Fine Dust Measurement with Electrical Fields – Concept of a Hybrid Particle Detector

Abstract

Fine dust measurements are only conducted at few locations in our daily environment, although it is getting clearer that fine dust poses a high risk on human health. A reason for this deficit is the lack of suitable measurement systems, especially for indoor environments. Of special interest are particles with critical dimension smaller than 10 μm. They constitute the highest risk to human health as they are not filtered out by the respiratory system. By miniaturizing particle detector concepts point-of-care applications are rendered possible and production costs can be greatly reduced with microsystem fabrication technologies. The pursued detector principle is based on the interaction of single particles with electric fields. The field is created within a micro-aperture machined in a silicon substrate. Two electrodes are deposited near the aperture and form a capacitive setup. An air flow drives particles through this aperture one by one. Passing particles distort the electric field, and their presence is detected by an impedance measurement. The changes induced by a single particle are tiny and require precise measurement circuits. Our contribution presents the design of a hybrid particle detector: The sensing element consists of an array of these micro apertures with lead-outs to a measurement circuit. This element is mounted on a LTCC module, which provides all necessary electrical and fluidic functions to operate the particle detector within a larger sensor platform. Sensitive parts of the measurement circuit are mounted on the LTCC module and positioned closely to the sensing elements. Microfluidic channels guide the air flow from the sensor platform to the micro-aperture and back. Therefore, the hybrid module is both: a ceramic interconnect and a ceramic microsystem.