Indirect Holography Research Articles

Spatial Domain Indirect Holography for a Full Phaseless Approach to Biomedical Microwave Imaging

Microwave imaging approaches generally require the knowledge of the complex incident field distribution inside the imaging domain. This task can be accomplished by probing the observation domain, thus resulting in a time-consuming process, or assuming a numerical/simulated model. Alternatively, the incident field can be collected on the measurement domain, and the field distribution can be successfully retrieved on the whole imaging space. In this paper, a full phaseless, two-step strategy is described, where the phase of the incident field is retrieved by exploiting a spatial domain indirect holography technique, applied to the acquisition points only. The retrieved complex incident field can be so used for the reconstruction of the incident field inside the domain of interest. More specifically, a modal expansion technique and a source reconstruction method are adopted and compared to perform the above task. Once performing the characterization of the incident field distribution, the proposed strategy is included in the framework of a phaseless inverse scattering problem, where intensity-only data of the total field are involved. The effectiveness of the combined approach is demonstrated by considering an imaging scenario which involves a series of breast models as inhomogeneous targets.

Early detection of cancerous tissues in human breast utilizing near field microwave holography

AbstractThis work demonstrates an application of near field indirect microwave holography for the detection of malignant tissues in human breast in an effective way. The holograms are recorded by two directive antennas aligned along each other's boresight while performing a raster scan over a 2D plane utilizing XY‐linear motorized translation stage and a uniform reference wave. The whole information that is, amplitude and phase of an object has been provided by indirect holography at microwave frequencies. The extracted phase values are used to determine the dielectric permittivity values which are further utilized for the identification and validating the positions of malignant tissues in the breast phantom. The experimental evaluations performed on the in‐house designed and developed tissue mimicking 3D printed breast phantoms. The experimental results demonstrate the ability of microwave holography using directive antennas in detecting and identifying the tumors upto the minimum size of 4 mm and maximum depth of 25 mm in fabricated phantom. The quantitative results present the potential of the Near Field Indirect Holographic Imaging (NFIHI) in order to develop an efficient and economical tool for breast cancer detection.

Indirect Holography Breast Cancer Detection System (IH-BCDS) Using VORD

Microwave Imaging is a prominent technique in current imaging modalities for breast cancer detection and its treatment, primarily due to the significant dielectric property contrast between normal and malignant breast tissues. This study describes how VORD Viewpoint-Oriented Requirement Definition (VORD) method is used to examine patients for early detection of cancer by microwave imaging by realizing the existence of multiple perspectives by terminating differences in the demands of stakeholders. The proposed system in this paper is based on microwave imaging by Indirect Holography for Breast Cancer Detection System (IH-BCDS) using Viewpoint-Oriented Requirement Definition (VORD) method. The suggested approach for developing such system is to investigate the possibility of detecting tumors at an early stage by utilizing VORD as analysis tool which is an activity oriented framework for IH-BCDS requirement elicitation. If the system gets implemented successfully, it can play a vital role in detecting the tumor at an early stage by helping a medical specialist in decision making to diagnose the patient.

Phaseless Characterization of Broadband Antennas

A new efficient method for broadband antenna characterization from phaseless acquisitions in the frequency-domain (FD) is presented. The phase-retrieval technique is based on an extrapolation of the off-axis indirect holography. In common with the conventional approach, the power of the interferometric field of the antenna under test (AUT) and a reference antenna, whose field is known in advance, as well as the power of the AUT alone, is measured at the desired frequencies. Nevertheless, the phase retrieval is accomplished independently at each spatial point by filtering in the time-domain (TD) rather than in the k -space. Thus, the dependency of the phase retrieval on the position accuracy is reduced and it can be accomplished simultaneously at all frequencies without resorting to iterative schemes. Moreover, it yields a less dense sampling and a phase-retrieval algorithm not dependent on the geometry of the acquisition. The method is illustrated with a numerical example in the $W$ -band as well as with two near-field (NF) measurement examples in the $K_a$ - and $W$ -bands.

A Modified Phaseless Inverse Scattering Setup Based on Indirect Holography Implemented at Submillimeter-Wave Band

The aim of this communication is to present an enhanced phaseless inverse scattering setup and its implementation at the submillimeter-wave band. This setup is based on a modified indirect holography with synthesized reference signal so that a phase shifter is not required. Thus, a phaseless scanner can be built using a simple power detector resulting in a simplified measurement scheme very suitable to work in the millimeter-wave band and beyond. Mechanical phase shifting is used to bypass the use of electrical phase shifters. In addition, the reference signal is injected by coupling the transmitter and receiver antennas so that directional couplers and power combiners are avoided. New errors introduced by these techniques are analyzed and quantified. The method is validated with simulations as well as measurements at 300 GHz.

Study of image reconstruction for terahertz indirect holography with quasi-optics receiver

In this paper, an indirect holographic image reconstruction algorithm was studied for terahertz imaging with a quasi-optics receiver. Based on the combination of the reciprocity principle and modified quasi-optics theory, analytical expressions of the received spatial power distribution and its spectrum are obtained for the interference pattern of target wave and reference wave. These results clearly give the quantitative relationship between imaging quality and the parameters of a Gaussian beam, which provides a good criterion for terahertz quasi-optics transceivers design in terahertz off-axis holographic imagers. To validate the effectiveness of the proposed analysis method, some imaging results with a 0.3 THz prototype system are shown based on electromagnetic simulation.

Investigations of resolution limits for indirect microwave holographic imaging

This work describes how indirect holography which has previously been applied to the determination of antenna radiation patterns can be adapted for the imaging of passive objects. It provides details of how complex scattered field values can be obtained in a simple and inexpensive manner from sampled scalar intensity measurements taken over a single scanning aperture. This work uses indirect holographic techniques to image a number of simple objects including a rectangular metallic plate, a small metal plate covered by a dielectric sheet and a small metallic circular annulus. This work demonstrates that good quality images can be reconstructed from simple scalar intensity patterns. It demonstrates that clear outlines can be obtained in particular from reconstructed phase patterns and that good images can be obtained from objects with dimensions of the order of a half wavelength. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A novel phaseless frequency scanning based on indirect holography

A phase retrieval technique for multifrequency scattered field acquisition is presented in this paper. The proposed setup is based on indirect holography schemes so that it combines the desired signal with a known reference signal. The setup is used together with a two-dimensional frequency scanning (FS) antenna and, therefore, the positions of scatterers can be retrieved without the need of moving either the antenna or the objects.

Inverse scattering with phase retrieval based on indirect holography via synthesised plane-waves

The aim of this study is to present a technique for object geometry retrieval using scattered field information based on phaseless acquisition, so that a scanning system can be implemented without the need of an expensive vector network analyser. The inverse scattering is accomplished through a two-step strategy that is powered thanks to the combination of the scattered signal with a synthesised reference wave. Thus, the phase is firstly recovered by considering the spectral properties of the mixed signal. Secondly, the reflectivity of the object is computed by means of an inverse scattering algorithm accelerated by a multipolar expansion. The technique is applied and validated for planar as well as spherical ranges considering simulated as well as measured data.

Microwave indirect holographic imaging using an adaptation of optical techniques

Indirect holography provides a quick and inexpensive three-dimensional (3-D) imaging technique at optical frequencies which has not been directly adapted to microwave imaging. This letter describes a technique whereby a radiated offset reference plane wave can be electronically synthesized allowing this technique to be used at microwave frequencies. In this letter, this technique has been applied to the problem of determining antenna radiation patterns and reconstructing complex near fields. Early experimental results compare favorably with results taken using traditional methods.