Fully-digital impedance bridges are emerging as measuring instruments for primary electrical impedance metrology and the realization of impedance units and scales. This paper presents a comprehensive analysis of electronic fully-digital impedance bridges, for both generating (based on digital-toanalog converters) and digitizing (based on analog-to-digital converters) bridges. The sources of measurement error are analyzed in detail and expressed by explicit mathematical formulæ ready to be applied to the specific bridge and measurement case of interest. The same can be employed also as a basis to optimize the design and the operating parameters of digital bridges, and to evaluate the measurement uncertainty. A practical application of the analysis to the digital bridges developed and measurements performed in the framework of an international research project is presented.

Interesting alternatives to expensive biodegradable polymers are their composites with natural fillers. The addition of biochar to a blend of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) was studied, and the resulting materials were evaluated for their properties and changes during degradation. Introducing biochar as a filler brought a noticeable improvement in electrostatic properties. Surface resistivity decreased from 3.80 × 10¹² for the sample without biochar to 1.32 × 10¹² for the sample with 30% filler content. Degradation tests revealed distinct differences in the degradation profile for composites due to the presence of filler. Composites with a lower biochar content displayed curling crack edges during hydrolytic degradation, and when the filler content reached 20 wt%, PLA loss accelerated. This study suggests that biochar-based composites have potential to be used as sustainable materials with improved properties.

Issues related to measurements of the complex ratio of two sinusoidal voltages based on digital sampling are considered in this article. Several algorithms for determination of the complex voltage ratio are discussed. Results of five algorithms are compared and minimizing their errors related to differences between the two sampling channels is examined. For verification, a sampling system with National Instruments PXI 4461 data acquisition module (DAQm) was used.

Results of investigations of selected highly stable wideband AC sources to be used in AC-DC transfer systems in the frequency range from 1 MHz to 10 MHz are presented in the paper. The most stable sources were pointed out and tested. Moreover, impact of the RF amplifier on the stability of the generated AC voltage was checked and discussed. Finally AC-DC transfer difference measurements were performed with and without an RF amplifier to prove its usefulness in the high-frequency AC-DC transfer.