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Advances in Fingerprint Technology.pdf

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L<br />

A B<br />

(a)<br />

F<strong>in</strong>ger Friction Surface<br />

R<br />

(b)<br />

Figure 8.6 Optical f<strong>in</strong>gerpr<strong>in</strong>t sens<strong>in</strong>g. (a) Imag<strong>in</strong>g geometry consists of a laser<br />

source (L) illum<strong>in</strong>at<strong>in</strong>g a f<strong>in</strong>ger rest<strong>in</strong>g on a glass platen/prism (P) and an imag<strong>in</strong>g<br />

surface (C). (b) Frustrated total <strong>in</strong>ternal reflection: the ray A <strong>in</strong>cident at the<br />

ridge/glass <strong>in</strong>terface scatters while the ray B fall<strong>in</strong>g at the valley/glass <strong>in</strong>terface<br />

suffers total <strong>in</strong>ternal reflection and the reflected rays are collected at the imag<strong>in</strong>g<br />

surface.<br />

V<br />

P<br />

P<br />

C<br />

C

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