The juggling act of making compact and mobile sensors

Non-contact measurements being made on clipfish. The measurement point (green) is surrounded by an illumination ring. Photos/cc: Jon Tschudi, SINTEF

SINTEF and Nofima want to make instruments that are smaller and mobile so that they address new ways of sorting of food, earlier in the value chain, before reaching the factory floor. This can play a part in the bigger goal of DigiFoods, to reduce waste, increase quality and increase margins.

SINTEF and Nofima have spent many years developing and commercializing inline instruments that measure the quality of food moving on conveyor belts. In the MobileSense project, they are taking a different approach, and addressing applications where you need to move the sensor to the food product and make it handheld or robot mounted. This requires a much smaller sensor that needs to handle a more unpredictable measurement environment.

One application being explored in MobileSense, is the use of sensors for robotic harvesting of strawberries. Based on the percentage of red over the surface, the sensor chooses which berries to pick. If the sensor can also probe deep into the strawberry, without contact, and measure the sugar content and sweetness of the strawberry, this could help optimize sorting earlier in the value chain, which can reduce waste – today strawberries that would perfectly suitable for jam are wasted at a later stage due to unsatisfactory color or sweetness.

“This kind of sensor technology could be used in a variety of potential applications in the food, agriculture and bio-industries. There are still industries where people use basic manual methods to determine quality and where conveyor sorting systems are not viable, for example, determining meat content in king crabs or water content in clipfish. In these cases, someone must squeeze or bend the product to literally get a feel for the quality, since it is not obvious from looking at the surface,” Research Manager and pillar leader Marion O’Farrell at SINTEF says.

“By making it possible to measure inside the product, we will not only contribute to reducing food waste and increasing quality, it can also take the subjectivity out of how products are graded for pricing, and this can make trading and negotiations run more smoothly,” she continues.

Industries like king crab and clip fish are surprisingly large and international markets. Norwegian exports of clipfish in 2021 were 91,100 tons, with export value of NOK 4.5 billion. Norwegian export of king crab in 2021 was 2,300 tons, with an export value of NOK 999 million.[1] To put this in the context of well known, large markets; the total salmon and cod exports for the same year were NOK 81.4 billion and NOK 9.8 billion, respectively.

Reduce the size, not the performance.

As part of Mobilesense, the goal is to squeeze the high performance of the existing instrument, SmartSensor, into a much more compact form factor, Mini SmartSensor. The original Smart Sensor was novel because it could measure non-contact, sub-surface quality measurements of complex foods. However, to make it mobile, size suddenly moves up on the critical design parameter list, and a new design is required.

“SINTEF’s role is to compress the size as much as we can, while not compromising too much on performance. In many applications we don’t have the luxury of reducing to pocket-sized devices at the cost of performance,” O’Farrell says.

“In the field of photonics, there is a big push to reduce the size of spectrometers – smaller, smaller; micro, nano – and while this has its place when simpler surface measurements suffice, it becomes a greater challenge if you want to measure deeper into the product,” Senior Research Scientist Jon Tschudi at SINTEF adds. He is the researcher behind the design of SmartSensor technology.

– The farther the photons, which are particles of light, travel into an object, the more information they gather along the way and the weaker the light gets. To measure this weaker, hard-working light instead of light that has bounced off the surface, you need to get plenty of photons into the object and help the maximum number of photons get back into the detector, he explains. More photons mean a stronger and cleaner signal, and the general rule of thumb is that the smaller the instrument, the fewer photons can get through at a given time.

 A cost-effective sensor in the making

It is crucial not only to make the Mini SmartSensor small enough, but also cost effective and power efficient. This is why SINTEF has been involved in many detailed technical discussions with photonics manufacturers on the availability and potential availability of suitable optical components and spectrometers. SINTEF has sourced several spectrometers, which have been adapted to their needs, and they have designed new efficient light sources, which are being tested in different combinations. A self-contained unit including batteries, electronics and a display can be made similar in size to a standard hairdryer. However, in the case of a measurement head that is mounted on the end of a robotic arm, it can be made much smaller.

“SINTEF can, if needed, develop our own core spectrometer, as we have done in SmartSensor. However, there is lot of development going on in the photonics industry, and it is important to understand and test off-the-shelf technology first, before going down that more extensive development track,” Tschudi says.

The research is still ongoing and there are several unanswered questions to be explored.

“How far can we push the compactness of our designs before we compromise too much on performance? To which degree should we adapt the design of the instrument to each application so that it is commercially viable? How can we help a lay-person or robot use this instrument as well as a trained expert,” Marion O’Farrell asks and concludes:

“We believe in the market potential of this concept and have already set in motion some steps towards further securing funding to continue developing the concept towards a commercial product.”