Wireless energy transfer with data transfer add-on through low-conductivity host rocks

Wireless energy transfer by applying low-frequency (LF) magnetic fields through the repository barriers has been proposed as one long-term power sourcing option of geological repository monitoring sensors. The general goal of this research has been to investigate the applicability and basic limitations of the wireless energy transfer for the powering of nuclear repository monitoring sensors. Another goal has been a feasibility study and pilot implementation of a wireless bi-directional data transfer add-on in the wireless energy transfer system without compromising the energy transfer performance. The main research methods have been performance analysis with 10 m operation distance by applying existing theory of inductive coupling and power transfer, and a 125 kHz pilot system design and experiments through medium representing repository barriers consisting of host rock with relatively low conductivity. The research until now has demonstrated that the wireless energy transfer through repository barriers is a relevant powering technology of wireless repository monitoring sensors. Tests of the pilot system also indicated that the wireless data transfer add-on can be implemented without compromising the power transfer performance significantly. Further elaboration of the pilot system towards the final repository monitoring implementations is needed for maintaining the antenna resonance during the long-term use, including an interim energy storage for sensor payload supply power conditioning, improving the immunity of the data uplink to the external noise, and the design of the TDM based protocol for powering, data uplink and data downlink. This paper gives an overview of the research carried out in this topic by VTT as a part of the European project Modern2020 Task 3.3. A more detailed description of the results can be found in Modern2020 deliverable D3.3.