Making sensors more sensitive with the touch of a cold finger (Under the Radar #13)

The lower the temperature, the less thermal noise and the better a sensor will be able to pick up even the tiniest signal. At Thales, Roel Arts is involved in developing cryogenic technology to cool things down, typically to around 200 degrees below zero.

Suddenly, Roel Arts leans over and pulls out a plaque. It’s from the National Aeronautics and Space Administration, awarding an exceptional achievement in innovating cryocooler technology. “Three of our coolers have been operating aboard the International Space Station for 3.5 years now. NASA’s Jet Propulsion Laboratory has set up an experiment there to monitor the surface temperature of Earth using infrared radiation. To reduce the noise, the instrument is chilled with our cryocoolers, which we supplied in record time, at an extremely competitive price. They were so impressed by this achievement that they gave us two awards: one for the company and one for me – I’m the only one in my circle of friends with a medal from NASA,” he says understatedly.

Arts works at Thales' Cryogenics department, in Eindhoven. “Like many companies in this area, we also have our roots in Philips,” he explains. “At the beginning of the 1980s, its Ultrasone Factory, USFA, decided to move into infrared cameras. They soon realized that infrared sensors would only function properly when cooled to about -200 degrees Celsius. To avoid having to mess around with liquid nitrogen, they started developing cryogenic coolers. This is now the core business of Thales Cryogenics.”

The career path followed by Arts exhibits notable parallels. In 2008, shortly after obtaining a master’s degree in applied physics from the University of Twente, he joined Thales Huizen as a system engineer, working on infrared cameras. “I was a customer of Cryogenics, using their products to cool mine,” he recalls. Having two more sites developing cooled IR cameras, however, Thales decided to consolidate these activities in 2012. As Arts saw the door close in Huizen, another one opened in Eindhoven. “While giving me notice, my manager also pointed me to a job opening at Cryogenics. They were looking for a techie who also had a feeling for customers. Who better to hire than a techie who used to be a customer?”

Gamma rays

In Eindhoven, Arts went from application engineering to project management to product line management, becoming responsible for the product policy of the so-called linear cryocoolers in 2018. Essentially, these devices are made up of two 10-20 cm long tubes – a compressor and a cold finger – connected by a thin conduit. In the compressor tube, helium gas alternately gets compressed and decompressed by two counter-moving pistons. This creates a pulse through the conduit, to the base of the cold finger, to the tip, and all the way back again. In the decompression phase, the expanding gas transfers heat from the fingertip to the base, where it dissipates through a heat exchanger – thus lowering the temperature at the tip. The coolers developed by Arts and his colleagues are called “linear” because the pistons move linearly toward and away from each other, as opposed to the rotary models built by Thales Cryogenics in France.

The temperature delta the coolers can achieve is adjustable but generally set close to -200 degrees. The super-cold finger is typically used to cool infrared sensors. “They take up a big chunk of the market,” acknowledges Arts. “Because IR photons have less energy and there are fewer of them, such sensors need to be a lot more sensitive than normal cameras. But that also makes them more sensitive to thermal noise. Regular CCD cameras suffer from a similar problem when you want to shoot a picture and there’s not much visible light, for example in astronomy. Extensive cooling gets rid of the thermal noise, thereby boosting image quality.”

Another important application is gamma spectroscopy, ie mapping out the energy spectra of gamma-ray sources. “You can identify a radioactive material based on its gamma signature, but again, you need a very sensitive detector to do that accurately. Here, too, cooling is key,” notes Arts. Gamma spectroscopy is used in the nuclear industry, geochemical investigation and astrophysics, for example. “And in airports and harbors, you have these gates that use super-cooled gamma detectors to scan passing cargo for hazardous materials.”

Long lifespan

“Generalizing, I’d say our cryocoolers are being used in one of three ways: for infrared instruments in space, IR sensors for military and industrial use, and civilian gamma detectors,” summarizes Arts. “Our solutions aren’t all that different across these three domains, but the reasons for choosing us are. Our civilian customers like our coolers for their long lifespan and low vibration figure. Our military customers value the long lifespan, robustness and ease of integration. Our space customers mostly appreciate our long lifespan and pricing – for them, we’re a real low-cost supplier, without compromising on quality.”

According to Arts, the long lifespan, low vibration figure and robustness can all largely be traced back to two things: the low number of moving parts, and the smart way in which these were designed. “Thanks to our flexure bearing technology, the pistons move almost frictionless in the compressor tube. This minimizes vibrations and reduces wear and tear, thus prolonging product life. And by using pulse tube technology to convert the pressure waves in the helium into cooling power, we can eliminate the need for moving parts in that part of the cooler, essentially making it wear free and giving it a nearly infinite lifespan.”

Arts and his colleagues are working hard to further improve the cryocoolers. “Sensor makers are looking at raising the operating temperature of their products, which also impacts our efforts. If we only have to go down to -130 or -120 degrees, instead of -200 degrees, we can make our coolers more energy efficient and we can make them smaller because they don’t have to work so hard. Sizing down also helps us lower the cost even further. This, in turn, will strengthen our position in what I expect will be one of our most important growth markets – space.”

Wide variety

As a product line manager, Arts sees it as his job to be the voice of the market within the company and the voice of the company within the market. “On the one hand, I have a strategic role, making product plans, explaining them, getting buy-in for them and then executing them. On the other hand, I’m providing technical assistance to our sales department, helping them find out what customers need and matching this to an existing product or new development. Next to all this, I’m lending a hand in project management and systems engineering.”

The diversity is what Arts likes most about working at Thales. Not only the broad mix of responsibilities but also the wide variety of customers. “Space, defense, medical, scientific – I get to see a lot of different tech companies from the inside and support their engineers with our products to solve their cooling challenges. That’s truly energizing.”

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