http://hdl.handle.net/10071/5707 Sat, 18 Apr 2026 07:57:15 GMT 2026-04-18T07:57:15Z http://hdl.handle.net/10071/36082 Título próprio: Learning-based lossless event data compression Autoria: Sezavar, A.; Brites, C.; Ascenso, J. Resumo: Emerging event cameras acquire visual information by detecting time domain brightness changes asynchronously at the pixel level and, unlike conventional cameras, are able to provide high temporal resolution, very high dynamic range, low latency, and low power consumption. Considering the huge amount of data involved, efficient compression solutions are very much needed. In this context, this paper presents a novel deep-learning-based lossless event data compression scheme based on octree partitioning and a learned hyperprior model. The proposed method arranges the event stream as a 3D volume and employs an octree structure for adaptive partitioning. A deep neural network-based entropy model, using a hyperprior, is then applied. Experimental results demonstrate that the proposed method outperforms traditional lossless data compression techniques in terms of compression ratio and bits per event. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10071/36082 2024-01-01T00:00:00Z http://hdl.handle.net/10071/35443 Título próprio: Best practices for accurate results using numerical solvers for microwave body screening Autoria: Martins, R. A.; Godinho, D.; Felício, J. M.; Savazzi, M.; Costa, J. R.; Conceição, R.; Fernandes, C. A. Resumo: In this paper, we indicate best practices that should be observed when using numerical solvers for microwave body sensing. We show the impact of not minding these aspects in the case of microwave breast scanning, using the Computer Simulation Technology software tool. To this end we simulate a homogeneous breast with a 5-mm radius spherical tumor placed inside. The breast is illuminated by a broadband antenna that operates in the 2-6 GHz band. The scattering parameters are then processed to reconstruct the reflectivity map of the breast. The results highlight that the conclusions drawn from simulations may be misleading or meaningless when the solver type or positioning of model elements (body and antennas) are not carefully applied. This is particularly critical when considering more complex scenarios, such as inhomogeneous or multilayer body models. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10071/35443 2024-01-01T00:00:00Z http://hdl.handle.net/10071/35432 Título próprio: Antenna position layout and frequency impact on tumor detection in microwave breast imaging Autoria: Martins, R. A.; Felício, J.; Costa, J. R.; Fernandes, C. A. Resumo: We present a systematic study in which we assess the antenna position layout and frequency point distribution of a MWI system, that can potentially improve tumor detection and minimize acquisition time. To this end, we performed measurements on a dry MW setup, using a slot-based antenna in the [2]–[5] GHz frequency range to scan an anthropomorphic breast phantom, with two different tumor positions, for 40 angular positions. Imaging and tumor-to-clutter ratio metric showed that there is a specific number of angular positions and frequency points beyond which the quality of imaging results does not increase substantially. We found the optimal frequency band for this kind of setup and that the use of lower frequencies seems more beneficial than the use of higher ones. Moreover, distributions of antenna position other from the regular circular one, should be explored further since it showed a decrease of imaging artefacts. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10071/35432 2024-01-01T00:00:00Z http://hdl.handle.net/10071/35375 Título próprio: Reconfigurable intelligent surfaces for THz: Hardware impairments and switching technologies Autoria: Matos, S.; Ma, Y.; Luo, Q.; Deuermeier, J.; Lucci, L.; Gavriilidis, P.; Kiazadeh, A.; Lain-Rubio, V.; Phan, T.; Soh, P.; Clemente, A.; Pessoa, L.; Alexandropoulos, G. Resumo: The demand for unprecedented performance in the upcoming 6 G wireless networks is fomenting the research on THz communications empowered by Reconfigurable Inteligent Surfaces (RISs). A wide range of use cases have been proposed, most of them, assuming high-level RIS models that overlook some of the hardware impairments that this technology faces. The expectation is that the emergent reconfigurable THz technologies will eventually overcome its current limitations. This disassociation from the hardware may mask nonphysical assumptions, perceived as hardware limitations. In this paper, a top-down approach bounded by physical constraints is presented, distilling from system-level specifications, hardware requirements, and upper bounds for the RIS-aided system performance. We consider D-band indoor and outdoor scenarios where a more realistic assessment of the state-of-the-art solution can be made. The goal is to highlight the intricacies of the design procedure based on sound assumptions for the RIS performance. For a given signal range and angular coverage, we quantify the required RIS size, number of switching elements, and maximum achievable bandwidth and capacity. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10071/35375 2024-01-01T00:00:00Z