Characterization of skin diseases via radiofrequency dielectric spectroscopy: complementarity o[...]

Overview

Organisation/Company Laboratoire Electronique, Systèmes de Communication et Microsystèmes Research Field Engineering » Electronic engineering Researcher Profile Recognised Researcher (R2) Leading Researcher (R4) First Stage Researcher (R1) Established Researcher (R3) Application Deadline 19 Apr 2026 - 22:00 (UTC) Country France Type of Contract Temporary Job Status Full-time Offer Starting Date 1 Sep 2026 Is the job funded through the EU Research Framework Programme? Not funded by a EU programme Is the Job related to staff position within a Research Infrastructure? No

Thesis Context

1. Context

1.1 Problem statement and challenges

Early detection and diagnosis of skin diseases represent a major challenge in dermatology. Traditional diagnostic methods rely either on visual examination—limited to the superficial properties of the skin—or on more in-depth but invasive and costly procedures. Dielectric spectroscopy at RF and microwave frequencies is emerging as an innovative technique for skin tissue analysis.

Unlike visual examination, this approach provides access to the properties of internal tissue layers. It offers a non-invasive alternative for analyzing skin tissue properties at adjustable depths, which could be exploited for early disease detection (before visible marks appear) or to refine a diagnosis.

This approach is based on the interaction of electromagnetic waves with biological tissues, providing precise information on their electrical properties (via conductivity σ) and dielectric properties (via complex permittivity ϵ), and by extension, their composition and structure. The RF and/or microwave probes to be developed must be specifically adapted to the characteristics of the targeted pathologies to ensure accurate and reliable measurements. They must also be optimized for reproducible results in real-world conditions. Furthermore, these probes must be easily integrated into portable devices to ensure they are practical for healthcare professionals in both hospital and private practice settings.

1.2 ESYCOM activities related to the subject

The research presented here follows several projects conducted within the ESYCOM laboratory by the supervising team:

Houssein Mariam’s Thesis (2020): Focused on developing a wideband microwave microfluidic sensor. Excellent results were obtained for characterizing small liquid volumes, showing sensitivity to micro-beads similar in size to biological cells.

Resonant Structures: Explored for their higher sensitivity. Work by Joséphine Pichereau (2025) utilized planar differential resonators to analyze liquids or solids within the opening of a rectangular resonator. Using two resonators allows one to serve as a reference, making the structure robust against experimental variations. The difference in permittivity between samples is reflected in the shift of resonance frequencies and bandwidths. This sensor was later made frequency-tunable using varactor diodes by Houssem Rouached.

This differential approach was also adopted in the doctoral work of Zied Fritiss, which focused on the design, simulation, and fabrication of a probe intended for the early detection of skin cancer. To this end, we designed a probe that transmits the electromagnetic field from the VNA (Vector Network Analyzer) to the skin or tissue under analysis as efficiently as possible. This is a wideband probe operating within a frequency band of 1 GHz to 5 GHz.

The analysis frequency band was chosen based on the significant variation in the relative permittivity between healthy skin (around 30) and melanoma (around 50-60) in this band, causing a change in the reflection of the electromagnetic signal at the tip of the probe, at the point of contact between the probe and the skin being examined. This effect was exploited in a differential structure comprising two identical probes connected to a coupler, so as to directly measure an indicator characteristic of a difference in skin properties at the two probed points. This original approach is particularly relevant for the intended application because it overcomes the difficulty inherent in in-vivo measurements related to the variability of individuals' physiological parameters: thus, by choosing an area of healthy skin on the patient as the reference medium, the reliability of the diagnosis is increased by adapting to the properties of the patient's skin in the area of interest and to his physiological state at the time of the test. However, the coupler used in the differential measurement device limits its operating frequency band, so that in our future work we will retain the principle of comparison with the patient's skin while moving away from the differential structure.

The thesis topic presented here is a continuation of the latter thesis and follows on from real-world tests that revealed necessary changes to the device developed.

1.3 Hospital testing and limitations of the current measurement device

Interest has been identified in monitoring the development of a rare disease that causes tumors on the skin, known as neurofibromatosis. It would be particularly useful to offer a device capable of detecting the development of a neurofibroma at an early stage, i.e., before a visible lump appears on the skin.

Experimental tests carried out on a patient and discussions with dermatologists at Henri Mondor Hospital in Créteil have highlighted desirable improvements to the sensor to make it easier to use and ensure that the device is a reliable aid to medical diagnosis. These various aspects will be examined in this thesis.

Thesis Objectives and Plan

2. Thesis Objectives

The proposed work will build on the knowledge acquired in Zied Fritiss' thesis in order to optimize the sensor according to the thickness of the skin to be probed and the desired spatial resolution. This will involve examining the influence of the measurement frequency band, the geometry of the sensor, and comparing results with electromagnetic simulations.

Two approaches are considered for probing the skin: measuring a reflection coefficient with a single probe or a transmission coefficient between two probes placed close to each other on the skin. To test the second configuration, a probe will be developed that can take transmission measurements between several points on the skin a few millimeters apart. These approaches yield different results, and a study will be conducted to evaluate their respective accuracy in extracting parameters useful for diagnosis (such as tissue properties, tumor width and depth), depending on the geometry of the sensor. This work requires an understanding of biological phenomena (such as tumor evolution) and will involve discussions with dermatologists.

To ensure satisfactory contact between the probe and the skin, the addition of a contact layer will be considered. Based on the properties of this layer, alternative material choices will be proposed and tested.

Finally, the goal is to design a more compact system to improve ergonomics and ease of use, and to propose an easy-to-follow measurement protocol that provides easily interpretable results. The current differential device has weaknesses (complex use, reduced operating frequency band, high sensitivity to connectivity); therefore an alternative approach will be explored. The aim is to propose a more ergonomic device and test the robustness of the measurement protocol, taking into account variability in skin properties.

Once the measurement protocol is established, the device will be made portable through programmable circuits and a nano-VNA.

3. Proposed work plan

The objective is to design and optimize an RF sensor for biomedical applications, particularly for detecting and monitoring skin abnormalities. The device should provide reliable diagnostic support despite variability in skin properties due to the individual, physiological condition, and body area, by enabling the determination of relevant biological parameters defined in collaboration with partner dermatologists.

Several sensor topologies will be tested, both for reflection measurements from a single excitation source and for transmission measurements between several closely spaced sensors. In the latter case, coupling between probes will be studied and incorporated into the design. The work will be based on measurements with different probes and electromagnetic simulations to determine the skin area probed (extent and depth) and to optimize the measurement configuration.

After this initial study, optimized probes for reflection or transmission measurements will be designed and tested. Several probe topologies may be selected to address different pathologies or to access different quantities. A measurement protocol that is easy to apply and ensures reliable results will be developed, with particular focus on robustness of diagnosis across skin with different properties. Tests will first be conducted on phantom tissues (non-toxic materials designed to mimic skin) and will later consider human testing.

The results will identify limitations of initial probes and guide modifications. Additional aspects include:

• Ensuring good contact between the probe and the skin to avoid air gaps, including studying flexible materials and testing options through simulation before prototype manufacturing.
• Optimizing ergonomics to facilitate precise positioning, based on test experience and doctor feedback.
• Making the device compact and portable to reduce cost and enable use with a nano-VNA, including circuit programming considerations.

Qualification

Ideally, the candidate will have completed a master's degree or engineering training in electronics and radio frequencies. Proficiency in electromagnetic simulation software and measurements using a VNA is expected. A strong interest in applications related to living organisms would be advantageous.

Additional Information

Work Location(s)

Number of offers available 1

Company/Institute Laboratoire Electronique, Systèmes de Communication et Microsystèmes

Country France

City Champs-sur-Marne