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Ultrasonic fingerprint sensor in underglass prototype using impedance mismatching


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.

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This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019R1F1A1062162). This work was supported by the research fund of Hanyang University (HY-2019).

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Correspondence to Kwan Kyu Park.

Additional information

Recommended by Editor No-cheol Park

Won Young Choi was born in Deajeon, Korea in 1988. He received the B.S. degree in mechanical engineering from Hanyang University, Seoul, Korea in 2014. He is currently pursuing the Ph.D. degree with the Department of Mechanical Convergence Engineering, Hanyang University, Seoul, Korea. His research interests include ultrasound sensing and imaging applications (pulse-echo, photoacoustic, impediography method) for biomedical imaging, biometric identification and industrial nondestructive inspection.

Ki Chang Kang was born in Seoul, Korea in 1989. He received the B.S. degree in mechanical engineering from Hanyang University, Seoul, Korea in 2015. He is currently pursuing the Ph.D. degree with the Department of Mechanical Convergence Engineering, Hanyang University, Seoul, Korea. His research interests include ultrasound sensing (ultrasound touchscreen for large panel) and nondestructive evaluation (laser ultrasonics, local wavenumber estimation).

Kwan Kyu Park received the B.S. degree in mechanical and aerospace engineering from Seoul National University, Seoul, Korea in 2001. He received the M.S. and Ph.D. degrees in mechanical engineering from Stanford University, Stanford, CA in 2007 and 2011, respectively. He was a Research Associate in the Edward L. Ginzton Laboratory, Stanford University from 2011 to 2013. Currently, he is an Assistant Professor of Mechanical Engineering at Hanyang University, Seoul, Korea. His research focuses on developing devices and system for ultrasound imaging and photoacoustic imaging. His interests also include chemical/bio sensors based on micromechanical resonators, multi-resonator systems, ultrasonic transducers, and RF MEMS.

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Choi, W.Y., Kang, K.C. & Park, K.K. Ultrasonic fingerprint sensor in underglass prototype using impedance mismatching. J Mech Sci Technol 34, 531–539 (2020).

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  • Ultrasound imaging
  • Fingerprint imaging
  • Biometric identification
  • Focused transducer