Optical sensor and method for producing the contact image

 

The invention relates to the field of biometric technology, namely, devices for removing fingerprints. The optical sensor includes a photosensitive element and a protective optically transparent element intended to protect the photosensitive element from static electricity. And protective optically transparent element is made in the form of a conductive fiber-optic plate with a surface electrical resistance greater than the resistance of human skin. The method of obtaining the contact image includes the installation of the finger on the contact surface of optical fingerprint sensor, sensor, receiving and processing the fingerprint image. And measure the electrophysical parameters of the contact surface with the set on her finger without it and plug in the sensor when the change of the measured electrical parameter is above the threshold value. 2 S. and 1 C.p. f-crystals, 5 Il., table 1.

The invention relates to the fields of electronics and biometrics can be used in electro-optical devices, biometric devices and systems for protection against wasda fake media.

There are many designs of electrically conductive optically transparent multilayer consisting of flat layers, performing separately electrically conductive and protective functions [1, 2, 3]. These designs are particularly widely used in the automotive industry to protect the glass from fogging and icing. However, the multilayer structure and different cover glass can significantly affect the metrological properties of the sensitive (or emitting) element of the optical sensor, so the optical sensor typically protects a homogeneous volume of optically transparent material or element (glass). It is known that any sensor, including optical, is quite sensitive to certain physical size and must be protected from the effects of other physical quantities.

Typically, to protect the optical sensor from external influences photosensitive element is placed in a sealed housing having an optically transparent input window of homogeneous material for input (output) optical radiation and serves as a protective element [4]. It is an optically transparent homogeneous entrance window should skip the input radiation is s in the dust sensor, dirt, water, and possess sufficient mechanical stability and strength. In a standard optical sensor, for example containing a photosensitive element FPPS, optical input window (protective element) represents an optically transparent glass, which is attached to the housing with adhesive, and between the protective glass and the photosensitive element is air or inert gas, performs the additional function of protecting the photosensitive element from the external environment. However, such an optical diagram of the sensor requires a lens for transmitting an optical image from an object to the photosensitive element, which increases as the actual dimensions of the sensor, and the distance from the sensor to the object, which is often disadvantageous.

There are optical sensors that allow you to obtain the optical image without the use of lens, for example by direct contact of the object (or image) on the photosensitive element. In this case, directly on the outer surface of the photosensitive element of the sensor is applied to a thin optically transparent layer, and its thickness should not exceed half the minimum size of the sensor without significant losses [5].

These optical sensors have the minimum possible dimensions, however, the mechanical and electrostatic durability of such devices is insufficient for their widespread use, since mechanical contact with such a thin coating can cause damage to optical coatings or sensing element. Also the malfunction of the sensor may occur as a result of its destruction by static electricity, for example by contact with hands or clothing of the person.

Known optical sensor [6], allowing to obtain the contact object image and has high strength.

The sensor includes a photosensitive multi-element transducer, for example a CCD or CMOS, and fiber-optic input window for image transmission from the contact surface on the photosensitive device.

Fiber-optic input window is optically transparent protective element.

The contact surface is the outer side of the protective element.

This sensor is taken as a prototype. The device prototype has high mechanical strength and can be used in fingerprinting to identify users.

However nanocage fiber (over 3 mm thick) not makes extensive use of this device, because, for example, to use it as a biometric (fingerprint) identification in a mobile phone, its thickness should be not more than 1.5 mm

The disadvantages of the prototype is the fact that this device must contain additional elements for determining when the start of its work, or to be constantly on, which is disadvantageous because of the large energy consumption, in addition, this device when it is used for fingerprinting does not allow to distinguish a live finger from the fake.

A known method of obtaining a surface image of the object [6].

The method consists of a contact object (finger) with the contact surface of the fiber-optic plate (GP), the activation of the sensor, the illumination of the object light passing through the object, transfer object image through the optical fiber on the photosensitive multielement transducer and converting the received image into an electric signal.

This method does not allow to distinguish live media fingerprint image from the fake and run the sensor when installing the finger, because the placement of any additional items (for example, a capacitive sensor) on optical fiber technology

The inventive apparatus and method allows to reduce the size and increase the reliability of the device and to extend the functionality of the device and method.

This is achieved by the fact that in the known optical sensor comprising at least one photosensitive element and optically transparent protective element, the outer side of which may be a contact surface, the protective element is electrically conductive.

In another embodiment, the proposed optical sensor is a fingerprint sensor that converts the fingerprint image into an electrical signal, optically transparent protective element is an optical fiber (fiber optic plate) with the surface electrical resistance greater than the electrical resistance of the human skin.

In the next version of the invention the optical sensor contains more sensitive to changes in the electrophysical parameters of the contact surface elements, electrically connected with the optical transparent protective member.

The problem is solved also by the fact that in the known method of obtaining a surface image of the object, vklyuchayuschego image, measure the electrophysical parameters of the contact surface with the set on her finger without it, and include the sensor when the change of the measured electrical parameter is above the threshold value.

The protective element, usually glass, combine the protective functions protection photosensitive (radiative) element from adverse effects of certain metrological properties, i.e., for example, to pass optical radiation with minimal losses. Moreover, until recently, optical sensors were relatively rare and were located in protected from electrostatic effects. The development of optoelectronics at the present time leads to the fact that optical sensors have different equipment in locations easily accessible to the touch of the human hand, with geometrical dimensions (volume) of the optical sensors is continuously reduced, and the area of the photosensitive surface increases. In these circumstances, the urgent protection of optical sensors not only from external mechanical and climatic influences, but also from the effects of static electricity, which can destroy the sensor not tajinaste electric field in the formation of static discharge exceeds the dielectric strength of the optical coating. Moreover, there are a number of applications of optical sensors that are directly related to the constant influence of static electricity, such as high-sensitivity television camera on the basis of articulated Tubes and CCD, and fingerprint sensors.

The authors found that the use of conductive, homogeneous depth optical coatings can significantly improve the security of the optical sensor from the damaging effects of static electricity.

Earlier protection against static electricity was used primarily for the protection of electric circuit elements, and one of the ways of protection was to increase the electrical resistance of the circuit elements. The standard approach to increase the electric strength of homogeneous insulators is even more increase the electrical resistance of the insulator, which was mainly achieved by increasing the dimensions of the homogeneous dielectric material. However, the reduction of the electrical resistance of the dielectric also reduces the likelihood of its breakdown by static electricity. This is probably due to the difference in mechanisms of development and flow elektrostaticheskaya conductive channel with low electric resistance, and for a short time in this channel is allocated a great deal of power, which leads to mechanical failure of the dielectric. Under conductive materials (may be more conductive little) authors understand almost all materials (substances) having a specific electric resistance between conductors (metals1102Omcm) and insulators (>11011Omcm).

In a conducting material such process does not happen because a certain conductivity, there is always a charge as would "spread" across the surface or volume and can not concentrate in one local point. In the conditions of constant electric field (voltage), likely, possible, and the formation of more conductive channels in the conductive material, however, the static electricity is intermittent process. Therefore, the presence of a conductive material (for example with a resistivity=103109Omcm) Privodino reduces the likelihood of electrical breakdown.

For the manufacture of optically transparent fiber-optic plate, there is no need to use both optically transparent and electrically conductive single material, since the electrically conductive can be the shell, and optically conductive - fiber core, however, the design and manufacture of such fiber is technically challenging. By careful selection of glasses for shell and Explorer was able to obtain samples of the GP with resistance from 106up to 109Omcm, and as conductive glass used glass sheath of the optical fiber. Because in the manufacturing process of the TPO membranes are sintered with each other, it formed the GPS, and have the necessary optical properties, has uniform throughout the sample electrical resistance.

Using this GPS for fingerprint sensor allows not only to protect the sensor from exposure to static electricity, but also to use conductive GPS to determine the presence of a finger on the sensor and activate the sensor, because when installing the finger on the contact surface of the sensor changes the electrical resistance in STW benefits and increases the sensitivity of the device. For this purpose, the optical sensor may further comprise an electrical circuit current measurement, one element of which is optically transparent protective element, for example an optical fiber. When installing the finger on the contact surface of the electrical resistance in the circuit will decrease and, for example, the current will increase (while maintaining a constant voltage), which may be a signal to activate the optical sensor elements.

The proposed device is substantially enhanced by adding conductive properties of optically transparent protective element of the optical sensor of uniform depth. In the simplest case, this extension of functionality associated with the extension of the protective properties of optical coatings, covering not only protection against mechanical and climatic factors, but also from static electricity.

In another embodiment, a device having electrically conductive properties optical coatings allows not only to implement protective properties in the usual sense, but also protective properties in the form of protection from fake media fingerprint images, and also implement power saving mode.

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In Fig.2 shows a variant in which the optical conductive protective element has an electrical contact with a grounded part of the optical sensor.

In Fig.3 shows a conventional circuit for measuring current in a conductive protective coating of the optical sensor.

In Fig.4 shows a simplified circuit diagram showing the installation of a finger on a conductive optical coating fingerprint sensor.

In Fig. 5 shows a top view of a conductive fiber-optic plate.

The proposed device consists of the following main elements: 1 - photosensitive element; 2 - protective optically transparent or optical fiber coating; 3 - ground contact sensor; 4, 5 - electroacoustically elements; 6 - thin (piscivorous) coating, which is part of the photosensitive element.

The optical sensor is carried out as follows. Protective conducting coating (1) transmits light to the photosensitive element (2), in the same way as conventional dielectric coating, however, in the case of exposure to static electricity protective coating electric charge uniformly spreads over egistered current not only from the appearance of static electricity, but also from changes in the resistance (R) of the formed circuit when her shunt resistance of the finger (Rf). The change of the current signal in this circuit is used to activate the photosensitive element of the sensor and determine the authenticity of the fingerprint of the media, including the sensor only when exceeding a certain threshold current. A thin dielectric coating (6), usually available from each of the photodetector, allows to isolate the current-carrying elements on the surface of a sensor (2) from the conductive protective coating (1), although in some cases, conductive materials with resistivity1107Omcm can be considered as insulators and their conductivity does not affect the operation of the optical sensor.

Naturally, the design of the optical sensor according to this invention is not limited to the given examples. In the drawings shown only the basic principles of design, which, in particular, can be quite diverse in view of the claims and the description. The same generalization applies to before the steel FPPS 1M with the number of photosensitive elements 512576 and the size of the photosensitive section 1015 mm On the photosensitive surface of the crystal is applied a thin dielectric coating of SiO with a thickness of 1 μm (6), which caused an optically transparent coating of polycrystalline silicon (Si*) of a thickness of 3 μm with a resistance of 1 kOhmcm (1).

When performing optical sensor according to Fig.1 conductive layer (1) had no electrical contact with the grounded substrate FPS 1M (3). When performing optical sensor according to Fig.2 conductive layer directly in contact with the grounded substrate of the device.

When performing optical sensor in accordance with Fig.3, the signal change in electrical circuits (4, 5) automatically starts the control sensor FPS 1M, and optically transparent protective element (6) made of an optical fiber with a specific electrical resistance=107Omcm, which is greater than the resistance of human skin. Conductive sheath fiber (shown in Fig.5 black) provides a uniform distribution of the electrical resistance across the sample fiber-optic layer is reported in the table 1, where indicated the magnitude of the breakdown voltage, where the electrostatic breakdown of the optical sensor.

The table shows that the introduction of the conductive protective layer significantly increases the durability of the optical sensor to static electricity.

Studies have shown that when you install your finger on a conductive optical fiber with=107there is a significant reduction of the total resistance in the circuit of the finger sensor, because the model's skin resistance is 100-200 ohms (although there are deviations from the 10 kω (moist skin) 1-2 mω (dry skin)). Thus the current in the circuit shown in Fig.5, increases several times when installing a live finger. For example, one experimentally manufactured fiber optic protective element measured resistance value in accordance with the simplified diagram of Fig.4 showed the following values: lg=6.8 Ωcm; Rv=5106Ω; Rs=20106Ohms, and expansion of the current S when installing the finger was 2.5 times when applied to the sample constant voltage of 5V, which is sufficient for wormhole:assuming that Rf<Rv<Rs, and showed a good approximation of this formula is obtained experimental values S theory/S expert = 2,7/2,5.

Thus, when the supply voltage of 5 V between the measuring elements in the rest of current flow around I=0.5 μa, which is incremented when installing your finger more than doubled to 1.25 μa.

It is known that the best material for volumetric fake fingerprint is sealers, which is a dielectric. Therefore, a false imprint, made, for example, sealers, simply will not include a sensor made in accordance with Fig.3 and operating in accordance with the described method.

Thus, studies have shown that the described invention can find wide application in optical contact and fingerprint devices and systems, where the static electricity on the optical sensor directly connected with the principle of image acquisition, as well as in the usual miniature optical sensors, where the static electricity may be accidental.

Sources of information 1. US 4778732, MKI 32 In 17/06, op. 18.10.88.

2. US 5805330, MKI G 02 F 1/15, op. 08.09.98.

3. US 6175641, the 7.03.95, the prototype.


Claims

1. An optical sensor comprising at least one photosensitive element and optically transparent protective element for protecting the photosensitive element from external influences, external side of which is a contact surface of the sensor, characterized in that the protective optically transparent element is made in the form of a conductive fiber-optic plate with a surface electrical resistance greater than the resistance of human skin, and is designed to protect against static electricity.

2. Optical sensor under item 1, characterized in that it additionally contains the elements that are sensitive to changes in the electrophysical parameters of the contact surface electrically connected with the protective optically transparent element.

3. A method of obtaining a surface image, including the installation of a finger on the contact surface of optical fingerprint sensor, sensor, receiving and processing the fingerprint image, wherein the measured electrical parameters of the contact surface with the set on her finger and without the deposits.

 

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