Using the principles behind the Doppler effect, wherein radio wave reflects off a moving object, Karl Woodbridge and Kevin Chetty, at University College London, have built a prototype unit that uses Wi-Fi signals and recognizes frequency changes to detect moving objects. The size of the prototype unit is more or less the size of a suitcase. The unit contains a radio receiver comprising of two antennas and a signal-processing unit reported Popsci.
The duo carried out test runs and the results were interesting. They managed to determine a person’s location, speed and direction and that too even through a one-foot-thick brick wall. The device can be used to spot intruders, monitor children or the elderly, and can even be used in military.
The device itself can’t be detected as it doesn’t emit any radio waves. If the device is working upon and improvements are carried out, it can also be used to detect subtle motions of the ribcage during breathing says Woodbridge.
The below image shows the entire thing in action:
- Wi-Fi signals bounce off moving objects thus changing frequency.
- A Wi-Fi router present in the room fills the area with radio waves of a specific frequency, usually 2.4 or 5 gigahertz, depending upon the 802.11 standard it supports.
- The baseline signal is tracked by one of the antennas of the radar system.
- The radio waves reflected off the moving objects will be detected by the second antenna.
- The two signals are compared using a computer and object’s location is calculated within a few feet along with its speed and direction.