Ladislav Polak

This paper presents the design of a passive fractional-order element with tunable pseudocapacitance, enabling adaptable circuit behavior without additional power consumption. This is an important feature for modelling and characterization in natural systems, as well as in the field of electrical and electronic engineering, particularly for the design of instrumentation and sensing systems. The proposed topologies are based on integrated unipolar transistor arrays. Two implementations are demonstrated, with fractional orders of 0.22 and 0.5, offering pseudocapacitance adjustment ranges from 65 to 1 670 mikroF/s^0.78 and from 6.7 to 51 mikroF/s^0.5, respectively. Tuning is achieved through a DC bias voltage ranging from 0.8 to 10 V. The devices operate across nearly two decades of frequency, from approximately 100 Hz to 200 kHz, and support signal amplitudes in the hundreds of millivolts. Two application examples highlight their potential: electronic tuning of the center frequency in a fractional-order band-pass filter, and adjustment of the oscillation frequency in a fractional-order oscillator with a fixed 22.5 degrees phase shift between output waves. All concepts and results are experimentally validated in the laboratory.

Cerebrovascular diseases are a leading cause of global mortality, underscoring the need for objective and quantitative 3D visualization of cerebral vasculature from dynamic imaging modalities. Conventional analysis is often labor-intensive, subjective, and prone to errors due to image noise and subtraction artifacts. This study tackles the challenge of achieving fast and accurate volumetric reconstruction from angiography sequences. We propose a multi-stage pipeline that begins with image restoration to enhance input quality, followed by neural segmentation to extract vascular structures. Camera poses and sparse geometry are estimated through Structure-from-Motion, and these reconstructions are refined by leveraging the segmentation maps to isolate vessel-specific features. The resulting data are then used to initialize and optimize a 3D Gaussian Splatting model, enabling anatomically precise representation of cerebral vasculature. The integration of deep neural segmentation priors with explicit geometric initialization yields highly detailed 3D reconstructions of cerebral angiography. The resulting models leverage the computational efficiency of 3D Gaussian Splatting, achieving near-real-time rendering performance competitive with state-of-the-art reconstruction methods. The segmentation of brain vessels using nnU-Net and our trained model achieved an accuracy of 84.21%, highlighting the improvement in the performance of the proposed approach. Overall, our pipeline significantly improves both the efficiency and accuracy of volumetric cerebral vasculature reconstruction, providing a robust foundation for quantitative clinical analysis and enhanced guidance during endovascular procedures.

This paper introduces Quality Fusion of Compressed Omnidirectional Images (QFCOI), an enhanced objective quality assessment method for compressed 360° images. QFCOI integrates linear fusion of feature metrics. Established conventional state-of-the-art measures were analyzed to select specific ones for effective fusion and to mitigate eventual overfitting. The feature metrics selection was based on statistical performance and ability to capture key aspects of image quality, including structural preservation, visual information fidelity, and artifact sensitivity. To optimize predictive performance of QFCOI, a genetic algorithm was utilized to determine optimal weight coefficients, maximizing the monotonic correlation with subjective quality scores. The QFCOI performance was validated through correlation coefficients, statistical significance testing, and Receiver Operating Characteristic (ROC) analyses. Results confirmed that QFCOI outperformed other conventional metrics, achieving the highest performance on the OMNIQAD dataset across multiple emerging compression algorithms, including High Efficiency Image File Format (HEIC), Joint Photographic Experts Group XL (JPEG XL), and AV1 Image File Format (AVIF). Further, validation on the relevant public CVIQ dataset for HEIC-compressed images confirmed the robustness of QFCOI, and the method modification on only 25% of the data, achieved the best performance on the CVIQ dataset. These results highlight the generalization properties and versatility of QFCOI. In contrast to learning-based models, the proposed method offers a transparent and interpretable alternative while achieving high accuracy and statistical reliability in objective quality assessment.

This paper introduces a novel unified second-order filtering topology for standard band-reject and inverting band-reject filtering, enabling selective response generation. It is applied in the design of special comb filters that allow attenuation as well as amplification of specific bands. The presented solution offers several advantageous features in topology, enhanced cascadability, better parameter-setting performance, and the use of readily available off-the-shelf components, all while reducing overall costs. This is a significant improvement compared to the previous solutions in this field, which relied on a very expensive CMOS process. The topology employs a combination of an operational transconductance amplifier and a current feedback amplifier. The intended center frequencies and transfer values of the comb filter are set to 50 Hz (−20 dB), 1 kHz (+26 dB), 10 kHz (+17 dB), and 100 kHz (−30 dB). The comb filter was experimentally verified via simulations as well as laboratory measurements utilizing LT1228 devices in a fabricated prototype.

This paper presents a unique study of objective and subjective image quality assessment (IQA) of 360º images, distorted by emerging and legacy compressions - AV1 Image File Format (AVIF), Joint Photographic Experts Group (JPEG), High Efficiency Image File Format (HEIC), JPEG XL from the cross-lab experiments carried out by two universities. The performance evaluation of objective conventional IQA methods relied on statistical data analysis employing not only traditional approaches with correlation coefficients but also advanced techniques such as Receiver Operating Characteristic (ROC) analysis, which offers several statistical advantages. The comprehensive statistical examination presented, utilizing an outcome from the subjective experiment with 66 observers, confirmed that the performance of specific IQA metrics depends not only on the image features but also on the applied image compression algorithm. Overall, the study examined nine IQA objective metrics. For instance, when evaluating distortion caused by the AVIF and HEIC codecs, the Multi-Scale Structural Similarity (MS-SSIM) metric exhibited the best performance , while the Feature Similarity chrominance (FSIMc) metric excelled in assessing JPEG-based compressions. Additionally, detailed outcomes of the subjective experiments, including eye-tracking data, are available in a public dataset. This study provides previously unexplored insights into the performance of conventional objective metrics for 360º images degraded by emerging image codecs. The presented results suggest suitable metrics for specific application scenarios (codecs) and, along with the dataset, lay the groundwork for further research on new objective quality assessment methods for omnidirectional images under emerging compressions.

Phase-Locked Loops (PLLs) are versatile electronic circuits that, among others, are used in various sensor applications (e.g., medical) for their ability to generate stable and precise clock signals. This paper introduces a novel PLL-based frequency demodulation system designed for processing very slow signals, ranging from a few Hz to several hundreds of Hz, with amplitudes in the order of several hundreds of millivolts. The system incorporates specialized analog multipliers tailored for essential PLL components, including the voltage-controlled oscillator, phase detector, loop filter with variable DC offset, and base-band filter, all optimized for the purpose of frequency demodulation. These multipliers were fabricated using the TSMC 0.18 μm, 1.8V CMOS process. The primary design objectives are simplicity, reduced complexity, low power consumption (merely 15 mW), and versatility for applications in sensing engineering. To validate the functionality of the proposed PLL system under practical conditions, we present an example of electrocardiogram signal demodulation, demonstrating its operational performance.

With the expansion of wireless mobile networks into both the daily lives of individuals as well as into the widely developing market of connected devices, communication is an increasingly attractive target for attackers. As the complexity of mobile cellular systems grows and the respective countermeasures are implemented to secure data transmissions, the attacks have become increasingly sophisticated on the one hand, but at the same time the system complexity can open up expanded opportunities for security and privacy breaches. After an in-depth summary of possible entry points to attacks to mobile networks, this paper first briefly reviews the basic principles of the physical layer implementation of 4G/5G systems, then gives an overview of possible attacks from a physical layer perspective. It also provides an overview of the software frameworks and hardware tool-software defined radios currently in use for experimenting with 4G/5G mobile networks, and it discusses their basic capabilities. In the final part, the paper summarizes the currently most promising families of techniques to detect illegitimate base stations—the machine-learning-based, localization-based, and behavior-based methods.

This paper compares the analytical approach and optimization algorithm for designing a two-bilinear-section-based two-port transfer function hinged on a numerical sweep with the intention of implementing fractional-order (FO) systems in many sensing areas. The study compares analytical and algorithm-based design approaches and tests their effectiveness in designing a two-port system that accommodates phase shifts within the 10° to 80° range and with various phase ripple limits. The impact of phase changes on usable bandwidth (yield maximization) is also explored. The proposed algorithm represents the most optimal approach and calculates zeros/poles frequencies to precisely keep the required mean phase value and phase ripple value for the defined center frequency. Experimental results are provided, utilizing two bilinear sections featuring the current feedback amplifier. Moreover, the implementation of the novel two-port Cole model as an application example of the proposed design is presented and evaluated. The approaches presented are useful in sensing, modeling, and instrumentation.