Smaller & lighter: Printed sensors for spectrometers

Imagine that a pipeline that stretches for miles and miles springs a leak. Traditionally, this would mean many miles of walking for someone tasked with finding the hole. In an ideal world, this search for the precise point of methanol leakage could also be performed by a drone, onto which a spectrometer has been mounted that specializes in analysing chemical samples. Existing devices are currently far too heavy; the drone would soon have to give up. Lisa-Marie Faller is working on a technology, with which the fitted spectrometers can be made much smaller and would therefore be suitable for this type of deployment, amongst others. In recognition of her work, the doctoral student received the Best Paper Award at the IEEE Conference EuroSimE in Dresden in April.

The device Lisa-Marie Faller brings with her to the interview is approximately 5 cm long and 1 cm wide. It is equipped with a round mirror – a so-called micro-mechanical mirror, roughly 5 mm in diameter – that can also be used in FTIR spectrometers. These are devices that can measure infrared absorbance and emissions by means of interferometers and infrared light: It is possible to infer the type and number of molecules from the interference, i.e. the interaction of light with chemical substances. As a result, the device is capable of finding the methanol used in the example above. The accuracy of such a spectrometer depends on the quality of the position measurement of the adjustable mirror in the interferometer; the current design requires the permanent addition of a second, a so-called reference interferometer, to measure this position.

When one considers that even small spectrometers are approximately the size of a shoebox, the dimensions of the problem become obvious. “It is rarely possible to use spectrometers on drones for purposes such as this, as they are too large and too heavy”, doctoral student Lisa-Marie Faller (Institute for Intelligent Systems Technologies) tells us. She is therefore working on a solution, which will render the second interferometer unnecessary for the reference measurement. “Instead, we want to install a printed capacitive sensor under the micro-mechanical mirror. The sensor is designed to be inkjet-printed, so it is customizable. When complete, the entire system should weigh less than 250 grams.” Her work on such a tiny thing could lead to great changes: “A lot of research effort has gone into inkjet-printed sensors and into micro-mechanical mirrors of this kind. But hardly anyone is looking into how to connect the two. If we were to succeed with the implementation of a miniaturized FTIR spectrometer with printed, capacitive sensor and enhanced accuracy, it would represent a significant milestone.” It is also possible to conceive of applications for aerospace, with a steadily growing deployment of drones to explore the surface of planets and to analyse chemical substances with the hep of mobile spectrometers.

The micro-mechanical mirror at the focus of Lisa-Marie Faller’s work belongs to the Fraunhofer Institute for Photonic Microsystems (IPMS) in Dresden, and is worth several thousand Euro. Thanks to the project partner Carinthian Tech Research (CTR), the equipment was made available to the researchers in Klagenfurt. Using this mirror, the team is about to test the newly developed sensor shortly. The most important thing here is precision, as Lisa-Marie Faller explains: “We need to achieve accuracy in the nanometre rage. For this purpose, we have designed and built bespoke measurement hardware, which meets the stringent demands in relation to measurement noise.”

Lisa-Marie Faller completed an apprenticeship with Infineon and then, pursuing the path of second-chance education, she studied systems engineering followed by control systems engineering at the University of Applied Sciences in Villach. When she commenced her doctoral studies, she joined the research group lead by Hubert Zangl at the Alpen-Adria-Universität. For Faller, who loves puzzling over problems, be they small or large, and who tends to think and work on a grander scale, this was a stroke of luck: “Science offers opportunities to discover something new in the very depths of a problem, and consequently leads to innovative developments.” Faller is set to complete her doctoral thesis by the end of the year; she would like to remain in the field of research afterwards. When asked whether she could get rich off what she has developed, she responds: “Probably not with this particular application. But I don’t want to be rich anyway, I want to be contented.” And, rather surprisingly for someone who deals with the highly complex: “ Maybe the things I research are complicated. What I wish for in my life is as little complexity as possible. Then I’ll be satisfied.”