WO1993025875A1

WO1993025875A1 - Radiation detector and measuring equipment for ultra-violet radiation

Info

Publication number: WO1993025875A1
Application number: PCT/HU1993/000001
Authority: WO
Inventors: János BODNÁR; Béla BOLDOG
Original assignee: Bodnar Janos; Boldog Bela
Priority date: 1992-06-08
Filing date: 1993-01-12
Publication date: 1993-12-23
Also published as: HU9201898D0

Abstract

The invention relates to an ultra-violet radiation detector comprising a device for decomposing light into spectrum and a semiconductor detector set up in the path of the ultra-violet light beam behind the spectrum decomposing device, wherein the device decomposing the light into spectrum is a diffraction grating (2, 2'), behind which a detector (3) of the surface width of two or more refraction orders of the decomposed light beams and with a partly uncovered surface, uncovered on places adequate to the distance of refraction orders, is set up in the path of the light. The diffraction grating (2) is a translucent holographic picture, behind which a detector (3) with a surface of the same dimension as the surface of the diffraction grating (2) is set up, or the diffraction grating (2) is a light-reflecting holographic picture, above which, parallel with it and shifted in the direction of the incoming light is located the photosensitive detector (3) with a partly uncovered surface. Preferably the UV radiation detector has an incidence angle indicator for indication of the direction of the incoming light in relation to the diffraction grating (2). The invention further relates to a measuring equipment in which said UV radiation detector is applied, said detector being connected to an evaluating electronic device. The output of the photosensitive detector (3) is connected via analogue amplifier (4) to an analogue-digital converter (5), and an LCD display (6) is connected to the output of the analogue-digital converter (5). Preferably a comparator and an integrating circuit are also connected to the output of the analogue-digital converter (5) and the measuring equipment is materialised as an integrated circuit furnished with UV permeable window, which is built in a wrist watch.

Description

RADIATION DETECTOR AND MEASURING EQUIPMENT FOR ULTRA-VIOLET RADIATION

Field of the Invention

Subject of the invention is an ultra-violet radiation detector comprising a device for decomposing light into spectrum and a semiconductor detector set up in the path of the ultra-violet light beam behind the spectrum decomposing device. Further subject of the invention is a measuring instrument for measuring ultra-violet radiation comprising a device for decomposing light into spectrum, and a semi¬ conductor detector set up in the path of the ultra-violet light beam behind the spectrum decomposing device, said detector being connected to an evaluating electronic device.

Weakening of ozone layer has increased the intensity of ultra-violet radiation coming from the sun to earth, which is detrimental for human being and fauna, and which has increased the possibility of epithelioma's rise on skin- surface radiated heavily by the sun. Injurious ultra-violet radiation comes through on clouds' layer to the earth, and for this reason it could be harmful not only in case of sun¬ bathing. Intensity of radiation reaching the earth depends on place, section of the day, and cloudiness, so there is arising demand for measuring the radiation's intensity.

Description of the Prior Art Presently devices for more general purposes are of large dimension and are generally located at measuring stations. They are used for measuring the ultra-violet radiation as well, but there is demand for an UV intensity measuring device, which is small, bracelet watch like, for the people all time available as well. There is available on trade the so called UV radiation measuring equipment (DE 3921951 Al) , which do not measure directly the radiation, but it measures the unfiltered light intensity of a wider wave band determined by the sensitivity range of the utilized detector, which maybe is not suitable for direct perception of UV radiation. The on this way measured value, corrected by the average UV contain figure, is used to determine for how long period could be staying some one under the sun. Insufficiency of this solution is, that it is not fit for measuring the UV radiation's instantaneous value and not a real, but a fictive, average value is measured and indicated, which could deviate significantly from the real value, depending on the circumstances. Many such type of proposals are known for solving the problem of measurement of harmful UV radiation (US PS 4,704,535, US PS 4,985,632), in which an UVB band-pass filter is set up in front of the photo detector, which is sensitive for the UV band at least. Insufficiency of these solutions is that beside the pass band on range UVB (300nm- 370nm) a further light transmitting range in the range on 650 nmlOOO nm exists in the known UV colour filters, in which the photo-diode is still sensitive and this sideeffect distorts the measurement. The solution introduced in the description EP 0392 442A1 aims to eliminate this imperfection. The substance ofthe UV radiation measuring device introduced here is, that the sunlight is measured by two detectors, and in front of one from both there is a light filter for blocking the UV radiation, and the difference of the two values is formed and this difference forms the measured value of the UV radiation. This arrangement could be implemented into a wrist watch as well. The handicap of this solution is, that the intensity of UV component in sunlight is smaller with two orders of magnitude than the full solar radiation, so the measuring is inaccurate and it is dubious, that it could be evaluated at all. The UV filter namely lets through light belonging to UVB range in certain amount as well and it distorts the measuring.

The well known way of precise measuring of the UV radiation is the analyzing the sunlight's composition. The base for this is to disintegrate the light to components according to frequency and to measure the intensities of different components. Relative values are formed from the comparison of the intensity values received on the above mentioned way and the intensity of the unfiltered light, introducing the composition of the sunlight. In measuring devices, suitable for this, on the so called Fresnel prism is the light broken and dissolved for its components and behind the prism measuring sensors are set up in the path of components one by one and each of them is for measuring only one (narrow frequency) component. This type of device is the so called Fabri-Perot interferometer. Equipment of this type can not be materialized in a small size suiting into the caseing of a wrist watch.

Further optical light measuring devices are the illumination measuring devices, which are however measuring devices in a broad frequency visible light range fit to the characteristic of the human being's eye or of films, they do not fit for analyzing light spectrum and they are generally insensible on the UV range. The frequency characteristic of light intensity measuring devices is adjusted by using colour filters and by modifying the sensor's characteristic.

It is well known, that decomposing light into a spectrum can be made not only by prism but by diffraction grating as well. The light coming on inclined at an incidence angle to the diffraction grating refracts depending on its wave¬ length, and light beams coming through on different gaps of grating are crossing each others' paths and on appropriate places they delete each others and on other places they cast up. These places are repeated along the diffraction grating and form the so called refraction orders of the ecomposed light beams, the distances between two refraction orders

SUBSTITUTESHEET being larger of some order of magnitude than the distance between two gaps of grating. Different light components are added together on different places located side by side iridescent in a refraction order on similar way as the distribution behind the Fresnel prism. Separation of shorter wavelengths can be achieved by increasing the grating's resolution. Higher density than 2000 lines/mm diffraction grating is requested for separating UV beams, which density could be acheaved by applying an expensive technology, therefore no diffraction grating is utilized for measuring UV radiation.

Further it is known, that diffraction grating can be made on holographical way with less expenditures as well. Diffraction gratings made on this way have been proved to be unfit for utilization in measuring devices because of their inaccuracy and instability.

Summary of the Present Invention

Object of the invention is to eliminate the shortcomings of the known devices by creating a direct measuring radiation detector and measuring instrument for UV radiation producible with miniature dimensions and on large scale production.

The invention is based on the recognition, on the one hand that a flat radiation detector can be prepared by utilization of diffraction grating and on the other hand that the sensitivity of the detector can be multiplied by utilizing a sensor covering more refraction orders of by the diffraction grating decomposed light beams, which in the case of utilization of small sised diffraction grating can be implemented even on one semiconductor chip. Further recognition of the invention is, that for this reason a holographic diffraction grating can be utilized because it is not necessary to brake up the UVB range for more fine details, and as the sensor can be set up under the holographic sensor in a distance of 1 mm, the instability and inaccuracy, which make the holographic grating unfit for

SUBSTITUTESHEET spectrum analysis, are not disturbing in achieving the invention's object.

In the ultra-violet radiation detector according to the invention the device decomposing the light into spectrum is a diffraction grating, behind which a detector of surface witdh of two or more refraction orders of the decomposed light beams and with partly uncovered surface, uncovered on places adequate to the distance of refraction orders, is set up in the path of the light. Typically the diffraction grating is a translucent holographic picture, behind which a detector with a surface of the same dimension as the surface of the diffraction grating is set up.

Preferably the ultra-violet radiation detector has an incidence angle indicator for indication of the direction of the incoming light in relation to the diffraction grating.

Favourable it has an indicator for an incidence angle of 45°.

Preferably the incidence angle indicator is a white area set up on the detector's covered surface behind the dif¬ fraction grating.

In an other radiation detector according to the inven¬ tion the diffraction grating is a lightreflecting holographic picture, above which, parallel with it and shifted in the direction of the incoming light the photosensitive detector with a partly uncovered surface is located .

According to the invention in the measuring equipment for measuring ultra-violet radiation the device decomposing the light into spectrum is a diffraction grating, behind which a detector of surface witdh of two or more refraction orders of the decomposed light beams and with partly uncovered surface, uncovered on places adequate to the distance of refraction orders, is set up in the path of the light, and the output of the photosensitive detector is connected via analogue amplifier to an analogue-digital converter.

SUBSTITUTESHEET Preferably the measuring equipment is equipped with an incidence angle indicator for indication of the direction of the incoming light in relation to the diffraction grating. Typically an LCD display is connected to the output of the analogue-digital converter.

Preferably a comparator is also connected to the output of the analogue-digital converter.

Favourably an integrating circuit is connected to the output of the analogue-digital converter. Preferably it is built in a wrist watch and favourably it is materialized as an integrated circuit furnished with UV permeable window.

According to the invention the advantage of ultraviolet radiation detector and measuring equipment is, that it is suitable for measuring the real and absolute value ofthe UV radiation, moreover within this for measuring the injurious, "hard" UV radiation as well, and it can be realised in smaller dimension than 1 cm² with thickness of some mm, and it gives solution suitable for massproduction.

Brief Description of the drawing

Examples of measuring equipment in accordance with the invention will now be described vith reference to the accompanying drawings in which Figure 1 is a schematic drawing of an UV radiation measuring equipment. Figure 2 is the schematic drawing of the reflection type UV radiation measuring equipment.

Detailed Description of the Preferred Embodiments

A realised measuring equipment based on an ultra-violet radiation detector with translucent diffraction grating 2 is schematically depicted on Figure 1. The UV radiation detector comprises a crystal glass window 1 with the diffraction grating 2 on its rear surface, a photosensitive detector 3 with about the same large, partly covered

SUBSTITUTESHEET photosensitive surface as the surface of the diffracttion grating 2, arranged about 1 mm behind of the rear surface of the window 1.

The diffraction grating 2 can be formed on the back side of the crystal glass window 1 on traditional way, but it is quite expensive. In the examples according to the invention the diffraction grating 2 is formed as a holographic picture, the density of which grating takes 2000 lines/mm.

About 1 mm behind the diffraction grating 2 is located the detector 3 with grating like covered photosensitive surface

(made up with each other parallel strips) furnished with light absorbing layer (i.e. metal oxide layer) . The uncovered photosensitive surface parts of the detector 3 are formed in a distance from each other according to the distance of the refraction orders.

The photosensitive detector 3 is a silicon photo- transistor, which has its highest sensitivity in the UV range and which is insensible in the red range.

The holographic picture behaving as a diffraction grating is producible on quite a simple way. Hologram originates when a laser beam, which is coherent in time and space, interferes with itself. This interference picture is fixed on film. This interference picture contains pattern made of black and white stripes. The phase hologram constitutes not only the picture visible for human's eye but it constitutes the on certain points incoming light waves* phase, too, which is constant, because the source's light is coherent as well. Advantage of the phase hologram is, that the refraction orders and within them some wavelengths not only can be separated, but its separation can be adjusted to a given direction, in our case a separation with the largest energy by 45° incidence angle can be adjusted. Light reflexing and light permeable diffraction grating 2,2' can be formed on holographic way as well. The material of light permeable film and the material of window must be a material letting through UV radiation.

SUBSTITUTESHEET Light falling in from a direction of 45° incidence angle to the diffraction grating 2 is breaking up on the diffraction grating for its iridescent components because of the light refraction, which refraction increases from UV to red range. The UV light components are going on almost straight, namely in 45° direction, while red components are going on to the direction about vertical to the surface. The on different grating lines incoming light beams interfere with each others, in some places they are summing up and in relatively large other places they are substracted from each others.

Refraction orders with macroscopic dimensions (in our case about 1 mm width) are formed on this way. In each order the light components of different wave length are summarized in different places and a rainbowlike separation is formed on this way.

The photosensitive surface of the detector 3 is covered, shadowed everywhere except one narrow line at the place, where the UV components are summarized, in each refraction order.

A diffraction grating in form of a holographic picture has allways inaccuracies depending on the dimension of the picture's grain. Because of this the spectrum separation of the refraction orders is not precise, edges of refraction orders overlap each others a little bit. But this does not disturb the intensity measuring of the UV radiation because on the not covered photosensitive surface of incoming UV spectrum's spot only the neighbouring order's red light can fall, for which the silicon detector is not sensitive. A diffraction grating materialized as holographic picture with 2000 lines/mm is not able to break up the wave length in the 200-300 n range. In our case this is not even necessary, because we want to measure the intensity of the total light quantity falling into this range. The ultra-violet radiation detector is feasible with light reflecting diffraction grating 2' as well (Figure 2.). In this case the photosensitive detector 3 is located about

SUBSTITUTESHEET 3-5 mm above the diffraction grating 2* and it is shifted about 3-5 mm horizontally from the light's incoming direction. In this case the dimension of detector 3, lying in the way of the incoming light beam, can not be selected at discretion. Its optimal dimension is restricted by the fact, that the body of the detector 3 shadows the diffraction grating 2' in space. As mentioned, the measuring is optimal if the incoming angle of sunlight is 45°. The ultra-violet radiation detector can be oriented to the direction of sunlight by many different means. The most simple means is the estimation of human's eyes or pointing it with direction measuring device, which can be supported by computer, for example a manager calculator giving the instantaneous position of the sun depending on the calender and time. Favourable is if we install on the UV radiation detector an incidence angle indicator for indication of the direction of the incoming light in relation to the diffraction grating 2.

The most simply indicator for incidence angle is a window, which is located in the space ahead the window 1 in a given distance from a signal point, which signal point is ligthable through the same window 1.

The indicator of incidence angle is feasible on the incoming spot of green light as a white surface on the covered surface of the detector 3, which will be lighted by the incoming green light component at a 45"incidence angle. The lighting of this white surface changes in its colour depending on the angle position and it is lighted with green, if the radiation detector's angle position is 45° to the sunbeam.

Harmful UV radiation exists in cloudy wether as well and hard UV radiation breaks through clouds. The radiation detector and the above type of incidence angle indicator can and should be used in cloudy wether, as well, which is possible by exploitation of the polarised state of the sunlight. Sunlight is partly polarized because of its diffraction and its polarisation's plane is normal to the

SUBSTITUTESHEET reflected light's polarisation plane. If the sunlight is conducted through a polarisation filter (which is favourably a hologram) to the indicator ofincidence angle introduced above, than the intensity of lighting depends on the angle of incidence, lighting is going to be less with directing the detector to a different direction as the angle of incidence, green colour appears on the effect incoming light coming from the appropriate direction.

Indicator of incidence angle is not necessary in the case of utilization of light reflecting diffraction grating 2', if it is hologram. Namely in a light reflecting hologramm is stored a spatial interference picture, which is possible by the thickness of film emulsion. This spatial interference picture is capable to mirror back the light with a given wave length to the same spot, independent from the direction of the sunlight at every time, so only the intensity of the collected light depends on the appropriate orientation.

Because of the small surface of the detector 3 the collected signal must be amplified, than the further signal- processing can go on expediently on digital procedure. The output of semiconductor detector 3 in the measuring equipment is connected to the input of a linear amplifier 4. To the output of the amplifier 4 is connected an analogue- digital converter 5. To the output of the analogue-digital converter 5 is a signal indicator 6 connected. The signal indicator 6 can be analogue or digital one, which indicates the intensity of ultra-violate radiation.

Beside the indication of instant intensity, with further processing of the measuring signal the measuring equipment can be made suitable for other objects as well. With a comparator connected to the output of the analogue-digital converter 5, and with to the comparator connected sound and light signalling device the measuring equipment gives a warning signal in the case of overstepping a dangerous level programmed previously. Connecting an integrating circuit to the output of the analogue-digital converter 5 the measuring

SUBSTITUTESHEET equipment is suitable for dose measuring, which measuring equipment measures in decided periods or continuously the ultraviolate radiation. This device can be deployed for following the position of the sun, controlled by a clock- work, and combined with a transmitter of radiofrequenzes. In this case the the mobile receiver(s) is a signalling device, which can be held by a child or a shepherddog, which dog can be trained to drive animals in an overshadowed place. The measuring equipment can be utilized for control the auto- matic moving of a shielding umbrella, which umbrella can be equipped with driving mechanism, or it can be an LCD platform controlled by the measuring equipment. The measuring equipment can be built into a wrist watch having a 10x10 mm window for the UV measuring equipment.

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Claims

CLAIMS :

1. Ultra-violet radiation detector comprising a device for decomposing light into spectrum and a semiconductor detector set up in the path of the ultra-violet light beam behind the spectrum decomposing device, characterised in that the device decomposing the light into spectrum is a diffraction grating (2,2'), behind which a detector (3) of surface witdh of two or more refraction orders of the decomposed light beams and with partly uncovered surface, uncovered on places adequate to the distance of refraction orders, is set up in the path of the light. Priority: 8th June 1992

2. Ultra-violet radiation detector according to claim 1, characterised in that the diffraction grating (2) is a translucent holographic picture, behind which a detector (3) with a surface of the same dimension as the surface of the diffraction grating (2) is set up. (Priority: 8th June 1992)

3. Ultra-violet radiation detector according to claim 1 °*c 2, characterised in that it has an incidence angle indicator for indication of the direction of the incoming light in relation to the diffraction grating (2) . Priority: 6th January 1993

4. Ultra-violet radiation detector according to claim 3, characterised in that it has an indicator for an incidence angle of 45°. (Priority: 6th January 1993)

5. Ultra-violet radiation detector according to claim 3 or 4, characterised in that the incidence angle indicator is a white area set up on the detector's (3) covered surface behind the diffraction grating (2) . Priority: 6th January 1993

6. Ultra-violet radiation detector according to claim 1, characterised in that the diffraction grating (2¹) is a lightreflecting holographic picture, above which, parallel with it and shifted in the direction of the incoming light is located the photosensitive detector (3) with a partly uncovered surface. (Priority: 8th June 1992)

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7. Measuring equipment for measuring ultra-violet radiation comprising a device for decomposing light into spectrum, and a semiconductor detector set up in the path of the ultra-violet light beam behind the spectrum decomposing device set up in the path of ultra-violet light beam, said detector being connected to an evaluating electronic device, characterising in that the device decomposing the light into spectrum is a diffraction grating (2,2'), behind which a detector (3) of surface witdh of two or more refraction orders of the decomposed light beams and with partly uncovered surface, uncovered on places adequate to the distance of refraction orders, is set up in the path of the light and the output of the photosensitive detector (3) is connected via analogue amplifier (4) to an analogue-digital converter (5) . (Priority: 8th June 1992)

8. Measuring equipment according to claim 7, character¬ ised in that it is equipped with an incidence angle indicator for indication of the direction of the incoming light in relation to the diffraction grating (2) . Priority: 6th January 1993

9. Measuring equipment according to claim 7 or 8, characterised in that an LCD display (6) is connected to the output of the analogue-digital converter (5) .

Priority: 8th June 1992 10. Measuring equipment according to any of claims 7 to 9, characterised in that a comparator is connected to the output of the analogue-digital converter (5) . Priority: 8th June 1992

11. Measuring equipment according to any of claims 7 to 10, characterised in that an integrating circuit is connected to the output of the analogue-digital converter (5) . (Priority: 8th June 1992 )

12. Measuring equipment according to any of claims 7 to 11, characterised in that it is built in a wrist watch. Priority: 8th June 1992

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13. Measuring equipment according to any of claims 7 to 12, characterised with, that it is materialized as an integrated circuit furnished with UV permeable window. Priority: 8th June 1992

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