RF-Powered Wireless Sensors

AutomationWorld has published an article on energy harvesting technologies demonstrated at the 2009 Sensors Expo, including information on Powercast.

Energy Harvesting Advances
http://www.automationworld.com/news-5664

“While vibration energy harvesting may be most common for industrial applications, a different approach was being shown by Pittsburgh-based Powercast Corp. (www.powercastco.com). At its Sensors Expo show booth, the company was demonstrating its Powercaster transmitter, which was beaming a radio frequency (RF) signal toward the company’s Powerharvester receivers mounted in other nearby booths. The receivers were harvesting energy from the RF field and converting it to DC power sufficient to operate low-power sensor devices. Harry Ostaffe, Powercast director of marketing, said the company has so far deployed the technology in custom projects for military and industrial clients, with typical transmission distances “in the 10s of feet” using a three-watt transmitter.”

Power was transmitted to booths for Esensors and Infinite Power Solutions and converted back to DC with the P2100 Powerharvester.  The Esensors wireless sensor was located about 35 feet from the Powercast transmitter.  It was connected to a Powercast Yagi antenna module and was activated about every 90 seconds.  The IPS energy cell was connected to a Powercast sleeve dipole antenna module and was pulse charged at about 25 feet.  Longer charge distances were possible for both devices, but they were mounted for display purposes.

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At the Darnell nanoPower Forum on May 18th, Powercast and CAP-XX presented a battery-free wireless power module for wireless sensors.  The module uses the Powercast P2100 Powerharvester receiver, a CAP-XX GZ 115 supercapacitor, and the Texas Instruments eZ430-RF2500 wireless board.  The modules work by receiving radio waves and converting them into DC, which is then stored in the supercap.  When a charge threshold is reached on the supercap, the output to the wireless sensor is turned on which activates the sensor.  The sensor can have zero stand-by power instead of using a sleep mode, and power can be sent on demand, o na scheduled basis, or continuously.

The joint press release by Powercast and CAP-XX contains additional details.

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Pittsburgh, PA – April 30, 2009 – Powercast, a leader in the commercialization of RF energy harvesting and wireless power solutions, announced it has joined the Texas Instruments Developer Network to support wireless powering of devices driven by TI’s MSP430.  The MSP430 is a market leading, low power microcontroller embedded in numerous portable and low-power wireless devices.

Powercast’s RF energy harvesting technology and embedded wireless power solutions enable controllable wireless power, over distance, between one or more sources and multiple receivers.  Devices with Powercast components can be designed for battery-free or battery-minimized operation, thereby eliminating disposable batteries and their adverse environmental impact.  These devices can be dormant, with zero stand-by power, and activated remotely with power being sent on-demand, on a scheduled basis, or continuously.

“We are pleased to have Powercast join TI’s Developer Network,” said Eric Siegel, MCU developer network manager at Texas Instruments.  “Combining wireless power technology with the ultra-low power consumption of the MSP430, Powercast’s innovative solutions eliminate the need to replace batteries by providing constant, unattended charge for applications in the low-power RF market.”

Powercast has also developed an integrated module for demonstrating battery-free wireless sensors.  The Powercast module contains an integrated power receiving antenna, a Powerharvester™ module, energy storage, and space for a low-power wireless module like Texas Instruments eZ430-RF2500T.

“The wireless sensor market is rapidly expanding and today’s wireless sensors are predominantly powered by disposable batteries.  Battery replacement creates a significant operational challenge that will greatly impact the willingness of end-users to scale sensor networks or deploy wireless sensors in hard to service locations.” said Harry Ostaffe, Director of Marketing for Powercast.  “Powercast’s wireless power solutions enable battery-free designs for wireless sensor devices, and allow for lifetime operation without changing batteries.”

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An article by Harry Ostaffe of Powercast was recently published in Industrial Embedded Systems.

The article is titled “Wireless power energizes wireless sensor networks”, and discusses how wireless power enabled by RF energy harvesting can provide a controllable and perpetual source of energy for wireless sensors.  The opening paragraphs are included below.

Battery replacement in wireless sensors is a key factor in limiting device location and scale. Through RF energy harvesting, wireless power can recharge wireless sensors remotely and eliminate battery replacement.

Wireless sensor applications and installations continue to grow as the technology evolves. The ability to add remote sensing points without the cost of running wires is resulting in numerous benefits, including energy and material savings, process improvements, and productivity increases.

Disposable, primary batteries typically supply the main power source for wireless sensors. Primary batteries are a readily available power source and have proven to be useful in many applications. However, with primary batteries as the source of power, sensor and component companies have had to focus on decreasing power consumption to overcome the objections of maintenance cost and disruption from repeated battery changes. The resulting benefit is that wireless sensors and protocols are now sufficiently low power as to be powered from sources of energy other than primary batteries.

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Battery-free wireless sensors can be a reality using RF as the power source.  To demonstrate this concept, Powercast has a created prototype battery-free wireless sensor with the temperature sensor board in our Lifetime Power™ Evaluation and Development Kit.

A short clip of the sensor in action is shown below.

The prototype sensor has a dipole receiving antenna and is operating from power being broadcast by a nearby 900MHz band transmitter.  The sensor operates continuously when close to the transmitter and intermittently as it is moved further away.  The frequency of operation decreases the further it is moved away from the transmitter.   For many applications, having the sensor wake-up once a minute to transmit a reading is sufficient.

The LCD driver and display requires much more power than low power RF radios like 802.15.4, ZigBee , ULP WiFi, etc, so radio-enabled sensors will work at an even greater distance than this prototype.

Applications include perpetual, wireless powering of battery-free wireless sensors for commercial buildings, industrial facilities, and process monitoring, or unattended ground sensors for military or surveillance activities that can be activated on-demand.

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