Miroslav Lunak

Tracing of Concrete Hydration by Means of Impedance Spectroscopy (New Tool for Building Elements Testing)

Concrete setting and hardening designate the concrete grade. The impedance spectroscopy method, as one of the non-destructive testing method group, was used to characterize concrete specimens and track the changes in the concrete spectrum. Variances in the tan δ (f) and Im Z(f) or Re Z(f) of the specimens under investigation have been observed. The specimen quality has been described by means of the loss type prevailing in the material. The results of this study are expected to provide information about the correlation between the n-factor and the concrete setting time.

Comparison of Impedance Spectra of Concrete Recorded with Utilizing Carbon Transition Paste

NDT method of impedance spectroscopy was used to characterize concrete slab specimens without and with contact graphite compound coating. Differences in tanδ(f), ImZ(f) and ReZ(f) spectra for dry specimens were observed. Furthermore, based on the predominant loss type, the material quality was characterized. Our measurements confirmed the reproducibility of this method. Furthermore, the influence of the concrete specimen composition on their electric parameters was assessed.

Dielectric Properties of Concrete Specimens after Heat Stress

Concrete quality depends on various stress factors. The impedance spectroscopy method, as one of the non-destructive testing method group, was used to characterize concrete specimens and track the changes in the concrete spectrum after heat stress. The temperature range was between 0°C and 1200°C. Variances in the tan δ (f) and Im Z(f) or Re Z(f) of the specimens under investigation have been observed. The specimen quality has been described by means of the loss type prevailing in the material. The results of this study are expected to provide information about the correlation between the relative permittivity and changes in the structure for heat stress samples.

Low-frequency noise, microplasma, and electroluminescence measurements as faster tools to investigate quality of monocrystalline-silicon solar cells

Abstract. Two sets of c-Si solar cells varying in front side phosphorus doped emitters were produced by standard screen printing techniques. The first group of samples, 3121, was prepared by a combination of standard washing and a bath with a highly dilute HF before diffusion of n+-emitter. The second group of samples, 3122, was treated only with standard washing. A comparison of solar cell conversion efficiency and results from a noise spectroscopy, microplasma, and electroluminescence presence are presented. As was already shown in previous publications noise spectral density reflects the quality of solar cells, and thus represents an alternative advanced cell diagnostic tool. Our results confirm this relationship and moreover bring clear evidence for the maximum spectral noise voltage density being related to the emitter structure. The best results were reached for the group of solar cells in sample 3122, which was treated only with standard washing.

Noise as characterization for GaSb-based laser diodes prepared by molecular beam epitaxy

A non-destructive method of reliability prediction for PN junction microelectronic devices is presented. Transport and noise characteristic of forward biased semiconductor lasers diodes GaSb based VCSE (Vertical Cavity Surface Emitting) lasers were prepared by Molecular Beam Epitaxy were measured in order to evaluate the new MBE technology.

Influence of Carbon Admixtures to the Electrical Conductivity of Slag Mortars

Applied research tries to offer new materials from the slag mortars. Basic research tries to explore these engineered materials from the perspective of all the possible test methods. Modern vector analyzer R&S ZNC with a coaxial probe DAK-12 from Speag company was used to determine permittivity and dielectric loss factor of the beams and interesting spectrums of electric resistance were measured for samples with varying content of carbon powder. Carbon contributes from the viewpoint of electrical properties, for example it improved antistatic properties of the floor. In addition to the vector analyzer – the simpler measuring unit was also used. In a frequency range of 40 Hz to 1 MHz values of electrical resistance and permittivity values of the beams with different content of graphite powder, labeled Cond 896 were determined. The higher content of graphite powder increases the electrical conductivity; building materials based on cement are becoming more measurable using electromagnetic measuring methods. The most striking change in the relative conductivity was observed at excitation frequency of the external electric field of 1 kHz. At high frequencies of electrical excitation field from 10 MHz to 3 GHz values of the real part of permittivity were determined by vector analyzer. These measurements are among the building materials used rarely and they open new possibilities of diagnostics.

Modern Electrical Measurement of Alkali Activated Slag Mortars with Increased Electrical Conductivity

Slag mortars belong to the new promising alternative construction materials. Conventional cementitious materials are harder to measure by electrical test methods. It is being researched if the dopant atoms in the form of powder improve the mechanical properties. This article describes how the test slag mortars with addition of carbon by electrical impedance spectroscopy measurement methods and their extensions in the form of using ZNC vector analyzer with a coaxial probe from Speag. Impedance spectra of samples were obtained in the 40 Hz to 1 MHz. Declines of impedance by adding more carbon were expected and confirmed. Electrical conductivity and permittivity were measured by vector analyzer for the 100 MHz to 3 GHz. The permittivity was varied from 4 to 20, depending on the addition of carbon, the conductivity of the samples from 1/2600 to 0.3 S·m-1.

Quality assessment of GaAs laser diodes with InAs quantum dots layer by low-frequency noise measurements

This paper deals with comparisons of noise spectroscopy and I-V characteristic of semiconductor lasers diodes GaAs with InAs quantum dots layer. We studied two groups with different technologies (A and B). Each group had 4 samples. The samples were quality screened using noise analysis. From the measurement results it follows that the noise spectral density related to defects is of 1/f or and can by use as a quality indicator.

Non-Destructive Tracking of Structural Changes of Concrete Mixtures during Thermal Stress

This paper deals with the application of the method of impedance spectroscopy to testing of cement-based composites prepared from a mix of cement mortar and quartz sand, which were intentionally degraded by high-temperature treatment (in the temperatures range from 25 °C to 400 °C). The monitoring of structural changes in the thermal stress is very important, for example for determining the reliability of the whole structure. Based on the Debye theory of dielectric the models were created, their applications and received parameters measured dielectric material is characterized and discussed the uniqueness of determining the values of model parameters. Development of electrical parameters and permittivity at each temperature areas reliably show these structural changes and thus the structural reliability.

Thermal Stress of Building Materials Containing Plasticizer Characterised by Alternating Electric Field

Paper deals with the applicability of impedance spectroscopy method to testing of cement-based composites prepared from a mix of type CEM I cement and siliceous sand, as well as by substituting 25 % of sand with shredded automobile tires and by adding acrylic polymer binder (10 % w/w of the polymer mass to cement mass). The monitoring of structural changes in the thermal stress is very important, for example for determining the reliability of the whole structure. Samples were intentionally degraded by high-temperature (in a temperature range from 25 °C to 400 °C). The primary monitored magnitudes were electrical capacitance C, the relative permittivity εr and components of electric impedance |Z|. Based on the Debye theory of dielectric the models were created, their applications and received parameters measured dielectric material is characterized and discussed the uniqueness of determining the values of model parameters. Development of electrical parameters and permittivity at each temperature areas reliably show thus structural changes and thus the structural reliability.