Temperature-compensated composites produced by spark plasma sintering for wireless communication and surveillance systems
Project Director: Dr. Liviu NEDELCU
Project: 82PED (PN-IV-P7-7_1-PED-2024-2315 )
Contractor: National Institute of Materials Physics (NIMP)
Project manager: Dr. Liviu Nedelcu
Project type: Program 5.7 - Partnership for Innovation, Subprogram 5.7.1 - Demonstration experimental project (PED)
Start date: 05/05/2025
End date: 04/05/2027
Contracting Authority: UEFISCDI
Project summary
The project focuses on developing temperature-compensated dielectric composites (TCDCs) capable of simultaneously achieving size reduction, performance enhancement, and thermal stability in passive microwave devices. The main objective is to exploit the capabilities of spark plasma sintering technology to fabricate low-loss Mg4Nb2O9 – TiO2 composites with a tailored drift of the relative permittivity. Using empirical equations such as Maxwell-Garnett and Bruggeman, Mg4Nb2O9 – TiO2 mixtures will be designed by varying the TiO2 content within the range where thermal compensation is anticipated. In addition to usual physico-chemical characterizations (X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy), the dielectric parameters of the composites will be explored through impedance spectroscopy, MW spectroscopy, and terahertz spectroscopy. By analyzing the “synthesis - microstructure – properties” cycle, the technology for fabricating “highly-densified” TCDCs with low dielectric loss in the microwave domain will be developed. The demonstrator device will be a small, lightweight antenna designed for operation in the X band.
Coordinator: National Institute of Materials Physics
Dr. Liviu Nedelcu, Project Manager
Dr. Petre Badica
Dr. Marian Gabriel Banciu
Dr. Viorica Stancu
Dr. Cristina Besleaga
Dr. Mihai Grigoroscuta
Dr. Lucia Leonat
Dr. Lucian Trupina
Dr. Roxana Patru
Eng. Dragos Cesar Geamnasu
Teh. Dalma Gaspar
Partner: Romanian InSpace Engineering
Claudiu Cherciu, Project Responsible
Mugurel Balan
Ionela Gaza
Activities carried out during Stage I (2025)
A.1.1 Synthesis of “Mg₄Nb₂O₉ – TiO₂” mixtures with different TiO₂ contents
The stoichiometric compound Mg₄Nb₂O₉ was obtained by solid-state reaction, with calcination parameters adjusted through a series of iterative steps, each monitored and evaluated by XRD and SEM. Based on empirical equations, it was estimated that, assuming the two phases do not react, thermal compensation occurs for 13 wt% TiO₂. Therefore, mixtures with different TiO₂ mass percentages (i.e. 5%, 10%, 15% and 20%) were prepared by homogenizing them in demineralized water for 24 hours in a roller mill.
A.1.2 Fabrication of “Mg₄Nb₂O₉ – TiO₂” composites by electric-field-assisted sintering (SPS)
Prior to the SPS processing of the “Mg₄Nb₂O₉–TiO₂” mixtures, sintering tests were carried out on Mg₄Nb₂O₉ powder calcined at 1100 °C / 10 h. MNO samples with relative densities between 96% and 99.5% were produced by SPS at 1150 °C / 3 minutes, 1200 °C / 3 minutes, and 1250 °C / 3 minutes. SPS consolidation tests of the “Mg₄Nb₂O₉–TiO₂” mixtures showed that the two phases react even for a dwell time of only 1 minute.
A.1.3 Fabrication of thermally compensated “Mg₄Nb₂O₉ – TiO₂” composites with optimized properties (Part I)
Thermal treatments of TiO₂ powder were performed to reduce its reaction with Mg₄Nb₂O₉ during SPS consolidation. Secondary phases were minimized by using mixtures based on Mg₄Nb₂O₉ powders calcined at 1100 °C / 10 h and TiO₂ powders thermally treated at 1300 °C / 4 h. Thermally compensated dielectric “Mg₄Nb₂O₉–TiO₂” composites were produced by SPS for TiO₂ mass concentrations around 20%. Activities will continue in 2026.
A.1.4 Simulation of the influence of dielectric parameters and geometry on the electromagnetic characteristics of dielectric resonator antennas (Part I)
Electromagnetic simulations using Ansys HFSS started from configurations with Mg₄Nb₂O₉ dielectric resonators excited through a microstrip line on a Rogers 5880 substrate. By coupling adjacent modes, an X-band antenna with reduced profile and mass was obtained. The experimental configuration with εᵣ ≈ 12.5 validates the design concept, and further numerical studies for variants with εᵣ ≈ 17.5 (via TiO₂ inclusion) and diameters of 17.5 mm and 20 mm show that additional miniaturization is possible by adjusting the resonator height. Activities will continue in 2026.
Deliverables for Stage I
• Homogeneously mixed Mg₄Nb₂O₉ – TiO₂ mixtures;
• Thermally compensated Mg₄Nb₂O₉ – TiO₂ composites;
• Modeled electromagnetic characteristics of compact antennas;
• 1 presentation at an international conference;
• 1 manuscript.
L. Nedelcu, C.D. Geambasu, M.G. Banciu, Low-profile dielectric resonator antenna using niobate-based ceramics for X-band applications, Microwave Materials and their Applications, Saint-Brieuc, France, 16-19.09.2025
Dr. Liviu Nedelcu
Scientific Researcher Rank II
Laboratory of Complex Heterostructures and Multifunctional Materials
Phone: +40-(0)21-2418 123
nedelcu@infim.ro
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