JPH08145787A - Pyroelectric infrared sensor - Google Patents

Abstract

PURPOSE: To provide a small and inexpensive pyroelectric infrared sensor excellent in sensitivity. CONSTITUTION: A window 3 with infrared rays incident on it on which a diffraction type optical lens 4 is formed and a pyroelectric body 1 positioned in the image point in relation to a dominant wavelength λ of the infrared rays from the detected article are attached, and a case 2 housing the pyroelectric body 1, and provided with an opening part 5 is provided. By this structure, it is not necessary to expressly provide a filter outside the case 2, and extreme miniaturization is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric infrared sensor for detecting infrared rays with a pyroelectric body.

[0002]

2. Description of the Related Art In recent years, pyroelectric infrared sensors have been capable of non-contact detection of objects and temperatures, and are capable of measuring the temperature of cooked food in microwave ovens, controlling room temperature in air conditioners, automatic doors, and alarm devices. It is used for human body detection in
The range of use is expected to expand in the future.

The pyroelectric infrared sensor utilizes the pyroelectric effect of LiTaO ₃ single crystal or the like. Pyroelectric materials have spontaneous polarization and always generate surface charges, but in the steady state in the atmosphere, they are electrically neutral because they are associated with the charges in the atmosphere. When infrared rays are incident on this, the temperature of the pyroelectric body changes, and along with this, the charge state on the surface also changes, breaking the neutral state. A pyroelectric infrared sensor measures the amount of incident infrared light by detecting the charge generated on the surface at this time. Generally, an object emits infrared rays according to its temperature, and the presence or temperature of the object can be detected by using this pyroelectric infrared sensor.

A conventional pyroelectric infrared sensor will be described below. FIG. 5 shows a schematic cross section of a conventional pyroelectric infrared sensor. A pyroelectric body 16 for detecting infrared rays,
A sealing case 17 that protects the pyroelectric body 16 from ambient light and electromagnetic noise, an infrared incident window 18 attached to the opening 21 of the sealing case 17, and a detection case located outside the sealing case 17. The filter 19 is configured to transmit only the main wavelength λ of infrared rays emitted by an object.

The filter 19 is 4.3 in case of flame detection.
Only infrared rays around μm are transmitted. In this case, sapphire is used as the filter material, and a bandpass filter film that transmits only infrared rays in the vicinity of 4.3 μm is formed on the surface by vapor deposition.

[0006]

However, in the above configuration, it is difficult to reduce the size because the filter 19 is located outside the sealing case 17. Infrared rays 2 emitted from the object
Since 0 reaches the pyroelectric body 16 after passing through the filter 19 and the window 18, infrared rays are reflected and absorbed by the filter 19, so that the overall transmittance becomes extremely small. Further, the filter 19 is expensive and costly. The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a pyroelectric infrared sensor which can be downsized, has high transmittance, and is inexpensive.

[0007]

In order to achieve this object, the present invention provides an infrared incident window, a diffractive optical lens for converging or forming an image of infrared rays having a specific wavelength at a specific position,
It consists of a pyroelectric body for detecting infrared rays provided at an image point of infrared rays of a specific wavelength behind the lens and its case.

[0008]

According to the pyroelectric infrared sensor of the present invention, it is not necessary to provide a filter on the outside of the case, so that the size can be made extremely smaller than the conventional one. In addition, since the infrared ray transmittance is significantly improved because there is no filter, a highly sensitive sensor can be realized. In addition, since the expensive filter is not required, the cost can be reduced.

[0009]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a pyroelectric infrared sensor according to the first embodiment of the present invention. 0.5m thickness with diffractive optical lens 4 formed
m, the infrared incident window 3 made of a Si substrate of 3.3 × 3.3 mm square, and the incident surface of 0.14 mm square located at the image point with respect to the wavelength λ, where λ is the main wavelength of infrared rays from the detection object. And a case 2 having a diameter of 5 mm, which has the infrared entrance window 3 and has an opening 5 having a diameter of 2.5 mm and which houses the pyroelectric body 1.

The operation of the pyroelectric infrared sensor constructed as described above will be described. First, of the infrared rays 6 radiated from a detection object that enters the visual field or moves within the visual field, the diffractive optical lens 4 serves as a filter to focus or image the infrared rays having the main wavelength λ on the pyroelectric body 1.
At this time, the temperature of the pyroelectric body 1 changes, and along with this, the charge state of the surface is also broken and the neutral state changes. At this time, the charge generated on the surface is detected, and the incident amount of infrared rays is measured.

When infrared rays of other wavelengths (wavelengths other than λ) are radiated from the object to be detected and are incident from the diffractive optical lens 4, the refractive index differs depending on the wavelength, so that they are not condensed on the pyroelectric body 1. That is, the pyroelectric body does not detect the incidence of infrared rays.

With this configuration, it is possible to detect a specific infrared ray without the need to provide a filter on the outside of the case 2, and it is possible to make the size extremely small. Also, since the external filter can be eliminated, the transmittance is greatly improved. Also, by eliminating the expensive external filter, a significant cost reduction was possible.

By setting the main wavelength λ to any wavelength of 3 to 5 μm which is the infrared wavelength emitted by the flame,
Flame detection is now possible. In particular, by setting the main wavelength λ to be around 4.3 μm, the influence of ambient light was eliminated, and flame detection without malfunctions became possible. The distance from the main surface to the image point at this time was set to 3.0 mm.

Further, the human body can be detected by setting the main wavelength λ to any wavelength of 7 to 14 μm, which is the infrared wavelength emitted by the human body. Especially the main wavelength λ is 9.5μ
By setting m around, the influence of ambient light disappears,
It has become possible to detect human bodies without malfunction. The distance from the main surface to the image point at this time was set to 1.2 mm.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a schematic cross section of a pyroelectric infrared sensor according to the second embodiment of the present invention. The difference from the first embodiment is that two or more (three in this case) pyroelectric bodies 8, 9 and 10 are image points when infrared rays 6 of different main wavelengths are incident on the stepwise block 7. Is a point located at. At this time, the design of the diffractive optical lens is performed based on, for example, the dominant wavelength λ that focuses or forms an image at the image point of the pyroelectric body 8. The object points with respect to the pyroelectric body at the positions of the image points are at slightly different positions, but they are not shown in the figure.

The operation of the pyroelectric infrared sensor constructed as described above will be described. First, infrared rays radiated from several types of detection objects that radiate infrared rays of several types having different main wavelengths that enter or move within the field of view are placed as corresponding filters by the diffractive optical lens 4 at corresponding image points. It is condensed or imaged on the pyroelectric bodies 8, 9 and 10. That is, as in the first embodiment, by installing the pyroelectric bodies at the image points corresponding to the flame and the human, it is possible to detect whether the object is a flame or a human.

With this configuration, it is possible to detect an object radiating infrared rays of different main wavelengths at the same time with only one pyroelectric infrared sensor without using different types of filters and pyroelectric infrared sensors. It is possible to realize extreme miniaturization and cost reduction.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a schematic cross section of a pyroelectric infrared sensor according to the third embodiment of the present invention. The difference from the first embodiment is that the two or more diffractive optical lenses 11 and 12 are provided with the infrared ray incident window 3.
Is formed, and has two or more pyroelectric bodies 13 and 14 at the image point when infrared rays having different main wavelengths λ1 and λ2 are incident. That is, lens 11 and lens 1
The focal lengths of 2 are different, and the infrared rays having different main wavelengths are matched to each other. It is formed on the same substrate.

The operation of the pyroelectric infrared sensor constructed as described above will be described. First, infrared rays radiated from several types of detection objects that radiate infrared rays of several types having different main wavelengths that enter or move in the field of view are used as filters by two or more diffractive optical lenses 11 and 1.
The infrared rays having the main wavelengths λ1 and λ2 are condensed or imaged on the pyroelectric bodies 13 and 14 placed at the image points corresponding to the diffractive optical lenses 11 and 12, respectively, by 2. As in the second embodiment, it is possible to know whether the object is, for example, a flame or a human by detecting which pyroelectric body the light is focused on.

With this configuration, it is possible to detect an object that emits infrared rays of different main wavelengths at the same time with only one pyroelectric infrared sensor without using different types of filters and pyroelectric infrared sensors. It is possible to realize extreme miniaturization and cost reduction.

CO ₂ , λ at the wavelength λ = 4.3 μm
= CO at 4.7 μm, SO ₂ at λ = 4 μm, λ =
NO at 5.3 μm, HC at λ = 3.4 μm, λ =
Since H ₂ O can be detected at 1.9 μm, gas analysis can be performed at the same time.

(Embodiment 4) A fourth embodiment of the present invention will be described below with reference to the drawings. FIG. 4 schematically shows a pyroelectric infrared sensor according to the fourth embodiment of the present invention. The difference from the first embodiment is that a shield plate 15 for shielding infrared rays incident from other diffractive optical lenses is provided near the current collector.

The operation of the pyroelectric infrared sensor constructed as described above will be described. First, diffractive optical lenses 11 and 12 are used as filters out of infrared rays emitted from an object to be detected that enters the field of view or moves within the field of view.
Thereby, the infrared rays having the main wavelength λ are condensed or imaged on the pyroelectric bodies 13 and 14. However, at this time, at the same time, the other diffractive optical lenses 11 and 12 block the infrared rays that are going to enter the pyroelectric bodies 14 and 13 as disturbance light by the shield plate 15.

With this configuration, it is possible to prevent disturbance light incident from other diffractive optical lenses, and at the same time, it is possible to accurately detect an object that radiates infrared rays of different main wavelengths.

Incidentally, by forming a non-reflective interference film on the surface of the infrared entrance window 3 of each of the above-described embodiments on which the diffractive optical lenses 4 and 11 and 12 are formed, or on the back surface thereof, the diffractive optical lens surface or Since there is almost no reflection on the back surface, the sensitivity of the pyroelectric infrared sensor could be further improved.

[0026]

The pyroelectric body is positioned at the image point of the diffractive optical lens formed in the infrared entrance window, and the filter effect is obtained by condensing or focusing only that wavelength.
Since it is not necessary to dispose a filter on the outside of the case, it is possible to make the size extremely smaller than before, and because the infrared transmittance is greatly improved because there is no filter, it is possible to realize a highly sensitive sensor. In addition, a pyroelectric infrared sensor that can be manufactured at low cost can be provided because no filter is required.

Further, such a filter effect largely depends on how much infrared rays are condensed on the pyroelectric body or not, and in this sense, the size of the surface of the pyroelectric body which receives the infrared rays is large. The smaller the diameter of the diffractive optical lens, the better the wavelength selectivity. Practical wavelength selectivity cannot be obtained unless the diameter of the surface of the pyroelectric body is at least half the diameter of the surface of the lens.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a pyroelectric infrared sensor according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a pyroelectric infrared sensor according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a pyroelectric infrared sensor according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a pyroelectric infrared sensor according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view of a conventional pyroelectric infrared sensor.

[Explanation of symbols]

 1 Pyroelectric body 2 Case 3 Infrared incident window 4 Diffractive optical lens 6 Infrared

Claims (10)

[Claims] 1. An infrared incident window having a diffractive optical lens formed thereon, and a main wavelength of infrared rays from a detection object are λ, and a wavelength λ
A pyroelectric infrared sensor comprising a pyroelectric body installed at an image point with respect to, and a case in which the infrared incident window is attached and which houses the pyroelectric body. 2. The pyroelectric infrared sensor according to claim 1, wherein the main wavelength λ is any wavelength within a range of 1 to 5 μm which is an infrared wavelength emitted by the flame. 3. The pyroelectric infrared sensor according to claim 1, wherein the main wavelength λ is set to around 4.3 μm. 4. The pyroelectric infrared sensor according to claim 1, wherein the main wavelength λ is any wavelength within the range of 7 to 14 μm which is an infrared wavelength emitted by a human body. 5. The pyroelectric infrared sensor according to claim 1, wherein the main wavelength λ is set to around 9.5 μm. 6. A pyroelectric type having a pyroelectric body at each image point when infrared rays from two or more detection objects having different dominant wavelengths enter the diffractive optical lens. Infrared sensor. 7. Two or more diffractive optical lenses are formed in an infrared ray entrance window, and two or more diffractive optical lenses corresponding to respective incident lights from the lenses are focused or image points when different wavelengths are incident. Pyroelectric infrared sensor characterized by having the above pyroelectric body installed. 8. The pyroelectric infrared sensor according to claim 7, wherein a shield plate for blocking infrared rays incident from another diffractive optical lens is provided near the pyroelectric body. 9. CO ₂ radiates a dominant wavelength λ of 4.3 μm.
Near, about 4.7 μm emitted by CO, about 4 μm emitted by SO _2, about 5.3 μm emitted by NO, about 3.4 μm emitted by HC, and 1.9 μm emitted by H ₂ O.
9. A pyroelectric infrared sensor according to claim 6, 7 or 8, wherein a plurality of combinations selected from the vicinity are used. 10. The pyroelectric infrared sensor according to claim 1, further comprising a non-reflection interference film on a surface of the infrared entrance window on which the diffractive optical lens is formed or a back surface thereof.