To ensure high quality output of biotechnological processes, relevant process parameters need to be monitored. As bioprocesses are increasingly executed in single use bioreactors, there is an increasing demand for new sensors applicable to these processes. In this work, we investigate different approaches for continuous non-invasive cell growth monitoring, especially for single use bioreactor applications. Therefore, the permittivity of the cell culture is used as a measure for the biomass. In a first step, a measuring procedure based on the transmission measurement of an electromagnetic wave is investigated. It appears that the penetration depth of this sensor is not sufficient for a noninvasive measurement through the polymer wall of a single use bioreactor. Therefore, alternative setups based on magnetic induction are investigated. The initial setup is very simple. It consists of a planar coil connected to an impedance analyzer. The coil is attached to the outside of the polymer foil of the single use bioreactor and an impedance spectrum is measured. To evaluate the sensor, E. coli cultivations are performed in a modified cultivation setup, which enables measurements through the polymer foil of a Sartorius BIOSTAT® CultiBag RM, and additionally allows sampling of culture medium for optical density reference measurements. The resonance peak of the coil in the impedance spectrum, is observed as measure for the optical density. Regardless of the simple sensor construction, we found a good correlation between optical density and the damping ratio of the resonance peak. However, the sensor signal shows saturation towards high optical densities. Therefore, an LTCC coil producing a higher magnetic flux density in the culture medium is investigated subsequently. This sensor shows a linear response up to high optical densities, but the sensitivity is reduced compared to the former used coil and therefore scattering of the data is increased. However, to increase the sensitivity, a linear variable differential transformer is realized. Using this setup, the influence of the primary magnetic flux is eliminated from the measuring voltage. This approach delivers the most promising results, as the sensor response is linear up to high optical densities and data scattering is low. Fig. 1. Four-electrode measurement without (left) and with (right) polymer foil (CST Simulation at 1 kHz with discrete port excitation (1 V Amplitude), 190000 Hexahedral Mesh cells and open (add space) boundaries).

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The paper presents simulated and measured results of a large millimeter-wave antenna array, designed by keeping mind the particular interests for proof of concepts in 5G demonstrations in South-Korean Winter Olympics 2018. The array consist of 16 (2x8) unit cells, each having four (2x2) linearly polarized patch elements exited with the same amplitude and phase. The desired-10 dB impedance bandwidth for the array is from 25.65 GHz to 27.50 GHz, and the proposed structure achieves lower than-30 dB mutual coupling between the unit cells. The presented simulation and measurement results show good match with each other, as well as with the specifications. The radiation pattern is measured element by element at 27 GHz, and the results are summed in post-processing to perform the array factor. Sidelobe levels are 15 dB below the maximum gain, whereas the measured maximum gain is around 20 dB as the numerical results predicted 21.5 dB.

This paper presents for the first time the fabrication of dielectric ceramic parts by 3D printing without sintering. The printable paste was prepared by mixing a carefully selected amount of water-soluble Li2MoO4 powder with water. A viscous mixture of solid ceramic particles and saturated aqueous phase was formed with a solid content of 60.0 vol.%. Printing of the sample discs was conducted with material extrusion using a low-cost syringe-style 3D printer. The consolidation and densification of the printed parts occurred during both printing and drying of the paste due to extrusion pressure, capillary forces, and recrystallization of the dissolved Li2MoO4. Complete drying of the paste was ensured by heating at 120 °C. The microstructure showed no delamination of the printed layers. Relatively high densities and good dielectric properties were obtained, especially when considering that no sintering and only pressure from the extrusion was employed. This approach is expected to be feasible for similar ceramics and ceramic composites.

Cell viability monitoring is an important part of biosafety evaluation for the detection of toxic effects on cells caused by nanomaterials, preferably by label-free, noninvasive, fast, and cost effective methods. These requirements can be met by monitoring cell viability with a capacitance-sensing integrated circuit (IC) microchip. The capacitance provides a measurement of the surface attachment of adherent cells as an indication of their health status. However, the moist, warm, and corrosive biological environment requires reliable packaging of the sensor chip. In this work, a second generation of low temperature co-fired ceramic (LTCC) technology was combined with flip-chip bonding to provide a durable package compatible with cell culture. The LTCC-packaged sensor chip was integrated with a printed circuit board, data acquisition device, and measurement-controlling software. The packaged sensor chip functioned well in the presence of cell medium and cells, with output voltages depending on the medium above the capacitors. Moreover, the manufacturing of microfluidic channels in the LTCC package was demonstrated.