An Autonomous, Optically-Powered, Direct-to-Digital Sun-Angle Recorder for Honey Bee Flight Tracking

An autonomous sensor for insect flight tracking that captures and stores solar angle-of-incidence without the use of a conventional ADC is presented. The chip uses pairs of Angle-Sensitive Pixels as differential 1-bit ADCs, and an array of these sensors provides a many-bit encoding of angle-of-incidence. Digitization occurs immediately within the pixel by use of a novel in-pixel comparator, thus enabling ultra-low-power, direct-to-digital capture of angle-of-incidence. These measurements are stored in an on-chip memory throughout the flight and can be uploaded to a base station via magnetic backscatter at the end of the flight. To permit full autonomy, the system is powered by on-chip photovoltaics, providing open-circuit voltages in the range of 0.40 − 0.50 V in natural sunlight, the intensity of which can vary throughout a flight. The system consumes a simulated 630nW at nominal supply voltage of 0.45 V, and circuit topologies amenable to photovoltaic power conditions are presented. The chip is envisioned as a flight recorder to be mounted on honey bees to track their trajectories, and bee flights were emulated by carrying the chip along a 226 m outdoor trajectory and downloading the recorded flight data from the chip at a base station in the field. Across 18 trials of the same trajectory, which emulates a small sample of tagged bees visiting known feeding sites and returning to their hive, the average reconstructed final position is 9.6 m away from the true final position, an error less than 5% of the total trajectory length.