JP2019076178A - Biological signal detector - Google Patents

Abstract

To provide a biological signal detector capable of accurately detecting a biological signal of a subject.SOLUTION: A biological signal detector 10 includes: a light source 100 for irradiating a first polarized light consisting of a near infrared ray onto a skin surface of a subject M; a main light reception part 211 for receiving a light reflected or scattered by the skin of the subject M after the light is applied from the light source 100; a main polarization filter 221 arranged at a position between the subject M and the main light reception part 211 so as to cause only a second polarized light having a polarization surface different from a polarization surface of the first polarized light to reach the main light reception part 211; and a signal detection part 330 for detecting a change in the brightness of the second polarized light received by the main light reception part 211 as a biological signal.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a biological signal detection apparatus that detects a biological signal of a subject.

  2. Description of the Related Art In recent years, studies on mounting a biological signal detection apparatus for detecting a biological signal such as a pulse on a vehicle have been advanced. In a vehicle equipped with a biomedical signal detection device, it is possible to acquire the awakening state of the driver based on the biomedical signal and to cause the driver to wake up by sound, vibration or the like as needed. In addition, it is also possible to confirm the driver's health condition, the presence or absence of stress, etc. based on the biological signal.

  In the device described in Patent Document 1 below, the face of the subject is irradiated with infrared light, and the biological signal is detected based on the change in the intensity of the infrared light reflected by the skin surface of the subject. Moreover, in the said apparatus, it is possible to detect a biosignal with sufficient accuracy by excluding the influence on the brightness | luminance change by the direction of a subject changing.

JP, 2011-130996, A

  The present inventors are not based on the brightness change of the near-infrared light reflected on the skin surface of the subject, but the near-infrared light reflected or scattered after reaching the blood inside the skin of the subject (in other words, Based on the change in brightness of near infrared rays not absorbed by the blood inside the skin of a subject, investigations have been made on detection of biosignals. According to such a method, it is possible to directly detect a change in blood flow, that is, a pulsation of a blood vessel due to a heartbeat, without the movement of the skin surface. For this reason, it becomes possible to detect a precise biosignal without causing phase delay.

  However, near infrared rays are reflected or scattered by the skin surface and the epidermis without blood vessel distribution, and the amount of light reaching the inside of the skin where blood vessels are distributed tends to be small. Furthermore, the absorbance of near-infrared light to blood is lower than the absorbance of visible light to blood. As a result, the change in brightness of near infrared rays reflected or scattered by blood (i.e., the change in brightness indicative of a biological signal) is significantly smaller than the change in brightness of near infrared rays reflected by the skin surface. Therefore, it has been difficult to accurately detect a biological signal.

  Furthermore, not only the near infrared rays emitted from the light source but also the infrared rays entering from outside the vehicle through the window glass are incident on the occupant who is the subject. Such near infrared rays are reflected on the skin surface of the subject and become disturbances, making it even more difficult to detect a biosignal based on the change in brightness of the near infrared rays reflected or scattered by blood. It had become.

  An object of the present disclosure is to provide a biological signal detection apparatus capable of accurately detecting a biological signal of a subject.

  A biological signal detection apparatus (10) according to the present disclosure includes a light source (100) for emitting first polarized light composed of near-infrared light toward the skin surface of a subject (M), and a test object after being irradiated from the light source A subject to receive only the second light having the light receiving part (211) for receiving the light reflected or scattered by the skin of the person and the second polarized light having a polarization plane different from the polarization plane of the first polarized light, And a light receiving unit, and a signal detection unit (330) detecting a change in the brightness of the second polarized light received by the light receiving unit as a biological signal. .

  In the biological signal detection apparatus having such a configuration, the first polarized light composed of near-infrared light is irradiated from the light source onto the skin surface of the subject. A part of the light irradiated to the skin surface is reflected on the skin surface, but a part of the light is reflected or scattered by the blood after entering the inside of the skin.

  Most of the light reflected by the skin surface is light having the same (that is, parallel) polarization plane as the polarization plane of the first polarized light. On the other hand, in the light reflected or scattered after entering the inside of the skin, the proportion of light having a polarization plane different from the polarization plane of the first polarization is relatively high. The ratio tends to be higher as the position to be reflected or scattered becomes deeper.

  Therefore, in the above-described biological signal detection apparatus, all the light reflected or scattered on the skin surface and the inside of the subject does not reach the light receiving unit, but has a polarization plane different from the polarization plane of the first polarization. A polarization filter is disposed at a position between the subject and the light receiving unit so that only the second polarized light reaches the light receiving unit. Therefore, the light receiving portion can receive the light reflected or scattered from the blood distribution layer inside the skin, with little influence of the light reflected by the surface of the skin. Since the amplitude of the luminance of the light received by the light receiving unit (that is, the amplitude of the biological signal) can be made larger than the dynamic range of the light receiving unit, the biological signal can be detected with high accuracy.

  According to the present disclosure, a biological signal detection device capable of accurately detecting a biological signal of a subject is provided.

FIG. 1 is a view schematically showing a configuration of a biological signal detection apparatus according to the present embodiment. FIG. 2 is a view for explaining reflection and scattering of near infrared rays in the skin. FIG. 3 is a diagram showing a configuration of a light receiving unit provided in the biological signal detection apparatus. FIG. 4 is a diagram illustrating an example of an image captured by the light receiving unit. FIG. 5 is a graph showing an example of the change in luminance of near-infrared light reaching the light receiving unit. FIG. 6 is a flow chart showing the flow of processing executed by the control device included in the biological signal detection device. FIG. 7 is a flowchart showing the flow of processing executed by the control device included in the biological signal detection device.

  Hereinafter, the present embodiment will be described with reference to the attached drawings. In order to facilitate understanding of the description, the same constituent elements in the drawings are denoted by the same reference numerals as much as possible, and redundant description will be omitted.

  The configuration of the biological signal detection apparatus 10 according to the present embodiment will be described with reference to FIG. The biological signal detection apparatus 10 is an apparatus mounted on a vehicle (not shown in its entirety), and is configured as an apparatus for detecting a biological signal of the subject M who is an occupant of the vehicle. In the present embodiment, the heartbeat of the subject M is detected as a biological signal. Instead of such an aspect, an aspect may be employed in which a biosignal other than the heart rate (for example, a respiration rate or the like) is detected. In addition, another biosignal may be calculated based on the detected heartbeat.

  The biological signal of the subject M detected by the biological signal detection apparatus 10 is used to determine the awake state or the health state of the subject M. As a result, it is possible to perform processing such as awakening the subject M or transmitting the health status of the subject M to the outside as needed. In the following description, only the process performed to detect a biological signal by the biological signal detection apparatus 10 will be described, and the description of the process performed using the detected biological signal will be omitted.

  In FIG. 1, the face portion of the subject M seated in the driver's seat of the vehicle and the window glass G1 (front glass) located in front thereof are schematically illustrated in a side view. As shown in the figure, the biological signal detection apparatus 10 includes a light source 100, a camera 200, and a control device 300.

  The light source 100 is a device that emits near-infrared radiation toward the skin surface of the subject M. The light source 100 is installed at a position (for example, a ceiling) on the front side of the subject M in the vehicle compartment, and irradiates the face of the subject M with near-infrared light from the front side. The near-infrared light emitted from the light source 100 of the present embodiment is light of a single wavelength, and is a light (that is, polarization) in which the changing direction of the electric field is along a single polarization plane. The near infrared rays emitted from the light source 100 toward the subject M will be hereinafter also referred to as “first polarized light”.

  The camera 200 is a device for receiving light reflected or scattered by the skin of the subject M after being irradiated from the light source 100. The camera 200 is installed at a position on the front side of the subject M in the vehicle compartment and in the vicinity of the light source 100. The camera 200 includes the image sensor 210 (see FIG. 3) as will be described later, and can output the luminance distribution of the received near-infrared light as an image. The biological signal detection device 10 detects the pulse of the subject M based on the change (pulsation) of the brightness of the near-infrared light received by the camera 200.

  The control device 300 is a device for controlling the overall operation of the biological signal detection device 10. The control device 300 is configured as a computer system having a CPU, a ROM, a RAM, and the like. The control device 300 has an output adjustment unit 310, an exposure adjustment unit 320, a signal detection unit 330, and a correction unit 340 as functional control blocks.

  The output adjustment unit 310 is a part that adjusts the output of the light source 100. As described later, the output adjusting unit 310 adjusts the output of the light source 100 to keep the intensity of the light received by the camera 200 substantially constant. The term "intensity" as used herein refers to the average level of luminance that changes with a biological signal or the like. The same applies to the following description. The adjustment of the output of the light source 100 is performed, for example, by changing the duty of the control signal output to the light source 100.

  The exposure adjustment unit 320 is a part that adjusts the exposure time of the camera 200. As described later, the exposure adjusting unit 320 adjusts the exposure time of the camera 200 to keep the intensity of the light received by the camera 200 substantially constant.

  The signal detection unit 330 is a part that performs a process of detecting a change in luminance of light received by the camera 200 as a biological signal. Inside the skin of the subject M, the state in which the blood flow is increasing and the state in which the blood flow is decreasing are alternately repeated based on the heartbeat. In a state where blood flow is increasing, the proportion of near infrared rays absorbed by blood increases, and the brightness of near infrared rays reflected or scattered inside the skin and directed to the camera 200 decreases. Further, in a state where blood flow is reduced, the proportion of near infrared rays absorbed by blood decreases, so that the brightness of near infrared rays reflected or scattered inside the skin and directed to the camera 200 is increased. That is, the brightness of the near-infrared light received by the camera 200 changes in synchronization with the heartbeat. For this reason, the signal detection unit 330 can detect a change in the brightness of the near infrared light received by the camera 200 as the heartbeat of the subject M.

  The correction unit 340 is a part that performs a process of correcting the luminance of the light received by the camera 200. As described later, the correction unit 340 performs the above-described correction to suppress the fluctuation of the intensity of the first polarized light received by the camera 200.

  The reflection and scattering of near-infrared light in the skin of the subject M will be described with reference to FIG. The dotted line DL1 shown in FIG. 2 is a line indicating the surface of the skin of the subject M. The portion below the dotted line DL1 is the stratum corneum and the epidermal layer of the skin (hereinafter, these are collectively referred to as "epidermal layer SK1"). The dotted line DL2 shown in FIG. 2 is a line indicating the boundary between the epidermal layer SK1 of the skin and the dermal layer. The portion below the dotted line DL2 is also referred to as "dermal layer SK2" below. The epidermal layer SK1 is a portion of the skin where no blood vessels are distributed, and the dermal layer SK2 is a portion of the skin where blood vessels are distributed.

  The arrow labeled P01 in FIG. 2 is a first polarized light emitted from the light source 100 toward the subject M. Hereinafter, the first polarization is referred to as "first polarization P01". In the present embodiment, the polarization plane of the first polarized light P01 (specifically, the vibration plane of the electric field) is parallel to the incident plane of the first polarized light P01. That is, the first polarized light P01 in the present embodiment is so-called "P-polarized light".

  A part of the first polarized light P01 incident on the skin layer SK1 is reflected by the surface of the skin layer SK1. The arrow labeled P02 in FIG. 2 indicates the near infrared rays reflected in this manner. Below, the thing of the said near-infrared is described as "surface reflected light P02." The surface reflected light P02 is polarized light (that is, P polarized light) having the same polarization plane as the first polarized light P01.

  A part of the first polarized light P01 incident on the skin layer SK1 enters the inside of the skin layer SK1. The arrow labeled P11 in FIG. 2 indicates the near infrared rays entering the skin layer SK1 in this manner. Below, the said near-infrared thing is described with "the approach light P11."

  A part of the entering light P11 that has entered the epidermal layer SK1 further enters the interior of the dermal layer SK2 and is absorbed by the blood in the blood vessels in the dermal layer SK2. The arrow labeled P21 in FIG. 2 indicates the near infrared rays absorbed in this manner. Of the entering light P11 that has entered the epidermal layer SK1, one that has not been absorbed by the blood as described above is reflected or scattered, and a part thereof travels toward the surface side of the skin. The near infrared rays thus reflected or scattered include polarized lights having various polarization planes.

  Among the polarized light reflected or scattered as described above, the polarized light having the same polarization plane as the first polarized light P01 is hereinafter also referred to as "first internally reflected light P12". In addition, the polarized light having a polarization plane orthogonal to the polarization plane of the first polarized light P01 is hereinafter also referred to as "second internally reflected light S12". The polarization plane (specifically, the vibration plane of the electric field) of the second internally reflected light S12 is perpendicular to the incident plane of the first polarized light P01. That is, the second internally reflected light S12 in the present embodiment is so-called "S polarization". In FIG. 2, each of the first internally reflected light P12 and the second internally reflected light S12 is shown as an arrow directed outward from the position of the dotted line DL2.

  As described above, the near infrared rays reflected or scattered by the skin of the subject M include the surface reflected light P02, the first internally reflected light P12, and the second internally reflected light S12. As shown in FIG. 3, all of these near infrared rays reach the camera 200.

  The specific configuration of the camera 200 will be described with reference to FIG. The cross section of the camera 200 shown in FIG. 3 is a cross section parallel to the incident plane of the first polarized light P01. The camera 200 has a main camera unit 201 which is a lower half portion in FIG. 3 and a sub camera unit 202 which is an upper half portion in FIG.

  The main camera unit 201 includes a main lens 231, a main light receiving unit 211, and a main polarization filter 221.

  The main lens 231 is a lens for forming near infrared rays incident on the main camera unit 201 on a main light receiving unit 211 described later. The main lens 231 is supported by support walls 252 and 253 provided on the surface of the image sensor 210.

  The main light receiving unit 211 is a portion between the support wall 252 and the support wall 253 in the image sensor 210 which is a CMOS. The main light receiving unit 211 transmits, as data, an image indicating the brightness distribution of near infrared rays formed on the surface to the control device 300 described later.

  The main polarizing filter 221 is a polarizing filter disposed at a position between the subject M and the main light receiving unit 211. The main polarizing filter 221 of the present embodiment is supported by the support walls 252 and 253 at positions between the main lens 231 and the main light receiving unit 211. The main polarizing filter 221 is arranged to cause only the polarized light having a polarization plane different from the polarization plane of the first polarized light P01 to reach the main light receiving section 211. Specifically, the main polarizing filter 221 transmits only polarized light having a polarization plane perpendicular to the polarization plane of the first polarized light P01, and blocks other polarized light.

  Therefore, among the surface reflected light P02, the first internally reflected light P12, and the second internally reflected light S12 directed to the camera 200, the light passing through the main polarizing filter 221 and reaching the main light receiving portion 211 is the second inside. It is only reflected light S12. The second internally reflected light S12 that can reach the main light receiving unit 211 corresponds to the “second polarization” in the present embodiment. The signal detection unit 330 described above detects a change in luminance of the second internally reflected light S12 (second polarized light) received by the main light receiving unit 211 as a biological signal.

  The sub camera unit 202 includes a sub lens 232, a sub light receiving portion 212, a sub polarization filter 222, and a light reduction filter 242.

  The sub lens 232 is a lens for forming near infrared rays incident on the sub camera unit 202 on a sub light receiving portion 212 described later. The sub lens 232 is supported by support walls 251 and 252 provided on the surface of the image sensor 210.

  Shown at the bottom of FIG. 4 is an example of an image IM1 formed on the main light receiving unit 211 by the main lens 231. Further, what is shown in the upper part of FIG. 4 is an example of an image IM2 formed on the sub light receiving unit 212 by the sub lens 232. The image IM1 and the image IM2 are images showing almost the same area. That is, the field of view of the main lens 231 and the field of view of the sub lens 232 overlap each other. Thus, the sub lens 232, together with the main lens 231 of the main camera unit 201, constitutes a "field overlapping lens array".

  Returning to FIG. 3, the description will be continued. The sub light receiving unit 212 is a portion between the support wall 251 and the support wall 252 in the image sensor 210 which is a CMOS. The sub light receiving unit 212 transmits an image indicating the brightness distribution of near infrared rays formed on the surface as data to a control device 300 described later.

  The sub polarization filter 222 is a polarization filter disposed at a position between the subject M and the sub light receiving unit 212. The sub polarizing filter 222 of the present embodiment is supported by the support walls 251 and 252 at a position between the sub lens 232 and the sub light receiving unit 212. The sub polarizing filter 222 is disposed to cause only the polarized light having the same polarization plane as the polarization plane of the first polarized light P 01 to reach the sub light receiving unit 212. That is, the main polarization filter 221 passes only polarized light having a polarization plane orthogonal to the polarization plane of the first polarized light P01, and blocks other polarized light.

  Therefore, among the surface reflected light P02, the first internally reflected light P12, and the second internally reflected light S12 directed to the camera 200, it is the surface reflected light that passes through the sub polarization filter 222 and reaches the sub light receiving unit 212. It is only P02 and the first internally reflected light P12. A signal indicating the brightness of the near infrared light received by the sub light receiving unit 212 is input to the control device 300.

  The light reduction filter 242 is a filter for attenuating the brightness of near infrared light toward the sub light receiving unit 212. The neutral density filter 242 is supported by the support walls 251 and 252 at a position closer to the subject M than the secondary lens 232.

  The luminance of near infrared rays (surface reflected light P02, first internally reflected light P12) directed to the sub light receiving portion 212 is larger than the luminance of near infrared light (second internally reflected light S12) received by the main light receiving portion 211. In the present embodiment, by providing the above-described light reduction filter 242 only on the side of the sub light receiving unit 212, the brightness of the near infrared light received by the sub light receiving unit 212 corresponds to the brightness of the near infrared light received by the main light receiving unit 211. It has dropped to the same level. Thereby, it is possible to bring the brightness of each near-infrared light within the dynamic range of the image sensor 210.

  The effect of having the biological signal detection apparatus 10 configured as described above will be described with reference to FIG. The line L1 in FIG. 5A is a graph showing an example of the change in the brightness of the near-infrared light when all the near-infrared light reflected or scattered by the skin is received by the camera 200. That is, FIG. 5A shows an example of the change in the luminance of near-infrared light received by the main light receiving section 211 when the main polarizing filter 221 is not provided. Note that “DH” shown in FIG. 5 is the upper limit of the dynamic range of the camera 200, and “DL” is the lower limit thereof.

  In such a case, all of the surface reflected light P02, the first internally reflected light P12, and the second internally reflected light S12 are received by the main light receiving unit 211. Therefore, the luminance change indicated by the line L1 includes not only the luminance change of the second internally reflected light S12 accompanying the change of the blood flow but also the luminance change of the surface reflected light P02 accompanying the change of the posture of the subject M Is also included. The absorbance of near-infrared light to blood is small, and near-infrared light is apt to be partially reflected on the skin surface. As a result, in the luminance change indicated by the line L1, the luminance change of the surface reflected light P02 is dominant, and the proportion of the luminance change of the second internally reflected light S12 is small. That is, in the line L1, the S / N ratio of the biological signal is reduced. For this reason, it is difficult to accurately detect a biological signal based on the change in luminance shown by the line L1.

  Further, the amplitude of the luminance change shown by the line L1 is smaller than the dynamic range. In order to detect a biological signal based on the line L1, for example, increasing the output of the light source 100 and increasing the amplitude may be considered.

  However, the luminance indicated by the line L1 is relatively large by including the luminance of the surface reflected light P02, and has a value close to the upper limit DH of the dynamic range. For this reason, when the output of the light source 100 is increased as described above, the brightness of the near-infrared light received by the main light receiving unit 211 exceeds the dynamic range, which makes measurement impossible.

  What is indicated by a line L2 in FIG. 5B is an example of the change in the brightness of near-infrared light received by the main light receiving unit 211 in the present embodiment (that is, the configuration shown in FIG. 3). In the present embodiment, the surface reflected light P02 and the first internally reflected light P12 are not received by the main light receiving unit 211, and only the second internally reflected light S12 is received by the main light receiving unit 211. Therefore, only the change in luminance of the second internally reflected light S12 accompanying the change in blood flow is included in the change in luminance indicated by the line L2. Therefore, based on the luminance change shown by the line L2, it is possible to detect the biological signal with high accuracy.

  The amplitude of the luminance change shown by the line L2 is also smaller than the dynamic range. For this reason, in order to detect a biosignal more accurately, for example, it is preferable to increase the output of the light source 100 and to increase the amplitude.

  The luminance indicated by the line L2 is relatively small because it does not include the luminance of the surface reflected light P02, and has a value close to the lower limit DL of the dynamic range. For this reason, even after the output of the light source 100 is increased as described above, it is possible to make the luminance change of the second internally reflected light S12 fall within the dynamic range. The line L3 in FIG. 5B is a graph showing an example of the luminance change of the second internally reflected light S12 when the output of the light source 100 is thus increased. In this case, since the S / N ratio of the biological signal is increased, it is possible to detect the biological signal more accurately than in the case based on the line L2.

  As described above, the biological signal detection apparatus 10 according to the present embodiment includes the main polarization filter 221 disposed at a position between the subject M and the main light receiving unit 211. The main polarizing filter 221 is disposed to cause only the second internally reflected light S12 (second polarized light) having a polarization plane different from the polarization plane of the first polarized light P01 to reach the main light receiving section 211. For this reason, the signal detection unit 330 can accurately detect a change in the brightness of the second internally reflected light S12 received by the main light receiving unit 211 as a biological signal.

  In the present embodiment, the polarization plane of the second internally reflected light S12 (second polarization) passing through the main polarization filter 221 is a polarization plane orthogonal to the polarization plane of the first polarization P01. The angle between the respective polarization planes may be 90 degrees as in this embodiment, but may be an angle different from 90 degrees. According to the examination by the present inventors through experiments etc., if the above angle is kept within the range of 90 degrees ± 30 degrees, the influence of the surface reflected light P02 can be excluded, and the biological signal is detected accurately. It has been confirmed that it will be possible.

  By the way, since the biological signal detection apparatus 10 according to the present embodiment is mounted on a vehicle, not only the near infrared light from the light source 100 but also the near infrared light incident from the outside through the window glass G1 reaches the subject M There is something to do. Such near infrared rays include near infrared rays having various polarization planes. For this reason, there is a concern that a part of the light passes through the main polarizing filter 221 and reaches the main light receiving unit 211, and the S / N ratio of the biological signal is lowered.

  In order to prevent this, the biological signal detection apparatus 10 according to the present embodiment further includes a filter F1 provided so as to cover the window glass G1 from the inside (see FIG. 1). The filter F1 causes the window glass G1 to cause only the light having the same polarization plane as the polarization plane of the first polarized light P01 to reach the skin of the subject M among the near infrared rays incident to the vehicle interior from the outside of the vehicle. It is a polarization filter provided in The provision of such a filter F1 prevents a situation in which near infrared rays different from near infrared rays emitted from the light source 100 reach the main light receiving portion 211 and are detected.

  The filter F1 provided on the window glass G1 may be a polarization filter as described above, but does not allow near infrared rays entering the vehicle interior from outside the vehicle to reach the skin of the subject M at all It may be shut off.

  The process performed by the control device 300 will be described with reference to FIG. The series of processes shown in FIG. 6 are repeatedly executed by the control device 300 each time a predetermined control cycle elapses.

  In the first step S01 of the process, the intensity of the near-infrared light (that is, the second internally reflected light S12) received by the main light receiving unit 211 is acquired. In step S02 following step S01, the intensity of the near infrared light (that is, the surface reflected light P02 and the first internally reflected light P12) received by the sub light receiving unit 212 is acquired.

In step S03 following step S02, processing is performed to correct the intensity of the near-infrared light received by the main light receiving unit 211. Assuming that the intensity of near infrared rays received by the main light receiving portion 211 (that is, the intensity before correction) is Is0 and the intensity of near infrared rays received by the sub light receiving portion 212 is Ip, the intensity Is after correction is It can be expressed as 1).
Is = Is0 × f (Ip) (1)

  “F (Ip)” in the equation (1) is a function that returns a value larger than 1 when Ip is large, and returns a value smaller than 1 when Ip is small. Therefore, the intensity of the near-infrared light received by the main light receiving unit 211 is corrected to be larger than the original value when the intensity of the near-infrared light received by the auxiliary light receiving unit 212 is large, and the auxiliary light receiving unit 212 receives light. When the intensity of the near-infrared light is small, it is corrected to be smaller than the original value. That is, the correction unit 340 performs processing to correct the second polarized light received by the main light receiving unit 211 to have a higher brightness as the brightness of the light received by the sub light receiving unit 212 increases.

  The secondary light receiving unit 212 according to the present embodiment receives light reflected or scattered by the skin of the subject M after being irradiated from the light source 100, through the secondary polarizing filter 222 without passing through the primary polarizing filter 221. It is a part. When the intensity of the near-infrared light received by the sub light-receiving unit 212 increases, the light amount of the near-infrared light reflected by the skin surface increases for some reason, and the near-infrared light entering the inside of the skin It is inferred that the light quantity of is reduced. In such a case, the intensity of the near-infrared light received by the sub light-receiving unit 212 is corrected to be larger than the original Is0.

  On the other hand, when the intensity of the near-infrared light received by the sub light-receiving unit 212 decreases, the light amount of the near-infrared light reflected by the skin surface decreases for some reason, and accordingly, the near-infrared light entering the inside of the skin It is presumed that the light quantity is large. In such a case, the intensity of near-infrared light received by the sub light receiving unit 212 is corrected to be smaller than the original Is0.

  As a result, the corrected intensity Is is maintained at a substantially constant level without depending on the amount of near-infrared light entering the inside of the skin. The signal detection unit 330 changes the luminance of the second internally reflected light S12 (second polarization) after the correction by the correction unit 340 as described above, that is, the intensity Is at which a constant level is maintained by the correction, It is detected as a biological signal. Therefore, the biological signal can be detected more accurately and easily without being affected by the intensity change of Is0.

  In the present embodiment, by providing the sub camera unit 202 separately from the main camera unit 201, it is possible to appropriately correct the intensity of the second polarized light. It is also possible to provide the sub camera unit 202 as an apparatus separate from the main camera unit 201. However, in view of suppressing the component cost, it is preferable to configure the entire main camera unit 201 and the sub camera unit 202 as an integrated device as in the present embodiment.

  Another process performed by the control device 300 will be described with reference to FIG. A series of processes shown in FIG. 7 are repeatedly executed by the control device 300 each time a predetermined control cycle elapses. The process is performed in parallel with the series of processes shown in FIG.

  In the first step S05, the intensity of the near-infrared light (that is, the second internally reflected light S12) received by the main light receiving unit 211 is acquired. The said process is the same as the process performed by FIG.6 S01.

  In step S06 following step S05, the output adjusting unit 310 adjusts the output of the light source 100. Here, the output of the light source 100 is adjusted such that the intensity of the near-infrared light received by the main light receiving unit 211 matches the predetermined level. That is, by feeding back the brightness of the near-infrared light received by the main light receiving unit 211, the process of adjusting the output of the light source 100 is performed. As described above, the output adjusting unit 310 in the present embodiment adjusts the output of the light source 100 based on the luminance of the second internally reflected light S12 (second polarized light) received by the main light receiving unit 211.

  In step S07 following step S06, the exposure adjustment unit 320 adjusts the exposure time of the camera 200. Here, the exposure time of the camera 200 is adjusted so that the intensity of the near-infrared light received by the main light receiving unit 211 matches the predetermined level. In other words, the processing of adjusting the exposure time of the camera 200 is performed by feeding back the luminance of the near-infrared light received by the main light receiving unit 211. As described above, the exposure adjustment unit 320 in the present embodiment determines the exposure time of the camera 200 (that is, the main light receiving unit 211) based on the luminance of the second internally reflected light S12 (second polarized light) received by the main light receiving unit 211. Adjust the exposure time of

  Note that only one of the processes in step S06 and step S07 may be performed. In the present embodiment, even if the intensity of the near-infrared light received by the main light receiving unit 211 varies depending on the individual difference of the subject M or the like by performing the above processing, the intensity is substantially constant. The level of This makes it possible to always detect the biological signal accurately.

  The present embodiment has been described above with reference to the specific example. However, the present disclosure is not limited to these specific examples. Those appropriately modified in design by those skilled in the art are also included in the scope of the present disclosure as long as the features of the present disclosure are included. The elements included in the above-described specific examples, and the arrangement, conditions, and shapes thereof are not limited to those illustrated, but can be appropriately modified. The elements included in the above-described specific examples can be appropriately changed in combination as long as no technical contradiction arises.

10: biological signal detection apparatus 100: light source 211: main light receiving unit 221: main polarization filter 330: signal detection unit M: subject

Claims (10)

A biological signal detection apparatus (10) for detecting a biological signal of a subject (M), comprising:
A light source (100) for irradiating a first polarized light composed of near infrared light toward the skin surface of the subject;
A light receiving unit (211) that receives light reflected or scattered by the skin of the subject after being irradiated from the light source;
A polarization filter (disposed at a position between the subject and the light receiving unit so that only the second polarized light having a polarization plane different from the polarization plane of the first polarized light reaches the light receiving unit 221),
A signal detection unit (330) that detects, as the biological signal, a change in luminance of the second polarized light received by the light receiving unit.   The biological signal detection apparatus according to claim 1, wherein the polarization plane of the second polarization is a polarization plane orthogonal to the polarization plane of the first polarization. The light receiving unit is a main light receiving unit,
The living body according to claim 1 or 2, further comprising a secondary light receiving section (212) for receiving the light reflected or scattered by the skin of the subject after being irradiated from the light source, without passing through the polarizing filter. Signal detection device. The polarizing filter is a main polarizing filter,
An auxiliary polarizing filter disposed at a position between the subject and the auxiliary light receiving unit so that only light having the same polarization plane as the polarization plane of the first polarization can reach the auxiliary light receiving unit. The biological signal detection apparatus according to claim 3, further comprising: (222). And a correction unit (340) for correcting the brightness of the second polarized light received by the main light receiving unit based on the brightness of the light received by the sub light receiving unit.
The biological signal detection apparatus according to claim 3, wherein the signal detection unit detects a change in luminance of the second polarized light after being corrected by the correction unit as the biological signal. The correction unit is
The biological signal detection apparatus according to claim 5, wherein the luminance of the second polarized light received by the main light receiving unit is corrected to be higher as the brightness of the light received by the sub light receiving unit is larger.   The biological signal detection according to any one of claims 1 to 6, further comprising an output adjusting unit (310) configured to adjust an output of the light source based on the brightness of the second polarized light received by the light receiving unit. apparatus.   The living body according to any one of claims 1 to 6, further comprising an exposure adjustment unit (320) configured to adjust the exposure time of the light receiving unit based on the brightness of the second polarized light received by the light receiving unit. Signal detection device. The biological signal detection device is configured to be mounted on a vehicle,
The subject is an occupant of the vehicle, and
Among the near infrared rays incident from the outside of the vehicle, only the light having the same polarization plane as the polarization plane of the first polarized light is allowed to reach the skin of the subject, to the window glass (G1) of the vehicle The biological signal detection apparatus according to any one of claims 1 to 8, further comprising a provided glass polarizing filter (F1). The biological signal detection device is configured to be mounted on a vehicle,
The subject is an occupant of the vehicle, and
The cutoff filter (F1) provided in the window glass of the said vehicle so that the near-infrared light which injects from the outside of the said vehicle may not reach the skin of the said subject, The any one of Claims 1-8 The biological signal detection apparatus according to claim 1.

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