The ohms during hot summer. By using

The heart beat rate of the fingertip can be used to identify artificial finger.  This method is accomplished by sensing the finger pulse as a liveness detection method.  Even the heartbeat rate of the same person is not same all the time.  When a wafer-thin silicon rubber is used on the gummy finger, it is accepted as a real finger.

paragraph{Conductivity}

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A sensor can be used to detect the conductivity cite{25} of the finger.  The normal conductivity value as the finger is about 200 ohms.  But the conductivity value is several mega ohms for a real finger during freezing winter and several kilo ohms during hot summer.  By using saliva on the gummy finger it is considered as a real finger by the sensor.

paragraph{Blood pressure}

Fingerprint sensors are used to detect the blood pressure on two different places (two hands) on the body. This type of sensor is not susceptible to wafer-thin silicon rubber artificial finger.

paragraph{Relative dielectric constant}

The dielectric constant of a specific material reflects the extent to which it concentrates the electrostatic lines of flux. Measuring the distinct values of relative dielectric constant (RDC) between a live and an artificial fingerprint is the foundation for this method. However, RDC is influenced by the humidity of finger in different conditions, and fooling such sensor is possible by wetting the silicone rubber using alcohol/water mixture before it is pressed on the fingerprint

paragraph{Detection under epidermis}

The pattern of lines under epidermis is detected by the sensor. These pattern of lines are similar to the pattern of lines in the fingerprint. This is based on detecting fingerprint patterns in the epidermis and between epidermis and dermis as a sign of liveness. There are two types of sensors: ultrasonic sensor and electric field one. Ultrasonic sensors focus on the fact that the underlying layer is softer and more flexible than the epidermis. While electric field alternative are focusing attention on the higher electric conductivity of the layer underneath the epidermis as compared to the epidermis itself. Two different layers of artificial fingerprints with the appropriate characteristics could fool the scanner when the characteristics of sensor are known.

paragraph{Odor}

Electronic nose is attached to the sensor to detect the odor cite{c23} of the materials used to make gummy finger. So the real finger is differentiated from the artificial using skin odor. An odor sensor (electronic nose) is used to sample the odor signal and an algorithm allows discrimination of the finger skin odor from that of other materials, such as latex, silicone or gelatine, usually employed to forge fake fingerprints The acquisition of an odor pattern consists of sampling the data coming from an odor sensor during a given time interval, usually a few seconds.

paragraph{Electrotactile Display system:}

A fake finger is detected using tactile detection. The tactile perception capability is absent in the fake or dead finger. It is also called as the electrocutaneous simulation. This method uses the electrical means of activating the nerves to stimulate the sense of touch. A matrix of surface electrodes is transducing small amount of current into the skin. A tactile pattern is presented as input to the fingerprint sensor. The tactile pattern does not provide any auditory clue. The tactile pattern can be changed. Several patterns are presented visually. One of them is the correct pattern. The user is required to select the pattern. If the selected pattern is correct, then the finger is the live finger.

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