Research Extends the Life and Reach of Sensors for Agriculture, Infrastructure and Border Protection

A team of researchers in the University of Virginia’s Charles L. Brown Department of Electrical and Computer Engineering have substantially reduced the stand-by power and increased the sensitivity of unattended wireless sensors. Steven M. Bowers, assistant professor of electrical and computer engineering, leads the team, which includes Benton H. Calhoun and N. Scott Barker, who are also professors of electrical and computer engineering at UVA.

Their research extends the life and reach of event-driven sensors used in agriculture, infrastructure and border protection. An event-driven sensor spends the vast majority of its time in an “asleep-yet-alert” state, responding to incoming radio frequency wake-up commands from an antenna. The wake-up receiver plays a critical role in the sensor system’s performance, to both reliably detect wake-up signals and reject false wake ups.

Bowers, Calhoun and Barker developed three generations for RF wake-up receivers that met and then surpassed the innovation challenge issued by the Defense Advanced Research Projects Agency’s Near Zero Power RF and Sensor Operations Program. The team established a fundamentally new capability for long-range, low-power wireless connectivity. Their receiver can be digitally tuned across DC power, latency and sensitivity to provide flexible functionality from indoor, short-range to outdoor, long-range applications.

The challenge was to reduce power by more than 10,000 times while increasing the receiver’s ability to detect wireless signals that are 10,000 times quieter. The first two generations of RF wake-up receivers leveraged a design that employs an envelope detector to immediately convert the RF signal down to a constant voltage. The initial design showed a sensitivity of minus 54 decibels per milliwatt using 8.3 nanowatts of power; the next showed a sensitivity of minus 76 decibels per milliwatt and used 7.4 nanowatts.

To reach their target goal of minus 100 decibels per milliwatt, the team needed to invent a new approach that uses amplifiers, which the team dubbed “samplifiers,” because they can turn on and off extremely quickly to sample the RF signal without consuming significant energy. With the samplifier, the team achieved minus 106 decibels per milliwatt using only 33 nanowatts. This represents a 10,000 times improvement over the world record in wake-up sensitivity. Compared to any other radio previously demonstrated with comparable sensitivity, the team’s new radio is more than 10,000 times lower power.