Special issue  

The paper shows how the precise knowledge of the sound field of an ultrasonic annular array can contribute to the development of novel measurement techniques. It demonstrates the locally resolved measurement of sound velocity in fluids, simultaneous measurement of thickness, sound velocity of layers and curvature. To demonstrate the methods, the principles as well as results of simulations and measurements are discussed.

This paper presents a novel method for the detection of sensor defects. Here, the consistency between measurements of sensor groups are utilized for this method. The sensor groups are pre-determined by the structure of an existing sensor fusion algorithm, which is in turn used to determine the health of a monitored system (e.g. a machine). Defect detection results of the presented method for different test cases and the method's capability to detect a number of typical sensor defects are shown.

This paper addresses the development of flow sensors optimised for heating, ventilating, and air conditioning systems. The sensors are based on the printed circuit board technology facilitating robust, flexible (in terms of layout), and cost-effective devices. Two approaches for measuring fluid quantities are investigated in this context and several sensor embodiments were investigated and fabricated. After experimental characterisation, measurement and simulation results were compared.

We present a non-destructive method to determine the material properties, for example elastic constants, of metal and polymer plates using laser-generated ultrasound. The ultrasonic signals are detected using an ultrasonic transducer that shows high sensitivity over a wide rage of frequencies. A method of signal processing to determine material properties is described and can be expanded upon to characterize more complex samples, such as fibre reinforced composites.

Metamaterials are artificial composite structures with unusual physical properties such as the perfect absorption of light, which can be exploited to improve the spectral sensitivity and selectivity of thermal detectors. The desired detector characteristics are engineered by tuning the absorption properties of metamaterials. The numerical simulations demonstrate polarization-independent absorption of disc-shaped dielectric/metallic absorbers and their integration capability in thermal detectors.

Piezoelectric devices are characterized non-destructively to ensure their functionality. The material is heated by laser diodes. The resulting temperature changes lead to a pyroelectric current. Analytical and numerical finite element models describe the temperature distribution and the current in frequency and time domain. Modelling and experimental results are compared for piezoelectric plates and integrated sensors and actuators.

For the application of indoor air quality monitoring, two types of tungsten oxide gas sensor layers were prepared via pulsed laser deposition. Analysis of the structure of the produced layers showed that they consist of nanoparticles and agglomerates of nanoparticles. The sensors showed significant sensitivity and selectivity towards naphthalene in the ppb concentration range. The results were achieved using temperature cycled operation of the sensors and pattern recognition signal treatment.

The interaction of sound and flow enables an efficient noise damping. Understanding this aeroacoustic damping phenomenon requires simultaneous measurement of flow and sound fields. Using a high-speed CMOS camera, two-component flow velocity measurements are performed in a three-dimensional region of interest. The sensor system can simultaneously capture sound and turbulent flow velocity oscillations. The presented measurements reveal that the sound energy is transferred into flow energy.

Hydrogels are swellable polymers, which exhibit superior sensor properties. However, the exploitation of these properties for innovative measurement technology has been prevented by the lack of a manufacturing technique for thin hydogel films that suits industrial needs. We suggest a paradigm change from the current recipe-driven sensor manufacturing to a specification-driven one. Our contributions are optimized processes for a controllable film formation and thermal curing of the hydrogels.

Tracer gas experiments demonstrate possible pathways of toxic gas propagation, especially in subsurface infrastructures like subway stations. Precise gas sensors are needed to record the concentration levels over time; thereby, a better understanding of how smoke or toxic gas affected evacuation routes can be achieved. The acquired knowledge can be used to optimize evacuation and reaction plans and might reduce the casualties in catastrophic circumstances.

The aim of this paper is to discuss different models that describe atmospheric transmission in the infrared. They were compared in order to choose the most appropriate one for certain atmospheric conditions. Universal models and different inaccuracies connected with them were analysed in this paper. There have been models analysed from the literature, and these are used in infrared cameras.

Infrared cameras based on microbolometer focal plane arrays (FPAs) are the most widely used cameras in thermography. For acceptable measurement uncertainty values, the disturbing influences of changing ambient temperature have to be considered. We propose a TEC-less and shutter-less correction approach based on additional temperature measurements inside the IR camera. The effects on the pixel responsivity and offset voltage are considered separately.

This article describes a new qualification concept for dimensional measurements on optical measuring systems, using the example of a prototypical multi-scale multi-sensor fringe projection system for production-related inspections of sheet-bulk metal-formed parts. A new concept is developed for determining the orientations and positions of the sensors' measuring ranges in a common coordinate system. The principle element of the concept is a newly developed flexible reference artefact.

We study the effect of HMDSO vapor on an SnO2-based gas sensor in temperature cycled operation (TCO). The poisoning can be quantified at early stages with a resolution of ±85 ppm*min using TCO. This approach provides a simple method for early detection of HMDSO poisoning. The stability of gas discrimination by linear discriminant analysis (LDA) can be improved using normalization, which in turn facilitates a more accurate determination of the poisoning state by hierarchical LDA discrimination.

A highly sensitive spectral camera for the judgement of cartilage quality, grown in a bioreactor using the methods of tissue engineering, is being developed. It is optimized to detect weak fluorescence signals of different collagen types, elastin and glycosaminoglycans in the spectral region of 380nm to 500nm. Tests with a one- and a two-dimensional version of the system prove that collagen I and II can be detected and discriminated by their different spectral distributions.

The effect of stored ammonia on the complex dielectric permittivity of H-ZSM-5 zeolites with varying storage site density was observed between 200 and 300 °C under reaction conditions by microwave cavity perturbation. Polarization and dielectric losses were differently affected. The sensitivity of the polarization to stored ammonia is almost independent, the sensitivity of the dielectric losses strongly dependent on the storage site density. The results can be explained by proton hopping.

A novel microwave-based approach for monitoring the state of aftertreatment systems such as diesel particulate filters (DPFs), three-way catalytic converters (TWCs), and selective catalytic reduction (SCR) catalysts is proposed. The interior of the catalyst metal housing serves as a communication channel between two wireless communication nodes. It is shown that, depending on the transmission channel characteristics, the properties of the catalyst, such as the catalyst state, can be inferred.