scholarly journals CALCULATION OF NON-STANDARD W-PARAMETERS OF FOUR-POLE ON BIPOLAR TRANSISTORS

2020 ◽  
pp. 122-128
Author(s):  
Oleksandr Vozniak ◽  
Andrii Shtuts
Keyword(s):  
Theoretical Model ◽  
Experimental Studies ◽  
Base Material ◽  
Negative Resistance ◽  
Bipolar Transistors ◽  
Microwave Range ◽  
Low Frequencies ◽  
Wide Range ◽  
Collector Junction ◽  
Transistor Model

Improving the performance of microwave devices can be achieved both through the use of a fundamentally new element base, and through the use of new circuit designs. In this respect, the direction of use of the reactive properties of transistors as well as transistor structures with negative resistance for the construction of information-measuring systems and operating and computing devices of the microwave range is promising in this respect. In order to confirm the proposed methods, it is necessary to compare the results of the experimental studies using the proposed methods and means of measuring the W-parameters of real potentially unstable four-poles. As such four-poles it is proposed to use bipolar and transistors with a wide range of frequencies of potential instability. The paper develops mathematical models of W-parameters of such structures and evaluates their parameters in the frequency range. The active four-pole is a transistor model. Its W parameters can be determined either experimentally - for specific conditions or calculated - by using a physical transistor replacement circuit. In most cases, the calculation path is more acceptable because it allows to obtain analytical expressions for the four-pole, it is important in the analysis of the influence of various factors on the characteristics of the scheme under study. The inertial properties of the transistor are already manifested at relatively low frequencies and must be taken into account in practically the entire operating range of the transistor. The theoretical model holds up to frequencies f  2fт (where ft is the limit frequency) [1,3]. At higher frequencies, it is necessary to consider the parasitic reactive parameters of real transistors, first of all, the inductance of the terminals. A physically T-equivalent equivalent transistor replacement scheme was proposed by Pritchard in a simplified version [4]. It has several varieties, differing in the configuration of the circuit consisting of the resistance of the base material and the capacity of the collector junction. If we carefully consider and compare the T and U-shaped circuits of the transistor substitution, it can be noticed that they differ only in the configuration of their inne r part - the theoretical model. At high frequencies P and T, such circuits are not exact mutual equivalents. This is due to the approximation used in the transition from one circuit to another. However, the frequency characteristics of the circuits are very close. Each of them models the processes in the transistor with approximately the same accuracy, and in this sense they are equivalent.

Design and modeling of a flexible longitudinal zigzag structure for enhanced vibration energy harvesting

2016 ◽  
Vol 28 (3) ◽  
pp. 367-380 ◽  
Author(s):  
Shengxi Zhou ◽  
Weijia Chen ◽  
Mohammad H Malakooti ◽  
Junyi Cao ◽  
Daniel J Inman
Keyword(s):  
Theoretical Model ◽  
Energy Harvesting ◽  
Free Vibration Analysis ◽  
Free Vibrations ◽  
Vibration Energy ◽  
Vibration Energy Harvesting ◽  
Element Analysis ◽  
Low Frequencies ◽  
Wide Range ◽  
Zigzag Structure

The use of piezoelectric materials for vibration energy harvesting at low frequencies is challenging and requires innovative structural design. Here, a flexible longitudinal zigzag structure is developed to enhance energy harvesting at low-frequency ambient vibrations. The proposed structure is composed of orthogonal beams which enable vibration energy harvesting in two directions. A theoretical model based on Euler–Bernoulli beam theory is formulated to study the dynamic response of the structure under free vibrations. The free vibration analysis demonstrates that low operating frequencies can be obtained by increasing the number of, and/or the length of, beams in the proposed structure. To validate the accuracy of the developed theoretical model, finite element analysis is performed using ANSYS. On verification of the model’s accuracy, the piezoelectric effect of the active beams is considered in the model to evaluate the energy harvesting performance of the proposed flexible longitudinal zigzag structure. Numerical results demonstrate that the output voltage and the working frequency of these energy harvesting structures can be tailored through simply altering the number of beams. Overall, the results indicate that the proposed structure is capable of efficient energy conversion at low frequencies, which makes them suitable for a wide range of working conditions.

INVESTIGATION OF RELAXATION OSCILLATIONS IN THERMISTOR–CAPACITOR SYSTEMS

1965 ◽  
Vol 43 (1) ◽  
pp. 131-143
Author(s):  
G. A. Morley
Keyword(s):  
Time Constant ◽  
Small Amplitude ◽  
Dynamic Properties ◽  
Negative Resistance ◽  
Thermal Time ◽  
Relaxation Oscillations ◽  
Static Properties ◽  
Low Frequencies ◽  
Thermal Time Constant ◽  
Wide Range

It is known that a thermistor displays negative resistance at low frequencies when biased with a current greater than turnover current. Thus, when shunted by a capacitance in this condition, sustained oscillations are possible. These oscillations range from a sinusoidal small-amplitude character, when the system is just above threshold for oscillation, to a strongly relaxational type when a large shunt capacitance is employed.The investigation involved a study of the dynamic properties of these oscillations and their relation to the static properties of the thermistor. The relevant thermistor parameters which were measured included the thermal time constant for which special very-low-frequency techniques were developed.The oscillations were studied over a wide range of capacitance covering the transition from sinusoidal to relaxational type. The voltage extrema and period were measured as functions of capacitance, voltage supply resistance, and operating point.An investigation was made of the features of the differential equations describing the behavior of the system, especially for limit cycles corresponding to relaxation oscillations. The asymptotic form of the cycles was derived for the case where the circuital time constant greatly exceeds the thermal time constant of the thermistor. The complicated nature of the equations precluded a solution in a closed form, and approximative methods were found to be necessary. However, in the case of sinusoidal oscillations of small amplitude, the period can be expressed exactly in terms of the system parameters (Burgess 1955b) and this result was confirmed experimentally.

scholarly journals Image Statistics Preserving Encrypt-then-Compress Scheme Dedicated for JPEG Compression Standard

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 421
Author(s):  
Dariusz Puchala ◽  
Kamil Stokfiszewski ◽  
Mykhaylo Yatsymirskyy
Keyword(s):  
Statistical Analysis ◽  
Image Encryption ◽  
Experimental Studies ◽  
Quality Measures ◽  
Input Image ◽  
Jpeg Compression ◽  
Image Statistics ◽  
Compression Stage ◽  
Wide Range ◽  
The Impact

In this paper, the authors analyze in more details an image encryption scheme, proposed by the authors in their earlier work, which preserves input image statistics and can be used in connection with the JPEG compression standard. The image encryption process takes advantage of fast linear transforms parametrized with private keys and is carried out prior to the compression stage in a way that does not alter those statistical characteristics of the input image that are crucial from the point of view of the subsequent compression. This feature makes the encryption process transparent to the compression stage and enables the JPEG algorithm to maintain its full compression capabilities even though it operates on the encrypted image data. The main advantage of the considered approach is the fact that the JPEG algorithm can be used without any modifications as a part of the encrypt-then-compress image processing framework. The paper includes a detailed mathematical model of the examined scheme allowing for theoretical analysis of the impact of the image encryption step on the effectiveness of the compression process. The combinatorial and statistical analysis of the encryption process is also included and it allows to evaluate its cryptographic strength. In addition, the paper considers several practical use-case scenarios with different characteristics of the compression and encryption stages. The final part of the paper contains the additional results of the experimental studies regarding general effectiveness of the presented scheme. The results show that for a wide range of compression ratios the considered scheme performs comparably to the JPEG algorithm alone, that is, without the encryption stage, in terms of the quality measures of reconstructed images. Moreover, the results of statistical analysis as well as those obtained with generally approved quality measures of image cryptographic systems, prove high strength and efficiency of the scheme’s encryption stage.

scholarly journals Analysis of a Cantilevered Piezoelectric Energy Harvester in Different Orientations for Rotational Motion

Sensors ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 1206 ◽  
Author(s):  
Wei-Jiun Su ◽  
Jia-Han Lin ◽  
Wei-Chang Li
Keyword(s):  
Theoretical Model ◽  
Resonant Frequency ◽  
Rotational Motion ◽  
Axial Load ◽  
Energy Harvester ◽  
Excitation Frequency ◽  
Experimental Studies ◽  
Piezoelectric Energy ◽  
Piezoelectric Cantilever ◽  
Tip Mass

This paper investigates a piezoelectric energy harvester that consists of a piezoelectric cantilever and a tip mass for horizontal rotational motion. Rotational motion results in centrifugal force, which causes the axial load on the beam and alters the resonant frequency of the system. The piezoelectric energy harvester is installed on a rotational hub in three orientations—inward, outward, and tilted configurations—to examine their influence on the performance of the harvester. The theoretical model of the piezoelectric energy harvester is developed to explain the dynamics of the system and experiments are conducted to validate the model. Theoretical and experimental studies are presented with various tilt angles and distances between the harvester and the rotating center. The results show that the installation distance and the tilt angle can be used to adjust the resonant frequency of the system to match the excitation frequency.

Measurements and Modeling of Ingress in a New 1.5-Stage Turbine Research Facility

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Marios Patinios ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
Gary D. Lock
Keyword(s):  
Theoretical Model ◽  
Gas Turbines ◽  
Test Facility ◽  
Radial Clearance ◽  
Operating Life ◽  
The Core ◽  
Wide Range ◽  
Purge Flow ◽  
Rotor Disk ◽  
Engine Components

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor disks as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance, and integrity of highly stressed, vulnerable engine components. Rim seals, fitted at the periphery of the disks, are used to minimize ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the disks. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. The fluid-dynamically scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure, and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

Experimental Investigations on Aluminium Ultrasonic Welding Parameters

2014 ◽  
Vol 657 ◽  
pp. 306-310
Author(s):  
Lăcrămioara Apetrei ◽  
Vasile Rață ◽  
Ruxandra Rață ◽  
Elena Raluca Bulai
Keyword(s):  
Microstructural Analysis ◽  
Base Material ◽  
Welding Process ◽  
Ultrasonic Welding ◽  
Experimental Investigations ◽  
Welding Parameters ◽  
Material Structure ◽  
Welding Temperature ◽  
Wide Range ◽  
Made In

Research evolution timely tendencies, in the nonconventional technologies field, are: manufacture conditions optimization and complex equipments design. The increasing of ultrasonic machining use, in various technologies is due to the expanding need of a wide range materials and high quality manufacture standards in many activity fields. This paper present a experimental study made in order to analyze the welded zone material structure and welding quality. The effects of aluminium ultrasonic welding parameters such as relative energy, machining time, amplitude and working force were compared through traction tests values and microstructural analysis. Microhardness tests were, also, made in five different points, two in the base material and three in the welded zone, on each welded aluminium sample. The aluminum welding experiments were made at the National Research and Development Institute for Welding and Material Testing (ISIM) Timişoara. The ultrasonic welding temperature is lower than the aluminium melting temperature, that's so our experiments reveal that the aluminium ultrasonic welding process doesn't determine the appearance of moulding structure. In the joint we have only crystalline grains deformation, phase transformation and aluminium diffusion.

scholarly journals Effects of electrical stimulation on isolated rodent gastric smooth muscle cells evaluated via a joint computational simulation and experimental approach

2009 ◽  
Vol 297 (4) ◽  
pp. G672-G680 ◽  
Author(s):  
P. Du ◽  
S. Li ◽  
G. O'Grady ◽  
L. K. Cheng ◽  
A. J. Pullan ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Electrical Stimulation ◽  
Pulse Train ◽  
Pulse Width ◽  
Computational Simulation ◽  
Minimum Energy ◽  
Experimental Studies ◽  
Single Pulse ◽  
Plateau Phase ◽  
Wide Range

Gastric electrical stimulation (GES) involves the delivery of electrical impulses to the stomach for therapeutic purposes. New GES protocols are needed that are optimized for improved motility outcomes and energy efficiency. In this study, a biophysically based smooth muscle cell (SMC) model was modified on the basis of experimental data and employed in conjunction with experimental studies to define the effects of a large range of GES protocols on individual SMCs. For the validation studies, rat gastric SMCs were isolated and subjected to patch-clamp analysis during stimulation. Experimental results were in satisfactory agreement with simulation results. The results define the effects of a wide range of GES parameters (pulse width, amplitude, and pulse-train frequency) on isolated SMCs. The minimum pulse width required to invoke a supramechanical threshold response from SMCs (defined at −30 mV) was 65 ms (at 250-pA amplitude). The minimum amplitude required to invoke this threshold was 75 pA (at 1,000-ms pulse width). The amplitude of the invoked response beyond this threshold was proportional to the stimulation amplitude. A high-frequency train of stimuli (40 Hz; 10 ms, 150 pA) could invoke and maintain the SMC plateau phase while requiring 60% less power and accruing ∼30% less intracellular Ca2+ concentration during the plateau phase than a comparable single-pulse protocol could in a demonstrated example. Validated computational simulations are an effective strategy for efficiently identifying effective minimum-energy GES protocols, and pulse-train protocols may also help to reduce the power consumption of future GES devices.

Durability of Cement Stabilized Cold-Recycled of Asphalt Pavement Materials

2012 ◽  
Vol 174-177 ◽  
pp. 1188-1192 ◽  
Author(s):  
Lian Yu Wei ◽  
Zhi Yu Guo
Keyword(s):  
Asphalt Pavement ◽  
Base Material ◽  
Road Construction ◽  
Thermal Shrinkage ◽  
Construction Process ◽  
Pavement Materials ◽  
Road Base ◽  
Wide Range ◽  
Dry Shrinkage ◽  
Recycled Material

In recent years, due to the dual pressures of resources and the environment,the clod recycled technology renovation and expansion of the old road and new road construction process increasingly attention increasingly wide range of applications. In this paper, the water stability of the cold recycled materials in asphalt pavement on cement additives, frozen stability, thermal shrinkage resistance, dry Shrinkage thefour indicators of experiments to evaluate its durability, and compared with the typical semi-rigid material. To verify the feasibility of the cold recycled material as road base material.

Dynamic Characterization of a Valveless Micropump Considering Entrapped Gas Bubbles

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Songjing Li ◽  
Jixiao Liu ◽  
Dan Jiang
Keyword(s):  
Numerical Simulation ◽  
Theoretical Model ◽  
Experimental Studies ◽  
Gas Bubbles ◽  
Chamber Pressure ◽  
Dynamic Characterization ◽  
Valveless Micropump ◽  
Performance Deterioration ◽  
Trapped Gas

Unexpected gas bubbles in microfluidic devices always bring the problems of clogging, performance deterioration, and even device functional failure. For this reason, the aim of this paper is to study the characterization variation of a valveless micropump under different existence conditions of gas bubbles based on a theoretical modeling, numerical simulation, and experiment. In the theoretical model, we couple the vibration of piezoelectric diaphragm, the pressure drop of the nozzle/diffuser and the compressibility of working liquid when gas bubbles are entrapped. To validate the theoretical model, numerical simulation and experimental studies are carried out to investigate the variation of the pump chamber pressure influenced by the gas bubbles. Based on the numerical simulation and the experimental data, the outlet flow rates of the micropump with different size of trapped gas bubbles are calculated and compared, which suggests the influence of the gas bubbles on the dynamic characterization of the valveless micropump.

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