Fingerprint imaging using capacitive micromachined ultrasonic transducer impediography with glass waveguide

Ultrasonic techniques for fingerprint imaging are emerging as an important alternative technology to the traditional capacitive methods. Recently, a pulse-echo based method using a solid interface layer with a waveguide has been investigated for fingerprint imaging. In addition, an impediography method was previously investigated by measuring the pulse damping of the contact area. Both methods require a complex pulse excitation circuit and short pulse duration. In this work, we present an impediography-based implementation, wherein the fingerprint image was acquired by measuring the device impedance instead of the pulse. By using a pseudo-continuous wave (CW) AC signal, we have performed fingerprint imaging, using a waveguide.