Wireless Power Transfer Systems for WSN applications
SpaceForest participates in recently established COST Action – IC1301 – WIPE (Wireless Power Transmission for Sustainable Electronics). The purpose of this COST Action is to propose and develop efficient Wireless Power Transfer (WPT) circuits, systems and strategies specially tailored for battery-less systems. Battery-free sensors, passive RFID, Near Field Communications (NFC) are all closely related concepts that make use of WPT and energy harvesting systems to power up mobile devices or charge up batteries remotely, contributing to the development and fostering of the Internet of Things (IoT) evolution.
SpaceForest proposed and developed a proof-of-concept WPT system for remote powering of wireless sensor network (WSN) nodes, which are designed and optimized within the DEWI project.
The proposed WPT system is based on microwave power transfer concept, in which high-gain antenna arrays optimized to operate at 2.45 GHz are used to transfer energy from a transmitter to a WSN node. The conversion from electrical energy to RF signal is carried out using a 2.45 GHz signal generator. At the receiver side, the conversion from the RF energy to electrical energy is carried out using a rectifier with voltage multiplier. The so generated electrical energy is stored in a supercapacitor powering up a ZigBee (WSN) node. Each powered ZigBee node repetitively sends measurement data to the WSN data sink, which is connected with the central processing unit for system performance evaluation.
WPT experimental verification
We obtained a positive energy balance for the proposed proof-of-concept WPT system for WSN operating at 6 measurements per second (R = 1m, transmitted power +28 dBm). In the next version of the system, a transmitter with phase steered radiation direction was used. In this proof-of-concept, a spatial coverage angle of 120 degrees, with a single ZigBee node performing up to 5 measurements per second and a positively sustained energy balance was obtained (R = 65 cm. transmitted power +30 dBm).
The system can be viewed in the Figure below.
With further improvements (the use of better materials), the range and the efficiency of the WPT system can be significantly improved.
In the next phase of the project, SpaceForest will implement intelligent WPT system switching algorithm, in order to direct the energy flow towards the nodes, which it will need most at a given time.