A 3-Stage Voltage Multiplier and Charge Pump has been successfully designed for Energy Harvesting System in Wireless Sensor Network by a team of researchers and the Analog Research Group, Texas Tech University, Lubbock.
In a paper presented at the IEEE Topical Conference on Wireless Sensors and Sensor Networks (WiSNet), 2013 under the section of Wireless Integrated Sensor Front-Ends and Building Blocks; Ravindranath D. Shrivastava, Devashish Deshpande, Changzhi Li and Richard Gale designed a Voltage Multiplier that is able to Harvest Energy for Input power as low as -9dBm under loaded conditions. The Charge Pump was able to maintain constant output voltage under large load variations. They achieved a High Efficiency by using the Charge pump for all load conditions.
One of the main difficulties of implementing wireless sensors widely in field applications is due to the power management and charging of batteries. The researchers proposed and implemented a Wireless Energy Harvesting System which can be used to charge the batteries of the sensors whenever required. They were able to harvest energy from a RF source, which is mostly a Master Transceiver Unit, with input power as low as -9dBm.
Also the Energy Harvester was used to charge batteries when the input power is as low as -27dBm. The power management part of the system includes a Charge Pump which handles large variation in load conditions. This charge pump can be used not only to boost the battery voltage but also to provide a regulated output independent of load conditions. Link variations can be an issue in a Wireless Sensors Network but their system introduces a low power data acquisition system that helps to monitor the link. Adjustments can be made accordingly for maximum energy transfer to take place between the transmit TX and receive RX coils.
The team presented a wireless energy harvesting unit in the first instance that uses only a single stage voltage multiplier which they extended to three stages in order to harvest energy much more efficiently with a Low-dropout regulator that cannot boost the rectified voltage. But with a regulated Charge pump they were able to boost the battery voltage up to 3.7 times the input DC Voltage.
They also proposed a frequency regulation technique to provide constant efficiency at all loads because of the incessant problems of using a Pulse Width Modulation pump with fixed frequency that leads to low efficiency at low load conditions
The Energy Harvester is designed using Dickson’s Charge Pump/Multiplier cascaded in 3-stages with a Bulk Modulation technique used to get better performance and better efficiency from CMOS diode. The next IEEE Topical Conference on Wireless Sensors and Sensor Networks conference is coming up between 19 -22 January 2014, at Newport Beach, CA, USA