High Frequency Characterization of Carbon Nanotube Networks for Device Applications

This work includes the microwave characterization of carbon nanotubes (CNTs) to design new CNTs-based high frequency components. A novel developed method to extract the electrical properties over a broad microwave frequency band from 10 MHz to 50 GHz of carbon nanotubes (CNTs) in a powder form is performed. The measured scattering parameters (S-parameters) with a performance network analyzer are compared to the simulated one obtained from an in-house computed mode matching technique (MMT). An optimized first order gradient method iteratively changes the unknown complex permittivity parameters to map the simulated S-parameters with the measured one until convergence criteria are satisfied. The mode matching technique accurately describes waveguide discontinuities as both propagating and evanescent modes are considered allowing an error less than 5% on the extracted permittivity over a broad frequency range. The very large values obtained at low frequencies of carbon nanotubes permittivity are explained theoretically and experimentally based on the percolation theory. The powder composed of semiconducting and conducting CNTs illuminated by an electromagnetic field is seen as series of nano-resistance-capacitance which significantly increase the real and imaginary parts of the complex effective permittivity until the percolation threshold is reached. Based on experimental results different CNTs-based composites material are engineered to design novel microwave components for possible electromagnetic compatibility (EMC) applications. As the extraordinary properties of the carbon nanotubes exist along their axis, the second part of this work is oriented on the alignment and the deposition of carbon nanotubes using a dielectrophoresis (DEP) technique. Micro/nano-electrodes are fabricated using a lift-off process consisting of photo-lithography and electron-beam lithography techniques where the carbon nanotubes suspended in an aqueous solution are attracted in the gap between the electrodes by applying an AC bias voltage. After burning the conducting carbon nanotubes an observed photocurrent with aligned semiconducting CNTs is used to develop high frequency photo-device prototypes

Rigorous Characterization of Carbon Nanotube Complex Permittivity over a Broadband of RF Frequencies

This work presents a comprehensive characterization of the frequency dependence of the effective complex permittivity of bundled carbon nanotubes considering different densities over a broadband of frequencies from 10 MHz to 50 GHz using only one measurement setup. The extraction technique is based on rigorous modeling of coaxial and circular discontinuities using mode matching technique in conjunction with inverse optimization method to map the simulated scattering parameters to those measured by vector network analyzer. The dramatic values of complex permittivity obtained at low frequencies are physically explained by the percolation theory. The effective permittivity of a mixture of nano-particles of alumina and carbon nanotubes versus frequency and packing density is studied to verify the previously obtained phenomenon

Engineered Carbon-Nanotubes Based Composite Material for RF Applications

Electrical properties of nano-composite materials are extracted to investigate the possibility to engineer novel material for microwave applications. A measurement setup is developed to characterize material in a powder form. The developed measurement technique is applied on nano-particles of alumina, carbon nanotubes (CNTs), and composite mixture of carbon nanotubes and alumina. The effect of packing density on dielectric constant and loss tangent is thoroughly characterized experimentally. The obtained results show that the real part of effective permittivity may be considerably enhanced by increasing the percentage of conducting nano-particles. In addition, it is possible to decrease the loss in a material by mixing low-loss dielectric nano-particles powder in a lossy material

340 Ghz Multipixel Transceiver

A multi-pixel terahertz transceiver is constructed using a stack of semiconductor layers that communicate using vias defined within the semiconductor layers. By using a stack of semiconductor layers, the various electrical functions of each layer can be tested easily without having to assemble the entire transceiver. In addition, the design allows the production of a transceiver having pixels set 10 mm apart

Compact duplexing for a 680-GHz radar using a waveguide orthomode transducer

A compact 680-GHz waveguide orthomode transducer (OMT) and circular horn combination has been designed, tested, and characterized in a radar transceiver's duplexer. The duplexing capability is implemented by a hybrid waveguide quasi optical solution, combining a linear polarization OMT and an external grating polarizer. Isolation between the OMT's orthogonal ports' flanges was measured with a vector network analyzer to exceed 33 dB over a >10% bandwidth between 630 and 710 GHz. Calibrated Y-factor measurements using a mixer attached to the OMT ports reveal losses through the transmit and receive paths that sum to an average of 4.7 dB of two-way loss over 660-690 GHz. This is consistent with radar sensitivity measurements comparing the new OMT/horn with a quasi-optical wire grid beam splitter. Moreover, the radar performance assessment validates the OMT as a suitable compact substitute of the wire grid for the JPL's short-range 680-GHz imaging radar

Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of the electron density for an individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closest neighbours reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%

Micromachined Waveguide Integrated RF MEMS Phase Sifter Operating between 500-600 GHz

This paper presents a 500-600 GHz submillimeter- wave MEMS-reconfigurable phase shifter. It is the first ever RF MEMS component reported to be operating above 220 GHz. The phase shifter is based on a micromachined rectangular waveguide which is loaded by 9 E-plane stubs, which can be individually blocked by using MEMS–reconfigurable surfaces. The phase-shifter is composed of three metallized silicon chips which are assembled in H-plane cuts of the waveguide.QC 20160418</p