Comparison of Two Thermal Probe Technologies for the Dosimetric Investigations of RF Exposure Systems

Exposure to radiofrequency waves (RF) happens everyday but little is know about the potential induced toxicity. It is therefore essential to carry out studies with rigorous experimental protocols and accurate dosimetry. To do this, we can characterize the dosimetric characteristics, namely the specific absorption rate (SAR) of the emitted RF waves and the induced thermal increment by monitoring the temperature over time. Different types of thermal probes may be used for such a study. We were interested in comparing two types of probes that can be used in conditions suitable for in vitro measurements, in a traditional biological consumable, 96-well plate. Such particular conditions require extreme precision in the positioning of the probe, its sensitivity and its measurement accuracy. We have chosen to compare a microscale thermocouple, an inexpensive but often criticized technology as it is metallic and therefore capable of interfering with the electromagnetic field, with a much more expensive fiber optic probe. We have highlighted the advantages and disadvantages of each in the context of this specific type of measurement.

I. Introduction

The study of the toxicity of radiofrequency waves on living organisms is nowadays an important topic within the scientific community. This is even more critical with the appearance of new communication standards and the exponential expansion of their use. Studies targeting the assessment of the impact of electromagnetic waves on living organisms can be carried out at different levels, from an epidemiological point of view [1], or using in vivo [2] or even in vitro [3] models. In our case, we focused on the in vitro model. We have developed devices to study the effect of RF waves in common biological consumables, 96-well plates in this case. It is then necessary to develop techniques for dosimetric characterization of the radiation of RF waves under these particular conditions. The electromagnetic power radiated in the well and absorbed by its contents is a key data for a biological test. Several dosimetry measurement techniques exist based either on the measurement of the electric field or by thermal measurement. We chose to focus on this last technique and more particularly to compare two types of temperature sensors allowing the characterization and Fig. 1.

Photographs of two RF applicator doublets placed side by side: on the left the radiating part, on the right the SMA connexion part

the calibration of the power and therefore Specific Absorption Rate (SAR) of our microwave range device, compatible with 96-well cell culture plates. A similar approach [4] has been carried out in the past with a different exposure system based on large 12-well plates and a millimeterwave range horn antenna as the radiating element.