Ultrasonic imaging of fingerprints using acoustical impediography

A new type of fingerprint sensor is presented. The sensor maps the acoustic impedance of the fingerprint pattern by estimating the electrical impedance of its sensor elements. The sensor substrate, made of 1-3 piezo-ceramic, which is fabricated inexpensively at large scales, can provide a resolution up to 50 μm over an area of 25×25 mm². Using FE modeling, this paper presents the numerical validation of the basic principle. It evaluates an optimized pillar aspect ratio, models spatial resolution and the point spread function for a 100 μm and 50 μm pitch model. The sensor manufacturing process is briefly addressed and the first fingerprints obtained with the prototype sensor are presented. Finally an outlook is given for deploying the sensor to obtain additional life information by using it as a pulse echo system.