174 research outputs found
Repulsive Casimir forces between solid materials with high refractive index intervening liquids
In order to explore repulsive Casimir/van der Waals forces between solid
materials with liquid as the intervening medium, we analyze dielectric data for
a wide range of materials as for example PTFE, polystyrene, silica and more
than twenty liquids. Although significant variation in the dielectric data from
different sources exist, we provide a scheme based on measured static
dielectric constants, refractive indices, and applying Kramers Kronig (KK)
consistency to dielectric data to create accurate dielectric functions at
imaginary frequencies. The latter is necessary for more accurate force
calculations via the Lifshitz theory allowing reliable predictions of repulsive
Casimir forces.Comment: 20 pages, 7 figures, 1 tabl
Electrical and radiation characteristics of semilarge photoconductive terahertz emitters
We present experimental characterization of semilarge
photoconductive emitters, including their electrical/photoconductive
parameters and terahertz spectra. A range of emitters
were studied and fabricated on both LT-GaAs and SI-GaAs,
having a variety of electrode geometries. The spatial cone of terahertz
radiation was defined. The dependencies of the photocurrent
and the terahertz power on the bias voltage and the laser power
were determined. A Fourier-transform interferometer is used to
determine the terahertz spectra and to clarify the effects of the
substrate and electrode geometry
Determination of renewable energy yield from mixed waste material from the use of novel image analysis methods
Two novel techniques are presented in this study which together aim to provide a system able to determine the renewable energy potential of mixed waste materials. An image analysis tool was applied to two waste samples prepared using known quantities of source-segregated recyclable materials. The technique was used to determine the composition of the wastes, where through the use of waste component properties the biogenic content of the samples was calculated. The percentage renewable energy determined by image analysis for each sample was accurate to within 5% of the actual values calculated. Microwave-based multiple-point imaging (AutoHarvest) was used to demonstrate the ability of such a technique to determine the moisture content of mixed samples. This proof-of-concept experiment was shown to produce moisture measurement accurate to within 10%. Overall, the image analysis tool was able to determine the renewable energy potential of the mixed samples, and the AutoHarvest should enable the net calorific value calculations through the provision of moisture content measurements. The proposed system is suitable for combustion facilities, and enables the operator to understand the renewable energy potential of the waste prior to combustion
Dielectric constants of bulk ferroelectric PZTmeasured by terahertz time-domain spectroscopy
The complex permittivity of bulk ceramic ferroelectric of nominal composition PbZr0.4Ti0.6O3 was measured in the range 0.2–2 THz using transmission time-domain spectroscopy. The results indicate strong absorption and dispersion in this frequency range as often seen in highly disordered and polar materials. The results are compared to equivalent thin film data in the literature, and significant differences in the real and imaginary permittivity suggest that substrate clamping and degree of polarisation of the ferroelectric thin film materials affect dielectric properties even at these high frequencies
Metrology State-of-the-Art and Challenges in Broadband Phase-Sensitive Terahertz Measurements
The two main modalities for making broadband phase-sensitive measurements at terahertz (THz) frequencies are vector network analyzers (VNA) and time-domain spectrometers (TDS). These measuring instruments have separate and fundamentally different operating principles and methodologies, and they serve very different application spaces. The different architectures give rise to different measurement challenges and metrological solutions. This article reviews these two measurement techniques and discusses the different issues involved in making measurements using these systems. Calibration, verification, and measurement traceability issues are reviewed, along with other major challenges facing these instrument architectures in the years to come. The differences in, and similarities between, the two measurement methods are discussed and analyzed. Finally, the operating principles of electro-optic sampling (EOS) are briefly discussed. This technique has some similarities to TDS and shares application space with the VNA
Spectrally-efficient high-speed wireless bridge operating at 250 GHz
A photonic wireless bridge operating at 250 GHz is presented. Using a pilot tone-assisted phase noise compensation technique, a data rate of 40 Gbit/s is achieved using 16-quadrature amplitude modulation. Furthermore, the wireless bridge is also demonstrated in a wavelength division multiplexing scenario
Building an end user focused THz based ultra high bandwidth wireless access network: The TERAPOD approach
The TERAPOD project aims to investigate and demonstrate the feasibility of ultra high bandwidth wireless access networks operating in the Terahertz (THz) band. The proposed TERAPOD THz communication system will be developed, driven by end user usage scenario requirements and will be demonstrated within a first adopter operational setting of a Data Centre. In this article, we define the full communications stack approach that will be taken in TERAPOD, highlighting the specific challenges and aimed innovations that are targeted
Analysis of Granular Packing Structure by Scattering of THz Radiation
Scattering methods are widespread used to characterize the structure and
constituents of matter on small length scales. This motivates this introductory
text on identifying prospective approaches to scattering-based methods for
granular media. A survey to light scattering by particles and particle
ensembles is given. It is elaborated why the established scattering methods
using X-rays and visible light cannot in general be transferred to granular
media. Spectroscopic measurements using Terahertz radiation are highlighted as
they to probe the scattering properties of granular media, which are sensitive
to the packing structure. Experimental details to optimize spectrometer for
measurements on granular media are discussed. We perform transmission
measurements on static and agitated granular media using Fourier-transform
spectroscopy at the THz beamline of the BessyII storage ring. The measurements
demonstrate the potential to evaluate degrees of order in the media and to
track transient structural states in agitated bulk granular media.Comment: 12 Pages, 9 Figures, 56 Reference
Development and implementation of a pneumatic micro-feeder for poorly-flowing solid pharmaceutical materials
Consistent powder micro-feeding (and reduces manufacturing waste. Current commercial micro-feeders are limited in their ability to feed < 20 g/h of cohesive (i.e. powders of poor flowability) active pharmaceutical ingredients (API) and excipients (e.g. lubricants) with low fluctuation. To breach this gap, this study presents an advanced micro-feeder design capable of feeding a range of pharmaceutical-grade powders consistently at flow rates as low as 0.7 g/h with to minimise flow rate variations. This work details the design of this pneumatic micro-feeder and its excellent micro-feeding performance even for cohesive powders. The experimental studies investigated the influence of the process parameters (air pressure and air flow rate) and equipment configurations (insert size and plug position) on the feeding performance of different pharmaceutical-relevant powders, i.e., microcrystalline cellulose (MCC), croscarmellose sodium (CCS), crospovidone (XPVP) and paracetamol (APAP). It was shown that the system is capable of delivering consistent powder flow rates with good repeatability and stability
Experimental investigation for laser linewidth tolerance on photonic THz wireless systems using PE algorithms
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