New fin-line devices for radiofrequency exposure of small biological samples in vitro allowing whole-cell patch clamp recordings.

The development and analysis of three waveguides for the exposure of small biological in vitro samples to mobile communication signals at 900 MHz (GSM, Global System for Mobile Communications), 1.8 GHz (GSM), and 2 GHz (UMTS, Universal Mobile Telecommunications System) is presented. The waveguides were based on a fin-line concept and the chamber containing the samples bathed in extracellular solution was placed onto two fins with a slot in between, where the exposure field concentrates. Measures were taken to allow for patch clamp recordings during radiofrequency (RF) exposure. The necessary power for the achievement of the maximum desired specific absorption rate (SAR) of 20 W/kg (average over the mass of the solution) was approximately P(in) = 50 mW, P(in) = 19 mW, and P(in) = 18 mW for the 900 MHz, 1800 MHz, and 2 GHz devices, respectively. At 20 W/kg, a slight RF-induced temperature elevation in the solution of no more than 0.3 °C was detected, while no thermal offsets due to the electromagnetic exposure could be detected at the lower SAR settings (2, 0.2, and 0.02 W/kg). A deviation of 10% from the intended solution volume yielded a calculated SAR deviation of 8% from the desired value. A maximum ±10% variation in the local SAR could occur when the position of the patch clamp electrode was altered within the area where the cells to be investigated were located.

Exposure set-ups for in vivo experiments using radial waveguides.

Radial waveguide set-ups are introduced as exposure devices for long-term experiments with large numbers of non-restrained animals exposed simultaneously. Methods are presented to ensure well-defined exposure conditions even for potentially overmoded waveguides and for the exposure of large groups of animals per cage. The proposed methods are applied for a four-generation study being performed on up to 2500 mice exposed to a generic UMTS test signal at prescribed averaged whole body specific absorption rates (SARs). The variation of the whole body SAR due to the movement of the mice inside the cage is calculated by using the finite-difference time-domain method and detailed animal models for selected configurations of the mice inside the cage for all stages of the study.

Generic UMTS test signal for RF bioelectromagnetic studies.

This report outlines the characteristics of universal mobile telecommunications system (UMTS) signals and discusses the signal parameters with respect to their possible biological relevance in order to define a generic UMTS test signal (GUS) for experiments aiming at the investigation of biological effects of weak electromagnetic fields. The GUS includes features of a real UMTS signal and especially the characteristics of UMTS, which differ from those of already applied second generation mobile communication systems (GSM 900, DCS1800, PCS1900, IS-95). It has been specified on the basis of the recommendations of a working group of the German Forschungsgemeinschaft Funk (FGF) with a focus on the mechanisms of UMTS which are responsible for slow term signal contributions, i.e., low frequency variations of the radio frequency (RF) envelope, since the hypothetical possibility of biological relevance of weak electromagnetic fields is often attributed to time variations of the RF envelope with frequencies close to those of natural processes. In this respect, it is also shown that the mandatory power control loop in UMTS gives rise to very strong 1.5 kHz variations on the air interface. Based upon the concept of the GUS, a UMTS test signal generator (GUS6960S) is described.

Membrane potential and currents of isolated heart muscle cells exposed to pulsed radio frequency fields.

The influence of radio frequency (RF) fields of 180, 900, and 1800 MHz on the membrane potential, action potential, L-type Ca(2+) current and potassium currents of isolated ventricular myocytes was tested. The study is based on 90 guinea-pig myocytes and 20 rat myocytes. The fields were applied in rectangular waveguides (1800 MHz at 80, 480, 600, 720, or 880 mW/kg and 900 MHz, 250 mW/kg) or in a TEM-cell (180 MHz, 80 mW/kg and 900 MHz, 15 mW/kg). Fields of 1800 and 900 MHz were pulsed according to the GSM-standard of cellular phones. The specific absorption rates were determined from computer simulations of the electromagnetic fields inside the exposure devices by considering the structure of the physiological test arrangement. The electrical membrane parameters were measured by whole cell patch-clamp. None of the tested electrophysiological parameters was changed significantly by exposure to RF fields. Another physical stimulus, lowering the temperature from 36 degrees C to 24 degrees C, decreased the current amplitude almost 50% and shifted the voltage dependence of the steady state activation parameter d(infinity) and inactivation parameter f(infinity) of L-type Ca(2+) current by about 5 mV. However, at this lower temperature RF effects (900 MHz, 250 mW/kg; 1800 MHz, 480 mW/kg) on L-type Ca(2+) current were also not detected.

Characteristic parameters of monomode fibers.

Based on a rigorous analysis of the Gaussian approximation applied to monomode optical fibers, a universal representation of the near- and far-field characteristics is given which covers all refractive-index profiles of practical interest. The accuracies of some methods of determining the most important parameters, e.g., the spot size w(0) and the cutoff wavelength lambda(c), are compared, assuming the actual profile is unknown.

Long-range backscattering experiments in single-mode fibers.

A setup was built that was suitable for practicable long-range backscattering measurements in single-mode fibers. To avoid nonlinear effects and to reduce costs, low-input powers from a laser diode were used. Three different fibers (0.8, 2, and 3 km long) were tested, and experimental results are given.