

Essentially it is possible to find exposure systems for *in vitro* and for *in vivo* biological experiments. In the first case, the biological target is constituted by cultured tissues or cells contained in sample holders such as flasks, tubes, Petri dishes, multiwells, and cuvettes. In the second case, the target is a specific animal or part of it, e.g. head, eyes, and ears.

*In vitro* experiments are an accepted method for determining, at cellular level, the SAR threshold for the onset of biological effects and damage (Guy et al., 1999). One of the main limitations of *in vitro* experiments is that the effects observed in cell cultures do not necessary imply any impairment at physiological level. For this reason, *in vivo* experiments, carried out on living animals, such as mice, rats, and rabbits, are of great scientific interest.

I*n vivo* exposure systems could be rather different from the *in vitro* ones (Lin et al., 2009). This is mainly due to the larger dimensions of animals with respect to the *in vitro* sample holders. Moreover, animals tend to move inside the exposure system, unless they are restrained inside special containers, as required in some experiments. Finally, requirements for the maintenance of the environment conditions depend on whether cells or animals have to be exposed. In the first case, generally an incubator is needed; in the second case, ventilation, food and water should be provided, especially for long-term exposures.
