The photonic sensors recorded data during the spring of 2017 under two scenarios: one was a real-time measurement of air temperature over 12 hours, and the other was an aerial mapping of temperature distribution with a sensor mounted on a drone in a St. Louis city park. Both measurements were accompanied by a commercial thermometer with a Bluetooth connection for comparison purposes. The data from the two compared very favorably.
In the grand world of the "internet of things" (IoT), there are vast numbers of spatially distributed wireless sensors predominately based on electronics. These devices often are hampered by electromagnetic interference, such as disturbed audio or visual signals caused by a low-flying airplane and a kitchen grinder causing unwanted noise on a radio. However, optical sensors are "immune to electromagnetical interference and can provide a significant advantage in harsh environments.
The study was led by Lan Yang, the Edwin H. & Florence G. Skinner Professor of Electrical & Systems Engineering in the School of Engineering & Applied Science and the findings were published in Light: Science and Applications.
"Optical sensors based on resonators show small footprints, extreme sensitivity and a number of functionalities, all of which lend capability and flexibility to wireless sensors," Yang said. "Our work could pave the way to large-scale application of WGM sensors throughout the internet."
Yang's sensor belongs to a category called whispering gallery mode resonators, so named because they work like the famous whispering gallery in St. Paul's Cathedral in London, where someone on the one side of the dome can hear a message spoken to the wall by someone on the other side. Unlike the dome, which has resonances or sweet spots in the audible range, the sensor resonates at light frequencies and also at vibrational or mechanical frequencies, as Yang and her collaborators recently showed.