Asynchronous method for sampling signals in metal detectors

A method for obtaining information related to a target presence and/or a target kind for metal detectors, the method comprising:

• sampling a signal by at least one ADC which is received through a receiver unit wherein said signal is generated as a result of a reaction of said target to a magnetic field transmitted by a transmitter unit;
• by a controller, utilizing a DFT based transformation technique consisting of summing of samples where each sample is multiplied by coefficients corresponding to a timing within a period in order to be expressed in terms of components of phase/magnitude or time constants for obtaining said information;
• by the controller, providing the transmitter unit to transmit a reference signal where said reference signal is divided into time intervals where said time intervals are indexed by reference timing values;
• by the controller, providing the receiver unit to receive and ADC to sample said reference signal;
• by the controller, detecting a phase shift for each sampling of ADC according to a reference timing value;
• by the controller, updating a transformation table, the transformation table defined for the timing intervals that are smaller than or equal to sampling intervals of the ADC and multiplying coefficients corresponding to a defined time with acquired samples,
• by the controller, providing transmitter unit to transmit a signal for detection,
• by the controller, providing receiver unit to receive and ADC to sample said signal,
• by the controller, defining nearest timing of each acquired sample from a table/array by using said the transformation table/array and determining corresponding coefficients for each sample;
• and
• by the controller, obtaining phase/magnitude and/or time constant components of targets by using the sum of the asynchronously acquired samples, each multiplied by the corresponding coefficient.