Re: barrier penetration, evanescent waves

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Coincidence:

Thursday September 19 @ 04.pm SCI 242
* Physics Seminar * Fall 2002 *

Professor Ramen Bahuguna
Physics Department
San Jose State University

A Holographic Fingerprint Sensor

A prism fingerprint sensor based on total internal reflection has an inherent

problem:  the image is aberrated and distorted.  The main reason is that the
image is inclined to the camera and expensive optics is needed to correct the

aberrations.
A simple holographic optical element (a holographic diffraction grating) can
correct the above problems.  A fingerprint sensor incorporating such a
grating will be demonstrated.


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Bernard Cleyet wrote:

> "... But a finger has
> just the right combination of compliance and texture
> so that the ridges of the fingerprint absorb the
> evanescent wave (while the intervening valleys don't),
> resulting in a very-high-contrast image of the fingerprint."
>
> I forgot to mention that this is the method for fingerprinting (a digital
> camera views the ftir image and sends it to the DOJ)
>
> Before I do my demo. (semi-quantitative) for the HS Physics class, the
> instructor has passed out glass prisms for the students to see for
> themselves.
>
> bc who was finger printed this way as a requirement for a teaching
> credential.
>
> "John S. Denker" wrote:
>
> > Bernard Cleyet wrote:
> > > A model for barrier penetration is FTIR (frustrated total internal
> > > reflection).  The model is exact in that the equations are of the same
> > > form (obvious, they're both described by the same wave equation).
> >
> > Yup.

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