These researchers were able to “detect the ripeness levels of fruits with an accuracy of over 90%”.

The testing fruit is placed in between a pair of closely spaced transmitter and receiver, thus blocking the lineof-sight (LOS) signal propagation. We rely on the received signal component that directly travels through the fruit to sense its physiological change. The phenomenon where radio waves travel through and modulated by the fruit is commonly referred as refraction, which describes the signal passes from one medium to another. In our case, it is the WiFi signal travels from air to fruit, and then from fruit to air.