Separating atrial near fields and atrial far fields in simulated intra-atrial electrograms

The detailed characterization of complex forms of atrial flutter relies on the correct interpretation of intra-atrial electrograms. For this, the near field components, which represent the local electrical activity, are decisive. However, far field components arising from distant electrical sources in the atria can obscure the diagnosis. We developed a method to separate and characterize atrial near field and atrial far field components from bipolar intra-atrial electrograms. First, a set of bipolar electrograms was created by simulating different propagation scenarios representing common clinical depolarization patterns. Second, near and far fields were detected as active segments using a non-linear energy operator-based approach. Third, the maximum slope and the spectral power were extracted as features for all active segments. Active segments were grouped accounting for both the timing and the location of their occurrence. In a last step, the active segments were classified in near and far fields by comparing their feature values to a threshold. All active segments were detected correctly. On average, near fields showed 15.1x larger maximum slopes and 40.4x larger spectral powers above 100 Hz than far fields. For 135 active segments detected in 72 bipolar electrograms, 5.2% and 6.7% were misclassified using the maximum slope and the spectral power, respectively. All active segments were classified correctly if only one near field segment was assumed to occur per electrogram. The separation of atrial near and atrial far fields was successfully developed and applied to in silico electrograms. These investigations provide a promising basis for a future clinical study to ultimately facilitate the precise clinical diagnosis of atrial flutter.

Jones matrix holography with metasurfaces

We propose a new class of computer-generated holograms whose far-fields have designer-specified polarization response. We dub these Jones matrix holograms. We provide a simple procedure for their implementation using form-birefringent metasurfaces. Jones matrix holography generalizes a wide body of past work with a consistent mathematical framework, particularly in the field of metasurfaces, and suggests previously unrealized devices, examples of which are demonstrated here. In particular, we demonstrate holograms whose far-fields implement parallel polarization analysis and custom waveplate-like behavior.

Model of microwave radiation absorption by biological tissues

А model of absorption of electromagnetic energy of radiofrequency range by biological tissues is described in the article. The problems of modeling the interaction of microwave radiation and biological tissues represented as multilayer structures are considered. Patch-antenna models for six sub-bands overlapping the 500–3500 MHz range are developed. The model of biological tissue was developed on the basis of MRI imaging, which allows for modeling under near real-life conditions. Based on the developed models of transceivers and biotissue, models have been created that allow to analyze the absorption of electromagnetic energy in the near- and far fields of the transmitter. From the results of modelling in the near field we can see that there are certain absorption maxima at frequencies of 750, 938, 1250 and 1357 MHz. Based on the results of the far field modeling it can be noted that in the range of 750 to 1000 MHz there is no absorption peak at 938 MHz. Also, as a result of the simulation, a decrease in the magnitude of absorption starting from 750 MHz was registered. Absorption peak absence is also observed in the area of 1357 MHz frequency. In the range of 2.5–3 GHz both in the near and far fields practically linear decrease of absorption value is observed. When analyzing the influence of structures' sizes on electromagnetic energy absorption in biological tissues, it was found that the nature of change in absorption value is a nonlinear value. In the range of 0.5–2 GHz both increase and decrease of absorption at thickening or thinning of layers is observed. It should also be noted that when the size of each layer increases by 10 %, the peak of absorption in the area of 1156 MHz frequency is observed. For the 2–3.5 GHz range there are no significant changes in the chart shape when the layer thickness changes.

Using Near Field Equivalent Sources in Combination with Large Element Physical Optics to Model a Slant 45 Degree Omni Directional Antenna over Ground

This paper compares the theoretical and measured antenna patterns of a slant 45-degree antenna on a rolled edge ground plane. Advantages of using sampled nearfield currents in combination with large element physical optics in determining the reflected far fields will be described.