Inhomogeneous Index Research Articles

Formation of In-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- films by magnetron sputtering on Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- (012) substrates

The results of studies of the microstructure and optical characteristics of In2O3 films deposited by the dc-magnetron sputtering of a polycrystalline target onto single-crystal sapphire substrates are summarized. The technological regimes of films preparation differed in the deposition time, substrate temperature, and the presence of additional heat treatment of film structures in air. It has been established that the optical refractive index of films deposited on a "cold" substrate increases in the direction from the substrate to the external interface. Heat treatment of the films eliminates the inhomogeneity of the refractive index and leads to a decrease in the band gap. The observed optical properties are explained by the thickness inhomogeneous microstructure of the films, which is formed during sputtering of a target with a relatively low mechanical strength. Keywords: In2O3 films, magnetron sputtering, Al2O3 substrates, refraction index, bandgap width.

Формирование плёнок In-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- методом магнетронного напыления на подложках Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- (012)

The results of studies of the microstructure and optical characteristics of In2O3 films deposited by the dc-magnetron sputtering of a polycrystalline target onto single-crystal sapphire substrates are summarized. The technological regimes of films preparation differed in the deposition time, substrate temperature, and the presence of additional heat treatment of film structures in air. It has been established that the optical refractive index of films deposited on a "cold" substrate increases in the direction from the substrate to the external interface. Heat treatment of the films eliminates the inhomogeneity of the refractive index and leads to a decrease in the band gap. The observed optical properties are explained by the thickness inhomogeneous microstructure of the films, which is formed during sputtering of a target with a relatively low mechanical strength.

Phase regulation of lightwave transmission in inhomogeneous atmospheric medium using plane acoustic field

Based on the acousto-optic effect and the Gladstone–Dale relationship, the relationship about variations of the refractive index of the isotropic homogeneous atmospheric medium and the inhomogeneous atmospheric medium with the sound pressure under the disturbance of the plane sound field is derived. Models for the transmission of plane light waves and Laguerre-Gaussian beams through homogeneous atmospheric medium and inhomogeneous atmospheric medium disturbed by plane acoustic waves are established. The results show that the refractive index distribution of the homogeneous atmospheric medium exhibits a homogeneous periodic distribution after being disturbed by the plane sound field. For large-scale angles of longitudinal variation of atmospheric pressure, the plane sound field has little effect on the distribution of the refractive index of the inhomogeneous atmosphere. For small-scale angles, the inhomogeneous atmospheric refractive index gradually decreases with height and fluctuates with the influence of sound pressure. When the plane acoustic wave disturbs the homogeneous atmospheric medium, the isophase plane of the plane light wave will fluctuate significantly due to the influence of the acoustic wave. The phase of the LG beam rotates and always returns to the original phase. When the plane acoustic wave disturbs the inhomogeneous atmospheric medium, the phase change of the plane light wave will change periodically with the change law of the sound wave. The overall optical path is an inclined plane, but due to the disturbance of the sound wave, the optical path will fluctuate. The phase of the LG beam still rotates, but unlike the homogeneous medium, its phase does not return to its original phase due to the change of its refractive index with height.

Novel volumetric capnography indices measure ventilation inhomogeneity in cystic fibrosis.

BackgroundVolumetric capnography (VCap) is a simpler alternative to multiple-breath washout (MBW) to detect ventilation inhomogeneity in patients with cystic fibrosis (CF). However, its diagnostic performance is influenced by breathing dynamics. We introduce two novel VCap indices, the capnographic inhomogeneity indices (CIIs), that may overcome this limitation and explore their diagnostic characteristics in a cohort of CF patients.MethodsWe analysed 320 N2-MBW trials from 50 CF patients and 65 controls (age 4–18 years) and calculated classical VCap indices, such as slope III (SIII) and the capnographic index (KPIv). We introduced novel CIIs based on a theoretical lung model and assessed their diagnostic performance compared to classical VCap indices and the lung clearance index (LCI).ResultsBoth CIIs were significantly higher in CF patients compared with controls (mean±sd CII1 5.9±1.4% versus 5.1±1.0%, p=0.002; CII2 7.7±1.8% versus 6.8±1.4%, p=0.002) and presented strong correlation with LCI (CII1 r2=0.47 and CII2 r2=0.44 in CF patients). Classical VCap indices showed inferior discriminative ability (SIII 2.3±1.0%/L versus 1.9±0.7%/L, p=0.013; KPIv 3.9±1.3% versus 3.5±1.2%, p=0.071), while the correlation with LCI was weak (SIII r2=0.03; KPIv r2=0.08 in CF patients). CIIs showed lower intra-subject inter-trial variability, calculated as coefficient of variation for three and relative difference for two trials, than classical VCap indices, but higher than LCI (CII1 11.1±8.2% and CII2 11.0±8.0% versus SIII 16.3±13.5%; KPIv 15.9±12.8%; LCI 5.9%±4.2%).ConclusionCIIs detect ventilation inhomogeneity better than classical VCap indices and correlate well with LCI. However, further studies on their diagnostic performance and clinical utility are required.

Free vibration analysis of a cylindrical micro-shell based on MCST

Dynamic analysis of a functionally-graded (FG) cylindrical micro shell is investigated in this work. Effect of small parameter in micro scale is included in fundamental relations based on modified couple stress theory (MCST). For more precise analyzing the structure, third-order shear deformation theory (TSDT) is employed as kinematic relations. The shell is made from FG materials, using power function law. A solution procedure based on an analytical method is developed for special boundary condition. The numerical results are computed in graphical form to seek how changes of main parameters of the study such as micro parameter, in-homogeneity index and some geometric values change the free vibration responses. As an important output of this paper, it is concluded that an increase in micro parameter leads to increase of natural frequency. Furthermore, increase of in-homogeneous index yields more soft structure and then decrease of natural frequency.

Spatial Ventilation Inhomogeneity Determined by Electrical Impedance Tomography in Patients With Chronic Obstructive Lung Disease.

The aim of this study was to examine whether electrical impedance tomography (EIT) could determine the presence of ventilation inhomogeneity in patients with chronic obstructive lung disease (COPD) from measurements carried out not only during conventional forced full expiration maneuvers but also from forced inspiration maneuvers and quiet tidal breathing and whether the inhomogeneity levels were comparable among the phases and higher than in healthy subjects. EIT data were acquired in 52 patients with exacerbated COPD (11 women, 41 men, 68 ± 11 years) and 14 healthy subjects (6 women, 8 men, 38 ± 8 years). Regional lung function parameters of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), forced inspiratory vital capacity (FIVC), forced inspiratory volume in 1 s (FIV1), and tidal volume (VT) were determined in 912 image pixels. The spatial inhomogeneity of the pixel parameters was characterized by the coefficients of variation (CV) and the global inhomogeneity (GI) index. CV and GI values of pixel FVC, FEV1, FIVC, FIV1, and VT were significantly higher in patients than in healthy subjects (p ≤ 0.0001). The ventilation distribution was affected by the analyzed lung function parameter in patients (CV: p = 0.0024, GI: p = 0.006) but not in healthy subjects. Receiver operating characteristic curves showed that CV and GI discriminated patients from healthy subjects with an area under the curve (AUC) of 0.835 and 0.852 (FVC), 0.845 and 0.867 (FEV1), 0.903 and 0.903 (FIVC), 0.891 and 0.882 (FIV1), and 0.821 and 0.843 (VT), respectively. These findings confirm the ability of EIT to identify increased ventilation inhomogeneity in patients with COPD.

Evaluation of atelectasis using electrical impedance tomography during procedural deep sedation for MRI in small children: A prospective observational trial

Study objectiveTo investigate the variation of poorly ventilated lung units (i.e., silent spaces) in children undergoing procedural sedation in a day-hospital setting, until discharge home from the Post-Anesthesia Care Unit (PACU). DesignProspective, single-center, observational cohort trial. SettingThis study was conducted at the radiology department and in PACU at Bern University Hospital (Switzerland), a tertiary care hospital. PatientsWe included 25 children (1–6 years, ASA I-III) scheduled for cerebral magnetic resonance imaging scan, spontaneously breathing under deep sedation. Children planned for tracheal intubation, supraglottic airway insertion, or with contraindication for propofol were excluded. InterventionAfter intravenous or inhaled induction, deep sedation was performed with 10 mg/kg/h Propofol. All children received nasal oxygen 0.3 ml/kg/min. MeasurementsThe proportion of silent spaces and the global inhomogeneity index were determined at each of five procedural points, using electrical impedance tomography: before induction (T1); before (T2) and after (T3) magnetic resonance imaging; at the end of sedation before transport to the PACU (T4); and before hospital discharge (T5). Main resultsThe median [interquartile range (IQR)] proportion of silent spaces at the five analysis points were: T1, 5% [2%–14%]; T2, 10% [7%–14%]; T3, 12% [5%–23%]; T4, 12% [7%–24%]; and T5, 3% [2%–11%]. These defined significant changes in silent spaces over the course of sedation (p = 0.009), but no differences in silent spaces from before induction to before discharge from the PACU (T1 vs. T5; p = 0.29). Median [IQR] global inhomogeneity indices were 0.57 [0.55–0.58], 0.56 [0.53–0.59], 0.56 [0.54–0.59], 0.57 [0.54–0.60] and 0.56 [0.54–0.57], respectively (p = 0.93). None of the children reported anesthesia-related complications. ConclusionDeep sedation results in significantly increased poorly ventilated lung units during sedation. However, this does not significantly affect ventilation homogeneity, which was fully resolved at discharge from the PACU.Trial registration: clinicaltrials.gov, identifier NCT04507581

Five Years of Spatially Resolved Ground-Based MAX-DOAS Measurements of Nitrogen Dioxide in the Urban Area of Athens: Synergies with In Situ Measurements and Model Simulations

Long-term nitrogen dioxide (NO2) slant column density measurements using the MAX-DOAS (multi-axis differential optical absorption spectroscopy) technique were analyzed in order to demonstrate the temporal and horizontal variability of the trace gas in Athens for the period October 2012–July 2017. The synergy with in situ measurements and model simulations was exploited for verifying the MAX-DOAS technique and its ability to assess the spatiotemporal characteristics of NO2 pollution in the city. Tropospheric NO2 columns derived from ground-based MAX-DOAS observations in two horizontal and five vertical viewing directions were compared with in situ chemiluminescence measurements representative of urban, urban background and suburban conditions; a satisfactory correlation was found for the urban (r ≈ 0.55) and remote areas (r ≈ 0.40). Mean tropospheric slant columns retrieved from measurements at the lowest elevation over the urban area ranged from 0.1 to 32 × 1016 molec cm−2. The interannual variability showed a rate of increase of 0.3 × 1016 molec cm−2 per year since 2012 in the urban area, leading to a total increase of 20%. The retrieved annual cycles captured the seasonal variability with lower NO2 levels in summer, highly correlated (r ≈ 0.85) with the urban background and suburban in situ observations. The NO2 diurnal variation for different seasons exhibited varied patterns, indicating the different role of photochemistry and anthropogenic activities in the different seasons. Compared to in situ observations, the MAX-DOAS NO2 morning peak occurred with a one-hour delay and decayed less steeply in winter. Measurements at different elevation angles are shown as a primary indicator of the vertical distribution of NO2 at the urban environment; the vertical convection of the polluted air masses and the enhanced NO2 near-surface concentrations are demonstrated by this analysis. The inhomogeneity of the NO2 spatial distribution was shown using a relevant inhomogeneity index; greater variability was found during the summer period. Comparisons with city-scale model simulations demonstrated that the horizontal light path length of MAX-DOAS covered a distance of 15 km. An estimation of urban sources’ contribution was also made by applying two simple methodologies on the MAX-DOAS measurements. The results were compared to NO2 predictions from the high resolution air quality model to infer the importance of vehicle emissions for the urban NO2 levels; 20–35% of the urban NO2 was found to be associated with road transport.

Simulation study using the spots deletion technique in spot scanning proton beam therapy for prostate cancers.

The aim of the present study was to investigate the effects on the dose distribution and beam delivery time in spot scanning proton beam therapy (PBT) incorporating the spot deletion technique. A spot scanning plan was created for 30 patients with prostate cancer. The plan was then modified via two processes: Spots with lower weighting depositions were deleted (process A) and spots that were distant from the clinical target volume (CTV) were deleted (process B). The dose distribution to the organs at risk (OAR), the expanded CTV (exCTV), which was defined by a uniform expansion of the CTV by a radius of 5 mm, and the beam delivery time were compared among initial and modified plans. The V50 Gy [relative biological effectiveness (RBE)] to the rectum and bladder, and V60 Gy(RBE) to the urethral bulb, inhomogeneity index (INH) of the exCTV showed a difference (P=1.1x10-14, P=6.4x10-14, P=2.7x10-7, P=3.2x10-17), although only changes by process B were significant. Modified plan by process B showed the V50 Gy(RBE) to the rectum and bladder decreased by -2.4±1.6 and -2.3±1.4%, and the V60 Gy (RBE) to the urethral bulb decreased by -15.9±19.4%. The INH of the exCTV increased by 0.05±0.03%. On the other hand, modification of the initial plan by process A did not affect the dose of the OAR, exCTV or beam delivery time. In spot scanning PBT, modification of the initial radiotherapy plan by systemic deletion of spots distant from the CTV could result in a dose reduction to the OAR.

Radial vibration analysis for functionally graded ring piezoelectric transducers based on electromechanical equivalent circuit method

Ring piezoelectric transducers (rPETs) have attracted multitudinous attentions due to their widespread applications in hydro-acoustic engineering, structural health monitoring, and energy harvesting. However, cracks are inevitably occurred by the concentrated stress at the interface between metal and piezoelectric ceramics, which will seriously affect the performance and service life of the devices. Hence, a novel functionally graded ring piezoelectric transducer (FG-rPET) has been designed and an accurate analytical system is constructed mainly including a three-port electromechanical equivalent circuit model (EECM) which can acquire exact solutions in radial vibration. In addition, the proposed three-port EECM has excellent generalizability, which is also applicable to conventional rPETs. The validity of the EECM is verified by experiments and the finite element method. The vibration characteristics (resonance/anti-resonance frequencies and effective electromechanical coupling coefficient (keff)) with fundamental and second modes for the FG-rPETs can be regulated via the inhomogeneity index and wall thickness. Markedly enhanced keff at second modes can be obtained for the FG-rPETs with specific wall thicknesses. The proposed analytical system has important guiding significance for structure optimization design of piezoelectric devices, and the designed FG-rPET is expected to break the bottleneck of mechanical properties for the conventional rPETs.

First Attempt at Using Electrical Impedance Tomography to Predict High Flow Nasal Cannula Therapy Outcomes at an Early Phase.

Objective: Spatial and temporal ventilation distributions in patients with acute respiratory failure during high flow nasal cannula (HFNC) therapy were previously studied with electrical impedance tomography (EIT). The aim of the study was to explore the possibility of predicting HFNC failure based on various EIT-derived parameters.Methods: High flow nasal cannula failure was defined reintubation within 48 h after HFNC. EIT was performed with the patients spontaneously breathing in the supine position at the start of HFNC. EIT-based indices (comprising the global inhomogeneity index, center of ventilation, ventilation delay, rapid shallow breathing index, minute volume, and inspiration to expiration time) were explored and evaluated at three time points (prior to HFNC, T1; 30 min after HFNC started, T2; and 1 h after, T3).Results: A total of 46 subjects were included in the final analysis. Eleven subjects had failed HFNC. The time to failure was 27.8 ± 12.4 h. The ROX index (defined as SpO2/FiO2/respiratory rate) for HFNC success patients was 8.3 ± 2.7 and for HFNC failure patients, 6.2 ± 1.8 (p = 0.23). None of the investigated EIT-based parameters showed significant differences between subjects with HFNC failure and success. Further subgroup analysis indicated that a significant difference in ventilation inhomogeneity was found between ARDS and non-ARDS [0.54 (0.37) vs. 0.46 (0.28) as evaluated with GI, p < 0.01]. Ventilation homogeneity significantly improved in ARDS after 60-min HFNC treatment [0.59 (0.20) vs 0.57 (0.19), T1 vs. T3, p < 0.05].Conclusion: Spatial and temporal ventilation distributions were slightly but insignificantly different between the HFNC success and failure groups. HFNC failure could not be predicted by changes in EIT temporal and spatial indexes of ventilation distribution within the first hour. Further studies are required to predict the outcomes of HFNC.

Ventilation improvement after pneumonia treatment evaluated with electrical impedance tomography: an observational study

Objective. Due to radiation exposure, not all patients with pneumonia receive chest x-rays or CT measurements to confirm treatment effectiveness. The aim of this study was to examine the ability to use electrical impedance tomography (EIT) to evaluate the treatment effectiveness in such patient group. Approach . A total of 35 consecutive patients with non-severe pneumonia were included in this prospective study. The patients received standard treatment according to our internal protocol. EIT measurements were performed in supine position before the treatment started and on day 6 of the treatment period. The EIT-based global inhomogeneity (GI) index and center of ventilation (CoV) index were calculated. The clinical pulmonary infection score (CPIS) was obtained at both time points. Main r esults. Clinically significant improvements in GI and CoV were found in the patient group (ΔGI: −34% ± 17% and ΔCoV: −10% ± 11%; p<0.001). Although the CPIS was also significantly improved (ΔCPIS −0.70 ± 0.17, p<0.001), no correlations were demonstrated when compared to ΔGI or ΔCoV. Significance. EIT demonstrated individual improvement of ventilation heterogeneity after standard treatment in non-severe pneumonia, and provided different information compared to CPIS. EIT has the potential to become a routine non-invasive, non-radiative tool to assess pneumonia treatment effectiveness.

Stereoscopic particle image velocimetry in inhomogeneous refractive index fields of combustion flows.

Particle image velocimetry (PIV) measurements in reactive flows are disturbed by inhomogeneous refractive index fields, which cause measurement deviations in particle positions due to light refraction. The resulting measurement errors are known for standard PIV, but the measurement errors for stereoscopic PIV are still unknown. Therefore, for comparison, the velocity errors for standard and stereoscopic PIV are analyzed in premixed propane flames with different Reynolds numbers. For this purpose, ray-tracing simulations based on the time-averaged inhomogeneous refractive index fields of the studied non-swirled flame flows measured by the background-oriented Schlieren technique are performed to quantify the resulting position errors of the particles. In addition, the performance of the volumetric self-calibration relevant to tomographic PIV is analyzed with respect to the remaining position errors of the particles within the flames. The position errors cause significant standard PIV errors of 2% for the velocity component radial to the burner symmetry axis. Stereoscopic PIV measurements result in measurement errors of up to 3% radial to the burner axis and 13% for the velocity component perpendicular to the measurement plane. Due to the lower refractive index gradients in the axial direction, no significant velocity errors are observed for the axial velocity component. For the investigated flame configurations, the position errors and velocity errors increase with the Reynolds numbers. However, this dependence needs to be verified for other flame configurations such as swirled flame flows.

The Effect of Physical Therapy on Regional Lung Function in Critically Ill Patients.

Early mobilization has become an important aspect of treatment in intensive care medicine, especially in patients with acute pulmonary dysfunction. As its effects on regional lung physiology have not been fully explored, we conceived a prospective observational study (Registration number: DRKS00023076) investigating regional lung function during a 15-min session of early mobilization physiotherapy with a 30-min follow-up period. The study was conducted on 20 spontaneously breathing adult patients with impaired pulmonary gas exchange receiving routine physical therapy during their intensive care unit stay. Electrical impedance tomography (EIT) was applied to continuously monitor ventilation distribution and changes in lung aeration during mobilization and physical therapy. Baseline data was recorded in the supine position, the subjects were then transferred into the seated and partly standing position for physical therapy. Afterward, patients were transferred back into the initial position and followed up with EIT for 30 min. EIT data were analyzed to assess changes in dorsal fraction of ventilation (%dorsal), end-expiratory lung impedance normalized to tidal variation (ΔEELI), center of ventilation (CoV) and global inhomogeneity index (GI index).Follow-up was completed in 19 patients. During exercise, patients exhibited a significant change in ventilation distribution in favor of dorsal lung regions, which did not persist during follow-up. An identical effect was shown by CoV. ΔEELI increased significantly during follow-up. In conclusion, mobilization led to more dorsal ventilation distribution, but this effect subsided after returning to initial position. End-expiratory lung impedance increased during follow-up indicating a slow increase in end-expiratory lung volume following physical therapy.

Monitoring postoperative lung recovery using electrical impedance tomography in post anesthesia care unit: an observational study

With electrical impedance tomography (EIT) recruitment and de-recruitment phenomena can be quantified and monitored at bedside. The aim was to examine the feasibility of EIT with respect to monitor atelectasis formation and resolution in the post anesthesia care unit (PACU). In this observational study, 107 postoperative patients were investigated regarding the presence and recovery of atelectasis described by the EIT-derived parameters Global Inhomogeneity Index (GI Index), tidal impedance variation (TIV), and the changes in end-expiratory lung impedance (ΔEELI). We examined whether the presence of obesity (ADP group) has an influence on pulmonary recovery compared to normal weight patients (NWP group). During the stay at PACU, measurements were taken every 15 min. GI Index, TIV, and ΔEELI were calculated for each time point. 107 patients were monitored and EIT-data of 16 patients were excluded for various reasons. EIT-data of 91 patients were analyzed off-line. Their length of stay averaged 80 min (25th and 75th quartile 52–112). The ADP group demonstrated a significantly higher GI Index at PACU arrival (p < 0.001). This finding disappeared during their stay at the PACU. Additionally, the ADP group showed a significant increase in ΔEELI between PACU arrival and discharge (p = 0.025). Furthermore, TIV showed a significantly lower value during the first 90 min of PACU stay as compared to the time period thereafter (p = 0.036). Our findings demonstrate that obesity has an influence on intraoperative atelectasis formation and de-recruitment during PACU stay. The application of EIT in spontaneously breathing PACU patients seems meaningful in monitoring pulmonary recovery.

On the reduction of stress concentrations in thick-walled hollow spheres under an arbitrary uniform axial symmetric outer traction

This paper presents an analytical solution for a thick-walled hollow sphere interiorly reinforced by a soft graded layer subjected to an arbitrary uniform axial symmetric outer traction. The elastic modulus of the graded reinforcement is assumed to vary through its thickness as a power-law function. The resultant inhomogeneous Navier’s equations of equilibrium are in the form of a system of second-order differential equations of the Euler type. The differential system is subsequently solved as an eigenvalue problem by the use of variable replacement and differential theory. Stress distributions and stress concentrations are analyzed for five inhomogeneity indices due to pure-shear, unidirectional, all-around and centrosymmetric outer tractions. For each loading configuration, the effects of property gradation of the reinforcement layer on stress reductions of hollow spheres are analyzed. The optimal inhomogeneity index that leads to the best stress distributions and therefore the least stress concentrations is also determined. For the purpose of verification and validation, finite element modelings are also conducted for some numerical examples. The fundamental mechanism of reducing stress concentrations is to drive the high-stress zone typically occurring along the inner surface of hollow spheres toward their outer boundary such that stresses may distribute more uniformly through the thickness dimension.

Large Eddy Simulations of the Dusty Martian Convective Boundary Layer With MarsWRF

AbstractLarge eddy simulation (LES) of the Martian convective boundary layer (CBL) with a Mars‐adapted version of the Weather Research and Forecasting model is used to examine the impact of aerosol dust radiative‐dynamical feedbacks on turbulent mixing. The LES is validated against spacecraft observations and prior modeling. To study dust redistribution by coherent dynamical structures within the CBL, two radiatively active dust distribution scenarios are used: one in which the dust distribution remains fixed and another in which dust is freely transported by CBL motions. In the fixed dust scenario, increasing atmospheric dust loading shades the surface from sunlight and weakens convection. However, a competing effect emerges in the free dust scenario, resulting from the lateral concentration of dust in updrafts. The resulting enhancement of dust radiative heating in upwelling plumes both generates horizontal thermal contrasts in the CBL and increases buoyancy production, jointly enhancing CBL convection. We define a dust inhomogeneity index (DII) to quantify how much dust is concentrated in upwelling plumes. If the DII is large enough, the destabilizing effect of lateral heating contrasts can exceed the stabilizing effect of surface shading such that the CBL depth increases with increasing dust optical depth. Thus, under certain combinations of total dust optical depth and the lateral inhomogeneity of dust, a positive feedback exists between dust optical depth, the vigor and depth of CBL mixing, and—to the extent that dust lifting is controlled by the depth and vigor of CBL mixing—the further lifting of dust from the surface.

About copying a free-space electromagnetic field by an invisible object

The structure of a monochromatic electromagnetic field inside a spherical object that does not distort the wave field of external sources outside its surface has been studied using transformation optics methods. It is assumed that the object is made of isotropic materials with equal values of permittivity and permeability and consists of a spherical volume of material with a positive spatially uniform refractive index and an adjacent spherical layer of material with a negative inhomogeneous refractive index (i.e., it is a spherical superlens made of isotropic materials). It is shown that the field inside a sphere with a positive refractive index is the reduced-size copy of the field in which the object was located. This copy contains information about the radiation field of external sources in a spherical free-space volume whose radius depends on the object parameters and can be significantly larger than the radius of the object. It is shown that the copying properties of the object with given dimensions can be fully preserved if its outer layer is made of anisotropic materials.

Light Confinement by Local Index Tailoring in Inhomogeneous Dielectrics

AbstractThe engineering of light confinement is a topic with a long history in optics and with significant implications for the control of light‐matter interaction. In inhomogeneous and disordered media, however, multiple scattering prevents the application of conventional approaches for the design of light fields with desired properties. This is because any local change to such a medium typically affects these fields in a non‐local and complicated fashion. Here, we present a theoretical methodology for tailoring an inhomogeneous 1D Hermitian dielectric index distribution that allows us to control the intensity profile of an incoming light field purely locally, that is, with little or no influence on the field profile outside of a designated region of interest. Strongly increasing or decreasing the light's intensity at arbitrary positions inside the medium thereby becomes possible without, in fact, changing the external reflectance or transmittance. These local modifications of the medium can thus be made undetectable to far field measurements. We apply this approach to locally control the confinement of light inside 1D materials with inhomogeneous continuous refractive index profiles and extend it to multilayer films as well as to chains of coupled micro‐resonators.

The Speed of Light Is Slowed Down as It Travels Near the Surface of an Obstacle

The speed of propagation of light that passes through a medium at a slower speed determines the refractive index with respect to the wavelength. Subsequently, the refractive index of vacuum (free space) that light travels at speed c is 1 by definition.&#x0D; This study proposes that the speed of light is slowed down in an inhomogeneous space close to the surface of the obstacles, including the edges of the apertures. Furthermore, the inhomogeneous refractive index near these surfaces will increase as the distance from the object is reduced. Therefore, light propagates through apertures as it encounters a medium with a variable refractive index.