The sensor, shown in Figure 1, captures the image of a fingerprint as the finger is swept vertically over the sensor window, as shown in Figure 2.
An image is produced when contact first occurs, but because it soon disappears as thermal equilibrium is reached, a sweeping method is necessary to acquire a stable fingerprint image. Fingerprint images are captured by sweeping the finger over a sensing area. A linear sensor, it combines detection and data conversion circuitry in a single CMOS IC. The Atmel ® AT77C104B FingerChip ® sensor captures fingerprints using this type of thermal imaging.
When a finger is in contact with a warmed sensor’s surface, the fingerprint ridges-which are closer to the sensor surface-retain a higher temperature than the valleys, which are farther from the sensor surface. Pyroelectric materials generate a voltage based on temperature differentials.
By acquiring data from the part of the skin that is untainted by injury or contamination, the sensor produces a more accurate and repeatable fingerprint sample than alternative optical or capacitive technologies that read only the surface of the skin. The RF field measures the electrical potential contours of the ridges and valleys of the finger’s underlying live epidermal layers. The AuthenTec ® TruePrint ® sensor uses a small RF signal between a conductive layer buried inside the silicon chip and the electrically conductive layer just below the surface of the skin. This live subsurface layer is the source of the fingerprint pattern, and it is rarely affected by damage or wear to the finger surface. Fingerprint sensors can be broadly classified as optical, ultrasound, or solid state-which includes capacitive, RF, thermal, and piezoelectric devices.īecause a finger’s outermost dry, dead skin cells have low electrical conductivity, an RF sensor acquires fingerprint data from the skin’s moist and electrically conductive boundary region where the live cells begin turning into keratinized skin.
Fingerprint sensors “read” the finger surface and convert the analog reading into digital form through an analog-to-digital converter (ADC). Minutiae, the local discontinuities in the ridge flow pattern, are used as discriminating features. Their images, formed of multiple curve segments, comprise high areas called ridges and low areas called valleys. Fingerprint Sensorsįingerprints, long one of the most widely accepted biometric identifiers, are unique and permanent.
Virtually all biometric techniques are implemented using a sensor, to acquire raw biometric data from an individual feature extraction, to process the acquired data to develop a feature-set that represents the biometric trait pattern matching, to compare the extracted feature-set against stored templates residing in a database and decision-making, whereby a user’s claimed identity is authenticated or rejected. Biometric signatures, or biometrics, are used to identify individuals by measuring certain unique physical and behavioral characteristics. Individuals must be identified to allow or prohibit access to secure areas-or to enable them to use a computer, personal digital assistant (PDA), or mobile phone. The need for effective security, implemented efficiently, is manifest in today’s world.
Fingerprint Sensor and Blackfin Processor Enhance Biometric-Identification Equipment DesignĪseem Vasudev Download PDF Biometrics and Security