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CLASS 349,	LIQUID CRYSTAL CELLS, ELEMENTS AND SYSTEMS
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SECTION I - CLASS DEFINITION

This is the generic class for cells, elements, and systems which include molecules of a material having both liquid and crystalline properties. Elements or systems included in this class are those which have a significant liquid crystal cell detail or liquid crystal response or properties, and in which the liquid crystal controls or changes the optical properties of electromagnetic radiation such as direction, phase, amplitude, frequency, or polarization state. This class also provides for nominal manufacturing methods for producing significant liquid crystal cell structure.

SECTION II - LINES WITH OTHER CLASSES AND WITHIN THIS CLASS

If the liquid crystal cell is an insignificant part of a system, or if there is no detail of the liquid crystal cell in the system, the apparatus should not be classified here.

Nominal manufacturing processes for producing significant liquid crystal cell structure, or nominally described "providing processes" that can only be classified by liquid crystal device structure are proper for Class 349. Processes having significant manufacturing steps for producing liquid crystal devices are provided in various manufacturing classes, depending on the steps or combination of steps involved in the process. While plural nominal manufacturing steps are considered significant manufacturing--placing the original in other manufacturing classes, a mandatory cross to this class is required if significant liquid crystal structure is present. See the SEARCH CLASS notes for some examples of manufacturing classes that provide for manufacture of liquid crystal devices.

Liquid crystal compositions with no more than nominal cell structure are excluded from this class; instead see elsewhere. In this case, nominal cell structure refers to a broad recitation of substrates, electrodes (or conductive plates or electrical excitation means), alignment layers, a seal, spacers, and polarizers. (See References to Other Classes, below.)

Driving waveforms and external driving circuitry for the liquid crystal are excluded from this class (see References to Other Classes, below). When the driving is in the context of a television, proper classification is elsewhere.

Electrooptic devices using materials other than liquid crystals and optical elements separate from liquid crystal devices are excluded from this class. (See References to Other Classes, below.)

Nominal liquid crystal display cell structure with specific chemical composition of nonconducting layers other than the liquid crystal are excluded from this class. (See References to Other Classes, below.)

SECTION III - REFERENCES TO OTHER CLASSES

SEE OR SEARCH CLASS:

SECTION IV - GLOSSARY

CELL*

For the purpose of this class, a cell is the minimum combination of elements necessary to physically contain an entire liquid crystal layer given a stimulus or excitation. In a matrix addressed liquid crystal device, a single pixel is not a cell.

EXCITATION*

For the purpose of this class, excitation is a force or energy which selects the state of the liquid crystal material.

LAYER*

For the purpose of this class, a layer is a periodic discontinuous material or materials within a single plane having a single function, or a continuous material having one or more functions.

SUBSTRATE*

For the purpose of this class, substrate is a flexible or rigid member which provides structural support in a cell.

SUBCLASSES

1	LIQUID CRYSTAL SYSTEM:
	This subclass is indented under the class definition.  Subject matter wherein the liquid crystal is a significant component of a larger system. (1) Note. Systems such as watches, computers, calculators, etc., in which the liquid crystal cell is merely used in the system, with no detail of the function or structure of the cell are excluded from this subclass. For such excluded subject matter, see the appropriate class for such external systems.

2	Liquid crystal for recording or imaging on photosensitive medium:
	This subclass is indented under subclass 1.  Subject matter wherein a liquid crystal cell is used as an image defining shutter for projecting light onto a medium sensitive to the action of radiant energy. (1) Note. Included here are liquid crystal image forming devices for cameras or motion picture films.

3	Printer or print bar:
	This subclass is indented under subclass 2.  Subject matter wherein the recording or image forming takes place in a device used for printing or a print bar. (1) Note. To be classified here there must be actual recitation of a printer or a print bar claimed or the preferred embodiment of the disclosure must be directed to a printer or a print bar.

4	Exposure device for lithography:
	This subclass is indented under subclass 2.  Subject matter wherein the liquid crystal cell is used as an automatic or adjustable mask in forming high definition exposures on very small areas. (1) Note. The liquid crystal cell forms the mask, not simply a shutter.

5	Projector including liquid crystal cell(s):
	This subclass is indented under subclass 1.  Subject matter wherein one or more liquid crystal cells modulate light for producing an image on a screen by a lens system. (1) Note. Excluded from this subclass are projectors with no liquid crystal cell or projectors including a liquid crystal cell with no detail of the liquid crystal material, its function, or the liquid crystal cell structure. For such excluded subject matter, see SEARCH CLASS below: SEE OR SEARCH CLASS: 353,  Optics: Image Projectors,   appropriate subclasses for projectors in general.

6	Overhead projector:
	This subclass is indented under subclass 5.  Subject matter wherein the direction of the light passing through the liquid crystal cell (or cells) is in the vertical direction and the projection of the light is in a direction substantially perpendicular thereto. (1) Note. Included here are projectors where the liquid crystal cell acts as an electrically driven transparency.

7	Video/motion picture projector:
	This subclass is indented under subclass 5.  Subject matter wherein images are sequentially projected to give the appearance of movement. (1) Note. Included here are recitations of sequential projections of red, green, and blue images.

8	Plural light path projectors:
	This subclass is indented under subclass 5.  Subject matter wherein incoming light begins as or is broken into separate paths according to a characteristic of the light and is combined or recombined before or after modulation by the one or more liquid crystal cells. (1) Note. "Characteristic" here includes polarization and wavelength, but excludes direction.

9	Having light separated into S and P polarization:
	This subclass is indented under subclass 8.  Subject matter wherein a characteristic determining the separation of light paths is the polarization of the light, such that the S polarization travels along one path and the P polarization travels along a different path.

10	Wherein liquid crystal cells include microencapsulated or polymer dispersed liquid crystal:
	This subclass is indented under subclass 8.  Subject matter wherein the liquid crystal cells are formed of small regions of a liquid crystal material embedded in a material of diverse composition.

11	Heads-up display:
	This subclass is indented under subclass 1.  Subject matter wherein a liquid crystal cell is utilized to combine a real world view and a generated information image or a liquid crystal cell is used for generating information to be displayed in a heads-up display device. SEE OR SEARCH CLASS: 359,  Optical: Systems and Elements,   subclasses 630+ for general heads-up display devices.

12	Liquid crystal writing tablet:
	This subclass is indented under subclass 1.  Subject matter wherein the system includes a stylus whose position is sensed and the liquid crystal is excited according to the sensed position.

13	Liquid crystal eyewear (glasses, goggles, etc.):
	This subclass is indented under subclass 1.  Subject matter wherein a liquid crystal cell is utilized as an electronically controlled lens, shutter, or display for covering an eye.

14	For protection:
	This subclass is indented under subclass 13.  Subject matter wherein the liquid crystal cells operate to shield eyes from light/ electromagnetic radiation. (1) Note. Included here are welding helmets, sunglasses, and laser eye protection devices.

15	Stereoscopic:
	This subclass is indented under subclass 1.  Subject matter wherein two liquid crystal cells form two images to be superimposed on each other or wherein two images to be superimposed on each other are formed separately from the liquid crystal cell, but wherein the liquid crystal cell is integrally involved in the image forming process. SEE OR SEARCH CLASS: 353,  Optics: Image Projectors,   subclass 7 for stereoscopic projectors not specific to liquid crystals. 359,  Optical: Systems and Elements,   subclass 462 for stereoscopic systems not specific to liquid crystals.

16	Liquid crystal window:
	This subclass is indented under subclass 1.  Subject matter wherein a liquid crystal cell acts as an electrically excited shade for a window, by blocking light and/or reducing glare. (1) Note. Included here are car, house, and building windows.

17	Computational system employing liquid crystal element (neural network, correlation device, optical computer):
	This subclass is indented under subclass 1.  Subject matter wherein liquid crystal cells are utilized to optically perform basic or more complex mathematical processes such as comparing, adding, subtracting, correlating, adaptive algorithms or neural network type algorithms. (1) Note. Excluded from this subclass are liquid crystal elements merely employed as memory storage for a computer and the mathematics inherent to any optical process. For such excluded subject matter, see SEARCH CLASS below. SEE OR SEARCH CLASS: 359,  Optical: Systems and Elements,   subclass 107 for optical computing without diffraction and subclass 561 for convolution, cross-correlation, or correlation using a diffraction grating. 706,  Data Processing: Artificial Intelligence,   subclass 40 for optical systems performing neural network type algorithms. 708,  Electrical Computers: Arithmetic Processing and Calculating,   subclasses 191 , 816, and 831 for electro-optical data processing systems.

18	Variable or rotatable retarder used with other retarders to produce filtering effects (Solc, Lyot, Partial):
	This subclass is indented under subclass 1.  Subject matter wherein a liquid crystal element forms a variable or rotatable retarder which is combined with other retarders to form a tunable filter, such that the relative orientations of the retarders produce a precise output.

19	PARTICULAR EXCITATION OF LIQUID CRYSTAL:
	This subclass is indented under the class definition.  Subject matter wherein a change in a liquid crystal optical property is exhibited in response to the active application of an external stimulus.

20	Thermal excitation:
	This subclass is indented under subclass 19.  Subject matter wherein a change in a liquid crystal optical property is exhibited in response to the application of heat energy. (1) Note. Structure merely maintaining the liquid crystal material at a particular temperature is excluded from this subclass. For such excluded subject matter, see SEARCH THIS CLASS, SUBCLASS below. SEE OR SEARCH THIS CLASS, SUBCLASS: 72, and 161, for using particular devices for keeping the liquid crystal material at a particular temperature.

21	By heating electrode:
	This subclass is indented under subclass 20.  Subject matter wherein the liquid crystal material exhibits an optical property change in response to thermal energy from a heating electrode adjacent to the liquid crystal. (1) Note. Included here are thermal heads and electrodes using resistance heating.

22	By light beam heating (e.g., IR, laser, etc.):
	This subclass is indented under subclass 20.  Subject matter wherein the liquid crystal material exhibits an optical property change in response to thermal energy derived from incident light rays. (1) Note. Included here are infrared light and laser beams which directly change the state of the liquid crystal. (2) Note. Excluded from this subclass is light used for optically exciting the liquid crystal. For such excluded subject matter see SEARCH THIS CLASS, SUBCLASS below. SEE OR SEARCH THIS CLASS, SUBCLASS: 24, for optical excitation of a liquid crystal cell. SEE OR SEARCH CLASS: 365,  Static Information Storage and Retrieval,   subclass 108 for a memory for liquid crystal using a light beam.

23	Magnetic or pressure excitation:
	This subclass is indented under subclass 19.  Subject matter wherein the liquid crystal material is responsive to either applied magnetic lines of force or mechanical stress. (1) Note. Included here is excitation produced by an acoustic wave.

24	Optical excitation:
	This subclass is indented under subclass 19.  Subject matter wherein the liquid crystal material exhibits an optical property change across the liquid crystal in response to the nonthermal application of light to corresponding areas of the liquid crystal. (1) Note. Included here are light activated switches. (2) Note. Excluded from this subclass is light used to excite the liquid crystal by heating. For such excluded subject matter, see SEARCH THIS CLASS, SUBCLASS below. SEE OR SEARCH THIS CLASS, SUBCLASS: 22, for changing the optical property of liquid crystal material in response to thermal application of incident light.

25	With photoconductive layer (e.g., spatial light modulator (SLMs)):
	This subclass is indented under subclass 24.  Subject matter wherein the liquid crystal material exhibits an optical property change when an electrical field is produced across the liquid crystal in response to the application of light to corresponding areas of a photosensitive layer. (1) Note. Included here are photoconductors and photodiodes.

26	Of an alloy of S, Se, or Te:
	This subclass is indented under subclass 25.  Subject matter wherein the photoconductive layer is formed of an alloy of S, Se, or Te.

27	With silicon photoconductive layer:
	This subclass is indented under subclass 25.  Subject matter wherein the photoconductive layer is formed of silicon.

28	With silicon photodiode, N-I-N photoconductor structure, or P-I-P photoconductor structure:
	This subclass is indented under subclass 27.  Subject matter wherein the silicon photoconductive layer has the structure of a photodiode, an N-I-N photoconductor, or a P-I-P photoconductor.

29	With particular light blocking layer for separating read and write lights:
	This subclass is indented under subclass 25.  Subject matter wherein a light preventing layer with a particular composition or structure is included for separating read and write lights.

30	With particular dielectric mirror for spatial light modulator (i.e., SLM):
	This subclass is indented under subclass 25.  Subject matter including a reflector formed of a multilayer nonconductive material having a particular composition or structure.

31	Electron beam excitation:
	This subclass is indented under subclass 19.  Subject matter wherein an optical property of the liquid crystal material is changed by the application of a ray of electrons. (1) Note. Included here are apparatus having an electron gun or field emission device.

32	Plasma excitation:
	This subclass is indented under subclass 19.  Subject matter wherein an optical property of the liquid crystal material is changed by application of a plasma charge.

33	Electrical excitation of liquid crystal (i.e., particular voltage pulses, AC vs. DC, threshold voltages, etc.):
	This subclass is indented under subclass 19.  Subject matter wherein an optical property of the liquid crystal material is changed by the application of an electric potential or current to the liquid crystal material. (1) Note. Nominal driving subject matter which depends on details of liquid crystal cell structure is classified in this subclass. Excluded from this subclass is driving of a liquid crystal device with a nominal liquid crystal cell structure. For such excluded subject matter, see SEARCH CLASS below. SEE OR SEARCH CLASS: 345,  Computer Graphics Processing and Selective Visual Display Systems,   subclasses 38+ and 87+ for driving of a liquid crystal device.

34	With application of holding or bias voltage (i.e., voltage which does not change the optical state of the liquid crystal):
	This subclass is indented under subclass 33.  Subject matter wherein a voltage applied to the liquid crystal does not change the optical state of the liquid crystal.

35	For driving Grandjean to focal conic or dynamic scattering type liquid crystal:
	This subclass is indented under subclass 33.  Subject matter wherein the electrical excitation is applied to a liquid crystal material to switch it from a Grandjean to a focal conic state or to exhibit dynamic scattering.

36	Including diverse driving frequencies:
	This subclass is indented under subclass 33.  Subject matter wherein the applied voltage has two or more frequencies. (1) Note. Included herein are different frequencies for changing the sign of the dielectric anisotropy of the liquid crystal material.

37	Polarity based driving:
	This subclass is indented under subclass 33.  Subject matter wherein the liquid crystal state is determined by the polarity of the voltage applied to the liquid crystal.

38	With supplemental capacitor:
	This subclass is indented under subclass 33.  Subject matter wherein a capacitor is in parallel to the liquid crystal such that the relaxation time (or the RC time constant) of the liquid crystal is increased.

39	In active matrix with separate dedicated capacitor line:
	This subclass is indented under subclass 38.  Subject matter wherein the supplemental capacitor is part of an active matrix and is formed from an electrical line different from the matrix lines and dedicated specifically to the capacitor.

40	With antistatic elements:
	This subclass is indented under subclass 33.  Subject matter including structure to distribute, eliminate, or block static electrical charges.

41	With particular switching device:
	This subclass is indented under subclass 33.  Subject matter including an electrical device which receives voltages from electrode drivers and toggles a portion of the liquid crystal on and off. (1) Note. Included here are micromechanical switches used to switch a portion of the liquid crystal on and off. SEE OR SEARCH CLASS: 257,  Active Solid-State Devices (e.g., Transistors, Solid-State Diodes),   appropriate subclasses for the use of a transistor in general. 345,  Computer Graphics Processing and Selective Visual Display Systems,   subclasses 90+ for using switching devices in a liquid crystal device. 438,  Semiconductor Device Manufacturing: Process,   especially subclasses 27+ for methods of packaging a semiconductor electronic device having an additional optical component and subclass 30 for methods of making a semiconductor electronic device including a liquid crystal optical component.

42	Transistor:
	This subclass is indented under subclass 41.  Subject matter wherein the switching device comprises a three-terminal semiconductor device.

43	Structure of transistor:
	This subclass is indented under subclass 42.  Subject matter wherein the particular layering of the transistor is specified. (1) Note. Included here are connective electrodes to buses, pixels, etc.

44	With light block conductively connected to transistor:
	This subclass is indented under subclass 43.  Subject matter including an opaque structure covering a portion of the transistor and conductively connected thereto. SEE OR SEARCH THIS CLASS, SUBCLASS: 110, for an opaque mask not associated with and electrically connected to a transistor.

45	Transferred transistor:
	This subclass is indented under subclass 43.  Subject matter wherein the transistor is fabricated on a film and then transferred to one of the substrates which forms the liquid crystal cell. (1) Note. An adhesive layer which attaches the transistor to the substrate is indicative of a transferred transistor. (2) Note. Transferred transistors typically result in a structure in which the layers at the side of the transistor adjacent to the liquid crystal material are more level than those at the side adjacent the cell substrate.

46	With particular gate electrode structure:
	This subclass is indented under subclass 43.  Subject matter wherein the material, location, or other detail of the gate electrode of the transistor is specified. (1) Note. Included here are thinned electrodes for easy disconnection.

47	With gate electrode between liquid crystal and semiconductor layer:
	This subclass is indented under subclass 46.  Subject matter wherein the gate electrode is located between the liquid crystal layer and the semiconductor layer.

48	Plural nonredundant transistors per pixel:
	This subclass is indented under subclass 42.  Subject matter wherein each pixel includes two or more transistors for purposes other than redundancy. (1) Note. Included here are a pair of N and P transistors for each pixel or a pair of transistors connected to different address lines for each pixel. (2) Note. Excluded from this subclass is the use of transistors for redundancy purposes. For such excluded subject matter, see SEARCH THIS CLASS, SUBCLASS below. SEE OR SEARCH THIS CLASS, SUBCLASS: 54, for the use of transistors for redundancy purposes.

49	Two terminal nonlinear switching device (e.g., N-I-N, S-I-S, Ferroelectric, etc.):
	This subclass is indented under subclass 41.  Subject matter wherein the switching device comprises a two-terminal element.

50	Diode:
	This subclass is indented under subclass 49.  Subject matter wherein the switching device has a rectifying function. (1) Note. Excluded from this subclass are photodiodes used for optically exciting the liquid crystal. For such excluded subject matter, see SEARCH THIS CLASS, SUBCLASS below. SEE OR SEARCH THIS CLASS, SUBCLASS: 25, and 28, for using photodiodes for optically exciting a liquid crystal cell. SEE OR SEARCH CLASS: 345,  Computer Graphics Processing and Selective Visual Display Systems,   subclass 91 for using diodes in a liquid crystal device.

51	Metal-insulator-metal (i.e., MIM):
	This subclass is indented under subclass 49.  Subject matter wherein the switching device is a bidirectional tunneling device with a metal-insulator-metal structure.

52	With particular insulating layer:
	This subclass is indented under subclass 51.  Subject matter wherein the MIM has an insulating layer of a particular composition between the two metal layers.

53	Varistor:
	This subclass is indented under subclass 49.  Subject matter wherein the switching device has a two-electrode semiconductor device with a voltage-dependent nonlinear resistance that drops markedly as the applied voltage is increased. SEE OR SEARCH CLASS: 345,  Computer Graphics Processing and Selective Visual Display Systems,   subclass 91 for using varistor in a liquid crystal device.

54	Matrix including additional element(s) which correct or compensate for electrical fault:
	This subclass is indented under subclass 33.  Subject matter including a structure or arrangement of additional buses, switching elements, or circuit elements for correcting and preventing electrical defects such as open or short circuits. (1) Note. The defect correction structure included in this subclass is that which is incorporated in the liquid crystal device when the device is manufactured. Excluded from this subclass are defect correction after the device has been made. For such excluded subject matter, see SEARCH THIS CLASS, SUBCLASS below. (2) Note. Included here are double buslines, double switches, and bypass lines. Also included are pixels connected directly to the busline to reduce defects. SEE OR SEARCH THIS CLASS, SUBCLASS: 192, for defect correction after the liquid crystal device has been made. SEE OR SEARCH CLASS: 345,  Computer Graphics Processing and Selective Visual Display Systems,   subclass 93 for the use of redundancy in a liquid crystal device.

55	Laser links:
	This subclass is indented under subclass 54.  Subject matter wherein the correction or compensation of the fault is accomplished by using a laser to conductively connect two conductors which were isolated from each other.

56	PARTICULAR STRUCTURE:
	This subclass is indented under the class definition.  Subject matter including a specific aspect of the structure of the liquid crystal device and not involving the application of electrical energy to the liquid crystal. (1) Note. The structure here includes the parts of the whole device. For example, light source, frame, liquid crystal cell, etc.

57

Lens or prism separate from projection system (i.e., it is not integral part of illumination system):

This subclass is indented under subclass 56.  Subject matter wherein the liquid crystal device includes a specific lens or prism near or adjacent to the liquid crystal cell, wherein the lens or prism is not an integral part of a projection system nor a light guide of the liquid crystal illumination system. (1) Note. Included here are collimating lenses and prisms for redirecting light entering or leaving the liquid crystal cell.