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Mechatronics research on cover page of MDPI Sensors

In their July edition, the international scientific journal MDPI Sensors chose to high-light research results to help diabetes patients.

As a result of the cross-border PhD studies of Said El-Busaidy, researchers from the Mads Clausen Institute (SDU Sønderborg) and the Department of Mechanical Engineering and Production (HAW Hamburg) have succeeded in optimizing a photoacoustic cell, ultimately intended for glucose measurement in human tissue. The glucose level in human skin indicates the blood sugar level and can thus be employed for regular blood sugar measurements as required by diabetes patients. The measurement method is based on an infrared laser beam hitting the skin. The skin absorbs the laser beam and transforms it into heat – similar to the rays of the sun on a summer day. The level of absorption depends on the glucose level present in the skin: the more glucose, the higher absorption. When modulating the laser beam - turning it on and off – the researchers essentially heat an area on the skin, let it cool off, heat it up again etc. This is done many times per second (5-50 kHz), and the heating and cooling rhythm then generates sound – which is nothing else but a pressure wave through air. Therefore, the irradiation of the skin causes a sound signal, which in strength is proportional to the blood sugar level. Unfortunately, the sound level is very low, so it needs to be acoustically amplified. This is the reason for creating a so called “cell” around the laser beam and skin irradiation area. The shape of this cell is nontrivial and strongly correlated with acoustic resonance and losses.

Source: MDPI Sensors, July 2019

Lars Duggen, Associate Professor at SDU Mechatronics explains it this way:

“In the article in MDPI Sensors, we have developed a mathematical model that describes the amplification of the sound generated by the absorption of a laser beam. Part of the challenge here was the fact that we had to use an open cell in order to alleviate accumulation of humidity from human skin. The open cell caused numerical difficulties of modelling an infinite domain. This problem is generally well known in acoustics and is usually solved by a technique called “perfectly matched layers”. These layers, however, do not work in conjunction with the employed eigenfunction expansion method, which was chosen for its fast calculation time compared to fully viscothermal models. We have subsequently used this model to optimize the dimensions of the cell as to give an amplification as large as possible.”

The article is a result of the PhD studies of Said El-Busaidy, who is carrying out his research by means of a collaboration between SDU Sønderborg and HAW Hamburg.

” We are really happy with the results that we have obtained and look forward to continuing research on this topic. Furthermore, we were all positively surprised when suddenly the editor of MDPI Sense asked us to provide high quality graphics for the cover page, since we were selected as cover story. This does not happen often and made us all even more proud of our achievements,” says Lars Duggen.

Editing was completed: 05.08.2019