Spectroscopy has long been a powerful tool for analyzing materials without destroying them, with applications spanning from agriculture and pharmaceuticals to astronomy. However, traditional spectrometers are often bulky and costly, limiting their use outside controlled laboratory environments. In response to the increasing demand for portable and efficient solutions, a groundbreaking thesis from Don van Elst, from TU Eindhoven, has led to the development of a novel spectral sensing technology that maintains high performance while significantly reducing size and complexity. As a result of this innovative research, Don van Elst will be receiving a PhD promotion. Don’s research is part of the Synergia programme, a crossover initiative uniting the Dutch Agri & Food, Horticulture & Starting Materials, and HighTech Systems and Materials sectors
How Spectroscopy reveals material secrets
Light interacts differently with a material depending on its wavelength, producing unique electromagnetic spectra in reflection or transmission. These spectra have fascinated humanity for centuries and they provide a powerful tool to see inside materials, without having to break them apart. Due to this non-destructive nature, spectroscopy is used in a wide field of applications ranging from agrifood and soil analysis to pharmaceutics and astronomy.
A couple decades ago, the only way to get detailed information on a spectrum in a wide range of wavelengths was through large and costly spectrometers. These still offer the best resolution and wavelength range, but are difficult to take into the field and the rapid advances in consumer products and industry have accelerated the demand for miniaturized and portable solutions. One of the key challenges when miniaturizing spectrometers is maintaining their performance while reducing their size.
Mimicking human vision to reveal the Invisible
To overcome these challenges this thesis proposes a robust multipixel array with wavelength-selective responses. These spectral sensing chips provide the spectral information needed for the characterization of materials without having the complexity of a spectrometer. Similar to how our eyes have 3 different types of colour cones, which for example allows us to identify how ripe a banana is, these chips have 16 “cones” with responses in the near-infrared. This allows us to see properties of materials that are not visible to the human eye. In particular, we develop a cleanroom process based on optical lithography to fabricate these spectral sensors. Additionally, the effectiveness of the approach is demonstrated on real-life sensing problems, such as measuring the fat content in milk and moisture content in rice, as well as classifying illicit drugs and plastic types.
Enhancing cost-effectiveness and efficiency while preserving high sensing performance
A main feature of this approach is the choice of prioritizing high optical throughput over ultrahigh resolution. Beyond this, to enhance the sensors’ functionality even further, this thesis explores tailoring its response to specific applications. By varying the number of channels and their individual responses, this customization optimizes the signal-to-noise ratio and possibly reduces fabrication complexity, making the sensors more cost-effective and efficient, while maintaining high sensing performance. Additionally, a pilot was performed to extend the sensors’ spectral range into the short-wave infrared, widening the view even further and opening up new possibilities for applications.
The Synergia programme
Don’s research is part of the Synergia programme, a crossover initiative uniting the Dutch Agri & Food, Horticulture & Starting Materials, and HighTech Systems and Materials sectors. It is funded by the Netherlands Organisation for Scientific Research (NWO), aiming to drive innovation and interdisciplinary collaboration in these fields.
For more details on this cutting-edge research, contact Don van Elst at d.m.j.v.elst@tue.nl.