Shimul Chandra Saha

A terahertz polarization insensitive dual band metamaterial absorber

Metamaterial absorbers have attracted considerable attention for applications in the terahertz range. In this Letter, we report the design, fabrication, and characterization of a terahertz dual band metamaterial absorber that shows two distinct absorption peaks with high absorption. By manipulating the periodic patterned structures as well as the dielectric layer thickness of the metal-dielectric-metal structure, significantly high absorption can be obtained at specific resonance frequencies. Finite-difference time-domain modeling is used to design the structure of the absorber. The fabricated devices have been characterized using a Fourier transform IR spectrometer. The experimental results show two distinct absorption peaks at 2.7 and 5.2 THz, which are in good agreement with the simulation. The absorption magnitudes at 2.7 and 5.2 THz are 0.68 and 0.74, respectively.

Polarization insensitive, broadband terahertz metamaterial absorber

We present the simulation, implementation, and measurement of a polarization insensitive broadband resonant terahertz metamaterial absorber. By stacking metal-insulator layers with differing structural dimensions, three closely positioned resonant peaks are merged into one broadband absorption spectrum. Greater than 60% absorption is obtained across a frequency range of 1.86 THz where the central resonance frequency is 5 THz. The FWHM of the device is 48%, which is two and half times greater than the FWHM of a single layer structure. Such metamaterials are promising candidates as absorbing elements for bolometric terahertz imaging.

Polarization insensitive terahertz metamaterial absorber

We present the simulation, implementation, and measurement of a polarization insensitive resonant metamaterial absorber in the terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us to maximize absorption by varying the dielectric material and thickness and, hence, the effective electrical permittivity and magnetic permeability. Experimental absorption of 77% and 65% at 2.12 THz (in the operating frequency range of terahertz quantum cascade lasers) is observed for a spacer of polyimide or silicon dioxide respectively. These metamaterials are promising candidates as absorbing elements for thermally based terahertz imaging.

Low-Loss Terahertz Artificial Dielectric Birefringent Quarter-Wave Plates

We have developed anisotropically etched low-loss artificial dielectric birefringent quarter-wave plates (QWPs) for use at 1.5 and 2.8 THz. The grating period for both QWPs is 20 ¿m. We etched 46- and 30- ¿m-deep gratings to obtain a ¿/2 phase retardance between transverse-magnetic and transverse-electric polarization propagating through the QWPs at 1.5 and 2.8 THz, respectively. A SU8 antireflection coating is used to further improve the transmission coefficient by up to 21%. The measured results from Fourier transform infrared spectroscopy show a good agreement with designed specifications.

Imprinted terahertz artificial dielectric quarter wave plates

We have developed low-loss polymer artificial dielectric quarter wave plates (QWP) operating at 2.6, 3.2 and 3.8 THz. The QWPs are imprinted on high density polyethylene (HDPE) using silicon masters. The grating period for the quarter wave plates is 60 microm. 330 microm, 280 microm and 230 microm deep gratings are used to obtain a pi/2 phase retardance between TE and TM polarization propagating through the QWPs. High frequency structure simulator (HFSS) was used to optimize the grating depth. Since the required grating depth is high, two plates, fixed in a back-to-back configuration were used for each QWP. A maximum aspect ratio (grating height/grating width) of 6.6 was used.

Terahertz Frequency-Domain Spectroscopy Method for Vector Characterization of Liquid Using an Artificial Dielectric

A device for performing vector transmission spectroscopy on aqueous and polar solvent specimens at terahertz frequencies is presented. The device works on the principle of artificial dielectric birefringence by making a microfluidic grating in silicon. The device enables the direct measurement of the complex dielectric function of a liquid, across a wide terahertz band using a Fourier transform infrared spectrometer. Characterization data from a range of liquid specimens, including alcohol, acetone, hydrogen peroxide and whiskies are presented. Using microfluidic sampling, specimen handling is straightforward and direct measurements on strongly terahertz absorbing solvents are possible. The method is scalable to longer or shorter wavelengths.

Modeling of Spring Constant and Pull-down Voltage of Non uniform RF MEMS Cantilever

In this paper, we are going to present a model of spring constant and pull down voltage for non uniform RF MEMS cantilever. In order to reduce the pull down voltage, it is usual to use a beam, which is narrower close to anchor and wider at the end or electrode area for a cantilever. Compare to uniform beam, this beam have lower spring constant which reduce the pull down voltage. A comprehensive model for spring constant and pull down voltage of the nonuniform cantilever is developed through basic force deflection mechanism of the suspended beam

Terahertz dual-band resonator on silicon

We have designed and fabricated a dual-band resonator in the terahertz frequency range on high-resistivity silicon. The device is designed to show resonances at 2.6 and 4.3 THz using the finite-difference time-domain modeling method. The characteristics of the fabricated device have been examined by using a Fourier-transform IR spectrometer. Measured results are in excellent agreement with the simulated data, showing two polarization-independent resonant peaks observed at 2.60 and 4.37 THz, respectively. The first resonance has a bandwidth of 0.56 THz, while the second one has a bandwidth of 0.70 THz. These dual-band resonant devices can be used for various applications such as dual-band spectral imaging and multiband biosensors.

Application of terahertz spectroscopy to the characterization of biological samples using birefringence silicon grating.

We present a device and method for performing vector transmission spectroscopy on biological specimens at terahertz (THz) frequencies. The device consists of artificial dielectric birefringence obtained from silicon microfluidic grating structures. The device can measure the complex dielectric function of a liquid, across a wide THz band of 2 to 5.5 THz, using a Fourier transform infrared spectrometer. Measurement data from a range of liquid specimens, including sucrose, salmon deoxyribonucleic acid (DNA), herring DNA, and bovine serum albumin protein solution in water are presented. The specimen handling is simple, using a microfluidic channel. The transmission through the device is improved significantly and thus the measurement accuracy and bandwidth are increased.

TUNABLE BAND-PASS FILTER USING RF MEMS CAPACITANCE AND TRANSMISSION LINE

In this paper we present the design and fabrication of an RF MEMS tunable band-pass fllter. The band-pass fllter design uses both distributed transmission lines and RF MEMS capacitances together to replace the lumped elements. The use of RF MEMS variable capacitances gives the ∞exibility of tuning both the centre frequency and the band-width of the band-pass fllter. A prototype of the tunable band-pass fllter is realized using parallel plate capacitances. The variable shunt and series capacitances are formed by a combination of parallel plate RF MEMS shunt bridges and series cantilevers. The fllter operates at C-X band. The measurement results agree well with the simulation results.