Biometric piezo scanner
View Patent ↗A piezoelectric thin film sensor array is used to scan and capture biometric data, for example, a fingerprint image. In one embodiment, a multi-layer structure includes a PVDF layer in between two conductor grids arranged orthogonally to one another. Urethane can be added to one side where a finger is placed. A foam substrate can be used as a support. In one feature, the PVDF, and grids can be peeled off like a label for easy replacement. Multiplexers are switched to scan the sensor. A single pixel or a group of pixels can be detected and output to an image memory. The presence of a fingerprint ridge is detected by virtue of a ring-down oscillation that arises from reflection when an electric field is applied to the piezoelectric thin film sensor array at a pixel in contact with the fingerprint ridge. For example, such a ring-down value associated with a fingerprint ridge can be detected at about 150 ns. (or 5 cycles at 30 MHZ). Other reflections indicative of additional biometrics (e.g. from tissue, blood, bone, fingernail, etc.) can also be detected. A Doppler effect due to reflections from circulating blood can also be detected. Such a Doppler effect can provide further information about direction and speed of blood circulation. An instantaneous pyroelectric effect can also be detected to indicate a live finger presence.
1. A piezoelectric film fingerprint scanner comprising:
an oscillator that generates an oscillation signal;
a gate counter coupled to said oscillator that counts cycles of said oscillation signal generated by said oscillator;
a controller coupled to said gate counter and each of a row multiplexer and a column multiplexer, said controller controls said row and column multiplexers responsive to said gate counter;
a pulser coupled between said gate counter and said row multiplexer, said pulser sends an input pulse of one cycle of said oscillation signal to said row multiplexer;
a piezo film sensor array including a first conductor grid coupled to said row multiplexer and a second conductor grid coupled to said column multiplexer, said first and second conductor grids disposed on first and second respective sides of said piezo film; and
a voltage detector coupled to said gate counter and to said column multiplexer, said detector detecting a voltage corresponding to a pixel or group of pixels of said piezo film sensor array selected by said row and column multiplexers;
wherein the voltage detector is configured to detect the voltage a predetermined number of cycles after the pulser sends the input pulse.
2. The piezoelectric film fingerprint scanner of claim 1 , further comprising image memory that stores at least one of a gray scale and a binary detected pixel value from a memory controller unit, said memory controller unit coupled between said image memory and said detector.
3. The piezoelectric film fingerprint scanner of claim 1 , wherein said oscillator unit generates a 30 MHz oscillation signal.
4. The piezoelectric film fingerprint scanner of claim 1 , wherein said gate counter initiates said pulser to send an input pulse to said row multiplexer.
5. The piezoelectric film fingerprint scanner of claim 1 , wherein detection of a reflection from a fingertip ridge is representative of a ring-down oscillation over a number of cycles of said oscillation signal.
6. A method for producing biometric data in a piezoelectric film sensor comprising the steps of:
(1) applying a generated oscillation signal to a gate counter;
(2) switching a piezo film sensor array to detect at least one of an initial pixel and a group of pixels;
(3) initiating a pulser to send an input pulse to one of a plurality of multiplexers in response to said gate counter;
(4) waiting a number of cycles after the input pulse is applied to the one of a pixel and a group of pixels to detect a signal at the pixel;
(5) measuring an output filtered voltage at a voltage detector as one of a gray scale and a binary pixel; and
(6) storing said one of a gray scale and a binary pixel values in an image memory.
7. The device of claim 6 , wherein the biometric data represents a portion of a fingerprint pattern.
8. The device of claim 6 , wherein the biometric data represents a portion of a fingerprint ridge.
9. The device of claim 6 , wherein the biometric data represents a portion of an arteriole-veinal map.
10. The device of claim 6 , wherein the biometric data represents a portion of a bone map.
11. The device of claim 6 , wherein the biometric data represents blood flow.
12. The device of claim 6 , wherein the biometric data represents arteriole blood flow.
13. The device of claim 6 , wherein the biometric data represents capillary blood flow.
14. The device of claim 6 , wherein the biometric data represents a ratio of arteriole and capillary blood flow.