A small, low-cost, wireless sensor node is important for ubiquitous sensing. However, the need for frequently replacing its battery has always been a problem which has always limited their widespread use. Energy harvesting is one of the key techniques used to solve this problem.
In this paper, we propose a low cost approach using RF energy harvesting from ambient RF fields; this approach mainly relies on TV broadcast signals. TV broadcast signals that are not received by the TV viewers are generally dissipated as heat resulting in a waste of energy.
This wasted energy can be utilized to power a low-power sensor node. Since the energy harvested from TV broadcasts is relatively time-invariant when compared with solar power, low-cost capacitors can be used instead of expensive rechargeable batteries in the sensor nodes.
The energy generated from an energy harvester varies in time and space. Therefore the use of RF energy harvesters also requires a change in both the hardware and the software of wireless sensor nodes. Since WSNs can be applied to many types of applications such as environment and habitat monitoring, healthcare applications, and industrial process monitoring and control.
We developed a sensor node prototype operating on RF energy harvesting from TV broadcast signals. This prototype makes use of the eZ430-RF2500 solar energy harvesting kit from Texas Instruments, which contains a rectenna, MSP430F2274 microcontroler and low power CC2500 2.4 GHz RF transmitter. The prototype stores electricity in an aluminum electrolytic capacitor to power the MCU.
We used SimpliciTI as a network protocol to gather data from the end nodes. SimpliciTI is a proprietary network protocol provided by Texas Instruments. SimpliciTI is capable of developing a small-scale network, which includes less than 256 nodes. SimpliciTI protocol consumes less power than Zigbee with RTOS.
As a first step to achieve our objective, we developed a wireless sensor node prototype and implemented an adaptive duty cycle determination method. This prototype is capable of sensing and transmitting temperature data every 5 seconds by RF energy harvesting.
Since our RF energy harvester consists only of a rectifier and an antenna, its manufacturing cost is low, and hence, a large number of sensor nodes can be placed densely. This RF energy harvesting technique can be effective in long- period measurement applications that do not require high power consumption.
To read more of this external content, download the complete paper from the online open conference paper archives at the State University of Campias, Brazil.http://www.decom.fee.unicamp.br/~cardieri/NotasDeAula_IE308/05690588_EnergyHarvesting_Artigo7.pdf