Fibre-sensor specialist breaks the price barrier

30 Jan 2004

A UK start-up has a cunning plan to make fibre-optic sensors a commodity item that sell in their thousands. Oliver Graydon visited Insensys in Southampton to find out more.

From Opto & Laser Europe February 2004

Last month was undoubtedly a milestone for the UK start-up Insensys. Just 18 months after it was founded the developer of fibre-optic strain and temperature sensors has begun to manufacture commercial products.

"The first units are rolling off the production line and we have orders for 70 systems in the first quarter of 2004," Martin Jones, its CEO, told Opto & Laser Europe just before we went to press.

The first batch of sensors will be used to monitor the strain in wind-turbine blades, measure temperature profiles in oil wells and monitor the stress in composite structures in the marine and aerospace industries.

The news is the first step towards Insensys's dream of becoming a volume supplier of low-cost fibre Bragg grating (FBG) sensor systems. "We envisage being able to get into serious volumes and aim to make hundreds of units this year and thousands in 2005," explained Jones. "At the moment, we've got clients that we're quoting for anything from 50 to 300 systems."

The Southampton-based firm, with a workforce of 18, will soon move into larger premises in the area and plans to open an overseas office before long.

According to Jones, the key to the company's success in winning orders is that it has managed to hammer down the price of its products. Conversations with potential customers convinced him that to be successful, Insensys would have to sell a complete fibre-optic sensing system for around €5000 - which many in the optoelectronics industry would say was impossible.

"It's the price-point that's the key; in this market you've got to be really aggressive," Jones said. "We're not quite there [€5000] yet but we're not far away, and that's what's made these orders possible."

Cutting costs So just how has Insensys managed to make such a cost-effective system? The first reason is a new kind of FBG sensor system, one much cheaper and simpler than conventional designs which rely on wavelength-division multiplexing (WDM).

In a traditional WDM sensing system, each grating is written at a specific but distinct wavelength and interrogated using a tunable laser or tunable filter. The wavelength shift in the reflection from each grating reveals the strain that it is under. While this technique is well-proven it has disadvantages, namely the cost of a wavelength-swept optical source and the complexity of writing all the gratings at a different wavelength.

As the number of sensors increases, so does the technique's cost and complexity. This is not ideal where tens or hundreds of measurement points are required.

Insensys decided that it was impossible to make this kind of system at a price that was attractive to its customer base, so it started searching for an alternative. The solution came from Indigo Photonics, a spin-off from Aston University in the UK which specializes in FBGs. Its scientists had a brainwave and came up with a revolutionary sensor design that relies on time-division multiplexing (TDM) rather than WDM.

Put simply, in the Indigo design all the FBGs are written (and interrogated) at the same wavelength but are read out at different time slots. As a result there's no need for a tunable laser and a single mask can be used to write all the gratings, which have a reflectivity of around 4%.

"Essentially, we approached Indigo and said what we wanted was a system where we could interrogate up to 100 sensors in a fibre with each measuring up to ±6000 microstrain - and the architecture couldn't be WDM," explained Jones. "We also said that it had to be a solid-state solution with no moving parts, and consume less than 3 W at 12 V - so that it could be powered by solar panels or batteries. They delivered and came back to us with the TDM design."

In fact, Insensys liked the Indigo design so much that it purchased the company in July 2003. Indigo's photonics know-how seemed to be a perfect fit with Insensys's experience of working with composite structures.

The second key to reaching a low price-point was Insensys's decision to outsource its manufacturing - a strategy that many start-ups would be wise to follow. All too often, fledgling ventures try to do everything in-house and end up floundering where they have no expertise or experience. Insensys was determined not to make this mistake.

"All the manufacturing is outsourced as we have to be cost-effective and able to scale quickly. Insensys provides the innovation and the applications expertise," said Jones. "We're having the [printed circuit] boards manufactured by Foundation Technology and the optics assembled by Sifam."

By making systems that break through the price barrier associated with optics, Insensys plans to get ahead of its competitors and change the perception that FBGs are an expensive, impractical technology.

"My honest feeling is that the sensing area frustrates a lot of people. They can come up with a great optical idea, but the distance between the idea and using it commercially is one that many companies are not capable of bridging," commented Jones. "On one side you've got specialists in optoelectronics saying 'This is a great technology - try it', and on the other you've got people saying 'You could never deploy this - it breaks and costs far too much'. I see our job as bridging that gap."

An array of applications As for markets, Insensys is not short of applications for its TDM-based sensor systems. One area which is proving fruitful is the wind-turbine business, as engineers wish to monitor the stress being placed on the composite turbine blades which are several tens of metres in length.

"If you can measure the stress on the blade very accurately then you can feed that back into the blade computer, adjust the blade angles and improve efficiency," Jones told Opto & Laser Europe. "That's a huge commercial driver for installing these systems."

Insensys's sensors are well-suited to this kind of application for several reasons. Firstly, they have been engineered to be deployed inside the composite material of the blades during manufacture. Secondly, since they are made of glass they are immune to electrical effects caused by lightning strikes or the generation of electricity at the hub of the turbine. Thirdly, the interrogator is compact, less than half the size of a laptop computer, and can be powered by a battery.

"Fibre-optic technology lends itself extremely well to wind turbines, as you've got a composite environment with high electric fields and serious risk of a lightning strike," said Jones. "A turbine typically needs 10-20 sensors, each with a wide strain range, and the customers require compact instrumentation with a 20 year life and minimal power consumption."

Two other markets which are a close fit with Insensys are the marine and aerospace industries. The firm fitted out Kingfisher2, the yacht of record-breaking sailor Ellen McArthur, with FBG sensors for monitoring stresses in the mast. A total of 12 FBG sensors were used. Arrays of four sensors were epoxyed to the inside of the mast at three heights in order to gain information about the mast's operating conditions.

Although the yacht broke in February 2003 during its attempt to beat the non-stop round-the-world sailing record, the data from the sensor were invaluable. Insensys is now collaborating with the Kingfisher team on their new carbon-fibre trimaran which launched last month.

Insensys is now working hard on another large marine project, to oversee the construction of sensor-equipped masts in the world's largest private yacht. When the yacht is complete in about 18 months' time it will feature three giant 60 m carbon-fibre masts that contain fibre sensors to measure the driving force of the rigs.

And that's not the only world first that Insensys is involved in. It's also part of a project to produce the first fully sensed composite aircraft, although details are being kept under wraps at the moment. Keep reading Opto & Laser Europe to find out more later in the year.

The most recent study involves putting FBG sensors into the hull of a lifeboat to measure slamming loads. The aim is to obtain some real data on the conditions that the boat has to cope with to aid designers. Although it's early days, Jones says that trials just before Christmas generated some excellent data. The sensors were so sensitive that they could even measure the pressure of the surrounding water as the lifeboat was lowered into the sea.

He is now looking forward to what 2004 brings and is optimistic about the development of the market.

"Ultimately, I think that fibre sensors will become a commodity, and that people will view a piece of fibre with an FBG as equivalent to a conventional strain gauge," explained Jones.

"The sensor companies that strive for volume will strike price-points that make it very difficult for others to compete. Insensys is well on track to be one of these players."