CN101950360A - Optical fingerprint identifier capable of identifying living body finger - Google Patents

Abstract

The invention provides an optical fingerprint identifier capable of identifying living body finger, comprising a fingerprint identification module and a capacitance type living body finger detection module; wherein the capacitance type living body finger detection module comprises an induction electrode and a capacitance measuring circuit, the induction electrode is arranged on an identification face of an identification prism, the bottom layer thereof is a transparent conductive layer and is connected with the identification prism, and the surface layer thereof is a transparent insulation layer and is contacted with a finger. In the invention, the induction electrode is arranged on the identification face, the transparent insulation layer thereof can be directly contacted by a finger, the distance between a living body finger and the induction electrode is reduced, and the living body finger can be effectively identified according to the coupling capacitance measured by the capacitance measuring circuit, thus preventing use of fake fingerprint.

Description

A kind of optical fingerprint acquisition instrument that can discern live finger

Technical field

The present invention relates to the optical fingerprint acquisition instrument field, relate in particular to a kind of optical fingerprint acquisition instrument that can discern live finger.

Background technology

Optical fingerprint acquisition instrument is a widely used fingerprint acquisition device in the existing fingerprint recognition system, and it is gathered the finger watch layer texture and imaging by optical sensor based on optical imaging concept, then fingerprint image is delivered to main frame and handles.Yet, some utilize the appearance of the false fingerprint of material such as rubber, gelatin, silica gel, make safe reliability be subjected to great threat based on the fingerprint recognition system of optical fingerprint acquisition instrument, its method is: make a prosthetic finger consistent with the finger print texture of the validated user of fingerprint recognition system, comprise real core prosthetic finger and fingerprint cover.Utilize optical fingerprint acquisition instrument to use optical imagery, false fingerprint imaging and living body finger print imaging do not have the characteristics of difference, and prosthetic finger is cheated fingerprint recognition system by the collection face that is pressed in the optically detecting instrument.

There is electrical characteristics difference between live finger and the prosthetic finger, therefore, live finger judged it is a kind of method of live finger detection based on capacitive transducer.Capacitive transducer comprises induction electrode and capacitance measurement circuit, is used to measure the coupling capacitance between induction electrode and the electric conductor.Because biosome is an electric conductor, produce coupling capacitance when pointing, so but capacitive transducer finger sensing contact near induction electrode.

Electric conductor and induction electrode near the time coupling capacitance C that produces _fFor:

$C_f=\frac{S}{\mathrm{\δ}/\mathrm{\ϵ}}=\frac{\mathrm{\ϵ}\·S}{\mathrm{\δ}}---\left(1\right)$

By formula (1) as can be known, coupling capacitance C _fSize be directly proportional with DIELECTRIC CONSTANT, capacitor plate area S, δ is inversely proportional to the two-plate spacing, as shown in Figure 4, when no electric conductor when the induction electrode 1, a unsettled side of induction electrode 1 is an air insulating layer 2, be equivalent between the coupling capacitance two-plate apart from the δ infinity coupling capacitance C that this moment, induction electrode 1 produced _fAlmost nil, C ₀Electric capacity for induction electrode 1 other directions produce records the coupling capacitance C and the C of induction electrode 1 this moment ₀Value equate.

As shown in Figure 5, when live finger 1 during near induction electrode 2, the coupling capacitance C that records is the capacitor C of induction electrode 2 other directions ₀With finger 1 near the time coupling capacitance C that produced _fSum:

C＝C ₀+C _f (2)

For the optical finger print instrument, finger contact surface is the optically detecting face, and the metal induction electrode can't be placed on finger contact surface, often is positioned over collection face edge or prism bottom.For preceding a kind of situation, can gather imaging with the live finger touch sensible electrode of non-validated user and with prosthetic finger, realize deception to fingerprint recognition system; For a kind of situation in back, thin fingerprint cover can be worn on the live finger of non-validated user, make it imaging also can make the capacitive transducer response, thus the deception fingerprint recognition system.

When live finger 1 during near induction electrode 2, the surface area of induction electrode 2 is S, and the specific inductive capacity of coupling capacitance is ε between live finger 1 and the induction electrode 2 ₁, the two-plate spacing is δ ₁, the coupling capacitance C that live finger 1 and induction electrode 2 produce _F1For:

${\mathrm{<figure-callout\; id="1"\; label="C\; f"\; filenames="HSA00000258584000022.png"\; state="\{\{state\}\}">C</figure-callout>}}_f=\frac{{\mathrm{\&epsiv;}}_1\&CenterDot;S}{{\mathrm{\&delta;}}_1}=\frac{S}{{\mathrm{\&delta;}}_1/{\mathrm{\&epsiv;}}_1}---\left(3\right)$

As shown in Figure 6, when non-validated user live finger 1 had on false fingerprint cover 3 near induction electrode 2, the specific inductive capacity of false fingerprint cover 3 was ε ₂, the thickness of false fingerprint cover 3 is δ ₂, make finger 1 far away, the coupling capacitance C that produce this moment with the distance of induction electrode 2 _F2For:

${\mathrm{<figure-callout\; id="2"\; label="C\; f"\; filenames="HSA00000258584000022.png,HSA00000258584000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_f=\frac{S}{{\mathrm{\&delta;}}_1/{\mathrm{\&epsiv;}}_1+{\mathrm{\&delta;}}_2/{\mathrm{\&epsiv;}}_2}---\left(4\right)$

As shown in Figure 7, when real core prosthetic finger 1 during near induction electrode 2, real core prosthetic finger 1 is ε with the specific inductive capacity of induction electrode 2 ₃, because of real core prosthetic finger 1 is an insulator, electric conductor and induction electrode apart from δ ₃Infinity, the coupling capacitance C that produce this moment _F3For:

${\mathrm{<figure-callout\; id="3"\; label="C\; f"\; filenames="HSA00000258584000032.png"\; state="\{\{state\}\}">C</figure-callout>}}_f=\frac{S}{{\mathrm{\&delta;}}_3/{\mathrm{\&epsiv;}}_3}=\frac{S}{\&infin;}---\left(5\right)$

The coupling capacitance C that produces when by formula (3), (4), (5) as can be known, live finger is near to or in contact with induction electrode _F1Bigger, the coupling capacitance that prosthetic finger is produced during near induction electrode is less.

$\frac{C_{f1}}{{\mathrm{<figure-callout\; id="3"\; label="C\; f"\; filenames="HSA00000258584000032.png"\; state="\{\{state\}\}">C</figure-callout>}}_f}=\&infin;\&CenterDot;{\mathrm{\&epsiv;}}_1/{\mathrm{\&delta;}}_1=\&infin;---\left(6\right)$

By formula (6) as can be known, C _F1＞＞C _F3, as shown in Figure 8, X, Y, Z be respectively live finger, the capacitance profile densimetric curve of induction electrode when wearing the live finger of non-validated user of false fingerprint cover and real core prosthetic finger near induction electrode, because value C _F1＞＞C _F3Capacitance profile densimetric curve X and real core prosthetic finger the capacitance profile densimetric curve Z distance during near induction electrode of live finger during near induction electrode is far away, according to the size of the capacitor C that records, capacitive transducer can be distinguished live finger and real core prosthetic finger reliably.

$\frac{C_{f1}}{{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HSA00000258584000022.png,HSA00000258584000031.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}=1+\frac{{\mathrm{\&epsiv;}}_1}{{\mathrm{\&epsiv;}}_2}\&CenterDot;\frac{{\mathrm{\&delta;}}_2}{\mathrm{\&delta;}1}---\left(7\right)$

By formula (7) as can be known, work as δ ₁＞＞δ ₂The time, coupling capacitance C _F1With C _F2Ratio near 1, will produce as the intersection region of shade sign among Fig. 8.This zone shows that capacitive transducer has certain probability can't distinguish live finger and the live finger of wearing false fingerprint cover.

Summary of the invention

Based on above-mentioned technical background, for allow fingerprint recognition system according to the electric capacity that measures identification wear the live finger and the live finger of false fingerprint cover, need manage to eliminate as shown in Figure 8 curve X and the intersection region of Y, two curves are separated fully, promptly increase C _F1With C _F2Ratio.By formula (6) as can be known, increase ε ₁/ ε ₂Or δ ₂/ δ ₁Value can both make C _F1Increase, promptly increase ε ₁And δ ₂, or reduce ε ₂And δ ₁, because of ε ₂And δ ₂Be Controlled not, DIELECTRIC CONSTANT ₁Be subjected to the constraint of material again, the most feasible method be reduce finger and induction electrode apart from δ ₁, δ ₁Value more little, C _F1With C _F2Ratio just big more, work as δ ₁Enough hour of value, just shade intersection region among Fig. 8 can be eliminated, draw width of cloth capacitance profile density map as shown in Figure 9, just can accurately distinguish live finger and real core prosthetic finger reliably according to the size of the coupling capacitance of induction electrode this moment.

Use a kind of novel capacitive sensing electrode, comprise transparency conducting layer and transparent insulating layer.On the laminated optically detecting face that is bonded in optical fingerprint acquisition instrument of the electrically conducting transparent of this induction electrode, insulation course is contacted with finger, can reach above-mentioned technical conditions.The transparent insulation layer thickness is less than 1mm, even reaches μ m magnitude.As shown in figure 10, this induction electrode is made of jointly the transparent insulating layer 2 of transparency conducting layer 1.

Be to reduce the transmittance loss, the refractive index of transparency conducting layer and transparent insulating layer equates with the refractive index of Collection prism or is approaching, and equates with Collection prism or approaching optical cement carries out bonding with refractive index.

The invention provides a kind of optical fingerprint acquisition instrument that can discern live finger, it comprises finger print acquisition module and condenser type live finger detection module, condenser type live finger detection module comprises induction electrode and capacitance measurement circuit, it is characterized in that, described induction electrode is positioned at Collection prism and gathers face, and its bottom is a transparency conducting layer, joins with Collection prism, its top layer is a transparent insulating layer, contacts with finger.

The insulation course of described induction electrode and the refractive index of conductive layer equate with the refractive index of Collection prism or are approaching that described induction electrode equates with Collection prism by refractive index or approaching optical cement is bonded on the collection face.

Described capacitance measurement circuit is connected with described induction electrode, and the output signal of capacitance measurement circuit is connected with main frame.

Described finger print acquisition module comprises: shell, Collection prism, light source, lens combination, semiconductor transducer imaging array.

The plane of incidence of described light source and Collection prism joins.

Described lens combination center overlaps with light path light axis.

The output signal of described semiconductor transducer imaging array is connected with main frame, and described semiconductor transducer is cmos sensor or ccd sensor.

The present invention has increased condenser type live finger detection module in optical fingerprint acquisition instrument, its induction electrode is made up of transparency conducting layer and transparent insulating layer, because of transparency conducting layer and transparent insulating layer have good electrical conductivity and light transmission, can place on the collection face and and directly contact by finger, reduced the distance between live finger and the induction electrode, can discern live finger effectively according to the coupling capacitance size that records, prevent the use of false fingerprint.

Description of drawings

Fig. 1 is an embodiment of the invention structural representation;

Fig. 2 is an embodiment of the invention left view;

Fig. 3 is a circuit connection diagram of the present invention;

Fig. 4 is the fundamental diagram that induction electrode one side produces coupling capacitance when unsettled;

Fig. 5 is electric conductor produces coupling capacitance near induction electrode a fundamental diagram;

Fig. 6 is the fundamental diagram that live finger and induction electrode produce coupling capacitance;

Fig. 7 is covered with the finger of false fingerprint cover and the fundamental diagram that induction electrode produces coupling capacitance;

Fig. 8 is the capacitance profile density map of capacitive transducer;

Fig. 9 is the capacitance profile density map of capacitive transducer can effectively discern the fingerprint true and false time;

Figure 10 is the synoptic diagram of condenser type live finger detection module induction electrode of the present invention.

Embodiment

Come in conjunction with the accompanying drawings the present invention is further described below by embodiment:

As shown in Figure 1, present embodiment provides a kind of optical fingerprint acquisition instrument that can discern live finger, is made up of finger print acquisition module 1 and condenser type live finger detection module 2.Finger print acquisition module 1 comprises shell 11, Collection prism 12, light source 13, lens combination 14, semiconductor transducer imaging array 15.Light source 13 joins with the plane of incidence of Collection prism 12, and light source 13 is connected with main frame; The center of lens combination 14 overlaps with light path light axis, and the output signal of semiconductor transducer imaging array 15 is connected with main frame, and described semiconductor transducer is cmos sensor or ccd sensor.As shown in Figure 2, condenser type live finger detection module 2 comprises induction electrode 21 and capacitance measurement circuit 22, induction electrode 21 is to be positioned at Collection prism 12 collection faces, the bottom of induction electrode 21 is a transparency conducting layer, join with Collection prism, the top layer is a transparent insulating layer, and the refractive index of its insulation course and conductive layer equates with the refractive index of Collection prism or be approaching, equates with Collection prism or approaching optical cement is bonded on the collection face by refractive index.When finger presses is on Collection prism collection face, refer to that face directly contacts with the insulation course of induction electrode 21.Capacitance measurement circuit 22 is positioned near shell 11 Collection prisms 12 and with the conductive layer of induction electrode 21 and is connected, and the output signal of capacitance measurement circuit 22 is connected with main frame.

As shown in Figure 3, when live finger by the collection face of being pressed on the time, the insulation course of live finger contact induction electrode 21, the conduction of live finger and induction electrode 21 forms capacitor and produces big coupling capacitance electric capacity of induction electrode 21 is changed, capacitance measurement circuit 22 detects the coupling capacitance after induction electrode 21 changes, and this capacitance signal is transferred to main frame, main frame sends instruction makes this optical fingerprint acquisition instrument in running order.When prosthetic finger by the collection face of being pressed on the time, because prosthetic finger makes the distance between live finger and induction electrode 21 conductive layers increase, the coupling capacitance that the coupling capacitance that is produced can produce when live finger is pressed on the collection face, capacitance measurement circuit 22 detects the coupling capacitance after induction electrode 21 changes, and be transferred to main frame, main frame is judged to be the non-living body finger, does not just send instruction, and this induction type optical fingerprint acquisition instrument remains in off working state.

Those skilled in the art can also carry out various modifications to above content under the condition that does not break away from the definite the spirit and scope of the present invention of claims.Therefore scope of the present invention is not limited in above explanation, but determine by the scope of claims.

Claims (7)

1. the optical fingerprint acquisition instrument that can discern live finger, it comprises finger print acquisition module and condenser type live finger detection module, condenser type live finger detection module comprises induction electrode and capacitance measurement circuit, it is characterized in that, described induction electrode is positioned at Collection prism and gathers face, and its bottom is a transparency conducting layer, joins with Collection prism, its top layer is a transparent insulating layer, contacts with finger.

2. a kind of according to claim 1 optical fingerprint acquisition instrument that can discern live finger, it is characterized in that, the insulation course of described induction electrode and the refractive index of conductive layer equate with the refractive index of Collection prism or are approaching that described induction electrode equates with Collection prism by refractive index or approaching optical cement is bonded on the collection face.

3. a kind of according to claim 1 optical fingerprint acquisition instrument that can discern live finger is characterized in that described capacitance measurement circuit is connected with the conductive layer of described induction electrode, and the output signal of capacitance measurement circuit is connected with main frame.

4. a kind of according to claim 1 optical fingerprint acquisition instrument that can discern live finger is characterized in that described finger print acquisition module comprises: shell, Collection prism, light source, lens combination, semiconductor transducer imaging array.

5. as a kind of optical fingerprint acquisition instrument that can discern live finger as described in the claim 4, it is characterized in that the plane of incidence of described light source and Collection prism joins.

6. as a kind of optical fingerprint acquisition instrument that can discern live finger as described in the claim 4, it is characterized in that described lens combination center overlaps with light path light axis.

7. as a kind of optical fingerprint acquisition instrument that can discern live finger as described in the claim 4, it is characterized in that the output signal of described semiconductor transducer imaging array is connected with main frame, described semiconductor transducer is cmos sensor or ccd sensor.

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