RF-Powered Wireless Sensors

Powercast demos prelude to mobile network RF energy harvester
Directed RF energy harvester demo is stepping stone to full ambient RF harvesters that can siphon energy from ubiquitous mobile networks

“After setting up an RF energy-harvesting demo at this week’s Sensors Expo collocated with ESC Chicago, Powercast’s director of marketing Harry Ostaffe presented a paper that outlined the concepts and paths to what he believes to be the endgame: full ambient RF harvesting capabilities that sip power from ubiquitous mobile networks and eliminate batteries and direct RF power sources completely.”  Read more…

Powercast presentation - Power Out of Thin Air (PDF)

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The P21110 Powerharvester receiver  has some great new features for power management in addition to RF Energy Harvesting.  A battery-free wireless sensor node (shown below) has been designed to demonstrate the improved performance capabilities of the P2110.

The sensor module has a P2110 Powerharvester, 50mF AVX BestCap, 3 sensors (temperature, humidity, light), a PIC24 microprocessor, and a 2.4 GHz radio module. This node was powered by a 4W EIRP, 915 MHz transmitter.  For testing purposes, an antenna was used with a linear gain of 4, or 6 dBi.  The PCB dimensions are approximately 1.5″x2.5″.

When a charge threshold of 1.25V is reached on the supercap, the DC output is turned on to power the MCU and radio.  A quick read of the sensors is performed, the received signal strength (RSSI) from the transmitter is determined, and that data is transmitted using the MiWi P2P protocol.  The PIC24 was programmed to use the new RESET feature to turn off power as soon as the data packet was transmitted.  With the energy management implemented in this node, a significant reduction in energy consumption was achieved from a previously unoptimized, off-the-shelf sensor demo.  The transmitter also has the ability to send low-rate data, such as a transmitter ID, that can be used for location-based applications or to activate only specific end devices.

The performance at different distances is as follows:

10 feet - every second
20 feet - every 6 seconds
30 feet - every 21 seconds
40 feet - every 89 seconds

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Powercast announced the release of new RF Powerharvester receivers.  The P1110 and P2110 Powerharvester receivers offer additional functionality for power management and intelligent control.  They are designed for the 915 MHz band, but have a wide bandwidth which includes other commonly used frequencies.  The components work with any standard 50-ohm antenna.

http://www.powercastco.com

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New Scientist magazine has written an article titled “Unplugged: Goodbye cables, hello energy beams” which discusses several technologies and companies in the wireless power market, including Powercast.

As it relates to wireless sensors, RF energy is the only controllable, practical technology to provide power over distance to multiple sensors simultaneously.  Other technologies are either too directional for one-to-many powering (i.e. IR LEDs), or have severe range limitations (i.e. induction, MR).  There are the critics that say RF power is not efficient and most of the energy is wasted.  However, using RF to power sensors at long range (e.g. energy management and building automation) is not about the efficiency of the charging mechanism, it’s about enabling applications and achieving greater system-wide efficiency.  Having a transmitter than consumes a few watts but provides power to sensors which feedback data to control thousands (or tens of thousands) of watts or BTUs provides a significant “energy ROI”.

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Powercast will be demonstrating RF energy harvesting at the IDTechEx Energy Harvesting & Storage Conference in Denver (USA) on Nov 3-4, 2009.   On display will be Powercast’s RF energy harvesting technology integrated with wireless sensors from Texas Instruments, Jennic, and EnOcean.

All of the demonstration modules are battery-free and are powered by RF energy that is converted to DC by Powercast’s P2100 Powerharvester module and stored in a supercapacitor.  Harry Ostaffe of Powercast will also be giving a presentation on Practical Applications of RF Energy Harvesting.

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Powercast’s wireless power technology, based on RF energy harvesting, was demonstrated at a recent trade show by the Government of Ontario (Canada).

(photos and details to be added)

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