Foreign researchers develop micro-spectrometers to bring new features to smartphones

[Chinese instrument network instrument research and development] Your smart phone is used to detect the degree of air cleanliness, whether the food is fresh, the mass is not malignant. These are thanks to a new type of spectrometer, which is very compact, can be easily installed in mobile phones and is very inexpensive. The miniature sensors developed by the Eindhoven University of Technology are as accurate as the conventional desktop model sensors used in scientific laboratories. Researchers described their invention on December 20 in Nature Communications.

The picture shows the structure of the device. The blue holed plane is the upper film layer with a photonic crystal cavity that captures light of a specific frequency.

Spectrometric methods for the analysis of visible and invisible light have a wide range of applications. According to the absorption and reflection of light, each material and each tissue has its own "footprint" and therefore can be discriminated by spectrometry. But the spectrometers that can be accurately measured are very large because they divide the light into different colors (frequencies) and measure them separately. After the light is decomposed, beams with different frequencies will still overlap with other beams. Therefore, highly accurate measurements can only be made after tens of centimeters after the decomposition.

Eindhoven researchers have developed a novel sensor that can perform accurate measurements in a completely different way by using a special "photonic crystal cavity" which is a few microns thick. "Trap", light can not escape after falling in the inside. This trap is contained in a film, and the light trapped in it produces a tiny current that can be measured. The cavity of the doctoral student Sarko Zobenica is very precise, only keeping a very small frequency interval, so only the light at that frequency can be measured.

To be able to measure a larger frequency range, the researchers placed the two membranes very closely together, one above the other. The two films interact with each other: if the distance between them changes slightly, the frequency of the light that the sensor can detect also moves with it. To this end, a MEMS (microelectromechanical system) was assembled by researchers led by Professor Andrea Fiore and associate professor Rob van der Heijden. This electromechanical system allows the distance between the membranes to change and thus measure the frequency. In the end, the sensor can cover a wavelength range of about thirty nanometers. Within this range, the spectrometer can discriminate hundreds of thousands of frequencies, which is very accurate. This can be achieved because the researchers set the distance between the membranes to tens of meters (10-15 meters).

As shown in the schematic structure of the above equipment. The blue holed plane is the upper film layer with a photonic crystal cavity that captures light of a specific frequency. When this happens, it produces a current (A) that can be measured.

To prove its usefulness, the team demonstrated several applications, including a gas sensor. They also made a very precise motion sensor and cleverly exploited the fact that the detected frequency changes when the two films move relative to each other.

Professor Fiore expects that the new spectrometer will take five years or even longer before it is actually applied to smart phones because the frequency range it covers is still too small. Currently, sensors cover only a few percent of the most common spectrum, the near infrared spectrum. So his team will work to expand the detectable spectrum. They will also integrate an additional device, a light source, into a miniature spectrometer that will keep the sensor out of the external light source.

Given the breadth of applications, miniature spectrometers are expected to eventually become just as important as cameras in smartphones. For example, measuring CO2, detecting smoke, determining what medicine you eat, measuring the freshness of food, determining your blood sugar level, and so on.

(Title: Miniature spectrometers bring many new features to smartphones)