The principle of a walk through metal detector is based on the use of electromagnetic fields to detect metallic objects on the person passing through it. When a person passes through the detector, the metal detector emits a magnetic field that interacts with any metallic objects on the person, causing a change in the field. The detector then senses these changes and triggers an alarm to alert security personnel to the presence of the metal object.
The metal detector works by generating a continuous electromagnetic field using one or more coils of wire. When a metallic object enters this field, it disrupts the magnetic field and causes a change in voltage in the coil. The detector then measures this change in voltage and uses it to trigger an alarm if a threshold is exceeded.
The sensitivity of the metal detector can be adjusted to detect different types of metal objects, and the detector can be calibrated to minimize false alarms caused by non-threatening metallic objects such as coins or keys. Different types of metal detectors use different technologies, but all work on the principle of using electromagnetic fields to detect metallic objects.