Original scientific paperIn this paper, a compact setup for measuring the radiation pattern of an arbitrary positioned antenna above the sea surface is presented. The antenna of interest was a vertical half-wave dipole. Due to impracticalities concerning the measurements using seaborne platforms, the setup was based around a shallow pool filled with actual sea water. The transmitting antenna-under-test (AUT) and the receiving antenna stands were placed on the solid ground, at the opposite sides of the pool, thus ensuring the stable platforms as well as the wave path over sea. The need for precise positioning of the receiving antenna along the circular path was avoided and the straight measurement line was used instead, yielding further simplification of the method. Both antennas were realized as printed half-wave dipoles. The measurements were carried out in ISM frequency band at 2.48 GHz. The chosen frequency enabled the realization of a compact setup for elevation radiation pattern measurements for AUT heights up to 2λ above the sea surface. The measurement results were compared to the theoretical and simulation results for a half-wave dipole over sea, showing a good agreement. Detailed evaluation of the measurement uncertainty was undertaken, indicating the critical points in the realized setup.Key words: Antenna above sea surface, Lossy dielectric ground plane, Radiation pattern measurement setup, Vertical half-wave dipole Dijagram zračenja vertikalnog dipola iznad mora i mjerni postav za njegovo mjerenje. U ovom radu predstavljen je kompaktni postav za mjerenje dijagrama zračenja proizvoljno postavljene antene iznad površine mora. Predmet analize je vertikalni poluvalni dipol. S obzirom na nepraktičnost mjerenja na plovećoj platformi, postav se temelji na plitkom bazenu napunjenom stvarnom morskom vodom. Stativi za ispitivanu odašiljačku antenu i prijamnu antenu postavljeni su načvrstom tlu na nasuprotnim stranama bazena, tako da se antene nalaze na stabilnim platformama, a putanja vala se nalazi u potpunosti iznad mora. Dodatna značajka predložene metode jest pravocrtno pomicanje prijamne antene tijekom mjerenja dijagrama zračenja. Time je izbjegnuta potreba preciznog pozicioniranja po kružnoj putanji, što je dovelo do dodatnog pojednostavnjenja metode. Obje antene izraîene su kao poluvalni dipoli u planarnoj tehnologiji. Mjerenja su provedena na ISM frekvenciji od 2.48 GHz. Odabrana frekvencija omogućuje izradu kompaktnog postava za mjerenje vertikalnog dijagrama zračenja za visine odašiljačke antene do 2λ iznad morske površine. Mjerni rezultati pokazuju dobro slaganje s analitičkim rezultatima i rezultatima simulacije za poluvalni dipol iznad mora. Provedena je i prikazana detaljna procjena mjerne nesigurnosti, kao pokazatelj kritičnih točaka u realiziranom postavu.Ključne riječi: antena iznad mora, dielektrik s gubicima, uzemljena ravnina, mjerni postav za mjerenje dijagrama zračenja, vertikalni poluvalni dipol
The electrostimulation excitation threshold of a nerve depends on temporal and frequency parameters of the stimulus. These dependences were investigated in terms of: (1) strength-duration (SD) curve for a single monophasic rectangular pulse, and (2) frequency dependence of the excitation threshold for a continuous sinusoidal current. Experiments were performed on the single-axon measurement setup based on Lumbricus terrestris having unmyelinated nerve fibers. The simulations were performed using the well-established SENN model for a myelinated nerve. Although the unmyelinated experimental model differs from the myelinated simulation model, both refer to a single axon. Thus we hypothesized that the dependence on temporal and frequency parameters should be very similar. The comparison was made possible by normalizing each set of results to the SD time constant and the rheobase current of each model, yielding the curves that show the temporal and frequency dependencies regardless of the model differences. The results reasonably agree, suggesting that this experimental setup and method of comparison with SENN model can be used for further studies of waveform effect on nerve excitability, including unmyelinated neurons.
Electromagnetic modeling of large scale problems arising from complex geometries, such as the human body or the specific organ, is generally undertaken by numerical methods implemented in simulation software packages. The structures involving high discretization density (mainly based on Magnetic Resonance Imaging and handled by Finite Difference Time Domain method) consume tremendously high computational cost. On the other hand, oversimplified numerical models may result in significantly less accuracy. The aim of this work was to investigate how detailed numerical model could be created using standard personal computer. Two rather complex cases of exposure were analyzed: human eye and pregnant woman exposed to radiofrequency electromagnetic radiation. The SAR distribution, peak localized 10g-averaged SAR and volume-averaged SAR in these models were determined using two software packages based on different numerical methods: FEKO software based on Finite Element Method and SEMCAD X software based on Finite Difference Time Domain method. The obtained results were compared to the results arising from other scientific studies which included the models of different complexity solved by different numerical methods.
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