Evanescence Field Particle Sensors

Solid particle aerosols in general, and in particular the fine dust fraction, are related to a number of health hazards. This creates a rising demand for personal detectors capable of monitoring the individual exposition. At present, however, and despite a number of pertinent national and international R&D activities, only comparatively large particle detectors of limited portability and constructed from discrete components are available. Thus, a tangible need for highly integrated particle sensors that could be integrated e.g. into smartphones or wearables exists, but no satisfactory solutions. A new idea evolved from the peripherals of a related R&D project dealing with the integration of established particle sensing principle into highly integrated particle sensors: to use the evanescent fields along the surface of optical waveguides to detect attached particles. While this is a well-established principle from optical-spectroscopic analysis and implemented in various chemical and bio-chemical sensors, up to now it has never been used specifically for the detection of particles. Although a potentially exploitable effect is known, up to there is not even a comprehensive understanding of the physical basics of the type(s) of interaction(s) between the evanescent field, one or several particle(s) on the surface, and the resulting changes in the signal transmitted through the waveguide.

Main objective of the research project EFiPaS is verifying the suitability and functionality of the selected waveguide approach as a sensor principle, and subsequently the realisation of a first functional demonstrator of such a particle sensor, prototyped using semiconductor technologies. The related scientific core objective is a generating a comprehensive understanding of the sensor effect, including specific, experimentally validated simulation models. Based on that, research will e.g. deal with the question whether the size distribution of the particles can be detected alongside the particle number/mass. The expected technological innovations include

1. a demonstrator of a 3 x 3 mm² on-chip particle sensor, which would equal a footprint reduction by more than one order of magnitude,
2. optical waveguides with applications-specifically optimised form and functionality that can be manufactured using semiconductor technologies, and
3. a number of presently not available processes needed for manufacturing such waveguides.

These processes would be of high interest for subsequent innovation in optical sensor technology and beyond. The substantial scientific and technological risks associated to the research into this, previously largely unproven principle, is thus associated by an appropriately high potential scientific, technological and – on the mid-term – commercial benefit.