JP2022002730A - Organism detection device - Google Patents

Abstract

To provide an organism detection device with discrimination accuracy higher than before by miniaturizing an organism detection sensor and also introducing a new evaluation index.SOLUTION: An organism detection device includes: a band-pass filter having split-ring resonators; a measurement section for measuring electromagnetic wave response characteristics; an evaluation value calculation section for calculating an evaluation value; and an organism determination section for determining whether an object is an organism on the basis of, the evaluation value. The band-pass filter has a structure which is constituted by coaxially arranging two sets of complimentary split-ring resonators where two large and small split-ring resonators are coaxially arranged so as to allow split parts to be inverted on an inner side and an outer side.SELECTED DRAWING: Figure 2

Description

The present invention relates to a biological detection device that determines whether or not a detection target is a living body.

Since biometric authentication technologies such as fingerprint authentication and vein authentication use information that only the person can have, they are more convenient and secure than conventional IC card and password authentication. However, since there is a concern about "spoofing" damage using a physical camouflage that imitates the biometric information of another person, in addition to the biometric authentication technology, a biometric detection technology for discriminating between the living body and the camouflage is used together. This is very important.

Therefore, one of the inventors of the present invention is a BPF (Band-) in which two sets of CSRR (Complementary Split-Ring Resonator) structures are arranged in series on the main plate of a microstrip line. A pass filter) (CSRR-BPF) is used as a biological detection sensor, and the electromagnetic response characteristics when the detection target site of the subject is brought close to or in contact with the CSRR-BPF are measured, and the measured value and the measured value are measured. We have already reported a biological detection device that determines whether a detection target site is a living body or a fake object by using two evaluation indexes, an average difference and a similarity calculated from a reference value of a living body (Patent Document 1).

JP 2015-221798

The above-mentioned biological detection device can determine whether it is a living body or a fake with a certain accuracy. However, for thin camouflage with characteristics similar to the human body, such as a skin phantom that simulates the electrical constants of the skin on the surface of the human finger, false positives cannot be completely eliminated, and false positives are further reduced and detected. Improvements in accuracy were needed.

As a factor of false detection, since the CSRR-BPF used as the biological detection sensor in the above-mentioned biological detection device has a structure in which two sets of CSRR structures are arranged in series, a finger or a fake object which is a detection target site is used. It was considered that one of the causes was that when the attached finger covered the CSRR portion, which is the placement area of the CSRR-BPF, the variation due to the imperfect adhesion was generated. Therefore, if the placement area of the detection target part of the biological detection sensor can be reduced, the adhesion between the detection target part and the biological detection sensor can be stably secured, and it is expected that false detection will be reduced. It has been required to make the biological detection sensor smaller.

On the other hand, it was also necessary to review the two evaluation indexes of the mean difference and the degree of similarity used in the above-mentioned biological detection device for discriminating between the living body and the fake object. As described above, the measured value of the electromagnetic wave response characteristic has a certain variance due to the variation when covering the CSR part even in the same detection target part of the same sample, but the similarity is an evaluation index that does not allow this dispersion. It was considered that the existence was one of the causes of the above-mentioned false positives. Therefore, instead of the degree of similarity, it is possible to allow dispersion of the electromagnetic wave response characteristics when the camouflage is not attached, while emphasizing and extracting the change in the electromagnetic wave response characteristics when the camouflage is attached. It was necessary to introduce an evaluation index. In addition, it has been required to improve the average difference so as to further improve the discrimination accuracy.

The present invention has been made in view of the above circumstances, and is to make the biometric detection sensor smaller so as to reduce the variation at the time of measurement, and on the other hand, to tolerate the variation at the time of measurement. By introducing the index, it is an object of the present invention to provide a biological detection device having improved discrimination accuracy as compared with the conventional case.

The biological detection device according to the present invention has a band-passing filter having a split ring resonator designed at a predetermined center frequency according to a detection target portion of a subject, generates an electromagnetic wave, and passes the detection target portion through the band. A measuring unit that measures the electromagnetic wave response characteristics in a predetermined frequency band when it is brought close to or in contact with a filter, the measured value of the electromagnetic wave response characteristics measured by the measuring unit, and the reference value of the electromagnetic wave response characteristics of a living body. An evaluation value calculation unit that calculates an evaluation value using the above, and a biological determination unit that determines whether or not the detection target site is a living body based on the evaluation value calculated by the evaluation value calculation unit. A biological detection device including which, the evaluation value calculation unit sets the measured value of the electromagnetic wave response characteristic measured by the measuring unit as S (f), and the reference value of the electromagnetic wave response characteristic of the living body as T (f). The standard deviation of T (f) is σ (f), the concordance index expressed by the following equation (2) is k (f), and the weighting function corresponding to k (f) is w _v (k (f)). When the weight function for each frequency is w _f (f), the lower limit of the frequency band used for evaluation is f _L , and the upper limit is f _H , the first evaluation value is represented by the following equation (1). It is characterized in that the evaluation value α is calculated.

Further, the biological detection device according to the present invention _{is a function represented by the following equation (3) when the weighting function w v} (k (f)) is set to a predetermined threshold value. It is a feature.

Further, in the biological detection device according to the present invention, the evaluation value calculation unit uses the second evaluation value β represented by the following formula (4) in addition to the first evaluation value α as the evaluation value. Is characterized by calculating.

According to the biological detection device according to the present invention, since the CSRR-BPF has a structure in which two sets of CSRRs are arranged coaxially, a detection target is compared with a conventional structure in which two sets of CSRRs are arranged in series. Since the placement area when covering the CSRR portion can be reduced depending on the portion, the variation in measuring the electromagnetic wave response characteristics is reduced, and thereby the accuracy of determining whether or not the detection target portion is a living body is improved.

According to the biological detection device according to the present invention, the evaluation value calculation unit calculates the first evaluation value α as an evaluation value, and the first evaluation value α is the electromagnetic wave response in the case of a living body without a fake object attached. Since it is an evaluation value that allows variation in the measured value of the characteristic and emphasizes and extracts the change in the measured value of the electromagnetic wave response characteristic when a fake object is attached, it is a living body compared to the conventional evaluation value of similarity. The accuracy of determining whether or not it is improved.

_{Further, by appropriately setting the weight function w v} (k (f)) used for calculating the first evaluation value α, the accuracy of determining whether or not it is a living body is improved.

Further, the evaluation value calculation unit calculates a second evaluation value β in addition to the first evaluation value α as an evaluation value, and the second evaluation value β is an average difference which is a conventional evaluation value. It is an evaluation value in which a weighting function w _{f (f) for each frequency is introduced, and by appropriately setting w f} (f) by an assumed camouflage or the like, the accuracy of determining whether or not it is a living body is improved.

It is a schematic block diagram which shows an example of the biological detection apparatus which concerns on embodiment of this invention. It is a schematic schematic diagram which shows an example of CSRR-BPF which concerns on embodiment of this invention, (a) shows the upper surface side, (b) shows the bottom surface side. It is an enlarged schematic diagram which shows a part of CSRR-BPF which concerns on embodiment of this invention, (a) shows the part A surrounded by the two-dot chain line in FIG. 2, (b) is two in FIG. The part B surrounded by the dotted line is shown. It is a graph which shows the passage characteristic | S21 | of the CSRR-BPF which concerns on embodiment of this invention, and the CSRR-BPF in which two sets of conventional CSRRs are arranged in series. It is a graph which shows the experimental result which performed in order to compare the CSRR-BPF which concerns on embodiment of this invention, and the CSRR-BPF which two sets of conventional CSRs are arranged in series. (A) is a graph relating to the CSRR-BPF according to the embodiment of the present invention, and (b) is a graph relating to the CSRR-BPF in which two sets of conventional CSRRs are arranged in series. It is a graph which shows the experimental result performed in order to compare the 1st evaluation value α which concerns on embodiment of this invention, and the degree of similarity which is a conventional evaluation value. (A) is a graph regarding the first evaluation value α according to the embodiment of the present invention, and (b) is a graph regarding the similarity which is the conventional evaluation value. It is a graph which shows the experimental result performed in order to compare the 2nd evaluation value β which concerns on embodiment of this invention, and the average difference which is a conventional evaluation value. (A) is a graph regarding the second evaluation value β according to the embodiment of the present invention, and (b) is a graph regarding the average difference which is the conventional evaluation value.

An embodiment of the biological detection device according to the present invention will be described below with reference to the drawings. Similar to Patent Document 1 described above, the biometric detection device 1 according to the present invention determines whether or not the detection target site of the human body to be the subject is a living body in order to prevent the act of "spoofing" by a counterfeit product. It is mainly used in combination with a biometric authentication device such as fingerprint authentication or vein authentication. As shown in FIG. 1, the biological detection device 1 according to the present invention has a BPF (Band Pass Filter) in which a CSRR (Complementary Split Ring Resonator) is arranged. In the following, it will be referred to as CRR-BPF) 2, the measuring unit 3 for measuring the electromagnetic wave response characteristics when the detection target part is in close proximity to or in contact with the CSRR-BPF 2, and the electromagnetic wave response characteristics measured by the measuring unit 3 are used. It is equipped with a computer 4 that performs arithmetic processing and the like for biological determination. As shown in FIGS. 2 and 3, the CSRR-BPF2 according to the present invention is characterized by having a structure in which two sets of CSRRs are arranged coaxially. The CSRR has two large and small split ring resonators (SRRs) arranged coaxially so that the split portions are reversed on the inside and outside, and as shown in FIG. 3, a pair of SRR21 and SRR22. Is a set of CSRR23, and a pair of SRR24 and SRR25 is a set of CSRR26. In each CSRR, the widths of the outer and inner SRRs and the width between the two SRRs are equal, and the widths of the splits are also equal. For example, in the case of CSRR23, the dimensions of a13, a14 and a15 are equal, and the dimensions of a9 and a12 are equal. Further, in the present embodiment, as shown in FIG. 1, an example in which only one CSRR-BPF2 is arranged is shown, but by arranging a plurality of CSRR-BPF2s, the electromagnetic wave response characteristics of a plurality of detection target parts of the subject can be measured at the same time. It may be possible to make it possible, or it may be possible to simultaneously measure the electromagnetic wave response characteristics of the detection target sites of a plurality of subjects.

The CSRR-BPF2 is designed to have a predetermined center frequency according to the desired information of the detection target site of the subject (human body), and has a CSRR strongly influenced by a nearby medium. When a medium is brought close to the CSR, the distribution of the electromagnetic field in the vicinity of the CSRR-BPF2 changes due to the influence of the medium, so that the response of the electromagnetic field to the depth direction of the medium, that is, the electromagnetic wave response characteristic can be obtained.

The detection target site includes, for example, a human finger that performs vein authentication or fingerprint authentication. The human finger is considered to have a layered structure of muscle, fat, and skin around the central bone. By defining a human body finger that is an approximate uniform medium using the volume ratio of each layer, the skin depth of the human body finger is calculated based on its relative permittivity and conductivity. At 5 mm and 16 GHz, it is about 2.5 mm, and the electromagnetic field penetrating in the depth direction of the human finger attenuates as the frequency increases. Therefore, when designing the CSRR-BPF2 of the biological detection device 1 used in combination with vein recognition, the vein recognition uses the blood vessel pattern distributed three-dimensionally as the authentication information, and the camouflage is a three-dimensional structure imitating the blood vessel pattern. Therefore, it is considered effective to set the low frequency side, which can acquire the electromagnetic wave response characteristics that reflect the characteristics of the entire human body finger, as the center frequency. On the other hand, when designing CSR-BPF2 to be used together with fingerprint authentication, fingerprint authentication uses the pattern on the surface of the tip of the human finger as authentication information, and the camouflage is a thin film that imitates the pattern and is attached to the surface of the human finger. Therefore, it is considered effective to set the center frequency on the high frequency side where the electromagnetic response characteristics that reflect the characteristics of the surface of the human finger can be obtained. Further, the detection target portion is not limited to the finger, and may be another portion. In that case, the CSRR-BPF2 may be designed with a frequency at which appropriate characteristics can be obtained at that portion as a center frequency.

In the present embodiment, as in Patent Document 1, the biometric detection device 1 used in combination with fingerprint authentication is assumed, and the CSRR-BPF2 is designed with a center frequency of 10 GHz. The structure is shown in FIG. FIG. 2A is a view seen from the top surface side, and FIG. 2B is a view seen from the bottom surface side. Further, FIG. 3 is an enlarged view of a part of CSRR-BPF2 in FIG. 2, and FIG. 3A is a diagram showing a part A surrounded by a two-dot chain line in FIG. 2A. FIG. 3 (b) is a diagram showing a portion B surrounded by a two-dot chain line in FIG. 2 (b). As described above, the skin depth of the human finger at 10 GHz is about 5 mm, which is about half of that when the thickness of the human finger is assumed to be about 10 mm. Therefore, in the CSRR-BPF2 designed at a center frequency of 10 GHz, It is considered that the electromagnetic wave response characteristics that reflect the influence of the structure in the depth direction from the surface of the human finger to about half can be obtained. Since the human finger has a layered structure, even if the electromagnetic wave response characteristics are up to half the depth of the human finger, it includes the skin on the surface, fat, muscles, and the central bone, which is peculiar to these fingers. It is expected that the electromagnetic wave response characteristics that reflect the influence of the structure will be acquired. Therefore, the CSRR-BPF2 designed at a center frequency of 10 GHz is suitable for use in combination with fingerprint authentication because it can acquire electromagnetic wave response characteristics that reflect the influence peculiar to the human finger while being relatively strongly influenced by the surface portion.

This CSRR-BPF2 is, for example, a glass curable PPO resin R-4726 (relative permittivity ε _γ = 3.4, dielectric loss tangent tan δ = 0) which is a dielectric substrate as a substrate, like the CSRR-BPF of Patent Document 1. .005, substrate thickness: 1.0 mm) can be used. Copper foil is attached to both sides of the surface of this dielectric substrate, and it can be manufactured by cutting a transmission line and a CSRR structure as shown in FIG. The hatched portion of FIGS. 2 and 3 is a copper foil. Further, as an example of the dimensions of each part of the CSRR-BPF2 designed with the central frequency of 10 GHz in the present embodiment, in FIGS. 2 and 3, a1 = 26.0 mm, a2 = 19.5 mm, a3 = 10.6 mm, a4. = 4.8 mm, a5 = 10.6 mm, a6 = 7.35 mm, a7 = 4.8 mm, a8 = 7.35 mm, a9 = 0.4 mm, a10 = 0.2 mm, a11 = 0.2 mm, a12 = 0 .4 mm, a13 = 0.4 mm, a14 = 0.4 mm, a15 = 0.4 mm, a16 = 0.3 mm, a17 = 0.2 mm, a18 = 0.2 mm, a19 = 0.2 mm, b1 = 11.6 mm , B2 = 11.6 mm, b3 = 8.55 mm, b4 = 2.4 mm, b5 = 8.55 mm, b6 = 0.4 mm, b7 = 1.2 mm, b8 = 1.2 mm, b9 = 1.6 mm, b10 = 1.6 mm. When measuring the electromagnetic wave response characteristics, it is necessary to cover the CSRR portion of the CSRR-BPF2 with the detection target portion, but the CSRR-BPF having a structure in which two sets of CSRRs described in the conventional Patent Document 1 are arranged in series. In the case of, in the design where the central frequency is 10 GHz as in the present embodiment, the length from one end to the other of the two sets of CSRR is 6.3 mm, whereas in the present embodiment, one place is used. Two sets of CSRRs are housed in a 4.8 mm square, and the CSRR section, that is, the mounting area, is reduced by 24% compared to the conventional method. Reducing the mounting area makes it possible to locally acquire the difference in the effect when the medium is brought close to the CSRR-BPF2, leading to reduction of false detection due to insufficient adhesion of the medium and improvement of detection accuracy. ..

Further, connectors (not shown) are provided at the ports P1 and P2 provided at both ends of the CSRR-BPF2, respectively, and as shown in FIG. 1, they are connected to the measuring unit 3 via the coaxial cable 5. There is. Further, in order to flatten the step of the CSRR due to wear or the like and prevent corrosion of the copper foil, a polypropylene film having a thickness of about 0.2 mm may be installed on the CSRR-BPF2.

The measuring unit 3 is composed of, for example, a vector network analyzer or the like, generates an electromagnetic wave for measurement, incidents on the CSRR-BPF2, and brings the detection target portion close to or in contact with the CSRR-BPF2. Measure the electromagnetic wave response characteristics. As for the electromagnetic wave response characteristics, when the input / output terminals of the CSR-BPF2 are two ports P1 and P2 as in the present embodiment, the passage characteristics S21 that are incident on the port P1 and pass through the port P2 and are incident on the port P2. It is possible to acquire four characteristics: a passage characteristic S12 that passes through the port P1, a reflection characteristic S11 that is incident on the port P1 and reflected to the port P1, and a reflection characteristic S22 that is incident on the port P2 and reflected to the port P2. I can.

The measured value of the electromagnetic wave response characteristic measured by the measuring unit 3 is input to the computer 4. The computer 4 uses the input measured value of the electromagnetic wave response characteristic to perform arithmetic processing for determining whether or not the detection target site is a living body, and for example, a CPU (Central Processing Unit: It includes a central processing unit) 6, a storage unit 7, an arithmetic processing unit 8, a display unit 10, an operation unit 11, and the like. Further, as shown in FIG. 1, each of these parts is connected to the system bus 12, various data and the like are input / output via the system bus 12, and various processes are executed under the control of the CPU 6.

The storage unit 7 can store the measured value of the electromagnetic wave response characteristic input from the measurement unit 3, and also provides a processing program for determining whether or not the detection target site is a living body. Stored. Although the storage unit 7 is provided in the present embodiment, another external computer-readable storage medium may be used.

The arithmetic processing unit 8 performs arithmetic processing and the like for determining whether or not the detection target portion is a living body under the control of the CPU 6 based on the processing program stored in the storage unit 7. The evaluation value calculation unit 81 of the calculation processing unit 8 calculates an evaluation value using the measured value of the electromagnetic wave response characteristic of the detection target site and the reference value of the living body, and the calculation processing unit is based on the calculated evaluation value. The biological determination unit 82 of 8 determines whether or not the detection target portion is a biological body.

The display unit 10 is composed of, for example, a liquid crystal display or the like, and displays a biological determination result or the like. Instead of the display unit 10, or together with the display unit 10, the biological determination result may be notified by voice. The operation unit 11 is composed of a mouse, a keyboard, or the like, and is used by the operator to input various data, operation commands, and the like. The display unit 10 and the operation unit 11 may be integrally configured as a touch panel.

Hereinafter, the flow of the biological detection process by the biological detection device 1 will be described. First, the subject to be detected brings the detection target site close to or in contact with the CSRR-BPF2. At that time, the CSRR portion of the CSRR-BPF2 is covered with the detection target portion. Then, the measuring unit 3 measures the electromagnetic wave response characteristic S (f) in a predetermined frequency band. In this embodiment, CSRR-BPF2 designed with a central frequency of 10 GHz for fingerprint authentication is used, the detection target portion is the portion beyond the first joint of the index finger of the right hand, and the electromagnetic wave response characteristic is the passage characteristic S21 at 3 GHz to 16 GHz. Absolute value | S21 | is used. However, the present invention is not limited to this, and any finger may be used for the detection target portion, and a portion other than the finger may be used if it is not for fingerprint authentication. In that case, the CSRR-BPF2 may be designed with a center frequency according to the desired information. Further, the electromagnetic wave response characteristic is not limited to the passage characteristic | S21 |, and other passage characteristics | S12 |, the reflection characteristic | S11 |, or the reflection characteristic | S22 | may be used. Further, a plurality of these may be used. Further, the frequency band for measuring the electromagnetic wave response characteristics may also be changed according to the characteristics of the designed CSRR-BPF2.

The measured value S (f) of the electromagnetic wave response characteristic measured by the measuring unit 3 is input to the computer 4. The evaluation value calculation unit 81 of the arithmetic processing unit 8 of the computer 4 calculates the evaluation value using the input measured value S (f) and the reference value T (f) of the electromagnetic wave response characteristic of the living body.

The reference value T (f) of the electromagnetic wave response characteristic of the living body is calculated by the evaluation value calculation unit 81, and in the present embodiment, the storage unit 7 is measured a plurality of times in advance under the same measurement conditions as the measured value S (f). Using the measured values of the electromagnetic wave response characteristics of the detection target site of the subject stored in the above, the value obtained by averaging them for each frequency is calculated as the reference value T (f). At this time, the standard deviation σ (f) of the reference value T (f) is also calculated at the same time. A fixed number of measurements of electromagnetic response characteristics may be used to calculate the reference value T (f), but as the number of measured values used increases, the reliability of the reference value T (f) increases and an error occurs. Since it is considered that the detection will be reduced, if it is determined to be a living body after the biological determination every time the biological determination is performed, the measured value S (f) is stored in the storage unit 7 and the reference value from the next time onward. It may be added to the measured value used for calculating T (f). At that time, for example, when used in combination with fingerprint authentication, it is considered that the biometric detection device 1 determines whether or not the fingerprint is a living body after the fingerprint authentication determines that the fingerprints match. The measured values of the response characteristics may be associated with each other and stored in the storage unit 7. Further, although the reference value T (f) used here is an average of the measured values of the electromagnetic wave response characteristics, the reference value T (f) is not limited to that, and other statistical values such as the median may be used. Further, here, the measured value of the detection target part of the subject measured in advance is used for the calculation of the reference value T (f), but the part other than the detection target part, for example, the detection target part is the index finger of the right hand. If so, other measured values of electromagnetic wave response characteristics such as the middle finger and the ring finger may be used. In this case, instead of storing the measured value for calculating the reference value T (f) in the storage unit 7, a plurality of CSRR-BPF2s are arranged to measure the electromagnetic wave response characteristic S (f) of the detection target portion. At the same time, the reference value T (f) may be calculated so that the electromagnetic wave response characteristic of the non-detection target portion used for the reference value T (f) can be measured. Further, the electromagnetic wave response characteristics of the detection target sites of a plurality of people different from the subject are measured in advance, the measured values are stored in the storage unit 7, and the reference value T (f) is calculated using those measured values. You may. However, in order to improve the discrimination accuracy, it is preferable to calculate the reference value T (f) using the measured values of the electromagnetic wave response characteristics of the same detection target site of the same subject as in the present embodiment.

The evaluation value calculation unit 81 calculates the first evaluation value α represented by the following equation (1) as the evaluation value. Here, k (f) is the consistency obtained by dividing the difference between the reference value T (f) represented by the equation (2) and the measured value S (f) by the standard deviation σ (f) of the reference value T (f). It is an exponent, w _v (k (f)) is a weighting function that weights according to the concordance index k (f) represented by the equation (3), p is a predetermined threshold value, and w. _f (f) is a weighting function that weights each frequency, f _L is the lower limit in the frequency band used, and f _H is the upper limit. _{First, the consistency weight w v} (k (f)) is calculated by the equations (2) and (3). The concordance weighting function w _v (k (f)) takes a value from 0 to 1, and the closer it is to 1, the closer the measured value S (f) is to the reference value T (f). If the difference between the measured value S (f) and the reference value T (f) is within the range of p times the standard deviation σ (f) of the reference value T (f), the weight of the consistency is considered to be consistent. It is assumed that w _v (k (f)) = 1 and if it exceeds that, there is no match, and w _v (k (f)) = 0. The measured values of the electromagnetic wave response characteristics do not completely match even in the same detection target part of the same subject, and the condition of the subject such as the sweating state at the time of measurement and the proximity of the detection target part to CSRR-BPF2 It has a certain dispersion depending on how it is made. Therefore, even if the measured value S (f) is due to the same detection target site of the same subject as the reference value T (f), the measured value may be different from the reference value T (f). The threshold value p determines how far away the values are considered to be the same as the reference value T (f). In this embodiment, p = 2.7 is used. This value is such that the measured value S (f) is the reference value T (f) when the measured value of the electromagnetic response characteristics of the detection target site of the subject multiple times used for calculating the reference value T (f) follows a normal distribution. ), The measured value S (f) has a 99.3% probability of _{falling within the range where w v} (k (f)) = 1 if the subject and the detection target site are the same. If the value of the threshold value p is too large, the probability that the measured value S (f) of the camouflage is considered to match the reference value T (f) increases, and if it is too small, the probability is increased. Since the probability that the measured value S (f) of the living body is regarded as inconsistent with the reference value T (f) increases, it is preferable to set the value from p = 2.0 to 3.0. Further, in the present embodiment _{, the equation (3) is used for calculating the consistency weighting function w v} (k (f)), but the present invention is not limited to this, and is appropriately set according to the type and thickness of the assumed camouflage. This makes it possible to improve the discrimination accuracy. Then, according to the equation (1), _{the value obtained by multiplying the consistency weight w v} (k (f)) by the frequency w _f (f) and arithmetically averaging in the frequency band used is used as the first evaluation value α. calculate. Here, the weighting function w _f (f) that weights each frequency reduces the influence on the evaluation value in the frequency band where the difference in electromagnetic wave response characteristics between the living body and the camouflage is not so much, and the difference due to the camouflage. It is used to emphasize the above, and it is possible to improve the discrimination accuracy by setting it appropriately according to the type and thickness of the assumed camouflage. w _{f (f)} has a value of from 0 to 1, for example, in the frequency band that you want to emphasize the difference w _{f (f)} = 1, in the frequency band you want to eliminate the influence on the difference is small evaluation value w _{f (f)} It may be set to = 0. Since the consistency weighting function w _v (k (f)) and the frequency-specific weighting function w _f (f) are both functions that take a value from 0 to 1, the first evaluation value α is also from 0 to 1. It is an evaluation value that takes the value of, and the closer the value is to 1, the higher the possibility that the measured value S (f) is due to the living body.

On the other hand, conventionally, as described in Patent Document 1, the similarity is calculated and used as an evaluation value. The similarity is calculated by the following equation (5). Here, S (f) is the measured value of the electromagnetic wave response characteristic measured by the measuring unit 3, T (f) is the reference value, f _H is the upper limit of the frequency band to be used, and f _L is the lower limit. It is the same as that used for the evaluation value α. The S _norm (f) is expressed by the equation (6), and is a value obtained by normalizing the measured value S (f) so that the minimum value of _{the S norm (f) and the minimum value of the reference value T (f) match.} Yes, D _n is expressed by the equation (7) and is the difference between the measured value S (f) and the reference value T (f) in the frequency band used. As can be seen from these equations, the similarity does not take into account the variation in the measured values of the electromagnetic wave response characteristics used in the calculation of the reference value T (f), so that in the case of an extremely thin camouflage, there is a difference from the living body. It was an evaluation value that was difficult to appear. On the other hand, the first evaluation value α calculated in the present invention allows for variations in the measured values of the electromagnetic wave response characteristics in the case of a living body without the attachment of the camouflage, while the attachment of the camouflage is attached. Since the evaluation value emphasizes and extracts the change in the measured value of the electromagnetic wave response characteristic in a certain case, the discrimination accuracy is improved even for an extremely thin fake object.

Further, the evaluation value calculation unit 81 calculates the second evaluation value β represented by the following equation (4) as an evaluation value in addition to the first evaluation value α. _{The second evaluation value β is a weight function w f for} each frequency in which the mean difference (MD) represented by the following equation (8), which has been conventionally used as the evaluation value as described in Patent Document 1, is used. (F) is introduced. The average difference is an evaluation value for averaging the difference between the graph curves of the measured value S (f) and the reference value T (f), and the closer the value is to 0, the more the measured value S (f) is due to the living body. The larger the value, the higher the possibility that the measured value S (f) is due to a camouflage.

In the biological determination unit 82, whether or not the detection target site is a living body based on two evaluation values of the first evaluation value α and the second evaluation value β calculated by the evaluation value calculation unit 81. Make a judgment. In the biological determination unit 82, for example, threshold values are set for the first evaluation value α and the second evaluation value β, respectively, and the first evaluation value α and the first evaluation value α are set within the respective threshold values. It is determined whether or not it is a living body by determining whether or not the evaluation value β of 2 is contained. That is, when both the first evaluation value α and the second evaluation value β calculated by the evaluation value calculation unit 81 are within the threshold value, it is determined that the detection target site is a living body, and other than that. In that case, it is determined that the detection target site is not a living body. It should be noted that the biological determination may be performed using only one of the first evaluation value α and the second evaluation value β, but in order to further improve the discrimination accuracy, the first evaluation value α and the second evaluation value β are used. It is preferable to use two evaluation values such as the evaluation value β of 2.

The above is the flow of the biological detection process by the biological detection device 1 according to the present embodiment. Hereinafter, the biological detection device 1 according to the present invention is an improvement point from the conventional biological detection device described in Patent Document 1. An experiment was conducted to evaluate how much the discrimination accuracy is improved by the first evaluation value α and the second evaluation value β calculated by the CSRR-BPF2 and the evaluation value calculation unit 81. The result is shown.

First, the experimental results for CSRR-BPF2 having a structure in which two sets of CSRRs according to the present invention are arranged coaxially are shown. The structure of the CSRR-BPF2 of the present invention is as shown in FIGS. 2 and 3. In the conventional CSRR-BPF having a structure in which two sets of CSRRs are arranged in series, when measuring the electromagnetic wave response characteristics of the detection target part, both of the two sets of CSRRs arranged in series are covered with the detection target part. However, in the CSRR-BPF2 according to the present invention, since the two sets of CSRRs are arranged in one place, it is easy to cover the detection target portion. Further, as described above, the dimensions of the CSRR portion of the CSRR-BPF2 (coaxial type 10GHz CSRR-BPF2) having a structure in which two sets of CSRRs designed with the center frequency of the present invention at 10 GHz are arranged coaxially are 4.8 mm square. On the other hand, in the CSRR-BPF (series type 10GHz CSRR-BPF) having a structure in which two sets of CSRRs designed at a conventional center frequency of 10 GHz are arranged in series, two sets of CSRR portions are arranged from one end to the other. The size is 6.3 mm, and the placement area of the detection target site is reduced by about 24%.

Further, FIG. 4 shows the measurement results of the passage characteristics | S21 | of the coaxial type 10 GHz CSRR-BPF2 of the present invention and the conventional series type 10 GHz CSRR-BPF. The solid line is the measurement result of the coaxial type 10 GHz CSRR-BPF2 of the present invention, and the bandwidth is 12 GHz of about 4 GHz to 16 GHz. The dotted line is the measurement result of the conventional series type 10 GHz CSRR-BPF, and the bandwidth is 4 GHz of about 8 GHz to 12 GHz. It can be seen that the operating frequency band has become wider.

Further, FIG. 5 shows the results of a biological detection experiment using the coaxial type 10 GHz CSRR-BPF2 of the present invention and the conventional series type 10 GHz CSRR-BPF. For 20 subjects, measurement was performed 10 times per person using the right index finger without a fake as a human finger, and the electrical constant of the skin on the surface of the fake human finger was simulated as a fake finger. A sheet-shaped skin phantom having a thickness of 0.3 mm was attached to the index finger of the right hand and measured 5 times per person. Here, as the evaluation value calculated by the evaluation value calculation unit 81, the conventional similarity and the average difference were used. This is to compare and evaluate how much the discrimination accuracy is improved by the CSRR-BPF2 according to the present invention with the conventional one. Further, the reference value T (f) is the averaged value of the five measurements of the human fingers of all the subjects, and the measurement value S (f) to be detected is used to calculate the reference value T (f). The 5 human finger measurements and the camouflaged finger measurements that were not used were used. Further, from FIG. 4, since the coaxial type 10 GHz CSRR-BPF2 of the present invention had the minimum passing characteristic | S21 | at 16 GHz, the frequency band for searching the minimum value used for calculating the similarity was calculated as 5 to 16 GHz. In both the present invention and the conventional method, a polypropylene film having a thickness of 0.2 mm was placed on the surface of the CSRR-BPF for measurement. FIG. 5A shows the results of the coaxial type 10 GHz CSRR-BPF2 of the present invention, in which the vertical axis shows the similarity and the horizontal axis shows the average difference, the hollow plot shows the human body finger, and the black-painted plot shows the camouflaged finger. .. FIG. 5B shows the results by the conventional series type 10 GHz CSRR-BPF, in which the vertical axis shows the similarity and the horizontal axis shows the average difference, the hollow plot shows the human body finger, and the black-painted plot shows the camouflaged finger. Looking at FIG. 5, it can be seen that the coaxial type 10 GHz CSRR-BPF 2 of the present invention has a separate plot of the human body finger and the camouflaged finger than the conventional series type 10 GHz CSRR-BPF, but the evaluation is more quantitative. Therefore, when the false acceptance rate (FAR) is 0% and the false rejection rate (FRR) is 0%, and when the FRR is 0%. Evaluation was performed using FAR and a value at which FAR and FRR are equal (Equal Error Rate, EER). The results are shown in Table 1 below. Here, the FRR when the FAR is 0% indicates the ratio at which the human finger is not accepted when a threshold value is set in which all the camouflaged fingers used for the measurement are not accepted. Specifically, the minimum value of the mean difference of the camouflaged fingers and the maximum value of the similarity are set as threshold values, and the ratio of human fingers that does not enter the region below the minimum value of the mean value of the camouflaged fingers and above the maximum value of the similarity. Is. Further, the FAR when the FRR is 0% indicates the ratio of accepting a fake finger when a threshold value for accepting all the human fingers used for the measurement is set. Specifically, with the maximum value of the average difference of the human fingers and the minimum value of the similarity as the thresholds, the camouflage that falls into the region below the maximum value of the average difference of the human fingers and above the minimum value of the similarity. It is a ratio. The lower these indicators are, the higher the discrimination accuracy is. From Table 1, the coaxial type 10 GHz CSRR-BPF2 according to the present invention has more significant results in all of FRR (FAR = 0%), FAR (FRR = 0%), and ER than the conventional series type 10 GHz CSRR-BPF. It can be seen that the discrimination accuracy is improved.

Next, FIG. 6 shows the results of an experiment for evaluating the first evaluation value α calculated by the evaluation value calculation unit 81 according to the present invention. Here, in order to compare the first evaluation value α of the present invention with the similarity, which is a conventional evaluation value, and to evaluate how much the discrimination accuracy is improved by the first evaluation value α, the CSRR-BPF2 is used. The same series type 10 GHz CSRR-BPF as before was used. The first evaluation value α is calculated by the equations (1) to (3) as described above, where the threshold value p is p = 2.7 and the weight w _f (f) for each frequency is the frequency to be used. It was set to w _f (f) = 1 in the entire band. As a camouflage to be attached to the human finger, a 0.5 mm thick skin phantom processed to a size of 22.0 mm × 14.0 mm was used. FIG. 6A shows the results using the first evaluation value α of the present invention, in which the vertical axis represents the first evaluation value α and the horizontal axis represents the average difference. FIG. 6B shows the results using the conventional evaluation values of similarity, with the vertical axis representing the similarity and the horizontal axis representing the average difference. The hollow plot in FIG. 6 shows the human body finger, and the black-painted plot shows the camouflaged finger. From FIG. 6, in the similarity, which is the conventional evaluation value, the human body finger has a value close to 1, while the camouflaged finger has a maximum value of 0.988, and most of them have a value of 0.9 or more. However, in the first evaluation value α of the present invention, the human finger has a value close to 1, while the camouflaged finger has a maximum value of 0.692, which is very often the human finger and the camouflaged finger. It can be seen that the distinction is made and the discrimination accuracy is improved.

Next, FIG. 7 shows the results of an experiment for evaluating the second evaluation value β calculated by the evaluation value calculation unit 81 according to the present invention. This was also measured using a conventional series type 10 GHz CSRR-BPF for CSRR-BPF2. As described above, the second evaluation value β is an evaluation value calculated by the equation (4), in which the weight w _f (f) for each frequency is introduced into the average difference which is the conventional evaluation value. Silicone rubber processed to a size of 22.0 mm × 14.0 mm was used as a camouflage to be attached to the human finger. In particular, when a 0.1 mm thick silicone rubber is used as a camouflage, the difference from the human finger becomes small in the high frequency range of the passage characteristic | S21 |. Therefore, in order to emphasize the difference due to the camouflage in the frequency band of 12 GHz or less, w _f (f) = 0 at 12-16 GHz and w _f (f) = 1 at 5-12 GHz. FIG. 7A shows the results using the second evaluation value β of the present invention, in which the horizontal axis represents the second evaluation value β and the vertical axis represents the first evaluation value α. FIG. 7B shows the result using the average difference which is the conventional evaluation value, and the horizontal axis is the average difference and the vertical axis is the first evaluation value α. Since it is difficult to understand the difference at first glance just by looking at FIG. 7, in order to perform a quantitative evaluation, the above-mentioned FAR when the FRR is 0% and the FRR when the FAR is 0% are used for evaluation. The results are shown in Table 2 below. _{By introducing an appropriate weight w f} (f) using the second evaluation value β according to the present invention, the FRR (FAR = 0%) is improved from 5.2% to 1.7%, and the discrimination accuracy is improved. You can see that it is improving.

Based on the above, the CSR-BPF2 of the biological detection device 1 according to the present invention, and the first evaluation value α and the second evaluation value β calculated by the evaluation value calculation unit 81 are all described in the conventional Patent Document 1. It contributes to the improvement of the discrimination accuracy as compared with the one used in the described biological detection device, and by using the biological detection device 1 according to the present invention, it is possible to perform biological detection with high discrimination accuracy.

The embodiment of the present invention is not limited to the above, and can be appropriately changed without departing from the scope of the idea of the present invention.

The biometric detection device according to the present invention can be effectively used as a highly reliable information security technology by using it in combination with personal biometric authentication technology such as fingerprint authentication and vein authentication, for example.

1 Biometric detection device 2 CSRR-BPF
3 Measurement unit 7 Storage unit 81 Evaluation value calculation unit 82 Biological judgment unit

Claims (3)

A bandpass filter having a split ring resonator designed at a predetermined center frequency according to the detection target site of the subject,
A measuring unit that generates electromagnetic waves and measures the electromagnetic wave response characteristics in a predetermined frequency band when the detection target portion is brought close to or in contact with the band pass filter.
An evaluation value calculation unit that calculates an evaluation value using the measured value of the electromagnetic wave response characteristic measured by the measurement unit and a reference value of the electromagnetic wave response characteristic of a living body.
A biological detection device including a biological determination unit that determines whether or not the detection target site is a living body based on the evaluation value calculated by the evaluation value calculation unit.
The evaluation value calculation unit
The measured value of the electromagnetic wave response characteristic measured by the measuring unit is S (f), the reference value of the electromagnetic wave response characteristic of the living body is T (f), the standard deviation of T (f) is σ (f), and the following. The concordance index represented by the equation (2) is k (f), the weight function corresponding to k (f) is w _v (k (f)), the weight function for each frequency is w _f (f), and the evaluation is performed. When the lower limit of the frequency band used is f _L and the upper limit is f _H ,
A biological detection device characterized in that a first evaluation value α represented by the following equation (1) is calculated as the evaluation value.

The weighting function w _v (k (f))
When the predetermined threshold is p,
The biological detection device according to claim 2, wherein the function is represented by the following equation (3).

The evaluation value calculation unit
The biological detection according to claim 2 or 3, wherein as the evaluation value, a second evaluation value β represented by the following formula (4) is calculated in addition to the first evaluation value α. Device.

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