**6.2.1 Propagating structures**

Propagating systems for real-time studies are generally closed structures modied with holes for sample observation and perfusion, and for online monitoring of biochemical or biophysical parameters.

They are mostly TEM cells and rectangular waveguides as described in (Linz et al., 1999), where the electrophysiological activity of myocyte cells was recorded, through the patchclamp technique, during the exposure to 900 MHz and 1800 MHz CW. The systems were equipped with two holes: one in the top wall to insert the recording electrode and the other in the bottom to observe the sample with a microscope. The solution adopted to avoid interference between the electric eld inside the guide and the metallic wire of the patchclamp electrode was the elongation of the glass microelectrodes used for sealing the cell in order to place the wire outside the exposure device. The power efciency was not bad: 1.66 (W/kg)/W at 900 MHz and 3.16 (W/kg)/W at 1800 MHz.

A rectangular waveguide (Lambrecht et al., 2006), operating between 0.75–1.12 GHz, was also used to measure, through a force transducer, the effects of the RF field on skeletal muscle inserted in a bath placed in the center of the waveguide. The waveguide was modified with slots in the walls to allow connection with measurement, control, and stimulating devices outside the system. The power efciency was good (> 3 (W/kg)/W) and SAR homogeneity, around 79 %, was in line with minimal requirements for *in vitro* experiments (homogeneity > 70 %). A modied rectangular waveguide was used for delivering CW or Universal Mobile Telecommunications System (UMTS) signals to neuronal networks during electrophysiological recordings from multiple electrodes (Koester et al.,

Real Time Radio Frequency Exposure for Bio-Physical Data Acquisition 307

A modied stripline, where the sample holder (a cuvette) and the temperature regulating chamber were part of the dielectric substrate, was described in (Ramundo-Orlando et al., 2004). The system was placed inside a spectrophotometer for monitoring the enzymatic activity of ascorbate oxidase trapped in liposomes during the exposure to a CW at 2.45 GHz.

Only one example of resonant structure used for real-time acquisition is presented in literature. The resonant system proposed by Hagan *et al.* (Hagan et al., 2004) was a short circuited rectangular waveguide designed to expose neural cells in the frequency range of 0.75–1.12 GHz while monitoring catecholamine release. The guide had slots on the plates to allow the communication between the cell perfusion apparatus, placed inside the

Even for radiating structures only one system has been published. A radiating system, based on a horn antenna, with the perfusion chamber placed in the far-eld region, was used in (Yoon et al., 2006). The biological protocol was the same described in (Hagan et al., 2004), but the exposure frequencies were higher (1-6 GHz). For this higher frequency range, a standard waveguide is too small to accommodate the sample and the cellperfusion apparatus and a radiating system is necessary. However, this solution required a special arrangement to avoid interference with the experimental equipment that was shielded in a conducting box behind the perfusion chamber and a layer of absorber material was used to prevent electric eld reection. The whole system was placed within

Real-time data acquisition in biomedicine is employed in a lot of different applications, both *in vitro* and *in vivo*. Examples are given in monitoring of chemical reactions (Shutes and Der, 2005), gene expression (Gubern et al., 2009), and drug release (Chouhan and Bajpai, 2009). Concerning living animals, the real-time acquisition is usually based on non-invasive

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

Focus of this chapter was a review of the exposure systems used in real-time biological experiments, i.e. in those investigations where bio-chemical or bio-physical data are acquired from the sample simultaneously with the exposure to the EM field. Real-time investigation is widely spreading, especially in the study of the interaction between nervous

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

imaging techniques (Ohtani et al., 2010; Li et al., 2010; Voyvodic et al., 2011).

correlated event. This is also the case of bioelectromagnetic investigations.

system and RF EM fields through *in vitro* electrophysiological techniques.

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

**6.2.2 Resonant structures** 

waveguide, and the exterior.

**6.2.3 Radiating structures**

an anechoic chamber.

**7. Conclusion** 

2007). The neuronal network was cultivated on a microsensor chip tted into a recess in the guide to avoid short circuiting the measuring probes while exposing the neuronal cells.

For a similar experiment at 1800 MHz, a different solution was proposed in (Merla et al., 2011). The exposure system consisted of a TEM cell open in correspondence of the lateral walls. The multiple electrode array used for the electrophysiological recordings was inserted in a circular hole in the TEM cell bottom plate. The power efficiency of 3.2 (W/kg)/W was comparable to that of the closed systems described above.

A waveguide terminated with an exposure cell containing the sample was used to expose heart slices (Pakhomov et al., 2000) and brain slices (Pakhomov et al., 2003) to high-power microwave pulses (repetition frequency 9.2 GHz). The system had an extremely high efciency of 3.3 (kW/kg)/W which decreased about twofold per millimeter with distance from the waveguide aperture. In this case, the sample was used as the load of the guide; the impedance matching was achieved through a sapphire matching plate to maximize the power absorbed by the slices.

To record brain slices electrophysiological activity simultaneously with the exposure to a 700 MHz eld, Tattersall *et al.* (Tattersall et al., 2001) utilized a waveguide made of two parallel plates. In this case, as in (Linz et al., 1999), the top and bottom plates of the guide had holes to observe the sample and insert both stimulating and recording electrodes. The coupling between the electric field and the electrodes was not avoided since the electrodes were placed at an angle of about 45° to the electric eld (Misfud et al., 2007). The estimated efciency value was lower than 0.03 (W/kg)/W.

A completely different solution, based on an open coplanar waveguide was adopted in studies involving patch-clamp recordings from neuronal cells (Liberti et al., 2004) and eld potential recordings from brain slices (Paffi et al., 2007). Both systems operate in the 800– 2000-MHz frequency band and differ from each other by the distance between the central and lateral conductors because of the different size of biological samples to be exposed to the EM fields. The open planar geometry and the transparent glass substrate allowed easy access to the samples through the microscope and the electrodes; the electric and magnetic elds were conned in a small volume around the surface that guaranteed the avoidance of interference with the data acquisition setup and high efciency values (> 17 (W/kg)/W) at all frequencies.

To perform patch-clamp recordings from the ear hair cells of Corti organ, three exposure systems were described in (El Ouardi et al., 2011), operating at 900 MHz, 1.8 GHz and 2 GHz, respectively. All of them are based on the concept of the fin-line: a quasi-planar transmission line structure embedded in a metallic rectangular waveguide. In this case, the two fins were placed in the magnetic field plane of the waveguide. The chamber containing the samples was placed onto the two ns with a slot in between, where the exposure eld concentrates, and inserted inside the guide through a circular opening in the top plate. This opening was also used to insert the electrodes and the microscope objective during the experiments. The efficiency was very high (> 40 (W/kg)/W for all systems), with a good homogeneity of 90 %. The drawback was the narrow band that imposed the fabrication of three different systems, one for each frequency band of interest (El Ouardi et al., 2011).

A modied stripline, where the sample holder (a cuvette) and the temperature regulating chamber were part of the dielectric substrate, was described in (Ramundo-Orlando et al., 2004). The system was placed inside a spectrophotometer for monitoring the enzymatic activity of ascorbate oxidase trapped in liposomes during the exposure to a CW at 2.45 GHz.
