JP2019037664A - Living body detection device - Google Patents

Abstract

To provide a living body detection device having discrimination accuracy improved as compared with conventional ones by downsizing a living body sensor and, on the other hand, introducing a new evaluation index.SOLUTION: A living body detection device comprises: a band pass filter including a split-ring resonator; a measurement unit for measuring an electromagnetic wave response characteristic; an evaluation value calculation unit for calculating an evaluation value; and a living body determination unit for performing living body determination on the basis of the evaluation value. The band pass filter has a structure in which two sets of complementary split-ring resonators, each of which includes a large and small two split-ring resonators arranged coaxially so that directions of the inside and outside resonators' split parts are opposite to each other, are arranged coaxially.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a living body detection apparatus that determines whether a detection target is a living body.

  Biometric authentication techniques such as fingerprint authentication and vein authentication use information that only the person can have, and are therefore more convenient and secure than authentication using conventional IC cards and passwords. However, since there is a concern about “spoofing” damage using physical impersonation that simulates the biometric information of another person, in addition to biometric authentication technology, biometric detection technology for discriminating between living organisms and impersonation is used in combination. This is very important.

  Accordingly, one of the inventors of the present invention has made a BPF (Band-R) in which two sets of CSRR (Complementary Split-Ring Resonator) structures are arranged in series on the ground plane of a microstrip line. pass filter (bandpass filter) (CSRR-BPF) is used as a living body detection sensor, and the electromagnetic wave response characteristic when the detection target part of the subject is brought close to or in contact with the CSRR-BPF is measured. There has already been reported a living body detection apparatus that determines whether a detection target part is a living body or a fake using two evaluation indexes, that is, an average difference calculated from a reference value of a living body and a similarity (Patent Document 1).

JP2015-111798

  The living body detection apparatus described above can determine whether a living body or a fake with a certain degree of accuracy. However, it is not possible to completely eliminate false detections for thin imitations with characteristics close to the human body, such as a skin phantom that simulates the electrical constant of the skin on the surface of the human finger, and further reduces false detection and detection. There was a need for improved accuracy.

  As a cause of erroneous detection, the CSRR-BPF used as a biological detection sensor in the above-described biological detection device has a structure in which two sets of CSRR structures are arranged in series. When covering the CSRR part which is a mounting area | region of CSRR-BPF with the attached finger | toe, it was thought that the dispersion | variation by the incompleteness of adhesiveness came out as one cause. Therefore, if the placement area of the detection target part of the biological detection sensor can be reduced, it is expected that the adhesion between the detection target part and the biological detection sensor can be stably secured, leading to a reduction in false detection. There has been a demand for further downsizing the living body detection sensor.

  On the other hand, it has been necessary to review the two evaluation indexes, that is, the average difference and the similarity, which are used in the above-described living body detection apparatus for discrimination between a living body and a fake. The measured value of the electromagnetic wave response characteristic has a certain variance due to variations in covering the CSRR portion as described above even for the same detection target part of the same specimen, but the similarity is an evaluation index that does not allow this variance. It was considered that there was a cause of the above-described false detection. Therefore, in place of the similarity, a new electromagnetic wave response characteristic can be dispersed when no fake material is attached, while a change in the electromagnetic wave response characteristic when a fake material is attached can be emphasized and extracted. It was necessary to introduce an evaluation index. Further, it has been required to improve the average difference so that the discrimination accuracy is further improved.

  The present invention has been made in view of the above circumstances, and it is possible to reduce the size of the living body detection sensor so as to reduce the variation at the time of measurement, and on the other hand, a new evaluation that can tolerate the variation at the time of measurement. It is an object of the present invention to provide a living body detection apparatus with improved discrimination accuracy by introducing an index.

  A living body detection apparatus according to the present invention generates a band-pass filter having a split ring resonator designed to have a predetermined center frequency according to a detection target part of a subject, an electromagnetic wave, and passes the band through the detection target part. A measurement unit that measures electromagnetic wave response characteristics in a predetermined frequency band when approaching or contacting a filter, a measurement 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 An evaluation value calculation unit that calculates an evaluation value by using, and a living body determination unit that determines whether or not the detection target part is a living body based on the evaluation value calculated by the evaluation value calculation unit. A biological detection apparatus comprising: a band-pass filter having a complementary (complementary) spring in which two large and small split ring resonators are arranged on the same axis so that the split portions are reversed on the inner side and the outer side. The string resonator, and having a structure disposed on 2 pairs coaxially.

A living body detection apparatus according to the present invention generates a band-pass filter having a split ring resonator designed to have a predetermined center frequency according to a detection target part of a subject, an electromagnetic wave, and passes the band through the detection target part. A measurement unit that measures electromagnetic wave response characteristics in a predetermined frequency band when approaching or contacting a filter, a measurement 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 An evaluation value calculation unit that calculates an evaluation value by using, and a living body determination unit that determines whether or not the detection target part is a living body based on the evaluation value calculated by the evaluation value calculation unit. A biological detection apparatus comprising: the evaluation value calculation unit S (f) for the measured value of the electromagnetic wave response characteristic measured by the measurement unit, T (f) for the reference value of the electromagnetic wave response characteristic of the biological body, Standard deviation of T (f) The sigma (f), the consistency index represented by the following formula (2) k (f), a weight function corresponding to _{k (f) w v (k} (f)), the weight function for each frequency When 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 α represented by the following expression (1) is calculated as the evaluation value. It is characterized by.

Furthermore, in the living body detection device according to the present invention, the weight function w _v (k (f)) is a function represented by the following expression (3), where p is a predetermined threshold value. Features.

  Further, in the living body detection device according to the present invention, the evaluation value calculation unit includes the second evaluation value β represented by the following expression (4) in addition to the first evaluation value α as the evaluation value. Is calculated.

  According to the living body detection device according to the present invention, the CSRR-BPF has a structure in which two sets of CSRRs are arranged on the same axis. Therefore, compared with a structure in which two sets of conventional CSRRs are arranged in series, Since the mounting area when covering the CSRR part with the part can be reduced, the variation in measuring the electromagnetic wave response characteristic is reduced, thereby improving the accuracy of determining whether the detection target part is a living body.

  According to the living body detection device of the present invention, the first evaluation value α is calculated as the evaluation value by the evaluation value calculation unit, and this first evaluation value α is an electromagnetic wave response in the case of a living body with no impersonation attached. Since this is an evaluation value that allows variation in the measured value of the characteristic, while emphasizing and extracting the change in the measured value of the electromagnetic wave response characteristic when the camouflage is attached, compared to the similarity that is the conventional evaluation value, The accuracy of determining whether or not is improved.

Furthermore, by appropriately setting the weighting 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.

In addition to the first evaluation value α, the evaluation value calculation unit calculates a second evaluation value β in addition to the first evaluation value α. The second evaluation value β is an average difference that is a conventional evaluation value. It is an evaluation value that introduces a weighting function w _f (f) for each frequency, and the accuracy of determining whether or not it is a living body is improved by appropriately setting w _f (f) with an assumed fake or the like.

It is a schematic block diagram which shows an example of the biometric apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows an example of CSRR-BPF which concerns on embodiment of this invention, Comprising: (a) has shown the upper surface side, (b) has shown the bottom face side. It is an expansion schematic diagram which shows a part of CSRR-BPF which concerns on embodiment of this invention, Comprising: (a) has shown A part enclosed with the dashed-two dotted line in FIG. 2, (b) is 2 in FIG. A portion B surrounded by a dotted line is shown. It is a graph which shows passage characteristic | S21 | of CSRR-BPF which arranged CSRR-BPF concerning the embodiment of the present invention, and two conventional CSRRs in series. It is a graph which shows the experimental result performed in order to compare CSRR-BPF which concerns on embodiment of this invention, and CSRR-BPF by which 2 sets of conventional CSRR were arrange | positioned in series. (A) is a graph regarding CSRR-BPF according to an embodiment of the present invention, and (b) is a graph regarding CSRR-BPF in which two conventional CSRRs are arranged in series. It is a graph which shows the experimental result performed in order to compare the 1st evaluation value (alpha) which concerns on embodiment of this invention, and the similarity degree which is the conventional evaluation value. (A) is a graph regarding the 1st evaluation value (alpha) which concerns on embodiment of this invention, (b) is a graph regarding the similarity which is a conventional evaluation value. It is a graph which shows the experimental result performed in order to compare the 2nd evaluation value (beta) which concerns on embodiment of this invention, and the average difference which is a conventional evaluation value. (A) is a graph regarding the 2nd evaluation value (beta) which concerns on embodiment of this invention, (b) is a graph regarding the average difference which is a conventional evaluation value.

  An embodiment of a living body detection device according to the present invention will be described below with reference to the drawings. Similarly to Patent Document 1 described above, the living body detection apparatus 1 according to the present invention determines whether or not the detection target part of the human body that is the subject is a living body, in order to prevent the “spoofing” action caused by counterfeits. It is mainly used in combination with biometric authentication devices such as fingerprint authentication and vein authentication. As shown in FIG. 1, the living body detection apparatus 1 according to the present invention includes a BPF (Band Pass Filter) in which CSRR (Complementary Split Ring Resonator) is arranged. (Hereinafter referred to as CSRR-BPF) 2, a measurement unit 3 that measures electromagnetic wave response characteristics when the detection target part is brought close to or in contact with CSRR-BPF 2, and an electromagnetic wave response characteristic measured by the measurement unit 3 And a computer 4 that performs arithmetic processing and the like for biometric determination. As shown in FIGS. 2 and 3, the CSRR-BPF 2 according to the present invention has a structure in which two sets of CSRRs are arranged on the same axis. In the CSRR, two large and small split ring resonators (SRR) are arranged on the same axis so that the split portion is reversed between the inside and the outside, and as shown in FIG. 3, a pair of SRR21 and SRR22 Is a set of CSRR 23, and a pair of SRR 24 and SRR 25 is a set of CSRR 26. 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, an example in which only one CSRR-BPF 2 is arranged as shown in FIG. 1 is shown, but by arranging a plurality, the electromagnetic wave response characteristics of a plurality of detection target parts of the subject can be measured simultaneously. Alternatively, the electromagnetic wave response characteristics of the detection target portions of a plurality of subjects may be measured simultaneously.

  The CSRR-BPF 2 is designed to have a predetermined center frequency according to information desired to be obtained from the detection target part of the subject (human body), and has a CSRR that is strongly influenced by the adjacent medium. When a medium is brought close to the CSRR, the electromagnetic field distribution in the vicinity of the CSRR-BPF 2 changes due to the influence of the medium. Therefore, an electromagnetic field response in the depth direction of the medium, that is, an electromagnetic wave response characteristic can be obtained.

  Examples of the detection target part include a human finger that performs vein authentication and fingerprint authentication. The human finger is considered to be a layered structure of muscle, fat, and skin around the central bone. By defining the human finger as an approximate uniform medium using the volume ratio of each layer, and calculating the skin depth of the human finger based on its relative dielectric constant and conductivity, it is about 10 mm at 6 GHz and about 10 GHz at 10 GHz. It becomes about 2.5 mm at 5 mm and 16 GHz, and the electromagnetic field penetrating in the depth direction of the human finger attenuates as the frequency increases. Therefore, when designing the CSRR-BPF 2 of the living body detection apparatus 1 used in combination with vein authentication, vein authentication uses a three-dimensionally distributed blood vessel pattern as authentication information, and the camouflage is a three-dimensional structure imitating the blood vessel pattern. Therefore, it is considered effective to use the low frequency side that can acquire the electromagnetic wave response characteristics reflecting the characteristics of the entire human finger as the center frequency. On the other hand, when designing CSRR-BPF2 to be used in combination with fingerprint authentication, fingerprint authentication uses the pattern on the surface of the human finger tip as authentication information, and the impersonation is a thin film that mimics the pattern, which is attached to the surface of the human finger. Therefore, it is considered effective to set the high frequency side that can acquire the electromagnetic wave response characteristics reflecting the characteristics of the surface of the human finger as the center frequency. Also, the detection target part is not limited to the finger, but may be another part. In that case, the CSRR-BPF 2 may be designed with a frequency at which an appropriate characteristic can be obtained at the part as a center frequency.

  In the present embodiment, as in the case of Patent Document 1, the living body detection apparatus 1 used in combination with fingerprint authentication is assumed, and the CSRR-BPF 2 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. Moreover, FIG. 3 is the figure which expanded a part of CSRR-BPF2 in FIG. 2, Comprising: FIG. 3 (a) is the figure which showed the A section enclosed with the dashed-two dotted line in FIG. 2 (a), FIG. 3B is a diagram showing a portion B surrounded by a two-dot chain line in FIG. As described above, the skin depth of the human finger at 10 GHz is about 5 mm, and is about half that when the thickness of the human finger is assumed to be about 10 mm. Therefore, in CSRR-BPF2 designed with a center frequency of 10 GHz, It is considered that electromagnetic wave response characteristics reflecting 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 the electromagnetic wave response characteristics up to half the depth of the human finger include the surface skin, fat, muscle, and central bone. It can be expected that electromagnetic wave response characteristics reflecting the influence of the structure will be obtained. Therefore, CSRR-BPF 2 designed with a center frequency of 10 GHz is suitable for use in combination with fingerprint authentication because it can acquire electromagnetic wave response characteristics reflecting the influence specific 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, which is a dielectric substrate, as in the case of the CSRR-BPF of Patent Document 1, (relative permittivity ε _γ = 3.4, dielectric loss tangent tan δ = 0 0.005, substrate thickness: 1.0 mm) can be used. Copper foils are pasted on both surfaces of the surface of the dielectric substrate, and can be manufactured by cutting the transmission line and CSRR structure as shown in FIG. The hatched portion in FIGS. 2 and 3 is a copper foil. In addition, examples of dimensions of each part of the CSRR-BPF 2 designed with the center frequency of 10 GHz in the present embodiment are as follows: a1 = 26.0 mm, a2 = 19.5 mm, a3 = 10.6 mm, a4 in FIGS. = 4.8mm, a5 = 10.6mm, a6 = 7.35mm, a7 = 4.8mm, a8 = 7.35mm, a9 = 0.4mm, a10 = 0.2mm, a11 = 0.2mm, 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, 10 = is 1.6mm. When measuring electromagnetic wave response characteristics, it is necessary to cover the CSRR part of CSRR-BPF2 with a detection target part, but CSRR-BPF having a structure in which two CSRRs described in Patent Document 1 are arranged in series In this case, as in the present embodiment, in the design with the center frequency of 10 GHz, the length from end to end of the two sets of CSRRs is 6.3 mm, whereas in the present embodiment, one location is provided. Two sets of CSRRs are contained in a 4.8 mm square, and the CSRR part, that is, the mounting area, is reduced by 24% compared to the conventional case. The reduction of the mounting area makes it possible to locally obtain the difference in influence when the medium is brought close to the CSRR-BPF 2, leading to reduction of false detection due to insufficient adhesion of the medium and improvement of detection accuracy. .

  The ports P1 and P2 provided at both ends of the CSRR-BPF 2 are provided with connectors (not shown), respectively, and are connected to the measuring unit 3 via the coaxial cable 5 as shown in FIG. Yes. Further, a polypropylene film having a thickness of about 0.2 mm may be installed on the CSRR-BPF 2 in order to flatten the level difference of the CSRR due to wear or the like and to prevent the copper foil from corroding.

  The measurement unit 3 is configured by, for example, a vector network analyzer or the like, and generates an electromagnetic wave for measurement, enters the CSRR-BPF2, and brings the detection target part close to or in contact with the CSRR-BPF2. Measure the electromagnetic wave response characteristics. As the electromagnetic wave response characteristics, when the input / output terminals of the CSRR-BPF 2 are two ports P1 and P2 as in this embodiment, the transmission characteristics S21 that enters the port P1 and passes through the port P2 and the port P2 enter. The transmission characteristic S12 passing through the port P1, the reflection characteristic S11 incident on the port P1 and reflected on the port P1, and the reflection characteristic S22 incident on the port P2 and reflected on the port P2 are acquired. I can do it.

  The measured value of the electromagnetic wave response characteristic measured by the measurement unit 3 is input to the computer 4. The computer 4 performs arithmetic processing or the like for biometric determination of whether or not the detection target site is a living body using the input measurement value of the electromagnetic wave response characteristics. For example, a CPU (Central Processing Unit: CPU) 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. As shown in FIG. 1, these units are connected to a system bus 12, and 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 measurement value of the electromagnetic wave response characteristic input from the measurement unit 3, and a processing program for performing a living body determination as to whether or not the detection target site is a living body. Storing. Although the storage unit 7 is provided in this embodiment, other external computer-readable storage media may be used.

  The arithmetic processing unit 8 performs arithmetic processing for determining whether or not the detection target part is a living body under the control of the CPU 6 based on a processing program stored in the storage unit 7. The evaluation value calculation unit 81 of the calculation processing unit 8 calculates an evaluation value by using the measured value of the electromagnetic wave response characteristic of the detection target part and the reference value of the living body, and the calculation processing unit based on the calculated evaluation value The living body determination unit 82 determines whether the detection target part is a living 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. The living body determination result may be notified by voice instead of the display unit 10 or together with the display unit 10. The operation unit 11 includes a mouse, a keyboard, and the like, and is used by an operator to input various data and operation commands. The display unit 10 and the operation unit 11 may be integrally configured as a touch panel.

  Hereinafter, the flow of the living body detection process by the living body detection apparatus 1 will be described. First, the subject to be detected brings the detection target part close to or in contact with CSRR-BPF2. At that time, the CSRR part of CSRR-BPF2 is covered with the detection target part. Then, the electromagnetic wave response characteristic S (f) in a predetermined frequency band is measured by the measuring unit 3. In the present embodiment, the CSRR-BPF 2 designed with a center frequency of 10 GHz for fingerprint authentication is used, the detection target part is the part from the first joint of the right index finger, and the electromagnetic wave response characteristic is a pass characteristic S21 at 3 GHz to 16 GHz. The absolute value of | S21 | is used. However, the present invention is not limited to this, and any finger may be used as the detection target part, or a part other than the finger may be used for fingerprint authentication. In that case, the CSRR-BPF 2 may be designed with a center frequency corresponding to the information desired to be obtained. Further, the electromagnetic wave response characteristic is not limited to the transmission characteristic | S21 |, but other transmission characteristics | S12 |, reflection characteristics | S11 |, or reflection characteristics | S22 | may be used. A plurality of these may be used. Moreover, you may change also about the frequency band which measures electromagnetic wave response characteristics according to the characteristic of 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 an evaluation value using the input measurement 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. In the present embodiment, the storage unit 7 performs measurement a plurality of times in advance under the same measurement conditions as the measurement value S (f). Using the measured values of the electromagnetic wave response characteristics of the detection target part of the subject stored in the above, the average of these values 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. For calculation of the reference value T (f), a fixed number of measured values of the electromagnetic wave response characteristics may be used. However, as the number of measured values used increases, the reliability of the reference value T (f) increases and the error is increased. Since it is thought to lead to a reduction in detection, whenever it is determined that it is a living body after the living body determination, the measured value S (f) is stored in the storage unit 7 every time the living body is determined, You may add to the measured value used for calculation of T (f). In this case, for example, when used in combination with fingerprint authentication, it is considered that the biometric detection device 1 determines whether or not it is a living body after it is determined that the fingerprints match in the fingerprint authentication. The measurement value of the response characteristic may be associated and stored in the storage unit 7. Here, the reference value T (f) is obtained by averaging the measured values of the electromagnetic wave response characteristics, but is not limited thereto, and other statistical values such as a median value may be used. Here, the measurement value of the detection target part of the subject that has been measured in advance is used to calculate the reference value T (f). However, a part other than the detection target part, for example, the detection target part is the right index finger. If so, other measured values of electromagnetic wave response characteristics such as the middle finger and ring finger may be used. In this case, the measurement value for calculating the reference value T (f) is not stored in the storage unit 7, and a plurality of CSRR-BPFs 2 are arranged to measure the electromagnetic wave response characteristic S (f) of the detection target part. At the same time, the reference value T (f) may be calculated such that the electromagnetic wave response characteristics of the non-detection target part used for the reference value T (f) can be measured. In addition, the electromagnetic wave response characteristics of a plurality of detection target parts different from the subject are measured in advance, and the measurement values are stored in the storage unit 7, and the reference value T (f) is calculated using these measurement values. May be. However, in order to improve the discrimination accuracy, it is preferable to calculate the reference value T (f) using the measured value of the electromagnetic wave response characteristics of the same detection target part of the same subject as in this embodiment.

The evaluation value calculation unit 81 calculates a first evaluation value α represented by the following formula (1) as an evaluation value. Here, k (f) is the coincidence 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). Is an index, w _v (k (f)) is a weighting function that performs weighting according to the coincidence index k (f) expressed by Equation (3), p is a predetermined threshold value, and w _{f (f)} is a weighting function for weighting of each frequency, the lower limit of the frequency band is f _L used, the f _H is the upper limit. First, the consistency weight w _v (k (f)) is calculated by the equations (2) and (3). The consistency weight function w _v (k (f)) takes a value from 0 to 1, and the closer 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 a range of p times the standard deviation σ (f) of the reference value T (f), it is determined that there is consistency and the consistency weight w _v (k (f)) = 1, and if it exceeds that, it is assumed 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, the condition of the subject such as the sweating state at the time of measurement, and the proximity of the detection target part to the CSRR-BPF 2 It has a certain variance depending on how it is applied. Therefore, even if the measured value S (f) is from the same detection target part of the same subject as the reference value T (f), the measured value S (f) may be a value that is far from the reference value T (f). The threshold value p determines how far away the values are regarded as being equal to the reference value T (f). In this embodiment, p = 2.7 is used. This value is obtained when the measured value of the electromagnetic wave response characteristic of the detection target part of the subject for a plurality of times used for calculating the reference value T (f) follows a normal distribution, the measured value S (f) is the reference value T (f ) Means that the measured value S (f) falls within a range where w _v (k (f)) = 1 at a probability of 99.3%. If the threshold value p is too large, the probability that the measured value S (f) of the camouflage will be regarded as coincident with the reference value T (f) is increased. If the threshold value p is too small, 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. In the present embodiment, the expression (3) is used to calculate the consistency weight function w _v (k (f)). However, the present invention is not limited thereto, and is appropriately set depending on the type and thickness of the assumed disguise. Thus, the discrimination accuracy can be improved. A value obtained by multiplying the consistency weight w _v (k (f)) by the weight w _f (f) for each frequency and using the arithmetic frequency in the frequency band to be used by the expression (1) is set as the first evaluation value α. calculate. Here, the weighting function w _f (f) for performing weighting for each frequency reduces the influence on the evaluation value in a frequency band in which a 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 possible to improve the discrimination accuracy by appropriately setting depending on the type and thickness of the assumed fake material. 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)} = 0. Since the consistency weight function w _v (k (f)) and the frequency-specific weight function w _f (f) both take values from 0 to 1, the first evaluation value α is also from 0 to 1. The evaluation value is a value closer to 1, and the closer the value is to 1, the higher the possibility that the measured value S (f) is due to a living body.

On the other hand, as described in Patent Document 1, conventionally, the similarity is calculated and used as the evaluation value. Similarity (Similarity) is calculated by the following formula (5). Here S (f) is the measured value of the electromagnetic response characteristics measured by the measurement unit 3, T (f) is the reference value, f _H is the upper limit of the frequency band used, f _L is the lower limit, the first of the above mentioned The same as that used for the evaluation value α. S _norm (f) is expressed by equation (6), and is a value obtained by normalizing the measured value S (f) so that the minimum value of S _norm (f) matches the minimum value of the reference value T (f). Yes, D _n is expressed by equation (7), and is the difference between the minimum value in the frequency band to be used between the measured value S (f) and the reference value T (f). As can be seen from these equations, the similarity does not take into account variations in the measured value of the electromagnetic wave response characteristic used to calculate the reference value T (f). The evaluation value was difficult to appear. On the other hand, the first evaluation value α calculated by the present invention allows variation in the measured value of the electromagnetic wave response characteristics in the case of a living body without attachment of a camouflage as described above. 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 camouflage.

In addition to the first evaluation value α, the evaluation value calculation unit 81 calculates a second evaluation value β expressed by the following formula (4) as an evaluation value. The second evaluation value β is obtained by adding a weight function w _{f for} each frequency to an average difference (Mean Difference, MD) represented by the following formula (8) used as a conventional evaluation value as described in Patent Document 1. (F) is introduced. The average difference is an evaluation value that averages the difference between the graph curves of the measured value S (f) and the reference value T (f). The closer the value is to 0, the more the measured value S (f) is from the living body. The higher the value, the higher the possibility that the measured value S (f) is due to the camouflage.

  In the living body determination unit 82, based on the two evaluation values of the first evaluation value α and the second evaluation value β calculated by the evaluation value calculation unit 81, whether or not the detection target site is a living body is determined. Make a decision. In the living body 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 are 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 included. That is, when the first evaluation value α and the second evaluation value β calculated by the evaluation value calculation unit 81 are both within the threshold value, it is determined that the detection target part is a living body, and other than that In this case, it is determined that the detection target part is not a living body. Note that the living body 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 first evaluation value α It is preferable to use two evaluation values such as an evaluation value β of 2.

  The above is the flow of the biological detection processing by the biological detection device 1 according to the present embodiment. Hereinafter, the biological detection device 1 according to the present invention, which is an improvement from the conventional biological detection device described in Patent Document 1, will be described. An experiment for evaluating how much the discrimination accuracy is improved by the CSRR-BPF2 and the first evaluation value α and the second evaluation value β calculated by the evaluation value calculation unit 81 is performed. Results are shown.

  First, the experimental result about CSRR-BPF2 which has a structure where two CSRRs according to the present invention are arranged on the same axis is shown. The structure of CSRR-BPF2 of the present invention is as shown in FIGS. In the CSRR-BPF having a structure in which two sets of conventional CSRRs are arranged in series, when measuring the electromagnetic wave response characteristics of the detection target part, both the two sets of CSRRs arranged in series are covered with the detection target part. Although it was necessary, in the CSRR-BPF 2 according to the present invention, two sets of CSRRs are arranged in one place, so that it is easy to cover the detection target part. As described above, the CSRR portion of the CSRR-BPF2 (coaxial type 10 GHz CSRR-BPF2) having a structure in which two sets of CSRRs designed with a center frequency of 10 GHz according to the present invention are arranged on the same axis is 4.8 mm square. On the other hand, in the CSRR-BPF (series type 10 GHz CSRR-BPF) having a structure in which two sets of CSRRs designed at a center frequency of 10 GHz are arranged in series, the two sets of CSRR sections are connected from end to end. The dimension was 6.3 mm, and the placement area of the detection target part was reduced by about 24%.

  FIG. 4 shows the measurement results of the pass characteristic | S21 | of the coaxial 10 GHz CSRR-BPF 2 of the present invention and the conventional serial 10 GHz CSRR-BPF. A solid line is a measurement result of the coaxial 10 GHz CSRR-BPF 2 of the present invention, and a bandwidth is approximately 12 GHz from 4 GHz to 16 GHz. A dotted line is the measurement result of the conventional serial type 10 GHz CSRR-BPF, and the bandwidth is about 4 GHz from 8 GHz to 12 GHz. It can be seen that the operating frequency band is widespread.

  Furthermore, the result of the living body detection experiment using the coaxial 10 GHz CSRR-BPF 2 of the present invention and the conventional serial 10 GHz CSRR-BPF is shown in FIG. 20 subjects were measured 10 times per person using the right index finger without a fake attachment as a human finger, and the electrical constant of the skin on the surface of the human finger, which is a fake finger, was simulated. The processed 0.3 mm-thick skin phantom was processed into a sheet shape and attached to the right index finger, and measurement was performed 5 times per person. Here, the conventional similarity and average difference were used for the evaluation value calculated by the evaluation value calculation unit 81. This is to compare and evaluate how much the discrimination accuracy is improved by the CSRR-BPF 2 according to the present invention. In addition, a value obtained by averaging five measurement values of human fingers of all subjects is used as the reference value T (f), and a measurement value S (f) to be detected is used to calculate the reference value T (f). Five human finger measurements and fake finger measurements were used. Further, from FIG. 4, the coaxial type 10 GHz CSRR-BPF 2 of the present invention has the minimum pass characteristic | S21 | at 16 GHz, so the frequency band for searching the minimum value used for calculating the similarity is calculated as 5 to 16 GHz. In both the present invention and the conventional method, measurement was performed by placing a polypropylene film having a thickness of 0.2 mm on the surface of CSRR-BPF. FIG. 5A shows the result of the coaxial 10 GHz CSRR-BPF 2 according to the present invention. The vertical axis indicates similarity, the horizontal axis indicates the average difference, the hollow plot indicates a human finger, and the black plot indicates a camouflaged finger. . FIG. 5B shows the result of the conventional serial 10 GHz CSRR-BPF. The vertical axis represents the similarity, the horizontal axis represents the average difference, the hollow plot indicates the human finger, and the black plot indicates the fake finger. FIG. 5 shows that the coaxial type 10 GHz CSRR-BPF 2 of the present invention separates the plots of the human finger and the camouflaged finger from the conventional series type 10 GHz CSRR-BPF, but the evaluation is more quantitative. In order to do this, the rate at which the rate at which a fake is determined to be a living body (False Acceptance Rate, FAR) is 0%, and the rate at which the body is determined to be a fake (False Rejection Rate, FRR). Evaluation was made using FAR and a value (Equal Error Rate, EER) at which FAR and FRR are equal. The results are shown in Table 1 below. Here, the FRR when the FAR is set to 0% indicates a ratio at which a human finger is not accepted when a threshold value is set that does not accept all the fake fingers used for measurement. Specifically, the percentage of human fingers that do not enter the area below the minimum value of the average value of the fake fingers and above the maximum value of the similarity, with the minimum value of the average difference of the fake fingers and the maximum value of the similarity as threshold values It is. The FAR when the FRR is set to 0% indicates the ratio of accepting a fake finger when a threshold value for accepting all human fingers used for measurement is provided. Specifically, with the maximum value of the average difference of the human fingers and the minimum value of the similarity as threshold values, the impersonator that enters the area 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 indices are, the higher the discrimination accuracy is. Table 1 shows that the coaxial type 10 GHz CSRR-BPF 2 according to the present invention has more significant results in all of FRR (FAR = 0%), FAR (FRR = 0%), and EER than the conventional serial type 10 GHz CSRR-BPF. It can be seen that the discrimination accuracy is improved.

Next, FIG. 6 shows a result of an experiment for evaluating the first evaluation value α calculated by the evaluation value calculation unit 81 according to the present invention. Here, the first evaluation value α of the present invention is compared with the similarity that is the conventional evaluation value, and in order to evaluate how much the discrimination accuracy is improved by the first evaluation value α, the CSRR-BPF 2 includes A serial 10 GHz CSRR-BPF similar to the conventional one was used. As described above, the first evaluation value α is calculated by the equations (1) to (3). Here, the threshold value p is p = 2.7, and the weight w _f (f) for each frequency is the frequency to be used. W _f (f) = 1 in the entire band. As a camouflage worn on 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 result of using the first evaluation value α of the present invention. The vertical axis represents the first evaluation value α, and the horizontal axis represents the average difference. FIG. 6B shows the result of using the similarity that is a conventional evaluation value, where the vertical axis represents the similarity and the horizontal axis represents the average difference. A hollow plot in FIG. 6 indicates a human finger, and a black plot indicates a fake finger. As shown in FIG. 6, in the similarity that is the conventional evaluation value, the human finger is a value close to 1, whereas the fake finger has a maximum value of 0.988, and most of the values are 0.9 or more. However, in the first evaluation value α of the present invention, the human finger is a value close to 1, whereas the fake finger has a maximum value of 0.692, which is very good. It can be seen that the discrimination accuracy is improved.

Next, FIG. 7 shows the result 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 10 GHz CSRR-BPF for CSRR-BPF2. As described above, the second evaluation value β is calculated by the equation (4), and is an evaluation value in which the weight w _f (f) for each frequency is introduced into the average difference that is the conventional evaluation value. As a camouflage worn on the human finger, silicon rubber processed to a size of 22.0 mm × 14.0 mm was used. In particular, when using 0.1 mm-thick silicon rubber as a camouflage, the difference from the human finger becomes small in the high range of the passing characteristic | S21 |. For this reason, in order to emphasize the difference due to the camouflage in the frequency band of 12 GHz or less, w _f (f) = 0 was set at 12-16 GHz and w _f (f) = 1 was set at 5-12 GHz. FIG. 7A shows the result of using the second evaluation value β of the present invention. The horizontal axis represents the second evaluation value β, and the vertical axis represents the first evaluation value α. FIG. 7B shows the result of using the average difference, which is a conventional evaluation value. The horizontal axis represents the average difference, and the vertical axis represents the first evaluation value α. Since it is difficult to understand the difference at first glance simply by looking at FIG. 7, in order to perform quantitative evaluation, evaluation was performed using the FAR when the FRR was set to 0% and the FRR when the FAR was set to 0%. 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, FRR (FAR = 0%) is improved from 5.2% to 1.7%, and the discrimination accuracy is improved. It can be seen that it has improved.

  As described above, the CSRR-BPF 2 of the living body detection apparatus 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 respectively described in the conventional Patent Document 1. It contributes to the improvement of discrimination accuracy than that used in the described living body detection device, and by using the living body detection device 1 according to the present invention, living body detection with high discrimination accuracy can be performed.

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

  The biometric detection apparatus according to the present invention can be effectively used as a highly reliable information security technique by using it in combination with personal biometric authentication techniques such as fingerprint authentication and vein authentication.

1 Living body detection device 2 CSRR-BPF
3 Measurement Unit 7 Storage Unit 81 Evaluation Value Calculation Unit 82 Biological Determination Unit

Claims (4)

A band-pass filter having a split ring resonator designed at a predetermined center frequency according to the detection target part of the subject;
A measuring unit that generates an electromagnetic wave and measures an electromagnetic wave response characteristic of a predetermined frequency band when the detection target part is brought close to or in contact with the band pass filter;
An evaluation value calculation unit that calculates an evaluation value using the measurement value of the electromagnetic wave response characteristic measured by the measurement unit and the reference value of the electromagnetic wave response characteristic of the living body,
A living body detection device comprising: a living body 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 band pass filter is
Two pairs of large and small split ring resonators are coaxially arranged so that the split portions are reversed on the inner side and the outer side, and two sets of complementary split ring resonators are arranged on the same axis. The living body detection apparatus characterized by the above-mentioned.
A band-pass filter having a split ring resonator designed at a predetermined center frequency according to the detection target part of the subject;
A measuring unit that generates an electromagnetic wave and measures an electromagnetic wave response characteristic of a predetermined frequency band when the detection target part is brought close to or in contact with the band pass filter;
An evaluation value calculation unit that calculates an evaluation value using the measurement value of the electromagnetic wave response characteristic measured by the measurement unit and the reference value of the electromagnetic wave response characteristic of the living body,
A living body detection device comprising: a living body 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 measurement 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 consistency 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), When the lower limit of the frequency band to be used is f _L and the upper limit is f _H ,
A living body detection apparatus that calculates a first evaluation value α represented by the following expression (1) as the evaluation value.

The weight function w _v (k (f)) is
When the predetermined threshold value is p,
The living body detection apparatus according to claim 2, wherein the living body detection apparatus is a function represented by the following expression (3).

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

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