Suppose a person (height of 1.8 m) walks in a room installed with a pyroelectric infrared (PIR) motion detector. The distance between the person and the PIR detector is 5 m. The PIR detector sensor is 3 cm x 1 cm in size.

Estimate the radiated power at the surface of the sensor from the person. Assume that emissivity of human skin/fabric and sensor cap is 0.9. Assume that the person’s body temperature is 37°C and the temperature at the surface of PIR detector is at 18°C. Also assume that there is no radiated power loss through air and Fresnel lens. You can roughly estimate surface area of the person.