A device and method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis

Abstract

The present invention relates to three-dimensional fingerprint analysis and reconstruction, and specifically to a device and method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis. The device comprises a fingerprint pressing block and a semiconductor refrigeration chip. The fingerprint pressing block is disposed on the cold end of the semiconductor refrigeration chip, and the method comprises the following steps: S1: cleaning and drying the fingerprint pressing block, and disposing the fingerprint pressing block on the cold end of the semiconductor refrigeration chip; S2: cleaning and drying the fingerprint, and pressing the fingerprint onto the fingerprint pressing block; S3: recording a two-dimensional fingerprint image and measuring the size of water droplets generated between the fingerprints, and constructing a three-dimensional fingerprint image based on the obtained two-dimensional fingerprint image and the size of the water droplets. Compared with the existing technology, the present invention utilizes condensed microdroplet analysis to reconstruct three-dimensional fingerprints, achieving high-precision, low-cost three-dimensional fingerprint construction, which can be used for personal information identification and criminal investigation.

Description

Technical Field

[0001] The present invention relates to an analysis and reconstruction of a three-dimensional fingerprint, and in particular to a device and method for analyzing and reconstructing a three-dimensional fingerprint using condensed micro-droplets. Background Art

[0002] Fingerprint recognition technology, or fingerprint identification, matches a person to their fingerprint and verifies their true identity by comparing their fingerprint with a previously stored fingerprint. Because the patterns, breakpoints, and intersections of skin textures (including fingerprints) vary from person to person and remain unchanged throughout life, fingerprint identification technology relies on this uniqueness and stability.

[0003] Fingerprint recognition technology is a ubiquitous part of our daily lives. Police use it to apprehend criminals, and ordinary citizens can use it to protect their personal information. However, traditional fingerprint recognition technology captures, processes, and identifies two-dimensional fingerprint images. While proven to be highly effective and accurate, two-dimensional fingerprint recognition suffers from inherent drawbacks: significant light sensitivity; human factors during collection, such as finger stains, scars, dryness, and moisture, can affect accuracy; and there is a risk of duplication. To address these challenges, three-dimensional fingerprint recognition is gaining attention and research. The development of a technology that can easily simulate three-dimensional fingerprints would provide greater assurance for investigations and information security, improving the efficiency of apprehending criminals and the security of our daily lives.

[0004] Currently, the commonly used fingerprint recognition technologies mainly adopt the following three methods: (1) Optical, which obtains fingerprint information through light reflection; (2) Capacitive, which obtains fingerprint information based on the electrical signal generated by the contact between the fingerprint and the capacitor; (3) Ultrasonic induction, which obtains fingerprint information based on the spectrum received by the ultrasonic wave. Each of these three technologies has its own advantages and disadvantages. The optical method is cheap but not very accurate; the capacitive method is small but relatively fragile; and the ultrasonic method is highly accurate but expensive. The above three methods all obtain two-dimensional fingerprint information. There is no mature technology on the market to obtain three-dimensional fingerprint information. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one of the above problems and to provide a device and method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis, thereby achieving the construction of high-precision, low-cost three-dimensional fingerprints that can be used for the identification of personal information and criminal investigation.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The first aspect of the present invention discloses a device for analyzing and reconstructing three-dimensional fingerprints using condensed micro-droplets, comprising a fingerprint pressing block and a semiconductor cooling plate;

[0008] The fingerprint pressing block is arranged on the cold end side of the semiconductor refrigeration plate.

[0009] Preferably, the fingerprint pressing block is a silicon wafer or a quartz wafer.

[0010] Preferably, the surface of the fingerprint pressing block is hydrophobically treated.

[0011] Preferably, thermal conductive silicone grease is coated between the fingerprint pressing block and the semiconductor refrigeration sheet. The thermal conductive silicone grease fixes the fingerprint pressing block and the semiconductor refrigeration sheet and can also reduce thermal resistance.

[0012] Preferably, the surface temperature of the cold end of the semiconductor refrigeration plate is the dew point temperature of the air, preferably the dew point of the air corresponding to the ambient temperature and humidity during measurement.

[0013] Preferably, the device further comprises a cold stage, which is arranged on the hot end side of the semiconductor refrigeration plate to take away the heat generated by the hot end of the semiconductor refrigeration plate and maintain the low temperature of the cold end.

[0014] Preferably, the cooling stage is a water chiller, which cools the hot end of the semiconductor refrigeration plate by circulating coolant.

[0015] A second aspect of the present invention discloses a method for analyzing and reconstructing three-dimensional fingerprints using the above-mentioned device for analyzing and reconstructing three-dimensional fingerprints using condensed microdroplets, comprising the following steps:

[0016] S1: Clean and dry the fingerprint pressing block, and place the fingerprint pressing block on the cold end side of the semiconductor refrigeration chip;

[0017] S2: Clean and dry the fingerprint, and press the fingerprint on the fingerprint pressing block, preferably lightly pressing the fingerprint on the fingerprint pressing block for 10 seconds;

[0018] S3: Record the two-dimensional fingerprint image and measure the size of the water droplets generated between the fingerprints, and construct a three-dimensional fingerprint image based on the obtained two-dimensional fingerprint image and the size of the water droplets.

[0019] Preferably, the cleaning and drying of the fingerprint press block in step S1 is to ultrasonically clean the fingerprint press block in an acetone solution at room temperature for at least 10 minutes, and after the ultrasonic cleaning is completed, rinse the surface of the fingerprint press block with isopropyl alcohol and deionized water several times in sequence until the residual acetone solution is completely removed, and then dry it with nitrogen.

[0020] Preferably, the cleaning and drying of the fingerprint in step S2 is to clean the fingerprint with isopropyl alcohol and deionized water several times, and then dry it with nitrogen.

[0021] Preferably, the recording of the two-dimensional fingerprint image and measuring the size of the water droplets generated between the fingerprints in step S3 is to record the two-dimensional fingerprint image with a camera and simultaneously record the water droplets generated at the small furrows between the fingerprints and measure the size of the water droplets through image analysis software such as Image J, calculate the opening and closing angles of the small furrows according to the measured water droplet size through a correlation function, and combine the two-dimensional fingerprint image and the opening and closing angles of the small furrows to obtain a three-dimensional fingerprint model.

[0022] Preferably, the camera is a CCD camera.

[0023] Preferably, the water drop recorded and measured is the largest water drop generated at the small furrow between fingerprints.

[0024] Preferably, the correlation function described in step S3 is established by fitting measured data, and the measured data is obtained by measurement using a three-dimensional scanner. The correlation function can be obtained by correlating the measured data with the maximum water droplet size in the corresponding small furrow, wherein the maximum water droplet can be obtained by the method of the present invention or by other conventional methods. The size of the water droplet can be measured by image analysis software, and the correlation function is a relationship between the maximum water droplet size in the small furrow and the opening and closing angle of the V-shaped fingerprint small furrow.

[0025] The working principle of the present invention is:

[0026] Fingerprints are complex structures composed of multiple furrows and papillary lines, exhibiting a three-dimensional topological configuration with varying furrow slopes at different locations. When a fingerprint contacts a cold surface, the fingerprint pressing block is at a lower temperature. When a warm finger touches an overly cold surface, water vapor released from the dermis in the furrows condenses on the cold surface. Because the furrows open and close at varying angles, the diameters of the condensed water droplets also vary. Therefore, by establishing a correlation function based on measured data, the opening and closing angles of the furrows, or their slopes, can be inferred from the measured water droplets of varying sizes. This relationship can then be used to construct a three-dimensional fingerprint image using the two-dimensional data.

[0027] The size of water droplets in the actual fingerprint image is related to the height from the corresponding position in the small furrow where the water droplets are produced to the surface. The water droplets produced at the highest point of the small furrow are the largest, and the closer to the papillary line, the smaller the water droplets are. The water droplets are centered at the highest point of the small furrow, and the sizes of the water droplets on both sides are roughly symmetrically distributed.

[0028] Based on real 3D data, the grooves of the small furrows are generally V-shaped, and the opening and closing angles of the small furrows can be measured through curve fitting. Measuring a 2D fingerprint image easily determines the fingerprint spacing. Based on the fingerprint spacing and the small furrow opening and closing angles, the height data at each location of the fingerprint small furrows can be obtained. Therefore, if the fingerprint spacing is known and the diameter of the largest water droplet is measured, the relationship between the water droplet diameter and the small furrow opening and closing angle can be calculated, thereby obtaining a 3D fingerprint image.

[0029] Fingerprint spacing and maximum droplet diameter can be easily obtained from fingerprint images captured by a CCD. By substituting the measured droplet diameter into the equation for the relationship between droplet diameter and furrow opening and closing angle, the furrow opening and closing angle can be calculated. Knowing the opening and closing angle and fingerprint spacing allows for the simulation of a true three-dimensional fingerprint image. Because each person's fingerprint is unique, the spacing between fingerprints and the maximum droplet size produced by pressing vary, resulting in a different simulated three-dimensional fingerprint image. This can be used as a means of identifying individuals and can be used for personal recognition.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Usually, two-dimensional fingerprints need to collect the entire or most of the fingerprint information for biometric identification, while three-dimensional fingerprints only need to collect partial fingerprints or even one or two fingerprints to meet the needs of biometric identification because they add one dimension of information (the slope of the small furrow). The present invention measures the size of the largest water droplets condensed in the small furrow, and then obtains three-dimensional fingerprint information based on the correlation function between the maximum water droplet size and the opening and closing angle of the small furrow. The detection method is simple, and the three-dimensional fingerprint model obtained by detection can store more identity information than the two-dimensional fingerprint, and is more suitable for actual applications that require confidentiality. A more accurate model can be obtained by performing correlation calculations through correlation formulas, thereby improving the accuracy of the three-dimensional fingerprint model.

[0032] 2. The method of obtaining a three-dimensional fingerprint model by calculating a correlation formula in the present invention is more universal. After the correlation function is obtained, it can be reused in subsequent measurements. The three-dimensional fingerprint of other people can also be simulated based on this correlation formula to identify their identity.

[0033] 3. The device of the present invention is compact and simple, and only requires a semiconductor refrigeration plate and a fingerprint pressing block to realize its function. A cold stage can be added to improve its refrigeration performance. The measuring part only needs to be large enough to be pressed by a finger. It is low in cost, easy to carry and easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1This is a schematic diagram of the structure of the device for analyzing and reconstructing three-dimensional fingerprints using condensed microdroplets according to the present invention;

[0035] Figure 2 This is a schematic diagram of water droplets on the surface of the fingerprint pressing block when the present invention is used;

[0036] Figure 3 A schematic diagram of the fingerprint shape;

[0037] Figure 4 A schematic diagram of water droplets and small furrow angles generated when pressing a fingerprint using the present invention;

[0038] In the figure: 1-fingerprint pressing block; 2-semiconductor cooling plate; 3-cold platform; 4-water droplets; 5-mastoid line; 6-small furrow; 7-fingerprint. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] A device for reconstructing three-dimensional fingerprints using condensed microdroplet analysis, such as Figure 1 As shown, the fingerprint pressing block 1 and the semiconductor cooling chip 2 are included. The back of the fingerprint pressing block 1 is coated with thermal grease, and the fingerprint pressing block 1 is fixed to the cold end surface of the semiconductor cooling chip 2 by the thermal grease. The thermal grease can also reduce the thermal resistance, thereby improving the heat transfer efficiency between the fingerprint pressing block 1 and the semiconductor cooling chip 2.

[0041] The fingerprint pressing block 1 can be made of silicon wafer or quartz wafer, preferably silicon wafer is more suitable for use. The front surface of the fingerprint pressing block 1 is hydrophobic treated to minimize the formation of water droplets 4 and prevent them from affecting the accuracy of the three-dimensional fingerprint model.

[0042] The surface temperature of the cold end of the semiconductor refrigeration chip 2 during operation is the dew point temperature corresponding to the ambient temperature and humidity. For example, when the room temperature is 20°C and the humidity is 60%, the cold end temperature is set to a dew point temperature of 12°C. Its hot end is in contact with the cold table 3. The cold table 3 is set to remove the heat generated by the hot end of the semiconductor refrigeration chip 2, maintaining the temperature of the cold end 2 at a low temperature. Preferably, the cold table 3 in the following embodiments all uses a chiller to cool the hot end of the semiconductor refrigeration chip 2 by circulating coolant. In this embodiment, cold water is selected as the circulating coolant of the chiller.

[0043] A method for analyzing and reconstructing three-dimensional fingerprints using the above-mentioned device for analyzing and reconstructing three-dimensional fingerprints using condensed microdroplets comprises the following steps:

[0044] S1: ultrasonically clean the fingerprint pressing block 1 in an acetone solution at room temperature for at least 10 minutes. After the ultrasonic cleaning, rinse the surface of the fingerprint pressing block 1 several times with isopropyl alcohol and deionized water in sequence until the residual acetone solution is completely removed. Dry the fingerprint pressing block 1 with nitrogen gas, and place the dried fingerprint pressing block 1 on the cold end side surface of the semiconductor refrigeration chip 2.

[0045] S2: Clean the fingerprint 7 several times with isopropyl alcohol and deionized water, and dry it with nitrogen. Press the dried fingerprint 7 onto the fingerprint pressing block 1 for 10 seconds, so that the papillae 5 of the fingerprint 7 are in close contact with the surface of the fingerprint pressing block 1, and the small furrows 6 and the surface of the fingerprint pressing block 1 form a space for the water droplets 4 to form;

[0046] S3: Use a CCD camera to record the two-dimensional fingerprint image and the water droplets 4 generated between the fingerprints 7 and use Image J software to measure the size of the largest water droplet 4. Based on the relationship function between the diameter of the largest water droplet 4 and the opening and closing angle α of the small furrow 6 obtained from the measured data, the slope of the small furrow 6 of the fingerprint 7 is inferred, and then combined with the information of the two-dimensional fingerprint image to obtain a three-dimensional morphology close to the fingerprint 7.

[0047] like Figure 2-4 As shown, the finger is pressed on the fingerprint pressing block 1. Due to the action of the semiconductor refrigeration plate 2, the fingerprint pressing block 1 is at the dew point temperature, so the water vapor released by the dermis will condense on the surface of the fingerprint pressing block 1. Since the opening and closing angles α of the small furrows 6 between the fingerprints 7 are different, water droplets 4 with different sizes will be formed. The sizes of these water droplets 4 are recorded and measured, and the slope of the small furrow 6 is calculated based on the correlation function between the size of the water droplets 4 and the opening and closing angle α of the small furrow 6. The three-dimensional fingerprint morphology is obtained by combining the two-dimensional image.

[0048] Example 1

[0049] Step (1): Take a 3×3cm 2 The silicon wafer was ultrasonically cleaned for 10 minutes using an ultrasonic cleaning machine. Subsequently, the ultrasonically cleaned sample was rinsed with isopropyl alcohol (IPA) and deionized water in sequence and dried with nitrogen.

[0050] Step (2): Use isopropyl alcohol (IPA) and deionized water to clean the oil stains in the fingerprint 7, and dry the fingerprint 7 with nitrogen.

[0051] Step (3): Place the silicon chip of step (1) on the semiconductor refrigeration chip 2. The working environment temperature is 20°C and the relative humidity is 60%. The cold end temperature of the semiconductor refrigeration chip 2 is set to the real-time dew point temperature of 12°C. Press the clean finger that has been cleaned and dried in step (2) on the silicon chip, and use a CCD camera to record the water droplets 4 generated between the fingerprints 7.

[0052] Step (4): Measure the size of the largest water droplet 4, calculate the opening and closing angle α of the small furrow 6 at the corresponding position through the correlation function, and construct a three-dimensional fingerprint image by combining the two-dimensional fingerprint image.

[0053] The size of the water droplets 4 in the actual fingerprint image is related to the height from the corresponding position in the small furrow 6 where the water droplets 4 are produced to the surface. The water droplets 4 produced at the highest point of the small furrow 6 are the largest in size. The closer to the papillary line 5, the smaller the size of the water droplets 4. The water droplets 4 are centered at the highest point of the small furrow 6, and the sizes of the water droplets 4 on both sides are roughly symmetrically distributed.

[0054] Based on real 3D data, the grooves of the small furrows 6 are essentially V-shaped, and the opening and closing angle α of the small furrows 6 can be measured through curve fitting. Measuring a 2D fingerprint image easily determines the distance between the fingerprints 7. Based on the distance between the fingerprints 7 and the opening and closing angle α of the small furrows 6, the height data at each location of the small furrows 6 can be obtained. Therefore, if the distance between the fingerprints 7 is known and the diameter of the largest water droplet 4 is measured, the relationship between the diameter of the water droplet 4 and the opening and closing angle α of the small furrow 6 can be calculated, thereby obtaining a 3D fingerprint image.

[0055] The distance between fingerprints 7 and the maximum droplet diameter can be easily obtained from a fingerprint image captured by a CCD. By substituting the measured diameter of water droplets 4 into the equation for the relationship between the diameter of the droplets 4 and the opening and closing angle α of the small furrows 6, the opening and closing angle α of the small furrows 6 can be calculated. Furthermore, knowing the opening and closing angle α and the distance between fingerprints 7, a realistic three-dimensional image of the fingerprint 7 can be simulated. Because each fingerprint 7 is unique to each person, the distance between fingerprints 7 and the maximum droplet size obtained by pressing vary, and therefore the simulated three-dimensional fingerprint image is also unique, making it a means of identifying individuals and can be used for personal recognition.

[0056] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis, characterized in that: The device used in the method comprises a fingerprint pressing block (1) and a semiconductor cooling plate (2); the fingerprint pressing block (1) is arranged on the cold end side of the semiconductor cooling plate (2); The method comprises the following steps: S1: cleaning and drying the fingerprint pressing block (1), and placing the fingerprint pressing block (1) on the cold end side of the semiconductor refrigeration plate (2); S2: Clean and dry the fingerprint (7), and press the fingerprint (7) onto the fingerprint pressing block (1); S3: Recording a two-dimensional fingerprint image with a camera and simultaneously recording the largest water droplet (4) generated at the small furrow between the fingerprint (7), and measuring the size of the largest water droplet (4) with image analysis software, calculating the opening and closing angle of the small furrow according to the measured size of the largest water droplet (4) through a correlation function, and further combining the two-dimensional fingerprint image and the opening and closing angle of the small furrow to obtain a three-dimensional fingerprint model; wherein, the correlation function is established by fitting measured data, and the measured data is obtained by measuring with a three-dimensional scanner, and the correlation function is obtained by correlating the measured data with the corresponding maximum water droplet size in the small furrow.

2. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: The fingerprint pressing block (1) is a silicon wafer or a quartz wafer.

3. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: The surface of the fingerprint pressing block (1) is subjected to a hydrophobic treatment.

4. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: Thermal conductive silicone grease is applied between the fingerprint pressing block (1) and the semiconductor cooling plate (2).

5. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: The cold end surface temperature of the semiconductor refrigeration plate (2) is the dew point temperature of the air.

6. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: The device further comprises a cold stage (3), which is arranged on the hot end side of the semiconductor refrigeration plate (2).

7. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: The cleaning and drying of the fingerprint pressing block (1) in step S1 is to ultrasonically clean the fingerprint pressing block (1) in an acetone solution at room temperature for at least 10 minutes, and after the ultrasonic cleaning is completed, rinse the surface of the fingerprint pressing block (1) with isopropyl alcohol and deionized water several times in sequence until the residual acetone solution is completely removed, and then dry it with nitrogen.

8. The method for reconstructing three-dimensional fingerprints using condensed microdroplet analysis according to claim 1, characterized in that: The cleaning and drying of the fingerprint (7) in step S2 is to clean the fingerprint (7) several times with isopropyl alcohol and deionized water, and dry it with nitrogen.

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