This paper describes the possibility of estimating the apparent power of a signal component using the interpolation of the products of amplitude discrete Fourier transform (DFT) coefficients. As with energy-based approach for the amplitude square estimation of the onechannel signal, the apparent power in the two-channel case can be estimated with the multiplied amplitude DFT coefficients around the component peak and a suitable interpolation algorithm. The use of the Hann window with well known frequency spectrum and the largest local amplitude DFT coefficients give lower systematic errors than the energy-based approach, although the frequency has to be estimated first.

This paper describes the recent improvements in the use of gene expression programming and genetic algorithms in impedance spectroscopy, namely in sensor modelling. Insight is given in the inner workings of the gene expression programming while highlighting the proposed improvements. The performance of the improved algorithm is also analyzed. It is further validated by the successful application to measurements of a real sensor.

The problem of the evaluation of the interference to signalling track circuits is considered and the specifications appearing in the recently issued European standard discussed. A broad class of track circuits is simulated by means of a band-pass filter and the focus is on the uncertainty related to its implementation.

The global positioning system (GPS) is a Global Navigation Satellite System (GNSS) uses a constellation of between 24 and 32 Medium Earth Orbit satellites that transmit precise microwave signals, which enable GPS receivers to determine their current location, the time, and their velocity. Initially, the GPS was developed for military applications, but very quickly became the most used technology in positioning even for end-user applications run by individuals with no technical skills. GPS reading are used also as reference points for many positioning techniques such as the techniques that depend on the transmitted electromagnetic signal to determine the position of the transmitter or the receiver, due to their superior accuracy comparing to such techniques. But how accurate are those readings, and how to obtain accurate reference points starting from raw GPS observations even when they are corrupted with errors.
In this paper, a practical study about GPS positioning is provided. Generating the ground-truth reference points depending on GPS observations is also provided and discussed in details.

The usage of eddy current probes including single magnetic field sensor represents a common solution for defect detection in conductive specimens but it is a time consuming procedure when large surface specimens are tested. In order to speed-up the nondestructive testing procedure, eddy current probes including a single excitation coil and an array of detection coils represent one of the solutions to reduce the NDT times but mainly detects the surface defects. Deep defects require different sensing elements such as GMRs. In this work an optimized uniform eddy current probe architecture including two planar excitation coils, a rectangular magnetic field biasing coil and a GMR magnetometer sensor array is presented. An ac current is applied to the planar spiral rectangular coil of the probe, while a set of GMR magnetometer sensors detects the induced magnetic field in the specimens under test. The rectangular coil provides the dc uniform magnetic field assuring appropriate biasing of the GMR magnetometers of the probe, setting-up the functioning point on the linear region and at the same branch of GMR static characteristics. The differences of the images obtained on the same specimen surface for each GMR are reduced if all sensors are biased on the same working point. Elements of automated measurement system for NDT, including a validation procedure based on a 2D template matching algorithm and the corresponding experimental results are included in the paper.