Wireless Test fixtures to Measure the Dielectric Properties of Materials in RF

Project Information

RFmatCarac

Grant agreement ID: 101156045

DOI

10.3030/101156045

Project closed

EC signature date 5 February 2024

Start date 1 July 2024

End date 31 December 2025

Funded under

• European Research Council (ERC)

Total cost

No data

EU contribution

€ 150 000,00

Coordinated by

INSTITUT POLYTECHNIQUE DE GRENOBLE
France

Periodic Reporting for period 1 - RFmatCarac (Wireless Test fixtures to Measure the Dielectric Properties of Materials in RF)

Reporting period: 2024-07-01 to 2025-12-31

Summary of the context and overall objectives of the project

Advanced dielectric materials play a central role in modern radio-frequency (RF) systems, underpinning applications such as antennas, resonators, 5G and satellite communications, radar, medical imaging, and emerging IoT technologies. The electrical performance and reliability of these systems critically depend on accurate knowledge of the complex permittivity of the materials used, often across wide frequency ranges. As RF technologies move toward higher frequencies, tighter integration, and more demanding performance constraints, the need for reliable, flexible, and affordable dielectric characterization tools has become increasingly acute.
Despite this need, current RF characterization techniques remain largely inaccessible to many industrial users. Established methods—including resonant cavities, coaxial probes, and free-space techniques—are either highly accurate but expensive and narrowband, or broadband but challenging to implement in practice. Comprehensive characterization across different materials, geometries, and frequency bands typically requires multiple dedicated test fixtures and advanced RF expertise, resulting in prohibitive costs and operational complexity. Consequently, many companies—particularly SMEs—are unable to perform systematic RF material characterization and are forced to rely on poorly specified or non-RF-grade materials, leading to suboptimal designs, increased development risks, and reduced innovation capacity.
The RFmatCarac project builds directly on the results of the ERC Consolidator Grant ScattererID, which introduced a new analytical framework linking the resonant behavior of chipless RF scatterers to the electromagnetic properties of their environment. RFmatCarac aims to exploit and valorize this ERC-funded research by demonstrating the feasibility of a radically new, wireless approach to dielectric characterization. The proposed method relies on simple, fully metallic resonant scatterers placed directly on or within the material under test and interrogated using a radar-like measurement principle. By extracting the resonance frequency and quality factor from the backscattered signal, the complex permittivity can be determined analytically.
The overall objective of this project is to reduce both the technical and economic barriers to RF dielectric characterization. The project has validated the approach across a broad frequency range and for a wide variety of materials, including solids and powders.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

A major outcome was the full experimental validation of a non-contact dielectric characterization method using simple metallic rectangular loop resonators remotely interrogated by a single antenna. The complex permittivity was retrieved from the resonance frequency and damping factor of the backscattered signal using closed-form analytical expressions. Extensive measurement campaigns demonstrated excellent repeatability, with relative permittivity errors below 1% and standard deviations below 0.5%, and the ability to extract loss tangents in the 10⁻³ range for low-loss RF substrates.
The approach was extended to broadband characterization by employing resonators of different lengths, enabling the extraction of frequency-dependent permittivity over the 2–4 GHz range. These results accurately tracked dispersive behavior while identifying limitations in loss extraction at higher frequencies. To overcome these limitations, a hybrid physics–data strategy combining full-wave electromagnetic simulations with Gaussian Process Regression was developed, significantly improving robustness and accuracy for very-low-loss materials.
In parallel, we applied this radar technique to powdered dielectrics. The remarkable thing was that it was possible to significantly improve measurement sensitivity by enhancing the quality factor. A novel resonator configuration based on sustained excitation by multiple delayed reflections within a dielectric guiding structure was theoretically analyzed, numerically validated, and experimentally demonstrated. This concept led to quality-factor increases of up to 55% in lossless configurations and more than 20% in realistic lossy materials, directly improving resonance selectivity and material-discrimination capability. In addition, a rigorous analytical model for the bistatic radar cross section of rectangular loop resonators was derived, providing accurate predictions of resonance frequencies, quality factors, and scattering levels, and strengthening the theoretical foundations of the method.
Finally, a major and highly innovative outcome of the project was the introduction of a wireless active feedback loop principle that enables spontaneous RF oscillation only in the presence of a resonant scatterer. This concept, experimentally validated through simulations and measurements, establishes a fundamentally new interaction paradigm in which the resonator and its electromagnetic environment directly set the oscillation frequency. Beyond communication applications, this principle lays the groundwork for a new generation of ultra-sensitive dielectric characterization methods, where material properties can be inferred from the frequency and stability of self-sustained oscillations, offering a clear pathway towards further improvements in measurement precision.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

RFmatCarac delivers results that significantly exceed the current state of the art in RF dielectric characterization by combining wireless measurements, analytical modeling, and enhanced resonator sensitivity in a single, compact approach. Unlike conventional techniques based on resonant cavities or coaxial fixtures, the proposed solution enables non-contact, broadband, and low-cost characterization of dielectric materials, including low-loss solids and powders, with minimal RF expertise.
From a technological perspective, the project demonstrates a new class of RF measurement tools based on resonant scatterers that drastically reduce system complexity and cost while maintaining accuracy levels compatible with industrial requirements. The validated concepts open the way to portable and scalable characterization systems that can address use cases currently underserved, such as in-situ material qualification, rapid prototyping, and quality control in real operating environments.
The potential impact is reinforced by favorable market conditions. The global RF test equipment market is expected to grow from approximately USD 4.2 billion in 2025 to USD 7.6 billion by 2035, with the RF dielectric characterization segment growing even faster, from around USD 269 million to more than USD 550 million over the same period. RFmatCarac directly targets this niche by addressing unmet needs for affordable, flexible, and easy-to-deploy solutions, particularly for SMEs, research laboratories, and industrial R&D departments.
To ensure further uptake and success, several key needs have been identified. These include additional system-level integration and validation against standards. Access to early demonstration sites, industrial partnerships, and dedicated funding for productization will be essential to accelerate market entry. Finally, work on intellectual property protection and commercialization strategy needs to continue.

wireless approach to dielectric characterization