Energy harvesting, from a diverse set of modes such as light, temperature or motion, has been viewed as the key to developing battery-less sensing devices. We have recently demonstrated the capability to harvest RF energy from WiFi transmissions, applying it to power a prototype wearable device that captures and transmits accelerometer sensor data. Our solution, WiWear, has two key innovations: 1) beamforming WiFi transmissions to significantly boost the energy that a receiver can harvest ∼3-4 meters away, and 2) smart zero- energy, triggering of inertial sensing, that allows intelligent duty-cycled operation of devices with power-hungry sensors We showcase an experimental system, which includes an 8-antenna WiFi AP and a batteryless wrist-worn wearable device, which uses an accelerometer data to continuously monitor and capture gestures performed during daily lifestyle activities.
Technology Features, Specifications and Advantages
Our system is described as a 3-step process. (1) A wearable device (wore by a user) sends a ping packet, only when the user makes significant gestures
(2) A multi-antenna AP receives the packet, estimates the direction (angle) of the device, and sends multiple energy beams to wirelessly charge the device.
(3) The device harvests energy from the energy beam, storing such energy for future use The device also operates sensors and sends the sensing data back to the AP.
The advantages of multi antenna WiFi AP: (left): Focus signal (energy) into specific directions - Beamforming. (right): Estimate the angle of arrival (AoA) of WiFi signal (from wearable device).
WiFi signal can be converted into operating energy by combining a fine-tuned matching circuit and a rectifier.
Our prototype system:
An 8-antenna array, currently implemented over the WARP WiFi research platform, operating at 2.4GHz.
- Estimate the direction of the signal from wearable
- Create energy beam toward the wearable
Our custom wearable device:
Harvester: Harvest energy from WiFi beam
Power Management Unit: Convert low voltage energy to usable energy
Sensing & Communication Unit: Operate sensors (Accelerometer) and transfer data to a server
Motion Trigger Unit: Trigger the system to sense/communicate. When user move his hand, the magnet move inside a coil and create a high voltage to trigger the system to work
Energy Storage Unit: Store harvested energy in a super capacitor
Result: With 8 antenna, our system can harvest around 400uW at ~1m while our wearable device consumes only about 65uW.
This technology is applicable in the following industries: Smart Spaces and In-Home Wellness
- Elderly care applications where the removal and recharge of the wearable is difficult
- IoT applications in smart home, smart office
- IoT applications in industrial environments, such as factories and warehouses
This is the first WiFi powered wearable which can operate on WiFi energy, thereby eliminating the need to remove the device periodically for recharging. There exist emerging studies on WiFi powered sensor, but we move beyond that. We integrate Angle of Arrival and Beamforming technology to support energy-hungry sensors and wireless communication to make it a real wearable. Customers across multiple verticals (especially industrial and in-home health & wellness) can start incorporating this advanced technology in building future batteryless, advanced sensing platforms.