There are two basic types of fingerprint biometrics: traditional epidermal-based technologies and sub-epidermal technologies. The former includes capacitive and temperature sensing methods; the latter includes advanced RF imaging technology.
A traditional electronic fingerprint sensor is a silicon chip containing a set of capacitive sensor plates. Each sensor plate produces a capacitance metric that represents the grayscale of a pixel. This method works well for young, healthy, and clean fingers; however, when the fingers are dirty, frayed, or old skin is loose, normal texture information is not available.
The temperature-sensitive fingerprint scanner detects the heat flow (heat flux) between a finger and a semiconductor chip to generate a texture image of the finger. The sensor uses a heating element to ensure that the sensor chip and the finger surface are at different initial temperatures. When a finger is placed on the scanner, a set of sensitive differential temperature detectors on the surface of the chip detects the slight difference in heat flux between the ridge region of the contact sensor and the valley region of the sensor without contact in a short time. This temporary heat flux difference is converted into an electrical signal, which then becomes the pixel gray value at the point. This surface sensing method is highly dependent on the quality of the thermal contact between the ridge and the sensor. When fingers are contaminated with dust, dirt, or other things, good thermal contact is prevented, and high-quality images cannot be obtained. Heating elements are also required in some environments to provide sufficient thermal differential, but also consume more power supply current.
The significant reduction in size is a key factor driving the development of biometrics . In the past, the size of a fingerprint sensor had to be large enough to capture the entire finger surface and determine the owner of the finger. Now it's different. The size of the sensor is smaller than the pen tip, and the user's identity can be determined using only part of the fingerprint, so there is no need to use a sensor as large as before. Moreover, the latest high-resolution slidesensors are smaller and more cost-effective. When the user swipes his finger across the surface of the sensor, he can scan to obtain clear fingerprint details and capture a large area of fingerprint features. Since the biggest factor influencing the cost of a fingerprint sensor is the chip size, the reduction in volume has also greatly reduced the cost. This is very attractive for OEMs who want to increase product prices by adding features without increasing manufacturing costs.
Accuracy and reliability are also one of the key factors that stimulate the rapid development of biometric technology. With the development of semiconductor technology, researchers have developed sensors that can image everyone under any conditions. Although some sensors still use traditional skin-based sensing technology, the most advanced scratch sensors currently can read fingerprints from under the epidermis of the skin, which means that even if the surface of the finger is worn, injured, or relatively dry, it can Read fingerprints reliably.
For example, AuthenTec's TruePrint technology uses a patented RF antenna array device technology to collect and detect images of the dermis layer by generating and detecting the electric field generated by the dermis layer. This is different from the spherical electric field created by capacitive sensors, which can only detect the superficial skin very close to the outer layer. RF antenna arrays can image a wider range of finger areas, so they can produce high-quality, information-rich fingerprint images. Another advantage of this method is that fingerprints cannot be copied.
The new sensor also has more features, such as replacing clumsy control buttons, providing comprehensive navigation capabilities, making it easy for users to play games and scroll the screen. These sensors also allow users to customize the functionality of their wireless devices like never before. For example, users can use different fingers to operate dials at different speeds, or open separate buddy lists.
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