Hyeok-Woo Son

A Novel Epsilon Near Zero Tunneling Circuit Using Double-Ridge Rectangular Waveguide

In this paper, an epsilon near zero (ENZ) tunneling circuit using a double-ridge rectangular waveguide (RWG) is proposed for the miniaturization of a waveguide component. The proposed ENZ channel and is located in the middle of the input-output RWG (IORWG). The ratio of the height to the width of the channel waveguide is very small compared to the IORWG. By properly adjusting the ridge dimensions, the tunneling frequency of the proposed ENZ channel can be lowered to near the cut-off frequency of the IORWG. For the proposed ENZ tunneling circuit, the approach adopted for extracting the effective permittivity, effective permeability, normalized effective wave impedance, and propagation constant from the simulated scattering parameters was explained. The extracted parameters verified that the proposed channel is an ENZ channel and electromagnetic energy is tunneling through the channel. Simulation and measurement results of the fabricated ENZ channel structure agreed.

Theoretical and Experimental Investigation on the Probe Design of a Ridge-loaded Slot Type for Near-Field Scanning Microwave Microscope

In this paper, a rectangular waveguide probe with a ridge-loaded straight slot (RLSS) is presented for a near-field scanning microwave microscope (NSMM). The RLSS is located laterally at the end wall of the cavity and is loaded on double ridges in a narrow straight slot to improve the spatial resolution compared with a straight slot. The probe consists of a rectangular cavity with an RLSS and a feed section of a WR-90 rectangular waveguide. When the proposed NSMM is located at distance of 0.1mm in front of a substrate without patches or strips, the simulated full width at half maximum (FWHM) of the probe improve by approximately 31.5 % compared with that of a straight slot without ridges. One dimensional scanning of the E-plane on a sample under test was conducted, and the reflection coefficient of the near-field scanning probe is presented.

Microwave imaging probe using Bowtie type of optical antenna structure

When a uniform plane electromagnetic wave is incident upon the small circular aperture in an infinite conducting plane, the transmitted power t P through the aperture is very small. More specifically, the transmission cross section(TCS) T of the aperture whose diameter D is much smaller than the wavelength λ is proportional to (D/λ)4 · D2 according to the Bethes theory. Here the TCS T is defined so that the transmitted power P t through the aperture may be given by the multiplication of the incident power density P inc [W/m2] and T [m2], i.e., P t = P inc T.

Two types of near-field microwave imaging probes

We consider two types of near-field microwave imaging probes. One employs the small circular ridged aperture and the other employs unsymmetrical transmission cavity whose closed ends comprise the small circular aperture with no ridge and capacitive iris of double ridge type which is placed half waveguide wavelength apart from the circular aperture. The relationship between working principles of the two types of probes is discussed in both transmission efficiency through a small aperture and spatial confinement of the electromagnetic energy.

Application of transmission-resonant aperture to the waveguide limiter design

H-shaped small resonant aperture is applied to the design of the combined structure of the band-pass filter and the limiter by incorporating PIN diode into the resonant aperture structure. Single stage and double stage limiters are designed and experimented and the utility of the proposed types is confirmed.

Electrostatic field of the semi-infinite electric dipole layer as (a) dual analogy to the Ampere`s law (b) capacitor`s fringing field

The similarity, analogy and equivalence between the phenomenon due to electric and magnetic dipoles have been discussed in the open literature for different situations. Here we are presenting the numerical proof of the trajectory of leakage electric field due to a semi-infinite electric dipole layer in the external periphery and the electric field in the space between oppositely charged surfaces. The result is also valid for the fringing electric field of a parallel plate capacitor. The result is also proved to be a dual of Ampre`s law in the electrostatics due to a semi-infinite electric dipole layer.

B 1 + Homogenizaion over Whole Field of View in High Field MRI

In high static field magnetic resonance imaging(MRI) systems, fields of 7 T and 9.4 T, the impressed RF field shows larger inhomogeneity than in clinical MRI systems with B0 fields of 1.5 T and 3.0 T. In multi-channel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the non-uniformity of the impressed RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected ROI(Region of Interest). To demonstrate the technique, the multichannel transmission line coil was modeled together with a human head phantom at 400 MHz for the 9.4 T MRI system and fields are obtained. In this paper, all the optimized in each isolated ROIs are combined to achieve significantly improved homogeneity over the entire field of view. The simulation results for 9.4 T MRI systems are discussed in detail.