A. Jeglic

Terahertz spectroscopic identification of explosive and drug simulants concealed by various hiding techniques.

Terahertz time-domain spectroscopy and imaging is used to study the effects of various hiding techniques of spectral features of drug and explosive simulants in combination with different paper and textile barriers. Results show that rapid detection and identification of concealed simulants is possible in the frequency range from 1.5 to 4.0 THz by using an organic-crystal-based terahertz time-domain system and the spectral peak analysis method.

Applications of Terahertz Spectroscopy in the Field of Construction and Building Materials

Abstract: In last two decades, rapid development in the field of terahertz (THz) technology has opened new possibilities for creating innovative imaging and sensing systems. Although the applications of THz technology in different sectors constantly increase, the construction industry lags behind them. The aim of this article is to review the current applications of THz spectroscopy in research and industry related to construction and building materials, along with the key drawbacks of technology and recommendations for future use. The review concludes that THz spectroscopy and imaging have promising potential and provide many opportunities for applications in construction and building materials characterization.

A learning algorithm for self-calibration of a voltage calibrator

An algorithm either to extend the calibration period or to reduce the measurement uncertainty of a DC voltage reference module is presented. This module is used either as a transfer, independent, or working standard, or as a reference module incorporated into a larger measuring system. The basic idea is that the deviation history of measured voltage differences of reference elements of a group reference module during the calibration period can be used as a learning period for a neural network. This neural network, when created, can numerically correct particular reference elements later in the working period. Results were obtained by simulation and evaluated on the basis of empirical data and simulated input functions. Hardware solutions to model this algorithm are discussed. >

Qualitative and quantitative analysis of calcium-based microfillers using terahertz spectroscopy and imaging

In different industrial applications, several strictly defined parameters of calcium-based microfillers such as average particle size, particle size distribution, morphology, specific surface area, polymorphism and chemical purity, play a key role in the determination of its usefulness and effectiveness. Therefore, an analytical tool is required for rapid and non-destructive characterization of calcium-based microfillers during the synthesis process or before its use in a further manufacturing process. Since spectroscopic techniques are preferred over microscopy and thermogravimetry, particularly due to its non-destructive nature and short analysis time, we applied terahertz (THz) spectroscopy to analyse calcite microfillers concentration in polymer matrix, its granulation and chemical treatment. Based on the analysis of peak absorbance amplitude, peak frequency position, and the appearance of additional spectral features, quantitative and qualitative analysis was successfully achieved. In addition, THz imaging was also applied for both quantitative and qualitative analysis of calcium-based microfillers. By using spatial distribution map, the inhomogeneity in concentration of calcium carbonate in polymer matrix was characterized. Moreover, by THz spectroscopy and imaging different calcium compounds were detected in binary mixtures. Finally, we demonstrated that the applied spectroscopic technique offers valuable results and can be, in combination with other spectroscopic and microscopic techniques, converted to a powerful rapid analytical tool.

An adaptive internal calibration of a voltage calibrator

An algorithm for adaptive internal calibration of a precision voltage calibrator is discussed. Due to the built-in metrology organization and real-time data processing of measurement results, improved traceability is obtained. An evaluation of internal calibration results indicates that a learning control algorithm is feasible, thus extending the normal calibration recall cycle. >

Case study of the predictive models used for improvement of the stability of the DC voltage reference source

The aim of this paper is to present a non-typical application of predictive models for voltage correction in a high precision solid-state DC voltage reference source (DCVRS). Several types of neural networks are trained until the correlation dimension and the leading Lyapunov exponent of the predicted signals reach the values of the same invariant measures of the original signals. The predictive models are used as a segment in the software controlled VRE. A control loop is implemented to reduce the sensitivity of the reference source which contributes to enhancement of the robustness of the system and thereby the stability of the reference voltage.

Low-distortion audio-frequency AC reference standard with AC-DC output switching capability

A digital AC voltage standard with well-known AC-to-DC output voltage difference is described. The proposed feedback configuration can effectively measure and correct for loading effects, caused by a measuring device. Because the AC standard can generate AC and DC voltages at the same output terminals, the automatic measuring setup for thermal voltage converters (TVC) is considerably simplified. The state-of-the-art stability of output voltage enables it to be used for intercomparison purposes. >

Case study of the predictive models used for stability improvement of the DC voltage reference source

The aim of this paper is to present a a typical application of predictive models for voltage correction in a high-precision solid-state DC voltage reference source (DCVRS). Several types of neural networks are trained until the invariant measures of dynamics, such as correlation dimension and leading Lyapunov exponent of the predicted signals, reach the values of the same invariant measures of the original signals. The predictive models are used as a segment in the software-controlled voltage reference element (VRE). A control loop is implemented to reduce the interference sensitivity of the reference source which contributes to enhancement of the robustness of the system and thereby the stability of the reference voltage.

Industrial experience with an intelligent AC/DC standard

An intelligent AC/DC voltage standard has been constructed to meet stringent demands for calibration in laboratories as well as in demanding industrial environments. The use of a microcomputer MC enables programmable output parameters, storage of calibration constants, and integration into a complex measuring and testing system. Stability of AC and DC parameters, reliability of operation, and reliability of metrological parameters were achieved by real-time data processing. The prototype exhibited the following characteristics: an output frequency range from 30 to 400 Hz with a resolution of 1 Hz, four voltage ranges from 0.1 to 1000 V with 12-bit resolution, and output power of 50 V.A with limitations of output voltage U/sub max/=1000 V/sub RMS/ and output current I/sub max/=5 A/sub RMS/. >

Evaluation of an alternatively designed digital phase angle standard

A phase reference source, that uses a direct digital frequency synthesizer as a digital sine sample generator was designed and a prototype was built. The paper explains how the experimental verification of the findings that were previously obtained via theoretical analysis and computer simulations was performed on the prototype. The output phase angle deviations are under investigation, especially the circumstances at which they occur. Some preliminary measurement results are presented that confirm the previously gained knowledge regarding the dependencies of the phase modulation intensity.