US2255933A - Variable density window - Google Patents

Description

L :earch Room sept. 1s, 1941. E H LAND" 2,255,933

VARIABLE DENS ITY WINDOW f" Filed Dec. l2, 1940 L `,yl-1G. l

FIG. 2

30 as L Sept. 16, 1941 Search Room VARIABLE DENSITY WINDOW Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Dover, Del., a corporation of Delaware Application December 12, 1940, Serial No. 369,763

(Cl. Sli-65) 9 Claims.

This invention relates to variable density windows.

An object of the invention is to provide a variable density window comprising a plurality of overlying, light-polarizing elements having means associated therewith for controlling at will the amount of light transmitted thereby.

Another object is to provide such Ia window wherein the light-polarizing elements are bonded together in laminated form and wherein the density of the window as a whole is varied by the application of suitable force directly to said lamination.

A further object is to provide such a window wherein the bonding means between the polarizing elements comprises a rubbery elastic, transparent cement which is substantially isotropic in its normal condition but which may be converted to act as a half wave retardation device upon the application of predetermined stress.

A still further object is to provide such a laminated window wherein the density of the window as a whole is varied by moving one polarizer with respect to the other and thereby exerting a shearing force on the cement layer suflicient to cause it to function as a half wave retardation device.

Other objects and advantages will in part appear and in part be pointed out in the course of the following description of an embodiment of the invention, which is given as a non-limiting example, in connection with the accompanying drawing, in which:

Figure 1 is a sectional view showing a variable density window embodying a form of the invention;

Figure 2 is an elevation of the window shown in Fig. 1; and

Figure 3 is a partial, sectional view showing a modification of a part of the window shown in Fig. 1.

In its simplest embodiment, the variable density window of the present invention comprises a pair of parallel, overlying polarizing surfaces which are preferably positioned with their transmission axes either relatively parallel or relatively perpendicular. Said polarizers are bonded together by means of a transparent, rubbery cement which is isotropic when not under stress but is capable of functioning as a half wave retardation element when subjected to a shearing force. Means are provided for moving one of said polarizers in the plane thereof with respect to the other and thus for exerting a shearing force on said cement layer.

The degree of motion of said polarzer may be carefully controlled, and thus the light passing through each polarizer may have its vibration characteristics altered at will so that it may be either transmitted or absorbed by the other said polarizing element.

Referring to Figs. 1 and 2, element I Il represents a channeled window frame formed in any conventional manner and providing a window aperture of substantial area. Mounted in frame I0, as by means of element I2, is a laminated window element comprising a pair of layers I4 and I6 of polarizing material, bonded together by means of a layer of cement I5 and covered by protecting plates I8, 20 of glass or other rigid, transparent plastic. The other side of frame I0 may be provided with any suitable ange means 22 of conventional design.

Polarizing layers I4 and I6 are of substantially uniform polarizing properties and may conveniently be made from one of the polarizing sheets or lms sold under the trade name Polaroid". They may be positioned with their respective transmission axes at any desired angle to each other, but preferably said axes will be relatively perpendicular and at angles of 45 to the vertical, as indicated-in Fig. 2, wherein arrows 24 and 25 represent the transmission axes of polarizers I4 and I6 respectively.

Cement layer I5 may comprise virtually any transparent, rubbery, adhesive material which will bond to polarizing layers I4 and I6 or to glass and other relatively hard plastics. Among satisfactory materials for this purpose there may be mentioned as illustrative examples vinyl acetate plasticized with dibutyl phthalate, and incomplete vinyl butyral, known as Vinylite X, plasticized with any suitable medium such as dibutyl phthalate. Layer I5 may be of any desired thickness, the controlling factor being that the thicker the layer, the greater the amount of shear necessary to cause it to function as a half wave retardation element. It will be understood, however, that layer I5 has been shown in Fig. l in highly exaggerated and diagrammatic form.

As is shown in Fig. l, there are provided within frame I0 suitable means for exerting force on one of the polarizing elements in such manner as to exert shear on layer I5. Glass cover plate 20 is provided along its upper edge with a channeled rim 26 which is slidable between spacer elements 28 and bears against one or more compression springs 30. Along its lower edge, plate 20 is provided with a similar rim 32 which is slidable between spacer elements 34 and is in contact with a suitable cam 35 or other similar device. Cam

35 is mounted on shaft 36 and provided with suitable means for controlling its rotation, said means comprising gear 38 meshing with worm 42, controlled by crank or knob 40 journaled in frame l0. It will of course be understood, however, that this cam mechanism is merely illustrative of the many similar means for exerting force on plate 20 in accordance with the practice of the invention.

It is believed that the operation of the above described window will now be apparent. Layer I5 is preferably of such characteristics that it is optically isotropic when the device is in the position shown in Fig. 1, that is to say, when cam 35 is exerting the least pressure. Inasmuch, therefore, as the operation of layer I5 may be disregarded, and inasmuch as polarizers I4 and I6 are positioned with their transmission axes relatively perpendicular, it will be seen that this is the position of maximum extinction for the window. As cam 35 is rotated, plate 20 is caused to move upward, and since plate I8 is rigidly held, this exerts a shearing force on cement layer I5. This force gradually causes the molecules or micells in the cement to become oriented and so causes layer I5 to become Vbirefringent. The 'birefringence increases with the orientation, and the layer therefore exerts a gradually increasing relative retardation with respect to one component of the polarized light transmitted by, for example, polarizer I4. As the relative retardation increases, more and more light has its polarization characteristics altered to a condition wherein it is transmitted by polarizer 20. When the stress reaches the degree whereat layer I5 becomes a half wave retardation plate, all of the light transmitted by polarizer I4 will have its vibration direction rotated through 90 and thus will be transmitted by polarizer I6. It follows that the position of maximum transmission is that wherein layer I5 is subjected to such a degree of shear that it functions as a half wave plate.

The positions of the polarizing elements with respect to their axes may be changed to a considerable extent. However, the illustrated position is preferred. It will be understood also that in order to obtain the maximum density variation in this arrangement, the direction of the force applied to layer I5 and plate 20 should be at 45 to the axes of the two polarizers, as in the arrangement shown in Figs. 1 and 2. It Will of course be obvious that the polarizers may be positioned with their axes parallel, and in this case also the force should preferably be at an angle of 45 to said axes. Various other relative positions of the polarizers and direction of force may also be used, but the positions above are preferred.

Fig. 3 shows a modication of the invention wherein the relative positions of the various layers in the lamination ar changed. Layer 45 in Fig. 3 corresponds to layer I5 in Fig. 1, and layers 44 and 46 represent polarizing layers corresponding to layers I4 and I6 in Fig. 1. Layers 48 and 50 represent sheets or plates of glass or other suitably rigid, transparent plastic, and layers 52 and 54 represent additional cover plates for the polarizing layers and may comprise thin sheets of glass or other plastic or a protective coating of a suitable substance such as a lacquer. It will be understood that the unit shown in Fig. 3 may be substituted for the corresponding unit in Fig. 1, and that the operation will be substantially the same as that described in connection with Fig. 1. Many other modifications of the aboye construction will also doubtless be apparent and are construed as within the scope of the invention and of the claims herein.

The plastic employed as the cement layer, I5

in Fig. 1 and 45 in Fig. 3, should be a plastic, as has been pointed out, which is rubbery-elastic, i. e., which possesses the property of returning to its initial condition after the stress to which it has been subjected has been removed, and it should show substantially no cold flow when subjected to the stress rendering it birefringent. Furthermore, it should preferably have a high positive or negative stress optical coeiiicient. The materials already mentioned for use in the device possess these characteristics to a satisfactory degree.

It should be understood furthermore that while a preferred embodiment of the invention constitutes the provision of means for subjecting the cement layer to a stress which results in it functioning as a half-wave retardation device, such a preferred condition is not necessary in the practice of the invention. It may for example be desirable only to permit a small percentage of light to be transmitted or it may be unnecessary for the device to function to completely block incident light in the position of maximum extinction. Any of these modifications are to be deemed to fall within the scope of the invention.

It may be said of the device of the present invention that it comprises a plurality of lightpolarizing elements bonded together either directly or by a bond connecting their supporting plates by means of a material such that the transmission of the entire device for light incident on either surface as a function of the stress applied to the bonding material through the relative motion of one of the light-polarizing elements with respect to the other in a direction substantially parallel to the plane of the other said polarizing element.

Since certain changes may be made in the above construction, and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the-accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A variable density window comprising, in combination, means providing a plurality of substantially superimposed, relatively parallel, lightpolarizing elements, a layer of transparent, rubbery cement between said polarizing elements, said cement being adapted under a predetermined stress to function as a half wave retardation element, and means for moving one of said polarizing elements with respect to the other and simultaneously exerting a shearing force on said cement layer sufficient to cause it to function substantially as a half wave retardation device.

2. A variable density window comprising, in combination, a plurality of light-polarizing elements, said elements being bonded together in substantially parallel and superimposed relation, said bonding means comprising a. transparent,

B8. OPTICS rubbery cement, said cement being capable under predetermined stress of functioning as a half wave retardation element, and means for moving one of said polarizing elements in the plane thereof with respect to the other said element and thereby exerting a shearing force on said cement layer sufficient to cause it to function substantially as a predetermined wave retardation device.

3. A variable density window comprising, in combination, a plurality of light-polarizing elements, said elements being bonded together in substantially parallel, superimposed relation with their respective transmission axes at a predetermined angular relation to each other, said bonding means comprising a transparent, rubbery cement, said cement being capable under a predetermined stress of functioning as a half wave retardation element, and means for moving one of said polarizing elements in the plane thereof with respect to the other said element, thereby exerting a shearing force on said cement layer suilicient to cause it to function as a predetermined Wave retardation device, said motion being in a direction at equal angles to the transmission axes of said polarizing elements.

4. A variable density Window comprising, in combination, a plurality of light-polarizing elements, said elements being bonded together in substantially parallel, superimposed relation with their respective transmission axes relatively perpendicular, said bonding means comprising a transparent, rubbery cement, said cement being capable under a predetermined stress of functioning as a half Wave retardation element, and means for moving one of said polarizing elements in the plane thereof with respect to the other said element, thereby exerting a shearing force on said cement layer suiiicient to cause it to function as a half Wave retardation element, said motion being in a direction at angles of 45 to the transmission axes of said polarizing elements.

5. A variable density window comprising, in combination, a plurality of light-polarizing elements, said elements being bonded together in substantially parallel, superimposed relation with their respective transmission axes relatively parallel, said bonding means comprising a transparent, rubbery cement, said cement being capable under a predetermined stress of functioning as a half wave retardation element, and means for moving one of said polarizing elements in the plane thereof with respect to the other said element, thereby exerting a shearing force on said cement layer sufficient to cause it to function as a half wave retardation element, said motion being in a direction at angles of 45 to the transmission axes of said polarizing elements.

6. A variable density window comprising, in combination, frame means providing a window aperture of substantial area, a plurality of substantially parallel glass plates positioned within said frame and overlying said aperture, means providing a plurality of light-polarizing surfaces `Search Roen-i of substantially the same area as said aperture, one of said polarizing surfaces being associated with each of said glass plates, means comprising a layer of transparent, rubbery cement bonding said plates together, said cement being adapted upon the application of a predetermined shearing force to function as a half wave retardation device, means for positioning one of said glass plates fixedly within said frame, and means for moving the other of said glass plates in the plane thereof and thereby exerting a predetermined shearing force upon said cement layer to vary the amount of light transmitted by said window.

7. A variable density Window comprising, in combination, means providing a plurality of substantially superimposed, relatively parallel, lightpolarizing elements, a layer of transparent, rubbery-elastic cement showing substantially no cold oW between said polarizing elements, and means for moving one of said polarizing elements with respect to the other and simultaneously exerting a shearing force on said cement layer, the transmission of said window for light incident normally on either surface thereof being a function of the force applied to said cement layer.

8. A variable density window comprising, in combination, a plurality of light-polarizing elements, said elements being bonded together in substantially parallel, superimposed relation with their respective transmission axes at a predetermined angular relation to each other, said bonding means comprising a transparent, rubberyelastic cement, said cement having a high stress optical coefficient and showing substantially no cold iiow, and means for moving one of said polarizing elements in the plane thereof with respect to the other said element, thereby exerting a shearing force on said cement layer suiiicient to cause it to function as a wave retardation device, said motion being in a direction at equal angles to the transmission axes of said polarizing elements.

9. A Variable density window comprising, in combination, frame means providing a window aperture of substantial area, a plurality of substantially parallel glass plates positioned within said frame and overlying said aperture, means providing a plurality of light-polarizing surfaces of substantially the same area as said aperture, one of said polarizing surfaces being associated with each of said glass plates, means comprising a layer of transparent, rubbery cement bonding said plates together, said cement showing substantially no cold flow when subjected to a stress and having a high stress optical coefcient, means for positioning one of said glass plates flxedly within said frame, and means for moving the vother of said glass plates in the plane thereof and thereby exerting a predetermined shearing force upon said cement layer to vary the amount of light transmitted by said window, the transmission of light by said window being a function of the shearing force applied to said cement.

EDWIN H. LAND.

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