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  1. Science and Technology Directorate
  2. News Room
  3. Feature Article: The Next Generation of Explosives Trace Detection is Here

Feature Article: The Next Generation of Explosives Trace Detection is Here

Release Date: October 6, 2022

The Science and Technology Directorate (S&T) has always placed a special focus on aviation security. That’s one of the reasons why the work that is being done by S&T’s Next Generation (NextGen) Explosives Trace Detection (ETD) program team is such a high priority.

Transportation Security Administration (TSA) checkpoint at an airport. A TSA employee is seated at the gate. Multiple lines of passengers are putting their belongings on conveyor belts to be scanned.
S&T puts special focus on airport security checkpoints. Photo credit: AZ-BLT/EnvatoElements.

The sophisticated research, development, testing and evaluation (RDT&E) that S&T performs is changing the scientific and security landscape. In coordination with government, academic, and industry partners, S&T is relentlessly committed to helping bring a variety of cutting-edge solutions to the field.

Launched in fiscal year 2020, NextGen ETD expanded the scope of a previous program to meet evolving operational needs at aviation checkpoints. This has resulted in the advancement of technologies that can quickly and accurately collect and analyze samples in a variety of ways, including from direct contact with the subject, non-contact sampling via vapors, and even through barriers.

To best grasp the role this innovative tech plays in securing the skies, one must first understand where and when they are used.

Understanding Alarm Resolution at Aviation Checkpoints

When an individual enters a Transportation Security Administration (TSA) checkpoint, they proceed through a primary screening phase. If something is detected and they (or their carry-on bags) trigger an alarm, the person is brought to a secondary screening area for additional examination.

Image from an x-ray scanner of two carry-on bags. The visible items inside the first bag that are highlighted appear to be small things like paper clips and zippers. Other items are mostly just see-through. The second bag appears to be a purse with multiple-colored objects inside.
Primary screening involves scanning of carry-on items. Photo credit: Jazzi/Pond5.

This phase is known as “Alarm Resolution” (AR), and it is where the officers manning the checkpoint begin an inquiry to determine what triggered the alarm.

According to Thoi Nguyen, S&T’s NextGen ETD Program Manager, “NextGen ETD concentrates on providing solutions for the AR phase of the checkpoint experience. The goal is to enhance our user’s capabilities to defeat emerging explosive threats.”

The innovations S&T develops (in collaboration with government, academia, industry, and international partners) include both advanced technologies and science-based methodologies. They are designed to quickly collect samples and then assess if an explosive is present. If explosives are detected, the solutions will also identify the specific type or types being analyzed.

Understanding ETD

Many airport security measures are easily recognized, like X-ray scanning equipment and detection canine teams, but a lot more happens behind the scenes to keep Americans safe when traveling. ETD, the ability to detect tiny or “trace” amounts of explosive residue or vapors, is an increasingly critical part of that safety effort.

Since inception, NextGen ETD has adapted its detection methods to address emerging security needs at airports, as well as at borders, marine ports-of-entry, and elsewhere. To fill those needs and combat concealed and homemade explosives threats, NextGen ETD has developed multiple advanced, but perhaps lesser-known, testing technologies.

Understanding Contact Sampling

During an AR, when Transportation Security Officers (TSOs) take someone to the secondary screening area, they are looking for tiny particles of explosive compounds that may have contaminated the individual or their belongings. This is where S&T’s new tech has been deployed.

“The NextGen Mass Spectrometry ETD addresses and meets the challenge of existing and emergent explosive trace detection,” said Nguyen. “The device has increased sensitivity and resolution that allows us to match explosives with a newly expanded library, that can be updated when novel explosives are identified.”

When an AR has been triggered at a checkpoint, a TSO takes a sample by wiping the individual’s hands, clothes, or belongings with a swab. The swabbed sample is then inserted into the NextGen Mass Spectrometry ETD. Once inside the 18-inch square cube, it is tested for explosive residue.

The mass spectrometer is a metal box about 18 inches square. It is on top of a desk or counter. Half of the front of the spectrometer is a computer screen facing us. There are other objects on the counter, like a computer mouse, rubber gloves, cleaning wipes, and an air spray can for cleaning surfaces.
Bruker prototype of a mass spectrometer. Photo credit: Courtesy of TSA Systems Integration Facility.

Currently, all deployed NextGen ETD contact sampling devices are based on ion mobility spectrometry (IMS). When the sample is placed in the instrument, it is vaporized and ionized (meaning that a positive or negative charge is added). Each type of molecule travels at a different speed when it is ionized. Inside the spectrometer is a special tube where precise measurements of the speeds of the molecules are taken. Clocking the exact speeds of the ionized particles (down to the millisecond!) reveals the type of molecules present.

When a molecule is verified to be traveling at a speed known to be that of an explosive, the TSOs can intervene.

Nguyen remarked upon S&T’s enduring commitment to RDT&E saying, “Bad actors are always trying to develop new explosives and better tactics to conceal them or otherwise evade detection. NextGen ETD is dedicated to staying at least one step ahead of them.”

Understanding Non-Contact Sampling

As good as the methods of contact sampling are, sometimes there just isn’t any residue on a surface to be sampled, or the situation does not allow for proper contact sampling. That is why S&T is working to improve existing (as well as develop new) non-contact sampling methods. This includes trace detection via vapor emissions, also known as Explosives Vapor Detection (EVD).

Historically, the gold standard for EVD has been explosive detection canine teams. A well-trained canine’s ability to sniff-out vapors emanating from explosives is quite effective.  However, even the best solutions have limitations. Some of the issues include the time-intensive specialized training needed for canine units to reach an elite skill level, and most importantly, there just aren’t enough of them to be at every airport or every security checkpoint.

Currently, NextGen ETD is conducting RDT&E of technologies that, like canines, can sniff out explosives. The process is known as vapor sampling, and it is a high priority for the TSA and other organizations.

Nguyen pointed out, “The future of ETD is non-contact sampling. The development of alternatives to current screening methods is something that both the public and TSOs have indicated they want. Our job is to develop solutions that balance the public’s need for speed during screening, with our security mission. Additionally, interest in non-contact screening processes has increased due to the COVID-19 pandemic, as concerns regarding physical proximity have become a public health issue.”

When S&T set its sights on making the next generation of EVD a reality, it knew the task would be complex. Mission success would include making the technology more accurate in identifying an even larger library of explosive types, while simultaneously reducing the time it takes to do it, thereby expediting the AR process at checkpoints.

With its partners, S&T is developing multiple types of non-contact particle vapor samplers. One of the prototypes is a handheld wand about the size of a universal TV remote controller. At the front end of the device is an air intake filter. To the left and right of the intake, are two small nozzles. When the wand is directed towards a person or object being examined, the two nozzles send out jets of air towards the subject. The jets of air collide with the subject and dislodge or “liberate” particles from the surface. As the air bounces off the subject it returns towards the device, like a wave bouncing off a wall, but this wave has the liberated particles in it. Simultaneously, the filter section turns on and sucks the returning air into the device, where any particles in the wave can be analyzed.

A cylindrical device is on a table next to a ballpoint pen (for size comparison). The device is about the size of a TV remote controller. At the end facing us, there is a circular cut-out area with an air intake filter where air and particles are sucked into the device. To the left and right of the filter are air blowers.
Non-contact vapor particle sampler prototype. Photo credit: Courtesy of University of Washington.

The particles that are sucked into the detector have been blasted with jets of air, so they are far more diluted than those that have been collected via direct contact sampling. This means that the sensitivity of the detector must be even greater because the concentrations of the explosive particles could be even lower— and that’s not the only challenge.

Nguyen put it eloquently saying, “Vapor detection is like smelling a bouquet of flowers. However, the challenge is akin to identifying the scents of each individual flower in that bouquet. You must separate the scent of each rose, each carnation, each lily, and so on. Our goal is to develop solutions that can differentiate between vapors from different explosives. This includes detecting vapors from both conventional explosives (like TNT), but also from homemade explosives, that are more unusual and exotic.”

Additionally, S&T is studying multiple aspects of vapor itself to better understand how technology can be used to identify, categorize, and counter each component of a threat. This analysis includes how vapors move through the air and how different explosive vapors permeate through materials, such as fabrics. S&T is also developing a relevant common testing methodology, as well as mass spectrometry-based vapor detectors.

These programs, conducted in collaboration with both academia and industry, are helping drive the next generation of EVD sampling and analysis tools, which will be brought to market by industry.

Nguyen reflected, “Vapor sampling has been talked about in the trace detection world for years, but the research and the technology just wasn’t there. Until now.”

A purposefully blurry vapor sampler is the in the background (Sampler & Detector). An in focus  is a hand, wearing a latex glove, holds a small brown vial/bottle (Vapor source) and  Distance (Source to detector).
Non-contact particle/vapor sampler prototype. Photo credit: Courtesy of Pacific Northwest National Laboratory.

Understanding Through Barrier Detection

Another strategy that adversaries might use to make explosives more difficult to detect is hiding them inside seemingly innocent, everyday items. These small bulk articles can be on an individual’s body, in their carry-on bags, or in their checked luggage. This means TSOs would need to detect explosives through barriers, for instance within a bottle of liquid.

When an alarm has been triggered at a checkpoint, years of scientific research spring into action. “To determine an unknown material’s composition, existing optical technologies use electromagnetic frequencies (e.g., infrared or radio frequencies) to interrogate and characterize the material. When an unknown material is inside a container, many of the existing techniques cannot penetrate through the container,” said Nguyen. “The next generation of through barrier detectors need to resolve an alarm on a suspicious item inside a container without opening it.”

The development of these advanced ETD technologies that can scan through barriers may sound like science fiction, but S&T is striving to make this science fact. Working with government and industrial labs, S&T is firing lasers at bottles to excite (or increase the energy level of) the contents inside the container. When the laser penetrates the outer surface of the bottle, it excites the contents, and they emit electromagnetic signatures. The device then collects the electromagnetic signatures and analyzes them to determine the composition of the bottle’s contents.

Nguyen added that, “Fine-tuning the new generation of through barrier detection technologies will ultimately make everyday travel more efficient and streamlined for both passengers and security officers. It will reduce the need for both the removal of goods from baggage, as well as direct-touch contact.”

Understanding the Future of ETD

NextGen ETD and S&T’s partners have already made significant advances in the identification and detection of explosive materials. Being able to differentiate benign substances from explosive material (even through barriers of different material types) is next-generation technology. The work in this field continues.  

In terms of how NextGen ETD will impact travel in the future, Nguyen said, “The vision is to get to a stage where passengers move through a checkpoint without stopping. They put their carry-on items on a conveyor belt and begin walking through a tunnel. Multiple types of non-intrusive, non-contact ETD screening are seamlessly done, automatically. If an AR is triggered, algorithms will assist with determining which type of additional testing should be performed, and it can be completed by the time the passenger finishes the tunnel. This will enhance the passenger experience while keeping everyone even safer.”  

Last Updated: 10/06/2022
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