Prem Chahal

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.

A Tunable Dual-Band Miniaturized Monopole Antenna for Compact Wireless Devices

A technique for producing miniaturized tunable planar monopole antennas for wireless communication applications is introduced. Miniaturization is achieved by optimizing the geometry of a pixelated metallic patch surrounding the monopole antenna. Tuning of the antenna is implemented by varying the capacitance of a varactor diode loaded between the pixelated metallic patch and the ground plane. The result is an ultra-compact, dual band, folded monopole antenna that fits into a hemisphere of radius λ0/20 at 2.1 GHz. Varying the capacitance of the varactor diode enables the two resonance frequencies to be tuned simultaneously, covering multiple frequency bands for different wireless applications. A prototype antenna has been fabricated and measured, confirming the feasibility of the proposed design.

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.

Large-area low-cost substrate compatible CNT Schottky diode for THz detection

In this paper, a novel process is developed for the fabrication of CNT Schottky diodes that is simple to implement and large area compatible. The process utilizes an undercut and self-alignment approach for the fabrication of devices having short lengths (< 1 um). Furthermore, many CNTs assembled in parallel are utilized in the fabrication of devices to attain good impedance matching. Details of THz detector NEP calculation, fabrication and test of diode devices after integration on a plastic substrate are presented. Measured I-V characteristics and sensitivity at 18 GHz demonstrate that high quality devices can be fabricated using the proposed approach. Preliminary results show that the device can attain NEP values in the range of 50–150pW/Hz05 over a frequency range of 10 GHz–1THz, respectively.

Design and test of wide-band terahertz dielectric sub-wavelength focusing probes

This manuscript presents two new wide-band terahertz (THz) dielectric sub-wavelength focusing probes for near-field measurements. The first design is characterized by being axially symmetric (conical) while the second is a rectangular based design (pyramidal). The axially symmetric design is specialized for doing spectroscopy and imaging due to its wideband and sub-wavelength focusing resolution. The rectangular design is characterized by its ability to preserve polarization. It will find applications in probing of terahertz planar devices and in polarization sensing and imaging. The probes have a wide bandwidth scanning approximately 0.1–1 THz. The probes were fabricated from low-loss high-density polyethylene. The axially symmetric probe has a sub-wavelength focusing resolution ranging from one fifth of a wavelength up to half a wavelength in a frequency band of about 150 GHz. In this paper, the design and properties of these two probes are presented. Applications of these probes are demonstrated by sub-wavelength near-field imaging, spectroscopy and probing of planar circuits.

Design study of electronically steerable half-width microstrip leaky wave antennas

A half-width microstrip leaky-wave antenna (HMLWA) having electronic beam steering capabilities is presented. Electronic beam scanning is demonstrated in X-, Ku- and Ka-bands through detailed design analysis and measurements. Two physical design approaches are studied; one requiring multi-layer processing and another requiring only a single layer metallization. In this paper, only the single layer design was implemented. Varactor diodes are edge coupled to the antenna element to achieve beam scanning as a function of the applied voltage at a fixed frequency. Beam scanning of 45-degrees for an 8 GHz design and 30-degrees for a 16 GHz antenna design are demonstrated. Details of design, fabrication and measurements are presented.

Terahertz packaging: Study of substrates for novel component designs

This paper will examine a new side to packaging: Terahertz (THz) Packaging. The goal of this paper is three fold: 1) characterizing dielectric materials for THz packaging applications; 2) Using these materials in the fabrication of THz passives (integrated and quasi-optical); and 3) Demonstrating non-destructive evaluation of packages using THz. In this manuscript, detailed characteristics of dielectric packaging materials in the THz spectral region are presented along with the theory used for the characterization procedure. THz non destructive evaluation (NDE) of electronics packages is observed in the form of delamination thickness detection and moisture content studies. Using the materials characterized, a planar THz power splitter and a quasi-optical THz bandstop interference filter are demonstrated. Furthermore, the power splitter is used as a THz microfluidic sensor.

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.

A NOVEL SUBWAVELENGTH MICROBOLOMETER FOR TERAHERTZ SENSING

A subwavelength aperture-microbolometer sensor was simulated using a finite-difference time domain (FDTD) numerical method. The system consisted of a focusing bullseye grating with a central subwavelength aperture. A thin vanadium oxide sensing layer was suspended behind the aperture for sensing purposes, backed by a thin layer of silicon dioxide. The maximum electric field across the vanadium oxide was measured as a function of incident field. Total noise equivalent power (NEP) was estimated to be 180 pW/√Hz at a frequency of 0.665 THz, comparable to similar current micro sensors. The formation of surface plasmonics greatly increases its sensitivity to particular incident wavelengths. This fact, along with its compact size, make this system a promising candidate for numerous low-cost, small-scale terahertz sensing applications.

Plastic injection micromolding of THz circuits and microfluidic sensors

In this paper, THz circuits and sensors are designed and experimentally implemented using a cost effective plastic injection micromolding process. Plastic resin, having low refractive index and loss in THz region, was used as the base material to manufacture THz circuits. Periodic structures such as photonic bandgap (PBG) were utilized to design THz circuits and sensors. Numerical simulations were performed using the finite element method (FEM). Design, fabrication and characterization were carried out for THz circuits operating at a center frequency of 0.25 THz. The fabricated circuits were combined with microfluidics to demonstrate sensor applications. This proposed fabrication method is useful in low cost fabrication and massive production of THz circuits and sensors.