Coupling Medium Research Articles

Ultrasonic C-scan techniques for the evaluation of impact damage in CFRP

Abstract In the present work, different ultrasonic C-scan approaches were used to evaluate Carbon Fiber Reinforced Polymers (CFRP) submitted to impacts of low energy, in order to evaluate their effectiveness for the detection and characterization of small defects. In particular, as to the question how useful could be the air-coupled C-scan approach, using low frequencies, for in-service application. For that goal, several samples with different stacking sequences and thicknesses were impacted with 1.5 and 3 J. Then, ultrasonic C-scan images were produced by immersion pulse-echo (in amplitude and time-of-flight (TOF)) and immersion through-transmission, and also by air-coupling through-transmission. The immersion C-scan images were produced using 5, 10 and 20 MHz probes and the air-coupled C-scan was made using two 400 kHz probes. The obtained images for the considered samples show that all used methods are able to detect the defects and give acceptable information about their size and shape. However, if the way of delamination evolving over thickness is of interest, the images by TOF should be used. As expected, good image resolution with sharp contour defects require high frequencies. Nevertheless, the air-coupled C-scan demonstrated similar capabilities to detect defects, with the advantage that the coupling medium is air, thus widening the range of applications, such as real-time damage monitoring of composite structures. As a disadvantage, the air C-scan system requires high power emission signals, and also great amplification of the received signals, to face the considerable attenuation in the air.

A Simulation-Based Methodology of Developing 3D Printed Anthropomorphic Phantoms for Microwave Imaging Systems.

This work is devoted to the development and manufacturing of realistic benchmark phantoms to evaluate the performance of microwave imaging devices. The 3D (3 dimensional) printed phantoms contain several cavities, designed to be filled with liquid solutions that mimic biological tissues in terms of complex permittivity over a wide frequency range. Numerical versions (stereolithography (STL) format files) of these phantoms were used to perform simulations to investigate experimental parameters. The purpose of this paper is two-fold. First, a general methodology for the development of a biological phantom is presented. Second, this approach is applied to the particular case of the experimental device developed by the Department of Electronics and Telecommunications at Politecnico di Torino (POLITO) that currently uses a homogeneous version of the head phantom considered in this paper. Numerical versions of the introduced inhomogeneous head phantoms were used to evaluate the effect of various parameters related to their development, such as the permittivity of the equivalent biological tissue, coupling medium, thickness and nature of the phantom walls, and number of compartments. To shed light on the effects of blood circulation on the recognition of a randomly shaped stroke, a numerical brain model including blood vessels was considered.

Bloch waves in an array of elastically connected periodic slender structures

This paper proposes the methodology to carry out the analysis of Bloch wave propagation in an array of vertically aligned and elastically connected structural elements such as beams, strings, plates, or other slender structures. The suggested approach is based on the Galerkin approximation and Floquet-Bloch theorem used in defining the eigenvalue problem and obtaining the band structure of the periodic systems. Special attention is devoted to the case of elastically connected Rayleigh beams with attached concentrated masses and wave propagation in the direction normal to the beam’s length. A validation study is performed by using the finite element model and the frequency response function to confirm the accuracy of the solution obtained via the Galerkin approximation. Two configurations of unit cells, having two and three elastically connected beams with different geometrical and material properties, are considered in the numerical study. The effects of various parameters are investigated to reveal their influence on the frequency band structure and emergence of the zero-frequency bandgap. The results of this study demonstrates the tunability properties of the proposed periodic systems due to changes in values of concentrated masses, stiffness of the coupling medium or boundary conditions on structural elements within the unit cell.

Assessing a Microwave Imaging System for Brain Stroke Monitoring via High Fidelity Numerical Modelling

This work presents the outcomes of a numerical analysis based on a 3-D high fidelity model of a realistic microwave imaging system for the clinical follow-up of brain stroke. The analysis is meant as a preliminary step towards the full experimental characterization of the system, with the aim of assessing the achievable results and highlight possible critical points. The system consists of an array of twenty-four printed monopole antennas, placed conformal to the upper part of the head; each monopole is immersed into a semi-solid dielectric brick with custom permittivity, acting as coupling medium. The whole system, including the antennas and their feeding mechanism, has been numerically modeled via a custom full-wave software based on the finite element method. The numerical model generates reliable electromagnetic operators and accurate antenna scattering parameters, which provide the input data for the implemented imaging algorithm. In particular, the numerical analysis assesses the capability of the device of reliably monitoring the evolution of hemorrhages and ischemias, considering the progression from a healthy state to an early-stage stroke.

High Frequency Breast Imaging: Experimental Analysis of Tissue Phantoms

This article presents the experimental proof of concept of high–frequency microwave breast imaging system operating from 16 to 20 GHz. At those frequencies the wavelengths are in the order of millimeter range which support better resolution in localizing cancerous tumors compared to the conventional microwave imaging systems. A new antenna is developed with a compact size of 7 × 7 mm2, which relies on an ultra-wideband, planar bowtie-like antenna structure. Practical results show that a bandwidth of 23.45 GHz is achieved (16 – 40 GHz) for a reflection loss higher than 10 dB. Furthermore, artificial breast tissue models based on glycerol–oil mixture with agar powder are developed. Dielectric properties of the tissue are stable over a wide frequency range up to 20 GHz at room temperature. The typical high microwave power losses within biological tissue at the operating frequency range are addressed by contacting the antennas directly to the tissue and slightly compressing the phantom without any coupling medium. Hence, the compressed breast geometry has a flat surface with well–defined boundaries, which simplifies tumor localization algorithms. For the purpose of demonstrating the current stage of research, a one–dimensional scanning system is used to localize the tumor’s positions inside the simulated, heterogeneous breast model of 36 mm thickness. Using the root mean square deviation algorithm, we can accurately detect positions of the tumors, which have a cross-sectional area down to 4 × 4 mm2. The preliminary results show the feasibility of achieving a high resolution with a compact microwave system for early-stage breast cancer detection.

Wideband antenna array pattern based on reinforcement epoxy materials & breast cancer diagnostic by composites

Abstract In this study, it is proposed to measure the numerical values of the depths of cancer tissues in the cancer organ. The creation of broadband antennas and the identification of cancer organs is a primary objective. A ΨU -shaped 2 × 2 grid antenna with a geographical coordinate has been modelled using mathematical modelling; simulated by Advanced Design Simulator (ADS); optimised using Moments of Methods (MoM); designed using Microwave Monolithic Integrated Circuits (MMIC) as the prototype and analytic microwave analysis by Agilent N99917A Analyzer represented Microwave Analyzer. It contains 18.64 × 17.92 × 1 mm3 compact dimensions. The model consists of the 2 × 2 array with four ΨU -shaped radiation slots, printed on a dielectric thickness of 1 mm of FR4 material and conductive ground level. The wideband spectrum from 4.5 GHz to 5.5 GHz was transmitted to 5.26 GHz operating frequency. In addition, the broadband antenna, a structure with a low profile and four number of radiating slots, is available. These broadband antennas have been developed for the application of breast cancer detection, which is the secondary provision of study. These broadband antennas with a dielectric model similar to the human breast are available on Debye test beds. These broadband antennas have impressed the materials for coupling that serve as the coupling medium. The findings were higher than the air medium. The higher and lower dielectric strength was demonstrated in these coupling materials. The average of distributed answers has been obtained. Distances between the cancerous organ and transceivers antennas, dielectric intensity and travelling times of spreading answers respectively have been determined by the degree of cancer present in the cancerous organ with the assistance of speed of propagation. This distributed response was therefore obtained in the Debye test bed from the cancer organ. Therefore the numerical depth value, which is validated under existing Debye test beds, and the coverage of the cancerous organ depth.

Special Topic on Coupled Oscillators for Non-von Neumann Computation

When oscillators are loosely coupled to each other, energy transfer between the individual oscillators causes their frequencies to synchronize. The same principle can be found in real life; for instance, metronomes placed on a floating wooden board, pendulums connected via springs, and internal organs following a circadian rhythm. Depending on the strength and time lag of the coupling medium, the phases of the oscillators settle in a way that minimizes the contentions among the oscillating signals.

Acousto-optic tunable flat top filter based on one-dimensional coupled-cavity photonic crystals

In this paper, an acousto-optic tunable flat top filter is proposed by using one-dimensional coupled-cavity photonic crystal, and two kinds of materials, i.e. magnesium fluoride and tellurium dioxide, are selected. Based on the theory of acousto-optic effect, the thickness and refractive index of one-dimensional coupled cavity photonic crystal acousto-optic medium are changed by varying the ultrasonic frequency. After the parameters of acousto-optic medium are changed, the central wavelength of flat top filter of transmission spectrum shifts toward the short wave direction, thus realizing tunable filtering function. Based on the transfer matrix method and the theory of acousto-optic effect, the theoretical model of the flat top filter is established. The rectangularity, passband bandwidth, insertion loss and tunability of flat top filter are simulated by COMSOL software. The results show that the tuning effect can be achieved by applying a certain frequency of ultrasound in the case of different ultrasonic amplitudes. The decreasing trends of transmittance are basically identical in the process of changing ultrasonic frequency in the case of different amplitudes. When the central wavelength of the flat top filter increases from 1510 nm to 1514 nm, the transmissivity corresponding to the central wavelength increases sharply from 37% to 90%; when the central wavelength of the flat top filter continuously increases to 1562 nm, the transmittance corresponding to the central wavelength increasing gently from 90% to 97% in the case of different amplitudes. Considering the transmissivity required to exceed 90% in the passband of flat top filter and the cost of ultrasonic generator, the ultrasonic wave with an amplitude of 0.4 nm is selected as the research object. The flat top filter with 5–6 nm central wavelength and 1514–1562 nm tunable flat top filter can be realized by applying ultrasonic wave with the frequency in a range of 6–11 MHz. In the tunable range, the highest insertion loss is only 2.23 dB, the lowest is only 0.78 dB, and the lowest rectangularity is 1.4. In a practical flat top filter with machining error within 5 cm, the deviation of center wavelength, rectangularity, insertion loss and passband bandwidth of flat top filter are all very small. The flat top filter has the characteristics of easy design and integration, flat passband, wide tunable range, stable passband bandwidth, low insertion loss and high quality factor. It has important applications in optical communication fields such as optical switch, tunable fiber laser and fiber sensing.

Development of a New, Wireless Acquisition System for EMATs Compatible With the Robotics Operating System

The deployment of transducers to perform in situ inspections of industrial components can be complicated, and in many cases is still performed manually by a team of operators, which involves significant costs and can be dangerous. Robots capable of deploying probes in difficult to access locations are becoming available. Electromagnetic acoustic transducers (EMAT) are well suited to be used with robots since they are non-contact transducers that do not require a coupling medium, and can easily perform scans. However, existing acquisition systems for EMATs are generally not suitable to be directly mounted on robots. In this paper, a new wireless acquisition system for EMATs is presented. The system is standalone, it transmits the inspection data over WiFi, and is compatible with the robotics operating system (ROS). In addition, it is designed to be modular, small and lightweight so that it can be easily mounted on robots. The system design in terms of hardware and software is described in this paper. The resulting performance of the system is also reported.

On the replacement of water as coupling medium in scanning acoustic microscopy analysis of sensitive electronics components

The present paper studies the use of isopropyl alcohol and fluorocarbon liquids as coupling fluids for acoustic microscopy non-destructive testing of electronic flight components. For these components the standard coupling liquid water sometimes should be avoided in order to minimize sample contamination. The sound velocities of three different fluorocarbon liquids are measured, their ultrasound attenuation coefficients are estimated, and comparative failure analysis images on various electronics components are obtained by using water and these four alternative coupling liquids.

Microwave Breast Imaging Using Rotational Bistatic Impulse Radar for the Detection of Breast Cancer: Protocol for a Prospective Diagnostic Study.

BackgroundMammography is the standard examination for breast cancer screening; however, it is associated with pain and exposure to ionizing radiation. Microwave breast imaging is a less invasive method for breast cancer surveillance. A bistatic impulse radar–based breast cancer detector has recently been developed.ObjectiveThis study aims to present a protocol for evaluating the diagnostic accuracy of the novel microwave breast imaging device.MethodsThis is a prospective diagnostic study. A total of 120 participants were recruited before treatment administration and divided into 2 cohorts: 100 patients diagnosed with breast cancer and 20 participants with benign breast tumors. The detector will be directly placed on each breast, while the participant is in supine position, without a coupling medium. Confocal images will be created based on the analyzed data, and the presence of breast tumors will be assessed. The primary endpoint will be the diagnostic accuracy, sensitivity, and specificity of the detector for breast cancer and benign tumors. The secondary endpoint will be the safety and detectability of each molecular subtype of breast cancer. For an exploratory endpoint, the influence of breast density and tumor size on tumor detection will be investigated.ResultsRecruitment began in November 2018 and was completed by March 2020. We anticipate the preliminary results to be available by summer 2021.ConclusionsThis study will provide insights on the diagnostic accuracy of microwave breast imaging using a rotational bistatic impulse radar. The collected data will improve the diagnostic algorithm of microwave imaging and lead to enhanced device performance.Trial RegistrationJapan Registry of Clinical Trials jRCTs062180005; https://jrct.niph.go.jp/en-latest-detail/jRCTs062180005International Registered Report Identifier (IRRID)DERR1-10.2196/17524

Dielectric antenna effects in integrating line piezoelectric sensors for optoacoustic imaging

This work studies the adverse effects, as regards noise, of immersing in water an integrating line piezoelectric detector devoted to optoacoustic imaging. We found that the sensor, in conjunction with the acoustic coupling medium (water), behaves as a resonant dielectric antenna. This phenomenon limits the performance of the system because it efficiently captures unwanted electromagnetic signals. The requirement of good acoustic coupling between the water and the sensor precluded the use of a standard metallic shielding enclosure. Therefore, we resorted to a silver-paint-based electrical shield deposited on the detector. This easy-to-implement and low-cost solution significantly increases the signal to noise ratio and does not degrade the acoustic performance. The noise reduction allows the use of a better transimpedance amplifier with higher gain and bandwidth; thus achieving a very sensitive, low-noise detection system.

Deep Learning for Automatic Segmentation of Hybrid Optoacoustic Ultrasound (OPUS) Images.

The highly complementary information provided by multispectral optoacoustics and pulse-echo ultrasound have recently prompted development of hybrid imaging instruments bringing together the unique contrast advantages of both modalities. In the hybrid optoacoustic ultrasound (OPUS) combination, images retrieved by one modality may further be used to improve the reconstruction accuracy of the other. In this regard, image segmentation plays a major role as it can aid improving the image quality and quantification abilities by facilitating modeling of light and sound propagation through the imaged tissues and surrounding coupling medium. Here, we propose an automated approach for surface segmentation in whole-body mouse OPUS imaging using a deep convolutional neural network (CNN). The method has shown robust performance, attaining accurate segmentation of the animal boundary in both optoacoustic and pulse-echo ultrasound images, as evinced by quantitative performance evaluation using Dice coefficient metrics.

A flexible and noncontact guided-wave transducer based on coils-only EMAT for pipe inspection

Ultrasonic guided wave testing technique, with its advantages of long propagation distance, low attenuation and high testing efficiency, has been widely used in nondestructive testing and structure health monitoring for pipes. In this paper, a flexible and noncontact guided-wave transducer based on a novel and coils-only electromagnetic acoustic transducer (EMAT) is proposed. In this new transducer, a planar magnetic coil of racetrack shape fed with rectangular-pulsed current is used to produce a quasi-static magnetic field, while a planar meander coil fed with RF-pulse current is used for pulsing and receiving guided-wave signals. Based on the magnetostrictive mechanism, the proposed transducer can generate and receive guided wave of L(0,2) mode in ferromagnetic metal pipes without coupling medium. Electromagnetic fields for the two coils and the induced ultrasonic waves are studied by simulation. Both the simulation and experimental results show that the proposed transducer is effective for generating and receiving ultrasonic guided wave of L(0,2) mode in ferromagnetic pipes, and can be applied on detection for corrosion. Due to the flexible, noncontact feature, and compact configuration of the proposed transducer, it can be conveniently applied for pipes in different diameter with rusty surface or coating in narrow space.

Study of the Refraction Effects in Microwave Breast Imaging Using a Dry Setup.

Medical Microwave Imaging (MWI) has been studied as a technique to aid breast cancer diagnosis. Several different prototypes have been proposed but most of them require the use of a coupling medium between the antennas and the breast, in order to reduce skin backscattering and avoid refraction effects. The use of dry setups has been addressed and recent publications show promising results. In this paper, we assess the importance of considering refraction effects in the image reconstruction algorithms. To this end, we consider a simplified homogeneous spherical model of the breast and analytically compute the propagating rays through the air-body interface. The comparison of results considering only direct ray propagation or refracted rays shows negligible impact on the accuracy of the images for moderately high permittivity media. Thus, we may avoid the computational burden of calculating the refracted rays in convex shapes.

A Two-Stage Rotational Surface Clutter Suppression Method for Microwave Breast Imaging With Multistatic Impulse-Radar Detector

Radar-based microwave imaging is a promising technique for multiple medical applications, such as breast health monitoring, breast cancer detection, ablation monitoring, and chemotherapy monitoring. In our previous work, a hand-held multistatic CMOS impulse-radar detector was developed. It was designed to be placed directly on the patient in a supine position without a coupling medium. In the radar-based microwave breast imaging, the surface clutters, which are generated from skin reflection, imperfect contacts, and antenna coupling, deteriorate the imaging quality. This article proposes a two-stage rotational clutter suppression method for the multistatic rotational configuration of the radar detector. It consists of a signal selection stage and an adaptive filtering stage. The novelty of the proposed method is that a prior constraint using L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> regularization is introduced to facilitate the filtering. Meanwhile, the antenna and channel variations are considered in the signal selection. The performance of the proposed method is verified in experiments with different surface conditions and patient trial. The results demonstrated that the proposed method is effective in suppressing the surface clutters and improving the image quality.

A Fast Interface Reconstruction Method for Frequency-Domain Synthetic Aperture Focusing Technique Imaging of Two-Layered Systems with Non-planar Interface Based on Virtual Points Measuring

Frequency-domain synthetic aperture focusing technique (SAFT), such as non-stationary phase shift migration (NSPSM), plays an essential role in the ultrasonic imaging of two-layered systems with non-planar interfaces. However, with NSPSM fast imaging under blind test conditions is hard to realize due to a lack of interface information in practice. To overcome this difficulty, a fast interface reconstruction method for NSPSM imaging of non-planar two-layered systems is proposed based on virtual points measuring. In blind testing conditions, a series of virtual points (VP) were created at the non-planar interface of the two-layered system by the time-of-flight (TOF) of the first incoming echo. Then, the interface for the two-layered system was quickly established by the interpolation of the VP. Finally, the NSPSM imaging for the two-layered system with non-planar interfaces was realized by the borderline which is used to distinguish the velocities of the coupling medium and tested part in the same extrapolating depth. The imaging results showed that the position of side-drilled holes was located correctly and the efficiency of the algorithm was significantly improved. Hence, the VP-NSPSM method is expected to achieve fast or even real-time imaging of two-layered systems with non-planar interfaces in practical NDT applications.

Optical-Resolution Photoacoustic Microscopy Using Transparent Ultrasound Transducer.

The opacity of conventional ultrasound transducers can impede the miniaturization and workflow of current photoacoustic systems. In particular, optical-resolution photoacoustic microscopy (OR-PAM) requires the coaxial alignment of optical illumination and acoustic-detection paths through complex beam combiners and a thick coupling medium. To overcome these hurdles, we developed a novel OR-PAM method on the basis of our recently reported transparent lithium niobate (LiNbO3) ultrasound transducer (Dangi et al., Optics Letters, 2019), which was centered at 13 MHz ultrasound frequency with 60% photoacoustic bandwidth. To test the feasibility of wearable OR-PAM, optical-only raster scanning of focused light through a transducer was performed while the transducer was fixed above the imaging subject. Imaging experiments on resolution targets and carbon fibers demonstrated a lateral resolution of 8.5 µm. Further, we demonstrated vasculature mapping using chicken embryos and melanoma depth profiling using tissue phantoms. In conclusion, the proposed OR-PAM system using a low-cost transparent LiNbO3 window transducer has a promising future in wearable and high-throughput imaging applications, e.g., integration with conventional optical microscopy to enable a multimodal microscopy platform capable of ultrasound stimulation.

Full noncontact laser ultrasound: first human data

Full noncontact laser ultrasound (LUS) imaging has several distinct advantages over current medical ultrasound (US) technologies: elimination of the coupling mediums (gel/water), operator-independent image quality, improved repeatability, and volumetric imaging. Current light-based ultrasound utilizing tissue-penetrating photoacoustics (PA) generally uses traditional piezoelectric transducers in contact with the imaged tissue or carries an optical fiber detector close to the imaging site. Unlike PA, the LUS design presented here minimizes the optical penetration and specifically restricts optical-to-acoustic energy transduction at the tissue surface, maximizing the generated acoustic source amplitude. With an appropriate optical design and interferometry, any exposed tissue surfaces can become viable acoustic sources and detectors. LUS operates analogously to conventional ultrasound but uses light instead of piezoelectric elements. Here, we present full noncontact LUS results, imaging targets at ~5 cm depths and at a meter-scale standoff from the target surface. Experimental results demonstrating volumetric imaging and the first LUS images on humans are presented, all at eye- and skin-safe optical exposure levels. The progression of LUS imaging from tissue-mimicking phantoms, to excised animal tissue, to humans in vivo is shown, with validation from conventional ultrasound images. The LUS system design insights and results presented here inspire further LUS development and are a significant step toward the clinical implementation of LUS.

Disposable ultrasound-sensing chronic cranial window by soft nanoimprinting lithography

Chronic cranial window (CCW) is an essential tool in enabling longitudinal imaging and manipulation of various brain activities in live animals. However, an active CCW capable of sensing the concealed in vivo environment while simultaneously providing longitudinal optical access to the brain is not currently available. Here we report a disposable ultrasound-sensing CCW (usCCW) featuring an integrated transparent nanophotonic ultrasonic detector fabricated using soft nanoimprint lithography process. We optimize the sensor design and the associated fabrication process to significantly improve detection sensitivity and reliability, which are critical for the intend longitudinal in vivo investigations. Surgically implanting the usCCW on the skull creates a self-contained environment, maintaining optical access while eliminating the need for external ultrasound coupling medium for photoacoustic imaging. Using this usCCW, we demonstrate photoacoustic microscopy of cortical vascular network in live mice over 28 days. This work establishes the foundation for integrating photoacoustic imaging with modern brain research.