85 research outputs found
A Superdirective Beamforming Approach with Impedance Coupling and Field Coupling for Compact Antenna Arrays
In most multiple-input multiple-output (MIMO) communication systems, the
antenna spacing is generally no less than half a wavelength. It helps to reduce
the mutual coupling and therefore facilitate the system design. The maximum
array gain equals the number of antennas in this settings. However, when the
antenna spacing is made very small, the array gain of a compact array can be
proportional to the square of the number of antennas - a value much larger than
the traditional array. To achieve this so-called ``superdirectivity" however,
the calculation of the excitation coefficients (beamforming vector) is known to
be a challenging problem. In this paper, we address this problem with a novel
double coupling-based superdirective beamforming method. In particular, we
categorize the antenna coupling effects to impedance coupling and field
coupling. By characterizing these two coupling in model, we derive the
beamforming vector for superdirective arrays. In order to obtain the field
coupling matrix, we propose a spherical wave expansion approach, which is
effective in both simulations and realistic scenarios. Moreover, a prototype of
the independently controlled superdirective antenna array is developed.
Full-wave electromagnetic simulations and real-world experiments validate the
effectiveness of our proposed approaches, and superdirectivity is achieved in
reality by a compact array with 4 and 5 dipole antennas.Comment: arXiv admin note: text overlap with arXiv:2204.1154
High piezoelectric sensitivity and hydrostatic figures of merit in unidirectional porous ferroelectric ceramics fabricated by freeze casting
High performance lead zirconate titanate (PZT) ceramics with aligned porosity
for sensing applications were fabricated by an ice-templating method. To
demonstrate the enhanced properties of these materials and their potential for
sensor and hydrophone applications, the piezoelectric voltage constants
hydrostatic parameters and AC conductivity as a function of the porosity in
directions both parallel and perpendicular to the freezing temperature gradient
were studied. As the porosity level was increased, PZT poled parallel to the
freezing direction exhibited the highest coefficients, and hydrostatic figures
of merit compared to the dense and PZT poled perpendicular to the freezing
direction. This work demonstrates that piezoelectric ceramics produced with
aligned pores by freeze casting are a promising candidate for a range of sensor
applications and the polarisation orientation relative to the freezing
direction can be used to tailor the microstructure and optimise sensitivity for
sensor and hydrostatic transducer applications
Wind-driven pyroelectric energy harvesting device
Pyroelectric materials have recently received attention for harvesting waste heat owing to their potential to convert temperature fluctuations into useful electrical energy. One of the main challenges in designing pyroelectric energy harvesters is to provide a means to induce a temporal heat variation in a pyroelectric material autonomously from a steady heat source. To address this issue, we propose a new form of wind-driven pyroelectric energy harvester, in which a propeller is set in rotational motion by an incoming wind stream. The speed of the propeller's shaft is reduced by a gearbox to drive a slider-crank mechanism, in which a pyroelectric material is placed on the slider. Thermal cycling is obtained as the reciprocating slider moves the pyroelectric material across alternative hot and cold zones created by a stationary heat lamp and ambient temperature, respectively. The open-circuit voltage and closed-circuit current are investigated in the time domain at various wind speeds. The device was experimentally tested under wind speeds ranging from 1.1 to 1.6 m s−1 and charged an external 100 nF capacitor through a signal conditioning circuit to demonstrate its effectiveness for energy harvesting. Unlike conventional wind turbines, the energy harvested by the pyroelectric material is decoupled from the wind flow and no mechanical power is drawn from the transmission; hence the system can operate at low wind speeds (<2 m s−1)
Control of electro-chemical processes using energy harvesting materials and devices
A detailed overview of pyro-electric, piezo-electric, tribo-electric, flexo-electric thermo-electric and photovoltaic charge generation mechanisms which are used to control electro-chemical reactions.</p
Energy harvesting from coupled bending-twisting oscillations in carbon-fibre reinforced polymer laminates
The energy harvesting capability of resonant harvesting structures, such as
piezoelectric cantilever beams, can be improved by utilizing coupled
oscillations that generate favourable strain mode distributions. In this work,
we present the first demonstration of the use of a laminated carbon fibre
reinforced polymer to create cantilever beams that undergo coupled
bending-twisting oscillations for energy harvesting applications. Piezoelectric
layers that operate in bending and shear mode are attached to the bend-twist
coupled beam surface at locations of maximum bending and torsional strains in
the first mode of vibration to fully exploit the strain distribution along the
beam. Modelling of this new bend-twist harvesting system is presented, which
compares favourably with experimental results. It is demonstrated that the
variety of bend and torsional modes of the harvesters can be utilized to create
a harvester that operates over a wider range of frequencies and such
multi-modal device architectures provides a unique approach to tune the
frequency response of resonant harvesting systems
Understanding the effect of porosity on the polarisation-field response of ferroelectric materials
This paper combines experimental and modelling studies to provide a detailed
examination of the influence of porosity volume fraction and morphology on the
polarisation-electric field response of ferroelectric materials. The broadening
of the electric field distribution and a decrease in the electric field
experienced by the ferroelectric ceramic medium due to the presence of
low-permittivity pores is examined and its implications on the shape of the
hysteresis loop, remnant polarisation and coercive field is discussed. The
variation of coercive field with porosity level is seen to be complex and is
attributed to two competing mechanisms where at high porosity levels the
influence of the broadening of the electric field distribution dominates, while
at low porosity levels an increase in the compliance of the matrix is more
important. This new approach to understanding these materials enables the
seemingly conflicting observations in the existing literature to be clarified
and provides an effective approach to interpret the influence of pore fraction
and morphology on the polarisation behaviour of ferroelectrics. Such
information provides new insights in the interpretation of the physical
properties of porous ferroelectric materials to inform future effort in the
design of ferroelectric materials for piezoelectric sensor, actuator, energy
harvesting, and transducer applications
Eogenetic karst and its control on reservoirs in the Ordovician Majiagou Formation, eastern Sulige gas field, Ordos Basin, NW China
To further ascertain the origin of the Ordovician Majiagou Formation reservoirs in the Ordos Basin, the M54-M51 sub-members of the Ordovician Majiagou Formation in the eastern Sulige gasfield of Ordos Basin were taken as examples to analyze the vertical development characteristics of eogenetic karst and to discover the dissolution mechanism and its control on reservoirs through observation of a large number of cores and thin sections. According to detailed analysis of petrologic characteristics, the reservoir rock types include micritic dolomite, grain dolomite and microbialite which have mainly moldic pore, intergranular (dissolved) pore, and (dissolved) residual framework pore as main reservoir space respectively. The study area developed upward-shallowing sequences, with an exposure surface at the top of a single upward-shallowing sequence. The karst systems under the exposure surface had typical exposure characteristics of early dissolution and filling, indicating these reservoirs were related to the facies-controlled eogenetic karstification. With the increase of karstification intensity, the reservoirs became worse in physical properties
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