Could Radar Be a More Cost-Effective Security Screening Alternative to X-Rays?

By: Damien Clarke
Lead Consultant

10th October 2019

5 minute read

Home » sensors

A key task in the security market is the detection of concealed threats, such as guns, knives and explosives. While explosives can be detected by their chemical constituents the other threats are defined by their shape. A threat detection system must, therefore, be able to produce an image of an object behind an opaque barrier.

X-rays are probably the most commonly known technology for achieving this and they are widely used for both security and medical applications. However, while they produce high-quality images, x-ray machines are not cheap and there are health concerns with their frequent use on or in the vicinity of people.

An alternative to x-rays often used at airports for full-body screening are microwave imaging systems. These allow the detection of concealed objects through clothes though the spatial resolution is relatively low and objects are often indistinguishable (hence the requirement for a manual search). The ability to detect and identify concealed items can, therefore, be improved by using a high-frequency mm-wave (60 GHz) system.

Plextek has investigated this approach through the use of a Texas Instruments IWR6843 60 – 64 GHz mm-wave radar which is a relatively inexpensive consumer component that could be customised to suit many applications. However, a single radar measurement only contains range information and not angle information. It is, therefore, necessary to collect multiple measurements of an object from different viewpoints to form an image. This is achieved through the use of a custom 2D translation stage that enables the radar to be automatically moved to any point in space relative to the target object. In this example, radar data was collected across a regular grid of 2D locations with millimetre spacing between measurements.

This large set of radar measurements can then be processed to form an image. This is achieved by analysing the small variations in the signal caused by the change in viewpoint when the object is measured from different positions. The set of range only measurements is then extended to include azimuth and elevation as well. In effect, this process produces a 3D cube of intensity values defining the radar reflectivity at each point in space. A slice through this cube at a range corresponding to the position of the box allows an image to be formed of an object that is behind an (optically) opaque surface.

In this case, a cardboard box containing a fake gun was used as the target object. Clearly, a visual inspection of this box would not reveal the contents, however, 60 GHz mm-waves can penetrate cardboard and therefore an image of the concealed object can be produced. In this case, the resulting image of the contents of the box clearly shows the shape of the concealed gun.

This example simulates the detection of a gun being sent through the post and automatic image analysis algorithms would presumably be capable of flagging this box for further inspection. This would remove the need for human involvement in the screening process for each parcel.

A more mature sensor system using this approach could be produced that did not require the manual scanning process but used an array of antenna instead. It would also be possible to produce similar custom systems that were optimised for different target sets and applications.

 

Acknowledgement

This work was performed by Ivan Saunders during his time as a Summer student at Plextek before completing his MPhys at the University of Exeter.

A key task in the security market is the detection of concealed threats, such as guns, knives and explosives. While explosives can be detected by their chemical constituents the other threats are defined by their shape. A threat detection system must, therefore, be able to produce an image of an object behind an opaque barrier.

X-rays are probably the most commonly known technology for achieving this and they are widely used for both security and medical applications. However, while they produce high-quality images, x-ray machines are not cheap and there are health concerns with their frequent use on or in the vicinity of people.

An alternative to x-rays often used at airports for full-body screening are microwave imaging systems. These allow the detection of concealed objects through clothes though the spatial resolution is relatively low and objects are often indistinguishable (hence the requirement for a manual search). The ability to detect and identify concealed items can, therefore, be improved by using a high-frequency mm-wave (60 GHz) system.

Plextek has investigated this approach through the use of a Texas Instruments IWR6843 60 – 64 GHz mm-wave radar which is a relatively inexpensive consumer component that could be customised to suit many applications. However, a single radar measurement only contains range information and not angle information. It is, therefore, necessary to collect multiple measurements of an object from different viewpoints to form an image. This is achieved through the use of a custom 2D translation stage that enables the radar to be automatically moved to any point in space relative to the target object. In this example, radar data was collected across a regular grid of 2D locations with millimetre spacing between measurements.

This large set of radar measurements can then be processed to form an image. This is achieved by analysing the small variations in the signal caused by the change in viewpoint when the object is measured from different positions. The set of range only measurements is then extended to include azimuth and elevation as well. In effect, this process produces a 3D cube of intensity values defining the radar reflectivity at each point in space. A slice through this cube at a range corresponding to the position of the box allows an image to be formed of an object that is behind an (optically) opaque surface.

In this case, a cardboard box containing a fake gun was used as the target object. Clearly, a visual inspection of this box would not reveal the contents, however, 60 GHz mm-waves can penetrate cardboard and therefore an image of the concealed object can be produced. In this case, the resulting image of the contents of the box clearly shows the shape of the concealed gun.

This example simulates the detection of a gun being sent through the post and automatic image analysis algorithms would presumably be capable of flagging this box for further inspection. This would remove the need for human involvement in the screening process for each parcel.

A more mature sensor system using this approach could be produced that did not require the manual scanning process but used an array of antenna instead. It would also be possible to produce similar custom systems that were optimised for different target sets and applications.

Acknowledgement

This work was performed by Ivan Saunders during his time as a Summer student at Plextek before completing his MPhys at the University of Exeter.

Further Reading

Being Your User

Nicholas Hill - Chief Executive Officer

By: Nicholas Hill
Chief Executive Officer

19th December 2018

Home » sensors

One of the important steps in the Design Council’s recommendations for good design is called “Being Your Users” and is a “Method to put yourself into the position of your user.” Its purpose is “building an understanding of and empathy with the users of your product …” Approaching product design from this perspective is critical to ensuring that the features incorporated are actually beneficial to the user – as opposed to features that are of benefit to the manufacturer, for example, or “because we can” features that have no obvious benefit at all.

It’s clear that domestic appliances are becoming more sophisticated, a trend which is facilitated by the availability of low-cost sensors and processing power. This has some clear benefits, such as the availability of more energy- or water-efficient wash cycles for example. And if designers stay focused on providing something of value to the end user this is a trend to be welcomed.

In practice, I see examples of what looks rather like engineers wondering what else they can do with all this additional sensor data, rather than being driven by user need. One example is the growing size of the error codes table in the back of most appliance manuals. These may occasionally add value, but for the most part, I see them as reasons why the product you paid good money for is refusing to do the job it is supposed to.

Here’s an example: the “smart” washing machine that I own doesn’t like low water pressure. It has a number of error codes associated with this. What does it do if the mains pressure drops temporarily – e.g. if simultaneously a toilet is flushed and the kitchen tap is running? It stops dead, displays the error code and refuses to do anything else until you power off the machine at the wall socket, forcing you to start the wash cycle again from scratch. This gets even more annoying if you’d set the timer and come back to a half-washed load. In the days before “smart” appliances, a temporary pressure drop would have either simply caused the water to fill more slowly, or else the machine would pause until pressure returned.

In what way does this behaviour benefit the user? Clearly, it doesn’t, and a few moments thought from a design team that was focussed on user needs, “being your user”, would have resulted in a different requirement specification being handed to the engineering team. It’s a good example of what happens when you start implementing a solution without properly considering the problem you are trying to solve.

My “intelligent” dishwasher has a different but equally maddening feature: it doesn’t like soft water. Its designers have clearly put water saving above all else, and the machine relies on either hard water or very dirty plates to counteract the natural foaming of the detergent tablets. With soft water, if you try washing lightly soiled dishes on a quick wash cycle (as you might expect appropriate), the machine is unable to rinse off the detergent. About 20 minutes into the cycle it skips to the end and gives up, leaving you with foamy, unrinsed plates.

I say unable, when the machine is actually unwilling, as all that is required is the application of sufficient water to rinse off the detergent – which is what I, as a user, then have to do manually. Who is working for whom here? Once again the user’s needs have not been at the top of the designer’s agenda when the requirement specification was passed to the engineering team. A truly smart device would finish the job properly, using as much water as was needed, and possibly suggest using less detergent next time.

Unless designers get a better grip, keeping the end user experience on the agenda, I fear examples of this type of machine behaviour will proliferate. We will see our devices, appliances and perhaps vehicles develop an increasingly long list of reasons why they can’t (won’t) perform the function you bought them for – because they’re having a bad hair day today, which becomes your problem to solve.

All to a refrain of “I’m sorry Dave, I’m afraid I can’t do that.”

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One of the important steps in the Design Council’s recommendations for good design is called “Being Your Users” and is a “Method to put yourself into the position of your user.” Its purpose is “building an understanding of and empathy with the users of your product …” Approaching product design from this perspective is critical to ensuring that the features incorporated are actually beneficial to the user – as opposed to features that are of benefit to the manufacturer, for example, or “because we can” features that have no obvious benefit at all.

It’s clear that domestic appliances are becoming more sophisticated, a trend which is facilitated by the availability of low-cost sensors and processing power. This has some clear benefits, such as the availability of more energy- or water-efficient wash cycles for example. And if designers stay focused on providing something of value to the end user this is a trend to be welcomed.

In practice, I see examples of what looks rather like engineers wondering what else they can do with all this additional sensor data, rather than being driven by user need. One example is the growing size of the error codes table in the back of most appliance manuals. These may occasionally add value, but for the most part, I see them as reasons why the product you paid good money for is refusing to do the job it is supposed to.

Here’s an example: the “smart” washing machine that I own doesn’t like low water pressure. It has a number of error codes associated with this. What does it do if the mains pressure drops temporarily – e.g. if simultaneously a toilet is flushed and the kitchen tap is running? It stops dead, displays the error code and refuses to do anything else until you power off the machine at the wall socket, forcing you to start the wash cycle again from scratch. This gets even more annoying if you’d set the timer and come back to a half-washed load. In the days before “smart” appliances, a temporary pressure drop would have either simply caused the water to fill more slowly, or else the machine would pause until pressure returned.

In what way does this behaviour benefit the user? Clearly, it doesn’t, and a few moments thought from a design team that was focussed on user needs, “being your user”, would have resulted in a different requirement specification being handed to the engineering team. It’s a good example of what happens when you start implementing a solution without properly considering the problem you are trying to solve.

My “intelligent” dishwasher has a different but equally maddening feature: it doesn’t like soft water. Its designers have clearly put water saving above all else, and the machine relies on either hard water or very dirty plates to counteract the natural foaming of the detergent tablets. With soft water, if you try washing lightly soiled dishes on a quick wash cycle (as you might expect appropriate), the machine is unable to rinse off the detergent. About 20 minutes into the cycle it skips to the end and gives up, leaving you with foamy, unrinsed plates.

I say unable, when the machine is actually unwilling, as all that is required is the application of sufficient water to rinse off the detergent – which is what I, as a user, then have to do manually. Who is working for whom here? Once again the user’s needs have not been at the top of the designer’s agenda when the requirement specification was passed to the engineering team. A truly smart device would finish the job properly, using as much water as was needed, and possibly suggest using less detergent next time.

Unless designers get a better grip, keeping the end user experience on the agenda, I fear examples of this type of machine behaviour will proliferate. We will see our devices, appliances and perhaps vehicles develop an increasingly long list of reasons why they can’t (won’t) perform the function you bought them for – because they’re having a bad hair day today, which becomes your problem to solve.

All to a refrain of “I’m sorry Dave, I’m afraid I can’t do that.”

Save

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Further Reading

Department for Transport Awards Plextek Funding for Vehicle Tagging Solution

Cambridge, UK – 8th August 2018 – Design and innovation consultancy, Plextek have been awarded funding by the Department for Transport (DfT) for development of a novel vehicle tagging solution for intelligent and autonomous vehicle systems.

Funded by DfT’s Transport Technology Research Innovation Grants (T-TRIG), Plextek have set out to develop a proof of concept demonstrator for a small, low-cost and ultra-low-power tag that bounces back automotive radar signals with a unique coded signature.

When this signature is detected it allows automotive radars to uniquely identify and locate objects – addressing a current challenge within the automotive sensor industry.

Chris Roff, Head of Sensor Systems, summarises the benefits:

In the future, these tags could be attached to vehicles (e.g. built into the number plate) or to roadside objects such as road signs. A unique aspect of our solution is that the tag’s power requirement is kept extremely low, which opens up a really broad range of use cases.

The tags could also allow vehicles to operate autonomously in complex environments with a higher level of confidence, in keeping with DfT’s aims for providing safe, secure and sustainable transport.”

This breakthrough in tagging technology extends the capability of standard automotive radars to allow them to uniquely identify a wide range of objects in their environment.

Information received by the radar can then be used for a number of applications including recognition of road signage and other infrastructure, identification of other road vehicles and supporting autonomous convoy operation. The technology could also be used in other transport domains, including the identification of drones and small aircraft, and the monitoring of small craft at sea in poor weather conditions.

Agnieszka Krysztul, Project Manager, concludes:

Our low-cost proof of concept embodiment has demonstrated technical feasibility and also given us a route for commercialisation in the automotive sector, where product cost will be paramount. We’re excited to be looking into these routes now so that we can share this capability within the industry.”

For more information about our work in industrial sensors, please visit our industrial sensors page.

Notes to editors

Based near Cambridge, UK, Plextek designs new products, systems, and services for its clients in a diverse range of industries including defence & security, medical & healthcare, and wireless communications.

Central to its culture is the company’s ability to innovate, taking an idea from concept to market. For more than 25 years the team of consultants, engineers and project managers has turned our clients’ business opportunities into commercial success, designing, manufacturing and supplying leading-edge products. Supported by our network of suppliers, commercial partners and research organisations, Plextek is the trusted partner of choice for more than 300 commercial clients, government agencies, and ambitious start-up companies.

For images, information or interview requests, please contact: Adam Roberts via email: press@plextek.com or call: 01799 533200