KR20100010960A - Liquid crystal x-ray detection device with low viewing angle effect - Google Patents

Liquid crystal x-ray detection device with low viewing angle effect Download PDF

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Publication number
KR20100010960A
KR20100010960A KR1020080071971A KR20080071971A KR20100010960A KR 20100010960 A KR20100010960 A KR 20100010960A KR 1020080071971 A KR1020080071971 A KR 1020080071971A KR 20080071971 A KR20080071971 A KR 20080071971A KR 20100010960 A KR20100010960 A KR 20100010960A
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South Korea
Prior art keywords
liquid crystal
degrees
ray inspection
angle
viewing angle
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KR1020080071971A
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Korean (ko)
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노봉규
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세심광전자기술(주)
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Publication of KR20100010960A publication Critical patent/KR20100010960A/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy

Abstract

The present invention relates to a liquid crystal X-ray inspection apparatus that reduces the viewing angle dependency. In the liquid crystal X-ray inspection apparatus, charges generated when X-rays are absorbed in the photoconductive layer change the arrangement of the liquid crystal layer, and thus reflect characteristics thereof are changed. Liquid crystal cells have different reflection characteristics depending on the viewing angle. If the difference in viewing angle characteristics is large, an error increases in the process of correcting this. In the present invention, the difference in viewing angle characteristics did not appear in the test, and the optimum conditions were found in the TN type and the VA type. In addition, the light source has been optimized to reduce viewing angle dependence. Liquid crystal X-ray inspection apparatus of the present invention can be used for industrial and medical purposes.

Description

Liquid Crystal X-Ray Detection Device With Low Viewing Angle Effect}

The present invention relates to a liquid crystal X-ray inspection apparatus, and relates to a liquid crystal optical design of the liquid crystal X-ray inspection apparatus and a structure of the liquid crystal X-ray inspection apparatus so that the viewing angle dependence of the liquid crystal X-ray inspection plate minimizes the inspection.

The liquid crystal X-ray inspection apparatus was first devised in 1983 by Huignard (nationality: France) in which a Cholesteric liquid crystal layer was placed on the photoconductive layer (Ref. USP4,368,386). In March 2008, a professor at the Women's University of Toronto, Toronto, announced a liquid crystal X-ray inspection system made of a structure bonded to an amorphous selenium and a nematic liquid crystal layer about 3 cm (Ref. Med. Phys. 35 (3)). , March, p959). LCD X-ray inspection apparatus has advantages such as low cost and low irradiation dose, but is still in the early stage of research. This is mainly due to the fact that specialized research in the liquid crystal fields such as the viewing angle dependence of the liquid crystal, the response characteristics of the liquid crystal, the voltage holding ratio of the liquid crystal, and the driving voltage waveform is not supported. The present invention deals with the viewing angle of the liquid crystal design portion of the liquid crystal X-ray detection apparatus.

A liquid crystal X-ray inspection apparatus is a device which determines the state of a sample by measuring the intensity distribution of the X-ray light which passed the sample. 1 is a schematic diagram of a liquid crystal X-ray inspection apparatus. The liquid crystal X-ray inspection apparatus is largely composed of the X-ray generator 500, the liquid crystal X-ray inspection plate 100, the mirror 200, the light source 300, and the image detector 400. The X-rays irradiated by the X-ray generator 500 and passed through the sample may change the arrangement distribution of liquid crystal molecules in the liquid crystal X-ray inspection plate 100. The liquid crystal X-ray inspection plate is a reflection type in which a polarizer is attached. The light emitted from the light source 300 is reflected by the mirror 200 to be incident on the liquid crystal X-ray inspecting plate 100, and is reflected back from the liquid crystal X-ray inspecting plate 100, thereby changing polarization reflection characteristics. The reflected light is reflected from the mirror and enters the image detector. In the liquid crystal X-ray inspection plate, the brightness distribution varies due to the difference in the polarization reflection characteristic, which is measured by the image detector 400. The image detection unit includes a lens and an image device such as a CCD or a CMOS.

2 is a cross-sectional view of the liquid crystal X-ray inspection plate 100. The upper glass substrate 111 makes the thickness thin. The reflective film 114, the photoconductive layer 113, and the upper electrode 112 are formed on the upper glass substrate. The reflective film is made of two layers of two dielectric films having different refractive indices. The lower electrode 122 is formed on the lower glass substrate 121. The bias voltage is applied to the upper electrode 112 and the lower electrode 122. The liquid crystal layer 130 is formed between the upper glass substrate and the lower glass substrate. The initial alignment structure of the liquid crystal layer in the state where no voltage is applied is determined by the vertical alignment layers 115 and 125.

The bias voltage waveform is usually DC. When the X-rays are irradiated on the photoconductive layer 113 subjected to the DC voltage, the X-rays are absorbed in the photoconductive layer to generate electrons and holes. The number of electrons and holes depends on the acceleration voltage and X-ray dose of the X-ray generator, the DC voltage applied to the photoconductive layer, the type of photoconductive layer, and the thickness of the photoconductor. Electrons and holes in the photoconductive layer are separated in the direction of the electrodes having opposite polarities due to the electric field generated by the bias voltage. Since the liquid crystal layer is an insulator, holes are laminated on the contact surface of the liquid crystal layer, and the holes cause a difference in voltage applied to the liquid crystal layer, and the polarization reflectance distribution of the liquid crystal layer is different. The difference in distribution is photographed by the image detector 400 to obtain X-ray image information. Although the thickness of the photoconductive layer varies depending on the material, the thickness of the photoconductive layer is about several hundreds (100 to 500) µm, which is an area where X-rays are absorbed to some extent. In the liquid crystal X-ray inspection apparatus, write beam is X-ray, and read beam is light emitted from the light source 300. Since the intensity of the light to be read is proportional to the intensity of the light to be written, the distribution of the light to be written can be known by finding the distribution of the light to be read. X-ray information is obtained by measuring the brightness of the light reflected from the LCD X-ray test plate. The light from the light source should not affect the photoconductor. If the energy of the read light is greater than the bandgap of the photoconductor, the read light is absorbed in the photoconductor layer, creating electrons and holes. Therefore, red or near infrared light with a large wavelength is suitable for the light source. When the photoconductor is amorphous selenium, the band gap is 2.3 eV, so the corresponding wavelength is about 540 nm. Therefore, if the wavelength of the light source is 600nm or more, the photoconductor can be applied to the liquid crystal X-ray inspection apparatus of selenium.

The liquid crystal X-ray inspecting plate 100 is the same as the reflective liquid crystal display device having optical properties of one polarizing plate. Compared with the transmission type which used two polarizing plates, the reflection type which has one polarizing plate has large viewing angle dependence. Considering the viewing angle characteristics, the light source 300, the image detector 400, and the liquid crystal X-ray inspection plate 100 should be designed.

3 illustrates the light receiving angle of the image detector. The light receiving angle is an angle between the outermost edge of the liquid crystal X-ray detection plate entering the image detection unit. If the light receiving angle is small, the distance L between two elements is large, so that the amount of light entering the detection unit is small and the inspection apparatus is large. On the other hand, if the angle is small, the amount of light increases, but the viewing angle characteristic of the liquid crystal becomes an important variable. 4 illustrates a case where two image detectors are provided. Although the light receiving angle can be reduced, the cost of manufacturing increases because an additional image detector is required. FIG. 5 increases the distance L 'compared to FIG. In this case, since the light receiving angle becomes smaller, the influence on the viewing angle characteristic of the viewing angle liquid crystal is reduced, but there arises a problem that the amount of light decreases and the volume of the inspection apparatus becomes large.

The present invention deals with a liquid crystal X-ray inspection plate having a small difference in viewing angle characteristics, a light receiving angle, and a condition of a light source, thereby treating a liquid crystal X-ray inspection apparatus with high measurement accuracy.

The liquid crystal X-ray inspection apparatus according to the present invention reduces the viewing angle dependency to increase the accuracy of the measurement. The liquid crystal X-ray inspection apparatus has less radiation dose and lower price than other digital radiography (DR) but has not been commercialized yet. This is because the liquid crystal X-ray inspection plate applying the reflective liquid crystal mode does not overcome the viewing angle dependency. In the present invention, the angle of incidence is optimized in accordance with the viewing angle of the liquid crystal plate to increase the accuracy of the measurement. The liquid crystal X-ray inspection apparatus of the present invention can be utilized for industrial and medical purposes.

Modes commonly used in liquid crystal displays are TN (Twist Nematic) and VA (Vertical Aligned). This liquid crystal mode is described in detail in the 32-page "LCD Engineering" booklet edited by the inventor and published by the Holy Land. The TN type has a horizontal orientation in a state where no voltage is applied, and the liquid crystal array becomes vertical when the voltage exceeds the saturation voltage. The VA mode is a vertical alignment in a state where no voltage is applied, and the liquid crystal array is horizontal when applied to a saturation voltage or more.

A chest X-ray detector is 50 cm x 50 cm, and a breast cancer x-ray detector is 30 cm x 30 cm. Table 1 shows a light receiving angle with respect to the separation distance L of the image detector.

  X-ray detector size and light receiving angle Light receiving angle (degrees) Separation distance (50cm × 50cm) Separation distance (30cm × 30cm) 60 43 cm 26 cm 50 54 cm 32 cm 40 68 cm 42 cm 30 93 cm 56 cm

To describe the viewing angle characteristic, a coordinate system must first be set. 6 is a coordinate system used in the present invention. In liquid crystals, the left-handed coordinate system is used because it mixes the Cholesteric liquid crystals that return to the left. In FIG. 6, the Z axis is a direction penetrating through the paper surface. The viewing angle direction shown in FIG. 6 is indicated by a thick line. The polar angle θ is an angle formed between the direction perpendicular to the plane and the viewing angle direction, and the azimuth angle Φ is an angle formed with the X axis when the viewing angle is projected onto the XY plane. Half of the light receiving angle may be regarded as the maximum polar angle θ. 7 is a diagram for illustrating the rubbing and polarizing plate directions of the liquid crystal X-ray inspection plate. 7 is a left hand coordinate system. In FIG. 7, α is a rubbing direction of the upper alignment layer 115, and β is a rubbing direction of the lower alignment layer 125. γ is the transmission axis direction of the polarizing plate 126.

The difference in characteristics of the electro-optic reflection curve according to the viewing angle can be summarized in two ways. First, threshold voltages vary depending on the viewing angle. 8 is an example. 8 is a case where the twist angle is 180 degrees. The curve shown in FIG. 8 is an electro-optic reflectivity curve when the azimuth angle Φ is the same and the polar angle θ is 0, 15, 30, and 45 degrees. If the polar angle is 0 degrees, it is the front viewing angle direction. Measurements shall be made where the reflectivity is simply increased or decreased with respect to the applied voltage. The effective voltage applied to the liquid crystal layer should be adjusted so as to be between the threshold voltage V (10) where the reflectance changes by 10% and the saturation voltage V (90) that changes by 90%. The change in the reflectance of the curve, which is 0 degrees in front, is not measured at 100% because it is not a simple increase at 70% at 15 degrees, 30% at 30 degrees and 45 degrees. Secondly, the threshold voltages are similar, but reflectivity varies with polar angles. 9 is a case where the twist angle is 60 degrees. A zero-degree curve at the front shows 100% change in reflectance, 80% at 15 degrees polarization, 45% at 30 degrees polarization, and 30% at 45 degrees polarization.

When designing the X-ray liquid crystal test plate 100, it is most important to select a liquid crystal mode having little viewing angle dependence. In addition, the structure of the light source and the image detector must be determined so that the light receiving angle is optimal for the selected liquid crystal mode.

When the liquid crystal X-ray test plate was manufactured in the TN reflective liquid crystal mode, the twist angles were computed at 60 degrees, 90 degrees, 120 degrees, and 180 degrees, and the conditions as shown in the following table were found. The wavelength of the light source is λ. Under the conditions shown in Table 2, for light having a wavelength of λ, the light becomes NB (Normal Black) mode, which becomes dark when no voltage is applied to the liquid crystal layer. Pretilt Angle was set at 5 degrees.

 Simulated liquid crystal cell conditions Twist angle Upper rubbing direction (α) Harving direction (β) Δnd / λ Polarizing plate transmission axis (γ) 60 degrees 0 degrees 60 degrees 1.25 15 degrees 90 degrees 0 degrees 90 degrees 1.18 40 degrees 120 degrees 0 degrees 120 degrees 1.14 60 degrees 180 degrees 0 degrees 180 degrees 1.09 0 degrees

10 is an electro-optical reflection curve of a liquid crystal cell when the twist angle is 60 degrees and the azimuth angle Φ is 0 degrees, 45 degrees, 90 degrees, and 135 degrees. Each figure has four curves, which are electro-optic reflection curves with an azimuth angle θ of 0 degrees, 15 degrees, 30 degrees, and 45 degrees. If the azimuth angle is 180 degrees, the shape of the curve is the same as the case where the azimuth angle is 0 degrees. The azimuth angle of 225 degrees is 45 degrees, and the azimuth angle of 270 degrees is 90 degrees and 315 degrees, the shape of the curve is almost similar. This means that the electro-optic reflection curve is symmetric with respect to the origin. 11 is a twist angle of the liquid crystal cell is 90 degrees, FIG. 12 is a twist angle of 120 degrees, and FIG. 13 is a twist angle of 180 degrees. The azimuth and polar angles of FIGS. 11, 12, and 13 are the same as in FIG. 10.

In FIG. 11 showing the viewing angle characteristic of the liquid crystal cell having a twist angle of 60 degrees, it can be seen that the difference in curve shape is severe according to the difference in the polar angle. In particular, when the azimuth angle is 0 degrees, it can be seen that the reflectivity is more than three times different when the polar angle is 0 degrees and the polar angle is 30 degrees. Therefore, when using a TN twisted 60 degrees, the light reception angle should be limited to less than 30 degrees to maintain the measurement accuracy.

In FIG. 11 showing the viewing angle characteristic of the liquid crystal cell twisted at 90 degrees, it can be seen that the difference in the shape of the curve varies with the polar angle at the azimuth angle of 0 degrees. If the polar angle is 0 degrees and the polar angle is 30 degrees, the reflectivity is more than 3.5 times different. Therefore, when using a TN twisted 90 degrees, the light reception angle should be limited to less than 30 degrees to maintain the accuracy of the measurement.

In FIG. 12, where the twist angle is 120 degrees, it can be seen that the difference in the shape of the curve varies with the polar angle when the azimuth angle is 45 degrees. If the polar angle is 0 degrees and the polar angle is 30 degrees, the reflectivity is more than 3.5 times different. Therefore, when using a TN twisted 120 degrees, the light reception angle should be limited to less than 30 degrees to maintain the accuracy of the measurement.

In FIG. 13 where the twist angle is 180 degrees, when the azimuth angle is 0 degrees, it can be seen that the shape difference of the curve is severe according to the polar angle. In particular, when the polar angle is 30 degrees or more, the polar angle is largely different from the curve having 0 degrees. When the polar angle is 0 degrees and the polar angle is 30 degrees, the reflectivity is about 2.0 times different, which is smaller than the case where the twist angle is smaller than 180 degrees. Therefore, when using TN twisted 180 degrees, some measurement is made even if the angle of light reception is about 40 to 60 degrees.

Referring to FIGS. 10, 11, 12, and 13, the accuracy of the measurement is maintained to some extent when the light receiving angle is 30 degrees. However, when the light receiving angle is 60 degrees, the difference in the curve except for the twist angle of 180 degrees of FIG. 13 is different. Large, precise measurement is difficult. In the case of the TN type liquid crystal mode, the accuracy of measurement is maintained by limiting the light receiving angle at which the reflectance difference is less than 30% to about 40 degrees.

14 is an electro-optical reflection curve in the VA mode. In the case of the reflective VA mode, it is difficult to create a dark state in the absence of voltage without a quarter wave plate. In FIG. 14, the vertical alignment film has a direction of 0 degrees and a polarizing plate has a transmission axis of 45 degrees. The optical axis of the quarter-wave plate was at 0 degrees. In VA mode, it can be seen that there is no difference in curve up to 30 degrees. In the case of the VA type liquid crystal mode, the light receiving angle is preferably limited to about 60 degrees.

The light source 300 is also a factor that affects the viewing angle of the liquid crystal X-ray inspection plate 100. The area of the light source should be at least larger than that of the X-ray liquid crystal test plate to minimize the influence at the corners. When the light source has a smaller area than the liquid crystal X-ray inspection plate, since the light reflected from the corner portion not overlapping with the light source and entering the image detection unit is very small, the detection characteristic is further reduced in combination with the viewing angle characteristic of the liquid crystal.

Instead of brightening the light source uniformly, certain areas can be brightened to reduce viewing angle dependence. In the case of TN twisted at 60 degrees in FIG. 10, the azimuth angle is 0 degrees and the polar angle is more than 15 degrees. In the case of TN twisted at 90 degrees, the azimuth angle is 0 degrees and the polar angle is more than 15 degrees. In the case of twisted TN, the azimuth angle is 0 degrees and 45 degrees and the polar angle is more than 15 degrees. In the case of TN twisted 180 degrees in FIG. 13, the azimuth angle is 0 degrees and the polar angle is more than 15 degrees. Can correct to some extent the viewing angle characteristic.

1 is a schematic diagram of a liquid crystal X-ray inspection apparatus.

2 is an explanatory diagram showing a liquid crystal X-ray inspection plate operation.

3 is a schematic diagram of an image receiving angle.

4 is an example of reducing the image receiving angle.

5 is an example of reducing the image receiving angle.

6 is a coordinate system of a reflective liquid crystal cell.

7 is a perspective view showing a rubbing direction and a polarizing plate transmission axis.

8 is an explanatory diagram for grasping the influence of the viewing angle.

9 is an explanatory diagram for grasping the influence of the viewing angle.

10 is a viewing angle characteristic of the TN type twisted at 60 degrees.

11 is a viewing angle characteristic of the TN type twisted 90 degrees.

12 is a viewing angle characteristic of the TN type twisted by 120 degrees.

13 is a viewing angle characteristic of the TN type twisted 180 degrees.

14 is a viewing angle characteristic of the VA mode.

<Brief description of the major symbols in the drawings>

100: liquid crystal X-ray inspection plate

111: glass substrate

112: phase electrode 113: photoconductive layer

114: reflecting film 115: upper alignment film

121: lower glass substrate 122: lower electrode

125: lower orientation film 126: polarizing plate

130: liquid crystal layer

200: mirror 300: light source

400: image detector 500: X-ray generator

Claims (4)

In the liquid crystal X-ray inspection apparatus in which the X-rays absorbed by the photoconductive layer 113 generates electric charges, and thus the arrangement distribution of the liquid crystal layer 130 is changed to obtain image information. The liquid crystal injected into the liquid crystal X-ray inspection plate 100 is nematic, The liquid crystal layer twist angle of the X-ray inspection plate is between 90 degrees and 180 degrees, The refractive index anisotropy Δn of the liquid crystal layer 130, the thickness d of the liquid crystal layer and the wavelength λ of the light source
Figure 112008053120160-PAT00001
 Satisfy the relation, Liquid crystal X-ray inspection apparatus, characterized in that the light receiving angle is less than 60 degrees. In the liquid crystal X-ray inspection apparatus in which the X-rays absorbed by the photoconductive layer 113 generates electric charges, and thus the arrangement distribution of the liquid crystal layer 130 is changed to obtain image information. The liquid crystal X-ray inspection apparatus characterized in that the liquid crystal injected into the liquid crystal X-ray inspection plate 100 is vertically aligned, a quarter wave plate is attached, and the light receiving angle is less than 60 degrees. In the liquid crystal X-ray inspection apparatus in which the X-rays absorbed by the photoconductive layer 113 generates electric charges, and thus the arrangement distribution of the liquid crystal layer 130 is changed to obtain image information. Liquid crystal X-ray inspection apparatus, characterized in that the light source 200 is larger than the liquid crystal X-ray inspection plate (100). 4. The liquid crystal X-ray inspection apparatus according to claim 3, wherein the viewing angle characteristic of the liquid crystal X-ray inspection plate 100 is compensated by varying the brightness of a portion of the light source 300.
KR1020080071971A 2008-07-24 2008-07-24 Liquid crystal x-ray detection device with low viewing angle effect KR20100010960A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10142584B2 (en) 2014-05-27 2018-11-27 Tribune Broadcasting Company, Llc Use of location lulls to facilitate identifying and recording video capture location
US10225489B2 (en) 2014-05-27 2019-03-05 Tribune Broadcasting Company, Llc Use of wireless connection loss to facilitate identifying and recording video capture location
KR20200099879A (en) * 2019-02-15 2020-08-25 세심광전자기술(주) Method for deciding x-ray image of liquid crystal x-ray detector

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10142584B2 (en) 2014-05-27 2018-11-27 Tribune Broadcasting Company, Llc Use of location lulls to facilitate identifying and recording video capture location
US10225489B2 (en) 2014-05-27 2019-03-05 Tribune Broadcasting Company, Llc Use of wireless connection loss to facilitate identifying and recording video capture location
US10375324B2 (en) 2014-05-27 2019-08-06 Tribune Broadcasting Company, Llc Use of wireless connection loss to facilitate identifying and recording video capture location
KR20200099879A (en) * 2019-02-15 2020-08-25 세심광전자기술(주) Method for deciding x-ray image of liquid crystal x-ray detector

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