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A modular microfluidic system can be used to quickly set up an individually adaptable microfluidic network by linking and delinking different functional building blocks. We present a convenient and reliable connection technology, which is based on magnets and casted O-ring-like structures leading to a sealed connection without the need of additional sealing materials. Based on an improved, previously presented fabrication technology, modular microfluidic polydimethylsiloxane (PDMS) blocks using a polyurethane (PU) mold, 3D printed acrylonitrile butadiene styrene (ABS) channel structures and a magnetic connection system in combination with a casted O-ring link, featuring various integration technologies have now been designed and experimentally evaluated. In particular, this paper will address the realization of directional valves, reciprocating pumps, finger pumps, directly-cast check- and Tesla-valves, fluidic flow sensors, fluidic mixers, commercial valves, and various sensors. By using different measurement setups, the feasibility of these devices is demonstrated. Moreover, limitations and issues encountered during fabrication as well as future work are discussed.

We demonstrate the utilization of the fundamental principle of nonlinear dynamics, namely, the Liénard-type representations of ordinary differential equations, also referred to as fast-slow systems, to describe and understand relaxation oscillations in electronic circuits. Relaxation oscillations are characterized by periods of slow signal changes followed by fast, sudden transitions. They are generated either intentionally by means of usually simple circuits or often occur unintentionally where they would not have been expected, such as in circuits with only one dominant energy storage device. The second energy storage required to promote oscillatory solutions of the governing equations can also be provided by spurious elements or mechanisms. The conditions that distinguish harmonic from (anharmonic) relaxation oscillations are discussed by considering the underlying eigenvalues of the system. Subsequently, we show how to intuitively understand relaxation oscillations through analyses of the phase diagram based on the fast-slow system representation of the nonlinear differential equation. Practical examples of oscillators including $RC$ and $LR$ op-amp circuits and the so-called “Joule thief” circuit are discussed to illustrate this principle. The applicability of the method is not limited to electrical circuits, but extends to a variety of disciplines, such as chemistry, biology, geology, meteorology, and social sciences.

Whether liquids in open microchannels show spontaneous capillary flow or not crucially depends on the involved surface energies and the shape of the microchannel. In this study, we present a two-dimensional model based on the Gibb’s free energy of a system that predicts the presence of spontaneous capillary flow in open microchannels. We expand our model to include curved microchannels and verify our findings using simulations of a liquid surface with Surface Evolver. Finally, we comment on how these results can be used to measure the liquid contact angle through open capillary flow.

We present the concept and a proof-of-principle experiment for an acoustofluidic single- particle sorter. In a microfluidic channel, a flow profile with the following three parallel fluid domains is generated: buffer fluid in the center and buffer plus particles in the lateral domains. Due to the laminar flow regime present in microfluidics, the particles essentially follow the stream line(s) along the channel. In the spatially confined sorting and detection region, by switching on the standing acoustic wave, particles of interest (POIs) are pushed into the center fluid domain, thus leaving the chip at the center outlet. For particles of non-interest (PONIs), the acoustic region remains silent, so PONIs are not centered and follow their path to the side outlet.

This research work focuses on the fabrication of ultrathin polymethylmethacrylate (PMMA) foils using a spin coating process of in anisole dissolved PMMA on a water-soluble polyvinyl alcohol (PVA) foil. Currently, layer thicknesses as low as 1 µm can be achieved and even thinner layers appear to be possible. Sensors and actuators can be applied to the foils and directly integrated into the center of the channel of a polymer-based microfluidic chip. Specifically, the foil acts as a supporting structure that helps to position the sensor in the center of the channel. Thermal sensors, in particular, benefit from the low heat capacity of the foil. This will improve the performance and the accuracy of these sensors of which the impact on the fluidic flow is minimized.

The objective of this study is the design and fabrication of a microfluidic thermal flow sensor using polymethylmethacrylate (PMMA) as a substrate. This enables the simple fabrication process of the channel structure and the sensor itself using a laser engraver/cutter machine and a solvent-based bonding process. A thin platinum wire called a Wollaston wire is directly integrated into the fluidic chip and acts as the only sensor element. The combination of this sensor and customized measurement electronics enables a measurement range at flow velocities from 4 mm/s up to 400 mm/s (volume flow rate range from 10 µL/min up to 1 mL/min).

This work reports on the fabrication and testing of force sensors integrated directly into a printed circuit board (PCB). For this purpose, a layer of poly(vinylidene fluoride-trifluoroethylen) (P(VDF-TrFE)) is printed onto two pieces of two two-layer PCBs, which are then stacked together to create a four-layer PCB. The devised and fabricated sensor with the described measurement setup features a nearly linear measurement characteristic in the range between 0.3 and 1.2 N and a detection limit of approximately 10 mN.

Here we present an alternative technological approach to paper-based microfluidics that, to the best of our knowledge, has not been reported so far. Instead of defining fluid conducting paths by cutting fluidic structures, or by printing hydrophobic substances on paper, we prepare cellulose/polymer composites that can be printed additively on, in principle, arbitrarily shaped substrates and surfaces. In this way, with respect to geometry and properties, well defined fluid conducting structures based on cellulose can be realized, that can additionally be fully embedded in an organic surface coating. Moreover, the composite can, prior to the printing step, be doped with a functional component, which facilitates the realization of printed analytical devices using just a single base material and process technology. In this sense, the proposed technology can be seen as an alternative pathway to paper-based microfluidics, that may be attractive for specific niche-applications such as, for example, bio-chemical assays embedded in the surface of everyday necessities or commodities. Especially lateral flow immunoassays, pandemic-driven needed in large quantities, may embody a future application field of the presented technology.

We report highly selective resonant emission from an aperiodic Tamm plasmon-polariton (TP) emitter featuring a targeted mid infrared emission wavelength in the region of 4.26 μm. This spectral region is of high interest in context with integrated CO2 absorption sensing. To the best of our knowledge, the measured thermal emission at peak temperatures up to 500 °C of TP emitters featuring a half-wavelength cavity have never been related to simulations in a satisfactory manner in terms of peak position, emission intensity and temperature behavior. The layer thicknesses quantified via scanning electron microscope (SEM) featured deviations from the targeted periodic configuration due to statistical variation of deposition and etching process. Simulations using the Transfer-Matrix Method suggested a higher Q-factor and higher peak emission associated with the obtained aperiodic configurations compared to the target periodic configuration featuring a quarter-wave stack (QWS). Although the improved spectral features of the aperiodic stack could not quite be resolved, the spectral position, the qualitative temperature behavior and the angular emission pattern in the range of 0° to 10° could be confirmed by Fourier-transform infrared (FTIR) spectroscopy.

In recent years, there has been a significant increase in research into silicon-based on-chip sensing. In this paper, a coupled cavity waveguide (CCW) based on a slab photonic crystal structure was designed for use as a label-free biosensor. The photonic crystal consisted of holes arranged in a triangular lattice. The incorporation of defects can be used to design sensor devices, which are highly sensitive to even slight alterations in the refractive index with a small quantity of analyte. The plane wave expansion method (PWE) was used to study the dispersion and profile of the CCW modes, and the finite difference time domain (FDTD) technique was used to study the transmission spectrum, quality factor, and sensitivity. We present an analysis of adiabatically coupling light into a coupled cavity waveguide. The results of the simulation indicated that a sensitivity of 203 nm/RIU and a quality factor of 13,360 could be achieved when the refractive indices were in the range of 1.33 to 1.55.

Concentration gradient generators are common components of microfluidic devices when specified mixing ratios have to be acquired. However, depending on their complexity, the creation of a suitable design is an elaborate task. Although approaches exist that derive such a design, they suffer from low flexibility and usability, which is why most concentration gradient generators are still mainly designed manually thus far—a time-consuming and error-prone task. To tackle this problem, we propose a method for the automatic design of tree-shaped concentration gradient generators and introduce a publicly available online tool that automatically generates a suitable design by adjusting the hydrodynamic resistances within the network. Moreover, the proposed tool is not only able to generate designs complying with user-defined requirements, such as mixing ratios, flow rates, and channel widths but also works for any number of outlets. Simulations using a Computational Fluid Dynamics (CFD) tool as well as evaluations on fabricated designs confirm the quality of the results obtained by the proposed tool.

This paper investigates the use of a miniaturized filter based on a triangular lattice of holes in a photonic crystal (PhC) slab. The plane wave expansion method (PWE) and finite-difference time-domain (FDTD) techniques were utilized to analyze the dispersion and transmission spectrum, as well as the quality factor and free spectral range (FSR) of the filter. A 3D simulation has demonstrated that for the designed filter, an FSR of more than 550 nm and a quality factor of 873 can be attained by adiabatically coupling light from a slab waveguide into a PhC waveguide. This work designs a filter structure that is implemented into the waveguide and is suitable for a fully integrated sensor. The small size of the device provides a strong potential for the realization of large arrays of independent filters on a single chip. The fully integrated character of this filter has further advantages such as reducing power loss in coupling light from sources to filters and also from filters to waveguides. The ease of fabrication is another benefit of completely integrating the filter.

Non-dispersive infrared (NDIR) absorption spectroscopy is a widespread approach to gas sensing due to its selectivity and conceptual simplicity. One of the main challenges towards the development of fully integrated NDIR sensors is the design and fabrication of microstructures, typically waveguides, that can combine high sensitivity with the ease of integrability of other sensor elements (sources, filters, detectors). Here, we investigate theoretically and experimentally a class of coupled strip-array (CSA) waveguides realized on a SiO2/Si3N4 platform with mass semiconductor fabrication processes. We demonstrate that this class of waveguides shows comparable sensitivity for a wide range of presented geometries, making it a very promising platform for satisfying multiple sensor and fabrication requirements without loss of performance.

In this work, we investigated the optimization of a plasmonic slot waveguide (PSWG) in the mid-IR region particularly for a representative wavelength of 4.26 µm, which is the absorption line of CO2 and thus particularly relevant for applications. We analysed the mode features associated with metal-dielectric-metal (MDM), dielectric-metal-dielectric (DMD), and truncated metal film (TMF) structures with respect to the considered PSWG. Subsequently, the mode features of the PSWG were considered based on what we outlined for MDM, DMD, and TMF structures. Furthermore, as confinement factor and propagation length are two crucial parameters for absorption sensing applications, we optimized the PSWG based on a figure of merit (FOM) defined as the product of the aforementioned quantities. To characterize the propagation length, the imaginary part of the effective mode index of a guided mode was considered, leading to a dimensionless FOM. Finally, we investigated the PSWG also for other wavelengths and identified particularly attractive wavelengths and geometries maximizing the FOM.

In this work, we present and analyze a design of an absorber–waveguide system combining a highly sensitive waveguide array concept with a resonant selective absorber. The waveguide part is composed of an array of coupled strip waveguides and is therefore called a coupled strip array (CSA). The CSA is then coupled to the end of a slab Tamm plasmon (STP-) resonator, which is composed of a quasicrystal-like reflector formed by the patterning of a silicon slab and an interfacing tungsten slab. The concept describes an emitter–waveguide or waveguide–detector system featuring selective plasmon-enhanced resonant absorption or emission. These are crucial properties for corresponding optical on-chip integrated devices in context with evanescent field absorption sensing in fluids or gases, for example. Thus, the concept comprises a valuable and more cost-effective alternative to quantum cascade lasers. We designed the lateral dimensions of the STP resonator via a simple quasi-crystal approach and achieved strong narrowband resonances (emittance and Q-factors up to 85% and 88, respectively) for different silicon thicknesses and substrate materials (air and silicon oxide). Moreover, we analyze and discuss the sensitivity of the complete emitter–waveguide system in dependence on the slab thickness. This reveals the crucial correlation between the expected sensitivity assigned to the absorber–waveguide system and field confinement within the silicon.