Radar to spot the bad guys from on high

http://www.china.org.cn/china/2019-02/15/content_74467346.htm

China's space engineers said they can now offer a new method to detect terrorists transporting explosives as well as track moving targets more efficiently than current modalities.

Researchers at the Beijing Institute of Radio Measurement, affiliated with the China Aerospace Science and Industry Corp, said they have developed the country's first terahertz radiation-enabled synthetic-aperture radar and they are working to utilize the technology in public security work.

Li Jun, a senior designer at the institute, explained that a terahertz is a unit of the electromagnetic spectrum between the microwave and the optical wavelengths. Among terahertz radiation's many physical characteristics, it has a special ability to identify proteins, the building blocks of living organisms. It can also detect TNT, one of the most oft used explosive materials, and can therefore be used to detect individuals carrying the material on their persons.

"Currently, it is very difficult for public security authorities to screen people for firearms or explosive devices from long, safe distances. Most methods rely on handheld detectors and visual clues, forcing law-enforcement personnel to check suspected people within a short range or manually and this has proved to be time-consuming and dangerous," Li said.

By comparison, terahertz radiation-enabled radar takes advantage of its high penetration capability, and is able to detect explosives and reveal hidden weapons from afar, which helps to improve safety at public buildings and at large events, as well as the safety of security officers, he said.

In addition to its potential applications in remote detection work, the radar technology also offers better solutions for law enforcement departments' surveillance of criminal suspects or terrorists, Li said.

"Existing optical, infrared or radar systems are subject to a host of external factors such as sunlight, cloud or smog, when they are used to monitor and track people on the move. But terahertz technology is immune to these factors, reducing the risk of losing targets," he said.

The institute is a leading research body in radar and terahertz technology in China and has taken part in the development of many advanced defense technologies. Encouraged by the government's policies to foster transfer of defense technologies to civilian industries, institute designers have been seeking to make use of their expertise to assist other sectors, Li said.

Engineers have built prototypes of terahertz radiation-enabled synthetic-aperture radar and are conducting tests.

"We mounted a prototype on a drone and recently conducted test flights in Shaanxi province," Li said. "A typical application of the radar in the future can be drone-based to help with large-scale detection of explosive-carrying terrorists or the placement of improvised explosive devices. This will be much more efficient and safer than deploying a lot of security personnel to do the same work."

Drones equipped with the radar can also perform uninterrupted surveillance of suspects, he added.

Abstract-Femtosecond laser induced breakdown spectroscopy based standoff detection of explosives and discrimination using principal component analysis

Abdul Kalam Shaik, Nageswara Rao Epuru, Hamad Syed, Chandu Byram, and Venugopal Rao Soma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-7-8069&origin=search

We report the standoff (up to ~2 m) and remote (~8.5 m) detection of novel high energy materials/explosive molecules (Nitroimidazoles and Nitropyrazoles) using the technique of femtosecond laser induced breakdown spectroscopy (LIBS). We utilized two different collection systems (a) ME-OCT-0007 (commercially available) and (b) Schmidt-Cassegrain telescope for these experiments. In conjunction with LIBS data, principal component analysis was employed to discriminate/classify the explosives and the obtained results in both configurations are compared. Different aspects influencing the LIBS signal strength at far distances such as fluence at target, efficiency of collection system etc. are discussed.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Grating-coupled surface plasmons on InSb: a versatile platform for terahertz plasmonic sensing (Conference Presentation)

Diyar Talbayev, Shuai Lin

Tulane Univ. (United States)

Jiangfeng Zhou, Khagendra Bhattarai

Univ. of South Florida (United States)

Proc. SPIE 10210, Next-Generation Spectroscopic Technologies X, 102100X (June 9, 2017); doi:10.1117/12.2263717

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2632318

Detection and identification of molecular materials based on their THz frequency vibrational resonances remains an open technological challenge. The need for such technology is illustrated by its potential uses in explosives detection (e.g., RDX) or identification of large biomolecules based on their THz-frequency vibrational fingerprints. The prevailing approaches to THz sensing often rely on a form of waveguide spectroscopy, either utilizing geometric waveguides, such as metallic parallel plate, or plasmonic waveguides made of structured metallic surfaces with sub-wavelength corrugation. The sensitivity of waveguide-based sensing devices is derived from the long (1 cm or longer) propagation and interaction distance of the THz wave with the analyte. We have demonstrated that thin InSb layers with metallic gratings can support high quality factor “true” surface plasmon (SP) resonances that can be used for THz plasmonic sensing. We find two strong SP absorption resonances in normal-incidence transmission and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The sensitivity of this approach relies on the frequency shift of the SP resonance when the dielectric function changes in the immediate vicinity of the sensor, in the region of deeply sub-wavelength thickness. Our computational modeling indicates that the sensor sensitivity can exceed 0.25 THz per refractive index unit. One of the SP resonances also exhibits a splitting when tuned in resonance with a vibrational mode of an analyte, which could lead to new sensing modalities for the detection of THz vibrational features of the analyte.

 © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Speedy terahertz-based system could detect explosives

An artist’s embellishment of an image of the “gain medium” used to produce terahertz frequency combs. The different colors indicate that different wavelengths of oscillating terahertz radiation travel different distances through the medium, which has a different refractive index for each of them.

Image: Yan Liang/L2Molecule.com

Larry Hardesty | MIT News Office
May 20, 2016

http://news.mit.edu/2016/speedy-terahertz-based-system-could-detect-explosives-0520

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Spectroscopic system with chip-scale lasers cuts detection time from minutes to microseconds.

Terahertz spectroscopy, which uses the band of electromagnetic radiation between microwaves and infrared light, is a promising security technology because it can extract the spectroscopic “fingerprints” of a wide range of materials, including chemicals used in explosives.

But traditional terahertz spectroscopy requires a radiation source that’s heavy and about the size of a large suitcase, and it takes 15 to 30 minutes to analyze a single sample, rendering it impractical for most applications.

In the latest issue of the journal Optica, researchers from MIT’s Research Laboratory of Electronics and their colleagues present a new terahertz spectroscopy system that uses a quantum cascade laser, a source of terahertz radiation that’s the size of a computer chip. The system can extract a material’s spectroscopic signature in just 100 microseconds.

The device is so efficient because it emits terahertz radiation in what’s known as a “frequency comb,” meaning a range of frequencies that are perfectly evenly spaced.

“With this work, we answer the question, ‘What is the real application of quantum-cascade laser frequency combs?’” says Yang Yang, a graduate student in electrical engineering and computer science and first author on the new paper. “Terahertz is such a unique region that spectroscopy is probably the best application. And QCL-based frequency combs are a great candidate for spectroscopy.”

Different materials absorb different frequencies of terahertz radiation to different degrees, giving each of them a unique terahertz-absorption profile. Traditionally, however, terahertz spectroscopy has required measuring a material’s response to each frequency separately, a process that involves mechanically readjusting the spectroscopic apparatus. That’s why the method has been so time consuming.

Because the frequencies in a frequency comb are evenly spaced, however, it’s possible to mathematically reconstruct a material’s absorption fingerprint from just a few measurements, without any mechanical adjustments.

Getting even

The trick is evening out the spacing in the comb. Quantum cascade lasers, like all electrically powered lasers, bounce electromagnetic radiation back and forth through a “gain medium” until the radiation has enough energy to escape. They emit radiation at multiple frequencies that are determined by the length of the gain medium.

But those frequencies are also dependent on the medium’s refractive index, which describes the speed at which electromagnetic radiation passes through it. And the refractive index varies for different frequencies, so the gaps between frequencies in the comb vary, too.

To even out their lasers’ frequencies, the MIT researchers and their colleagues use an oddly shaped gain medium, with regular, symmetrical indentations in its sides that alter the medium’s refractive index and restore uniformity to the distribution of the emitted frequencies.

Yang; his advisor, Qing Hu, the Distinguished Professor in Electrical Engineering and Computer Science; and first author David Burghoff, who received his PhD in electrical engineering and computer science from MIT in 2014 and is now a research scientist in Hu’s group, reported this design in Nature Photonics in 2014. But while their first prototype demonstrated the design’s feasibility, it in fact emitted two frequency combs, clustered around two different central frequencies, with a gap between them, which made it less than ideal for spectroscopy.

In the new work, Yang and Burghoff, who are joint first authors; Hu; Darren Hayton and Jian-Rong Gao of the Netherlands Institute for Space Research; and John Reno of Sandia National Laboratories developed a new gain medium that produces a single, unbroken frequency comb. Like the previous gain medium, the new one consists of hundreds of alternating layers of gallium arsenide and aluminum gallium arsenide, with different but precisely calibrated thicknesses.

Getting practical

As a proof of concept, the researchers used their system to measure the spectral signature of not a chemical sample but an optical device called an etalon, made from a wafer of gallium arsenide, whose spectral properties could be calculated theoretically in advance, providing a clear standard of comparison. The new system’s measurements were a very good fit for the etalon’s terahertz-transmission profile, suggesting that it could be useful for detecting chemicals.

Although terahertz quantum cascade lasers are of chip scale, they need to be cooled to very low temperatures, so they require refrigerated housings that can be inconveniently bulky. Hu’s group continues to work on the design of increasingly high-temperature quantum cascade lasers, but in the new paper, Yang and his colleagues demonstrated that they could extract a reliable spectroscopic signature from a target using only very short bursts of terahertz radiation. That could make terahertz spectroscopy practical even at low temperatures.

“We used to consume 10 watts, but my laser turns on only 1 percent of the time, which significantly reduces the refrigeration constraints,” Yang explains. “So we can use compact-sized cooling.”

“This paper is a breakthrough, because these kinds of sources were not available in terahertz,” says Gerard Wysocki, an assistant professor of electrical engineering at Princeton University. “Qing Hu is the first to actually present terahertz frequency combs that are semiconductor devices, all integrated, which promise very compact broadband terahertz spectrometers.”

“Because they used these very inventive phase correction techniques, they have demonstrated that even with pulsed sources you can extract data that is reasonably high resolution already,” Wysocki continues. “That’s a technique that they are pioneering, and this is a great first step toward chemical sensing in the terahertz region.”

This Tool Could Sniff Out a Paris Bomb More Than a Football Field Away

National Journal Short

FRIDAY, NOVEMBER 20, 2015

Patrick Tucker, Defense One

http://www.nationaljournal.com/s/102523/this-tool-could-sniff-out-paris-bomb-more-than-football-field-away?mref=scroll

Parisi­an po­lice moved in to ap­pre­hend people sus­pec­ted of launch­ing last week’s ter­ror at­tacks, a wo­man det­on­ated a sui­cide-bomb vest. The re­cent ap­pear­ance of such weapons in West­ern cit­ies has alarmed many in law en­force­ment. One pos­it­ive out­come of the mil­it­ary’s ex­tens­ive ex­per­i­ence with such devices is a new sys­tem that can help guards de­tect a bomb vest from up to 100 meters away.

The new ex­per­i­ment­al set of sensors is dubbed the Stan­doff Sui­cide Bomber De­tec­tion Sys­tem, or SS­BDS. De­veloped by the Joint Im­pro­vised-Threat De­feat Agency, or JIDA, it has already seen ac­tion; in 2012, the De­fense De­part­ment took an early ver­sion to Afgh­anistan.

The SS­BDS is not a single ma­gic lens, but an en­semble of sensors that meas­ure ra­di­ation at the mid­wave and long­wave in­frared as well as the tera­hertz wavelengths. There’s also a vis­ible-light cam­era. Tera­hertz ra­di­ation may sound like something to avoid—but be­cause it uses low en­ergy and isn’t ion­iz­ing, it’s less dan­ger­ous to hu­man tis­sue than x-rays. It has been used as part of se­cur­ity ap­plic­a­tions since 2004.

On Tues­day, JIDA of­fi­cials demon­strated the sys­tem to re­port­ers at Vir­gin­ia’s Fort Bel­voir. When dir­ec­ted at a per­son, the SS­BDS of­fers three views: a grainy black-and-white, which is the in­frared; a bright or­ange glow, which is the tera­hertz; and a reg­u­lar pic­ture from the cam­era.

The pres­ence of a sui­cide belt won’t set off alarms but a trained—or simply at­tent­ive—eye can use the mul­tiple sensors to see dark shapes or spots—areas of neg­at­ive space that in­dic­ate an ab­nor­mal­ity, which should prompt a closer in­vest­ig­a­tion. In es­sence, you’re look­ing not for ex­plos­ives but for holes in the pic­ture where there should be sol­id white or or­ange.

“It’s a per­fect sys­tem for dual use with De­part­ment of Home­land Se­cur­ity. Just think of Par­is,” one JI­DA scient­ist said.

The SS­BDS is not a small sys­tem. Each bank of sensors stands at per­haps three feet tall, and a hand­held ver­sion would be prac­tic­ally im­possible. “You’re lim­ited by phys­ics,” said an­oth­er one of the De­fense De­part­ment sci­ent­ists on the team. But it could be in­cor­por­ated in­to the ar­chi­tec­ture of a train sta­tion, foot­ball sta­di­um, or con­cert ven­ue.

In JIDA’s demon­stra­tion, which was modeled on a real-world test­ing scen­ario, a base in Afgh­anistan, a sub­ject, dressed in a thawb, or white dress­ing gown, stood in a booth. The booth shiel­ded him from sun­light, which can in­ter­fere with the tera­hertz sensor—which points out just one of the dif­fi­culties in turn­ing the SS­BDS in­to a use­ful, de­ploy­able sys­tem.

The next step for SS­BDS, if its re­ques­ted re­search-and-de­vel­op­ment money comes through, is the in­teg­ra­tion of a new, cut­ting-edge sensor for hy­per­spec­tral ima­ging. Take a thermal im­age of the sort you would see with a heat cam­era and then slice it up in­to dif­fer­ent wavelengths, al­low­ing op­er­at­ors to identi­fy not just dark spots but also, po­ten­tially, the pres­ence of ex­plos­ives. That would cut down on false pos­it­ives and in­crease the range of the device.

“We can take dif­fer­ent ma­ter­i­als, such as your jack­et, my jack­et, her shirt. Al­though they’re very sim­il­ar in ma­ter­i­al makeup, they ac­tu­ally have their own unique sig­na­tures, so every piece of ma­ter­i­al has its own sig­na­ture, just like a fin­ger­print,” said a third sci­ent­ist.

The cost of a pro­duc­tion sys­tem could run past a mil­lion dol­lars, but those num­bers could come down as man­u­fac­tur­ing comes up since all of the sensors are com­mer­cial off-the-shelf.

SS­BDS wasn’t in­ten­ded for use in a ci­vil­ian set­ting or a West­ern city but to pro­tect troops on for­ward op­er­at­ing bases. But the need for sys­tems like it has evolved tre­mend­ously—and rap­idly.

On Fri­day even­ing, just 15 minutes in­to a soc­cer match between France and Ger­many, a man wear­ing a vest laced with ex­plos­ives ap­proached one of the en­trances to the St­ade de France, a sta­di­um filled with 80,000 spec­tat­ors in­clud­ing French Pres­id­ent François Hol­lande. When guards frisked him, he backed away and det­on­ated the vest.

New York City Po­lice Com­mis­sion­er Wil­li­am Brat­ton seized on this as an omin­ous sign of the fu­ture: “All of them, were equipped with these sui­cide vests, which are a great con­cern if you’re ask­ing your of­ficers to rush in, which is the tac­tic here in Amer­ica now, [when] re­spond­ing to the act­ive-shoot­er scen­ario,” he said on the pop­u­lar Morn­ing Joe news pro­gram.

No sensor sys­tem can re­place the judg­ment of an in­tel­li­gent and ob­ser­v­ant hu­man be­ing, a be­ing, hope­fully, armed with the best equip­ment. The events last week and this week in Par­is are test­a­ment to that.

Abstract-Discrimination and identification of RDX/PETN explosives by chemometrics applied to terahertz time-domain spectral imaging

J. Bou-Sleiman, J.-B. Perraud, J.-P. Guillet, P. Mounaix

IMS, CNRS, Bordeaux Univ. (France)

B. Bousquet

CELIA, CNRS, Bordeaux Univ. (France)

N. Palka

Military Univ. of Technology (Poland)

Proc. SPIE 9651, Millimetre Wave and Terahertz Sensors and Technology VIII, 965109 (October 21, 2015); doi:10.1117/12.2197442

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2466618

Detection of explosives has always been a priority for homeland security. Jointly, terahertz spectroscopy and imaging are emerging and promising candidates as contactless and safe systems. In this work, we treated data resulting from hyperspectral imaging obtained by THz-time domain spectroscopy, with chemometric tools. We found efficient identification and sorting of targeted explosives in the case of pure and mixture samples. In this aim, we applied to images Principal Component Analysis (PCA) to discriminate between RDX, PETN and mixtures of the two materials, using the absorbance as the key-parameter. Then we applied Partial Least Squares-Discriminant Analysis (PLS-DA) to each pixel of the hyperspectral images to sort the explosives into different classes. The results clearly show successful identification and categorization of the explosives under study.
 © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Inspecting letters with terahertz waves

The prize-winning team presents terahertz scanner for the secure identification: Professor René Beigang and Thorsten Sprenger (from left to right). Credit: Dirk Mahler/Fraunhofer

http://phys.org/news/2014-05-letters-terahertz.html#jCp

Is it a harmless parcel or a bomb, an innocent letter or a drug shipment? A new terahertz scanner is capable of detecting illicit drugs and explosives sent by post without having to open suspicious packages or envelopes

Alert at Schloss Bellevue. A suspicious letter addressed to German President Joachim Gauck has been detected, which might contain a bomb. Not willing to take any risks, the bomb squad is called out to destroy the package. Later investigations revealed that the envelope did not contain any explosives, but better safe than sorry. A year ago, this event created turmoil in the mail sorting office in Berlin, because at the time there was no safe and simple way of reliably detecting the presence of explosives or drugs in letters and small packets. A new solution is offered by the terahertz scanner developed by researchers at the Fraunhofer Institute for Physical Measurement Techniques IPM in Kaiserslautern in collaboration with Hübner GmbH & Co. KG in Kassel. Their T-COGNITION system is capable of detecting and identifying the hidden content of suspicious packages or envelopes without having to open them. One of this year's Joseph von Fraunhofer prizes was awarded to Prof. Dr. René Beigang of Fraunhofer IPM and Dipl.-Ing. Thorsten Sprenger, Head of Public Security and Photonics at Hübner, for their work on the terahertz scanner for the secure identification of hazardous materials and illicit drugs in postal consignments.

But why did the scientists choose to use terahertz waves for this application? Professor René Beigang explains: "The terahertz range lies midway between microwave and infrared in the electromagnetic spectrum, and thus combines the advantages of both." Like microwaves, these low-energy frequencies can easily penetrate paper, wood, lightweight fabrics, plastics, and ceramics. Moreover, terahertz waves generate characteristic spectra depending on the type of material they travel through, which can be analyzed quickly using intelligent software. A further significant advantage is that terahertz waves are non-ionizing and therefore safe to use in an unprotected environment, unlike X-rays. This makes the technology an interesting option for use in mail scanners.

Scaling up terahertz technology for industrial applications

Terahertz technology is still in its infancy, and until now it has found relatively few applications. The department of Material Characterization and Testing at the University of Kaiserslautern, sponsored jointly by Fraunhofer IPM and the Land of Rheinland-Pfalz, hopes to change this situation. "Our goal is to scale up terahertz technology and extend its range of use to include security applications," says Beigang. The engineers at Hübner were among the first to recognize the potential of the Fraunhofer researchers' work. The company's traditional line of business is manufacturing key components for the transportation industry (e.g. rail vehicles, buses, airport technology, automotive). A new division for public security was added in 2006, when the company first started to look for cooperation partners. The mail scanner project was launched four years later, based on previous joint development projects. In the meantime, the company has brought its T-COGNITION solution onto the market.

This is how the mail scanner works. Suspicious envelopes and packages are fed into the scanner on a retractable tray. They are then exposed to terahertz waves which are absorbed at different frequencies within the spectral range depending on the substance they travel through (characteristic absorption properties). Detectors at the output of the scanner record the transmitted wavelengths. "Within a few seconds, T-COGNITION produces a spectroscopic fingerprint that allows the detected hazardous material to be compared with database samples and definitively identified," says Thorsten Sprenger.

The system triggers an alarm if the consignment contains explosives or illicit drugs.The system is capable of examining the content of postal items up to C4 format with a thickness of up to two centimeters. Sprenger says: "It is the ideal mailroom solution for prisons, customs offices, government agencies, company headquarters, and embassies or consulates, because it helps to improve security and protect human lives."

T-COGNITION recently received the PrismAward, the equivalent of an Oscar in the photonics world, at the Photonics West 2014 international congress in San Francisco.

 Explore further: Nonlinear optical materials convert terahertz radiation into infrared light

Award-winning Letter Bomb Detector

FREIBURG and KASSEL, Germany, May 21, 2014 /NEWS.GNOM.ES/ –

http://news.gnom.es/pr/award-winning-letter-bomb-detector

- Thorsten Sprenger from Hübner GmbH and René Beigang from the Fraunhofer Institute for Physical Measurement Techniques receive the Joseph von Fraunhofer Prize 2014

Spotting letters and parcels containing explosives has just gotten easier thanks to the T-COGNITION system from Hübner GmbH, a global company headquartered in Kassel, Germany. The system uses terahertz technology to detect illegal substances without having to open the mail item. At today’s Fraunhofer-Gesellschaft Annual Meeting,Thorsten Sprenger and René Beigang were presented with this year’s Joseph von Fraunhofer Prize for their terahertz system for detecting dangerous substances such as explosives and narcotics.

Thorsten Sprenger heads Hübner’s Public Security and Photonics unit. The German company has been manufacturing components and systems for the transportation industry since 1946, adding security technologies to its portfolio in 2005. The collaboration with René Beigang from the Fraunhofer Institute for Physical Measurement Techniques in Kaiserslautern, Germany, was launched in 2006 with a feasibility study on the non-contact identification of hazardous materials using terahertz technology. Hübner has since developed a range of products for various applications

T-COGNITION is easy to operate. After being placed in the machine’s tray, the postal item is penetrated with terahertz waves of various frequencies, which are absorbed depending on the contents of the item. Every substance has its own unique absorption spectrum. This “fingerprint” is captured by the device and compared with referential spectrums in a database. An alarm sounds when a listed dangerous substance is identified. An important fact: terahertz waves are not harmful to humans.

The T-COGNITION system can enhance the work and safety in the police force, customs controls and prisons. It can also be used to protect prominent individuals. Hübner’s new product is designed to supplement, not replace, conventional x-ray scans. Postal items identified as potentially dangerous during a preliminary inspection by x-ray or by the Hübner Terahertz Imager T-SENSE can be examined by T-CONGNITION for a final check.  

The Oscar of the photonics industry

The Joseph von Fraunhofer Prize is not the first for Hübner’s innovation. Its T-COGNITION and the revolutionary C-WAVE – a technology for tunable laser light frequencies, were recognized at the Photonics West 2014 trade fair with the Prism Award, the Oscar of the photonics sector.

Contact:
Stefanie Schürmann
HÜBNER GmbH & Co. KG
Tel.:  +49-561-998-1930
Fax:  +49-561-998-1819
 stefanie.schuermann@hubner-germany.com

http://www.hubner-germany.com

http://www.publicsecurity.de

http://www.hubner-photonics.com

SOURCE HUEBNER GmbH & Co. KG

Identified for the first time what kind of explosive has been used after the device has been detonated

http://www.basqueresearch.com/berria_irakurri.asp?Berri_Kod=5061&hizk=I#.U3ybL9q9KSM

There are objects we cannot see within the range of the visible but which we can with imaging systems that use the terahertz (THz) wavelength. Within this range we can detect, for example, not only a foreign body hidden under clothing, but also determine what material it is made of. David Etayo, a telecommunications engineer and PhD holder of the NUP/UPNA-Public University of Navarre, has been able to identify explosive components not only in their pure state, but also, and for the first time, after the detonation has taken place. What is more, he has worked on other terahertz applications for agriculture and the food industry. His PhD thesis is entitled “New developments in the THz field for imaging applications”.

Characterising (identifying) a material means finding out its distinctive features so that when the substance is subsequently subjected to a detector system, the system will indicate what it is. As this researcher pointed out, “what we have done is gone a step further in the imaging system: besides detecting that an object is there, we have characterised different materials to see how they react within the THz range. We have characterised explosives and, for the first time, a type of explosive like gunpowder, which was a material present, for example, in the March 11 attack”. He has also characterised other materials like TNT, hexogen and pentrite.

One of the achievements of this PhD thesis has been the characterising also of explosives that have already been detonated. "The normal thing is to characterise explosives in their recently produced laboratory form, when they are safe, but what happens, for example, after an attack, is that only a few remains are left behind and are totally different from the original materials."

In the course of his research and in collaboration with the Guardia Civil (Spanish Gendarmerie) samples were taken before and after detonation. Furthermore, the materials were characterised in different forms: pure, commercial and homemade explosive materials, for example. That way, it has been possible to detect explosives in minimum sample quantities of between 5 and 10 milligrams. Blends of different explosives were also analysed and in all the cases it was possible to identify each of the components.

"Using the remains of a detonation as a sample, we can find out almost immediately what kind of explosive has been detonated. In the end, it is a chemical process that modifies the initial product, but the good thing is that in the pure as well as in the detonated state is it possible in the terahertz range to characterise, determine and find out what it is." The use of this technology could also allow these systems to be incorporated into crawler robots employed to dispose of devices, and thus enable them to detect the explosive involved.

Various applications

Another part of the thesis focussed on THz technology applications in the fields of agriculture and the food industry. In the first case, work was done on vines since THz are very sensitive to the water content of a sample: “Although at first sight no variations can be detected, if you analyse the imaging of a vine leaf in terahertz you can see perfectly how the water content varies from one day to the next. This allows one to exercise greater control over the plants, cut irrigation costs and that way improve the quality of the wine, etc.”

As regards the food industry, work was done in collaboration with a chorizo producing plant. On the one hand, the amount of water in the product was measured during the drying process which enables one to estimate how much longer the chorizo curing process will take. “The good thing about THz technology is that it is non-destructive; you don’t need to cut the chorizo to carry out the measuring, all you have to do is bring the sensor up to the product," explained David Etayo. Furthermore, the most direct application they have found is the use of the system to detect remains or foreign bodies that may have ended up in the production chain of sliced chorizo.

Finally, during the work a double band was designed; it allows two different frequency ranges (infrared and terahertz) to be combined into a single measurement so that hidden objects can be detected and identified. Within the electromagnetic spectrum, THz radiation is located between microwaves and infrared light waves. The infrared range works at a higher frequency and provides resolution and greater imaging quality, while the THz part is the one that is used to identify and characterise the materials. “The idea is that a single detector can provide us with the resolution of the imaging and the identification of the material at the same time,” pointed out the researcher. In this thesis we have designed and manufactured a detector that enables us to make this measurement. What is more, the use of Fresnel zones has enabled us to achieve a gain increase in the infrared band."

Notes

David Etayo-Salinas did his university and PhD studies at the NUP/UPNA-Public University of Navarre, where he has lectured in subjects on the Engineering degree course in Telecommunications Technologies. During his training as a researcher he spent a period of time at the German University of Siegen, at the Institute for High Frequency Technology and Quantum Electronics. He has participated in about fifteen congresses and conferences and is the co-author of half a dozen scientific papers.

Internet reference

www.unavarra.es/actualidad/berriak?contentId=181367

References

D. Etayo, I. Maestrojuan, J. Teniente, I. Ederra, R. Gonzalo. (2013). "Experimental Explosive Characterization for Counterterrorist Investigation". Journal of Infrared, Millimeter, and Terahertz Waves, 34, 7-8: 468-479

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