The New York Times recently ran an article on various projects and products related to RF energy harvesting, including some commentary on Powercast.
Title: Bye-Bye Batteries: Radio Waves as a Low-Power Source
A joint article by Powercast (Harry Ostaffe, Charlie Greene) and AVX (Bharat Rawal), titled “Power Module and Double Layer Capacitor Harvest Energy From Radio Signals“ was recently published in Power Electronics Technology. Combining Powercast’s P2110 Powerharvester receiver with an AVX Double-Layer Capacitor (super-capacitor) results in a battery-free, wireless power supply that can be used for low power applications such as wireless sensors. The article describes in detail the operation of the P2110 Powerharvester.
Figure 1 shows a general block diagram of the P2110 Powerharvester. The RF energy is converted to DC and stored into an external capacitor. For some applications a small electrolytic capacitor may be sufficient, but other cases will require more energy and therefore a larger double-layer capacitor (super-capacitor). The voltage on the external capacitor is typically managed between the operating range of 1.25V, when the output voltage is turned on, and turned off at the low threshold of 1.05V. The boost converted is used to provide a regulated output voltage from a range of 2-5.25V to accommodate a wide range of applications.
The timing diagram in Figure 2 provides more detail on the operation. The INT pin provides a logic-level output to indicate when Vout is active, and the RESET pin enables an external device such as a microtontroller or external timer to turn off Vout. The RESET function saves energy and allows the P2110 to recharge the capacitor more quickly.
Figure 3 show a system-level implementation that is typical in a wireless sensor, such as HVAC control sensors using ZigBee, WiFi, or other protocols, or industrial sensors using ISA100 or WirelessHART.
The Economist has has written an interesting article about wireless power as envisioned by Telsa and today’s efforts on ambient RF energy harvesting:
Power from thin air
Wireless technology: It is already possible to send electricity without wires. Can devices be powered using ambient radiation from existing broadcasts?
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)
Powercast will participate as an exhibitor at the 2010 Sensors Expo & Conference. At the event Power will be demonstrating a battery-free wireless sensor module powered by RF energy and designed for ultra-low power consumption. The sensor module provides temperature and humidity data to an access point along with the received signal strength (RSSI) and the ID number of the Powercaster™ transmitter from which it is receiving power.
Powercast has recently released the P1110 and P2110 Powerharvester™ Receivers which are capable of converting radio waves in the range of 850-950 MHz into DC power. The demonstration sensor module uses the P2110 Powerharvester receiver to store the received energy into a capacitor, and then performs a voltage boost to supply the module components will a regulated voltage. Both the P1110 and P2110 enable a microcontroller to determine the signal strength of the received power, as well as to recover low-rate data encoded in the power broadcasted from the power transmitter.
Harry Ostaffe, Director of Marketing and Business Development for Powercast, will also be delivering two presentations during the event. During the pre-conference symposium on June 7, 2010 he will speak on “Design Techniques for RF Energy Harvesting Devices”, and during the main conference on June 8, 2010 he will also present “Power Out of Thin Air: Ambient RF Energy Harvesting for Wireless Sensors”.
Powercast’s exhibit and wireless sensor demonstration will be located at Booth 1022 in the exhibition hall.
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
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.
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”.
Lot’s of people have an interest in harvesting RF energy as a “free” source of power. It’s important though to understand the applications that have a good fit and those that don’t.
At the 2010 CES, an RCA-branded device called the Airnergy WiFi Energy Harvester was demonstrated. The device has an RF energy harvester and an internal battery. It was claimed that the device recharged most of a BlackBerry battery in 90 minutes. We can only conclude that was from the internal battery and not from a WiFi router (a typical WiFi router puts out only 100mW). We’ve posted below the CES video and an entertaining analysis of this device by David Jones of the Electronics Engineering Video Blog.
Dave Jones - EEV Blog
RCA Airnergy video from 2010 CES
Darnell Group has determined that the “crossover” from the “Introduction” phase to the “Growth” phase for energy harvesting and related micro battery products will take place in the 2009/10 timeframe. Their brief news report can be read here.
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