Passive UHF RFID Tag Design with Harvest Energy- Solar Cell and Vibration

Abstract

Enhanced RFID tag technology especially in the UHF frequency range provides extended functionality like high operating range and sensing and monitoring capabilities. Such functionality requiring extended system structures including data acquisition units, real time clocks and active transmitters causes a high energy consumption of the tag and requires an on board energy store (battery). As a key parameter of the reliability of an RFID system is the lifetime, the energy budget of the higher class tag has to be as balanced as possible. This can be achieved by using energy harvesting devices as additional power supply. The PowerTag 1 project and thus this paper proposes special power management mechanisms in combination with special energy storage structures interfacing energy harvesting devices and dealing with their special requirements. First various power management and power saving techniques are simulated and their performance is evaluated. In a second step different implementation variants of energy storage structures are compared by using accurate simulation models of the various parts of the system. The results are compared to manufacturer given and guaranteed system performance parameters of a state-of-the-art higher class UHF RFID system. The presented approach combines two simulations for the design and the evaluation of different tag architectures and power saving techniques.

Introduction

The next generation of UHF RFID tags (called higher class UHF RFID tags - HCT ) provides extended functionality in terms of independent sensing and monitoring, high communication range and large memory areas. This requires continue operation of the tag itself - also if it is not powered by the reader as in formerly pure passive UHF RFID systems (Raghunathan: 457 - 462)

. Thus an on-board energy supply is necessary, which forces a renaming of the previously called passive UHF RFID technology to semi-passive and active technology. This change in the tag architecture pushes new issues in the area of UHF RFID; the operational lifetime, which is limited by the on-board energy reservoir and thus the need of long time power saving techniques. The energy, which is stored on a tag, is limited by the state-of-the-art energy storage technology and so even with profound power saving techniques the achievable lifetime is often dissatisfying. The way to solve this issue is to supply energy from the environment by energy harvesting devices. As the energy converted by such devices comes from the environment, it is generally unpredictable, non-continues and unstable special energy storage architectures are necessary to deal with this particular requirements, which are presented in the following sections. The difference between semi-passive and active technology is the tag to reader communication. Semi-passive UHF RFID tags provide extended functionality as mentioned before but the communication is based on the same passive method as passive UHF RFID tags simply reflecting and modulating the reader signal. The operating range of such tags is much higher, as the reader signal is used for the communication only but not for powering the whole tag like in pure passive ...