Aiming for the cloud - a study of implanted battery-free temperature sensors using NFC

In this paper we present results based on measurements of implantable devices which can be powered externally and communicated with using the near-field communication (NFC) infrastructure. NFC allows us to not have a dedicated gateway and intra-body communication to bridge the data from sensors to phone. In our trials, we have used commercially available sub-components and mounted them on a thin plastic with printed interconnections and coated them for bio-compatibility. Devices were implanted in porcine models during one week. We could during this time measure the in-vivo body temperature through skin and subcutaneous tissue ranging in thickness from some mm to a couple of cm. The implanted sensor devices are mounted on thin, printed-electronics plastic sheets where the coils and conductors are designed with different types of materials. The choice of materials is done in order to offer a low-cost solution to read out data from in-vivo sensors. We compile measured data, practical results and guidelines, together with theoretical results referring to the design of the implanted inductive NFC coil as well as the energy transfer from one mobile device to another.