Potentials of the Application of the Electrical Transmission Line Theory for Thermal Investigations on Cables

In this contribution, similarities and differences between electrical and thermal effects on cables are investigated. In the electrical transmission line theory, a wide variety of methods is known to describe the voltage and current along cables. The potential for the adaption of some of those methods to thermal problems is discussed. Exemplarily, for an unshielded single cable, an analytical solution based on the Laplace transform and an approach based on cascaded equivalent circuits are compared with a numerical reference solution and measurement results.

Consideration of Air Bubble Dynamics in 1D Hydraulic Pipeline Simulation – Source Term Development and Verification Utilizing Transmission Line Theory

In fluid power systems, the presence of undissolved air greatly influences the properties of the liquid-gas mixture. Even marginal amounts of undissolved air may drastically reduce the apparent bulk modulus of the mixture. In current state-of-the-art 1D simulation tools, the estimation of the apparent bulk modulus of the mixture is based on the assumption that both liquid and gas fractions act as springs. However, the so-called Rayleigh-Plesset equation frequently used for cavitation analysis shows that the gas bubbles should rather be regarded as non-linear mass-spring-damper systems, implicating a frequency-dependent stiffness of the gas phase. In the present paper, these dynamic effects are investigated by considering monodisperse as well as polydisperse mixtures. For the polydisperse case, a log-normal bubble size distribution is used. First, a frequency domain solution for the bubble dynamics is developed by linearizing the Rayleigh-Plesset equation. An expression of the mixture bulk modulus is derived, which is complex-valued and frequency-dependent. Based on the bulk modulus, a theoretical solution for the dynamics of a whole pipeline is developed by utilizing transmission line theory. It is shown that the dynamics of the bubbles leads to a significant shift of the system’s natural frequencies towards lower values — a phenomenon that needs to be accounted for during the design phase of a fluid power system. After the development of this analytical solution, by introducing a bubble dynamics source term, an established numerical scheme for 1D pipe simulation based on the method of characteristics is expanded. Finally, the newly developed numerical approach is compared with the analytical solution in order to determine its accuracy. The findings and simulation approaches in this work will enable fluid power system engineers to predict dynamic system behavior more precisely during early stages of system layout.

The problems in the quarter-wavelength model and impedance matching theory in analysising microwave absorption material

It is shown here that many concepts in current mainstream microwave absorption theory are used inappropriately. Reflection loss RL has been used to characterize microwave absorption from material instead of film and the results have been rationalized by impedance matching theory. The quarter-wavelength model states that the reflection of microwaves with wavelength l from a film is minimized if the thickness of the film is m l /4 where m is an odd integer. But we show here that the model is wrong because the phase effects from interfaces have been overlooked. RL is an innate property only for metal-backed film. Impedance matching theory is developed from transmission-line theory for scattering parameter s 11 but cannot be generalized to RL.

Estimation of Microwave Absorption Properties of RGO-SiC-LLDPE Composites

The present work investigate the microwave absorption properties of reduced graphene oxide (RGO)-Silicon carbide (SiC)-Linear low-density polyethylene (LLDPE) composites prepared in different concentration of fillers(10, 20, 30, 40 wt. %) with LLDPE matrix. Synthesis of RGO is confirmed from XRD analysis and SiC is used as received from supplier. Complex permittivity of the composites is measured using Nicolson Ross method showing an increasing trend with increasing filler concentrations with maximum and for 40 wt. % composite sample. Based on transmission line theory and using measured value of complex permittivity, conductor backed single and double layer absorber is designed by thickness optimization. The calculated reflection loss (RLc) value of ~-71 dB at 11.23 GHz is observed for 40 wt. % composite sample of 7 mm thickness with -10 dB absorption bandwidth of 1.48 GHz and -20 dB bandwidth of 0.64 GHz.

Preliminary study on the new wound monitoring technology using co-planar waveguide sensor: Modeling and simulation

BACKGROUND: Wound monitoring is very meaningful for the clinical research, diagnosis and treatment. But the existing wound monitoring technology is hard to meet the needs of modern medical care in terms of real-time, non-invasive and anti-interference. OBJECTIVE: To solve this problem, this paper proposed a new kind of monitoring technology based on the co-planar waveguide transmission line theory and assessed the application value of this method as a wound monitoring technology. METHODS: The simplified wound model included the skin, fat, muscle, tissue fluid and bandage and a new co-planar waveguide sensor were designed and established. All of the simulation was achieved in the electromagnetic special software. The data processing method was based on the transmission line theory. RESULTS: Detailed analyses of the results from the simulation were conducted. The sensor has a good monitoring effect in the low frequency band. The monitoring results could be influenced by the thickness of the bandage outside the wound. The thickness of the bandage should not be larger than 10 mm. The effective monitoring area of the sensor is 30 × 20 mm2. CONCLUSIONS: The proposed sensor based on the CPW transmission principle in this paper has good wound monitoring potential.