Method, apparatus and system for detecting metal objects in a detection zone

A non-transitory computer-readable medium carrying a program configured to perform a method, when run on a computer, of detecting a metal object in a detection zone between a transmitting antenna and a receiving antenna installed in proximity of a revolving door, the method comprising:

• demodulating a signal received via the receiving antenna to provide a first signal;
• filtering the first signal by a first adaptive notch filter to suppress at least a fundamental tone or a fundamental tone and one or more harmonic tones of the fundamental tone in a filtered signal;
• processing the filtered signal to detect an impulse;
• while the impulse develops, computing a feature value of the impulse and determining whether the feature value exceeds a threshold;
• and
• in case the feature value exceeds the threshold, setting a first alarm detector.

An apparatus comprising:

• a transmitting antenna;
• a receiving antenna, wherein the transmitting antenna and the receiving antenna are installed in proximity of a revolving door for detecting a metal object in a detection zone between the transmitting antenna and the receiving antenna;
• and
• a processing module loaded with a computer program configured to perform a method when coupled to the transmitting antenna and the receiving antenna, wherein the method comprises:
• demodulating a signal received via the receiving antenna to provide a first signal;
• filtering the first signal by a first adaptive notch filter to suppress at least a fundamental tone or a fundamental tone and one or more harmonic tones of the fundamental tone in a filtered signal;
• processing the filtered signal to detect an impulse;
• while the impulse develops, computing a feature value of the impulse and determining whether the feature value exceeds a threshold;
• and
• in case the feature value exceeds the threshold, setting a first alarm detector.

A system comprising:

• a transmitter coupled to a transmitting antenna for emitting an electromagnetic interrogation signal;
• a receiver with a demodulator coupled to a receiving antenna, wherein the transmitting antenna and the receiving antenna are installed in proximity of a revolving door for detecting a metal object in a detection zone between the transmitting antenna and the receiving antenna;
• a processor configured to:
• demodulate a signal received via the receiving antenna to provide a first signal;
• filter the first signal by a first adaptive notch filter to suppress at least a fundamental tone or a fundamental tone and one or more harmonic tones of the fundamental tone in a filtered signal;
• process the filtered signal to detect an impulse;
• while the impulse develops, computing a feature value of the impulse and determining whether the feature value exceeds a threshold;
• and
• determine whether the feature value exceeds the threshold and in accordance therewith setting a first alarm detector.