Microwave Holographic Imaging Research Articles

Holographic Microwave Image Classification Using a Convolutional Neural Network.

Holographic microwave imaging (HMI) has been proposed for early breast cancer diagnosis. Automatically classifying benign and malignant tumors in microwave images is challenging. Convolutional neural networks (CNN) have demonstrated excellent image classification and tumor detection performance. This study investigates the feasibility of using the CNN architecture to identify and classify HMI images. A modified AlexNet with transfer learning was investigated to automatically identify, classify, and quantify four and five different HMI breast images. Various pre-trained networks, including ResNet18, GoogLeNet, ResNet101, VGG19, ResNet50, DenseNet201, SqueezeNet, Inception v3, AlexNet, and Inception-ResNet-v2, were investigated to evaluate the proposed network. The proposed network achieved high classification accuracy using small training datasets (966 images) and fast training times.

Fast, Robust, and Low-Cost Microwave Imaging of Multiple Non-Metallic Pipes

The use of non-metallic pipes and composite components that are low-cost, durable, light-weight, and resilient to corrosion is growing rapidly in various industrial sectors such as oil and gas industries in the form of non-metallic composite pipes. While these components are still prone to damages, traditional non-destructive testing (NDT) techniques such as eddy current technique and magnetic flux leakage technique cannot be utilized for inspection of these components. Microwave imaging can fill this gap as a favorable technique to perform inspection of non-metallic pipes. Holographic microwave imaging techniques are fast and robust and have been successfully employed in applications such as airport security screening and underground imaging. Here, we extend the use of holographic microwave imaging to inspection of multiple concentric pipes. To increase the speed of data acquisition, we utilize antenna arrays along the azimuthal direction in a cylindrical setup. A parametric study and demonstration of the performance of the proposed imaging system will be provided.

Miniaturized microstrip circuit board using off-the-shelf components for microwave holography

Microwave holographic imaging is a swift and versatile technique that is optimized for near-field applications, such as biomedical imaging and metallic imaging. Although the holographic setup is efficient, the use of waveguides makes the setup bulky. In this work, a miniaturized holographic configuration on a microstrip circuit board is proposed. The circuit board comprises a directional coupler, a power combiner, a tunable phase shifter and a hybrid ring. Here, the phase shifter is electronically tunable by up to 360° in the frequency range from 9.6 to 10.3 GHz. Therefore, N-step phase shifting holography and interferometry can be combined for better phase accuracy. In addition, to make the system economic and portable, off-the-shelf components are embedded in a single chip. Simulation and measurement results are presented to validate the performance of the proposed circuit board.

Effect of Eccentricity in Microwave Imaging of Multiple Composite Pipes

The use of non-metallic composites that are durable, low cost, and lightweight is growing fast in various industries. A commonly used form of these materials is in the shape of pipes that can be used, for instance, in oil and gas industry. Such pipes can be damaged due to material loss (defects and holes), erosions, and more which may cause major production failures or environmental mishaps. To prevent these issues, non-destructive testing (NDT) methods need to be employed for regular inspections of such components. Since traditional NDT methods are mainly used for metallic pipes, recently microwave imaging has been proposed as a promising approach for examination of non-metallic pipes. While microwave imaging can be employed for inspection of multiple layers of pipes, the effect of undesired eccentricity of the pipes can impose additional imaging errors. In this paper, for the first time, we study the effect of eccentricity of the pipes on the images reconstructed using near-field holographic microwave imaging when imaging double pipes.

Holographic Near-Field Microwave Imaging With Antenna Arrays in a Cylindrical Setup

Holographic microwave imaging is fast and robust and it has been adapted for near-field applications such as biomedical imaging and nondestructive testing. While the imaging technique is fast, synthesizing a 2-D aperture by mechanical scanning of the antennas takes time. Here, antenna arrays are used to expedite data acquisition along the azimuthal direction in a cylindrical holographic near-field microwave imaging setup. To deal with the limited and nonuniform samples along the azimuthal direction, three holographic imaging approaches are evaluated, in which, we use interpolation, uniform or nonuniform discrete Fourier transform (DFT), standardized low-resolution brain electromagnetic tomography (sLORETA), and exact low-resolution brain electromagnetic tomography (eLORETA). Besides, to make the system low-cost and portable, off-the-shelf components are used to construct a data acquisition system replacing the vector network analyzers. Simulation and experimental studies are conducted to validate the performance of the proposed imaging system. Structural similarity (SSIM) index is used to assess the quality of the reconstructed images.

Microwave Holographic Imaging of Nonmetallic Concentric Pipes

Recently, nonmetallic materials, which are resilient to corrosion, low cost, and lightweight, have been exploited in many industrial sectors such as oil and gas field. A common application of them is in the form of pipes. Despite the advantages, these pipes can be damaged by delamination, defects, holes, and erosion, which may lead to major production failures or even environmental catastrophes. To prevent these issues, nondestructive testing (NDT) of these pipes is required to replace these components in a timely manner. Due to the fact that the traditional NDT methods are mostly effective for metallic pipes, microwave holographic imaging is proposed for inspection of multiple concentric nonmetallic pipes. Besides, standardized minimum norm (SMN) is used to mitigate the depth biasing problem in the proposed imaging technique. To reduce the complexity of the imaging system, we aim at using the narrowest possible frequency band using an array of receiver antennas. The performance of the proposed NDT method is validated through simulation and experimental data in two scenarios including the antennas placed outside the pipes and inside the pipes.

Quality Enhancement in Holographic Imaging by Background Property Estimation

In this communication, we propose a technique to enhance the quality of images obtained from holographic microwave imaging. It is based on estimating the electrical properties of the background medium. To accomplish that, background properties to be estimated are assumed to be within a preknown range. Then, two sets of frequencies are employed in wideband holographic imaging and images are reconstructed from each set and for the assumed property values within the predetermined range. An error is calculated according to the differences between the two sets of images. The error is expected to be minimum at the true values of the background medium's properties. The estimated properties, in turn, are used to reconstruct images with the best quality. The validity of the proposed technique is demonstrated via simulation and experimental results.

Nondestructive Testing of Nonmetallic Pipes Using Wideband Microwave Measurements

Conventional nondestructive testing techniques do not suffice to efficiently inspect the defects in multiple nonmetallic pipes. Thus, in this article, we propose a novel method for inspection of these components based on near-field microwave holographic imaging augmented with beamspace transformation. This approach harnesses the ability of microwaves for 3-D imaging by measuring the backscattered fields in the near-field region. In the proposed technique, we augment the solution of near-field holographic imaging through the use of beamspace transformation which allows for focusing on each pipe during the solution process. This improves the quality of the reconstructed images, in particular, for the pipes which are further away from the measuring antennas. First, we demonstrate the performance of the proposed imaging technique using simulations. Then, we present the experimental results for imaging of concentric cylindrical polyvinyl chloride (PVC) pipes using wideband microwave data.

Three-Dimensional Microwave Holography Based on Broadband Huygens' Metasurface

Benefiting from prominent performance in various scientific fields, metasurface research has been flourishing over the past decade. Huygens' metasurface, as an emerging subcategory of metasurface, can theoretically achieve full control of electric field distribution within the subwavelength scale. Driven by its outstanding manipulation capacity, the three-dimensional holography utilizing broadband Huygens' metasurface is demonstrated in the microwave regime in this paper. For the broadband working properties, two types of equivalent circuit are integrated into the design of Huygens' meta-atom. Besides, for high image quality, the modified weighted Gerchberg-Saxton (GSW) algorithm is implemented for specific interfacial phase distribution. The proof-of-concept experiments show notable microwave holographic images, with an 86.2% transmittance efficiency, a 62.7% imaging efficiency, and an 88.1 signal-to-noise ratio at 12 GHz. The proposed holography extends the route to broadband microwave applications in security, data storage, and antenna systems.

A Low-Cost and Compact Three-Dimensional Microwave Holographic Imaging System

With the significant growth in the use of non-metallic composite materials, the demands for new and robust non-destructive testing methodologies is high. Microwave imaging has attracted a lot of attention recently for such applications. This is in addition to the biomedical imaging applications of microwave that are also being pursued actively. Among these efforts, in this paper, we propose a compact and cost-effective three-dimensional microwave imaging system based on a fast and robust holographic technique. For this purpose, we employ narrow-band microwave data, instead of wideband data used in previous three-dimensional cylindrical holographic imaging systems. Three-dimensional imaging is accomplished by using an array of receiver antennas surrounding the object and scanning that along with a transmitter antenna over a cylindrical aperture. To achieve low cost and compact size, we employ off-the-shelf components to build a data acquisition system replacing the costly and bulky vector network analyzers. The simulation and experimental results demonstrate the satisfactory performance of the proposed imaging system. We also show the effect of number of frequencies and size of the objects on the quality of reconstructed images.

SAR analysis of directive antenna on anatomically real breast phantoms for microwave holography

AbstractMicrowave holography utilizes antennae for the detection of cancerous tissues in the human breast. The safety assessment of an antenna is required prior to its radiation interaction with biological tissues. In this work, a specially designed and developed Vivaldi antenna with directivity at 45° for microwave holographic imaging has been presented. A detailed simulation of Specific Absorption Rate (SAR) and thermal analysis due to the radiation exposure of the designed antenna on self‐designed anatomically real breast phantoms is performed in CST environment. SAR values for 3D printed breast phantoms are also calculated experimentally. The quantitative results of SAR reveal the variation of ±10% in between the simulation and experimental results. It has been found that SAR due to the radiation of the designed antenna lies in the permissible limit. The thermal analysis in CST shows the rise of 0.096% in temperature after the exposure of 2 hours. Hence, the antenna can be used in microwave holography for breast cancer detection.

Dual-Probe Probe- and Phase-Compensated Reflection-Coefficient-Only 3-D Microwave Holographic Imaging

A probe- and phase-compensated 3-D microwave holographic imaging algorithm based on dual-probe scanning setup and using only the reflection coefficients is proposed. It is extended from the one based on single-probe setup, in which an auxiliary equation must be used to ensure a reasonable numerical stability. The difference between the algorithms is discussed first, and then the numerical stabilities are investigated qualitatively and quantitatively. It is shown that the numerical stability of the dual-probe imaging algorithm is dominated by the reflection coefficients and that the contributions of transmission coefficients to numerical stability as well as the image quality are negligible. Moreover, the condition number of the proposed dual-probe reflection-coefficient-only imaging algorithm is equal to that of the single-probe algorithm exploiting the auxiliary equation. This implies that the lossless assumption imposed by the auxiliary equation can be discarded in the proposed dual-probe algorithm. Therefore, the proposed algorithm is also feasible for imaging lossy dielectric targets at no extra computational cost. Lastly, for verification, a series of images reconstructed from the simulated scattering data are presented.

Multifrequency Microwave Imaging for Brain Stroke Detection

Early diagnosis of stroke with timely treatment could reduce adult permanent disability significantly [1]. Conventional medical imaging tools such as X-ray, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) have been widely used for diagnosis of brain disease. However, each of these methods has some limitations. X-ray imaging produces harmful radiation to the human body and challenging to identify early-stage abnormal tissue due to the relatively small dielectric proprieties contrast between the healthy tissue and abnormal tissue at X-ray frequencies [2]. PET provides useful information about soft tissues, but it is expensive and produces poor resolution. CT and MRI are unsuitable for continuously monitoring strokes due to produce harmful radiations (CT), expensive (MRI), time-consuming and not easy to develop a portable system [3,4]. Therefore, develop a new screening method is urgently needed to improve the effectiveness of disease detection. <br/> Microwave imaging is a relatively new non-invasive and cost-effective method for imaging of breast and brain tissues, which has continuously attracted many researchers’ interests over the past two decades [5,6]. The authors previously developed a holographic microwave imaging (HMI) method for dielectric object detection with a particular focus on brain stroke [7]. This paper investigates the feasibility of multifrequency HMI for brain stroke detection. A numerical system was developed to demonstrate the proposed theory. Various experiments were carried out to evaluate the performance of the proposed method. Results of experiments carried out using multifrequency HMI have been compared with the results obtained by using single frequency HMI. Results showed that multifrequency HMI could detect strokes and provide more accurate results of size and location than the single frequency HMI algorithm.

Multi-Frequency Holographic Microwave Imaging for Breast Lesion Detection

This paper presents the development of a multi-frequency holographic microwave imaging (HMI) algorithm and investigates the feasibility and effectiveness of the proposed algorithm for breast imaging. A realistic numerical system, including various realistic breast models and image data acquisition model, has been developed using the MATLAB software to demonstrate the working principle of the multi-frequency HMI method. Several numerical experiments have been conducted to evaluate the performance of the proposed method for breast tumor detection. A comparison study of single- and multi-frequency HMIs have been performed to investigate the effectiveness, sensitivity, and accuracy of the proposed method. Results demonstrated that the multi-frequency HMI could improve the breast image quality and accurately detect the small tumors even when they located inside dense tissue. Compared to the single-frequency HMI, the multi-frequency imaging approach could obtain detailed structural information about the breast and identify small lesions more accurately and effectively. The proposed method has the potential to become a great and helpful vision tool for investigating microwave diagnostic techniques.

Enhanced Holographic Microwave Imaging for MNP Target Tumor Detection

Holographic microwave imaging (HMI) has been proposed as a potential imaging tool for breast cancer detection. However, this method is not sensitive enough to small tumors especially when they located inside the fibro-glandular tissue. This paper investigates the possibility of the use of enhanced HMI to improve the quality of breast image and diagnostic sensitivity by applying magnetic nanoparticles (MNP). A numerical system, including a realistic breast model, 16-element transducer array, a 2-element magnetic coil array, and an image processing model, has been developed to evaluate the effectiveness of the enhanced HMI method for mapping of a dense breast. The numerical results demonstrated that the proposed method could detect the MNP target breast tumor and distinguish the small tumor from fibro-glandular tissue in a dense breast, which has the potential to develop a useful imaging tool for early breast cancer detection in the future.

Huygens Metasurface Holograms with the Modulation of Focal Energy Distribution

AbstractHuygens metasurface, an implementation of Huygens principle with metasurface, shows great potential in the manipulation of electromagnetic wave by elaborately designed subwavelength scale metaatoms with full phase coverage and high transmission amplitude. Here, a multiphase hologram with Huygens metasurface is demonstrated in microwave regime, and a novel algorithm method is proposed to modulate energy distribution among focal points. The proof‐of‐concept experiments show superior microwave holographic images with 89% transmittance efficiency, 59% imaging efficiency, and 1.65 root‐mean‐square error of focal intensity ratio. The proposed Huygens metasurface hologram expands the route to microwave applications for holographic technologies, including computer‐generated holograms, antennas, security, and data storage.

Compressive Sensing Holographic Microwave Random Array Imaging of Dielectric Inclusion

Holographic microwave imaging is an innovative method to image biological objects based on their dielectric properties, which has the advantages of high spatial resolution. However, the image reconstruction method is always a critical issue in holographic microwave imaging. This research aims to investigate the feasibility and effectiveness of applying compressive sensing (CS) technique to the holographic microwave imaging for small dielectric object detection. This paper presents a compressive sensing holographic microwave random array imaging (CS-HMRAI) method for imaging of dielectric objects. A numerical system consists of various dielectric models and imaging processing model are developed to evaluate the proposed approach. The split Bregman (SB) and orthogonal matching pursuit (OMP) algorithms are applied to HMRAI for evaluation of small inclusions embedded in dielectric objects. Various experiments are conducted to identify lesions using the proposed CS-HMRAI method and results are compared with HMRAI and HMRAI via OMP methods. Both simulation and experimental results demonstrate that CS-HMRAI via SB can produce high-quality images and detect arbitrarily shaped small inclusions with random sizes and locations by using significantly fewer sensors and scanning times than the HMRAI and CS-HMRAI via OMP approaches. The proposed approach has the potential for further investigation for breast tumor detection in a fast and cost-effective manner.

3-D Microwave Holographic Imaging With Probe and Phase Compensations

A 3-D microwave holographic imaging algorithm compatible with reflection-coefficient measurement setup is proposed. It can be divided into four parts. First, starting from the open-circuit voltage of antenna, the algorithm compensates for both transmitting and receiving properties of the probe antenna, leading to antenna-independent least squares problems. However, the problems tend to be ill-conditioned. An auxiliary equation is thus derived and exploited to effectively improve the numerical stability and image quality. Third, to accurately locate the unknown target in range direction, a phase compensation method that requires only phase correction to the associated entries of the kernel matrix is proposed based on a simple ray model. Last, considering the finite size of the scanning aperture and beamwidth of the probe antenna, a numerical low-pass filter in the spatial-frequency domain is utilized to effectively locate the worth-solving area. For verification, a series of images reconstructed from the simulated and measured data using the proposed algorithm are presented. Thanks to the enhanced image quality, the geometry, location, and dielectric constant of the target can be retrieved. The range and cross-range resolutions achieved are about $\lambda /10$ and $\lambda /4$ , respectively.

Resolution Limits in Near-Distance Microwave Holographic Imaging for Safer and More Autonomous Vehicles

Resolution Limits in Near-Distance Microwave Holographic Imaging for Safer and More Autonomous Vehicles

Microwave holography using a magnetic tunnel junction based spintronic microwave sensor

In this work, a spintronic sensor based microwave holographic imaging system is developed, demonstrating the feasibility of microwave holographic imaging applications using a spintronic microwave sensor. The high sensitivity of the microwave phase measurement allows the coherent imaging of the target reconstructed in noise environments. Adapting the broadband measurement, not only the shape but also the distance of target can be determined, which implies that a three-dimensional imaging is achievable using a spintronic device.