Special issue  

The development of optical design is characterized by the desire for more applications and better performance. The latest result of this development is freeform optics offering almost unlimited possibilities for the designers. However, an optical component has also to be manufactured and tested by metrology. We propose a measurement technique for the surface characterization of freeform optical components and highlight the possible error sources and their influence on the measurement result.

A novel experience replay particle swarm optimization algorithm is presented and successfully deployed to improve the optimization performance for reconfigurable analog integrated circuits of industry 4.0. An optimization approach is introduced that relied on THD-based indirect measurement method that varies from the traditional calibration approach. Instead, the proposed calibration methodology optimizes all characteristics of the reconfigurable amplifier at once.

Detection of flammable gases is necessary to avoid explosive atmospheres. Commercial pellistors require an operation temperature above 450 °C for the detection of methane. We present a novel wireless low-power catalytic gas sensor system based on non-precious metal catalyst for the detection of methane and propane operated at 350 °C. The combination of a MEMS-based sensor with a low-power radio system provides the opportunity to monitor complex infrastructures without using a power grid.

A new metrological atomic force microscope (MAFM) head design is shown. We investigated the MAFM head in the nanomeasuring machine (NMM-1) for different high-precision and large-scale traceable measurement tasks. Due to their integration, the MAFM head can benefit from the large measuring range, high-precision and traceability of the NMM-1 for efficient measurements on different samples. The presented results show the realised macroscale measurements with sub-nanometre resolution.

The actuators of precise positioning based on LiNbO₃ or LiTaO₃ bimorph structures are considered. They consist of two joined plates: one of them lengthens and the other one shortens under the influence of an electric field and, as a result, the actuator bends. Such a device ensures small movements of probes in scanning probe microscopes, micro-electromechanical systems, micro-motors, etc. We determine the optimal orientations of the plates, ensuring the highest possible actuator displacements.

Virtual assembly (VA) is a method for the quality prediction of assemblies considering local form deviations of relevant geometries. Point clouds of measured objects are registered in order to recreate the objects’ hypothetical physical assembly state, which is strongly influenced by the measurement uncertainty of individual points. Thus, we studied the propagation of uncertainties by VA. The results reveal larger propagated uncertainties by VA compared to the unconstrained Gaussian best fit.

Ion-selective electrodes have been proven useful in water analysis. They are usually used as single-rod measuring chains in different designs, which are manufactured using precision mechanical manufacturing and assembling technologies. The paper describes a microsystem technology approach for the fabrication of miniaturized electrochemical sensors. Design, manufacture, and performance of the novel ceramic multilayer-based sensor array are presented in the paper using various examples.

A novel, low-cost measurement device for simultaneous high temperature measurements of the electrical conductivity and Hall coefficient has been developed. Simulations were used to design a suitable screen-printed planar platinum heating structure that generates temperatures of up to 600 °C. Simulations of the temperature distribution have been validated using thermal imaging. Measurements were compared with data from the literature to validate the functionality of the novel device.

This paper deals with the electrical investigation of various sand mixtures used in foundries for mold and core production. It is possible to classify various molding sand mixtures reproducibly on the basis of their electrical characteristics. This knowledge can now be used to develop measurement systems for processes in the foundry industry and thus increase product quality. In addition, resources can be conserved, and functioning closed-loop systems can be integrated into foundry processes.

Differential thermal analysis (DTA) was used to examine the effect of the particle size and morphology of Co₃O₄ on its thermal response under exposure to 1 % CH₄. The DTA response results from the catalytic oxidation of methane. Co₃O₄ samples differing in particle size and morphology were produced by ball milling or were synthesized. The investigations performed with temperatures between 250 and 450 °C reveal that both particle size and shape have a considerable effect on thermal response.

The estimation of the six-degree-of-freedom position and orientation of an end effector is of high interest in industrial robotics. High precision and data rates are important requirements when choosing an adequate measurement system. In this work, a six-degree-of-freedom pose estimation setup based on laser multilateration is described together with the measurement principle and self-calibration strategies used in this setup. In an experimental setup, data rates of 200 Hz are achieved.

The dose rate and spectral distribution of X-ray emissions from laser materials processing have been determined using a thermoluminescence detector (TLD)-based spectrometer. The penetration depth of the radiation into the spectrometer depends on its energy, so that the energy-resolved spectrum of the radiation can be calculated from the TLD dose values by means of mathematical methods (Bayesian deconvolution). The measurements are traceable to the SI.

The selective catalytic reduction, an after-treatment method using diesel exhaust fluid (AdBlue), is needed to reduce the emissions of diesel combustion processes. It is crucial to monitor the diesel exhaust fluid. This article presents a platinum thin-film sensor using the 3-omega method to characterize the diesel exhaust fluid. The information about the concentration of urea in water can be extracted. The results show that this sensor can determine the urea content to within 1 % by weight.

Effective from 20 May 2019, the kilogram is now defined in terms of the numerical value of the Planck constant h. Replacing the artefact definition of the kilogram by a new one based on the mass of a particle, or the atomic mass constant m_u, would have been preferable for ease of understanding, among other reasons. In this paper we will discuss some educational limitations of teaching to different audiences the new definition and corresponding realizations of the kilogram.

The new concept of a unified pH scale can be used to compare acidities of different kinds of solvents and their mixtures. The aim of the work was to investigate the robustness of the measurement method with four commercially available glass electrodes for non-aqueous media in comparison with the rather specific type of cell used so far for this measurement. The measurement results in aqueous mixtures of ethanol show good agreement.

The necessity to measure harmonic emissions between 2 and 150 kHz is outlined by several standard committees and electrical utilities. This paper presents a measurement system and its traceable characterization designed to acquire and analyze voltages up to 230 V and currents up to 100 A with harmonics up to 150 kHz that may occur in smart grids. The uncertainty estimation is carried out and described in detail for both the fundamental and suprahmarmonics components.

In this paper, we present a tactile sensor based on the interaction of coils with a magnetic elastomer. The first experimental approach is sampling the sensor with indentations of constant depth at different positions. A mathematical model is used to reproduce the data. Afterwards, this model is applied to random indentations at the same depth. As a result, we provide conceptual proof for position determination in one direction as a basis for a refined sensor design and further model approaches.

Deep learning has become a state-of-the-art method in machine learning, with a broad range of successful applications. Our goal is to explore the benefits of deep learning techniques for computational optical form measurements. The research is based on solving a nonlinear inverse problem aimed at the reconstruction of optical topographies from given processed interferograms. A U-Net network structure is chosen and tested on a simulated database. The obtained results are promising.