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A new terahertz spectrometer can now provide reliable, contact-free identification of chemical substances.

This past December, security forces intercepted a letter bomb addressed to Josef Ackermann, the head of Deutsche Bank. At almost the same time, a letter bomb exploded in an office in Rome. The manager in charge of Equitalia, the tax-collection authority, suffered an injury to his hand.

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Until now, security personnel have had to conduct painstaking inspections of any suspicious parcels and letters by hand, which is not the best way to go about determining the contents.

However, a new hands free option may be available. It is the scanner T-Cognition 1.0 from the Hübner company of Kassel, Germany. The device, developed with the assistance of Fraunhofer University in Germany, researches, detects, without contact, substances such as drugs or explosives contained in unopened letters or flat packages.

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“You place the suspicious parcels or letters in a kind of drawer, and the device uses terahertz waves to determine whether it contains explosives. This protects confidentiality, and the mail can then be delivered safely,” said Dr. Joachim Jonuscheit, deputy division director at the Kaiserslautern facility of the Fraunhofer Institute for Physical Measurement Techniques IPM and the researcher in charge of terahertz analysis. The attacks in Rome and Frankfurt fueled the security industry‘s interest in the analysis device.

“Most dielectric materials, such as plastics, clothing or paper, are transparent to microwaves and can also be penetrated by terahertz waves with comparatively low reduction,” Jonuscheit said. “For non-destructive testing, the terahertz range is extremely interesting.”

On the electromagnetic spectrum, terahertz waves are at the junction between microwaves and infrared radiation. The frequency range extends from 100 GHz to 10 THz; this corresponds to a wavelength from 3 mm to 30 µm. Terahertz waves combine the benefits of the adjoining spectral ranges: High penetration depth and low scatter, accompanied by good spatial resolution and the capability of spectral identification of unknown substances.

Like radiation in the infrared range, Terahertz waves reveal a substance’s spectral signature. The measurement device features a database with the spectral “fingerprints” of hazardous materials and can extend to include additional materials at any time. The device compares the spectral fingerprint of the substance to analyze with values in its database and returns a clear result. The scanner operates using transmission and reflection analysis. In safety checks, the terahertz wave offers low-loss penetration of envelopes made of paper or plastic to detect any chemical substances within. If a package contains, something like metal – as housing for an explosive device – the wave reflects and the receiver measures it. This is how they can quickly identify suspicious packages.

Now the researchers want to gain a foothold in the pharmaceutical and chemical industries.

“Up until now, makers of pharmaceuticals had to prepare extra samples if they wanted to find out whether the mixture ratio in a particular drug was right, whether the chemical was in the desired crystalline structure, and whether quality was all right,” Jonuscheit said. “Depending on the substance and the material involved, our device clearly detects all of the chemicals found. It also provides basic analysis of the mixture ratio of multiple substances. Terahertz analysis also allows conclusions about the substances’ crystalline structure. For instance, you can determine whether a potentially unwanted recrystallization has taken place. In the future, this can spare chemical and pharmaceutical manufacturers painstaking preliminary analysis and sample preparation,” he said.

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