scholarly journals Dispersion characteristics of complex electromechanical parameters of porous piezoceramics

2021 ◽  
pp. 2160004
Author(s):  
I. A. Shvetsov ◽  
M. A. Lugovaya ◽  
M. G. Konstantinova ◽  
P. A. Abramov ◽  
E. I. Petrova ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Piezoelectric Ceramics ◽  
Dispersion Characteristics ◽  
Pore Former ◽  
Piezoelectric Resonance ◽  
Physical Mechanisms ◽  
Resonance Analysis ◽  
Modified Method ◽  
Relative Porosity ◽  
Frequency Dependences

In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.

scholarly journals Microstructure characterization and properties of porous piezoceramics

2021 ◽  
pp. 2160006
Author(s):  
N. A. Shvetsova ◽  
I. A. Shvetsov ◽  
M. A. Lugovaya ◽  
E. I. Petrova ◽  
A. N. Rybyanets
Keyword(s):  
Porous Ceramics ◽  
Electromechanical Properties ◽  
Pore Former ◽  
Modified Method ◽  
The Matrix ◽  
Relative Porosity ◽  
New Applications ◽  
Type 3 ◽  
Porosity Range ◽  
Comprehensive Study

In this paper, a comprehensive study of microstructure/properties interrelations for porous piezoceramics based on PZT composition was performed. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. Porosity dependencies of elastic, dielectric, piezoelectric and electromechanical coefficients of the porous ceramics in the relative porosity range 0–50% were obtained and analyzed. As a result of microstructure analysis, it was found that at any connectivity type (3–0, 3–3) and porosity up to 50% the real structures of porous piezoceramics were close to the matrix medium structure with continuous piezoceramic skeleton. It was also revealed that the microstructural features of porous piezoceramics define the character of the dependences of the dielectric, piezoelectric and electromechanical properties of porous piezoelectric ceramics on porosity. In conclusion, microstructure/properties interrelations, as well as new applications of porous piezoceramics were discussed.

Analytical and Experimental Studies of Diffuser/Nozzle Valve-Less Micro-Pump

2008 ◽  
Author(s):  
Seiichi Tanaka ◽  
Shun Moriyama ◽  
Hiroshi Tsukamoto ◽  
Koji Miyazaki
Keyword(s):  
Pressure Loss ◽  
Experimental Studies ◽  
Measured Data ◽  
Dimensionless Numbers ◽  
Physical Mechanisms ◽  
Micro Pump ◽  
Unsteady Operation ◽  
Loss Coefficients ◽  
Bernoulli’S Theorem ◽  
Simplified Analysis

A valve-less micro-pump was realized with just one diffuser/nozzle element. The pressure-loss in a nozzle is lower than that in a diffuser, and therefore one-way flow may be realized in the nozzle direction. The frequency characteristics and the pump characteristics are measured. Dimensionless numbers are introduced to rearrange the measured data and to understand the physical mechanisms of the micro-pump. Simplified analysis was done for unsteady operation of the pump by considering the channel geometries and pressure-loss coefficients based on Bernoulli’s theorem. The calculated pump characteristics agreed with the measured ones. Numerical calculations were made using the commercial CFD (computational fluid dynamics) code CFX. The calculated flow patterns showed differences between the diffuser and nozzle directions.

scholarly journals Implementation of the Configuration Structure of an Integrated Computational Core of a Pulsed NQR Sensor Based on FPGA

Sensors ◽  
2021 ◽  
Vol 21 (18) ◽  
pp. 6029
Author(s):  
Andriy Samila ◽  
Oleksandra Hotra ◽  
Jacek Majewski
Keyword(s):  
Software Defined Radio ◽  
Pulse Sequence ◽  
Experimental Studies ◽  
Low Frequency ◽  
Stable Operation ◽  
Direct Digital Synthesizer ◽  
Quadrupole Resonance ◽  
Field Programmable ◽  
Quadrature Signals ◽  
Frequency Dependences

This paper presents a method for implementing the configuration structure of an integrated computational core of a pulsed nuclear quadrupole resonance (NQR) sensor based on a field-programmable gate array (FPGA), which comprises the following modules: a three-channel direct digital synthesizer (DDS), a pulse sequence shaper and a software-defined radio. Experimental studies carried out using the in-circuit analyzer SignalTap Logic Analyzer have confirmed the reliability of the correct and stable operation of the functional modules of the configuration structure at all stages of signal transformations, starting from the formation of the envelope of the excitation pulses and ending with the obtainment of low-frequency quadrature signals at the outlet of the compensating filters. The time and frequency dependences of the amplitude of the output signals generated using the DDS based on a 48 bit phase accumulator are investigated. This development can be used when creating pulsed coherent NQR sensors in the frequency range of 1 MHz–50 MHz.

The generation of sound in turbulent motion

2008 ◽  
Vol 112 (1133) ◽  
pp. 381-394 ◽  
Author(s):  
G. M. Lilley
Keyword(s):  
Noise Reduction ◽  
Turbulent Flows ◽  
High Speed ◽  
Experimental Studies ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Aerodynamic Noise ◽  
Turbulent Shear ◽  
Noise Generation ◽  
Physical Mechanisms

Abstract The present paper reviews and discusses the physical mechanisms of noise generation and reduction in turbulent flows with their applications towards aircraft noise reduction at takeoff and on the approach. This work began in 1948 when Lilley undertook an experimental investigation into the source of jet noise as a necessary precursor to finding methods for the reduction of high speed jet engine noise on civil jet airliners. Westley and Lilley completed this experimental programme in 1951, which included the design of a range of devices for high speed jet noise reduction. It was about this time that similar studies on jet noise were being started elsewhere and in particular by Lassiter and Hubbard in USA. The major contribution to the subject of turbulence as a source of noise came from Sir James Lighthill’s remarkable theory in 1952. In spite of the difficulties attached to theoretical and experimental studies on noise from turbulence, it is shown that with the accumulated knowledge on aerodynamic noise over the past 50 years, together with an optimisation of aircraft operations including flight trajectories, we are today on the threshold of approaching the design of commercial aircraft with turbofan propulsion engines that will not be heard above the background noise of the airport at takeoff and landing beyond 1-2km, from the airport boundary fence. It is evident that in the application of this work, which centres on the physical mechanisms relating to the generation of noise from turbulence and turbulent shear flows, to jet noise, there is not one unique mechanism of jet noise generation for all jet Mach numbers. This author in this publication has concentrated on what appears to be the dominant mechanism of noise generation from turbulence, where the mean convection speeds of the turbulence are subsonic. The noise generated at transonic and supersonic jet speeds invariably involves extra mechanisms, which are only briefly referred to here.

Admittance of mis-structures based on pentacene with two-layer dielectric SiO2-Al2O3

2021 ◽  
pp. 96-102
Author(s):  
A.V. Voitsekhovskii ◽  
◽  
S.N. Nesmelov ◽  
S.M. Dzyadukh ◽  
T.N. Kopylova ◽  
...  
Keyword(s):  
Equivalent Circuit ◽  
Experimental Studies ◽  
Surface States ◽  
Mis Structure ◽  
Voltage Sweep ◽  
Wide Range ◽  
Capacitance Voltage ◽  
Frequency Dependences ◽  
Mis Structures ◽  
Weak Accumulation

Experimental studies of the admittance of MIS structures based on pentacene with a two-layer dielectric SiO2-Al2O3 and various materials for backward contact (Au, Al, In, Ag) have been carried out in a wide range of frequencies, temperatures, and biases. The concentration of holes in the organic film of pentacene, found from the capacitance-voltage characteristics, took rather high values (in the range (4-40)×1017 cm-3). The magnitude of the hysteresis of the electrophysical characteristics turned out to be minimal for structures with Ag and In reverse contacts. Significant hysteresis was found for structures with reverse contacts made of Au and Al at 300 K. For a structure with a reverse contact made of Al, with a forward voltage sweep in a weak accumulation mode, a maximum capacitance was observed, which can be associated with a recharge of the level of surface states at the interface between the inorganic insulator and pentacene. An equivalent circuit of a pentacene-based MIS structure is proposed, which allows one to calculate the frequency dependences of the impedance under various conditions. The values of the elements of the equivalent circuit are found at various biases and temperatures. For structures with backward contacts made of Au and Ag, maxima on the temperature dependence of the conductance associated with the recharge of bulk traps in the organic pentacene film were found.

Micro-Channels: Reality and Myth

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
G. Hetsroni ◽  
A. Mosyak ◽  
E. Pogrebnyak ◽  
L. P. Yarin
Keyword(s):  
Measurement Accuracy ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Ionic Composition ◽  
Experimental Studies ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Physical Mechanisms ◽  
Sufficient Detail ◽  
Micro Channels

Many important problems connected to flows in micro-heat exchangers were not studied in sufficient detail. In particular, the governing physical mechanisms are still not well understood for flows in pipes and channels with hydraulic diameter ranging from 5 to 103 μm, which are often defined as micro-tubes or micro-channels. Experimental and numerical results of pressure driven laminar, continuous, incompressible, flow in different scale and shape channels are analyzed to highlight variations between various studies and these discrepancies are considered. The main objective is to determine whether the classical fluid flow theory based on the Navier- Stokes equations is valid to predict velocity distribution, pressure drop and transition from laminar to turbulent flow in micro-channels. No differences were found between results in micro-channels, unaffected by fluid ionic composition and the nature of the wall, and conventional size channels. The distinctions between different experimental studies must be attributed to different initial conditions, difference between actual conditions of a given experiment and conditions corresponding to the theoretical model, and measurement accuracy.

Considerations for Use of Square-Paddle Resonators for Arrays of Micro- and Nanoscale Devices

2009 ◽  
Author(s):  
John A. Judge ◽  
Teresa J. Woods ◽  
Joseph F. Vignola
Keyword(s):  
Vibration Mode ◽  
Experimental Studies ◽  
Two Dimensional ◽  
Quality Factors ◽  
Fundamental Vibration ◽  
Beam Resonator ◽  
Physical Mechanisms ◽  
Beam Geometry ◽  
Simple Geometry ◽  
Potential Applications

Mechanically coupling microscale or nanoscale resonators in more than one dimension requires a departure from classic beam resonator designs. A square paddle resonator is a simple geometry that allows easy coupling into two-dimensional arrays. These resonators can have high quality factors in the fundamental vibration mode if operated in vacuum. In this paper we summarize the behavior of such a resonator and describe several design considerations. We develop an expression for the inter-resonator coupling in terms of coupling beam geometry, estimate energy dissipation due to a variety of physical mechanisms, and empirically determine the vibration amplitude at which geometric nonlinearity becomes significant. Future experimental studies can exploit the expressions presented here, which facilitate design of two-dimensional arrays of square-paddle resonators that will be useful for a variety of potential applications.

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