Johannes K. Sell

Methods for the robust measurement of the resonant frequency and quality factor of significantly damped resonating devices

For many applications, resonating sensors can be designed which exhibit excellent sensitivity of the resonant parameters (resonant frequency and quality factor) to the wanted physical parameters. When the resonant parameters are to be derived from measured data, the utilized signal processing algorithm significantly affects the precision of the obtained results, in particular, when the resonance is impaired with spurious contributions. In particular, for systems with low Q-factors (e.g., electromechanical resonators in viscous liquids with Q < 100), the measurement precision suffers from various unwanted spectral components induced by parasitic effects of the resonator and measurement errors. In order to separate the adverse effects from the ideal second-order characteristics, three related methods for estimating the parameters of second-order resonant systems are introduced in this paper extending established methods. To this end, the spectrum is separated into a component induced by a second-order resonant system and an unknown background spectrum.

Reactance-locked loop for driving resonant sensors

Quartz tuning fork resonators are suitable sensors for the measurement of density and viscosity of a surrounding gas. For the continuous measurement with these sensors, a digital reactance-locked loop is proposed in this contribution. Furthermore, insight on the theoretical background of density and viscosity measurement with tuning fork resonators is given and the application of the system for simultaneous density and viscosity measurement in gases with a tuning fork resonator is presented.

Concept for printed ferroelectric sensors on coated metallic substrates

In this work we report on the integration of all-printed multi-layer ferroelectric sensor stacks into organic coatings on metallic surfaces like sheet steel. Manufacturing techniques for realizing thin film sensor layers on top of organic coatings using screen printing are presented. Results for the piezo/pyroelectric sensor layer with variable printing parameters are then analysed and compared.

Printed capacitive touch sensors embedded in organic coatings on sheet steel

We present the first realization of printed capacitive touch buttons and touch pads integrated into the organic coatings on sheet steel. The properties of coated sheet steel relevant for printing are discussed and compared to substrates, commonly used for printed electronics. Different designs and read-out methods for capacitive buttons on sheet steel have been screen printed and their sensitivity in dependence on design parameters is rated.

PDMS membrane with integrated open-porous foam featuring a gradient in pore-size for simultaneous filtration and pumping of fluids in microfluidic structures

In this contribution we present a concept for simultaneous filtration and pumping solely realized with a single polymer based membrane. An open-porous foam with a gradient in pore size, which essentially resembles a nozzle-diffuser structure, is integrated into the center of a flexible PDMS (Polydimethylsiloxane) membrane, which is placed into a small fluid cavity with symmetric inlet and outlet geometry. The actuation of the membrane is achieved with an electromagnetic coil from the outside and a small magnetic ring, which has also been integrated into the membrane. The sinusoidal excitation of the membrane leads to a vibrational movement of the membrane in the fluid cavity, and due to the asymmetry in pore size of the integrated foam a unidirectional fluid flow evolves in the system. Thus, the proposed device can be used for simultaneous pumping and filtration with the additional advantage of reduced sensitivity to fouling.

A simple mid-infrared measurement system based on a tunable filter for the analysis of ternary gas mixtures

An infrared absorption measurement system, suitable for the analysis of simple gas mixtures with known constituents is under investigation. A theoretical insight into the problems arising from the filter bandwidth when measuring infrared absorption in gases at higher pressures is given. It is demonstrated that the proposed measurement system can be used for the analysis of infrared absorbing ternary gas samples when suitable evaluation algorithms, e.g., partial least-squares regression, are used.