METHOD OF DETECTING ILLEGAL SUBSTANCES WITH ARCHED METAL DETECTOR Russian patent published in 2016 - IPC G01V3/11 

FIELD: safety systems.

SUBSTANCE: invention relates to detection of prohibited objects and identification of their carriers in stream of people, alternately crossing curved metal detector opening. Summary: probing signal is emitted in form of short pulses sequence with high porosity. Receiving reflected signal by two pairs of receiving coils installed at height h₁₂ and h₃₄ in left and right arched posts respectively. From output signals of S₁(t) and S₂(t) of first and second S₂(t) receiving coils and output signals S₃(t) and S₄(t) of third and fourth receiving coils gradiometric signal S₃₄(t)=S₃(t)-S₄(t) is formed. Arched signal S_∑(t)=S₁₂(t)-S₃₄(t) is formed. Frequency filtration and time selection of arched signal S_∑(t) are performed, followed by extraction of instantaneous values of its amplitude A(t). Floating threshold P(t) is formed by averaging A(t) on interval (t-T;t), where T is time allocated for monitoring of one face in flow. Forbidden object carrier is determined as person crossing arched opening at moment A(t) of threshold P(t) exceeding.

EFFECT: high noise immunity of arch-pulse metal detectors relative to external interference generated by remote radio-frequency sources.

1 cl, 3 dwg