Search

This study systematically investigated the influence of the position and inclination angle of an externally mounted hollow cathode in 1.35 kW magnetically shielded Hall thrusters to establish the r...

In this letter, a novel 4 b multistate frequency-selective surface is proposed. Four p-i-n diodes are used to maneuver multifunction behavior of the structure with seven different functional states. The 4 b binary state operations 0000, 1100, 0011, and 1111 offer transverse electric (TE)/transverse magnetic (TM) waves both transmit, TE transmit/TM shield, TM transmit/TE shield, and TE/TM both shield, respectively, at 2 GHz frequency. The passband at 2 GHz frequency has $-\text{10}$ dB fractional bandwidth of 117%. The binary states 1101 and 1110 are symmetric, which select the TE wave transmit/TM wave shield to the passband at 3.45 GHz frequency with $-\text{10}$ dB fractional bandwidth of 49%, whereas binary states 1011 and 0111 allow the TM wave to transmit at 3.45 GHz and shield the TE wave. The four symmetric binary states 0101, 0110, 1010, and 1001 provide transmission band at 3.45 GHz frequency for dual-polarized plane wave incidence. The transmission of both the passbands can be shielded by selecting the binary state equal to 1111. An equal circuit model is used to elaborate the contribution of different passive structural elements in terms of lumped components. A prototype of the structure is fabricated, and transmission coefficients for different states at normal and oblique incidence of the electromagnetic plane wave are measured, which verifies the simulated responses of the structure.

In this paper, the shielded open-circuited probe operating in the wide frequency range from 75MHz to 2GHz is proposed. The probe is made of an SubMiniature version A (SMA) flange connector. The central rod of the SMA connector emerges from a coaxial transition in the flange and shielded by four rods. The robe design allows us to calculate of the probe reflection coefficient S11 used simple analytical transmission line model (TEM wave mode), the parameters of which were calibrated on a set of substances with a known frequency spectrum of permittivity. The refractive index (RI) and normalized attenuation coefficient (NAC) retrieval technique is based on solving the inverse problem of minimizing the residual norm between measured and calculated frequency spectra of reflection coefficient S11. After calibration, the root-mean-square error (determination coefficient) between the measured and calculated module and phase of the reflection coefficient S11 for the sets of calibration media air, distilled water, butanol, pure ice, water solution with NaCl of salinity of 8.9% do not exceed 0.26dB (0.995) and 0.03 rad (0.999), respectively, in the frequency range from 75MHz to 2GHz. The root-mean-square error (determination coefficient) between the measured RI and NAC spectra for four soil cover samples (variation of the clay fraction from 10.5 g/g to 47.6 g/g) using the proposed probe and a precision coaxial cell not exceeds 0.109 (0.993) and 0.057 (0.986), respectively, in the frequency range from 75 MHz to 2 GHz. As a result, it is experimentally shown that RI и NAC can be measured by the proposed non-precision probe with an error comparable to the precision coaxial cell.

This work presents the design and fabrication of a novel uniplanar microstrip patch antenna that is simultaneously dual-band and dual-polarized. By embedding a carefully designed metamaterial-based electromagnetic bandgap structure (MTM-EBG) into the edges of a conventional square patch, operation with orthogonal linear polarizations at both 3.6 and 5.8 GHz is achieved. The design is fully printed, compact, low-profile, and pin-fed using a shielded microstrip configuration, and it is 17% smaller than a conventional square patch at the lower operating frequency. The presented antenna shows a reflection coefficient better than −16 dB at each frequency and over 24 dB of port-to-port isolation. Radiation patterns are patch-like in both operating bands, with broadside gains of 6.4 and 5.3 dBi at the lower and higher operating frequencies, respectively. The antenna is fabricated using conventional PCB manufacturing methods, and measurement results are in very good agreement with simulations.

Recent developments in gamma spectroscopy and data processing techniques opened up the possibility of providing high degrees of flexibility for different kinds of ambient, cosmic, and sample-related background suppression. The BALQARAD clover active shield is a newly acquired germanium detector that offers extraordinary and non-conventional time registers in the List File mode to optimize the setup in its different operation modes. The setup's geometry has been optimized for clover-active shield detector coincidences or anti-coincidences, depending on the details of the particular radioactive sources (22Na, 60Co, and 137Cs). The system consists of plastic scintillation plates that detect cosmic rays within coincidences with the clover. The time delay between the cosmic and clover detector was tested, and the time window of 640 ns was detected by addressing two desired prompt and delayed signals. The registered spectra were characterized by very prominent continua, obscuring low-intensity peaks of weak gamma-ray emissions. The peak-to-Compton ratio and peak-to-total ratio were greatly improved after using offline veto techniques, leading to much greater accuracy in determining the full-energy peak. The offline coincidence method's quick assessment points out the importance of reducing the Compton and background continua in detecting low activities and yields. This study will serve as a basis for more advanced national-level applications. It can benefit from advanced gamma detection systems with highly improved signal-to-background ratios associated with event selection techniques.

Prior experiments have demonstrated that the pole in a magnetically shielded Hall thruster sputters and erodes visibly, in contrast with that in an unshielded thruster. To determine the reason for this, a particle-in-cell simulation was conducted, and the difference between shielded and unshielded thrusters in terms of plasma behavior near the exit plane was studied. The results show that in the case of the magnetically shielded thruster, the ion flux peak is on the magnetic pole face with higher ion energy, indicating severer erosion at the pole. By contrast, the flux peak of the unshielded thruster is on the head face of the channel wall, indicating severer bombardment at the wall and milder erosion at the pole. Therefore, pole erosion occurs in the magnetically shielded thruster, and channel head face erosion can be observed in the unshielded thruster. In addition, the simulation results indicate that the greater the outward shift of the magnetic field, the severer the pole erosion.

PURPOSE This is a computational study to develop a rugged self-powered Radioisotope Identification Device (RIID). The principle of operation relies on the High Energy Current (HEC) concept (Zygmanski and Sajo, Med Phys. 43 4-15, 2016) with measurement of fast electron currents between low-Z and high-Z thin-film electrodes separated by nanoporous aerogel films in a multilayer detector structure whose prototypes were previously investigated (Brivio, Albert, Freund, Gagne, Sajo and Zygmanski, Med Phys, 46 4233-4240, 2019), (Brivio, Albert, Gagne, Freund, Sajo and Zygmanski, J Phys D Appl Phys, 53 265303, 2020). Here, we present an optimal detector design that accounts for a wide energy range (keV-MeV) of x-ray-emitting radioisotopes that are of interest to national security and radiation therapy. MATERIALS We studied numerous multilayer detector geometries with N = 1..24 basic detector elements composed of 3 electrodes: N x (Al-aerogel-Ta-aerogel-Al). The thicknesses of electrodes and their total number were varied depending on the incident x-ray spectra and its ability to penetrate and interact with the different layers, producing fast electrons. We used radiation transport simulations to find a balanced geometry that accounts for all energies from 10 keV to 6 MeV in a single design with relatively few detector elements (N = 24). In the balanced design, the electrodes have increasing thickness as a function of depth in the detector, ranging from 0.5 μm-Ta and 10 μm-Al at the entrance to 10 mm-Ta and 2.5 mm-Al at the exit. Aerogel thickness was fixed at 50 μm. Electron currents forming RIID signals were acquired from all Ta electrodes. A model function M(x, Ei ) representing the detector yield as a function of the cumulative Ta thickness (x) for 70 monoenergetic incident beams (E) was derived. We also investigated the detector response to selected radioactive isotopes (Pd-103, I-125, Pu-239, U-235, Ir-192, Cs-137, Co-60). Additional studies were performed with Bremsstrahlung spectra produced by electron beams in kVp tubes and in MV Linacs used in radiology and radiation therapy departments. We investigated different algorithms for radioisotope identification that would work for unknown unshielded as well as shielded sources. RESULTS Characteristic features of response functions for monoenergetic beams and radioisotopes were determined and used to develop two inverse algorithms of radioisotope identification. Using these algorithms, we were able to identify the unshielded and shielded sources, quantify the minimum, mean and maximum effective energies of the shielded spectra, and estimate the amount of Compton background in the spectrum. CONCLUSIONS A multilayer sensor based on fast electron current was optimized and studied in its abilities as RIID. A balanced design permits the identification of radioisotopes with of a wide range of keV-MeV energies. The device is low cost, rugged, self-powered and can withstand very high dose rates, allowing deployment in difficult conditions, including radiation incidents. The algorithm we developed for radioisotope identification and spectral unfolding is robust and it is an important component in practical applications.

We analyze the motion of the electron beam in the collector of a gyrotron with the shielded magnetic system. The methods of optimization of the collector are proposed, depending on the limitations imposed on its transverse dimensions. Calculations are performed for collectors of the technological gyrotrons capable of operating in a wide range of magnetic fields (1.0–1.8 T), which allows generating radiation at a frequency of 24 to 48 GHz at the fundamental cyclotron resonance and, correspondingly, up to 100 GHz when exciting oscillations at the second gyrofrequency harmonic.

PURPOSE A prototype 169 Yb source was developed in combination with a dynamic rotating platinum shield system (AIM-Brachy) to deliver intensity modulated brachytherapy (IMBT). The purpose of this study was to evaluate the dosimetric characteristics of the bare/shielded 169 Yb source using Monte Carlo (MC) simulations and perform an independent dose verification using a dosimetry platform based on a multipoint plastic scintillator detector (mPSD). METHODS The TG-43U1 dosimetric parameters were calculated for the source model using RapidBrachyMCTPS. Real-time dose rate measurements were performed in a water tank for both the bare/shielded source using a custom remote afterloader. For each dwell position, the dose rate was independently measured by the three scintillators (BCF-10, BCF-12, and BCF-60). For the bare source, dose rate was measured at distances up to 3 cm away from the source over a range of 7 cm along the catheter. For the shielded source, measurements were performed with the mPSD placed at 1 cm from the source at four different azimuthal angles ( 0∘ , 9 0∘ , 18 0∘ , and 27 0∘ ). RESULTS The dosimetric parameters were tabulated for the source model. For the bare source, differences between measured and calculated along-away dose rates were generally below 5-10%. Along the transverse axis, deviations were, on average (range), 3.3% (0.6-6.2%) for BCF-10, 1.7% (0.9-2.9%) for BCF-12, and 2.2% (0.3-4.4%) for BCF-60. The maximum dose rate reduction due to shielding at a radial distance of 1 cm was 88.8 ± 1.2%, compared to 83.5 ± 0.5% as calculated by MC. CONCLUSIONS The dose distribution for the bare/shielded 169 Yb source was independently verified using mPSD with good agreement in regions close to the source. The 169 Yb source coupled with the partial-shielding system is an effective technique to deliver IMBT.

The airborne radomes have to cater superior electromagnetic (EM) performance with bandpass characteristics of stealth application. In this regard, a hybrid A-sandwich radome is proposed in this paper. The proposed radome consists of a novel strongly coupled frequency selective surface (FSS) core sandwiched between two dielectric layers (acts as skin) to form an A-sandwich structure. The dielectric layers are cascaded in such a way that the middle layer has less dielectric parameters than the skin dielectric. The core layer comprises a modified FSS array using strongly coupled FSS layers through a series of metallic vias. This strongly-coupled FSS element will have the advantage of eliminating inter-element interference and improves the EM performance characteristics of the structure. The structure exhibits very good band-pass characteristics (>90%) at a normal impinging angle with sharp roll-off characteristics. To show the efficacy of the proposed structure, the transmission loss has been compared with that of conventional A-sandwich radomes at 0°, 50° incidence angle for both TE and TM polarization. Conformal analysis of the unit cell has been carried out, and sector-wise thickness optimization was performed to analyze the structure for the conformal shaped radome application. Finally, a physical prototype has been fabricated and measured its scattering parameters, radiation characteristics in a fully shielded anechoic chamber. The results are encouraging and prove its suitability for radome application.

The results from an experimental study of crosstalk interference between twisted pairs of conductors of an electrical wire bundle model are presented. The aim of the study is to determine the crosstalk interference levels in a shielded twisted pair of conductors when there is heterogeneity in the form of a gap between the shield of bundle conductors and the electrical connector body. The studies were carried out on the electrical wire bundle mockup consisting of shielded and unshielded twisted pairs of conductors. The unshielded twisted pair of conductors was used as a source of crosstalk interference. The shielded twisted pair of conductors had a gap between the shield of conductors and the electrical connector body and was a receptor for the crosstalk interference. To study the crosstalk interference levels, the gap length of the shielded twisted pair of conductors was varied. As a result of the study, the crosstalk interference levels for gaps of different lengths were determined. The effect of an electrically conducting connection made using a jumper in the gap between the shield of a twisted pair of conductors and the electrical connector body of the electrical wire bundle mockup on the crosstalk interference levels was studied. A comparative analysis of the results obtained from measurements of the crosstalk interference levels in a shielded twisted pair of conductors with heterogeneities in the form of gaps of different lengths with the crosstalk interference levels in a shielded twisted pair of conductors with a homogeneous shield is carried out. A conclusion about the need to ensure connection of the shields of electrical bundle conductors with the bodies od electrical connectors without gaps has been formulated.

The aim of the work, the results of which are presented in the framework of the article, was to study the of electromagnetic radiation interaction laws in the frequency range 0.7…17 GHz with two-layer structures, the surface layer of which was made using powdered titanium dioxide, and the inner layer was made using a powder material based on oxide ferric iron. The thickness of the layers of the studied structures varied from 0.3 to 1 cm. To achieve this goal, theobjectives associated with the development of a methodology for the manufacture of multilayer structures based on composite materials containing transition metal oxides, as well as with the measurement of such structures samples electromagnetic radiation reflection and transmission coefficients in the frequency range 0.7...17 GHz. These measurements were carried out using a panoramic meter of reflection and transmission coefficients SNA 0.01–17. Based on the obtained measurement results, it was shown that in the frequency range 0.7…2 GHz, the lowest values of electromagnetic radiation reflection coefficient, reaching –20 dB, are characterized by structures whose surface layer thickness is 1 cm, and in the range 2 ... 17 GHz – structures, thickness the surface layer of which is 0.5 or 1 cm (depending on the thickness of the inner layer). The values of electromagnetic radiation transmission coefficient in the frequency range of 0.7...17 GHz of such structures reach –23 dB. Based on the results of the study, it is proposed to use the considered structures in the process of creating shielded rooms or improving the latter (for example, in cases, when it's necessary to reduce the level of passive interference in rooms shielded with metal materials).

In order to enhance the signal-to-noise ratio (SNR) of ultralow field magnetic resonance imaging (MRI) measurements, a prepolarization ( B p) coil is usually introduced to generate a magnetic field with magnitude in the order of tens of mT or even stronger to prepolarize the sample before MRI sequences. The macromagnetization M of the sample is now directly determined by the B p strength, thus the SNR is effectively improved. However, the rapid turn-off of B p current induces eddy currents in the conductive shielded room and the surrounding conductors, which in turn causes unwanted transient magnetic fields in the imaging area. In this paper, according to the relative position of the B p coil and the shielded room, two physical models of the conductive shielded room are described to simulate the transient fields at the sample position: the B p coil plane parallel to the ceiling and floor of the shielded room, and the coil plane perpendicular to the walls. The simulation is in good agreement with the experimental results. This paper will help us design the structure of the conductive shielded room as well as develop the eddy current cancellation technique.

High temperature and luminous plasma make it difficult to study the surface of nanopowders during combustion, particularly, the combustion of aluminum-based nanopowders. The noncontact observation method–laser speckle correlation (LSC) in this work is used for remote characterization of changes in the surface of aluminum nanopowder during combustion in air. The observation results using LSC at a varying distance of up to 5 m were verified by simultaneous high-speed video recording of speckle patterns, analyzing the correlation coefficient of speckle patterns, and comparing the data obtained with direct observation of the combustion process. The results demonstrated the efficiency of using the LSC method for remote characterization of changes in the surface of an object shielded by a luminous layer. The simple hardware implementation makes the LSC method potentially more valuable in the study of various high-temperature processes.

The results of simulation study aimed at development of a sub-THz traveling-wave tube (TWT) with a converged sheet electron beam are presented. The dual grating staggered slow-wave structure with a 100-um-height beam tunnel is designed and its cold electromagnetic parameters are calculated. The results of 3D PIC-simulation of the gain and output power in small-signal and large-signal operating regimes are presented. We compare the characteristics of the TWT driven with the converging sheet beam produced by an electron gun with shielded cathode and with a rectilinear beam produced by a gun immersed in the uniform magnetic field.

The problems are considered of the propagation of surface TE-polarized electromagnetic waves in the Goubau line (perfectly conducting cylinder covered with a concentric dielectric layer) and a shielded two-layer dielectric waveguide filled with an inhomogeneous medium. Numerical results are presented of the comparison of the wave spectra.

In the framework of the High-Luminosity Large Hadron Collider (HL-LHC) project, larger and shielded beam screens will be installed in the beam pipe of the superconducting magnets of the insertion next to the ATLAS and CMS detectors. The beam screen is a complex assembly that guarantees the vacuum requirements while shielding the magnet cold mass from the induced heat loads. Such an assembly has to withstand high intensity electromagnetic forces induced during magnet quenches. The mechanical stability was verified in a dedicated quench test campaign performed at the magnet test station of CERN. Strain gauges, custom-made probes, and optical fibers were installed in the beam screen to measure deformations during a quench. Magnetic field measurements were also carried out by means of pick-up coils mounted within the assembly. The main outcomes of this work are the elastic behaviour of the beam screen after 52 quenches and a satisfactory agreement between measurements and simulations.

The identification of energetic materials in containments is an important challenge for analytical methods in the field of safety and security. Opening a package without knowledge of its contents and the resulting hazards is highly involved with risks and should be avoided whenever possible. Therefore, preferable methods work non-destructive with minimal interaction and are capable of identifying target substances in a containment quickly and reliably. Most spectroscopic methods find their limits, if the target substance is shielded by a covering material. To solve this problem, a combined laser drilling method with subsequent identification of the target substance by means of Raman spectroscopic measurements through microscopic bore holes of the covering material is presented. A pulsed laser beam is used for both the drilling process and as an excitation source for Raman measurements in the same optical setup. Results show the ability of this new method to gain high-quality spectra even when performed through microscopic small bore channels. With the laser parameters chosen right, the method can even be performed on highly sensitive explosives like triacetone triperoxide (TATP). Another advantageous effect arises in an observed reduction in unwanted fluorescence signal in the spectral data, resulting from the confocal-like measurement setup with the bore hole acting as aperture.

—A theoretical and experimental study of band-stop frequency-selective structures (FSSs) for reducing the scattering properties of linear antenna arrays outside of their operating band is presented. To perform the study, a two-layer FSS based on square loops located in different layers of the dielectric base has been selected. An electrodynamic simulation of the backscattering diagram (BSD) of a linear periodic structure shielded by the FSS has been carried out. An effect of nonsuppression of certain diffraction scattering lobes has been discovered and experimentally confirmed. The discovered effect has been physically explained and measures to eliminate it have been proposed. The results of the electrodynamic simulation of an antenna system consisting of an L-band phased antenna array (PhAA), a two-layer FSS located in front of the PhAA, and an absorbing material are presented.

A novel quasi-Cassegrain metasurfaces (MS) antenna with wide bandwidth operating in 8 GHz band is proposed. Initially, the article demonstrates a complete set of working principles and design approach for the proposed antenna. Then, this antenna is optimised, manufactured, and measured. The profile of the antenna is further reduced by using the reflect-array based on MS, and the gain is improved by loading shielded vias. Note that the second resonant frequency generated from sub-reflector is utilised to extend the bandwidth. The measured results indicate that the antenna achieves the peak gain of 15.9 dBi, impedance bandwidth of 1.07 GHz, and half power beam width of 26° in E plane and 21.5° in H plane. It has a low profile of 26.5 mm (0.71 λ 0 ) and occupies an area of 120 mm × 120 mm (3.20 λ 0 × 3.20 λ 0 ). The article not only completes the antenna operating in 8 GHz band but also provides a reference for the design of the proposed quasi-Cassegrain antenna in microwave band.

The spectral and energy characteristics of two planar dielectric resonators (DRs), open and shielded from the curvilinear surface, excited in higher-order modes as whispering gallery modes (WGMs) in Ka-waveband are investigated. These resonators are formed by a thin (compared to the operating wavelength) disk dielectric structure, located between two conducting planes. Thus, the E-field of the resonator was limited along the height of the planar disk by two conducting surfaces. The resonance properties of such a structure are determined by the condition of total internal reflection of waves from the internal curvilinear surface of a dielectric disk. The carried out investigations shown that the unloaded Q-factor is increased at the arrangement of planar dielectric disk inside the ring metal shield at the certain ratio of the radiuses of the shield and dielectric disk. The Q-factor of the shielded resonant structure at the high-frequency edge increases to 40 %. The partial displacement of the resonant field of the WGMs modes from the dielectric to the air gap is the cause of this effect. It leads to decrease in losses in the dielectric material. A computer simulation of the WGMs fields in the planar DR was carried out using the CST Microwave Studio 2013 software to confirm this effect. In addition, computer simulation results shown that these WGMs in the planar DR are characterized by a homogeneous distribution of the resonant field along the axial coordinate. The perspectives of using planar DR in solid-state Ka-band oscillators are shown.

—Based on the theory of high-density electron flows with the elliptical current tubes, a model of a ribbon beam from a shielded cathode in the case of emission in the ρ mode has been built. Algorithms of formation of high-compression flows passing into the Brillouin mode without oscillations with preserved elliptical cross section not rotated or strained have been developed.

The variation of the arc area in DC interruption was investigated. By the use of the vacuum interrupter with glass shielded, DC interruptions were carried out to obverse the arc appearance in the situation of axial magnetic. Meanwhile, using the CMOS high speed camera, arc images were obtained under the conditions of different commutation frequency, arcing time and pre-charged capacitor voltage. Subsequently, the arc area was obtained through the image processing technology. According to the obtained arc area, the factors influencing on the arc area were investigated, including the commutation frequency, arcing time and pre-charged voltage. The results indicated that the duration time of the commutation stage became shorter and the arc area decreased with the increase of commutation frequency. The rise rate of arc area in initial stage and the drop rate of arc area in commutation stage present the same trend under different arcing time. Considering the experimental results in this paper, arcing time of 2 ms is better for DC interruption. High pre-charged capacitor voltage leads to the increase of the current going through load. The capacitor voltage can be charged a little higher than the rated value for the reliable interruption of DC current.

Single Photon Emission Computed Tomography (SPECT) scanners based on photomultiplier tubes (PMTs) are still largely employed in the clinical environment. A standard camera for full-body SPECT employs $\sim50$-100 PMTs of 4-8~cm diameter and is shielded by a thick layer of lead, becoming a heavy and bulky system that can weight a few hundred kilograms. The volume, weight and cost of a camera can be significantly reduced if the PMTs are replaced by silicon photomultipliers (SiPMs). The main obstacle to use SiPMs in full-body SPECT is the limited size of their sensitive area. A few thousand channels would be needed to fill a camera if using the largest commercially-available SiPMs of 6$\times$6~mm$^2$. As a solution, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We developed a LASiP prototype that has a sensitive area 8 times larger than a 6$\times$6~mm$^2$ SiPM. We built a proof-of-concept micro-camera consisting of a 40$\times$40$\times$8~mm$^3$ NaI(Tl) crystal coupled to 4 LASiPs. We evaluated its performance in a central region of $15\times15$~mm$^2$, where we were able to reconstruct images of a $^{99m}$Tc capillary with an intrinsic spatial resolution of $\sim2$~mm and an energy resolution of $\sim11.6$\% at 140 keV. We used these measurements to validate Geant4 simulations of the system. This can be extended to simulate a larger camera with more and larger pixels, which could be used to optimize the implementation of LASiPs in large SPECT cameras. We provide some guidelines towards this implementation., Corresponding author: D. Guberman (daniel.guberman@pi.infn.it). Accepted for publication in Physica Medica. 25 pages, 15 figures

An electromagnetic field penetrating through an aperture or slot of a metallic enclosure generates many standing-waves due to the resonance inside the metallic enclosure, which results in reduced shielding performance. This paper examines the effect of absorbent material (absorber) to improve shielding effectiveness (SE) of large metallic rooms with apertures or slots. First, a theoretical formulation to extract the Q-factor of an absorber with any shape is proposed. Using this, the contribution of the absorber to the SE improvement of a shielded room with different sized circular apertures was investigated. Second, the resonant mode density inside the shielded room was classified into non-resonant, under-moded, and over-moded states with an increase in frequency, and the effect of the absorber in each frequency range was examined. The analysis was conducted through numerical simulation using a commercial full-wave simulator and experimental measurement using a fabricated actual shielded room and commercial absorbers. The accuracy of the analysis results was verified through the comparison of simulated and measured results. The analysis results ensured that the absorber was not effective in improving the SE in the non-resonant state of the metallic room. It was also confirmed that the absorber was effective in improving the SE in the over-moded state of the metallic room where a severe standing-wave occurs. In addition, the SE improvement level differed depending on the location of the absorber in the room.

Due to a growing interest for microwave radiation sources with a radiation frequency of several tens of GHz and output power of several tens of kW, we developed a new generation of technological gyrotron setups. The key feature of these systems is a novel magnetic system based on magnetically shielded solenoids (MSS). This magnetic system is several times more energy efficient than the common warm solenoids and it also allows to control the properties of the helical electron beam to make it interact with various cavity modes. The developed MSS provides a high field induction in the interaction space and a small stray field, so the gyrotron can operate in wide range of magnetic fields (from 1 T to 1.8 T in relatively low-consumption regime). It allows a gyrotron complex to operate within a wide frequency range (from 24 to 50 GHz on main cyclotron resonance). A total system efficiency expected to be about 35%, which is significantly higher than the existing analogs.

The filter-fluorescer x-ray diagnostic (FFLEX) in the Shenguang (SG) laser facility has been upgraded to infer the time-resolved behavior of hot electrons in inertial confinement fusion experiments. It significantly increases the bandwidth and anti-interference ability requirements of readout electronics. The current readout method is difficult to meet these requirements. A dedicated front-end waveform digitizer (DFWD) for the FFLEX is presented in this paper. It is very convenient to be installed in the front-end detectors of the FFLEX, and so the DFWD could be shielded as well as detectors. The test results show that it works well in the front-end environment. Compared with the existing system, the DFWD can minimize the impact of radiation on signal measurement and significantly improve the accuracy of the status and time-trend diagnosis of hot electrons.

This paper proposes the application of Synthetic Aperture Interferometric Imaging to the detection of electromagnetic leakage from shielded equipment and buildings. By conducting laboratory experiments, we demonstrate the efficiency of this technique for the accurate detection and location of electromagnetic leakage from a metallic cavity with faulty faradization and adjustable quality factor.

A gradient coil with integrated second and third order shims has been designed and constructed for use inside an actively shielded 310 mm horizontal bore 9.4 T small animal MRI. An extension of the boundary element method, to minimise the power deposited in conducting surfaces, was used to design the gradients, and a boundary element method with a constraint on mutual inductance was used to design the shims. The gradient coil allows for improved imaging performance and was optimized for an imaging region appropriate for marmoset imaging studies. Efficiencies of 1.5 mT m-1 A-1 were achieved in a 15 cm wide bore while maintaining gradient uniformity ≤5% over the 8 cm region of interest. Two new cooling methods were implemented which allowed the gradient coil to operate at 100 A RMS, 25 % of max current with a temperature rise below 30 C.

Gynecologic cancers are often asymmetric, yet current Ir-192 brachytherapy techniques provide only limited radial modulation of the dose. The shielded solutions investigated here solve this by providing the ability to modulate between highly asymmetric and radially symmetric dose distributions at a given location. To find applicator designs that can modulate between full dose and less than 50% dose, at the dimensions of the urethra, a 2D calculation algorithm was developed to narrow down the search space. Two shielding design types were then further investigated using Monte Carlo and Boltzmann-solver dose calculation algorithms. 3D printing techniques using ISO 10993 certified biocompatible plastics and 3D printable tungsten-loaded plastics were tested. It was also found that shadowing effects set by the shape of the shielding cannot be easily modulated out, hence careful design is required. The shielded applicator designs investigated here, allow for reduction of the dose by over 50% at 5 mm from the applicator surface in desired regions, while also allowing radially symmetric dose with isodose line deviations less than 0.5 mm from circular. The shielding designs were also chosen with treatment delivery time in mind. Treatment times for these shielded designs were found to be less than 1.4 times longer than a 6-channel unshielded cylinder for the equivalent fully symmetric dose distribution. The 2D calculation methods developed here provide a simple way to rapidly evaluate shielding designs, while the 3D printing techniques also allow for devices with novel shapes to be rapidly prototyped. Both TOPAS Monte Carlo and Acuros BV calculations show that significant dose shaping and organ at risk sparing can be achieved without significantly compromising the plan in regions that require the full dose.

The paper investigates the propagation of the ultrashort pulse along the conductors of the power supply (PS) bus with improved design. The common-mode and differential-mode excitations of the 100 V ultrashort pulse were used. Eight propagation ways were considered. The voltage maximum of 13.569 V was obtained with a common-mode excitation, and the voltage minimum (minus 16.683 V) was obtained with differential-mode excitation for 50 Ohm terminations.

Ultracold polar molecules can be shielded from fast collisional losses using microwaves, but achieving the required polarization purity is technically challenging. Here, we propose a scheme for shielding using microwaves with polarization that is far from circular. The setup relies on a modest static electric field, and is robust against imperfections in its orientation.

A new metagrating topology is proposed to enable perfect anomalous reflection of electromagnetic plane waves at two independent bands at microwave frequencies. Two reactively loaded segmented single-band gratings are interleaved together to form a composite metagrating. The constituent halves are electromagnetically shielded from each other through incorporation of PEC baffles, allowing them to be designed independently. Furthermore, isolation between the two frequency channels is achieved with dual-resonant grating wires which can be tuned to be inactive at prescribed frequencies. A dual-band metagrating that performs perfect anomalous reflection at 10 GHz and 15.11 GHz is designed and numerically verified.

The EMI-compatibility of the LabPET II detection module to develop a high-resolution simultaneous PET/MRI system is investigated. The experimental set-up evaluates the performance of two LabPET II detection modules in close proximity to RF coils excited at three different frequencies mimicking the electromagnetic environments of 3 T, 7 T, and 9.4 T MRI scanners. A gradient coil, with switching frequency from 10 kHz to 100 kHz, also surrounds one of the detection modules to investigate the effects of the gradient field on the individual detector performance, such as the baseline of the DC-voltage and noise level along with both the energy and coincidence time resolutions. Measurements demonstrate a position shift of the energy photopeaks (≤ 9%) and a slight deterioration of the energy and coincidence time resolutions in the presence of electromagnetic interferences from the gradient and RF coils. The electromagnetic interferences cause an average degradation of up to ~ 50% of the energy resolution (in time-over-threshold spectra) and up to 18% of the timing resolution. Based on these results, a modified version of the detection module, including a composite shielding as well as an improved heat pipe-based cooling mechanism, capable of stabilizing the temperature of the detection module at ~ 40 oC, is proposed and investigated. This shielded version shows no evidence of performance degradation inside an MRI-like environment. The experimental results demonstrate that a properly shielded version of the LabPET II detection module is a viable candidate for an MR-compatible PET scanner.

Objective: Electroneurography has been an essential method for assessing peripheral nerve disorders for decades. During this procedure, a nerve is briefly electrically excited, and nerve conduction properties are identified by indirect means from the behavior of the innervated muscle. The magnetic field of the resulting muscle response can also be recorded by novel, uncooled magnetometers, which have become very attractive for different medical applications over recent years. These highly sensitive magnetometers are called optically pumped magnetometers. Methods: We performed unaveraged and averaged magnetic signal detection of electrically evoked muscle responses using optically pumped magnetometers. We then discussed the suitability of this procedure for clinical applications in the context of diagnostic value and in direct comparison with the current electrical gold standard. Results: The magnetic detection of muscle responses is possible using optically pumped magnetometers. Our magnetic results (averaged and unaveraged) closely match those from electrical measurements. Conclusion: Optically pumped magnetometers provide an alternative, contactless technology for electrode-based motor studies, but they are currently not ready for routine clinical use. This costly technology requires additional earth magnetic shielding because this is a prerequisite for proper operation. Currently, there are no diagnostic advantages over electrical measurements. Additionally, the required measurement setup and procedure are much more complicated. Significance: In contrast to already published proof-of-principle studies for magnetomyography, we report in detail the results of the magnetic measurements of electrically evoked muscle responses in a shielded environment by applying supramaximal stimulation and finally validate our findings with electroneurography data as a reference.

We experimentally demonstrate the nuclear magnetic resonance (NMR) detection at 1.9 kHz using a detection system comprised of a high-sensitivity single-beam atomic magnetometer and a flux transformer. The single-beam atomic magnetometer has been commercialized by QuSpin for typical operation at low frequencies below 200 Hz with a bandwidth of 135 Hz [1]. However, this magnetometer operation can be extended to much higher frequencies about 2 kHz by applying optimal-bias magnetic fields. The sensitivity of the detection system with a demonstrated signal-to-noise ratio of about 50 for a 20 ml water sample, even without magnetic field shimming, is quite competitive with that in other ultra-low field NMR detection systems, such as the Magritek Terranova system or the system based on our home-built atomic magnetometer installed inside a magnetically shielded room [2]. This ultra-low field NMR approach can be applied to Earth-field NMR detection and imaging. We estimate that the detection system with a modified flux transformer can be sensitive to underground-water detection at depth of 1 meter and deeper, and to field mapping applications.

PURPOSE The LabPET II detection module is a potential candidate to create an magnetic resonance imaging (MRI) compatible positron emission tomography (PET)-insert with submillimeter spatial resolution for small animal applications. However, the feasibility of such an insert is hampered by the large radial size of the LabPET II front-end electronics and by components containing ferromagnetic materials. In this paper, a new low-profile front-end design based on the LabPET II architecture, called "low-profile detection module," is investigated. MATERIALS AND METHODS The performance of the low-profile detection module in the presence of MRI-like RF signals and gradient coil pulses was independently examined. The baseline of the analog signal, its RMS noise level, and the energy resolution, determined by a dual time-over-threshold (dTOT) method for each pixel of the new low-profile detection module, was measured in the presence of RF signals at different frequencies equivalent to the Larmor frequency of 3, 7, and 9.4 T MRI. The same parameters were investigated in the presence of a gradient coil switching at frequencies from 10 to 100 kHz. The performance of the low-profile detection module inside a 7 T MRI and its effects on an MR image have also been studied using gradient echo sequences. The same measurements were repeated for the shielded low-profile detection module, inside and outside the MRI. RESULTS Our results show that pulses in both the kilohertz and megahertz ranges cause up to 50% increase in the noise level of the baseline (DC analog signal at the output of the shaper filter) and up to 17% degradation in TOT energy resolution. By inserting a conducting composite layer as shielding around the low-profile detection module, these degrading effects were avoided. The performance measurement of the low-profile PET detection module inside a 7 T small animal MRI scanner confirmed that the shielded low-profile detection module behavior was similar inside and outside the MRI bore. In addition, gradient echo images of a water-filled phantom without and with the shielded and unshielded low-profile detection modules were acquired. The results demonstrated no evidence of artifacts in the MR image, either due to eddy currents or ferromagnetic materials with the shielded modules. CONCLUSION A low-profile detection module based on the LabPET II technology was shown to be a viable candidate as a PET-insert for simultaneous PET/MRI applications considering its thin radial size and its EMI immunity due to placing it between two electronic boards. In comparison to the standard LabPET II detection module, it provides better performance in the presence of electromagnetic interferences, but a shielding layer is still required. When properly shielded, the proposed low-profile detection module can be operated inside an MRI without degrading the PET count rate or the MRI performance.

A double helical antenna excited by microwave power provides super high-density ionisation in gas inside dielectric tube at certain conditions. Designed antenna and matching circuit have resonant frequency of 434 MHz reserved for industrial, scientific and medical (ISM) applications. Frequency bandwidth at coupling optimization reach ±3% at -3 dB level that improve absorption of microwave power for variable antenna load determined by helicon discharge. To prevent power loss due to radiation outside dielectric tube electromagnetic shield around antenna is applied. The shield also concentrate electromagnetic field inside the tube increasing ionisation efficiency. The results of experimental study and computer simulation are presented.

Identification method for a hidden or shielded gamma-ray source using a vehicle-mounted 4$\pi$ gamma-ray imager was proposed. Since 4$\pi$ gamma-ray imaging provides direction of incident gamma-rays into the imager and its intensity, a position and an activity of a gamma-ray source can be estimated by several 4$\pi$ gamma images obtained by the imager moving around the source in combination with locations and orientation data of the imager. Using a 3D pixel array CdTe detector as a prototype of 4$\pi$ Compton gamma-ray imager, both the position and activity of a single 137 Cs point source was estimated quantitatively in 3D voxel space by 4$\pi$ Compton gamma-ray images measured at three positions. In addition, 4$\pi$ gamma images were obtained by off-line processing of data acquired during the movement of the vehicle-mounted imager with processing time less than measurement time.

An analog, low-profile and shielded spectrum analyzer is proposed for operation at mm-wave frequencies around the 60 GHz band based on a novel side-fire Leaky-Wave Antenna (LWA) configuration. The proposed side-fire periodic LWA is systematically developed from a conventional 3-port waveguide T-junction which is modified to a LWA unit cell with an internal matching mechanism to suppress the stop-band and enable broadside radiation based on unit cell symmetry considerations. The resulting periodic side-fire antenna radiates in the plane of the antenna, whereby the leakage power be either be allowed to radiate in free-space or kept confined inside a PPW structure. The proposed side-fire structure thus can be completely shielded useful as an analog broadband spectrum analyzer using Substrate Integrated Waveguide (SIW) Technology. Furthermore, a convex side-fire antenna is demonstrated to focus the radiated beams in the near-field of the structure to make the entire system compact. The integrated spectrum analyzer is experimentally demonstrated between 59 GHz - 66 GHz providing 1 GHz frequency resolution. Furthermore, a simple mathematical model consisting of array of line sources is proposed to efficiently model the beam-scanning characteristics of the curved side-fire LWA in the near-field of the structure., Comment: 11 pages, 11 figures

Purpose An electrically floating radio frequency (RF) shielded PET insert with individual PET detectors shielded by separate Faraday cages enables the MRI built-in body RF coil to be used at least as an RF transmitter, in which the RF field penetrates the imaging region inside the PET ring through the narrow gaps between the shielded PET detector modules. Because the shielded PET ring blocks more than 90% of the imaging region for the transmit field from the body RF coil, it is very challenging to obtain the required RF field inside a full-ring floating PET insert. In this study, experiments were performed on the dependence of RF penetrability on different geometric aspects of the shielded PET modules and PET rings to optimize the design parameters to obtain the required RF field inside the PET ring. Methods We developed several prototype cylindrical full-ring PET inserts using completely enclosed empty RF shield boxes (considered as dummy PET modules). Considering the RF shield box, we conducted studies for different axial lengths (240 and 120 mm) and heights (30 and 45 mm) of the shield boxes. On the other hand, considering the PET ring geometry, we also performed studies on three different categories of PET rings: a long-ring insert (longer than the MRI phantom), a short-ring insert (shorter than the MRI phantom), and a two-ring insert that combined two short-rings. In each ring category, two different inter-shield box gaps (1 and 3 mm) were considered. In the case of the two-ring insert, three different ring-gaps (5, 10, and 20 mm) were studied. In total, 21 PET inserts were studied with an inner diameter (i.d.) of 210 mm. To study the effect of ring diameter, another long-ring insert was studied for the 270 mm i.d. Experiments were conducted for the transmit RF (B1 ) fields and signal-to-noise ratios of spin-echo and gradient-echo images using a homogeneous phantom in a 700 mm bore-diameter 3 T clinical MRI system. RF pulse amplitudes generated automatically by the MRI system were recorded for comparison. Results A PET insert with a 3 mm inter-box gap was found to perform the best, at a level which is acceptable for PET imaging. In the case of an insert of multiple short-rings instead of one long-ring insert, the 5 and 10 mm ring-gaps provided higher RF field penetration. Increasing the inter-box gap improved the RF field penetration, whereas a ring-gap that was too wide concentrated the field near the ring-gap region. Relatively reduced RF power was required for wider inter-box gap or ring-gap or larger shield box height. Moreover, the rectangular shield box outperformed the trapezoidal shield box. On the other hand, when we changed the inner or outer diameter of the PET ring by keeping the same transaxial width of the shield boxes, we did not see any noticeable variation. Conclusions Our study results provide comprehensive guidance on the geometrical design aspects of RF-penetrable PET inserts for efficient RF penetration inside the PET ring. By choosing proper geometric design parameters, we could get the RF field that was similar to the MRI-only case.