Digital remote passenger scanning

Nuria Llombart is working on innovative airport security techniques. In the future, you will be remotely scanned for concealed objects before you even reach the traditional scanner.

How do you scan people from so far away?

‘It is similar to how body scanners at Schiphol work today, only from a greater distance. You might compare it to how a radar works: an antenna is used to focus radio waves onto a passenger. These waves pass through clothing, but are reflected by the body. By capturing the reflected waves, you can build an image of the body and of any objects concealed under clothing on the body. Incidentally, the radiation is not harmful – that is a question I get asked a lot.’ 

What sort of things can you see, and are you also taking passenger's privacy into consideration?

‘You see reflections of various layers of clothing, with the body underneath. In fact, only looking at the reflected waves is not enough. The system actually measures the time it takes for the signals to return to the antenna. This enables you to build a three-dimensional image. Once you have that, you can use an algorithm to try and identify objects that are not part of the body.
Looking through people’s clothing naturally raises privacy issues. The same discussion arose when body scanners were introduced at Schiphol. In order to address these concerns, the system cannot show actual images to security guards. The system needs to interpret the images independently and raise the alarm if a suspect object is detected. This can be challenging at times. In that sense, body scanners at Schiphol are certainly not perfect.’

Does the reflected signal also offer information about the type of material?

‘In theory, it is possible to identify materials based on the reflected signals. This reflection is dependent on both the shape and electrical properties of the materials. With a flat surface, which has a predictable reflection, it is relatively easy to determine these material properties. However, scans at airports never involve a perfectly flat surface. The objects that you scan are unpredictable and erratic. Which also results in an erratic signal, from which it is not possible to infer material properties.
We are now exploring whether we can develop a system that uses higher-frequency radiation and a large bandwidth to determine both the shape and material properties of an object. The strategy is to first determine the shape of an object in order to predict how the object scatters the radio waves. By eliminating this aspect from the reflection, you can identify the material properties.’

Will existing passenger security checks be replaced by a remote system?

‘Probably not. Before allowing passengers to board an aircraft, you want to be absolutely certain that they have been fully checked. You therefore want to conduct the best possible scans. There is too great a risk of missing something when you scan a moving person. But I do think that this system offers added value, as it enables you to conduct random checks in the airport lobby. And you might also consider street checks in conflict areas, where there is an increased risk of terrorist attacks.’

How long will it be before a system like this is on the market?

‘We are going to test the system at an airport next year, but it may still take years before something like this actually hits the market. Incidentally, how long this takes is out of researchers’ hands. We are only at the very start of the process, and development into an actual product is always dependent on a company willing to invest. If that happens, it can be on the market within a few years. The security market is not a very large market, and developments here are not as rapid as in the smartphone industry, for example.’  

Your work is not focused solely on security systems?

‘No, the development of new antenna systems is actually the main theme of my research. These may be antennas for security systems, but also for wireless communications or for radio telescopes that listen to background radiation in space. Space technology has always played a significant role in my research.’

How did you end up in this field of research?

‘I was good at mathematics and physics, so I decided to study electrical engineering in Valencia. I did not yet know what I wanted to be, but I knew that the degree programme would in any case offer me a decent chance of getting a job. From my PhD at TNO in The Hague onwards, I have worked with antennas a lot. I like the fact that it involves plenty of physics - you are not only designing electronics.’

I cannot see many women here?

‘You’re absolutely right, there are indeed few women working in this department. I sometimes give a lecture to a room of nearly 100 students, with perhaps only a single girl amongst them. I would like to see this change, but you cannot force people. I have a young daughter, and I would like her to have the freedom to choose her own path. If she turns out to be good at physics, she should certainly enter this field! Perhaps it helps that her father is also a physician. Physics are a frequently discussed theme at the dinner table.’

Processing and keeping the rapidly rising numbers of passengers at Amsterdam Airport Schiphol safe is a tall order, and things do not always run smoothly. In recent months, the airport (which handled 63.6 million passengers in 2016) hit the news multiple times due to overcrowding. In the most extreme cases, passengers missed their flights as they were unable to reach their departure gate on time. One of the bottlenecks is at the security checks, through which every passenger needs to pass.
Security guards and military police responsible for security at the airport may soon receive assistance from researchers at TU Delft. Nuria Llombart, Associate Professor in the Terahertz Sensing group at the Center for Wireless Systems and Technology, looks at ways of quickly screening passengers for objects concealed under their clothing. Next year, Llombart and her European colleagues will test a system at Helsinki Airport that can digitally scan passengers from distances of up to two metres. ‘This will allow security guards to carry out checks in the airport lobby, without passengers having to stand in a scanner,’ explains Llombart.

Nuria Llombart


'It enables you to conduct random checks in the airport lobby'

Text: Roel van der Heijden | Photo: Mark Prins | March 2017