Infrared sensors works on the basis of non-visible light, the range of infrared frequency is 3 GHz-400 THz. The Wavelength of the IR is bigger than the visible lights that’s why they are not Visible to human eye. There are two main parts of the infrared sensors,
1): IR Transmitter
2): IR Receiver
IR Transmitter transmits non-visible light to IR Receiver, the object whose speed is required to be calculated is placed between IR Transmitter and IR Receiver, the amount of light energy received changes when there is an object placed between IR Transmitter and IR Receiver, this moving object interrupts the light and less amount of light energy is received at IT Receiver. Higher the interruption in the light means high moving speed of the of the object.The circuitry deployed at receiver end which calculate the energy generated by IR Receiver and measure the speed of the object.
IR speed sensor are very fast in response because the speed of the light is very high, also they require very less power to operate.