Optical pressure-sensing system using optical resonator cavity
First Claim
1. An optical pressure-sensing system, comprising:
- an airtight, optical resonator cavity formed by a substrate having a transparent base with a planar inner surface, a resilient diaphragm and a sidewall extending between said substrate and diaphragm to surround said cavity, said diaphragm having a planar inner surface facing the inner surface of said substrate, the distance between the inner surfaces of said base and diaphragm being selected so that light having a predetermined wavelength resonates in said cavity;
a light source generating light having at least one wavelength on a resonant cycle of said optical resonator;
a light detector; and
an optical system conveying light from said light source to the outer surface of the base of said substrate and the from the outer surface of the base of said substrate to said light detector so that light entering said cavity resonates at a frequency that is a fraction of the distance between the planar inner surfaces of said diaphragm and substrate, said light detector generating an electrical signal corresponding to a characteristic of the optically resonant frequency of said cavity, whereby the electrical output of said light detector varies as a function of the deflection of said diaphragm, resulting from the pressure differential across said diaphragm.
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Abstract
An optical pressure-sensing system in which an optical beam splitter couples input light from a light source to an optically resonant pressure sensor and couples output light reflected from the sensor to a light detector. The light detector may divide the output light into bands having different wavelengths and then take the ratio of the light in one band to the light in the other band in order to provide an output that is insensitive to various spurious responses in the system. The optical beam splitter may be formed by two pairs of graded refractive index lenses. A partially reflective, partially transmissive mirror is sandwiched between the lenses of one pair, while a dichroic mirror is sandwiched between the second pair. The pairs of lenses are placed in abutting relationship to each other. The optical beam splitter may also be formed by a block of transparent material having a partially reflective, partially transmissive mirror on one edge. The optical pressure sensor is formed by a transparent substrate having a cylindrical recess and a resilient diaphragm positioned over the recess to form an optically resonant cavity. Differential pressure may be sensed by placing a second substrate having a cylindrical recess over the side of the diaphragm opposite from the first substrate. The optical pressure sensor may be specifically adapted for use as a microphone by utilizing a relatively thick cavity having a pedestal projecting from the substrate close to the diaphragm to form an optically resonant cavity. The optical pressure sensor may also sense gas density by filling the optically resonant cavity with the gas being measured having a pressure at a predetermined density and temperature that matches the pressure of the gas being measured at that same density and temperature.
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Citations
45 Claims
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1. An optical pressure-sensing system, comprising:
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an airtight, optical resonator cavity formed by a substrate having a transparent base with a planar inner surface, a resilient diaphragm and a sidewall extending between said substrate and diaphragm to surround said cavity, said diaphragm having a planar inner surface facing the inner surface of said substrate, the distance between the inner surfaces of said base and diaphragm being selected so that light having a predetermined wavelength resonates in said cavity; a light source generating light having at least one wavelength on a resonant cycle of said optical resonator; a light detector; and an optical system conveying light from said light source to the outer surface of the base of said substrate and the from the outer surface of the base of said substrate to said light detector so that light entering said cavity resonates at a frequency that is a fraction of the distance between the planar inner surfaces of said diaphragm and substrate, said light detector generating an electrical signal corresponding to a characteristic of the optically resonant frequency of said cavity, whereby the electrical output of said light detector varies as a function of the deflection of said diaphragm, resulting from the pressure differential across said diaphragm. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. An optical pressure sensor, comprising:
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an airtight, optical resonator cavity formed by a substrate having a transparent base with a planar inner surface, a resilient diaphragm and a sidewall extending between said substrate and diaphragm to surround said cavity, said diaphragm having a planar inner surface facing the inner surface of said substrate, the distance between the inner surfaces of said base and diaphragm being selected so that light having a predetermined wavelength resonates in said cavity; a fluid conduit extending between said optical resonator cavity and an external pressure port, said conduit being formed by a radial extension of said cavity projecting into said substrate sidewall and then to an external surface. - View Dependent Claims (36, 37)
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38. An optical pressure sensor comprising:
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a first substrate having a transparent base with a planar inner surface; a resilient diaphragm having a planar inner surface, the distance between the inner surfaces of said base and diaphragm being selected so that said cavity forms an optical resonator; a first sidewall extending between said base and diaphragm and, together with said base and disphragm, forming a first airtight cavity; a second substrate; a second sidewall extending between said second substrate and said diaphragm on the surface opposite the surface to which said first sidewall extends so that said diaphragm, second substrate, and second sidewalls form a second airtight cavity; first and second fluid conduits communicating between respective first and second fluid ports and said first and second airtight cavities; and means for determining the deflection of said diaphragm solely from the optical resonance in said first airtight cavity. - View Dependent Claims (39, 40)
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41. A microphone responding to variations in pressure occurring at audio frequencies, said microphone comprising:
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a substrate having a transparent base; a pedestal mounted on and projecting axially away from the base of said substrate at a location where light is adapted to be conveyed to said base, said pedestal having a planar surface; a resilient diaphragm having a planar inner surface mounted over the planar surface of said pedestal, the distance between the inner surface of said diaphragm and the planar surface of said pedestal being selected to form an optical resonator therebetween; a sidewall extending between said base and diaphragm to form an airtight, optically resonant cavity surrounded by said sidewall; and a fluid conduit extending between said airtight cavity and an external pressure port. - View Dependent Claims (42, 43)
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44. A gas density sensor specifically adapted to sense the density of a gas in an enclosed vessel, said gas density sensor comprising:
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a substrate having a transparent base and a planar inner surface; a resilient diaphragm having a planar inner surface mounted over the inner surface of said base, the distance between the inner surfaces of said base and diaphragm being selected so that said cavity forms an optical resonator; and a sidewall extending between said base and diaphragm so that said base, diaphragm and sidewall form an airtight, optically resonant cavity, said airtight cavity being filled with a gas having a predetermined pressure at a predetermined temperature corresponding to the pressure of the gas in said vessel at a predetermined density. - View Dependent Claims (45)
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Specification