Thermocouples classically consist of two metals or semiconductor components that are joined at one end, where temperature is measured. Carbon black is a low-cost semiconductor with a Seebeck coefficient that depends on the structure of the carbon particles. Different carbon black screen-printing inks generally exhibit different Seebeck coefficients, and two can therefore be combined to realize a thermocouple. In this work, we used a set of four different commercially available carbon-black screen-printing inks to print all-carbon-black thermocouples. The outputs of these thermocouples were characterized and their Seebeck coefficients determined. We found that the outputs of pure carbon-black thermocouples are reasonably stable, linear, and quantitatively comparable to those of commercially available R- or S-type thermocouples. It is thus possible to fabricate thermocouples by an easily scalable, cost-efficient process that combines two low-cost materials.

This work deals with the realization of a fully printed thermocouple-array on a flexible substrate for condition monitoring applications. The thermocouple-array consisting of carbon black and silver was fabricated on PET-foil in a screen printing process and characterized up to a junction temperature of 150 °C. To ensure that no spurious voltages of the thermocouple occur due to deformations of the flexible substrate, the cross-sensitivity to deformation of the foil was investigated as well. Finally, as a test case, the temperature gradient of a plastic bar heated on a single end was measured with the thermocouple-array.

In order to control the flow inside microchannels, measuring the flow velocity of fluids is an important task. A possible way to determine flow velocity is by measuring the thermal time-of-flight. To this end, in this paper, a full screen printed combination of microheater and thermocouple is presented. Screen printing represents a technology that is attractive for fabricating low-cost sensor systems for microfluidic devices which can be directly integrated into the channel. The structure presented here has been manufactured using high-temperature stable screen printing inks. The thermocouple is calibrated and then the sensor setup is used to determine the flow velocity in a microchannel at various flow rates. The measurement is performed using a frequency domain approach by evaluating phase shifts of slow steady-state oscillations, and alternatively in the time-domain by estimating the heat transfer function from a step response measurement. The measurement results are compared to theoretically predicted values and show good agreement for a flow velocity range from 20 $\mu 1$ /min to 70 $\mu 1$ /min.

Microfluidic co-flow viscometers require the measurement of the interface position between two fluids (one sample and one reference fluid) flowing in parallel inside a microfluidic channel. From the interface position, the flow rates of both fluids and the known viscosity of the reference fluid, the viscosity of the sample fluid can be calculated. The detection of the interface position is usually done by optical means, therefore requiring optical access, and often coloring of the liquids or suspension of tracer particles to achieve optical contrast. In this contribution we present a device that is capable of determining the interface position in an alternative manner by capacitive measurements. The fully polymeric microfluidic chip is fabricated by simple processes requiring no specialized equipment. The capacitive sensor is fabricated by screen-printing. In order to enhance sensitivity, an insulation coating made from PMMA and barium titanate is applied. To assess the interface detection by capacitive means, measurements using different water/glycerol mixtures are performed and compared to optical images of the interface position establishing a relationship between capacitance and interface position. The capacitive measurement does not require coloring of the liquids or suspension of tracer particles if there is a dielectric contrast at the measurement frequency.

Embedding functional sensor layers directly into mechanical systems in heavy-duty surroundings facilitate the real-time monitoring of the system’s state. This work presents a fully-spray coated pressure sensor that is suitable for applications in the high pressure range. It is embedded into functionalized organic coatings that additionally act as a dielectric for the capacitive sensing mechanism. The sensitivity of the sensor, as well as its long-time stability, has been determined. Additionally, testing has been performed at elevated temperatures to determine the temperature dependent sensitivity that arises from the temperature dependence of the Young’s moduli.