Semi-analytical Modeling of Single Loop Inductive RF Sensors Used to Sense and Locate Inclusions in Dielectric Media

The electromagnetic characterization of dielectric media is a major issue in many industrial flelds. Non-contact radiofrequency (RF) inductive techniques are well suited for the non-invasive evaluation and monitoring of dielectric media. In this paper, we investigated the relevance of a semi-analytical modeling technique, so-called distributed point source method (DPSM) to model the interactions of a RF single loop antenna with a dielectric medium containing a dielectric inclusion. The resistance of the antenna, which is related to the conductivity of the investigated media, can be estimated using DPSM. A series of experiments were carried out to validate the computed results. Furthermore, a simple system constituted of two RF single loop antennas is considered to locate the position of an inclusion. The DPSM was used to study the ability of such a system to locate the inclusion. The dielectric properties (electrical conductivity ae and dielectric permittivity ") of organic media are recognized as relevant indicators of their physical state. The estimation of these properties is an interesting issue in many industrial flelds, such as civil engineering, oil, food (1) or medicine (2). Indeed, the dielectric spectroscopy techniques are widely used to characterize the state of the storage or processing of the food product (3) and the dielectric properties in the fleld of RF or in the fleld of microwave can be used as relevant indicators to detect and monitor the pathological evolution for human health and well-being (4{7). However, because of contact issues (8), these techniques show limitations for in-vivo, for non-invasive or for wearable implementations. So the contactless inductive techniques have been developed for the dielectric characterization of organic media (7,8). Since the state of organic media afiects both dielectric parameters (9), it seems relevant to consider RF techniques. To implement such a method, an RF antenna can be used as a transmit and receive sensor. The antenna radiates a variable magnetic fleld which induces eddy currents (related to the electrical conductivity) and displacement currents (related to the permittivity) of the medium. In turn, the induced currents change the radiated magnetic fleld by magnetic coupling. These changes may be sensed by reading out the RF antenna impedance changes. As a result, the analysis of the sensor impedance enables to read out the dielectric property changes of the medium. In this study, we aim at modeling the interactions between an RF antenna (a coil) and a dielectric medium (e.g., a tissue) containing a dielectric object of difierent properties (e.g., a lesion in a tissue). We investigate here the relevance of a semi analytical modeling, called the distributed point source method (DPSM), to accurately and e-ciently model the interactions at stakes. In Section 2 of the paper, we present the studied conflguration and the basic principle of the implementation of the DPSM. In Section 3, computations results are presented and validated by the experiment. In Section 4, a two coils conflguration is studied so as to evaluate the possibility of localizing a