Comparison of different technologies
Table of ContentsBasic knowledge about VIS NIR spectroscopy
- What is spectroscopy
- The 4 steps of spectroscopic measurements
- What is chemometrics
- How to create a chemometric model for Material Sensing
SILICON, INGAAS AND SENORICS
NIR spectroscopy with and without conventional dispersive elements
The main difference between the commercially available spectroscopic technology and our innovative technology is that, up to now, a dispersive element was necessary to separate the spectral components of the reflected or transmitted light. With our technology it is possible to do NIR spectroscopy without a conventional dispersive element and pave the way for new applications.
Dispersive elements as longstanding tools for spectroscopic technology
Dispersive elements used in spectroscopy have been known for decades and one classic example is a prism; typically, a triangular shaped object made from glass. If white light enters the surface of the prism, it will be refracted and dispersed into its spectral components. All in all, leading to a rainbow-like splitting of the incoming white light as illustrated in the sketch. If you would like to learn more about this phenomenon, it is described by Snell’s law.
Necessary components to perform spectroscopic measurements
To obtain the spectroscopic information of an object, the following 4 components are required:
- This can be a broad band light source which radiates light and interacts with the object of interest. It could also be a light source that only covers a certain spectral range, for example near-infrared light when using NIR spectroscopy.
Object of interest
- The object interacts with the light, leading to absorption, reflection and transmission.
- In spectroscopy we need to analyze spectrally resolved information of reflected or transmitted light. Therefore, the light needs to be split into its spectral components and directed to a detection unit where it is measured.
- A detector receiving the reflected or transmitted light and converting it into an electronic signal which can be measured precisely. Analyzing the spectral components enables us to quantify properties of the object, such as the ingredients and composition of the material.
Spectroscopy without conventional dispersive elements
In contrast to the established methods, we invented a sensor which consists of a spatial arrangement of detectors that are sensitive to specific wavelengths. The main advantage is that the wavelength selection and measurement happen within the same device. Therefore, our solutions are much smaller and more robust than conventional spectrometers. Our sensors do not need any moving optic components, which is one of the main reasons why our technology is the ideal solution for small and mobile spectroscopy applications.
Paving the way for a new level of spectroscopy
With our sensor solutions and the omission of a conventional dispersive element, the foundation for a new era of Material Sensing applications is laid, taking spectroscopy out of the laboratory and bringing it into people’s pockets.
Full spectrum of lab spectrometers versus 16 pixels of Senorics hardware
Have you ever wondered how measurements made by a lab spectrometer differ from those made by our SenoCorder Solid? Or how a small chip can do spectral measurements just like conventional lab spectrometers? Let’s take a closer look to answer these questions…
How a lab spectrometer records a spectrum
In labs worldwide most spectrometers used in the VIS and NIR range are based on silicon, covering the wavelength range from 200nm to 1,100nm, or on InGaAs, covering the range from 800nm to 1,700nm (under special conditions up to 2,500nm).
They provide high resolution spectral analysis up to 1nm. To provide such detailed insights the dispersive elements in the lab spectrometers must be adjusted exactly, which results in devices that are quite sensitive to vibrations and shocks as well as being large and bulky. Of course, they have their advantages: measurements are very precise, you can set the resolution just as you need it (ranging from 1nm to 10nm) and therefore, you get a spectrum with the desired level of detail.
If you would go to a lab with some pasta, asking for spectral measurement, the diagram you will get would look something like this:
This diagram shows the spectrum of pasta in the wavelength range from 1,100nm to 1,800nm with a resolution of 2nm. That means there is a measuring point every 2nm, resulting in 350 measuring points shown in this diagram.
Let’s illustrate it with an analogy: If you would draw a birch tree for example, this would correspond to a very detailed picture with roots, trunk and bark, leaves as well as the tiny little leaf veins.
How our chip records a spectrum
The technology of our chip is based on organic semiconductors in a thin film stack configuration and therefore requires no dispersive elements. It is a handy, light and robust device that is made for applications in everyday life.
The chip inside has 16 wavelength channels called pixels. Each pixel covers a certain wavelength in the VIS or NIR range (wavelength range from 450 nm to 1,800 nm). The specific wavelengths that the 16 pixels cover can be adjusted depending on the application.
With our SenoCorder Solid for example you can do the measurement of the pasta on your own. You just take the pasta, place the device on it and you are immediately ready to measure.
With our Software SenoSoft you get this diagram:
It shows the measurement of the same pasta as in the previous diagram but measured with our SenoCorder Solid. The wavelength range is 1,100nm to 1,800nm and the resolution is 45nm, resulting in 16 measuring points.
Let’s come back to the example with the birch tree. If you would draw a birch tree now, this would be a sketch that shows little detail except for the most important characteristics such as the bright bark and the relatively small, jagged leaves.
Now that we talked about the technical background, let’s answer the question of whether 16 pixels are enough.
Are 16 pixels enough? Lab spectrometer vs. Senorics technology
Comparing the two diagrams, you notice that the lab spectrometer provides significantly more measuring points (in this case 350) than the SenoCorder Solid (16 measuring points). Another difference is that the measured values of the SenoCorder Solid differ slightly from those of the lab spectrometer.
However, it is obvious that the 16 measuring points represent the most important characteristics, or in other words: the SenoCorder Solid can qualitatively reproduce the spectrum.
Let’s come back to the birch tree again, thinking of this information:
- It is a tree.
- It has a white bark.
- It has many small and serrated leaves.
You would immediately know that it has to be a birch tree. You don’t get information about the height of the tree, whether it’s healthy or not or what kind of insects are living in the bark – questions that might be important for a biologist or a forest scientist.
But you get the information that it is a birch tree, which is totally sufficient for everyday life. It is exactly the same with this spectrum. A few measuring points covering the most important features are perfectly sufficient for most everyday applications.
In daily life you ask questions like “Is this pasta gluten free or not?” “Is this textile polyester or silk?” “Is this a genuine drug or fake?” To answer these questions you often need even less than 16 measuring points – depending on the spectrum of the material.
So to answer the question of whether 16 pixels are enough: Yes, in most everyday applications it is perfectly sufficient.