Battery-free wireless underwater camera

How Does it work?

The camera's operation is demonstrated below in Fig. a. A remote acoustic projector (speaker) transmits sound toward the camera. The acoustic energy is harvested by the camera's piezoelectric transducer and converted to electrical energy that powers up the batteryless backscatter sensor node. The energy accumulates in a super-capacitor that powers up an FPGA unit, a monochromatic CMOS sensor that captures an image, and three LEDs which enable RGB active illumination. The captured image is communicated via acoustic backscatter modulation on the uplink, and a remote hydrophone measures the reflection patterns to reconstruct the transmitted image. 

The image in Fig. b shows an experimental trial of the batteryless sensor where it is used to image an underwater object with active illumination that enables capturing color images. The plot in Fig.c shows the voltage in the supercapacitor, which is harvested from acoustic energy and varies over time as a function of the power consumption of different processing stages.  The spectrogram in Fig.d shows the frequency response of the signal received by the hydrophone over time, demonstrating its ability to capture reflection patterns due to backscatter modulation and decode them into binary to recover the transmitted image.

We used a battery-free camera to capture underwater pollutants, African starfish, and aquatic plant growth over multiple days. These images are shown below:

This research is sponsored by the Office of Naval Research (N00014-19-1-2325, N00014-20-1-2531), the Sloan Research Fellowship, the National Science Foundation (CNS-1844280), the MIT Media Lab, and the Doherty Chair in Ocean Utilization.