Terahertz nondestructive evaluation
Encyclopedia
Terahertz nondestructive evaluation pertains to devices, and techniques of analysis
occurring in the terahertz domain
of electromagnetic radiation
. These devices and techniques evaluate the properties of a material, component or system without causing damage.
After the Shuttle Columbia accident in 2003, Columbia Accident Investigation Board
recommendation R3.2.1 stated “Initiate an aggressive program to eliminate all External Tank Thermal Protection System debris-shedding at the source….” To support this recommendation, inspection methods for flaws in foam are being evaluated, developed, and refined at NASA.
flight in July of 2005, significant foam shedding was still observed. The ability to nondestructively detect and characterize crushed foam after that flight became a significant priority when it was believed that the staff processing the tank had crushed foam by walking on it or from hail damage
when the shuttle is on the launch pad
and in preparation for launch.
Additionally, density
variations in the foam are also potential points of flaw initiation causing foam shedding. The innovation described below answered the call to develop a nondestructive, totally non-contact, non-liquid-coupled method that could simultaneously and precisely characterize thickness variation (from crushed foam due to worker handling and hail damage) and density variation in foam materials. It was critical to have a method that did not require fluid (water) coupling; i.e; ultrasonic inspection
methods require water coupling.
There are millions of dollars of ultrasonic equipment in the field and on the market that are used as thickness gauges and density meters. This technology
, when fully commercialized into a more portable form, and as the technology gets less expensive, will be able to replace the ultrasonic instruments for structural plastic
, ceramic
, and foam
materials. The new instruments will not require liquid coupling thereby enhancing their usefulness in field applications and possibly for high-temperature in-situ applications where liquid coupling is not possible. A potential new market segment can be developed with this technology.
, and aerospace
industries. This new method can play a significant role in those industries for materials characterization applications where precision thickness mapping (to assure product dimensional tolerances within product and from product-to-product) and density mapping (to assure product quality within product and from product-to-product) are required.
This non-contact, single-sided terahertz electromagnetic measurement and imaging method characterizes micro-structural (e.g., spatially-lateral density) and thickness variation in dielectric (insulating) materials. This method was demonstrated for space shuttle external tank sprayed-on foam insulation and has been designed for use as an inspection method for current and future NASA thermal protection systems and other dielectric material inspection applications where no contact can be made with the sample due to fragility and it is impractical to use ultrasonic methods.
Detect trace amounts of explosives - THz spectroscopy can detect trace amounts of explosives in less than one second. Because explosives continually emit trace amounts of vapor, it should be possible to use these methods to detect concealed explosives from a distance.
It can locate and track chemical and radioactive plumes. THz-wave radar can sense radioactive plumes from nuclear plants have been detected several kilometers away based on radiation-induced ionization effects in air.
Nondestructive testing
Nondestructive testing or Non-destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage....
occurring in the terahertz domain
Terahertz radiation
In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-waves, T-light, T-lux, THz...
of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
. These devices and techniques evaluate the properties of a material, component or system without causing damage.
After the Shuttle Columbia accident in 2003, Columbia Accident Investigation Board
Columbia Accident Investigation Board
The Columbia Accident Investigation Board was convened by NASA to investigate the destruction of the Space Shuttle Columbia during STS-107 upon atmospheric re-entry on February 1, 2003. In addition to determining the cause of the accident, the panel also recommended changes that should be made...
recommendation R3.2.1 stated “Initiate an aggressive program to eliminate all External Tank Thermal Protection System debris-shedding at the source….” To support this recommendation, inspection methods for flaws in foam are being evaluated, developed, and refined at NASA.
Overview
During the STS-114STS-114
-Original crew:This mission was to carry the Expedition 7 crew to the ISS and bring home the Expedition 6 crew. The original crew was to be:-Mission highlights:...
flight in July of 2005, significant foam shedding was still observed. The ability to nondestructively detect and characterize crushed foam after that flight became a significant priority when it was believed that the staff processing the tank had crushed foam by walking on it or from hail damage
Hail
Hail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...
when the shuttle is on the launch pad
Launch pad
A launch pad is the area and facilities where rockets or spacecraft lift off. A spaceport can contain one or many launch pads. A typical launch pad consists of the service and umbilical structures. The service structure provides an access platform to inspect the launch vehicle prior to launch....
and in preparation for launch.
Additionally, density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
variations in the foam are also potential points of flaw initiation causing foam shedding. The innovation described below answered the call to develop a nondestructive, totally non-contact, non-liquid-coupled method that could simultaneously and precisely characterize thickness variation (from crushed foam due to worker handling and hail damage) and density variation in foam materials. It was critical to have a method that did not require fluid (water) coupling; i.e; ultrasonic inspection
Ultrasonic inspection
In ultrasonic testing , very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz and occasionally up to 50 MHz are launched into materials to detect internal flaws or to characterize materials...
methods require water coupling.
There are millions of dollars of ultrasonic equipment in the field and on the market that are used as thickness gauges and density meters. This technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...
, when fully commercialized into a more portable form, and as the technology gets less expensive, will be able to replace the ultrasonic instruments for structural plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
, ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
, and foam
Styrofoam
Styrofoam is a trademark of The Dow Chemical Company for closed-cell currently made for thermal insulation and craft applications. In 1941, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene...
materials. The new instruments will not require liquid coupling thereby enhancing their usefulness in field applications and possibly for high-temperature in-situ applications where liquid coupling is not possible. A potential new market segment can be developed with this technology.
Terahertz imaging
Terahertz imaging is an emerging and significant nondestructive evaluation (NDE) technique used for dielectric (nonconducting, i.e., an insulator) materials analysis and quality control in the pharmaceutical, biomedical, security, materials characterizationMaterials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, and aerospace
Aerospace
Aerospace comprises the atmosphere of Earth and surrounding space. Typically the term is used to refer to the industry that researches, designs, manufactures, operates, and maintains vehicles moving through air and space...
industries. This new method can play a significant role in those industries for materials characterization applications where precision thickness mapping (to assure product dimensional tolerances within product and from product-to-product) and density mapping (to assure product quality within product and from product-to-product) are required.
Nondestructive evaluation
Sensors and instruments are employed in the 0.1 to the 10 THz range for nondestructive evaluation, which includes detection.Terahertz Density Thickness Imager
The Terahertz Density Thickness Imager is a nondestructive inspection method uses terahertz energy for density and thickness mapping in dielectric, ceramic, and composite materials.This non-contact, single-sided terahertz electromagnetic measurement and imaging method characterizes micro-structural (e.g., spatially-lateral density) and thickness variation in dielectric (insulating) materials. This method was demonstrated for space shuttle external tank sprayed-on foam insulation and has been designed for use as an inspection method for current and future NASA thermal protection systems and other dielectric material inspection applications where no contact can be made with the sample due to fragility and it is impractical to use ultrasonic methods.
Rotational spectroscopy
Rotational spectroscopy uses electromagnetic radiation in the wavelength range from 0.1 to 0.5 terahertz (THz). This range includes millimeter-range energies and is particularly sensitive to chemical molecules. The resulting THz absorption produces a unique and reproducible spectral pattern that identifies the material.Detect trace amounts of explosives - THz spectroscopy can detect trace amounts of explosives in less than one second. Because explosives continually emit trace amounts of vapor, it should be possible to use these methods to detect concealed explosives from a distance.
THz-wave radar
THz-wave radar can sense gas leaks, chemicals and nuclear materials. In field tests, THz-wave radar detected chemicals at the 10-ppm level from 60 meters away. This method can be used in a fenceline or aircraft mounted system that works day or night in any weather.It can locate and track chemical and radioactive plumes. THz-wave radar can sense radioactive plumes from nuclear plants have been detected several kilometers away based on radiation-induced ionization effects in air.
Passive imaging techniques
Passive detection and imaging techniques can be used to perform medical imaging. Because THz radiation is biologically safe, it can be used in high resolution imaging to detect.See also
- Destructive testingDestructive testingIn destructive testing, tests are carried out to the specimen's failure, in order to understand a specimen's structural performance or material behaviour under different loads...
- InspectionInspectionAn inspection is, most generally, an organized examination or formal evaluation exercise. In engineering activities inspection involves the measurements, tests, and gauges applied to certain characteristics in regard to an object or activity...
- Maintenance testingMaintenance testingMaintenance testing is that testing which is performed to either identify equipment problems, diagnose equipment problems or to confirm that repair measures have been effective...
- Product certificationProduct certificationProduct certification or product qualification is the process of verifying that a certain product has passed performance tests and quality assurance tests or qualification requirements stipulated in contracts, regulations, or specifications...
- Quality controlQuality controlQuality control, or QC for short, is a process by which entities review the quality of all factors involved in production. This approach places an emphasis on three aspects:...
- Risk-based inspection
- Failure analysisFailure analysisFailure analysis is the process of collecting and analyzing data to determine the cause of a failure. It is an important discipline in many branches of manufacturing industry, such as the electronics industry, where it is a vital tool used in the development of new products and for the improvement...
- Forensic engineeringForensic engineeringForensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with...
- Materials scienceMaterials scienceMaterials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
- Predictive maintenancePredictive maintenancePredictive maintenance techniques help determine the condition of in-service equipment in order to predict when maintenance should be performed...
- Reliability engineeringReliability engineeringReliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...
- Stress testingStress testingStress testing is a form of testing that is used to determine the stability of a given system or entity. It involves testing beyond normal operational capacity, often to a breaking point, in order to observe the results...
- Terahertz radiationTerahertz radiationIn physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-waves, T-light, T-lux, THz...
- Terahertz metamaterialsTerahertz metamaterialsTerahertz metamaterials are a new class of composite, artificial materials which interact at terahertz frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz...
Further reading
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- On this page also see the sections that follows for use of the Terahertz domain: Small Organic Molecular Crystals / Materials Properties (Glasses etc.), Understanding of Vibrational Modes at Terahertz Frequencies, Quantum Cascade Laser Applications, Implementation of Novel Sensing Paradigms, and Dynamics in Biomolecules.
- Original PhD. dissertation by Christopher D. Stoik, Lieutenant Colonel, USAF. December 2008. Free online article.