Computational polarimetric microwave imaging

We propose a polarimetric microwave imaging technique that exploits recent advances in computational imaging. We utilize a frequency-diverse cavity-backed metasurface, allowing us to demonstrate high-resolution polarimetric imaging using a single transceiver and frequency sweep over the operational microwave bandwidth. The frequency-diverse metasurface imager greatly simplifies the system architecture compared with active arrays and other conventional microwave imaging approaches. We further develop the theoretical framework for computational polarimetric imaging and validate the approach experimentally using a multi-modal leaky cavity. The scalar approximation for the interaction between the radiated waves and the target---often applied in microwave computational imaging schemes---is thus extended to retrieve the susceptibility tensors, and hence providing additional information about the targets. Computational polarimetry has relevance for existing systems in the field that extract polarimetric imagery, and particular for ground observation. A growing number of short-range microwave imaging applications can also notably benefit from computational polarimetry, particularly for imaging objects that are difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure

Microwave Breast Imaging Techniques and Measurement Systems

Electromagnetic waves at microwave frequencies allow penetration into many optically non-transparent mediums such as biological tissues. Over the past 30 years, researchers have extensively investigated microwave imaging (MI) approaches including imaging algorithms, measurement systems and applications in biomedical fields, such as breast tumor detection, brain stroke detection, heart imaging and bone imaging. Successful clinical trials of MI for breast imaging brought worldwide excitation, and this achievement further confirmed that the MI has potential to become a low-risk and cost-effective alternative to existing medical imaging tools such as X-ray mammography for early breast cancer detection. This chapter offers comprehensive descriptions of the most important MI approaches for early breast cancer detection, including reconstruction procedures and measurement systems as well as apparatus

Ultra-Wideband Microwave Imaging of Heterogeneities

International audienceThe technique of time-reversal acoustics was applied to image a bottle filled with saline, using an eight element Vivaldi antenna array with frequency bandwidth 2 to 8 GHz. At these short length scales, a smooth three-dimensional image of the bottle was obtained, with the usual limitations imposed by limited offset and frequency. Time snapshots of the wavefield evolution in reversed time are presented for two real data sets. The first, shows the focusing for the single target of the bottle, while the second demonstrates the principle for two targets

Different Approaches of Numerical Analysis of Electromagnetic Phenomena in Shaded Pole Motor with Application of Finite Elements Method

In this paper is used Finite Element Method-FEM for analysis of electromagnetic quantities of small micro motor – single phase shaded pole motor-SPSPM. FEM is widely used numerical method for solving nonlinear partial differential equations with variable coefficients. For that purpose motor model is developed with exact geometry and material’s characteristics. Two different approaches are applied in FEM analysis of electromagnetic phenomena inside the motor: magneto-static where all electromagnetic quantities are analysed in exact moment of time meaning frequency f=0 Hz and timeharmonic magnetic approach where the magnetic field inside the machine is time varying, meaning frequency f=50 Hz. Obtained results are presented and compared with available analytical result

Novel Approaches for Nondestructive Testing and Evaluation

Nondestructive testing and evaluation (NDT&E) is one of the most important techniques for determining the quality and safety of materials, components, devices, and structures. NDT&E technologies include ultrasonic testing (UT), magnetic particle testing (MT), magnetic flux leakage testing (MFLT), eddy current testing (ECT), radiation testing (RT), penetrant testing (PT), and visual testing (VT), and these are widely used throughout the modern industry. However, some NDT processes, such as those for cleaning specimens and removing paint, cause environmental pollution and must only be considered in limited environments (time, space, and sensor selection). Thus, NDT&E is classified as a typical 3D (dirty, dangerous, and difficult) job. In addition, NDT operators judge the presence of damage based on experience and subjective judgment, so in some cases, a flaw may not be detected during the test. Therefore, to obtain clearer test results, a means for the operator to determine flaws more easily should be provided. In addition, the test results should be organized systemically in order to identify the cause of the abnormality in the test specimen and to identify the progress of the damage quantitatively

Non-Destructive Crack Detection Technique by Means of Microwave Imaging

Bangunan-bangunan dan struktur awam selalunya terbeban dengan beban melebihi had sehingga membawa kepada kemerosotan dan kelemahan struktur penahanan dan mengakibatkan keretakan. Keretakan dalam konkrit atau bahan berasaskan simen membawa ancaman besar kepada mana-mana struktur awam: ianya sangat berbahaya dan telah membawa kepada banyak kemusnahan dan kerosakan. Walaupun satu keretakan kecil yang kelihatan tidak penting boleh membesar sehingga akhirnya menyebabkan kegagalan struktur yang serius. Selain daripada pemeriksaan manual yang tidak efektif dan memakan masa, beberapa teknik ujian penilaian tanpa musnah pernah digunakan untuk mengesan keretakan. Contohnya, ultrasonik, getaran dan teknik regangan, namun ada di antara penderia yang digunakan samada terlalu besar ataupun beresolusi rendah. Objektif utama adalah untuk mengkaji kemungkinan pengesanan keretakan di dalam konkrit atau simen menggunakan gelombang mikro bersama dengan algoritma lengah-dan-campur. Pertama sekali model pelbagai jenis keretakan di dalam bata disimulasikan menggunakan teknik FDTD. Keputusan dari simulasi digunakan untuk menentukan parameter persediaan eksperimen. Bata dan struktur konkrit dengan keretakan telah digunakan sebagai bahan ujikaji. Daripada keputusan eksperimen, didapati isyarat dengan frekuensi 1 hingga 7 GHz menghasilkan resolusi dan penembusan yang optimum. Keretakan sekurang-kurangnya sebesar 5 mm telah berjaya dikesan dengan resolusi λ/4, yang membolehkan pengesanan keretakan tahap awal. Kesimpulannya teknik pengimejan gelombang mikro mempunyai potensi untuk mengesan keretakan di dalam konkrit atau bahan berasaskan simen dengan resolusi yang tinggi. ________________________________________________________________________________________________________________________ Building and civil structures are often overburdened with load above their threshold value that led to deterioration and weakening of the supporting members, and resulted in cracks. Cracks in concrete or cement based materials present a significant threat to any civil structures; they are very dangerous and have caused much destruction and damages. Even small cracks, which look insignificant grow and eventually lead to severe structural failure. Besides manual inspection that is ineffective and time-consuming, several non-destructive evaluation techniques have been used for crack detection. For instance, ultrasonic, vibration and strain-based techniques, however some of the sensors used are either too big or limited in resolution. The main objective is to study the possibility of crack detection in concrete or cement based materials using microwave imaging with Delay-and-Sum, (DAS) algorithm. First, models of various crack types in bricks were simulated using finite difference time domain method (FDTD) method. The simulation results were used to determine the design parameters for the experimental setup. Single brick and a constructed concrete structure with cracks were used as phantoms. From the experimental results, signal with frequency of 1 to 7 GHz gave an optimum resolution and signal penetration. Cracks of at least 5 mm in size were detected with a resolution of λ/4 that enabled crack detection at the early stage of development. In conclusion, microwave imaging technique showed the potential to detect cracks in concrete or cement-based materials with high-resolution image

Investigating Key Techniques to Leverage the Functionality of Ground/Wall Penetrating Radar

Ground penetrating radar (GPR) has been extensively utilized as a highly efficient and non-destructive testing method for infrastructure evaluation, such as highway rebar detection, bridge decks inspection, asphalt pavement monitoring, underground pipe leakage detection, railroad ballast assessment, etc. The focus of this dissertation is to investigate the key techniques to tackle with GPR signal processing from three perspectives: (1) Removing or suppressing the radar clutter signal; (2) Detecting the underground target or the region of interest (RoI) in the GPR image; (3) Imaging the underground target to eliminate or alleviate the feature distortion and reconstructing the shape of the target with good fidelity. In the first part of this dissertation, a low-rank and sparse representation based approach is designed to remove the clutter produced by rough ground surface reflection for impulse radar. In the second part, Hilbert Transform and 2-D Renyi entropy based statistical analysis is explored to improve RoI detection efficiency and to reduce the computational cost for more sophisticated data post-processing. In the third part, a back-projection imaging algorithm is designed for both ground-coupled and air-coupled multistatic GPR configurations. Since the refraction phenomenon at the air-ground interface is considered and the spatial offsets between the transceiver antennas are compensated in this algorithm, the data points collected by receiver antennas in time domain can be accurately mapped back to the spatial domain and the targets can be imaged in the scene space under testing. Experimental results validate that the proposed three-stage cascade signal processing methodologies can improve the performance of GPR system