JPH0441307Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention is installed in, for example, an infrared imaging device, and uses an infrared sensing element made of HgTdTe or InSb that is cooled to a cryogenic temperature, for example, around 80K. Regarding infrared detectors.

[Conventional technology]

FIG. 2 is a diagram showing a conventional infrared detector. Infrared detectors are generally divided into two types: dual 2, which has an infrared detection element 1 built in, and dual 2, which has an infrared detection element 2 built in.
It is composed of a refrigerator 3 for cooling the water to an extremely low temperature, for example, around 80K. As the refrigerator 3, one that utilizes a refrigeration cycle such as a Stirling cycle or a Gifford-McMahon cycle is often used, and FIG. 2 shows an example of a refrigerator that utilizes a Stirling cycle. The refrigerator 3 is composed of a compressor 4, an expander 5, and a connecting pipe 6, and the expander 5 is equipped with a cold finger 7.
The cold finger 7 is provided with an elongated cylindrical projection called a cylindrical projection, and is structured to generate freezing at the tip of the cold finger 7.

The Dua 2 has a double wall structure consisting of 8 outer shells and 9 inner shells,
The infrared detecting element 1 is attached to the tip of the inner shell 9, and the outer shell 8 is provided with a window 10 that transmits infrared rays. The space between the outer shell 8 and the inner shell 9 is kept in a vacuum so that heat does not enter the tips of the infrared detecting element 1 and the cold finger 7 from the outside. On the surface facing the vacuum space, a vapor-deposited film or a plating film of a material with a low radiation rate, such as aluminum or silver, is formed, and the inner shell 8 is made of a material with a low thermal conductivity, such as glass. . 11 is a thermal interface, and the thermal interface 11 is attached to the tip of the cold finger 7 and is generally made of metal, and the inner shell 9 is generally made of glass. This is to absorb the dimensional change due to the difference in coefficient. For example, an elastic material such as laminated copper foil and a material with high thermal conductivity is used, and the tip thereof is always in close contact with the bottom surface of the inner shell 9. It's getting old.

Next, the operation of the conventional device shown in FIG. 4 will be explained. When the refrigerator 3 starts operating and begins to generate refrigeration at the tip of the cold finger 7, the infrared sensing element 1 receives heat from the refrigerator 2 via the thermal interface 11, and its temperature drops. When the temperature drops to around 80K, the infrared rays transmitted through the window 10 are converted into electrical signals. As described above, the dual layer 2 includes a vacuum layer provided between the outer shell 8 and the inner shell 9, and a vapor deposited film or a plating film with a low radiation rate provided on the surfaces of the outer shell 8 and the inner shell 9 facing each other. With inner shell 9 made of material with low thermal conductivity,
Heat intrusion from the outside due to convection, radiation, and conduction is reduced, and the load on the refrigerator 3 is reduced.

[Problem that the invention attempts to solve]

The conventional infrared detectors described above have the following problems.

When the infrared detector is continuously cooled by a refrigerator, the temperature of the infrared detecting element usually fluctuates as shown in FIG. Such temperature fluctuations are caused by, for example, fluctuations in the voltage of the power supply supplied to the refrigerator, fluctuations in the environmental temperature in which the refrigerator is operated, or fluctuations in the cooling capacity of the refrigerator due to changes within the refrigerator itself. When the temperature of the infrared detection element fluctuates as shown in FIG. 3, the sensitivity of the infrared detection element changes with the temperature fluctuation even if the fluctuation is within the range in which infrared detection is possible. When such an infrared detector is installed in an infrared imaging device, etc., if the sensitivity of the infrared detection element changes as described above, the image may become unclear or
There were some problems that caused confusion.

[Means for solving problems]

The infrared detector according to this invention is provided with a ventilation hole that communicates the space inside the inner shell into which the cold finger is inserted with the surrounding atmosphere.

[Effect]

With this design, the space inside the inner shell is always maintained at atmospheric pressure, so when the refrigerator is operating, the temperature at the tip of the cold finger reaches the boiling point of air.
When the temperature reaches 78.8K, the air begins to liquefy, so even if the cold finger tries to cool the infrared sensing element further, the latent heat of the air overwhelms the cooling effect, and the temperature does not drop below 78.8K. Therefore, when the air is liquefied inside the inner shell, the temperature of the infrared detection element is kept constant, so stable infrared detection is possible without changing the sensitivity of the infrared element. .

〔Example〕

FIG. 1 is a diagram showing an embodiment of this invention.
1 to 10 have exactly the same configuration as the conventional device shown in FIG. 2, except that a vent hole is provided at the bottom of the outer shell 8 to communicate the space inside the inner shell 9 with the surrounding atmosphere.

In the infrared detector configured as described above, the refrigerator 3 cools the infrared element 1 via the thermal interface 11, and when the temperature of the infrared detection element 1 drops to around 80K, light passes through the window 10. The point that infrared rays are detected by the infrared detection element 1 is similar to the conventional device shown in FIG. 2, but the space inside the inner shell 9 into which the cold finger 7 is inserted is Since air at atmospheric pressure always exists, the temperature at the tip of the cold finger 7 of the refrigerator 3 is the boiling point of the air.
When the temperature reaches 78.8K, the air starts to liquefy at the tip of cold finger 7. Even if the refrigerator 3 tries to further cool down the infrared sensing element 1, the cooling effect is eclipsed by the latent heat of liquefaction of the air, and the temperature at the tip of the cold finger 7 is kept constant at 78.8K. Therefore, as long as the refrigerator 3 has the ability to cool the tip of the cold finger 7 to below 78.8K, the infrared sensing element 1 will be kept at a constant temperature no matter how much the refrigerator 3's capacity fluctuates. Infrared element 1 like the device
Since the sensitivity of the sensor does not fluctuate, stable infrared detection can be performed.

[Effect of idea]

As explained above, this idea has a simple structure of providing a ventilation hole that communicates the space inside the inner shell where the cold finger is inserted with the surrounding outside air, which changes the cooling capacity of the refrigerator and increases the detection of the infrared detection element. This has the effect of solving the problem of sensitivity fluctuation and allowing stable infrared detection.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of this invention, Fig. 2 is a diagram showing a conventional infrared detector, and Fig. 3 is a diagram showing temporal fluctuations in the temperature of an infrared sensing element in a conventional infrared detector. be. In the figure, 1 is an infrared detection element, 3 is a refrigerator, 7 is a cold finger, 8 is an outer shell,
9 is an inner shell, and 12 is a ventilation hole. In addition,
In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] A refrigerator having a cylindrical cold finger whose tip is at a low temperature, an inner shell forming a hole-like space into which the cold finger is inserted, and a vacuum layer covering the outside of the inner shell and between the inner shell and the inner shell. , an infrared sensing element attached to the inner shell, and a ventilation hole that communicates a hole-shaped space formed by the inner shell into which the cold finger is inserted with the surrounding atmosphere. Infrared detector.