Theoretical investigation on transverse mode combustion instability for liquid propellant rockets

Mathematical solution of nonlinear transverse combustion instability problems in thin annular liquid propellant rocket chamber

Monitoring thermal ablation via microwave tomography. An ex vivo experimental assessment

Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital's routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances

GPR prospecting in a layered medium via microwave tomography

The tomographic approach appears to be a promising way to elaborate Ground Penetrating Radar (GPR) data in order to achieve quantitative information on the tested regions. In this paper, we apply a linearized tomographic approach to the reconstruction of dielectric objects embedded in a layered medium. The problem is tackled with reference to a two-dimensional geometry and scalar case when data are collected over a linear domain with finite extent. In particular, in order to increase the amount of independent available data, a multi-frequency/multi-view/ multi-static measurement configuration is considered. With reference to stepped-frequency radar, this means that for each working frequency and for each position of the transmitting antenna (moved along a linear domain), the electric field scattered by the buried targets is measured in several locations along the same linear domain. The proposed inversion approach is based on the Born approximation and a regularized solution is introduced by means of the Singular Value Decomposition (SVD). The problem of determining the optimal measurement configuration (in terms of number of frequencies and number of transmitting and receiving antennas) is also tackled by a numerical analysis relying on the Singular Value Decomposition (SVD). Numerical examples are provided to assess the effectiveness and robustness of the proposed approach against noise on data

Microwave Tomography for Food Contamination Monitoring

The security of packaged food needs to be guaranteed to safeguard customers health. A raise of complaints of physical contaminations into food products pushes for the development of additional monitoring techniques to prevent any kind of hazards, but also to protect brands from customers trust loss. In this work, a prototype working at microwave frequencies is assessed and tested in a significant environment. It exploits the dielectric contrast between contaminants and food content, and it is it is mainly focused on two classes of intrusions matters, i.e. plastic and glass fragments of few mm size, that have limited detection by the existing in-line technologies, such as X-rays systems. The measurements and the resulting 3-D image reconstructions are encouraging and allow to aim at the development of an industrial prototype, monitoring packaged food in real-time along a production line

A Simple Quantitative Inversion Approach for Microwave Imaging in Embedded Systems

In many applications of microwave imaging, there is the need of confining the device in order to shield it from environmental noise as well as to host the targets and the medium used for impedance matching purposes. For instance, in MWI for biomedical diagnostics a coupling medium is typically adopted to improve the penetration of the probing wave into the tissues. From the point of view of quantitative imaging procedures, that is aimed at retrieving the values of the complex permittivity in the domain under test, the presence of a confining structure entails an increase of complexity of the underlying modelling. This entails a further difficulty in achieving real-time imaging results, which are obviously of interest in practice. To address this challenge, we propose the application of a recently proposed inversion method that, making use of a suitable preprocessing of the data and a scenario-oriented field approximation, allows obtaining quantitative imaging results by means of quasi-real-time linear inversion, in a range of cases which is much broader than usual linearized approximations. The assessment of the method is carried out in the scalar 2D configuration and taking into account enclosures of different shapes and, to show the method’s flexibility different shapes, embedding nonweak targets

Electromagnetic imaging and sensing for food quality and safety assessment [Guest Editorial]

The six articles in this special present to the antennas and propagation community some of the emerging research activities on the application of EM-based technologies in such a societally relevant topic. The articles address food industry applications as different as sensing food quality and food spoilage indicators and monitoring food items to detect contaminants

A Microwave Imaging Device for Detecting Contaminants in Water-based Food Products

Food and beverage industries are paying an increasing attention to the development of new technologies for non-invasive assessment of food products. In particular, there is a need of deploying tools to detect low-density plastic, rubber, wood and glass that are unlikely to be detected by X-Rays, currently used in the most powerful commercial systems. To this end, we propose a microwave-based device, exploiting the dielectric contrast between potential intrusions (e.g., plastic fragments) and the surrounding medium, represented by the food/beverage product. In particular, this work aims to numerically assess this principle of detection to water-based products that are, due to the medium losses, a challenging category at microwaves. An antennas array surrounds the object moving along the production line, to monitor the electromagnetic signal variations with respect to a reference case. The working frequency is chosen by selecting a proper trade-off between penetration depth and image resolution. Then, a procedure, based on the application of the distorted-Born approximation is applied to reconstruct a 3-D image of the contaminant position. Finally, the successful detection of a millimetric-sized plastic sphere is presented in the case of a common commercial bottle filled with water

A high order compact scheme for hypersonic aerothermodynamics

A novel high order compact scheme for solving the compressible Navier-Stokes equations has been developed. The scheme is an extension of a method originally proposed for solving the Euler equations, and combines several techniques for the solution of compressible flowfields, such as upwinding, limiting and flux vector splitting, with the excellent properties of high order compact schemes. Extending the method to the Navier-Stokes equations is achieved via a Kinetic Flux Vector Splitting technique, which represents an unusual and attractive way to include viscous effects. This approach offers a more accurate and less computationally expensive technique than discretizations based on more conventional operator splitting. The Euler solver has been validated against several inviscid test cases, and results for several viscous test cases are also presented. The results confirm that the method is stable, accurate and has excellent shock-capturing capabilities for both viscous and inviscid flows

Experimental Validation of a 3D Microwave Imaging Device for Brain Stroke Monitoring

In this work we present the experimental validation of a 3D microwave imaging device to brain observation. The device is conceived as a way to monitor stroke development, supporting physicians in the follow-up of patients in the aftermath of cerebrovascular accidents, and giving to them extra information for decision-making and application of therapies. The device acquires data through antennas placed around the patient head, in a low-complexity system that guarantees that available information is enough for reliable outcome. Experimental testing is performed on a 3-D human-like head phantom with promising results