Optical microsensors are increasingly becoming more popular in the field of medical technology. The research institute for microsensor technology, CiS, has developed an in-ear sensor that takes pulse and blood oxygen saturation readings in a non-invasive manner and can transmit the data to a recording device. The system for long-term monitoring of vital parameters consists of a miniaturised light source with dimensions of only 0.6 x 0.7 x 1.4 millimetres and laser-Doppler sensors. “The measurement principle is based on detecting a frequency shift when laser light is scattered by the components of blood due to the Doppler effect, with the frequency shift being reliant on the flow rate and direction,” explained Dr. Hans-Georg Ortlepp from CiS. By superimposing this on the original wave, interference effects within the measurable range of frequency occur at the detector. There are endeavours being made to establish a point of measurement at the entrance of the ear canal. The sensor should be integrated in an earmould so that the measuring unit can be worn like a hearing aid.

Hearing with light


Seeing thanks to light is normal, hearing by means of light is a new approach that the CSEM centre (Centre Suisse d’Electronique et de Microtechnique) located in Central Switzerland is pursuing. This is because light is not only being used in the field of diagnostics but also in the field of therapy. Up until now, cochlea implants have functioned via electrical simulation that is, however, limited in many perspectives, such as poor spatial resolution, the so-called crosstalk, for example. With “optical acoustical” stimulation, the CSEM is participating in the EU project entitled ACTION (ACTive Implant for Optoacoustic Natural sound enhancement). “The project should strengthen the level of hearing of severely hearing-impaired patients by eliminating constraints of spatial and temporal stimulation of cochlea implants that are based on electrical stimulation," emphasized Dr. Stefan Mohrdiek from CSEM. ACTION builds on the discover that pulsed infrared laser light is capable of triggering auditor activity in hair cells. The primary components of the optical microsystem include lasers providing optical stimulation, for which semiconductor laser diodes are favoured, response electrodes as well as connection elements with printed electronic circuits. There are still a lot of challenges to overcome until the implementation of such systems can be achieved. This includes a rigorous level miniaturisation, sophisticated VCSEL lasers for long wavelengths, biocompatibility, the production of micro-lenses on a wafer basis as well as the possibility of manufacturing them in small batches.

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