Near-field Area Research Articles

Elastographic and Morphological Testicular Changes in Hypothyroidism - An Experimental Study.

IntroductionMethimazole-induced hypothyroidism is a clinical problem in the treatment of hyperthyroidism in people and animals and is an example of metabolic disease that can lead to fertility disorders and can give elastographic testicular changes.Material and MethodsUltrasound elastography using the Esaote MyLab Twice ultrasound system and a morphological examination of testes were performed in seven methimazole-administered (group E) and seven healthy rats (group C).ResultsThe elasticity ratio of strains in the scrotal wall of the near-field test area to testicular tissue (ELX-T-RAT) and hardness percentage of strained tissues in the defined area of a testicle (ELX-T%HRD) in group E were statistically significantly lower than in group C. The degree of spermatogenesis was statistically significantly higher in group E than in group C and similarly seminiferous tubule diameters in group E were statistically significantly higher than in group C. Body weight and testicular weight in group E were statistically significantly lower than in group C.ConclusionChanges in the elastographical parameters of testes may result from disorders secondary to hypothyroidism. The usefulness of elastography is noteworthy in the case of evaluation of testis function in patients with some metabolic disorders.

Analytic spherical harmonic coefficients for polygonal area lights

Spherical Harmonic (SH) lighting is widely used for real-time rendering within Precomputed Radiance Transfer (PRT) systems. SH coefficients are precomputed and stored at object vertices, and combined interactively with SH lighting coefficients to enable effects like soft shadows, interreflections, and glossy reflection. However, the most common PRT techniques assume distant, low-frequency environment lighting, for which SH lighting coefficients can easily be computed once per frame. There is currently limited support for near-field illumination and area lights, since it is non-trivial to compute the SH coefficients for an area light, and the incident lighting (SH coefficients) varies over the object geometry. We present an efficient closed-form solution for projection of uniform polygonal area lights to spherical harmonic coefficients of arbitrary order, enabling easy adoption of accurate area lighting in PRT systems, with no modifications required to the core PRT framework. Our method only requires computing zonal harmonic (ZH) coefficients, for which we introduce a novel recurrence relation. In practice, ZH coefficients are built up iteratively, with computation linear in the desired SH order. General SH coefficients can then be obtained by the recently developed sparse zonal harmonic rotation method.

Multiobjective Optimization Design for Electrically Large Coverage: Fragment-Type Near-Field\/Far-Field UHF RFID Reader Antenna Design

The design of an ultrahigh-frequency (UHF) radio-frequency identification (RFID) reader antenna covering an electrically large near-field area is challenging for near-field UHF RFID applications. In such a design, magnetic field distribution on a large coverage area is required to be as uniform as possible. For some specific UHF near-field RFID applications, given radiation pattern characteristics are expected. A fragment-type wire structure is quite suitable for these demands because uniform magnetic field distribution and given patterns could be generated through optimizing the fragmented wires in a designated electrically large area to obtain corresponding current distribution. In this article, the concept of a fragment-type structure as well as some design guidelines are reviewed and summarized. Then, two omnidirectional fragment-type wire antennas with different cell size and two directional fragment-type wire antennas are designed. Both simulation and experiment results show that there is no reading null within an electrically large near-field zone having a perimeter of four operating wavelengths at 915 MHz (i.e., 320 mm x 320 mm). The omnidirectional designs are promising in the applications of UHF near-field RFID tag detection in self-confined volumes, and the directional designs are potential in the systems of UHF near-field/far-field RFID.

Interzonal airflow rates for use in near-field far-field workplace concentration modeling

ABSTRACTInterzonal air flow rates (β) for a workspace above a table were measured in 12 indoor air spaces using an experimental apparatus simulating a vapor release into an occupied near zone. The near field was modeled as a 0.32 m3 rectangular cube volume 0.60 m high above the 0.60 m × 0.90 m table. A total of 74 experimental measurements of β were made. The apparatus consisted of photoionization detectors measuring concentrations of acetone around an evaporating liquid surface with a robot arm simulating worker motion in the near field. The vapor release rate and the resulting concentrations were used in a near-field far-field (NF-FF) model to calculate β. Measures of mixing within the near-field supported the assumption of the NF-FF model that the near field is well-mixed. Measured values of β ranged from 0.4–19 m3/min with an average of 4.8 m3/min. This corresponds to 1.2–59 air changes per minute in the near field and an average of 15 air changes per minute. The values of β were log normally distributed with a geometric mean of 3.4 m3/min and a geometric standard deviation of 2.3. The 95% confidence interval on the geometric mean of β was 2.8–4.2 m3/min. The product of the random air speed in the room and one half of the near-field free surface area was shown to be a good method of determining β. There was a slight correlation seen between room volume and β, but the effect size was small. Room air change rate was not found to be correlated with β. The observed distribution of β will be helpful in selecting values for interzonal airflow rate in NF-FF modeling of worker exposures.

Detecting Surface Changes from an Underground Explosion in Granite Using Unmanned Aerial System Photogrammetry

Efficient detection and high-fidelity quantification of surface changes resulting from underground activities are important national and global security efforts. In this investigation, a team performed field-based topographic characterization by gathering high-quality photographs at very low altitudes from an unmanned aerial system (UAS)-borne camera platform. The data collection occurred shortly before and after a controlled underground chemical explosion as part of the United States Department of Energy’s Source Physics Experiments (SPE-5) series. The high-resolution overlapping photographs were used to create 3D photogrammetric models of the site, which then served to map changes in the landscape down to 1-cm-scale. Separate models were created for two areas, herein referred to as the test table grid region and the nearfield grid region. The test table grid includes the region within ~40 m from surface ground zero, with photographs collected at a flight altitude of 8.5 m above ground level (AGL). The near-field grid area covered a broader area, 90–130 m from surface ground zero, and collected at a flight altitude of 22 m AGL. The photographs, processed using Agisoft Photoscan® in conjunction with 125 surveyed ground control point targets, yielded a 6-mm pixel-size digital elevation model (DEM) for the test table grid region. This provided the ≤3 cm resolution in the topographic data to map in fine detail a suite of features related to the underground explosion: uplift, subsidence, surface fractures, and morphological change detection. The near-field grid region data collection resulted in a 2-cm pixel-size DEM, enabling mapping of a broader range of features related to the explosion, including: uplift and subsidence, rock fall, and slope sloughing. This study represents one of the first works to constrain, both temporally and spatially, explosion-related surface damage using a UAS photogrammetric platform; these data will help to advance the science of underground explosion detection.

A time-domain model and experimental validation of the acoustic field radiated by air-coupled transducers

This paper presents a time-domain model for the prediction of an acoustic field in an air-coupled, non-contact, ultrasonic setup, which includes an air-coupled Emitter, the Propagation space and an air-coupled Receiver (EPR). The model takes into account the finite size of the aperture receiver, attenuation in air, and the electric response of the emitter-receiver set he. The attenuation is characterized by a causal time-domain Green’s function, allowing the wideband attenuation of a lossy medium obeying the power law α(ω)=α0ωη,1⩽η⩽2 to be included. The electrical response is recovered experimentally using a procedure which includes the deconvolution of air absorption effects. The model is implemented numerically using a discrete representation approach. In order to study the influence of receiver size and attenuation, five different computational approaches are proposed; each of these is evaluated quantitatively, by comparing the predicted acoustic field with the experimentally measured signal. The prediction error is studied in both the near and far fields, for three typical field features: the system’s impulse response, the on-axis field distribution, and the directivity pattern, for the case of air-coupled transducers operating at two different central frequencies, namely 50kHz and 350kHz, with a 10mm diameter wideband receiver. It is shown that when the attenuation in air, the receiver size, and the accurately recovered electric response he, are correctly taken into account, the model allows the system’s impulse response to be accurately predicted, with on-axis errors ranging between 0.2% in the far field and 1% in the near field. In the near-field area and within the far field −3dB beam spread width, the error is generally greater than on the axis, but globally remains smaller than 1%. Inclusion of the size of the receiver dimension in the model appears to be crucial to the accuracy of the near field predictions, and an approximate criterion is proposed for the evaluation of the influence of receiver. The procedure used to recover the electric response he is also presented in detail. The results obtained from this study are used to formulate various recommendations related to EPR modelling.

Observation of the Talbot effect for ultrasonic waves

The diffraction of ultrasonic radiation on an amplitude diffraction grating in the near-field area (Fresnel diffraction) has been studied. The effect of self-imaging of the grating (Talbot effect) has been detected for ultrasonic radiation at distances from the grating in the range from z = 0 to z = 2L T, where L T is the Talbot length. The fractional Talbot effect, i.e., the ultrasonic image of the grating with the period d/2, has been observed.

Design and Imaging of Ground-Based Multiple-Input Multiple-Output Synthetic Aperture Radar (MIMO SAR) with Non-Collinear Arrays.

Multiple-Input Multiple-Output (MIMO) radar provides much more flexibility than the traditional radar thanks to its ability to realize far more observation channels than the actual number of transmit and receive (T/R) elements. In designing the MIMO imaging radar arrays, the commonly used virtual array theory generally assumes that all elements are on the same line. However, due to the physical size of the antennas and coupling effect between T/R elements, a certain height difference between T/R arrays is essential, which will result in the defocusing of edge points of the scene. On the other hand, the virtual array theory implies far-field approximation. Therefore, with a MIMO array designed by this theory, there will exist inevitable high grating lobes in the imaging results of near-field edge points of the scene. To tackle these problems, this paper derives the relationship between target’s point spread function (PSF) and pattern of T/R arrays, by which the design criterion is presented for near-field imaging MIMO arrays. Firstly, the proper height between T/R arrays is designed to focus the near-field edge points well. Secondly, the far-field array is modified to suppress the grating lobes in the near-field area. Finally, the validity of the proposed methods is verified by two simulations and an experiment.

Compact Multiservice UHF RFID Reader Antenna for Near-Field and Far-Field Operations

This letter presents a compact ultrahigh frequency multiservice radio frequency identification reader antenna for near-field and far-field operations. The far field is circularly polarized, and the strong near field is generated using inductive coupling. The dimension of the prototype is 83 × 83 × 1.6 mm 3. The prototype is based on a rectangular slot antenna, fed by an L-shaped feed. An integrated near-field and far-field radiator along with asymmetric slot perturbation result in circular polarization. The strong magnetic field in the near-field is generated by a configuration of stubs in the radiator, which bring oppositely directed current over the antenna plane. The antenna exhibits an impedance bandwidth of 110 MHz. The axial-ratio bandwidth (ARBW) of 37 MHz is also reported. A near-field interrogation area of 220 × 180 mm2 is reported for this antenna.

Near-fild optical lithography in application to plasmonic antennas characterization

Proposed a method of measurements for both electrical field enhancement and size of near-field localization area for plasmonic antenna-probe. The method is based on optical modification of photosensitive sample. Shown the results of the proposed method and subdiffraction resolution of test image is demonstrated.

PCB current identification based on near-field measurements using preconditioning and regularization

Abstract. Radiated electromagnetic fields from a PCB can be estimated when the source current distribution is known. From a measured near-field distribution, the PCB source current distribution can be found. Accuracy depends on the measurement method and its limitations, the radiation model and the choice of the observation area. Many known methods are based on optimization algorithms for inverse problems that vary a set of elementary radiation sources and create a radiation model. However, apart from the time-consuming optimization process, such methods find one possible solution for a near-field distribution. As this distribution might not reflect the real current distribution, accuracy outside of near-field scan area can be low. Furthermore numerical problems can often be observed. Solving the given inverse problem with a system of linear equations and complex near-field data it can be very sensitive to noise. Regularization methods and an adjusted preconditioning can increase the accuracy. In this paper, an improved radiation model creation approach based on complex near-field data is presented. This approach is based on regularization methods and extended by current estimations from near-field data. Preconditioning is done considering some physical properties of the PCB and its possible current paths. Accuracy and stability of the method are investigated in the presence of noisy data.

Volumetric MR-guided high-intensity focused ultrasound ablation to treat uterine fibroids through the abdominal scars using scar patch: a case report.

BackgroundAbdominal scars pose a challenge in magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) therapies, limiting patient selection and increasing the risk of skin burns. Especially, scars arising from longitudinal incisions are problematic as they usually lie medially at the lower abdomen where the ultrasound beam has to go through. Volumetric sonication has been shown to efficiently enlarge the ablated volume per sonication, but they nevertheless require more thermal energy to be deposited per sonication which increases the temperature in the near-field area located between the transducer and the target region.Case presentationThe scar patch was used in three patients undergoing MR-HIFU ablation of fibroids using volumetric technique, one with transverse incision and the other two with longitudinal incision. No severe adverse effects were observed. The relative shrinkage of the fibroid of these patients at 6-month follow-up were 67, 78, and 59 %, respectively.ConclusionsOur preliminary experience suggests that the use of scar patch on MR-HIFU ablation of fibroids using volumetric technique provides an effective treatment option for patients who were previously excluded from MR-HIFU treatment due to the abdominal scars.

Design of near‐field ultra‐high frequency radio‐frequency identification antenna with fragmented wires for electrically‐large coverage

Design of ultra-high frequency radio-frequency identification (UHF RFID) reader antenna covering electrically-large near-field area is still challenging for near-field UHF RFID applications. In such design, magnetic field distribution on a large coverage area is required to be as uniform as possible. Fragment-type wire antennas are quite suitable for such demand because distribution of fragmented wires in a designated electrically-large area can be optimised to counterpoise the magnetic fields generated by non-uniform current distribution. By optimisation searching with multiobjective evolutionary algorithm based on decomposition combined with enhanced genetic operators, fragment-type RFID reader antenna is designed to provide uniform magnetic field distribution within dynamic range of 4 dB in an electrically-large near-field coverage of 320 × 320 mm at 915 MHz. The designed antenna is fabricated and tested. Both simulation and measurement results show good impedance matching, satisfactory near-field coverage, and desirable omni-directional pattern.

Release and dispersion behaviour of carbon dioxide released from a small-scale underground pipeline

The development of carbon capture and storage (CCS) brings challenges for safety issues regarding carbon dioxide (CO2) transmission pipelines. Once a pipeline is punctured or full-bore ruptured, the leaked CO2 is hazardous to personnel and the environment. Small-scale devices were established with the aim of studying the release and dispersion behaviour of gas and liquid CO2 from a punctured underground pipeline. A sandbox was built to simulate the underground conditions. The parameters of the sand used in the experiments were tested. CO2 concentrations on the ground and temperatures around the release orifice in the sand were analysed. The results indicate that in the CO2 gas release experiments, the CO2 concentration on the sand surface decreases with increasing horizontal distance in the form of a power function. CO2 concentrations in upward release are slightly larger than those in horizontal release at the same location but are obviously bigger than values in downward release. The temperature-drop region is much smaller than that in air. A frozen ice ball can be generated near the release orifice during the gas phase of the CO2-release process. In the liquid phase of CO2-release experiments, a large amount of dry ice is generated near the release orifice. Dry ice can only be generated in the area close to the release orifice, especially in the near-field area.

Near-Field Cross Section Imaging of Wideband Millimeter Wave

Near-field millimeter wave imaging has been a hot topic recent years for its importance applications in the area of anti-terrorism. The penetrating characteristic of millimeter wave is of significant importance to security, such as the concealed weapons detection, ground-penetrating radar imaging, through-barrier imaging and so on. Cross section imaging is a basic aspect for near-field millimeter wave imaging, which includes antenna array distribution and wideband signal processing. This paper utilizes back projection method in space area to realize ultra-band near- field cross section imaging. We induce two dimensional direction integral formulas to obtain the reconstruction image of the near-field imaging area, and the simulation results validate the effectiveness of this imaging algorithm.

The multiphase flow simulations of CO2 plume and jet under the background current

The Carbon Capture Storage (CCS) is considered as a promising atmospheric CO2 mitigation solution. There is some risk that the high concentrated carbon dioxide could be leaked accidentally from the CCS facilities. It requires making attention on the behavior of carbon dioxide (CO2) in the ocean. In particular, how such substances behave in the different phases (such as gaseous, liquid, hydrate or non-hydrate) should be understood with the forms of existences as like as in bubble/droplet form or CO2 lake. This study focused on the characteristics of liquid CO2 jet/plume in a near-field area mainly and investigated the behavior of a liquid CO2 jet/ plume released at 800 m depth using a series of numerical simulation. The numerical results were verified by comparing with the theoretical and previous experiments and showed a good agreement in appearance of bifurcation as well as the trajectory of the flow centerline. The present work described the development of CO2 flow, a turbulent buoyant fluid driven by concentration difference, both with time and spatial aspects. The dependency of jet/plume cross sectional areas on the Reynolds number, the centerline density distribution, the completely dissolving distance, and the characteristic of turbulent intensity and turbulent dissipation rate were also investigated.

Metal semishell-substrate coupled structures with enlargened near-field enhancement area

Metal antennas-substrate coupled structures have unique features of strong nanoscale light confinement and field enhancement at the gap, which make them attractive and promising in a variety of applications such as sensing, lasing, and solar cell. Here, we built a coupled system consisting of a gold spherical semishell antenna and gold substrate. Through numerical simulation, it is found that due to the unique geometric shape of the antenna, the near-field enhancement area of the localized resonance is enlarged dramatically in the designed plasmonic structure, which is beneficial to increasing the active region, allowing more molecular adsorbed and also replaced easily. Moreover, the far-field extinction spectra of the localized dipole mode in the designed structure has higher quality factor and is more robust to the gap separation than its solid counterpart, which may relax the fabrication tolerances.

Near-Field Sound Localization Based on the Small Profile Monaural Structure.

The acoustic wave around a sound source in the near-field area presents unconventional properties in the temporal, spectral, and spatial domains due to the propagation mechanism. This paper investigates a near-field sound localizer in a small profile structure with a single microphone. The asymmetric structure around the microphone provides a distinctive spectral variation that can be recognized by the dedicated algorithm for directional localization. The physical structure consists of ten pipes of different lengths in a vertical fashion and rectangular wings positioned between the pipes in radial directions. The sound from an individual direction travels through the nearest open pipe, which generates the particular fundamental frequency according to the acoustic resonance. The Cepstral parameter is modified to evaluate the fundamental frequency. Once the system estimates the fundamental frequency of the received signal, the length of arrival and angle of arrival (AoA) are derived by the designed model. From an azimuthal distance of 3–15 cm from the outer body of the pipes, the extensive acoustic experiments with a 3D-printed structure show that the direct and side directions deliver average hit rates of 89% and 73%, respectively. The closer positions to the system demonstrate higher accuracy, and the overall hit rate performance is 78% up to 15 cm away from the structure body.

Multi-gradient echo MR thermometry for monitoring of the near-field area during MR-guided high intensity focused ultrasound heating

The multi-gradient echo MR thermometry (MGE MRT) method is proposed to use at the interface of the muscle and fat layers found in the abdominal wall, to monitor MR-HIFU heating. As MGE MRT uses fat as a reference, it is field-drift corrected. Relative temperature maps were reconstructed by subtracting absolute temperature maps. Because the absolute temperature maps are reconstructed of individual scans, MGE MRT provides the flexibility of interleaved mapping of temperature changes between two arbitrary time points. The method’s performance was assessed in an ex vivo water bath experiment. An ex vivo HIFU experiment was performed to show the method’s ability to monitor heating of consecutive HIFU sonications and to estimate cooling time constants, in the presence of field drift. The interleaved use between scans of a clinical protocol was demonstrated in vivo in a patient during a clinical uterine fibroid treatment. The relative temperature measurements were accurate (mean absolute error 0.3 °C) and provided excellent visualization of the heating of consecutive HIFU sonications. Maps were reconstructed of estimated cooling time constants and mean ROI values could be well explained by the applied heating pattern. Heating upon HIFU sonication and subsequent cooling could be observed in the in vivo demonstration.

Probing cytochrome c in living mitochondria with surface-enhanced Raman spectroscopy.

Selective study of the electron transport chain components in living mitochondria is essential for fundamental biophysical research and for the development of new medical diagnostic methods. However, many important details of inter- and intramembrane mitochondrial processes have remained in shadow due to the lack of non-invasive techniques. Here we suggest a novel label-free approach based on the surface-enhanced Raman spectroscopy (SERS) to monitor the redox state and conformation of cytochrome c in the electron transport chain in living mitochondria. We demonstrate that SERS spectra of living mitochondria placed on hierarchically structured silver-ring substrates provide exclusive information about cytochrome c behavior under modulation of inner mitochondrial membrane potential, proton gradient and the activity of ATP-synthetase. Mathematical simulation explains the observed enhancement of Raman scattering due to high concentration of electric near-field and large contact area between mitochondria and nanostructured surfaces.