Non-contact inductive radiofrequency monitoring of a beef muscle tissue decomposition

The dielectric properties of tissues have been widely used to detect and monitor different pathologies. One of the remaining challenges is to timely and accurately characterize the evolution of the dielectric properties of tissues in a non-invasive and contactless way, with a simple and portable monitoring system. This paper proposes investigating the use of a loop-shaped transmission line passive resonators (TLR) to sense organic tissue changes in the radiofrequency bandwidth (in the hundreds of MHz bandwidth), through inductive coupling with the tissue. This kind of sensor can be wirelessly excited, and is able to distantly detect the dielectric modifications in the targeted tissue through the changes of the transmitted electromagnetic field. TLR-based sensors are therefore very promising for the non-invasive, wearable and continuous monitoring of tissues. In this paper, a first study is carried out to monitor the decomposition of a beef muscle sample for six consecutive days with two different TLR-based sensors featuring two investigation frequencies (160 MHz and 350 MHz). The obtained results confirmed the ability of such sensors to follow the modifications of an organic tissue through the assessment of both the conductivity and the relative permittivity of the investigated sample. Results also confirmed that the investigation frequency, for which the loss factor within the tissue is around unity, is particularly well suited to sense changes within the tissue under investigation. A second study was realized with other soft matter samples (water, cottage cheese, water/gelatin mix) to determine the ability of TLR-sensors to discriminate between soft matter of various nature. Thanks to the ability of the TLR-based sensor to assess the loss factor of the monitored samples, it was found that i) the proposed sensor is relevant to discriminate between the considered soft matter samples and ii) that this discrimination can be made particularly efficient when using the appropriate investigation frequency. Furthermore, the benefits of the use of several investigation frequencies were also demonstrated for enhanced tissue characterizations. TLR-based sensors are therefore good candidates for the non-invasive, low-cost and sensitive sensing devices dedicated to the monitoring of pathologies such as wound healing and cancer detection.