**6.2.2 Resonant structures**

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

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

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

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

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

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).

comparable to that of the closed systems described above.

efciency value was lower than 0.03 (W/kg)/W.

power absorbed by the slices.

all frequencies.

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 waveguide, and the exterior.
