Acta IMEKO

Characterization of high-reflectance diffuse coatings for 3D-printed optics

2026-03-23T10:25:22+00:00

Low-cost diffuse reflectance coatings were characterized for use on 3D-printed optical assemblies. Barium sulfate (BaSO₄) and titanium dioxide (TiO₂) suspensions were deposited on polylactic acid (PLA) substrates through a multilayer drop-casting process with an acrylic binder, and compared to commercial white paints and Spectralon® standards. Hemispherical reflectance was measured using an integrating sphere over the 300 nm to 1000 nm range, while angular scattering was assessed from −85° to 85° using a collimated xenon source. BaSO₄ achieved the highest broadband performance, with a mean hemispherical reflectance of 98.9 % and a mean angular deviation of 6.3 % from the ideal cosine law. TiO₂ showed slightly lower reflectance (96.6 %) and stronger angular directionality, consistent with its smoother and glossier surface finish. Commercial acrylic coatings exhibited markedly lower reflectance (70 % to 86 %) and large deviations from cosine behaviour, while office paper provided good diffusivity but insufficient spectral uniformity. The results demonstrate that a simple BaSO₄-based coating can deliver stable, broadband, and highly diffuse reflectance when applied to 3D-printed substrates, enabling the fabrication of low-cost optical diffusers and reflectance references for custom laboratory setups.

On the effectiveness of the Meteorological Optical Range for representing visibility as perceived by human drivers and by ADAS employing visible cameras

2026-03-17T19:59:19+00:00

Adverse weather conditions continue to present a significant challenge for Advanced Driver Assistance Systems (ADAS). Quantification of visibility in fog is typically accomplished by measuring the Meteorological Optical Range (MOR). Despite the MOR's extensive recognition and utilisation across diverse domains, including aviation, navigation, and traffic management, there exists a potential discrepancy between the visibility estimated using the MOR, i.e. the optical path length in the atmosphere necessary to diminish the luminous flux of a collimated beam to 5 percent of its original value, and that actually perceived by drivers or camera-based ADAS systems operating within the visible range. Indeed, the anisotropy of the scattering generated by fog particles, in conjunction with the fact that, in the automotive sector, visibility is generally supported by the headlights and street lighting, can lead to phenomena not considered by the MOR. The present study proposes a measurement method and setup for investigating the degree to which visibility estimated exploiting the MOR represents the visibility perceived by drivers or camera-based ADAS systems. The experimental findings indicate that the lighting angle can substantially influence visibility. Thus, the study will propose a simplified analysis to identify the primary contributors to this discrepancy.

A comparative analysis of reactive power/energy measuring algorithms in non-sinusoidal conditions by using the fundamental reactive power as a reference

2026-04-21T20:09:28+00:00

The measurement of reactive power and energy in harmonically distorted conditions is accompanied with multiple challenges. In the first place, there is the ambiguous definition of these quantities, when the systems’ signals lack sinusoidal waveforms. The international standard IEEE 1459 addresses this by emphasizing the need to measure fundamental frequency power components only, even in harmonically polluted environments. Another complication arises because of different measuring algorithms implemented in the modern meters. Although these algorithms provide consistent results for ideal sinusoidal waveforms, the instruments’ recordings may diverge significantly when distortion is present. In this work, the readings of different, commercially available, reactive power/energy instruments in harmonically distorted conditions will be experimentally verified. In the primary experiment, the meters’ outputs are going to be analyzed against the fundamental reactive power as a reference quantity, in accordance with IEEE 1459. Later on, a mutual inter-comparison between different algorithm-based instruments will be conducted, as a contribution to the perspective of an unbroken traceability chain establishment in the domain of reactive power and energy in non-sinusoidal conditions. In order to ensure a high metrological accuracy, reference standards of the highest accuracy class available, traceable to BIPM intrinsic standards, are implemented.

Integration of Monte Carlo simulation for uncertainty evaluation into intra-laboratory comparison for reference standards consistency assessment

2026-04-09T14:37:42+00:00

Accredited calibration and test laboratories are required to participate periodically in inter-laboratory comparisons and proficiency testing schemes, as part of their quality assurance procedures, for ensuring the validity of the data, which is provided to their clients. In this paper, an intra-laboratory comparison, as an additional tool for quality assurance, is presented. The proposed concept is practically realized in an accredited calibration laboratory for electrical quantities instruments, in the domain of high-resistance reproduction and measurements. Reference standards of the highest accuracy class available, which are traceable to BIPM intrinsic standards through different national metrology institutes, are used, covering the range above 100 MΩ. A methodology for the calculation of the criterion, in accordance with the ISO/IEC 17043 guidelines, is deployed. The measurement uncertainty is evaluated according to the principles presented in the Guide to the expression of uncertainty in measurement (GUM), as well as by using the Monte Carlo simulation concept of distribution propagation. By regarding the different principles for resistance measurement, implemented in the selected instrumentation and the two methods for uncertainty calculation, this intra-laboratory comparison offers a quantitative assessment of the consistency and reliability of the selected reference standards, thereby enhancing confidence and credibility of the measurement results provided by the laboratory.