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OBJECTIVE The current grading system for moyamoya disease (MMD) is focused on angiographic studies with limited clinical application. The authors aimed to determine relevant factors that may impact postoperative outcome and establish a scoring system to predict the functional outcome. METHODS Adult patients with MMD who underwent treatment between 1998 and 2016 were included. Factors such as age, sex, comorbidity, smoking, MMD family history, initial presentation, multimodal imaging modalities, and types of surgical revascularization were thoroughly reviewed. These factors were analyzed to determine possible risk factors related to unfavorable 6-month postoperative outcomes using the modified Rankin Scale (mRS) (unfavorable: mRS score ≥ 3). A scoring system was developed using these independent risk factors to predict the outcome and validated using prospectively collected data from multiple centers between 2017 and 2018. RESULTS Of 302 patients for whom applications were submitted, 260 patients (321 hemispheres) met the diagnostic criteria. In multivariate analysis, hyperlipidemia, smoking, cerebral infarction on preoperative CT or MRI, and moderately to severely reduced regional cerebrovascular reserve results from Diamox SPECT were significantly related to unfavorable outcome. The authors developed a scoring system and stratified patients into risk groups according to their scores: low-risk (score 0–3), intermediate-risk (score 4–6), and high-risk (score 7–9) groups. This model demonstrated both good discrimination and calibration using C-statistics and the Hosmer-Lemeshow goodness-of-fit test showing 0.812 (95% CI 0.743–0.881) (p = 0.568) for the development and 0.954 (95% CI 0.896–1) (p = 0.097) for the temporal and external validation cohort. CONCLUSIONS The authors’ scoring system is readily adoptable to predict the postoperative outcome for MMD. Their data revealed the importance of smoking and hyperlipidemia, which were the only modifiable factors included in the scoring system. The authors validated their scoring system both internally and externally and maintained good performance, highlighting the system’s generalizability and reliability.

A new DC current-voltage droop control method for a hybrid high-voltage direct-current (HVDC) system featuring a voltage-sourced converter (VSC) rectifier and a line-commutated converter (LCC) inverter is presented. The proposed method utilizes DC voltage droop control to reduce the AC voltage fluctuation at the inverter side, to exploit the hybrid HVDC system for connecting offshore wind farms to weak grids without necessitating continuous reactive power compensation facilities. Additionally, an optimal droop coefficient calculation method is proposed to keep the AC voltage constant for wind power fluctuations. To evaluate the stability of the proposed method, a small-signal state-space (SS) model of the target system is derived and the root locus analysis is given. Simulation case studies are performed using an electromagnetic transient model in PSCAD and an SS model in MATLAB. The results demonstrate that a hybrid HVDC system with the proposed method successfully integrates offshore wind energy and weak grids without additional facilities because the AC voltage can be maintained at a near constant during wind fluctuations.

A design technique for modulated surface reactances for 1-D leaky-wave antenna applications based on complete aperture field synthesis is presented. For a given visible-region spectrum corresponding to desired radiation and polarization patterns, the evanescent or invisible-region spectrum is introduced and systematically optimized to render the antenna surface passive and lossless everywhere, while generating the specified far-zone characteristics. Design techniques for linear and circular polarizations excited by a TM-polarized feed surface wave are provided together with design examples with simulation validation. Not based on local periodicity, the proposed technique does not suffer from limitations associated with the traditional sinusoidally modulated reactance surfaces.

Background: To analysis the role of gamma knife radiosurgery (GKRS) in treatment of the recurrent or residual World Health Organization (WHO) grade II and III meningiomas.Methods: Between 1995 and ...

Background We investigated the risk factors for leptomeningeal carcinomatosis (LMC) and compared clinical efficacies of various treatment modalities including intrathecal (IT) chemotherapy in patients with lung adenocarcinoma harboring epidermal growth factor receptor (EGFR) mutations. Methods Using clinical research data from the Asan Medical Center, we retrospectively analyzed data of patients diagnosed with LMC, confirmed via cerebrospinal fluid (CSF) analysis from January 2008 to December 2017. Results We identified 1189 patients with lung adenocarcinoma harboring EGFR mutations. Among these, 9.8% had a median duration of 13.5 (interquartile range [IQR] 6.8–23.6) months from the initial lung cancer diagnosis to LMC occurrence. Younger age (hazard ratio [HR] 1.043, P

Objective Pediatric intracranial aneurysms (IAs) are rare and differ from their adult counterparts in terms of their aneurysmal characteristics, presentation, treatment, and outcomes. Their treatment is often more difficult and complex compared with that of adults. However, studies outlining the clinical effect of pediatric IAs remain sparse. Methods We retrospectively reviewed the data from patients aged ≤18 years admitted to our hospital from 2000 to 2017 with a diagnosis of IAs. Results From the sample of 8207 patients with an IA diagnosis, 26 patients with 33 IAs were involved. Our cohort included 17 males and 9 females, with a mean age of 12.5 years. The mean follow-up duration was 4 years and 3 months. Seven patients (26.92%) were assumed to have a traumatic origin for their IAs. Ruptured aneurysms were more common than unruptured ones (61.53% vs. 38.46%). Complex features were observed in 14 aneurysms (42.42%). Initially, microsurgical and endovascular treatment were both performed in 10 patients (38.46%). A good recovery was obtained in 16 patients (61.54%) as determined by the Glasgow outcome scale scores at the 6-month follow-up visits. The complete obliteration of aneurysms was observed in 17 patients (65.38%). Endovascular treatment was the initial treatment in 3 patients with incomplete obliteration. Conclusions The treatment of pediatric IAs is challenging and technically demanding owing to their discrete nature compared with adult IAs and the need for greater surgical skills. We found a male predominance, with internal carotid artery bifurcation as the most frequent location of the aneurysms. Despite the greater incidence of ruptured and complex aneurysm cases, many patients had experienced a good recovery at the 6-month follow-up examinations.

Objective Little is known about the long-term efficacy, prognostic factors, and tolerability of gamma knife radiosurgery (GKS) for acromegaly. The aim of this study was to investigate long-term hormonal effects, prognostic factors, and tolerability of GKS in patients with growth hormone-secreting adenoma. Methods A retrospective multicenter study over 25 years with a median follow-up of 85.2 months was performed. A total of 138 patients from 3 tertiary referral centers in South Korea were included in this study between 1991 and 2017. Main outcome measures were endocrine remission, endocrine control under somatostatin analogues, and hypopituitarism. Results With a mean follow-up period of 85.2 months (range, 12-304 months), overall median time to the endocrine remission and control under long-acting somatostatin analogues was 138 months and 96 months, respectively. Female sex, normal age-adjusted insulin growth factor-1 (IGF-1) ≤ 2, and GKS as an adjuvant treatment were significantly favorable factors for remission (P = 0.004, P = 0.001, P = 0.010, respectively). The early response group had a significantly lower proportion of normal age-adjusted IGF-1 levels >2 than did the late response group (22.2% vs. 51.7%, P = 0.035); also, the early response group had lower radiation dose than the late response group (24.3 Gy vs. 27.0 Gy, P = 0.003). The incidence of GKS-induced hypopituitarism (1 or more) was 12 of 138 patients (8.6%) at the last follow-up. Conclusions In acromegalic patients, women with normal age-adjusted IGF-1 ≤ 2 and GKS as an adjuvant treatment have a better response to GKS. We should take into account the variability of radiosensitivity of the tumor according to the gender and IGF-1 level.

Planar metasurfaces for efficient unidirectional conversion of a plane wave into a surface wave are presented. They are designed as a reciprocal device of a decoupler or leaky-wave antenna based on spatially modulated reactance surfaces. In a surface wave-to-leaky wave conversion, the surface reactance is determined from optimization of the complete aperture field over the propagating and evanecent spectra such that the conversion surface becomes locally and globally passive and lossless, while the desired wave conversion is achieved. The coupling efficiency is given by the aperture efficiency of the reciprocal antenna, which can closely approach unity for large apertures. The optimized surface reactance is spatially discretized and translated into physical metasurfaces, comprising an array of subwavelength inclusions. In TM polarization, three lossless metasurface design examples of 40 and 80 wavelengths are provided with performance validation using full-wave simulations: a metallic groove array, a thickness-modulated grounded dielectric substrate, and a width-modulated grounded dielectric ridge array. Deviations of the surface reactance from the optimized distribution reduce the conversion efficiency, but high coupling efficiencies in excess of 98% for the metallic structure and 60% for dielectric structures are predicted.

This paper proposes a semiconductor optical amplifier (SOA)-based multilevel polarization shift on–off keying (MPS-OOK) transmission for free-space optical (FSO) communication. At the transmitter end, the MPS-OOK signal is modulated with a constant linear state of polarization (SOP) at the high-intensity level and various SOPs at the low-intensity level in order to improve the spectral efficiency (SE) with the transmitted power efficiency. At the receiver end, first, a polarization-independent SOA was introduced to optically suppress the turbulence-induced scintillation effect and equalize the intensities of the various SOPs in the deep gain saturation state without polarization distortion. Then, a linear polarizer (LP) with a high extinction ratio (ER) was deployed to convert the equalized SOPs into a known intensity. Finally, the converted MPS-OOK signal was detected using a single photodiode (PD) and distinguished using a multilevel fixed-threshold decision (M-FTD). The proposed technique was evaluated using experiments. A Mach–Zehnder modulator (MZM)-based fading simulator was introduced to emulate the turbulence-induced scintillation effect. The experimental results demonstrated that the scintillation effect was effectively mitigated and the SE was improved by up to 2 bit/s/Hz using the proposed four-level polarization shift on–off keying (4PS-OOK) transmission.

Modulated reactance surfaces for ideal 1-D leaky-wave radiation are designed based on complete aperture field synthesis over both propagating and evanescent spectra. For a desired far-zone radiation pattern specified by the visible-region part of the aperture field, the invisible-region part is introduced and optimized such that the total aperture fields render the radiation aperture passive and lossless everywhere. When excited by a surface wave, the resulting modulated reactance surface generates the synthesized near fields and produces the intended far-zone pattern.

An electromagnetic illusion technique for free-standing objects for far-field observation using passive lossless metasurfaces is presented. Over a closed surface, the electric and magnetic surface currents needed for generating the scattered fields associated with a given physical scatterer are obtained using the surface equivalence principle. The closed surface defines an impenetrable metasurface characterized by surface impedance. A set of auxiliary evanescent surface waves are introduced and optimized over the entire surface to make the metasurface pointwise passive and lossless. Example 2D designs in TE polarization show that desired scattered fields are established immediately away from the illusion device surface. The illusion metasurfaces may be realized as tensor gradient metasurfaces.

Although stereotactic radiosurgery (SRS) has been proven to be effective and safe for treating intracranial meningiomas, concerns have been raised about the use of SRS for large-sized tumors involving the skull base that frequently encroach onto adjacent critical neural structures. The purpose of this study was to investigate the role of hypofractionated SRS as a therapeutic option for large-sized skull base meningiomas. Thirty-one consecutive patients (median age: 55 years, 9 men and 22 women) who had been treated with hypofractionated SRS using CyberKnife for large-sized skull base meningiomas (> 10 cm3 in volume, median of 18.9 cm3, range 11.6–58.2 cm3) were enrolled. All patients harbored middle or posterior skull base tumors, most frequently of cavernous sinus (n = 7, 22.6%), petroclival (n = 6, 19.4%), or tentorial edge (n = 6, 19.4%) locations. SRS was delivered in five daily fractions (range 3–5 fractions) with a median cumulative dose of 27.8 Gy (range 22.6–27.8 Gy). With a median follow-up of 57 months (range 9–98 months), tumor control was achieved for 28 (90.3%) of 31 patients. Treatment response on MRI included partial response (volume decrease > 20%) in 17 (54.8%) patients, stable in 11 (35.5%), and progression (volume increase > 20%) in 3 (9.7%). Of 21 patients with cranial neuropathy, 20 (95.2%) showed improved neurological status. Our current results suggest a promising role of hypofractionated SRS for large-sized skull base megningiomas in terms of tumor control and neurological outcomes. It is a reasonable therapeutic option for select patients.

In this paper, we investigate video signal transmission through an FPGA-based free-space optical (FSO) communication system prototype. We use a channel emulator that models the turbulence, scintillation, and power attenuation of the FSO channel and the FPGA-based real-time prototype for processing transmitted and received video signals. We vary the setup environment of the channel emulator by changing the amount of turbulence and wind speed. At the end of the demonstration, we show that through our testbed, even 4K ultra-high-definition (UHD) resolution video with 60 fps can be successfully transmitted under high turbulence and wind speed., Comment: 2 pages, 2 figures, IEEE WCNC 2020

In this paper we present the theoretical considerations and the design evolution of a proof-of-concept reconfigurable metasurface, primarily used as a tunable microwave absorber, but also as a wavefront manipulation and polarization conversion device in reflection. We outline the design evolution and all considerations taken into account, from the selection of patch shape, unit cell size, and substrate, to the topology of the structure that realizes the desired tunability. The presented design conforms to fabrication restrictions and is co-designed to work with an integrated circuit chip for providing tunable complex loads to the metasurface, using a commercially available semiconductor process. The proposed structure can perform multiple tunable functionalities by appropriately biasing the integrated circuit: Perfect absorption for a wide range of incidence angles of both linear polarization states, accommodating a spectral range in the vicinity of 5 GHz, with potential also for wavefront control, exemplified via anomalous reflection and polarization conversion. The end vision is for such a design to be scalable and deployable as a practical HyperSurface, i.e., an intelligent multi-functional metasurface capable of concurrent reconfigurable functionalities: absorption, beam steering, polarization conversion, wavefront shaping, holography, and sensing., 15 pages (incl. author bios), 16 figures. Published online at 19 August 2020 in the IEEE Transactions on Antennas and Propagation, Vol. 68 (tentative)

OBJECTIVE We investigated the effect of optimization in dose-limiting shell method on the dosimetric quality of CyberKnife (CK) plans in treating brain metastases (BMs). METHODS We selected 19 BMs previously treated using CK between 2014 and 2015. The original CK plans (CKoriginal) had been produced using 1 to 3 dose-limiting shells : one at the prescription isodose level (PIDL) for dose conformity and the others at lowisodose levels (10-30% of prescription dose) for dose spillage. In each case, a modified CK plan (CKmodified) was generated using 5 dose-limiting shells : one at the PIDL, another at intermediate isodose level (50% of prescription dose) for steeper dose fall-off, and the others at low-isodose levels, with an optimized shell-dilation size based on our experience. A Gamma Knife (GK) plan was also produced using the original contour set. Thus, three data sets of dosimetric parameters were generated and compared. RESULTS There were no differences in the conformity indices among the CKoriginal, CKmodified, and GK plans (mean 1.22, 1.18, and 1.24, respectively; p=0.079) and tumor coverage (mean 99.5%, 99.5%, and 99.4%, respectively; p=0.177), whereas the CKmodified plans produced significantly smaller normal tissue volumes receiving 50% of prescription dose than those produced by the CKoriginal plans (p

Objective Metastatic brain tumors (MBTs) often present with intracerebral hemorrhage. Although Gamma Knife surgery (GKS) is a valid treatment option for hemorrhagic MBTs, its efficacy is unclear. To achieve oncologic control and reduce radiation toxicity, we used a radiosurgical targeting technique that confines the tumor core within the hematoma when performing GKS in patients with such tumors. We reviewed our experience in this endeavor, focusing on local tumor control and treatment-associated morbidities. Methods From 2007 to 2014, 13 patients with hemorrhagic MBTs were treated via GKS using our targeting technique. The median marginal dose prescribed was 23 Gy (range, 20-25). GKS was performed approximately 2 weeks after tumor bleeding to allow the patient's condition to stabilize. Results The primary sites of the MBTs included the liver (n=7), lung (n=2), kidney (n=1), and stomach (n=1); in two cases, the primary tumor was a melanoma. The mean tumor volume was 4.00 cm3 (range, 0.74-11.0). The mean overall survival duration after GKS was 12.5 months (range, 3-29), and three patients are still alive at the time of the review. The local tumor control rate was 92% (tumor disappearance 23%, tumor regression 46%, and stable disease 23%). There was one (8%) instance of local recurrence, which occurred 11 months after GKS in the solid portion of the tumor. No GKS-related complications were observed. Conclusion Our experience shows that GKS performed in conjunction with our targeting technique safely and effectively treats hemorrhagic MBTs. The success of this technique may reflect the presence of scattered metastatic tumor cells in the hematoma that do not proliferate owing to the inadequate microenvironment of the hematoma. We suggest that GKS can be a useful treatment option for patients with hemorrhagic MBTs that are not amenable to surgery.

We propose and experimentally demonstrate a secure visible light communication (VLC) system using light-emitting diode and liquid crystal cell. By employing this secure VLC system, transmitted data with useful message can be well protected and received by authorized users. After applying the pre-emphasis and zero-padding technique, clear eye diagrams and high bit error rate performance for the deciphered signal were obtained. We also report the optimal amplitude range for original message data and encryption signals. In addition, the influence of the proposed security process on the broadcast VLC system was explored.

To facilitate differentiated services in visible-light communication systems, we propose an authorization method in the physical layer using interchannel interference based on polarization division multiplexing and a newly proposed signal-mapping process. The proposed system experimentally demonstrated that a 100-Mbit/s broadcasting signal transmission for a lower class user and two types of 100-MBd signal transmission for different higher class groups could be simultaneously enabled using pulse-amplitude modulation. Analysis of the performance of the lower and higher class signals' according to the polarization state of the receiver and the transmitted signal power imbalance is discussed. The proposed authorization method in the physical layer can be applied to many areas because classes can be subdivided when the number of channels increases by using wavelength division multiplexing. Furthermore, the ratio between the lower and higher class signals can be controlled in accordance with the environment.

Pituitary metastases (PMs) are uncommon, representing only 1% of pituitary lesions. The diagnosis of PMs can be challenging and an optimal management remains to be determined. Here, we present a pilot clinical study on the efficacy and safety of hypofractionated stereotactic radiosurgery (SRS) with an optimized dosimetric plan in treating PMs. Between June 2013 and December 2014, seven consecutive patients (4 men and 3 women; median age 62 years) had been diagnosed with PMs based on their characteristic clinical and radiological features and subsequently treated using hypofractionated SRS. Primary cancers originated from the lung (n = 5) or the breast (n = 2). All patients presented with diabetes insipidus (DI). Anterior pituitary and visual dysfunction were combined in 4 and 3 patients, respectively. On magnetic resonance imaging (MRI), PMs involved the pituitary stalk and/or the posterior lobe in all patients. SRS of a cumulative marginal dose 31 Gy with dose-volume constraints for the optic apparatus was delivered in 5 daily fractions. As results, tumor was locally controlled in all patients with substantial responses on MRI (including complete remission in 4 patients). The median survival time was 14 months (range, 6-24 months) after SRS. DI and visual dysfunction improved in all patients, although anterior pituitary dysfunction did not recover. No patients experienced any deterioration in visual, pituitary, or other cranial nerve functions. These results suggest a promising role of hypofractionated SRS in treating PMs in terms of both tumor control and functional outcomes.

Null steering arrays for antijam GPS applications are modeled using dual-polarized antenna elements. Realistic performance is evaluated using the effective carrier-to-noise ratio to determine the percentage of the upper hemisphere, for which GPS satellites are recoverable in the presence of interference. The impact of array size and jammer power level on antijam performance is evaluated, and average results are compared to the literature. The realistic metric is shown to predict higher coverage than previously reported.

A metamaterial-embedded 2-D electric line source radiating inside a ground recess is presented. The media embedding a recessed antenna is designed based on transformation electromagnetics (TE) such that the embedded antenna yields the same far-field radiation characteristics as an antenna over a flat conducting ground plane, i.e., forming a virtual antenna. The transformation media comprise a negative-index superlens of finite dimensions and anisotropic impedance-matching blocks. Resonant inclusion-based metamaterials are designed at 5 GHz for their realization using standard printed-circuit technologies. Required metamaterial blocks are assembled for an effective 2-D TE-polarized configuration in a parallel-plate waveguide simulator. Field-mapping measurement confirms formation of a virtual radiator above the ground.

A four-port anti-jam GPS antenna array is used to electronically steer pattern nulls in the direction of incoming RF interference. Null-steering weights are applied using physical hardware and reception pattern measurements are made in an anechoic chamber for multiple jammer angles-of-arrival. Jammer suppression and null misalignment for two null steering reference element cases are compared.

Given recently suggested utility of hypofractionated stereotactic radiosurgery (SRS) in treating large brain metastases (BMs) > 3 cm, we sought to prospectively control tumor size variable to investigate the efficacy and safety of hypofractionated SRS for medium-sized BMs (2.5 to 3 cm) compared with single-fraction SRS. Between 2011 and 2015, a total of 100 patients with newly diagnosed BMs (n = 105) of 2.5 to 3 cm had been treated with either single-fraction (n = 67; median dose 20 Gy) or hypofractionated SRS (n = 38; median cumulative dose 35 Gy in 5 daily fractions). No patients received any prior or upfront whole brain radiotherapy. In each patient, treatment outcome was measured by local tumor control (LTC), overall and progression-free survival (OS and PFS), and the occurrence of radiation necrosis (RN). With a median follow-up of 14 months, significant differences were observed between the single-fraction versus hypofractionated SRS groups in the incidence of RN (29.9% vs. 5.3%, P

A perpendicular E-plane transition between rectangular waveguide (WG) and suspended stripline (SSL) in the Ku-band is presented. The topology of coupling network is studied and design guidelines are provided. A 10-dB return loss bandwidth (BW) of 12% was obtained using a patch resonator on a double-sided single-layer dielectric substrate combined with a cavity behind the resonator of a very shallow depth as low as 1 mm for a compact design. An insertion loss of 0.18 dB at 13.8 GHz was achieved in the measurement of a back-to-back SSL–WG–SSL transition. Comparison of the measured performances with the state-of-the-art WG transitions to SSL shows a 1.5 times improvement in frequency bandwidth and a three times reduction in electrical dimensions. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1831–1834, 2016

Objective: Many studies have shown favorable outcome of Gamma knife radiosurgery (GKRS) for vestibular schwannomas (VSs). However, there have been few studies which have shown the treatment result of cystic VSs (CVSs) for GKRS. The aim of this study was to confirm whether GKRS for CVSs continues to be safe and effective. Methods: The study population consisted 511 patients (172 males, 339 females) with VSs treated with GKRS between May 1990 and December 2013. Group 1 defined as cyst/tumor volume >30%, group 2 was cyst/tumor volume >50%, and group 3 was solid tumor or cyst/tumor volume ≤30%. To analyze factors that correlated with treatment outcomes, the following factors were assessed: tumor volume, cyst volume, tumor/cyst ratio, cyst type (single vs. multicystic), previous resection history, marginal radiation dose. Results: The median follow up period was 52 months (range, 12-110 months). Tumor progression in group 1 was 5 (18.5%), group 2 was 1 (11.1%) and group 3 was 31 (6.4%). In group 1, 2 patients underwent delayed microsurgery at 31 and 36 months after GKRS. Conclusion: In this study we found that GKRS for large CVS was associated with poor treatment outcome. Further study is needed to identify the mechanism of the tumor progression of CVS after GKRS

A design technique for lossless surface invisibility cloaks for free-space objects using surface waves is presented. For a time-harmonic plane wave of known incidence direction and polarization, the bounding surface of a cloaked region can be designed to transform and guide the illuminating plane wave around and along the surface as surface waves. The cloak design is characterized by an inhomogeneous tensor surface impedance that is pointwise lossless everywhere. The proposed designs are promising for realization as ultra-thin metasurface cloaks for electrically large objects in free space.

For impenetrable metasurfaces described by a scalar surface impedance, a field optimization technique is presented for anomalous plane-wave reflector applications. To the incident and reflected plane waves, a set of evanescent waves co-polarized with the propagating waves are introduced. The discrete evanescent waves are numerically optimized toward obtaining a passive and lossless surface characterization everywhere. Full-wave simulation of an example design characterized by an optimized reactive surface impedance predicts near-perfect anomalous reflection.

Full-wave electromagnetic software may be employed to accurately simulate the reception pattern of antenna elements for use in a controlled reception pattern antenna (CRPA). The implementation of an in-situ anti-jam CRPA model utilizing full-wave element patterns requires more computation time than employing free space patterns, but includes coupling between elements and material effects in the environment. The added work associated with the in-situ model is justified by confirmation of the null-steering results using a non-radiating network in the full wave environment, and comparisons are made between an in-situ CRPA and a simple free space model that does not include coupling effects and dielectric losses.

Electrically thin composite layers (metasurfaces) can be used to shape transmitted fields. It is usually desirable that reflections from the metasurface are absent, while the phase of the transmission coefficient can be fully controlled by tuning the metasurface structure. More generally, it is desirable to shape both the phase and amplitude of transmitted waves, still allowing no reflections. In this presentation we discuss necessary physical conditions for realizing these properties, both for normal and oblique illuminations, and present examples of new topologies of metasurfaces for control of transmitted waves.

System constraints for a wearable anti-jam GPS antenna are explored, including antenna size, design of textile-integrated wearable antennas, null steering algorithms to maximize anti-jam performance, system power consumption, and data rate limitations into a GPS receiver. A textile-integrated pin-fed GPS patch antenna is analyzed through simulation and measurement and found to perform reasonably well, though with a size that may be restrictive for employing an anti-jam antenna on the human body. A dual polarized null steering algorithm is explored through analytical simulation to assess its ability to increase the anti-jam performance of a controlled reception pattern array without increasing the overall size of the array. Finally, overarching limitations for man-portable anti-jam GPS systems such as RF front end power consumption and data rate limits of the interface between an anti-jam module and a standalone GPS receiver are discussed and related to both antenna design and null-steering algorithm selection.

Background We aimed to evaluate the factors associated with de novo brain cavernoma formations after patients underwent gamma knife radiosurgery (GKRS) and confirmed whether developmental venous anomaly (DVA) presented with a cavernoma and whether the cavernoma was included in the GKRS target location. Methods From January 2003 to December 2008, 95 patients underwent radiosurgery for brain cavernoma at our institution. Of these, 15 with multiple cavernomas related to familial cavernoma or with a history of surgical treatment for cavernoma were excluded. A total of 80 patients (44 men and 36 women; average age, 39.4 years) with sporadic cavernoma were retrospectively analyzed by considering the patient characteristics, including sex, age, target volume, radiation dose, clinical symptoms, cavernoma location, radiosurgery complications, and morphology of DVA. Results The average target volume, mean radiation dose, and mean target percentage were 1019.2 mm3, 13.7 Gy, and 51.1%, respectively. Nineteen patients showed cavernomas associated with DVA; of these, de novo cavernoma formations were noticed in 4 patients at a median of 49.5 months after undergoing GKRS. All de novo cavernomas were related to the presence of DVA and were located near the brainstem or cerebral peduncle. De novo cavernomas occurred when DVAs were not included in the GKRS-target location. Conclusions All de novo cavernomas were located near the brainstem or cerebral peduncle, and they occurred in the presence of DVAs. The presence of DVA in the radiosurgery target location might be potentially an important factor associated with de novo cavernoma formation.

We demonstrate tunable perfect anomalous reflection with metasurfaces incorporating lumped elements. The tunable capacitance of each element provides continuous control over the local surface reactance, allowing for controlling the evanescent field distribution and efficiently tilting the reflected wavefront away from the specular direction. The performance of the metasurface is evaluated for both TE and TM polarization and for reflection to the first and second diffraction order., 3 pages, 2 figures, 12th International Congress on Artificial Materials for Novel Wave Phenomena (METAMATERIALS 2018)

For transmissive applications of electromagnetic metasurfaces, an array of subwavelength Huygens' meta-atoms are typically used to eliminate reflection and achieve a high transmission power efficiency together with a wide transmission phase coverage. We show that the underlying principle of low reflection and full control over transmission is asymmetric scattering into the specular reflection and transmission directions that results from a superposition of symmetric and anti-symmetric scattering components, with Huygens' meta-atoms being one example configuration. Available for oblique illumination in TM polarization, a meta-atom configuration comprising normal and tangential electric polarizations is presented, which is capable of reflectionless, full-power transmission and a 2π transmission phase coverage as well as full absorption. For lossy metasurfaces, we show that a complete phase coverage is still available for reflectionless designs for any value of absorptance. Numerical examples in the microwave and optical regimes are provided.

For elements of an infinite planar phased array in free space, fundamental bandwidth bounds are derived from the optical theorem for periodic scatterers. The bounds are based on Gustafsson’s theory of fundamental bandwidth limits for electrically small antennas of arbitrary shape, but extended to periodic configurations. The element bandwidth bound is found to be a function of the strengths of the induced static dipole moments in constant background fields as well as the unit-cell dimensions and the scan angle. Explicit bandwidth bound expressions are found for narrowband and ultrawideband array cases. They are numerically tested using example free-space array designs.

For infinite planar phased array elements, a vector effective height is determined and the receiving area and receiving efficiency are found in terms of transmitting performance descriptors. The vector effective height allows the open-circuit received voltage to be expressed as an inner product with the incident electric field, as is for an isolated antenna. Generalizing a previously known expression, the effective area is expressed in terms of polarization mismatch, radiation efficiency, impedance mismatch, and the projected unit cell area, together with the element Floquet directivity introduced in this study that quantifies the unidirectional or bidirectional nature of radiation. An element’s total receiving efficiency is defined and its expression is inspected for maximizing the received power.

ObjectBrain metastases from hepatocellular carcinoma (HCC) are rare, and the evidence of the effectiveness of Gamma Knife surgery (GKS) in this disease is lacking. The authors report their institutional experience with GKS in patients with brain metastases from HCCs.MethodsThe authors retrospectively reviewed the medical records of 73 consecutive patients who had a combined total of 141 brain metastases arising from HCCs and were treated with GKS. Sixty-four (87.7%) patients were male, and the mean age of the patients was 52.5 years (range 30–79 years). The mean tumor volume was 7.35 cm3 (range 0.19–33.7 cm3). The median margin dose prescribed was 23 Gy (range 15–32 Gy). Univariate and multivariate survival analyses were performed to identify possible prognostic factors of outcomes.ResultsThe estimated rate of local tumor control was 79.6% at 3 months after GKS. The median overall survival time after GKS was 16 weeks. The actuarial survival rates were 76.7%, 58.9%, and 26.0% at 4, 12, and 24 weeks after GKS, respectively. In the univariate analysis, an age of ≤ 65 years, Child-Pugh Class A (pertaining to liver function), high Karnofsky Performance Scale score (≥ 70), and low Radiation Therapy Oncology Group recursive partitioning analysis class (I or II) were positively associated with the survival times of patients. No statistically significant variable was identified in the multivariate analysis.ConclusionsAlthough survival was extremely poor in patients with brain metastases from HCCs, GKS showed acceptable local tumor control at 3 months after the treatment. The authors suggest that GKS represents a noninvasive approach that may provide a valuable option for treating patients with brain metastases from HCCs.

For passive, lossless impenetrable metasurfaces, a design technique for arbitrary beam control of receiving, guiding, and launching is presented. Arbitrary control is enabled by a custom surface wave in an orthogonal polarization such that its addition to the incident (input) and the desired scattered (output) fields is supported by a reactive surface impedance everywhere on the reflecting surface. Such a custom surface wave (SW) takes the form of an evanescent wave propagating along the surface with a spatially varying envelope. A growing SW appears when an illuminating beam is received. The SW amplitude stays constant when power is guided along the surface. The amplitude diminishes as a propagating wave (PW) is launched from the surface as a leaky wave. The resulting reactive tensor impedance profile may be realized as an array of anisotropic metallic resonators printed on a grounded dielectric substrate. Illustrative design examples of a Gaussian beam translator-reflector, a probe-fed beam launcher, and a near-field focusing lens are provided.

A new modeling method for high voltage direct current (HVDC) systems and associated controllers is presented for the power system simulator for engineering (PSS/E) simulation environment. The aim is to improve the estimation of the transient DC voltage and current in the event of an AC line-to-ground fault. The proposed method consists primary of three interconnected modules for (a) equation conversion; (b) control-mode selection; and (c) DC-line modeling. Simulation case studies were carried out using PSS/E and a power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) model of the Jeju– Haenam HVDC system in Korea. The simulation results are compared with actual operational data and the PSCAD/EMTDC simulation results for an HVDC system during single-phase and three-phase line-to-ground faults, respectively. These comparisons show that the proposed PSS/E modeling method results in the improved estimation of the dynamic variation in the DC voltage and current in the event of an AC network fault, with significant gains in computational efficiency, making it suitable for real-time analysis of HVDC systems.

For impenetrable electromagnetic surfaces, a metasurface design approach for perfect control of the reflection phenomena using gradient anisotropic tensor surface impedance is presented. It utilizes a set of orthogonally polarized auxiliary surface waves to create pointwise reactive impedance characteristics by channeling power along the tangential direction of the surface in the near zone in a carefully designed manner. The propagating incident and reflected fields do not interfere with the surface waves due to the polarization orthogonality. Design examples of an anomalous reflector and a power splitter for an incident plane wave are presented and numerically verified. Realization possibilities using an array of rotated metallic resonators on a thin grounded dielectric substrate are discussed.

We investigate multi-channel reflectors, such as a three-channel power splitter and a five-channel isolating mirror. These metasurface reflectors are able to control reflections from and into several directions while possessing a flat surface. We design, fabricate, and experimentally study these new devices, confirming that the performance is nearly perfect., Comment: 2 pages

Reflected and transmitted waves can be shaped by controlling the phase of reflection and transmission coefficients of antenna arrays or thin composite layers. This is the operational principle of phased array antennas and reflectarrays, which can be used also to design reflecting and transmitting metasurfaces. Recently, it has been recognized that such phase-gradient reflectors always produce some parasitic scattering into unwanted directions. In this review talk we present and discuss our recent results on non-local (spatially dispersive) gradient meta-surfaces which do not have this drawback and demonstrate perfect anomalous reflection and transmission of plane waves into any desired direction.

A four element dual-linear polarized pin-fed patch antenna array is modeled as a controlled reception pattern array for anti-jam GPS applications. Full-wave electromagnetic simulation is used to refine the model and account for parasitic effects such as mutual coupling. The effects of using full-wave simulated antenna radiation patterns rather than analytically calculated patterns for calculation of weight vectors to implement null steering are explored.

High-voltage dc (HVDC) systems are being adopted for grid connections by grid operators and transmission owners. Among the converter topologies, the line-commutated converter (LCC) is more economical than the voltage-sourced converter (VSC); however, its reactive power cannot be controlled. Hybrid HVDC, a mixed topology containing both LCC and VSC, demonstrates the benefits of both topologies. In this paper, a hybrid HVDC control scheme with an LCC sending end and a VSC receiving end is proposed. It is used to control sending-end reactive power. Using the proposed secondary controller, hybrid HVDC — using only shunt devices, filters, or capacitor banks — can have the same reactive abilities as VSC HVDCs. This reduces the cost of connecting the voltage-weak grids and ensures that the voltage-weak grids are not afflicted by voltage stresses. The proposed secondary controller was verified to be effective through PSCAD/EMTDC simulations.

We discuss possible topologies of physically different metasurfaces with equivalent macroscopic electromagnetic responses. We specifically demonstrate that the presence of normal components (with respect to the metasurface plane) of the polarization currents does not add any functionality in engineering the reflection and transmission characteristics which cannot occur in metasurfaces maintaining only tangential currents. Therefore, if a certain property is achievable using general volumetric inclusions, polarizable along all three directions, the same response can be achieved using some equivalent perfectly planar elements, polarizable only in the metasurface plane. Our results clarify what physical properties are necessary for realizing desired metasurface responses and promote flat microwave and optical designs, providing possibilities for dramatic complexity reduction of metasurfaces for rather general field transformations, including asymmetric reflection and transmission.

In this study we categorize metasurfaces with respect to the direction of their polarization currents i.e., either tangential or normal to the metasurface plane. We theoretically investigate whether or not normal polarization currents can add extra degrees of freedom in engineering the reflection and transmission characteristics of functional metasurfaces. We then present a general formalism in which two different metasurface design scenarios with distinct polarization directions perform equally in engineering desired reflection and/or transmission properties. The result of our study provides a valuable tool to choose the most convenient approach in the design of functional metasurfaces.

In this presentation we explain how reflectarrays can be made “perfect”, in the sense that no power is scattered into unwanted directions. In particular, we present examples of impenetrable metasurfaces for anomalous reflection and beam splitting. We show that passive perfectly performing anomalous reflectors must be non-local and that this property can be realized by proper engineering the reactive impedance of the metasurface.

An indirect impedance measurement approach that does not require direct cable attachment or large space using a two-port network is presented. Using a straight wire monopole as an interrogating antenna and measured impedances of three calibration standards, the input impedance of a small spherical helix dipole over a ground plane is retrieved. It is found that accurate result is obtained around the dipole resonance frequency. The accuracy and sources of error are discussed.