Ultrasound Systems for Biometric Recognition

Abstract

Biometric recognition systems are finding applications in more and more civilian fields because they proved to be reliable and accurate. Among the other technologies, ultrasound has the main merit of acquiring 3D images, which allows it to provide more distinctive features and gives it a high resistance to spoof attacks. This work reviews main research activities devoted to the study and development of ultrasound sensors and systems for biometric recognition purposes. Several transducer technologies and different ultrasound techniques have been experimented on for imaging biometric characteristics like fingerprints, hand vein pattern, palmprint, and hand geometry. In the paper, basic concepts on ultrasound imaging techniques and technologies are briefly recalled and, subsequently, research studies are classified according to the kind of technique used for collecting the ultrasound image. Overall, the overview demonstrates that ultrasound may compete with other technologies in the expanding market of biometrics, as the different commercial fingerprint sensors integrated in portable electronic devices like smartphones or tablets demonstrate.

Keywords: biometrics; ultrasonic transducers; ultrasound imaging.

Figure 1

Example of simultaneous renderings of 2D images orthogonal to the three axis extracted from a 3D ultrasound image: (a,b) brightness (B)-mode images, and (c) C-mode image.

Figure 2

Simulation of the electrical impedance of a piezoceramic element when loaded with air or water to illustrate the impediography technique. The lower the acoustical impedance of the load, the lower the value of the impedance at the series resonance frequency $f_s$.

Figure 3

Schematic structures of micromachined ultrasound transducers: (a) capacitive micromachined ultrasonic transducer (CMUT) cell: the flexural vibration of the membrane is generated by a bias voltage and an alternate signal; (b) piezoelectric micromachined ultrasonic transducers (PMUT) cell: the membrane is composed of at least one piezoelectric layer and one passive elastic layer and the flexural motion is generated by applying only an alternating voltage [55].

Figure 4

A fingerprint collected by scanning a linear CMUT array along the elevation direction: (a) 3D voxel representation, (b) 2D image extracted at an under-skin depth of 0.2 mm. In both images, sweat pores are clearly visible. Reprinted with permission from [68].

Figure 5

Example of a palm vein pattern collected through power Doppler analysis: (a) 2D pattern and (b) 3D pattern, which provides improved distinctiveness. Reprinted with permission from [88].

Figure 6

3D palmprint: (a) a 3D render of a human palm where palm curvature can be appreciated and (b) 3D template accounting for lines’ depth. Reprinted with permission from [95].