Passive millimeter wave radiometer system for calibration of infrared cameras

Patent metadata

Field	Value
Publication number	US-10876898-B2
Application number	US-201816058855-A
Country	US
Kind code	B2
Filing date	Aug 8, 2018
Priority date	Aug 8, 2018
Publication date	Dec 29, 2020
Grant date	Dec 29, 2020

Abstract

An apparatus for accurate measurement of surface and sub-surface temperatures of an object from a distance without contacting the object is provided. Illustrative embodiments provide for simultaneous measurement of thermal emission and emissivity in the mm-wave regime thereby enabling real-time non-contact measurement of emissivity. Corrected temperatures for the object which may be used for calibration of infrared thermographic cameras are determined from the measurement of emissivity.

First claim

What is claimed is:

1. A light wave radiometer configured to measure light received from a source, the light wave radiometer comprising:
a window disposed in a primary light path to pass focused light from the source;
a parabolic mirror disposed in the primary light path from the window;
a waveguide disposed in the primary light path from the parabolic mirror, the waveguide configured to collect and guide the focused light along the waveguide;
an optical chopper disposed in the primary light path from the parabolic mirror and the waveguide, the optical chopper disposed at an angle relative to an axis of the primary light path such that the optical chopper periodically allows the focused light to pass into a secondary light path and a tertiary light path;
a first radiometer receiver disposed in the secondary light path;
a second radiometer receiver disposed in the tertiary light path;
a first lock-in amplifier electrically connected to the first radiometer receiver and configured to generate a first signal in response to receiving the focused light in the secondary light path; and
a second lock-in amplifier electrically connected to the second radiometer receiver and configured to generate a second signal in response to receiving the focused light in the tertiary light path.

2. The light wave radiometer of claim 1 , further comprising:
a computer in communication with the first lock-in amplifier and the second lock-in amplifier, the being computer programmed to combine the first signal and the second signal to generate a combined signal, and to calculate an emissivity and a corrected temperature of the source based on the combined signal.

3. The light wave radiometer of claim 1 , further comprising:
a chopper controller electrically connected to the optical chopper and configured to moderate operation of the optical chopper.

4. The light wave radiometer of claim 1 , further comprising:
a first digital voltmeter connected to the first lock-in amplifier; and
a second digital voltmeter connected to the second lock-in amplifier.

5. The light wave radiometer of claim 1 , wherein the angle of the optical chopper is about a forty-five degree angle.

6. The light wave radiometer of claim 1 , wherein the light wave radiometer comprises a millimeter wave radiometer and wherein the window comprises a sapphire window.

7. The light wave radiometer of claim 1 , further comprising:
a light beam differentiator disposed in the primary light path before the optical chopper, the light beam differentiator configured to allow light of a first wavelength to continue along the primary light path and to deflect light of a second wavelength, different than the first wavelength, along a quaternary light path.

8. The light wave radiometer of claim 7 , wherein the light beam differentiator comprises one of a dichroic mirror and an optical beam splitter.

9. The light wave radiometer of claim 7 , wherein the first wavelength comprises light in a millimeter wavelength range and wherein the second wavelength comprises light in an infrared wavelength range.

10. The light wave radiometer of claim 7 , further comprising:
an infrared camera disposed to receive light along the quaternary light path.

11. The light wave radiometer of claim 10 , further comprising:
a computer in communication with the first lock-in amplifier, the second lock-in amplifier, and the infrared camera, the computer being programmed to:
combine the first signal and the second signal to generate a combined signal;
calculate a first estimated emissivity and a corrected temperature of the source based on the combined signal;
calculate an estimated temperature of the source based on a third signal transmitted from the infrared camera; and
calibrate the infrared camera based on a comparison of the corrected temperature and the second estimated temperature.

12. A method of measuring a temperature of a source using a light wave radiometer configured to measure light received from the source, the light wave radiometer comprising: a window disposed in a primary light path to transmit focused light from the source; a parabolic mirror disposed in the primary light path from the window; an optical chopper disposed in the primary light path from the parabolic mirror and a waveguide, the optical chopper disposed at an angle relative to an axis of the primary light path such that the optical chopper periodically allows the focused light to pass into a secondary light path and a tertiary light path; a first radiometer receiver disposed in the secondary light path; a second radiometer receiver disposed in the tertiary light path; a first lock-in amplifier electrically connected to the first radiometer receiver and configured to generate a first signal in response to receiving light in the secondary light path; and a second lock-in amplifier electrically connected to the second radiometer receiver and configured to generate a second signal in response to receiving light in the tertiary light path, the method comprising:
receiving the light from the source into the window to form the primary light path;
collecting the light through the window and focusing the light using the parabolic mirror;
chopping the light with the optical chopper into a secondary light beam and the tertiary light beam, thereby directing the light into the secondary light path and the tertiary light path;
receiving the secondary light beam at the first lock-in amplifier and generating the first signal with the first lock-in amplifier;
receiving the tertiary light beam at the second lock-in amplifier and generating the second signal with the second lock-in amplifier;
combining the first signal and the second signal with a computer to form a combined signal; and
calculating an emissivity and corrected temperature of the source based on the combined signal.

13. The method of claim 12 , further comprising:
moderating operation of the optical chopper to change amounts of light in the secondary light beam and the tertiary light beam.

14. The method of claim 12 , further comprising:
measuring a first voltage using a first digital voltmeter connected to the first lock-in amplifier; and
measuring a second voltage using a second digital voltmeter connected to the second lock-in amplifier.

15. The method of claim 12 , further comprising:
splitting, using a light beam differentiator disposed in the primary light path before the optical chopper, the light in the primary light path into a first wavelength that continues along the primary light path and into a second wavelength, different than the first wavelength, that is deflected into a quaternary light path.

16. The method of claim 15 , wherein the light beam differentiator comprises one of a dichroic mirror and an optical beam splitter.

17. The method of claim 15 , wherein the first wavelength comprises light in a millimeter wavelength range and wherein the second wavelength comprises light in an infrared wavelength range.

18. The method of claim 15 , further comprising:
receiving, at an infrared camera, light along the quaternary light path.

19. The method of claim 18 , further comprising:
combining the first signal and the second signal to generate the combined signal;
calculating a first emissivity and a corrected temperature of the source based on the combined signal;
calculating an estimated temperature of the source based on a third signal transmitted from the infrared camera; and
calibrating the infrared camera based on a comparison of the corrected

Assignees

• Nat Tech & Eng Solutions Sandia Llc
• Woskov Paul P
• Massachusetts Inst Technology

Inventors

• Murphy Ryan D
• Forrest Eric C
• Woskov Paul P
• Stanford Joshua

Classifications

• G01J5/0814

  Particular reflectors, e.g. faceted or dichroic mirrors · CPC title

• G01J5/0804

  Shutters · CPC title

• G01J5/808

  using linearising circuits · CPC title

• G01J5/806

  by correcting for reflection of the emitter radiation · CPC title

• G01J5/802

  by correcting for emissivity · CPC title