Terahertz nondestructive evaluation pertains to devices, and techniques of analysis occurring in the terahertz domain of

electromagnetic radiation In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength ...

. These devices and techniques evaluate the properties of a material, component or system without causing damage.

Terahertz imaging

Terahertz imaging is an emerging and significant

nondestructive evaluation Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage. The terms nondestructive examination (NDE), n ...

(NDE) technique used for

dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...

(nonconducting, i.e., an insulator) materials analysis and quality control in the

pharmaceutical Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the ...

biomedical Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine)

, security, materials characterization, and

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial, and military applications. Aerospace engineering consists of aeronautics and astron ...

industries. It has proved to be effective in the inspection of layers in paints and coatings, detecting structural defects in

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

and

composite materials A composite or composite material (also composition material) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or physical properties and are merged to create a ...

and

imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

the physical structure of paintings and manuscripts. The use of THz waves for non-destructive evaluation enables inspection of multi-layered structures and can identify abnormalities from foreign material inclusions, disbond and delamination, mechanical impact damage, heat damage, and water or hydraulic fluid ingression. This new method can play a significant role in a number of industries for materials characterization applications where precision thickness mapping (to assure product dimensional tolerances within a product and from product-to-product) and density mapping (to assure product quality within a 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

, which includes detection.

Terahertz Density Thickness Imager

The Terahertz Density Thickness Imager is a nondestructive inspection method that employs terahertz energy for density and thickness mapping in

, and

composite material A composite or composite material (also composition material) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or physical properties and are merged to create a ...

s. This non-contact, single-sided terahertz

electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...

measurement and

method characterizes micro-structure and

thickness Thickness may refer to: * Thickness (graph theory) * Thickness (geology), the distance across a layer of rock * Thickness (meteorology), the difference in height between two atmospheric pressure levels * Thickness planer a woodworking machine * O ...

variation in dielectric ( insulating) materials. This method was demonstrated for the

Space Shuttle external tank The Space Shuttle external tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen fuel and liquid oxygen oxidizer. During lift-off and ascent it supplied the fuel and oxidizer under pressure to the ...

sprayed-on foam insulation and has been designed for use as an inspection method for current and future NASA

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

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 Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, includi ...

methods. Nondestructive inspection method uses terahertz energy. * *John H. Glenn Research Center * *

Rotational spectroscopy

Rotational spectroscopy uses electromagnetic radiation in the frequency range from 0.1 to 4 terahertz (THz). This range includes millimeter-range wavelengths and is particularly sensitive to chemical molecules. The resulting THz absorption produces a unique and reproducible spectral pattern that identifies the material. 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 fence line or aircraft mounted system that works day or night in any weather. It can locate and track chemical and radioactive plumes. THz-wave radar that can sense radioactive plumes from nuclear plants have detected plumes several kilometers away based on radiation-induced ionization effects in air.

THz tomography

THz tomography techniques are nondestructive methods that can use THz pulsed beam or millimeter-range sources to locate objects in 3D. These techniques include tomography, tomosynthesis, synthetic aperture radar and time of flight. Such techniques can resolve details on scales of less than one millimeter in objects that are several tens of centimeters in size.

Passive/active imaging techniques

Security imaging is currently being done by both active and passive methods. Active systems illuminate the subject with THz radiation whereas passive systems merely view the naturally occurring radiation from the subject. Evidently passive systems are inherently safe, whereas an argument can be made that any form of "irradiation" of a person is undesirable. In technical and scientific terms, however, the active illumination schemes are safe according to all current legislation and standards. The purpose of using active illumination sources is primarily to make the signal-to-noise ratio better. This is analogous to using a flash on a standard optical light camera when the ambient lighting level is too low. For security imaging purposes the operating frequencies are typically in the range 0.1 THz to 0.8 THz (100 GHz to 800 GHz). In this range skin is not transparent so the imaging systems can look through clothing and hair, but not inside the body. There are privacy issues associated with such activities, especially surrounding the active systems since the active systems, with their higher quality images, can show very detailed anatomical features. Active systems such as the L3 Provision and the Smiths eqo are actually mm-wave imaging systems rather than Terahertz imaging systems like Millitech systems. These widely deployed systems do not display images, avoiding any privacy issues. Instead they display generic "mannequin" outlines with any anomalous regions highlighted. Since security screening is looking for anomalous images, items like false legs, false arms, colostomy bags, body-worn urinals, body-worn insulin pumps, and external breast augmentations will show up. Note that breast implants, being under the skin, will not be revealed. Active imaging techniques can be used to perform medical imaging. Because THz radiation is biologically safe (non ionisant), it can be used in high resolution imaging to detect skin cancer. Sensors and Instrumentation and Nondestructive Evaluation
Argonne test facility

Nondestructive Evaluation
* – Please see above links

Space Shuttle inspections

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Space Shuttle The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...

inspections are an example of this technology's application. After the

Shuttle Columbia Space Shuttle ''Columbia'' (OV-102) was a Space Shuttle orbiter manufactured by Rockwell International and operated by NASA. Named after the first American ship to circumnavigate the globe, and the female personification of the United States ...

accident in 2003,

Columbia Accident Investigation Board The ''Columbia'' Accident Investigation Board (CAIB) was an internal commission convened by NASA to investigate the Space Shuttle Columbia disaster, destruction of the Space Shuttle Columbia, Space Shuttle ''Columbia'' during STS-107 upon atmo ...

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.

STS-114 STS-114 was the first "Return to Flight" Space Shuttle mission following the Space Shuttle ''Columbia'' disaster. ''Discovery'' launched at 10:39 EDT (14:39 UTC) on her 31st flight on July 26, 2005. The launch, 907 days (approx. 29 months) a ...

employed Space Shuttle ''Discovery'', and was the first "Return to Flight"

mission following the Space Shuttle ''Columbia'' disaster. It launched at 10:39 EDT, 26 July 2005. During the

flight significant foam shedding was observed. Therefore, 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 was on the

launch pad A launch pad is an above-ground facility from which a rocket-powered missile or space vehicle is vertically launched. The term ''launch pad'' can be used to describe just the central launch platform (mobile launcher platform), or the entire c ...

or during other preparations for launch. Additionally,

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

variations in the foam were 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 testing Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse waves with centre frequencie ...

methods require water coupling. There are millions of dollars of ultrasonic equipment in the field and on the market that are used as

thickness gauge Thickness may refer to: * Thickness (graph theory) * Thickness (geology), the distance across a layer of rock * Thickness (meteorology), the difference in height between two atmospheric pressure levels * Thickness planer a woodworking machine * O ...

s and

density meter A density meter (densimeter) is a device which measures the density of an object or material. Density is usually abbreviated as either \rho or D . Typically, density either has the units of '' kg/m^3 '' or '' lb/ft^3 ''. The most basic principl ...

s. When ''terahertz nondestructive evaluation'' is fully commercialized into a more portable form, and becomes less expensive it will be able to replace the ultrasonic instruments for structural

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

, and

foam Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...

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.