The hypersonic flight regime is conventionally defined for Mach > 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but, in typical situations of interest, it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ the equivalence theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free-space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life reentry vehicle with full 3-D plasma computed via computational fluid dynamic (CFD) simulations. We address both scattering [radar cross section (RCS)] from the entire vehicle and radiation from the onboard antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses to an extent that matches well the usually perceived blackout in crossing layers in the cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.

A horizontal planar scanner with an approximate size of 40 m $\times40$ m has been implemented using the Unmanned Aerial Vehicle (UAV) technology. The UAV is not wired to the ground to maintain the flexibility and short setup time of a non-tethered flight. In this configuration, the UAV-mounted continuous-wave source is not phase-locked to the on-the-ground receiver. A dual-polarized reference antenna placed on the ground is hence used to retrieve the relevant phase information. The presented approach has been applied on the Pre - Aperture Array Verification System (Pre -AAVS1) of the Square Kilometre Array, which is a digital beamformed array with 16 active elements. An inverse source technique has been applied on measured Near-Field (NF) data acquired on two different sets of points (one for each electric field component) from all the receiver channels. In this way, Embedded Element Patterns (EEPs), array calibration coefficients and pattern have been determined from NF data only. The achieved results have been validated using a complementary set of Far-Field (FF) measurements and simulations.

Microwave hyperthermia aims at selectively heating cancer cells to a supra-physiological temperature. For non-superficial tumors, this can be achieved by means of an antenna array equipped with a proper cooling system (the water bolus) to avoid overheating of the skin. In patient-specific treatment planning, antenna feedings are optimized to maximize the specific absorption rate (SAR) inside the tumor, or to directly maximize the temperature there, involving a higher numerical cost. We present here a method to effect a low-complexity temperature-based planning. It arises from recognizing that SAR and temperature have shifted peaks due to thermal boundary conditions at the water bolus and for physiological effects like air flow in respiratory ducts. In our method, temperature focusing on the tumor is achieved via a SAR-based optimization of the antenna excitations, but optimizing its target to account for the cooling effects. The temperature optimization process is turned into finding a SAR peak position that maximizes the chosen temperature objective function. Application of this method to the 3D head and neck region provides a temperature coverage that is consistently better than that obtained with SAR-optimization alone, also considering uncertainties in thermal parameters. This improvement is obtained by solving the bioheat equation a reduced number of times, avoiding its inclusion in a global optimization process.

Oncological microwave hyperthermia is a clinically proven sensitizer of radio- and chemo-therapies; it acts by selectively increasing the temperature of tumor cells by means of antenna applicators. Its current limitations mostly come from the inability to reliably predict, and hence control, temperature inside the patient during treatment, especially for deep-seated tumors. Simulations are employed in treatment planning, but due to related uncertainties invasive thermometry is necessary, usually via catheters. Being invasive, their use must be minimized and provides very limited spatial information. Here, we demonstrate an approach to obtain 3D temperature information in real time from few measurement points via massive use of high-performance simulations carried out prior to treatment. The proposed technique is tested both in a fully anthropomorphic in-silico scenario, and in an experimental controlled setting. The obtained results demonstrate the potential of the proposed method as a low-cost real-time temperature monitoring technique in cancer hyperthermia. Use with intra-luminal, minimally-invasive catheters is supported by the positive outcome experimentally obtained using data points directly acquired in the trachea-mimicking phantom structure.

The aim of the article is to provide a summary of the work carried out in the framework of a research project funded by the Italian Ministry of Research. The main goal of the activity was to introduce multiple tools for reliable, affordable, and high-performance microwave hyperthermia for cancer therapy. The proposed methodologies and approaches target microwave diagnostics, accurate in vivo electromagnetic parameters estimation, and improvement in treatment planning using a single device. This article provides an overview of the proposed and tested techniques and shows their complementarity and interconnection. To highlight the approach, we also present a novel combination of specific absorption rate optimization via convex programming with a temperature-based refinement method implemented to mitigate the effect of thermal boundary conditions on the final temperature map. To this purpose, numerical tests were carried out for both simple and anatomically detailed 3D scenarios for the head and neck region. These preliminary results show the potential of the combined technique and improvements in the temperature coverage of the tumor target with respect to the case wherein no refinement is adopted.

We describe a method to use numerical simulations concurrently with measurements (Near Field data) to characterize the radiation properties of an antenna (Far Field) with a strongly reduced number of samples. Both simulations and experimental data are dealt with as sources of information towards obtaining the desired characterization. Simulations compensate for data scarceness, allowing to obtain an accurate characterization with fewer data than with measurements only, and the few measured data allow the comprehensive numerical proxy to get tuned to the true antenna under test. The method uses partial knowledge of the antenna and leverages accelerated asymptotic numerical methods to perform the numerical simulations needed by the algorithm. We report experimental tests of performance, both in term of accuracy and speed-up with respect to classical methods, with reflector antennas up to 27 wavelength. It is important to note that good results are obtained both when samples are taken on irregular optimized grids and on the regular grids usually resulting from conventional measurement rigs.