Answer with Explanation:
A "metal detector" helps detect metals such as "guns" in the airport through "pulse induction." It is electromagnetic in nature which means it uses one or more coils of wire, which acts as a transmitter and receiver. It transmits a time-varying electric magnetic field, which is propagated in several directions, including towards the metal (which is the target). These are considered "short burst of pulses." Once it detects a metal object, an opposite magnetic field is then created by the pulse in the object. The magnetic field will then collapse resulting to a reflected pulse that is marked by an echo. Such pulse takes quite a long time to disappear (if the object detected is metal). This is the indicator then that even if a gun is wrapped in towels inside a suitcase, it can still be detected by a metal detector.