On the Use of Focused Incident Near-Field Beams in Microwave Imaging

Abstract

We consider the use of focused incident near-field (NF) beams to interrogate the object of interest (OI) in NF microwave imaging (MWI). To this end, we first discuss how focused NF beams can be advantageously utilized to suppress scattering effects from the neighbouring objects whose unknown dielectric properties are not of interest (i.e., undesired scatterers). We then discuss how this approach can also be helpful in reducing the required measured data points to perform imaging. Driven by the relation between the electromagnetic inverse source and inverse scattering problems, our approach emphasizes the importance of tailoring the induced contrast sources in the imaging domain through the utilized incident NF beams. To demonstrate this idea, we consider two recently-proposed NF beams, and simulate them for imaging applications. The first one is a subwavelength focused NF beam generated by a passive NF plate, and the other is a Bessel beam generated by a leaky radial waveguide. Simple imaging examples are considered to explore the potential advantages of this approach, in particular, toward mainly seeing the object of interest, and not the unknown undesired scatterers. The scope of this paper is limited to homogeneous dielectric objects for which the induced total field distributions in the interrogated objects are similar to the incident field distributions (e.g., those that satisfy the Born approximation). Simple inversion results for focused and non-focused beams are presented accompanied by discussions comparing the achieved reconstructed values.

Microwave Tomography With LSTM-Based Processing of the Scattered Field

“…This source generates a transverse-magnetic incident radiation whose z-component of the electric field is E i (r t , f ) = j2π f μ 0 Ig(r t |r TX t , f ), where f is the frequency, μ 0 is the magnetic permeability of vacuum, and g(r t |r TX t , f ) = jH (2) 0 (k 0 |r t − r TX t |)/4 is the related Green's function, with k 0 = 2π f √ μ 0 0 , 0 being the dielectric permittivity of vacuum. Under these hypotheses, if the object under test is infinite along the z axis, it causes a scattered field [7] E sc (r t , f ) = −k 2 0 I g r t |r t , f H(f )x r t E t r t , f dr t , (13) where the properties of the object are expressed with the term x(r t ) = ( (r…”

“…The attractive possibility of analyzing unknown targets and bodies by means of microwave radiation has stimulated the research community for decades and is nowadays at a turning point [6], [7]. On the one hand, the development of advanced inverse scattering techniques is demonstrating the ability to deal with complex scenarios [8]- [12], which is supported by the design of proper antennas [13]- [17] and measurement systems [18]- [20]. On the other hand, the ever-increasing available computing power is providing unvaluable tools for the practical implementation of the proposed solution techniques.…”

Electromagnetic Torso Scanning: A Review of Devices, Algorithms, and Systems

“…The other important requirement of antenna design for EM scanning systems is focused beam radiation in near field and/or far-field. In EM imaging systems, unidirectional radiation is preferred to reduce the adverse effects of environmental noise and scattered fields on signal-to-noise ratio, hence providing better detection results [ 51 , 52 ]. The effects of the focused beam antennas on the reconstructed images in EMI systems are thoroughly investigated in [ 51 ].…”

Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band

“…Throughout the last few decades, near-field focusing (NFF) techniques have risen in popularity as an approach to concentrate the power density of the antenna on a point within the outer boundary , where D is the antenna aperture. NFF antennas have received great interest in several application such as radio frequency identification (RFID) [ 1 , 2 ], microwave imaging [ 3 , 4 ], or medical hyperthermia [ 5 , 6 ]. Recent applications such as wireless power transfer (WPT) or 5G communications have led to emerging needs for high efficiency wireless communications between multiple devices and sensors, mostly closely distributed and within the near-field region of their antennas.…”