Models of hybrid meander structures with additional shields are presented in this paper. The influence of additional shields and their grounding positions on the electromagnetic characteristics of the hybrid meander structures was investigated. Three-dimensional models were created and analyzed using the method of moments (MoM) in the Sonnet^® and finite-difference time-domain (FDTD) method in CST Microwave Studio^® commercial software packages. The computer-based modeling was verified by physical experiment. The analysis showed that it is possible to control the delay time characteristic using different values of lumped inductive elements without the need to change the overall size of the hybrid meander structure. The delay time varied by 1.2 ns in the range of 1.3 ns to 2.5 ns when the inductivity changed from 1 nH to 10 nH in our investigation. On the other hand, the passband decreased from 2.384 GHz to 0.508 GHz. The additional shields and their grounding positions allowed for increasing the passband by up to 1.6%.

Paper investigates transport control protocol (TCP) acknowledgment (ACK) optimization in low power or embedded devices to improve their performance on high-speed links by limiting the ACK rate. Today the dominant protocol for interconnecting network devices is the TCP and it has a great influence on the entire network operation if the processing power of network devices is exhausted to the processing data from the TCP stack. Therefore, on high-speed not congested networks the bottleneck is no longer the network link but low-processing power network devices. A new ACK optimization algorithm has been developed and implemented in the Linux kernel. Proposed TCP stack modification minimizes the unneeded technical expenditure from TCP flow by reducing the number of ACKs. The results of performed experiments show that TCP ACK rate limiting leads to the noticeable decrease of CPU utilization on low power devices and an increase of TCP session throughput but does not impact other TCP QoS parameters, such as session stability, flow control, connection management, congestion control or compromises link security. Therefore, more resources of the low-power network devices could be allocated for high-speed data transfer.

This study explores the practical application and impact of bioimpedance analysis in mobile devices for monitoring human health. The objective of the study is to propose a feasible application of non-invasive bioimpedance analysis by using the tetrapolar electrode connection method and the Cole–Cole model. Bioimpedance measurements and the calculation of electrical parameters are performed using ANSYS HFSS software for theoretical calculations and digital signal processing technology for real-time measurements using hardware devices. The study focuses on a model of the front arm, including tissues such as bone, fat, muscles, arteries and skin, with glucose concentrations as test cases. The simulated characteristic impedance with the ANSYS HFSS software package at 125 kHz varied from 315.8 Ω to 312.6 Ω, and the measured forearm characteristic impedance with hardware varied from 150.1 Ω to 151.3 Ω. The measured characteristic impedance when the heart is in systole and diastole also differed, with a difference of about 0.85% of the maximum impedance measured. The study demonstrates the potential of non-invasive bioimpedance analysis to address health issues such as obesity and heart disease. It also highlights its usefulness as a non-invasive alternative for measuring glucose concentration in diabetic patients to reduce the risk of infection. The findings indicate the feasibility of using bioimpedance analysis in mobile devices for health monitoring purposes.

Typically, analyses of meander structures (MSs) for transfer characteristics are conducted using specialized commercial software based on numerical methods. However, these methods can be time-consuming, particularly when a researcher is seeking to perform a preliminary study of the designed structures. This study aims to explore the application of neural networks in the design and analysis of meander structures. Three different feedforward neural network (FFNN), time delay neural network (TDNN), and convolutional neural network (CNN) techniques were investigated for the analysis and design of the meander structures in this article. The geometric dimensions or top-view images of 369 different meander structures were used for training an FFNN, TDNN, and CNN. The investigated networks were designed to predict such electrodynamic parameters as the delay time ($t_{\mathrm{d}}$), reflection coefficient ($S_{11}$), and transmission coefficient ($S_{21}$) in the 0–10 GHz frequency band. A sufficiently low mean absolute error (MAE) was achieved with all three methods for the analysis of MSs. Using an FFNN, the characteristic $t_{\mathrm{d}}$ was predicted with a $3.3$ ps average MAE. The characteristic $S_{21}$ was predicted with a $0.64$ dB average MAE, and $S_{11}$ was predicted with a $2.47$ dB average MAE. The TDNN allowed the average MAEs to be reduced to $0.9$ ps, $0.11$ dB, and $1.63$ dB, respectively. Using a CNN, the average MAEs were $27.5$ ps, $0.44$ dB, and $1.36$ dB, respectively. The use of neural networks has allowed accelerating the analysis procedure from approximately 120 min on average to less than 5 min.

Multilayer meander structures for wireless communications are presented in this paper. The miniaturization of meander structures is solved by positioning the meander conductor in multiple layers. The influence of the increasing number of layers and connecting vias on the operational parameters of the meander structures is investigated. Three-dimensional models of the meander structures are designed and analyzed in the CST Microwave Studio^© software package. The general mathematical model of the meander structure is presented. The computer-based simulation is verified by a physical experiment and analytical calculations. The investigation shows that it is possible to miniaturize the meander structure by placing it into different layers and connecting the meander conductors with vias. The overall length of the meander structure is decreased by 48% from 16.24 mm to 8.4 mm, while the delay time ${\mathit{t}}_{\mathrm{d}}$ is changed only by less than 3.2% and increased till 1.145 ns, which is 35 ps. The overall dimensions of the miniaturized meander structure are 8.4 × 17.35 × 0.76 mm. The designed structure is suitable for operation at a 2.4–2.5 GHz ISM frequency band.