Kyoung Youl Park

Microwave artificially structured periodic media microfluidic sensor

In this paper, microstrip-based spiral structured artificial magnetic media (metamaterial) coupled with microfluidic channel is experimentally demonstrated for sensing applications. It is found that the resonant frequency and the amplitude changes due to dielectric loading from the introduction of chemical substances in the microfluidic channels. Different concentrations of water — methanol and water — isopropanol samples are used in the characterization of the sensor. For water — methanol mixtures, the resonant frequency shifts from 2.15 GHz to 2.0 GHz with change in dielectric constant from 25 to 75. Results show that the wave propagation in LH-media can be used for interrogation of minute volumes of samples with high sensitivity.

Wafer-level integration of micro-lens for THz focal plane array application

Design and fabrication of dielectric lenses for terahertz (THz) focal plane arrays are presented in this paper. Lenses are designed using optical lens and ellipsoid function theory in the terahertz range (centered at f = 300GHz). In order to enhance coupling to planar circuits on wafer, two types of lenses are considered: modified hemispherical, such as extended hemispherical and hypo-hemispherical. Full wave analysis of the lens design is carried out both in near- and far-field regimes. The lenses are fabricated using a 3D plastic printer. An approach to use the 3D printed structure as a mold to fabricate micro-injection molded lenses is also introduced. Measured results on 3D printed lens array show high transmission characteristics and measured results correlate closely with simulation results.

Metamaterial-inspired absorbers for Terahertz packaging applications

In this paper, thin metamaterial-inspired structures are investigated for wide-band absorption of stray signals for THz packages. The absorber itself consists of a low-index, low-loss dielectric sandwiched between a patterned, two-dimensionally periodic, thin metallic layer, and a metal backing. Numerical simulations were performed using both the finite element (FEM) and finite-difference time domain (FDTD) numerical methods. Design, fabrication and tests were carried out for absorbers having center frequencies of 0.2 THz and 0.4 THz. Ultra-wide bandwidth and strong absorption were obtained by taking advantage of skin-effect losses in metamaterial structures, and through multi-stacking of these structures. Absorbers having high absorption coefficients and bandwidth (> 1THz) can easily be fabricated using the approach demonstrated in this paper. Two measurement approaches are applied to characterize these structures, details of which are presented in this paper.

Metamaterial inspired periodic structure used for microfluidic sensing

A novel metamaterial inspired resonating structure coupled with a microfluidic channel has been evaluated for sensing applications in the microwave frequency range. The structure is based on an open split ring resonator (OSRR) design, was simulated in a finite element analysis tool (Ansys HFSS®) and tested using a Vector Network Analyzer to detect changes in resonant frequency, amplitude, and phase due to dielectric loading from different chemicals in the microfluidic channel. The sensor was tested as a single unit cell, in a three cell aperiodic array and as an array of three different frequencies. Different concentrations of water-isopropanol (IPA) and watermethanol were used to characterize the sensor. Additionally, a biosensor application was demonstrated in detecting glucose-d concentration in deionized water.

Metamaterial-inspired miniaturized microwave sensing probes

In this paper, two microstrip transmission line based metamaterial structures (sub-wavelength sized resonators) are designed and implemented in near field sensing of dielectric materials. One structure is designed for band-stop and the other for band-pass performance in the X-band region. These resonators load the microstrip lines on both the sides. Resonator on one side is used in interrogation of sample and the other side is used for reference. Upon introduction of sample, the resonance frequency shifts relative to the reference resonance frequency. This approach provides high sensitivity detection with built in reference providing high signal to noise ratio. Fabricated samples were characterized for sensing applications by loading with solid dielectric samples. An array of sensors can be linearly cascaded for high throughput sensing of multiple samples using single input output ports. Details of design, fabrication and measurements are presented in the paper for these two designs.

Surface plasmon-assisted terahertz imaging array

In this paper, a spoof surface plasmon assisted antenna is paired with a metamaterial enhanced bolometer structure in the formation of a THz focal plane array pixel. The antenna element focuses the electromagnetic wave onto the bolometer element and the bolometer detects this incident power through resistance change. Numerical analysis was performed in order to simulate the plasmonic structure at 0.1 and 0.3 THz. This system was then fabricated and detailed measurements were carried out. This system shows high sensitivity at the desired operating frequency. The performance of the spoof plasmon antenna is favorable when considering the same size of the aperture without exciting plasmonic modes.

3D printed metalized-polymer UWB high-gain Vivaldi antennas

This paper introduces a UWB high gain Vivaldi antenna fabricated with a polymer-based 3D printer. 3D printing technology allows for simple fabrication that is easier, faster, and lower cost compared to traditional microfabrication and metal fabrication techniques. Two 3D printed designs are presented, the first of which is a simple Vivaldi notch antenna with a radiating slotline cavity. The second design consists of a bilateral Vivaldi with a partially covered cavity, which increases the bandwidth and gain of the antenna. Both designs are printed with an acrylic-based polymer, blanket metalized with a thin copper layer, and fed with a 50 Ω coaxial feed. Both antennas show an extremely wide bandwidth of approximately 14 GHz from 4 to 18 GHz. In addition, the maximum gain of the antennas is approximately 12 dB. The measured results match well with the simulated results, showing the potential for these antennas as low cost, wideband, high gain alternatives which could be used in modern UWB communication systems.

Planar surface plasmonic structures for terahertz circuits and sensors

This paper presents planar metal patterned structures that support surface plasmon polaritons (SPPs) like propagation mode. Four unit cells, each having a solid ground plane, were designed that support SPPs. To optimize return loss, these structures were first simulated as infinitely periodic in two dimensions. These were then further optimized by designing waveguide structures. Using multi-band unit cell designs, THz circuits (transmission line and power splitter) were fabricated and tested. A new approach to probe these planar plasmonic devices is presented using wide band THz dielectric probes. Measured results of THz circuits match closely with simulation results. It is also shown through simulations that these structures can be used in the design of THz chemical and biological sensors.

A new metamaterial unit cell for compact microstrip circuit designs

In this paper, a new metamaterial (MTM) unit cell implemented in a microstrip transmission line configuration is proposed. The new MTM unit cell, based on split-ring resonators (SRRs) is electrically small. The unit cell avoids the use of vias, and requires only single level processing. By tuning the physical parameters of the resonator structures, strong magnetic coupling between microstrip line and rings emerges at the resonant frequency of SRRs. This impedes signal propagation in the proximity of the resonant frequency. A compact X-band power divider is designed to validate the practical use of the new unit cell. While maintaining similar performance, a 71% reduction in impedance transformer is achieved in comparison to a conventional design.

Reduced graphene oxide based Schottky diode on flex substrate for microwave circuit applications

This paper demonstrates fabrication and characterization of reduced graphene oxide (RGO) based Schottky diodes on a flexible substrate. Current-voltage measurements on the fabricated devices show strong non-linearity. Diodes are tested for high frequency applications such as detection, frequency multiplication and mixing over a frequency range of 1-18 GHz. The devices show third order frequency multiplication for measured fundamental frequencies of 1, 2, 3, and 4 GHz and shows low-loss frequency mixing. Details of DC characteristics, RF rectification, mixing and multiplication using RGO Schottky diodes are presented.