Ultrasonic fingerprint sensor in underglass prototype using impedance mismatching

Abstract

Fingerprint imaging is a powerful tool in biometric identification systems. There are several methods for measuring fingerprints, such as optics, capacitive, and ultrasonic methods. The previous ultrasonic imaging techniques have been available in immersion systems which require the hands to be put into water. Also, pulse-echo system in dry condition has coupling layer which is similar acoustic impedance to human tissue or high impedance materials based on waveguide. For fingerprint imaging in the dry state, we propose an ultrasonic imaging technique in underglass by using the impedance mismatch between the fingertip and the solid plate. We present the image results according to the plate material such as acrylic, glass and PDMS. In addition, simulation results based on small 2-D array transducers in a near field suggest the feasibility of compact and fast fingerprint scanning system. Therefore, this work presents feasibility of ultrasonic pulse-echo fingerprint sensing method for dry hand.