5 minute read
Surveilling aging infrastructure using fi ber-optics
Somni Solutions, a small startup from The Hague, provided fiber-optic tilt sensors for the new Genoa bridge, which recently reopened, two years after the tragic collapse. CTO Remco Nieuwland explains how his company acquired this prestigious assignment and why we should start monitoring our own aging infrastructure.
Advertisement
Jessica Vermeer
On 14 August 2018, the Morandi bridge near the Italian city of Genoa collapsed during a rainstorm. When it was opened in 1967, the number of vehicles and their average weight was much lower than it is today. Bridges were typically designed for a 50-year lifespan. The Morandi bridge failed just under 51 years after its opening.
After the collapse, the leftovers were demolished and a new bridge was built. The construction of the replacement was completed in April of this year. Somni Solutions, a small startup from The Hague, provided glass fiber sensors that will monitor the misalignment of the pillars. These sensors will give much-needed insight into the condition of the new bridge.
“Monitoring with glass fiber sensors is pretty standard in China and Japan,” says Remco Nieuwland, CTO of Somni. “But in Europe, we’re lagging.” He has seen some pilot projects but no permanent setups for bridge monitoring. “In Europe, we seem to need an actual disaster before we’re willing to prevent further damage.”
When Somni started initial discussions with the customer, the sensor design wasn’t yet finished. Acquisition of the assignment took about a year and the startup spent that time sketching, developing and gaining the customer’s trust. After one year of hard work, the long-awaited purchase order finally fell in favor of Somni. Nieuwland: “It hasn’t been easy, but we were highly motivated to get this assignment and show the world our capabilities.”
Credit: Somni
The two sensors within each set are placed at a 90-degree angle.
Credit: Pergenova
The new Genoa bridge has eighteen pillars upon which the road surface lies. Each pillar has four tilt sensors, two up top and two at the bottom.
Fiber Bragg grating
Somni Solutions was founded in late 2017 by Nieuwland and Jac Gofers. Both recognized the enormous potential of fiber-optic sensors for Europe’s aging infrastructure. With a team of highly skilled professionals, they shaped Somni, a startup that designs, develops and manufactures fiber-optic sensors that monitor the structural integrity of large assets. The company name expresses the goal to solve sensor problems everywhere – the “s” standing for “sensors” and “omni” being Latin for “everywhere.”
Somni uses standard telecommunication glass fiber for its sensors. “But we modify them,” explains Nieuwland. “Using lithography, we write a pattern on the inner fiber core over a few millimeters length.” He compares the pattern to a bar code. “When we slightly compress or stretch the fiber, the reflected light will have a slightly different color.”
The microstructure Somni applies is called a fiber Bragg grating (FBG). It allows for the reflection of a specific wavelength depending on the periodicity of the grating. “We built a mechanism around the FBG – a transducer – that converts the parameter we want to measure into stretch or compression of the fiber.” For the Genoa bridge, that parameter is the tilt of the pillars. The stretch or compression is measured from the wavelength shift that results from the grating.
In total, Somni has delivered 72 sensors to Genoa. The new bridge has eighteen pillars upon which the road surface lies. Each pillar has four tilt sensors, two up top and two at the bottom. The two sensors within each set are placed at a 90-degree angle.
Somni writes several FBG patterns in the glass fiber, all with a slightly different periodicity. Every grating reflects a slightly different color. “That means we can accommodate several sensors using one glass fiber cable, without the need for a return cable,” points Nieuwland out. “Depending on the spectral bandwidth of the light source and the dynamic range needed for one sensor, up to a hundred sensors can be built using just one cable.”
“The best thing about these sensors is that they don’t work on electricity as many conventional sensors do,” says Nieuwland. “They work solely based on light.” Conventional electric sensors need at least two electric wires to read the information from one sensor. If such sensors are used to monitor a bridge, the data needs to be transported over a kilometer distance. “That’s quite complicated. Usually, the analog signal is converted into a digital signal, which requires a bunch of extra electrical components inside the sensor. And every component has a risk of failure. If one component fails, the entire sensor fails.”
Photonic sensors are simpler. They have several advantages, such as low maintenance and high reliability. Also, glass fiber is completely insensitive to electromagnetic radiation. Nieuwland: “It could even be used in an MRI scanner. And the data quality over long distances is excellent.”
An added advantage – the light is sent into and reflected by the same cable. “That means we have built-in redundancy,” explains Nieuwland. “All we need to do is lay down a return cable. If the cable breaks somewhere, we can read the sensors from the other side.”
Merwedebrug
Soon after the Genoa sensors were successfully delivered, Somni received a new challenge. ITER, the nuclear fusion reactor in France, asked to supply sensors. This high-profile project required sensors that are robust and reliable, compatible with vacuum conditions and resistant to neutrons and gamma radiation. In addition, they need to operate at temperatures above 300 °C. The Somni team has taken up this challenge and is currently in the development phase. Installation is slated for the first months of 2021.
Nieuwland hopes the success of the Genoa project will open up new possibilities. In the future, Somni aspires to collaborate with Rijkswaterstaat to monitor roads and bridges in the Netherlands, to prevent cases like the Merwedebrug near Gorinchem, which was closed for heavy freight traffic in October 2016 after measurements by TNO revealed hairline cracks in the construction. “Trucks are becoming heavier and no one really knows which arteries are worn out,” says Nieuwland. “If we monitor our infrastructure properly, we won’t be forced to close down an important thoroughfare like the Merwedebrug ever again.”
