Metallic Objects Research Articles

Corrosion and material properties of 316L stainless steel produced by material extrusion technology

Material Extrusion (ME) multi-step additive manufacturing of highly filled metal filament Ultrafuse 316L offers a notable alternative to cutting-edge additive technologies of metal alloys. It allows the creation of metal objects with debinding and sintering processes. Especially Powder Bed Fusion (PBF) technologies using laser or high-energy electron beams require costly maintenance, professional operators, and demanding process conditions during printing. On the other hand, such requirements do not incorporate ME printing.This study aims to comprehensively investigate and describe the behavior of material printed out of Ultrafuse 316L stainless steel filament on an affordable ME office-friendly printer. The main focus was on tests of fracture toughness, porosity, and corrosion resistance determined by the Tafel extrapolation method. The secondary objective was verifying the mechanical properties found in other studies (differing in results). For this purpose, several sets of fully dense samples were printed, debinded, and tested.

Detection of the Altitude and On-the-Ground Objects Using 77-GHz FMCW Radar Onboard Small Drones

Small drones are being utilized by researchers for applications such as object tracking, imaging and remote sensing as they have become more available, inexpensive and mobile with the advancements in sensor and UAV technologies. They can be equipped with sensors such as cameras and radars. Radars can be used onboard for navigation aid by detecting range and velocity, as well as for radar imaging applications. Although they are used in the latter commonly, radars can be used in navigation aid as well since they are barely affected by weather conditions or smoke. FMCW radars are suitable for drones since they can be lightweight and can detect range and velocity. Therefore, an FMCW radar-equipped drone system is designed and implemented for UAV positioning applications. A postprocessing algorithm is developed for detecting the altitude above ground level as well as the amount of reflection coming from the material on the ground surface, and a range compensation method is proposed to improve the performance of the algorithm. The results of a field experiment showed that the radar system and the postprocessing algorithm can be used for drone-based airborne positioning applications. Altitude values obtained with the radar postprocessing are in agreement with the altitude of the drone. Reflections coming from the metal objects are distinguished from those coming from the ground. With the range compensation method, minimum detectable altitude value is improved and the magnitude of ground reflections obtained from different altitudes became similar. The proposed system and algorithm can be utilized in navigation and in landing aid applications.

Quantitative evaluation of the reduction of distortion and metallic artifacts in magnetic resonance images using the multiacquisition variable‑resonance image combination selective sequence.

Magnetic resonance imaging (MRI) is superior to computed tomography (CT) in determining changes in tissue structure, such as those observed following inflammation and infection. However, when metal implants or other metal objects are present, MRI exhibits more distortion and artifacts compared with CT, which hinders the accurate measurement of the implants. A limited number of reports have examined whether the novel MRI sequence, multiacquisition variable-resonance image combination selective (MAVRIC SL), can accurately measure metal implants without distortion. Therefore, the present study aimed to demonstrate whether MAVRIC SL could accurately measure metal implants without distortion and whether the area around the metal implants could be well delineated without artifacts. An agar phantom containing a titanium alloy lumbar implant was used for the present study and was imaged using a 3.0 T MRI machine. A total of three imaging sequences, namely MAVRIC SL, CUBE and magnetic image compilation (MAGiC), were applied and the results were compared. Distortion was evaluated by measuring the screw diameter and distance between the screws multiple times in the phase and frequency directions by two different investigators. The artifact region around the implant was examined using a quantitative method following standardization of the phantom signal values. It was revealed that MAVRIC SL was a superior sequence compared with CUBE and MAGiC, as there was significantly less distortion, a lack of bias between the two different investigators and significantly reduced artifact regions. These results suggested the possibility of utilizing MAVRIC SL for follow-up to observe metal implant insertions.

Metal artefact reduction in digital tomosynthesis using component decomposition

We propose a technique for metal artefact reduction in digital tomosynthesis reconstruction. Although the problem was addressed earlier in the literature, we suggest another approach, which is, in our opinion, simpler, and easier to implement. It is a two-stage algorithm. At the first stage, attenuation images are segmented by decomposing their intensity distributions into gaussian-like components. Statistical information contained in each component is used for pixel classification. Components corresponding to metallic objects are identified, and a pixel threshold value separating regions occupied by metal objects from the rest of the image is found. Based on this value, at the second stage, a smooth mapping of image intensity is applied. This makes dense regions transparent, resulting in the artefact reduction in reconstruction. The methodology is demonstrated by several examples.

Tic-“tack”-toe, out I go: A strategic implementation of flexible bronchoscopy in the removal of an aspirated thumbtack

Thumbtack aspiration is a medical emergency as the sharp end poses a risk of injuring the respiratory tract and potentially causing fatal complications. Its removal can be difficult, even under bronchoscopy guidance, as the sharp end can potentially lead to bronchial mucosal tears and perforation. We present a case of a 16-year-old male who was admitted following the unintentional ingestion of a thumbtack which was removed via flexible bronchoscopy. These sharp metal objects are commonly removed using rigid bronchoscopy, but removal by flexible bronchoscopy, although challenging, is still possible.

Metal Artifact Reduction in Dental CBCT Images Using Direct Sinogram Correction Combined with Metal Path-Length Weighting.

Metal artifacts in dental computed tomography (CT) images, caused by highly X-ray absorbing objects, such as dental implants or crowns, often more severely compromise image readability than in medical CT images. Since lower tube voltages are used for dental CTs in spite of the more frequent presence of metallic objects in the patient, metal artifacts appear more severely in dental CT images, and the artifacts often persist even after metal artifact correction. The direct sinogram correction (DSC) method, which directly corrects the sinogram using the mapping function derived by minimizing the sinogram inconsistency, works well in the case of mild metal artifacts, but it often fails to correct severe metal artifacts. We propose a modified DSC method to reduce severe metal artifacts, and we have tested it on human dental images. We first segment the metallic objects in the CT image, and then we forward-project the segmented metal mask to identify the metal traces in the projection data with computing the metal path length for the rays penetrating the metal mask. In the sinogram correction with the DSC mapping function, we apply the weighting proportional to the metal path length. We have applied the proposed method to the phantom and patient images taken at the X-ray tube voltage of 90 kVp. We observed that the proposed method outperforms the original DSC method when metal artifacts were severe. However, we need further extensive studies to verify the proposed method for various CT scan conditions with many more patient images.

Electrochemical Polarization as a Sustainable Method for the Formation of Bronze Patina Layers on a Quaternary Copper Alloy: Insight into Patina Morphology and Corrosion Behaviour

The bronze patina is aesthetically pleasing and enhances the corrosion resistance of the metallic object. This corrosion product layer can develop naturally, through aging or artificially. However, artificial methods require substances that are hazardous to human health and the environment. In this study, a sustainable approach to patina development, based on the anodic polarization of a 85.5Cu-4.2Pb-4.5Sn-5.7Zn copper alloy immersed in 0.1 M NaCl + 0.01 M NaHCO3 were characterized using polarization curves, chronoamperometry, electrochemical impedance spectroscopy, electrochemical noise measurements, X-ray diffraction, and scanning electron microscopy. The results indicate that the anodic potential modifies the current density as well as the diffusion coefficient of oxygen associated with a thicker corrosion product layer. Electrochemical Impedance spectroscopy and electrochemical noise show that the porous behaviour and corrosion resistance increases as the potential becomes more anodic due to the formation of a protective layer. This behaviour corresponded with the results acquired by chronoamperometry. The surface characterization shows that the potential applied changes the surface morphology and composition of the corrosion products, being identified the crystalline phases of nantokite and atacamite although Cu, Cl, O, Zn, and Pb elements were also detected.

Textiles in a Viking Age hoard: Identifying ephemeral traces of textiles in metal corrosion products

This paper presents a novel method and terminology to identify and describe textiles from ephemeral traces in metal corrosion products. Since the 1980s, mineralised textiles (positive and negative casts in Janaway’s terminology) have been an important source of archaeological evidence. A major issue now is the identification of textiles in metal corrosion products when only faint traces remain. These traces no longer appear like textiles and are vulnerable to misinterpretation. Confused with metal dendritic structures or the form of corrosion products themselves, they are often lost through handling or cleaned off through conservation practices. This loss is cumulatively significant. To remedy this issue, this paper defines and characterises the form and structure of ephemeral traces of archaeological textiles through examination of metal corrosion products on a Viking Age hoard from Scotland. It defines a new terminology to supplement Janaway: petal shapes, remnant textile surface, ghost textile surface. The analysis follows an investigative inquiry from assessment to laboratory analysis using a Dinolite portable digital microscope, optical light microscopy with Z stacking and scanning electron microscopy (SEM). The results allow the secure identification of textiles from previously unidentified corrosion features. The method has wide applicability to corroded archaeological metal objects and has the potential to significantly increase the identification of textiles associated with metals and transform current understanding of hoards.

Utilization of harmonics in phaseless near-field microwave computational imaging based on space–time-coding transmissive metasurface

Based on a space–time-coding (STC) transmissive metasurface (TMS), we present the utilization of electromagnetic harmonic spectra in phaseless near-field microwave computational imaging (CI). Each element of the TMS integrates one PIN diode as a switch to independently regulate the transmission amplitude, giving rise to a 14-dB modulation depth at 21 GHz. Using the TMS and two standard horn antennas, a phaseless near-field microwave CI system is established in a single-pixel manner. A simple and effective space–time-coding scheme is detailed to covert a monochromatic signal into multiple harmonics that can be applied to sample the objects. To obtain the sensing matrix built by the harmonics, we propose a method that is developed from the Fresnel diffraction theory. Moreover, we experimentally validate our CI system by reconstructing two metallic objects. The reported STC scheme and the corresponding CI system using TMS could inspire future studies on low-cost imaging hardware development and harmonic wave utilization for high-resolution CI systems.

Fast, Fully-Automatic Characterization of Metallic and Water-Based Threat Objects for Millimeter-Wave Personnel Screening Systems

Efficient characterization of concealed person-worn objects enhances the security of air travel and reduces the inspection time. Mm-wave nearfield radar can detect metallic objects such as guns or knives, as well as water-based materials that might be associated with peroxide threats. However, it cannot discriminate these potential threats from benign objects to decrease the nuisance alarm rate. Moreover, distinguishing these potential threats from benign objects in the presence of human skin is even more challenging. The authors have previously developed a method using mm-wave imaging to estimate the nominal body contour (NBC) with attached objects. This paper extends the image-processing-based algorithm to identify concealed metallic and water-based objects, as thin as 1 cm, attached to arms, legs, torso, and the pelvic region. The algorithm determines if the anomaly in the image is due to lossless or conductive material seen respectively as a depression or protrusion relative to the NBC. Next, high-loss water-based objects are distinguished from metallic and benign low-loss objects. The developed method is verified experimentally via actual images of human subjects, with foreign attached objects of various types and sizes. The images were captured by the High Definition-Advanced Imaging Technology (HD-AIT) scanner, a laboratory prototype system developed recently by the U.S. Department of Homeland Security (DHS). The developed codes resulted in zero miss and 7% rate of false alarm, while the rest of objects were either characterized correctly or referred to for a secondary pat down. Our method is performed fully-automatically and within a few seconds.

A Shared Method of Metal Object Detection and Living Object Detection Based on the Quality Factor of Detection Coils for Electric Vehicle Wireless Charging

High power alternating magnetic fields can cause lesions and pathological changes in living object bodies entering the wireless charging area. Also, as for metal objects, the eddy effect can cause the security risks such as fire and ignition hazards. Hence, metal object detection (MOD) and living object detection (LOD) are the necessary functions for a wireless power transfer (WPT) system. A shared method of MOD and LOD based on the quality factor of detection coils for electric vehicle wireless charging was proposed in this paper to realize the dual functions by the same detection coil array. Firstly, the effect of metal objects and living objects on the detection coil quality factor was analyzed in detail. Secondly, a method of real-time calculation of quality factor was proposed to detect whether the foreign object exists. Then, a distinction algorithm based on the phase variation trend of resonant capacitor voltage was designed to classify the type of foreign objects. Finally, a 3.3 kW experimental prototype, including a foreign object detection (FOD) system, was established to verify the validity. The advantage of the quality factor as the core indicator for FOD was analyzed in detail. Under the condition of an iron wafer, aluminum wafer, and beef chunk placed on the detection coil, the quality factor calculation results of the detection coil in contrast to those without foreign objects decreased by 80.8%, 50.5%, and 69.9%, respectively. Meanwhile, the phase difference of the excitation relative to the resonant capacitor voltage changed -61.3°, -74.6°, and 49.4°, respectively.

Metal artifact reduction by virtual monoenergetic reconstructions from spectral brain CT

PurposeConventional computed tomography (CT) images are severely affected by metal artifacts in patients with intracranial coils. Monoenergetic images have been suggested to reduce metal artifacts.The aim of this study was to assess metal artifacts in virtual monoenergetic images (VMIs) reconstructed from spectral brain CT. MethodsThirty-two consecutive patients with intracranial coils examined by spectral non contrast brain CT (NCCT) at our center between November 2017 and April 2019 were included. Attenuation and standard deviations were measured in regions of interest (ROIs) at predefined areas in artifact-free and artifact-affected areas. Measurements were performed in conventional polyenergetic images (CIs) and the corresponding data for VMIs were retrieved through spectral diagrams for the each ROI. Subjective analysis was performed by visual grading of CIs and specific VMIs by two neuroradiologists, independently. ResultsIn artefact-affected image areas distal from the metal objects, the attenuation values decreased with higher energy level VMIs. The same effect was not seen for artefact-affected image areas close to the metal.Subjective rating of the artefact severity was significantly better in VMIs at 50 keV for one of the two reviewers compared to the CIs. Overall image quality and tissue differentiation scores were significantly higher for both reviewers in VMIs at 60 and 70 keV compared to CIs. ConclusionOur quantitative and qualitative image analysis shown that there is a small significant reduction of intracranial coils artifacts severity by all monoenergetic reconstructions from 50 to 200 keV with preserved or increased overall subjective image quality compared to conventional images.

Evaluation of Artifacts Produced by Different Dental Crown Materials on Ultrashort Echo Time Magnetic Resonance Imaging

Objectives: Many patients with metallic objects in the head and neck region may require magnetic resonance imaging (MRI). The aim of this study was to assess the artifacts produced by different dental crown materials on ultrashort echo time (UTE) MRI. Materials and Methods: Cobalt-chromium (Co-Cr) and zirconia (Zr) crown and fixed bridges were included and embedded in agar gel. UTE sequence by 1.5T MRI was performed and the artifact area produced by these materials, were measured within the region of interest (ROI). Mean artifact areas were recorded. Results: Mean artifact area produced by Co-Cr and Zr was 140.055 mm2 and 102.349 mm2, respectively. Zr material produced less artifacts than metal restoration. It was stated that the amount of artifact increased as the number of elements increased. Conclusions: Co-Cr metal restorations have stronger effect than Zr material on UTE MRI. UTE sequence is useful in evaluating susceptibility artifacts from different materials. Knowing the amount of artifact produced by different materials will help to produce new materials that cause less artifact formation or to improve the properties of existing materials.

Broadband one-dimensional range profiles characteristic of rough surface in terahertz band

<sec>The one-dimensional (1D) range profile is an important back scattering characteristic of objective, which reveals the longitudinal distribution of radar cross section (RCS) along the detection beam. Since the shape and posture can be reflected by the 1D range profile, it is of great significance in military to determine the target orientation, velocity and whether it is armed. In this paper, broadband terahertz 1D-range-profile measurement system is built based on the time-domain spectroscopy (TDS) system. It is in bistatic configuration (bistatic angle of 9°) and the signal-to-noise ratio (SNR) is 34.5 dB, with a gold mirror used as a reflector. Benefiting from the ultrashort terahertz pulse width (full pulse width of 0.52 ps), the bandwidth covers the frequency range from 0.1 THz to 2.5 THz (peaked at 0.9 THz), corresponding to the range resolution on a submillimeter scale.</sec><sec>Firstly, the 1D range profiles of several objects in different shapes are measured, including the step, cylinder, step cone and their combination, which indicates that the geometric profile of the target in the detection direction is adequate to identify the shape feature of the target and proves the reliability of the 1D range profile measuring system based on TDS. Secondly, aluminum plates with different surface roughness in a range of 0–25 μm are also characterized. The Kirchhoff approximation theory and small perturbation method (SPM) are introduced to illustrate the characteristics of broadband terahertz 1D range profile related to the surface roughness of target. It is found that the scattering characteristic of metal object in the terahertz range is sensitive to surface roughness. If the surface roughness of the object is larger, the peak intensity of the 1D range profile will be weaker and the echo signal pulse width becomes wider. The rule is also applicable for the cases with different incident angles. Furthermore, it is revealed that the time delay of the 1D range profile in the bistatic system is related to the rotation direction of the target, which is useful in estimating the posture of the target. In summary, the characteristics of 1D range profile for metal objects relating to shape, surface roughness and posture are studied. The conclusions have certain guiding significance for the target detection and recognition of terahertz radar.</sec>

Online physics experiment creation on resonance in the LC circuit with a simple metal detector circuit

Online learning is necessary and challenging to develop effective teaching strategies to support student learning during the COVID-19 period. This course has seven students. Some essential equipment is sent to students by post. We demonstrate a simple experiment on the resonance frequency in the LC circuit with a simple metal detector circuit based on an IC555-timer transistor. In principle, Metal objects within the magnetic field of inductance affect the resonance frequency resulting in oscillator frequency changes. So, we could study the resonance frequency of the LC circuit from frequency changes by changing the inductance of the inductor. The sound frequency has been generated from the metal detector circuit and is altered depending on the coil’s inductance. The frequency change is measured by a sound detector application on the smartphone. From the results, we discuss the equation of the resonance frequency and the oscillator frequency changes and calculate the relationship between the frequency of sound and the inductance value of the coil. As a result, it is possible to adapt the simple metal detector to use the study of the resonance formula and calculate the inductance of any coil with accuracy.

An acoustic analysis of a sample of English and Ukrainian onomatopoeias: A pilot study

Much has been written about the position of onomatopoeias in languages nevertheless, sources dealing with the phonetic nature of these sound-echoing words are very rare. Some notes about the phonetic substance of onomatopoeias can be found in the work of Bredin and also Tsur who offers a more detailed phonetic investigation of sound-imitating expressions in relation to real sounds. On the basis of acoustic analysis of the onomatopoeic expression /ku:ku:/ and of the real sound the cuckoo produces, Tsur comes to the conclusion that such speech sounds are used as equivalents of natural sounds/noises whose phonetic properties best fit the imitated natural sounds. To evaluate this assumption, this pilot study includes acoustic analysis of onomatopoeias from English and Ukrainian. The selected English and Ukrainian verbal imitations of natural sounds (a cat’s meowing, an owl’s hooting, hitting two metal objects together and knocking on a door) were acoustically analyzed in terms of the structure of their sound spectra for comparison with the sound spectra of the natural sounds they imitate.

The impact of dental metal restorations on the oral oxidative stress level.

Dental materials may influence the equilibrium between production and destruction of free radicals, thus creating conditions for developing of local or general oxidative stress. Metal ions, emitted from base dental alloys, may cause changes in cell structures and functions. Isoprostane concentration may indicate possible cell damage, caused by free radicals, and can be used for evaluation of the oxidative stress level. The aim of this study was to compare the level of 8-isoPGF2-alpha in saliva in patients with and without metal dental restorations. 35 patients were divided in two groups according to the presence or absence of metal dental objects. Non-stimulated and stimulated saliva samples were collected. The concentration of 8-isoPGF2-alpha was measured by liquid chromatography tandem mass spectrometry. For statistical analysis non-parametric Mann-Whitney test, Kruskal Wallis test, and Wilcoxon signed-rank test were applied. There was a significant difference in the concentration of 8-isoPGF2-alpha between the samples of non-stimulated and stimulated saliva. The concentration of 8-isoPGF2-alpha in non-stimulated saliva in patients with metal dental restorations was significantly higher than the one in the group of patients without metal objects. The presence of metal dental restorations increases the concentration of 8-isoPGF2-alpha in non-stimulated saliva. Key words:Saliva, dental metal restorations, oxidative stress.

Clinical Practice Guidelines for the Therapeutic Use of Repetitive Transcranial Magnetic Stimulation in Neuropsychiatric Disorders.

Clinical Practice Guidelines for the Therapeutic Use of Repetitive Transcranial Magnetic Stimulation in Neuropsychiatric Disorders.

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

Terahertz time-domain spectroscopy (THz-TDS) is a promising tool for high-resolution 3D imaging of objects due to the high center frequency and bandwidth compared to microwave systems. In addition, terahertz waves have a higher penetration depth than visible or near-infrared radiation. Typically, optics are used to focus the terahertz radiation onto an object under test. This limits the imaging capability in the axial dimension to the depth of field and limits simple imaging of complex surfaces. In this work, we adapt a backpropagation algorithm from synthetic aperture radar (SAR) imaging to reconstruct high-resolution 3D images from time-domain traces acquired with a lensless THz-TDS system. For this purpose, an inverse cylindrical aperture is used and an equation that describes the maximum achievable resolution as a function of the beam pattern, the bandwidth, and the length of the synthetic aperture is derived. The calculated resolution is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$960 \mu \text{m}$ </tex-math></inline-formula> for the linear dimension of the aperture and 75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> for the rotationally symmetric dimension of the cylindrical aperture for a bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\,\text {THz}$ </tex-math></inline-formula> . The resolving power is verified by measurements on metallic and dielectric objects. In the future, this method can be used for non-destructive testing of objects with complex shaped surfaces and internal structures.

Planar Inverted Antenna With Embedded Patch Excitor for On-Metal Tag Design

For the first time, a non-resonating patch is embedded inside a planar inverted antenna structure for the design of a low-profile metal-mountable tag antenna. The tag has a compact and low profile with a footprint of 40 mm × 40 mm × 3.3 mm. Efficient coupling between the excitation patch and the radiating patch, which are separated by a narrow and long slotline can improve the radiation efficiency. The slotline can provide sufficient shunt capacitance so that the antenna reactance can match with the chip reactance. The antenna and chip impedances are in conjugate match for the proposed tag, maximum power transfer between the chip and the antenna is possible for a better radiation performance. Being tested with 3.28 W effective isotopically radiated power (EIRP), the proposed tag can attain a good read range of 16 m. The tag antennas resonant frequency is very stable, and it is not significantly impacted by the metallic backing object underneath.