Simultaneous noncontact precision imaging of microstructural and thickness variation in dielectric materials using terahertz energy

• US 7,876,423 B1
• Filed: 06/27/2008
• Issued: 01/25/2011
• Est. Priority Date: 06/27/2008
• Status: Expired due to Fees

• Current Assignee: National Aeronautics and Space Administration (Government of the United States of America)
• Original Assignee: The United States Of America As Represented By The National Aeronautics And Space Administration
• Inventors: Roth, Donald J
• Primary Examiner(s): NGUYEN, SANG H
• Application Number:
  US12/163,382
• Time in Patent Office: 942 Days
• Field of Search: 356/497, 356/502, 356630-636, 356 27- 285, 736/55, 736/29, 736/22, 735/97, 735/93
• US Class Current: 356/27
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation

Abstract

A process for simultaneously measuring the velocity of terahertz electromagnetic radiation in a dielectric material sample without prior knowledge of the thickness of the sample and for measuring the thickness of a material sample using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of the terahertz electromagnetic radiation in the sample is disclosed and claimed. The process evaluates, in a plurality of locations, the sample for microstructural variations and for thickness variations and maps the microstructural and thickness variations by location. A thin sheet of dielectric material may be used on top of the sample to create a dielectric mismatch. The approximate focal point of the radiation source (transceiver) is initially determined for good measurements.

Claims

1. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, comprising the steps of:

emitting terahertz electromagnetic radiation from said source;

measuring the travel time of said terahertz electromagnetic radiation to and from said substrate without said sample present, t″

;

placing said sample on said substrate;

measuring the travel time of said terahertz electromagnetic radiation to and from said substrate with the sample present, t′

;

subtracting t″

from t′

to determine the transmission time difference with said sample present and without said sample present, Δ

t;

measuring the travel time of said terahertz electromagnetic radiation to and from said sample, 2t₁;

determining the time difference between t′ and

the 2t₁, 2τ

;

dividing Δ

t by 2τ and

determining the quotient;

subtracting said quotient from 1 to obtain a factor; and

multiplying said factor by, c, to determine the velocity of said terahertz electromagnetic radiation in said sample.

2. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 1 wherein said emission of said terahertz electromagnetic radiation is continuous.

3. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 1 wherein said emission of said terahertz electromagnetic radiation is pulsed.

4. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 3 further comprising the step of:

determining the microstructural variation of said sample.

5. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 4 wherein said step of determining the microstructural variation of said sample includes determining the density of the material.

6. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 5 wherein said sample is a dielectric.

7. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 4 wherein said sample is foam.

8. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 4 wherein said sample is a dielectric.

9. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 4, further comprising the steps of:

evaluating, in a plurality of locations, said sample for microstructural variations; and

mapping said variations by location.

10. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 3 wherein said sample is foam.

11. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 10 wherein said sample is foam.

12. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 3 wherein said sample is a dielectric.

13. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 3 wherein the step of measuring the travel time of said terahertz electromagnetic radiation to and from said sample, 2t₁ includes placing a sheet of plastic paper onto said sample to create an adequate dielectric mismatch.

14. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 13 wherein said sheet of plastic paper is less than or equal to 250 μ

m thick.

15. A process for measuring the thickness of a material sample using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of said terahertz electromagnetic radiation in said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 13, further comprising the steps of:

evaluating, in a plurality of locations, said sample for thickness variations; and

mapping said thickness variations by location.

16. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 3, further comprising the step of controlling said spacing between said source (transceiver) and said sample.

17. A process for measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 3, wherein said step of controlling said spacing between said source (transceiver) and said sample under test includes determining, initially, the approximate time location of said sample from said terahertz radiation source.

18. A process for measuring the thickness of a material using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of said terahertz electromagnetic radiation in said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, comprising the steps of:

emitting terahertz electromagnetic radiation from said source;

measuring the travel time of said terahertz electromagnetic radiation to and from said substrate without said sample present, t″

;

placing said sample on said substrate;

measuring the travel time of said terahertz electromagnetic radiation to and from said substrate with said sample present, t′

;

subtracting t″

from t′

to determine the transmission time difference with said sample present and without said sample present, Δ

t;

measuring the travel time of said terahertz electromagnetic radiation to and from said sample, 2t₁;

determining the time difference between t′ and

2t₁, 2τ

;

subtracting Δ

t from 2τ

to obtain a subtraction result;

dividing said subtraction result by 2 to obtain a quotient;

multiplying said quotient by, c, to obtain the thickness of said sample; and

,

determining the thickness of the sample.

19. A process for simultaneously measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample and for measuring the thickness of a material sample using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of said terahertz electromagnetic radiation in said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, said sample residing on a substrate, comprising the steps of:

emitting terahertz electromagnetic radiation from said source;

measuring the travel time of said terahertz electromagnetic radiation to and from said substrate without said sample present, t″

;

placing said sample on said substrate;

measuring the travel time of said terahertz electromagnetic radiation to and from said substrate with said sample present, t′

;

subtracting t″

from t′

to determine the transmission time difference with said sample present and without said sample present, Δ

t;

measuring the travel time of said terahertz radiation to and from said sample, 2t₁;

determining the time difference between t′ and

2t₁, 2τ

;

dividing Δ

t by 2τ and

determining the quotient;

subtracting said quotient from 1 to obtain a factor;

multiplying said factor by, c, to determine the velocity of said terahertz electromagnetic radiation in said sample;

subtracting Δ

t from 2τ

to obtain a subtraction result;

dividing said subtraction result by 2 to obtain a quotient;

multiplying said quotient by, c, to obtain the thickness of said sample;

evaluating, in a plurality of locations, said sample for microstructural variations and for thickness variations, and mapping said microstructural and thickness variations by location.

20. A process for simultaneously measuring the velocity of terahertz electromagnetic radiation in a material sample without prior knowledge of the thickness of said sample and for measuring the thickness of a material sample using terahertz electromagnetic radiation in a material sample without prior knowledge of the velocity of said terahertz electromagnetic radiation in said sample, said terahertz electromagnetic radiation produced by a source, namely, a transceiver, spaced apart from said sample under test and propagated at the speed of light, c, in a medium located between said source, namely, said transceiver, and said sample, said sample residing on a substrate, as claimed in claim 19 wherein a sheet of plastic paper is utilized to determine the travel time of said terahertz radiation to and from said sample, 2t₁.