Energy Harvester for Wireless Sensor with RFID Interface I.B.Vendik, IEEE, V.A. Gerasimov, S.Y. Dudnikov, L.M. Selivanov, A.A. Uhov Saint-Petersburg State Electrotechical University “LETI”, Saint-Petersburg, Russia Abstract – a mobile device for the environmental temperature and humidity monitoring has been developed. The device is powered from two sources – battery and energy harvester. Environmental parameters are transferred to an external computer by means of RFID link. This communication system does not require any exter- nal power supply that extends battery lifetime depending on the data acquisition rate. The harvesting system taking energy from mains wires has been assessed and proposed as a possible solution to a further extend the battery lifetime. Proposed harvester construc- tion is based on collapsible current transformers made of a stand- ard power inductor and additional magnetic circuit part. Index Terms – RFID, energy harvesting, sensor. I. INTRODUCTION ONITORING of the environmental conditions is widely used in many fields of human activity. It is especially im- portant for controlling storage and transportation of food, biolog- ical substances, pharmaceutical goods, and chemicals [1] and requires long-time continuous operation of the devices collecting data from different kind of sensors. Temperature and humidity of the air are the most important monitoring parameters of the con- trolled objects [2]. Large buildings and warehouses usually have different environment conditions in different locations inside the same area depending on the building construction, relative posi- tion of controlled object in respect to the air conditioners, heat- ers, doors, windows and so on. It means that a set of multiple local monitoring systems is required to achieve better controlling results. Location of monitoring devices should be quickly changeable depending on the new product batches movement without any changing in the layout of the building and its infra- structure. Automated warehouses efficiently solve the problems men- tioned, however, they are expensive, require large investments and long installation time. As a result, it makes them inconven- ient in some cases, like for seasonal activities such as harvesting and local storage of agricultural products. In addition, automated warehouses usually do not track stored objects parameters: stor- age time, transportation within the warehouse in combination with local environmental conditions. Many products transported in containers also requires continu- ous monitoring of the environment conditions inside containers but this monitoring is much more problematic due to absence of electric power supply and communication infrastructures. All mentioned problems could be easily solved by using mo- bile device with appropriate sensors, memory for local data stor- age and wireless interface for data exchange with external com- puter. Embedded power supply should be able to provide a long autonomous operation of this device. II. PROBLEM DEFINITION Mobile monitoring systems use a radio link for data transfer from mobile sensor-enabled unit to an external computer. The same channel allows setting the operation parameters and mobile unit options. Usually it requires radio receiver active operation for long time waiting for the request from the external computer to guarantee short response time. In this mode, mobile unit pow- ers up the radio receiver every few seconds or even more fre- quent. Modern digital radio transceivers consume from few mA to few tens of mA at few volts in receiving mode that dramatical- ly decreases the battery lifetime. When the real-time reaction to the radio request is required, the typical operation time for mo- bile radio-enabled devices rarely exceeds one year. The battery lifetime can be extended up to few years but only when data are sent every few minutes and there is no need to guarantee the real- time data update on request from the external computer. As a result, the most native way to extend the device operation time is to decrease power consumption of radio interface of the mobile monitoring system. Further improvement of the device operation time (from few years to almost infinite) is possible only by means of energy har- vesting technology, because any battery has a limited shelf- life- time due to self-discharge and aging. The most promising extra energy source for such devices is energy harvesting from mains (AC) power line electromagnetic field [3]. III. TECHNOLOGY AND DESIGN A. RFID technology as a communication channel in envi- ronment monitoring system Environment monitoring process by itself does not create a significant power consumption because controlled parameters (relative humidity and temperature) are changed very slowly. In fact, it is necessary to measure these parameters every few minutes or even more rarely. From other hand, the monitoring system cannot stay in low-power mode within long periods be- cause it is necessary to guarantee the reliable connection with an external system (PC, reader) within few seconds. RFID technology application is the best way to solve the prob- lem because it enables fully independent radio communication with external terminal even if microcontroller of the mobile M 2016 IEEE International Conference on RFID Technology and Applications (RFID-TA) 978-1-5090-1407-1/16/$31.00 ©2016 IEEE 44