Non-destructive testing system employing a liquid crystal detector cell

Claim 2

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles and the liquid crystal alignment as indicated by the director being oblique relative to the covers, and said cell exhibiting high sensitivity and high image resolution.

Claim 3

A system as in claim 1, wherein the optical viewing axis is substantially parallel to the liquid crystal alignment.

Claim 4

A system as in claim 2, wherein the liquid crystal image is enhanced by electric field alignment and wherein the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule.

Claim 5

A system as in claim 3, wherein the difference in dielectric constants is less than zero and the electric field causes said oblique alignment.

Claim 6

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles and wherein the liquid crystal alignment as indicated by the director being oblique relative to the cover and said cell exhibiting high sensitivity and high image resolution.

Claim 7

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles and wherein the liquid crystal alignment as indicated by the director being oblique relative to the cover and said cell exhibiting high sensitivity and high image resolution.

Claim 8

A cell as in claim 5, wherein the liquid crystal image is enhanced by electric field alignment and wherein the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule.

Claim 9

A cell as in claim 6, wherein the difference in dielectric constants is less than zero and the electric field causes said oblique alignment.

Claim 10

A cell as in claim 5, wherein the liquid crystal image is enhanced by electric field alignment, the liquid crystal material exhibiting a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and the difference in dielectric constants is less than zero and the electric field causes a slight oblique alignment.

Claim 11

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and one of said covers comprising a multi-layer graphite fiber/epoxy composite.

Claim 12

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and one of said covers comprising a multi-layer graphite fiber/epoxy composite.

Claim 13

A system as in claim 9, wherein the graphite fibers in the composite are substantially parallel to each other.

Claim 14

A system as in claim 9, wherein the graphite fibers are at substantially right angles to each other.

Claim 15

A system as in claim 9, wherein each of said cell covers includes a protective layer to prevent chemical reaction between the liquid crystal material and the cell cover.

Claim 16

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and one of said covers comprising a multi-layer graphite fiber/epoxy composite.

Claim 17

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and one of said covers comprising a multi-layer graphite fiber/epoxy composite.

Claim 18

A cell as in claim 13, wherein the graphite fibers in the composite are substantially parallel to each other.

Claim 19

A cell as in claim 13, wherein the graphite fibers in the composite are at substantially right angles to each other.

Claim 20

A cell as in claim 13, wherein each of said cell covers includes a protective layer to prevent chemical reaction between the liquid crystal material and the cell cover.

Claim 21

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, said liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein at least one of said cell covers is of a polymeric material and there is provided on said cover a protective barrier layer to prevent chemical reaction between the liquid crystal material and the cell cover.

Claim 22

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, said liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein at least one of said cell covers is of a polymeric material and there is provided on said cover a protective barrier layer to prevent chemical reaction between the liquid crystal material and the cell cover.

Claim 23

A system as in claim 17, wherein said polymer is a polyester.

Claim 24

A system as in claim 17, wherein said polymer is substantially rigid so as to maintain a uniform spacing between said cover surfaces and thereby maintain the liquid crystal layer of a uniform thickness.

Claim 25

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel acoustically transparent covers, the ultrasonically active area of each of which is of substantially uniform thickness and which encase a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles and wherein the liquid crystal material is selectively aligned, said cell exhibiting high sensitivity and high image resolution, wherein at least one of said cell covers is of a polymeric material and there is provided on said cover a protective layer to prevent chemical reaction between the liquid crystal material and the cell cover.

Claim 26

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel acoustically transparent covers, the ultrasonically active area of each of which is of substantially uniform thickness and which encase a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles and wherein the liquid crystal material is selectively aligned, said cell exhibiting high sensitivity and high image resolution, wherein at least one of said cell covers is of a polymeric material and there is provided on said cover a protective layer to prevent chemical reaction between the liquid crystal material and the cell cover.

Claim 27

A cell as in claim 20, wherein said polymer is a polyester.

Claim 28

A cell as in claim 20, wherein said polymeric is substantially rigid so as to maintain a uniform spacing between said cover surfaces and thereby maintain the liquid crystal layer of a uniform thickness.

Claim 29

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned and said cell exhibiting high sensitivity and high image resolution, and wherein said liquid crystal exhibits a nematic/isotropic phase transition temperature just above the ambient temperature at which said system is expected to operate.

Claim 30

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned and said cell exhibiting high sensitivity and high image resolution, and wherein said liquid crystal exhibits a nematic/isotropic phase transition temperature just above the ambient temperature at which said system is expected to operate.

Claim 31

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely-spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein said liquid crystal exhibits a nematic/isotropic phase transition temperature just above the ambient temperature at which said cell is expected to operate.

Claim 32

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely-spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein said liquid crystal exhibits a nematic/isotropic phase transition temperature just above the ambient temperature at which said cell is expected to operate.

Claim 33

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein the liquid crystal image is enhanced by electric field alignment and the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and said dielectric constant changes with frequency, and wherein said ultrasonic source emits pulses of ultrasonic energy in a pulse-on mode and is quiescent in the pulse-off mode, and wherein an electric field of a first frequency is applied to align the liquid crystal molecules in a direction perpendicular to the electric field when the ultrasonic generator is in the pulse-on mode and a second electric field at a second frequency is applied to align the liquid crystal molecules in a direction parallel to the electric field when the ultrasonic generator is in the pulse-off mode.

Claim 34

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein the liquid crystal image is enhanced by electric field alignment and the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and said dielectric constant changes with frequency, and wherein said ultrasonic source emits pulses of ultrasonic energy in a pulse-on mode and is quiescent in the pulse-off mode, and wherein an electric field of a first frequency is applied to align the liquid crystal molecules in a direction perpendicular to the electric field when the ultrasonic generator is in the pulse-on mode and a second electric field at a second frequency is applied to align the liquid crystal molecules in a direction parallel to the electric field when the ultrasonic generator is in the pulse-off mode.

Claim 35

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, wherein the liquid crystal image is enhanced by electric field alignment and the liquid crystal material exhibiting a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and wherein said dielectric constant changes with frequency and wherein an electric field of a first frequency is applied to align the liquid crystal molecules in a direction perpendicular to the electric field when an ultrasonic source is on and a second electric field at a second frequency is applied to align the liquid crystal molecules in a direction parallel to the electric field when the ultrasonic field is off.

Claim 36

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each of which is of substantially uniform thickness, said covers encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, wherein the liquid crystal image is enhanced by electric field alignment and the liquid crystal material exhibiting a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and wherein said dielectric constant changes with frequency and wherein an electric field of a first frequency is applied to align the liquid crystal molecules in a direction perpendicular to the electric field when an ultrasonic source is on and a second electric field at a second frequency is applied to align the liquid crystal molecules in a direction parallel to the electric field when the ultrasonic field is off.

Claim 37

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said cover encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein said liquid crystal material exhibits its maximum frequency response at the ultrasonic frequency selected for imaging.

Claim 38

An ultrasonic imaging system for use in non-destructively and non-invasively testing objects, which includes a source or beam of ultrasonic energy, a liquid crystal detector cell acoustically coupled to said beam for displaying a real-time image of a test object, and an optical viewing system for illuminating the image on the cell, wherein said cell includes a pair of closely spaced and parallel covers, the ultrasonically active area of each being of a substantially uniform thickness, said cover encasing a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting field birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by each of said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution, and wherein said liquid crystal material exhibits its maximum frequency response at the ultrasonic frequency selected for imaging.

Claim 39

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of acoustically transmissive covers, the ultrasonically active area of each of which is of substantially uniform thickness and which encase a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution and wherein the liquid crystal material exhibits its maximum frequency response at the ultrasonic frequency selected for imaging.

Claim 40

A liquid crystal detector cell for use in an ultrasonic imaging system to non-destructively and non-invasively test objects and produce a real-time image thereof, wherein said cell includes a pair of acoustically transmissive covers, the ultrasonically active area of each of which is of substantially uniform thickness and which encase a nematic liquid crystal material whose alignment is indicated by a director, said material exhibiting birefringence in response to acoustic energy, said cell being matched to the frequency of the ultrasonic energy, by said covers being substantially acoustically transparent to ultrasonic beams incident on said covers at normal and oblique angles, the liquid crystal material being selectively aligned, said cell exhibiting high sensitivity and high image resolution and wherein the liquid crystal material exhibits its maximum frequency response at the ultrasonic frequency selected for imaging.

Claim 41

A system as in claim 1, 9 or 17, wherein the liquid crystal exhibits a nematic/isotropic phase transition temperature just above the ambient temperature at which said system is expected to operate.

Claim 42

A cell as in claim 5, 13 or 20, wherein the liquid crystal exhibits a nematic/isotropic phase transition temperature just above the ambient temperature at which said system is expected to operate.

Claim 43

A system as in claim 1, 9 or 17, wherein said liquid crystal material exhibits its maximum frequency response at the ultrasonic frequency selected for imaging.

Claim 44

A cell as in claim 5, 13 or 20, wherein said liquid crystal material exhibits its maximum frequency response at the ultrasonic frequency selected for imaging.

Claim 45

A system as in claim 9 or 17, wherein said liquid crystal material is obliquely aligned relative to the covers.

Claim 46

A cell as in claim 13 or 20, wherein the liquid crystal material is obliquely aligned relative to the cell cover.

Claim 47

A system as in claim 9 or 17, wherein the liquid crystal image is enhanced by electric field alignment and the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and said dielectric constant changes with frequency, and wherein said ultrasonic source emits pulses of ultrasonic energy in a pulse-on mode and is quiescent in the pulse-off mode, and wherein an electric field of a first frequency is applied to align the liquid crystal molecules in a direction perpendicular to the electric field when the ultrasonic generator is in the pulse-on mode and a second electric field at a second frequency is applied to align the liquid crystal molecules in a direction parallel to the electric field when the ultrasonic generator is in the pulse-off mode.

Claim 48

A cell as in claim 13 or 20, wherein the liquid crystal image is enhanced by electric field alignment and the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule, and said dielectric constant changes with frequency, and wherein said ultrasonic source emits pulses of ultrasonic energy in a pulse-on mode and is quiescent in the pulse-off mode, and wherein an electric field of a first frequency is applied to align the liquid crystal molecules in a direction perpendicular to the electric field when the ultrasonic generator is in the pulse-on mode and a second electric field at a second frequency is applied to align the liquid crystal molecules in a direction parallel to the electric field when the ultrasonic generator is in the pulse-off mode.

Claim 49

A system as in claim 9 or 17, wherein the ultrasonic beam and the liquid crystal alignment as indicated by the director are oblique to each other.

Claim 50

A system as in claim 9 or 17, wherein the nematic liquid crystal is homeotropically aligned.

Claim 51

A system as in claim 1, 9 or 17, wherein the acoustic impedance of each of said cell covers is of the same order of magnitude as the coupling medium.

Claim 52

A system as in claim 9 or 17, wherein the optical viewing axis is substantially parallel to the liquid crystal director.

Claim 53

A system as in claim 1, 9 or 17, wherein the acoustic transmission through each cover of said cell is at least 85 percent at any frequency between 1 and 10 MHz.

Claim 54

A system as in claim 1, 9 or 17, wherein at least one of said covers is optically transparent.

Claim 55

A system as in claim 42, wherein the optical system is of the reflective type and there is only one optically transparent cover and said optically transparent cover is positioned toward the viewing system.

Claim 56

A system as in claim 1 or 17, wherein both of said covers are optically transparent.

Claim 57

A system as in claim 44, wherein said optical system is of a transmission type whereby light is directed through the cell so as to permit viewing of the image.

Claim 58

A system as in claim 1, 9 or 17, wherein each of said cell covers is chemically inert with respect to the liquid crystal material.

Claim 59

A system as in claim 1, 9 or 17, wherein at least one of said cell covers is a three-ply glass laminate and wherein the thickness of each glass ply is about 0.0085 inch.

Claim 60

A system as in claim 1 or 9, wherein each of said covers is substantially rigid so as to maintain a uniform spacing between said cover surfaces and thereby maintain the liquid crystal layer of a uniform thickness.

Claim 61

A system as in claim 9 or 17, wherein said nematic liquid crystal molecules are aligned substantially normal to the cell covers.

Claim 62

A system as in claim 1, 9 or 17, wherein said liquid crystal material is a substantially pure nematic.

Claim 63

A liquid crystal material as in claim 1, 9 or 17, wherein said liquid crystal is a mixture of substantially pure nematics.

Claim 64

A system as in claim 9 or 17, wherein said liquid crystal is a mixture of nematic and approximately 0.03 percent by weight cholesteric added thereto.

Claim 65

A system as in claim 1, 9 or 17, wherein said liquid crystal material maintains its biased alignment and does not stream at the ultrasonic intensity employed by said system.

Claim 66

A system as in claim 1, 9 or 17, wherein said liquid crystal material is at least 0.015 inch thick.

Claim 67

A system as in claim 9 or 17, wherein the liquid crystal image is enhanced by electric field alignment and wherein the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule.

Claim 68

A system as in claim 55 wherein a thin film electrode is applied to each of said cell covers and each of said electrodes is connected to an AC generator for applying an electric field to said liquid crystal material.

Claim 69

A system as in claim 1, 9 or 17, wherein a uniform ultrasonic beam is generated and said object to be inspected is illuminated by the uniform beam.

Claim 70

A system as in claim 57, wherein said ultrasonic source is unfocused coherent sound source and said uniform illumination occurs at the near field/far field transition.

Claim 71

A system as in claim 57, wherein said ultrasonic transducer is focused transducer which focuses a uniform beam on a test object.

Claim 72

A system as in claim 57, wherein said uniform beam is obtained using an array of transducers.

Claim 73

A system as in claim 57, wherein the frequency of said transducer is between 1 and 10 MHz.

Claim 74

A system as in claim 57, wherein said ultrasonic transducer generates an incoherent ultrasonic beam.

Claim 75

A cell as in claim 5, 13 or 20, wherein the acoustic transmission through each cover of said cell is at least 85 percent at frequencies between 1 and 10 MHz.

Claim 76

A cell as in claim 5, 13 or 20, wherein at least one of said covers is optically transparent.

Claim 77

A cell as in claim 64, wherein the optical system is of the reflective type and there is only one optically transparent cover and said optically transparent cover is positioned toward the viewing system.

Claim 78

A cell as in claim 5 or 20, wherein both of said covers are optically transparent.

Claim 79

A cell as in claim 5, 13 or 20, wherein each of said cell covers is chemically inert with respect to the liquid crystal material.

Claim 80

A cell as in claim 5, 13 or 20, wherein at least one of said cell covers is a three-ply glass laminate and wherein the thickness of each glass ply is about 0.0085 inch.

Claim 81

A cell as in claim 5 or 13, wherein each of said covers is substantially rigid so as to maintain a uniform spacing between said cover surfaces and thereby maintain the liquid crystal layer of a uniform thickness.

Claim 82

A cell as in claim 13 or 20, wherein said nematic liquid crystal molecules are aligned substantially normal to the cell covers.

Claim 83

A cell as in claim 5, 13 or 20, wherein said liquid crystal material is a substantially pure nematic.

Claim 84

A cell as in claim 5, 13 or 20, wherein said liquid crystal is a mixture of substantially pure nematics.

Claim 85

A cell as in claim 13 or 20, wherein said liquid crystal is a mixture of nematic and approximately 0.03 percent by weight cholesteric added thereto.

Claim 86

A cell as in claim 5, 13 or 20, wherein said liquid crystal material maintains its biased alignment and does not stream at the ultrasonic intensity employed by said system.

Claim 87

A cell as in claim 5, 13, or 20, wherein said liquid crystal material is at least 0.015 inch thick.

Claim 88

A cell as in claim 13 or 20, wherein the liquid crystal image is enhanced by electric field alignment and wherein the liquid crystal material exhibits a different dielectric constant in a direction parallel to the longitudinal axis of the molecule than in a direction perpendicular to the longitudinal axis of the molecule.

Claim 89

A cell as in claim 76, wherein a thin film electrode is applied to each of said cell covers and each of said electrodes is connected to an AC generator for applying an electric field to said liquid crystal material.