Nophadon Wiwatcharagoses

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 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.

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.

Metamaterial-Inspired Sensor on Porous Substrate for Detection of Volatile Organic Compounds in Air

In this paper, a compact multi-use volatile molecular sensor with high sensitivity is demonstrated. The sensor design is based on a planar metamaterial-inspired modified split ring resonator with open gap (OmSRR) forming an effective inductive-capacitive (LC) resonant tank having high quality (Q) factor with operating frequency near 7.4 GHz. Between two ring structure a capacitive gap is designed to achieve high electricfield intensity. A small change in the effective dielectric properties of the substrate in this region leads to a large shift in resonant frequency. To further enhance the sensitivity, capillary condensation in the pores of the substrate is utilized to localize the material in the high field region. Different molecular densities and specificity of vaporized liquids are determined by examining change in resonant frequency, Q-factor of the reflection coefficient, and by measuring the desorption rate of compounds from the resonant structure. The proposed sensor is compact and is compatible with wireless sensing.

Capillary Condensation Based Wireless Volatile Molecular Sensor

In this paper, a LC (inductor capacitor) wireless gas sensor is demonstrated for the identification of volatile organic compounds (VOCs) in the air environment. A near-field LC resonant tank consisting of an interdigitated capacitor fabricated on a porous flexible substrate coupled with an inductor coil is used as a sensor and its resonance is interrogated using an external pick up coil. The porous substrate enables capillary condensation of volatiles leading to a change in effective dielectric constant of the substrate which in turn shifts the resonance frequency. The designed sensor has multiple reuse capability and is applicable for continuous monitoring of volatiles such as methanol, iso-propyl alcohol, acetone and n-octane. The proposed sensor can wirelessly detect a 0.15 cc volume of volatiles in air making it highly sensitive. These sensors can be integrated with passive RFIDs in an array format for simultaneous detection of multiple volatile gases similar to an electronic nose. It can also be integrated with food packages to detect volatiles from food along the supply chain for quality control applications.

Metamaterial-inspired miniaturized microwave edge coupled surface scanning probe

This paper introduces a new concept on sub-wavelength resolution imaging and surface scanning using metamaterial based near field sensor array. Multiple split ring resonator structures (SRRs), having different band stop frequencies, are implemented in a microstrip transmission line configuration. A mirror image copy of these resonators is also incorporated on the transmission line to achieve built in frequency references. A smart card is scanned to detect buried antenna and Si chip within the plastic card.

Miniaturization of microstrip band stop filter using a novel periodic structure

This paper presents a new compact bandstop filter designed using a novel periodic structure. The proposed periodic resonant structure is based upon a split ring resonator (SRR) design, and it shows the characteristics of a bandstop LC resonator. The designed bandstop filter has the desired characteristics such as wide bandwidth, sharp and deep skirt performance and small physical size. Details of the proposed structure and its application in the design of a filter are presented here.