Near-field detection at microwave frequencies based on self-adjoint response sensitivity analysis

Abstract

A new detection method is proposed for the localization of electrically small scatterers in a known background medium. The method requires the knowledge of the electric field distribution inside the known background medium where no scatterers are present. It is based on a self-adjoint response sensitivity computation which can be performed in real time. Using the E-field distribution in the background medium, it provides three-dimensional maps of the Fréchet derivative within the imaged volume. The peaks and dips in these maps identify the locations where the permittivity and conductivity of the measured medium differ from those in the background medium. The background medium can be heterogeneous. In a homogeneous-medium example, the performance of the detection algorithm is studied in terms of the number of transmission/reception points, the dielectric contrast of the scatterer compared to the background medium, and the size of the scatterer. Its resolution is also addressed. The detection of a small scatterer in a heterogeneous background is demonstrated.

Resolution and robustness to noise of the sensitivity-based method for microwave imaging with data acquired on cylindrical surfaces

“…The spatial resolution of a promising new microwave imaging technique [14,15] based on response-sensitivity analysis is studied. The technique yields an image of the contrast in the dielectric properties of the examined object and a known RO.…”

“…Under realistic non-ideal conditions, the spatial resolution is expected to be poorer depending on factors, such as spatial and frequency sampling rates, SNR and the fidelity of the EM model of the RO. Note also that the method has been proven to rely on the linear Born approximation [14]; therefore, the contrast and size of the targets would impact the spatial resolution if the respective limits (18) are not observed.…”

“…The derivatives of ( 2) with respect to the real part of the complex permittivities ε(m) RO (r ) (Fréchet derivatives) can be written as follows [14,18]:…”

“…The respective incident and scattered fields are computed as explained in sections 5.1 and 5.2. In particular, the incident E-field E (m) RO is computed using (13); the S-parameters S (m) RO, jk in the RO are calculated using (14); and S (m) OUT, jk in the OUT are calculated using (23). Here, m = 1, .…”

“…A microwave detection algorithm based on a response-sensitivity formulation has been proposed in [14,15]. It aims at uncovering abnormalities in the OUT (e.g.…”