Patent ID: 8593160

Claim:
A method for detecting the presence of a biometric object on or in the vicinity of a biometric object sensing area in a biometric object imaging apparatus, the method comprising: transmitting a probing signal to the biometric object sensing area, comprising a capacitive gap between at least one of a plurality of transmitter electrodes and a single receiver electrode or at least one of a plurality of receiver electrodes and a single transmitter electrode, the probing signal comprising a burst of high frequency pulses, transmitted across the capacitive gap between the at least one of a transmitter electrode from the plurality of transmitter electrodes to the single receiver electrode or to the at least one of a plurality of receiver electrodes from the single transmitter electrode; receiving a response signal on the respective receiver electrode in response to the probing signal, the response signal comprising a burst of high frequency pulses; establishing an upper reference level for the amplitude of pulses in the burst of high frequency pulses comprising the response signal; and monitoring whether the peaks of the response signal exceed the upper reference level to determine the presence of the biometric object in the biometric object sensing area due to the presence of the biometric object modifying the amplitude of the pulses in the burst of high frequency pulses in the response signal from the amplitude of the pulses in the probing signal.