Fast quantitative microwave imaging with resolvent kernel extracted from measurements

Abstract

A quantitative imaging method is proposed based on microwave measurements where a direct inversion in real space is employed. The electrical properties of penetrable objects are reconstructed using a resolvent kernel in the forward model, which is extracted from calibration measurements. These measurements are performed on two known objects: the reference object (RO) representing the scatterer-free measurement and the calibration object representing a small scatterer embedded in the RO. Since the method does not need analytical or numerical approximations of the forward model, it is particularly valuable in short-range imaging, where analytical models of the incident field do not exist while the fidelity of the simulation models is often inadequate. The experimentally determined resolvent kernel inherently includes the particulars of the measurement setup, including all transmitting and receiving antennas. The inversion is fast, allowing for quasi-real-time image reconstruction. The proposed technique is demonstrated and validated through examples using simulated and experimental data. Its performance with noisy data is also examined. The concept of experimentally determined resolvent kernel in the forward model may be valuable in other imaging modalities such as ultrasound, photonic imaging, electrical-impedance tomography, etc.

Optimal Illumination Schemes for Near-Field Microwave Imaging

“…The validation of the expected improvement due to the ANI is carried out with the SPM direct imaging method proposed in [22]. Since the method does not need analytical or numerical approximations of the forward model, it is particularly beneficial in near-field imaging.…”

“…In such cases, it is recommended to enlarge the scatterer size and/or the contrast. On the other hand, the small scatterer in the CO should be small enough to feature an approximately uniform internal field distribution which is assumed in the forward model of SPM [22]. If the scatterer is not electrically small and its response is a summation of point scatterers, the acquired response is not a system point-spread function and the reconstruction is likely to fail.…”

“…The CO used consists of air with a dielectric cylinder identical to those in OUT, placed in the center of the imaged plane. The cylinder represents a point scatterer and its size determines the expected imaging resolution [22].…”

“…The cross-range resolution limits with planar scanning are derived analytically in the far zone allowing for a comparison between the conventional single-source illumination and the double-source illumination. These limits are then validated through inversion with the direct reconstruction method proposed in [22], referred to as scattered-power mapping (SPM). This method is fast (quasi-real time), easy to implement and accurate within the limits of the linear Born approximation.…”

Comparative Study of the Rytov and Born Approximations in Quantitative Microwave Holography

“…Direct inversion approaches are attractive due to their ability to produce images in real time, simultaneously with measurements. Some examples of direct inversion methods include confocal radar imaging, diffraction tomography, microwave holography, and scattered-power mapping [13][14][15][16]. The speed of these methods is due to the linearized models of scattering, which view the observed domain as a collection of uncoupled point scatterers.…”