Electrically thin flat lenses and reflectors.

We introduce electrically thin dielectric lenses and reflectors that focus a plane wave based on the principles of phase compensation and constructive wave interference. Phase compensation is achieved by arranging thin rectangular slabs having different dielectric permittivity according to a permittivity profile obtained through analytic design equations. All incident rays parallel to the optical axis converge to a focal point with equalized optical paths resulting in constructive interference. Plane wave simulations indicate strong focusing, even in the presence of impedance mismatch between free space and the dielectric layers composing the lens. We demonstrate focusing at 9.45 GHz using a lens fabricated with commercially available dielectric materials. In addition to focusing, the flat lens proposed here demonstrates relatively high power gain at the focal point. We also present a flat reflector based on the same concept. We believe that the proposed dielectric lens and reflector are strong candidates to replace heavy metallic dishes and reflectors used in a variety of applications, especially satellites.

Dielectric sensors based on electromagnetic energy tunneling.

We show that metallic wires embedded in narrow waveguide bends and channels demonstrate resonance behavior at specific frequencies. The electromagnetic energy at these resonances tunnels through the narrow waveguide channels with almost no propagation losses. Under the tunneling behavior, high-intensity electromagnetic fields are produced in the vicinity of the metallic wires. These intense field resonances can be exploited to build highly sensitive dielectric sensors. The sensor operation is explained with the help of full-wave simulations. A practical setup consisting of a 3D waveguide bend is presented to experimentally observe the tunneling phenomenon. The tunneling frequency is predicted by determining the input impedance minima through a variational formula based on the Green function of a probe-excited parallel plate waveguide.

Anti-reflecting metasurface for broadband polarization independent absorption at Ku band frequencies.

An impedance matched metasurface can efficiently channel the electromagnetic fields for maximum power transfer. The thin film based impedance matching techniques often utilize highly dissipative materials and destructive interference of reflection components from multiple subwavelength layers. Here, we propose a novel method to achieve anti reflection characteristics through destructive interference of antiparallel electromagnetic scattering emerging from chiral metasurface. The supercell structure of metasurface consists of four adjacent multi split-rings on FR-4 substrate. The split-rings are arranged to induce anti-parallel surface currents leading to destructive interference for scattered fields. The antireflection characteristics results in near perfect broadband absorption at dual frequency bands. A broadband absorption of 983 MHz is achieved between 12.687 and 13.669 GHz. Similarly, a narrow band absorption of 108 MHz is achieved in frequency range of 15.307-15.415 GHz. The impedance matched with unique symmetric design of supercell results in identical absorption for both x- and y-polarized incident fields. The numerical and experimental results verify broadband absorption characteristics at Ku band frequencies. The proposed metasurface absorber can be used for microwave energy harvesting applications.

An infrared energy harvester based on radar cross-section reduction of chiral metasurfaces through phase cancellation approach.

Conventional metasurface absorbers rely on high dissipation losses by incorporating lossy materials. In this paper, we propose a novel mechanism of absorption based on phase cancellation of polarization states of scattered fields emerging from adjacent L-shaped chiral meta-atoms (unit cells). A linearly polarized wave forms helicoidal currents in each meta-atom leading to diagonally polarized radiated waves. When phase cancellation is employed by reorienting four such meta-atoms in a supercell configuration, contra-directed chiral currents flow in adjacent cells to cancel all the radiated fields in far-field region leading to a minimal broadside radar cross-section. From the reciprocity, the currents that are induced in the meta-atoms produce a null towards the incident direction which can be utilized for infrared energy harvesting. Full wave electromagnetic simulation indicates near perfect resonant absorption around 52.2 THz frequency. Enhanced bandwidth is shown by adding smaller resonators inside the supercell in nested form leading to dual band absorption at 45.2 THz and 53.15 THz.

Wave discrimination at C-band frequencies in microstrip structures inspired by electromagnetically induced transparency.

We present the design and practical implementation of a microstrip diplexer based on the wave discrimination property associated with the electromagnetically induced transparency (EIT)-like effect. The EIT is a quantum interference phenomenon which happens between two atomic transition pathways and allows wave propagation within a medium's absorption spectrum. Here, we exploit an analogous interference mechanism in a three-port microstrip structure to demonstrate a diplexer based on the EIT-like effect in the microwave regime. Since the transparency is accompanied by a high transmission and strong dispersion characteristics, compact frequency discriminating structures that can resolve nearby frequencies with high isolation can be devised. Our proposed C-band diplexer consists of pairs of unequal open-circuit stubs, which resonate at detuned frequencies and interfere to form the EIT-like passbands for diplexer action. The design is highly compact and scalable in frequency for both PCB and on-chip applications. A prototype of diplexer is fabricated for the center frequencies of lower and upper passbands at 4.6 GHz and 5.5 GHz respectively. The transmission zeros are designed at the complementary channels so that the two passbands are highly isolated presenting the isolation of about 40 dB. The measured insertion loss of lower and upper passband is 0.59 dB and 0.61 dB respectively. Measured input return loss is better than - 15 dB, while the output return losses are well below - 12 dB. Moreover, a decent value of about 200 is achieved for the group refractive index around the EIT-like passbands, which reveals the slow wave characteristics of the proposed EIT-based diplexer.

Slow Wave Applications of Electromagnetically Induced Transparency in Microstrip Resonator.

We report a novel guided-wave resonator that supports multiple bands of electromagnetically induced transparency (EIT). The platform for the spatial and spectral interference is obtained by a microstrip transmission line loaded with proximity-coupled open-circuited stubs. We show experimentally that with two microstrip open stubs, a complete destructive interference takes place leading to a single EIT band with near-unity transmission efficiency. More interestingly, the addition of a third stub results in a supplementary EIT band with a Q-factor of 147 and an effective group refractive index of 530. With the open-stub configuration, the EIT phase response can be dynamically controlled by varying the capacitance between the adjacent stubs without breaking the transmission path of the underlying electromagnetic waves. Therefore, the proposed structure is well suited for buffering and tunable phase modulation applications. Since the proposed structures are compact and fully planar, we anticipate seamless integration with low-profile high frequency electronics.

Author Correction: Slow Wave Applications of Electromagnetically Induced Transparency in Microstrip Resonator.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Quasi-Crystal Metasurface for Simultaneous Half- and Quarter-Wave Plate Operation.

We present a quasi-crystal metasurface that can simultaneously work as efficient cross-polarizer and circular polarizer for wide range of frequencies. The quasi-crystal technique benefits from individual resonant response of anisotropic patch and the coupled response due to periodic perturbations in the square lattice. It is shown that quasi-crystals offer broadband response for cross-polarization as well as high efficiency circular-polarization conversion of reflected fields. The quasi-crystal metasurface achieves cross-polarization (above -3 dB) for two broad frequency bands between 10.28-15.50 GHz and 16.21-18.80 GHz. Furthermore, the proposed metasurface can simultaneously work as high efficiency circular-polarizer from 10.15-10.27 GHz and 15.51-16.20 GHz. The metasurface design is also optimized to suppress co-polarization below -10 dB between 10.5-15.5 GHz. This metasurface can find potential applications in reflector antennas, imaging microscopy, remote sensing, and control of radar cross-section etc.

Non-Seminomatous Germ Cell Tumor Presenting with Superior Vena Cava Syndrome.

BACKGROUND Primary mediastinal non-seminomatous germ cell tumors (NSGCTs) are aggressive and carry a poor five-year disease free survival rate even with aggressive treatment. We describe a young adult male with primary mediastinal NSGCT presenting with airway obstruction and superior vena cava syndrome (SVCS). CASE REPORT The patient presented with four weeks of nonproductive cough, weight loss, and right-sided pleuritic chest pain. Chest computed topography (CT) imaging demonstrated a right-sided mediastinal mass determined as a yolk sac tumor on biopsy. The patient underwent induction chemotherapy with etoposide and cisplatin for stage III NSGCT. In the interim, he developed SVCS warranting a second cycle of chemotherapy along with intravenous steroids, with notable improvement in symptoms. However, serial alpha-fetoprotein (AFP) measurements showed progressively increasing levels up to a maximum of 18,781 ng/mL indicating treatment failure. He is currently on salvage chemotherapy. CONCLUSIONS Obstruction of the SVC by external compression is often a manifestation of a malignant process in the thorax. SVCS is a medical emergency and occurs in 6% of patients with mediastinal GCTs. Historically, irradiation was initiated without a histologic diagnosis to relieve the life-threatening obstruction. However, newer data suggest that it is acceptable to defer therapy until a full diagnostic workup is completed. This case highlights the malignant nature of primary mediastinal NSGCTs. In addition, inasmuch as SVCS is dramatic in presentation, it is important to recognize that symptomatic obstruction often develops over weeks or longer. In a hemodynamically stable patient, an accurate histologic diagnosis prior to starting treatment is essential in guiding therapy.

A Non-Invasive Phase Sensor for Permittivity and Moisture Estimation Based on Anomalous Dispersion.

The traditional microwave resonance sensors are based on the measurement of the frequency shift and bandwidth of a resonator's amplitude spectrum. Here we propose a novel sensing scheme in which the material properties are estimated by determining the changes in the phase spectrum of an anomalous-phase resonator. In the proposed phase sensing, we exploit the unique double phase reversal which takes place on the edges of the anomalous dispersion region as a signature to detect the resonance. We show that with the phase sensing, a significant reduction in detection errors compared to the traditional sensing can be obtained because of the noise immunity offered by the phase detection and also due to the strong dispersive phase response that reduces the sensor's dependence on the external environment. We also show that the bandwidth determination procedure of the resonance which is needed to characterize the sample losses is significantly simplified. The concept of phase sensing is shown by devising an experimental microstrip open stub resonator whose frequency response lies in the anomalous dispersion region. The dielectric characteristics of the samples placed on the stub are extracted from the resonant frequency and the slope of the phase response. We also demonstrate that the changes in moisture levels can also be detected by utilizing the phase sensing method.

C20209T prothrombin gene mutation associated deep venous thrombosis in a hemodialysis patient.

Venous thromboembolism (VTE) represents the formation of a blood clot in one of the deep veins of human body. The significant morbidity and mortality rates associated with VTE have spurred increasing investigations seeking to identify causative factors for this complex condition. While the most frequent causes of an inherited hypercoagulable state are the Factor V Leiden mutation and the prothrombin gene mutation, polymerase chain reaction (PCR) analysis has helped to identify other rare causes of inherited VTE. We report a case of a recurrent deep venous thrombosis in an end-stage renal disease patient. All laboratory tests for hypercoagulable states were normal. However, PCR analysis detected a rare polymorphism of prothrombin gene mutation at position C20209T, instead of G20210A. The patient was treated successfully with a high dose of warfarin to maintain adequate anti-coagulation during the 2-year follow-up.