Articles | Volume 13
03 Nov 2015
 | 03 Nov 2015

Investigations and system design for simultaneous energy and data transmission through inductively coupled resonances

C. Schmidt, E. Lloret Fuentes, and M. Buchholz

Abstract. Wireless Power Transfer (WPT) with simultaneous data transmission through coupled magnetic resonators is investigated in this paper. The development of this system is dedicated to serve as a basis for applications in the field of Ambient Assisted Living (AAL), for example tracking vital parameters remotely, charge and control sensors and so on. Due to these different scenarios we consider, it is important to have a system which is reliable under the circumstance of changing positioning of the receiving device. State of the art radio systems would be able to handle this. Nevertheless, energy harvesting from far field sources is not sufficient to power the devices additionally on mid-range distances. For this reason, coupled magnetic resonant circuits are proposed as a promising alternative, although suffering from more complex positioning dependency.

Based on measurements on a simple prototype system, an equivalent circuit description is used to model the transmission system dependent on different transmission distances and impedance matching conditions. Additionally, the simulation model is used to extract system parameters such as coupling coefficients, coil resistance and self-capacitance, which cannot be calculated in a simple and reliable way.

Furthermore, a mathematical channel model based on the schematic model has been built in MATLAB©. It is used to point out the problems occurring in a transmission system with variable transmission distance, especially the change of the passband's centre frequency and its bandwidth. Existing solutions dealing with this distance dependent behaviour, namely the change of the transmission frequency dependent on distance and the addition of losses to the resonators to increase the bandwidth, are considered as not inventive. First, changing the transmission frequency increases the complexity in the data transmission system and would use a disproportional total bandwidth compared to the actually available bandwidth. Additionally, adding losses causes a decrease in the energy transmission efficiency.

Based on these facts, we consider a system that changes the channel itself by tuning the resonant coils in a way that the passband is always at a fixed frequency. This would overcome the previously described issues, and additionally could allow for the possibility to run several independent transmission systems in parallel without disturbing each other.

Short summary
In this paper, wireless power and data transmission through coupled magnetic resonators is investigated. Measurements on a simple prototype lead to a simplified schematic model. Based on this, the transfer channel's behaviour is modeled for arbitrary channel states (e.g. transfer distances) and can be fitted into a mathematical model. This is finally used to show that shifting the resonant frequencies of the individual resonators is a good means to ensure stabele data and energy transmission.