Frequency Of Probe Signal Research Articles

О возможности реализации нелинейного радиолокатора с обработкой на частоте зондирующего сигнала

The conditions for the implementation of a nonlinear radar using a probing signal having a form as a periodic sequence of pairs of radio pulses with different amplitudes and equal energies, are considered. The energies of the reflected pulses are compared in the locator receiver for each pair, which makes it possible to detect reflections from nonlinear devices at the probing signal frequency by violating the equality of these energies. A numerical experiment was performed to evaluate the dependence of the current form through germanium and silicon diodes and their amplitude parameters at the frequency of the acting sinusoidal voltage with variable amplitude. As a result, it was found that the amplitude nonlinearity can be detected before the diode is completely "opened" if the two voltage amplitudes on the diode differ from each other by at least one and a half to two times. Since the pulse energies are proportional to their powers, and the pulse durations are unchanged, it should be possible to detect non-linearity by determination of a ratio between the radar cross-sections of non-linear objects for different pulse amplitudes. To obtain quantitative estimates, a simulation of the incidence of a flat, linearly polarized wave on a half-wavelength dipole and a half-wavelength folded dipole loaded with a diode was performed. It was found that the model type and parameters significantly affect both the values of the radar cross-sections and the degree of influence of nonlinearity on these values, so that the detection of non-linearity requires significantly higher power levels of the probing signal than the theory predicts.

Resonant Activation of Resistance Switching in Memristors Based on YSZ Films with Au Nanoparticles

The resonant activation of resistance switching (RS) of a memristor based on an yttria stabilized zirconia (YSZ) film with embedded Au nanoparticles (NPs) was investigated. The switching was made by triangular pulses with high frequency (HF) sinusoid added. A non-monotonous dependence a ratio of the electric current through the memristor in the low resistive state to the current in the high resistive one on the HF sinusoid frequency was found. The effect was explained by a finite electron tunneling time between the Pt electrode and Au NPs. This conclusion was supported by measuring a dependence of HF memristor capacitance on the probing signal frequency.

Effect of probing signal on the output signals spectrum of nonlinear spin waves in a cross based on waveguides of iron-yttrium garnet film

Subject. A change in the spectrum of spin waves (SW) in a magnetic cross is investigated when two signals pass through it: a pump signal and a probe signal. Objective. Detection of specific features in formation of the spectra of the output signals of SW in the multiport structure based on a yttrium iron garnet (YIG) film in the case of excitation of two magnetostatic surface waves (MSSW) simultaneously by the input antenna, where the first, with power higher than the first-order parametric instability threshold is the pump, and the second one is a probe. Methods. The experiments were performed for a cross structure from YIG film in the form of two orthogonal waveguides with the SW wire antennas placed at the ends of the waveguides, where one of the antennas on the transversely magnetized waveguide was considered as the input. Result. It was found that by choosing the probing signal frequency, one can significantly (by 10 dB) change the relative signal levels for the satellite waves at the output antennas, which are secondary MSSWs with some new frequencies and appear in the output signals spectrum as a result of the thresholdless processes of merging of parametric spin waves generated by MSSW pumping. In this case the secondary MSSWs frequencies can differ at the output antennas located on orthogonal waveguides. Discussion. The discovered effect is associated with the nonreciprocal nature of propagation of both the pumping wave and the waves generated at parametric instability condition in the structure.

High frequency impedance characteristics of a tunable microplasma device

Computational studies on high frequency impedance characteristics of a microplasma device are reported. While microplasma is ignited using a primary excitation signal, frequency response of plasma impedance is determined by a secondary high frequency probe signal with significantly lower voltage amplitude such that it does not influence the plasma parameters. The computational model utilizing the drift–diffusion approximation is first validated by comparing with experimental data for microplasmas ignited at pressures ranging from 1 to 5 Torr. In spite of quantitative discrepancies, good overall agreement is obtained between the measured frequency response of impedance of the discharge. Comparisons are also presented for various plasma parameters including mean electron number density, sheath thickness, mean electron temperature, and collision frequency that were inferred from the impedance measurements. The computational model is then used to perform simulations of near-atmospheric pressure microplasmas with the probe signal frequency ranging from 3 to 20 GHz. The simulations demonstrate the presence of a resonance frequency at which the impedance vanishes. More importantly, it is shown that this resonant frequency can be tuned effectively by suitably modifying the operating parameters (gap size, pressure, and excitation voltage). The simulated impedance characteristics are used to determine the effective plasma inductance and capacitance using a non-linear fitting approach, thereby showing the dependence of these electrical parameters on the plasma operating conditions.

Deep trap analysis in green light emitting diodes: Problems and solutions

Some green light emitting diodes (LEDs) based on GaN/InGaN multiquantum-well (MQW) structures exhibit strong frequency and temperature dependence of capacitance and prominent changes in capacitance–voltage profiles with temperature that make it difficult to obtain reliable deep level transient spectroscopy (DLTS) measurements. DLTS performed at low probing signal frequency and with constant capacitance between the measurements by controlling applied bias mitigates these issues. This allows measurement of deep electron and hole traps in specific quantum wells (QWs) in the MQW structure. The dominant electron and hole traps detected have levels near Ec− (0.45–0.5) eV and Ev+ (0.6–0.63) eV. Their density increases significantly after aging for a long period (2120 h) at high driving current and elevated temperature. The reason for the observed anomalies in DLTS spectra of these green LEDs is the high density of states in the QWs with activation energies near 0.08, 0.12–0.14, and 0.3 eV, detected in admittance spectra, and, for the 0.08 eV and 0.3 eV, these states are likely related to defects.

Precision Ultrasonic Meters of Fluid Level in Sealed Containers

The problems of measuring the fluid level in steel containers through a wall by acoustic methods are considered. When measuring the level by sound propagation time in a fluid in case of an inelastic wall the best accuracy is provided by the correlation-phase reception of compound signals. But for measurements in steel containers, such a technique is usually not used due to phase structure distortions of a signal with a broad frequency bandwidth when transmitting through an elastic wall (having multiple resonances in this band). The use of correlation-phase reception in such cases may be possible by choice a probing signal, a phase structure distortion of which will be small when transmitting through a wall. The aim of the work is to determine the possibilities of using the correlation-phase reception and the achievable accuracy of level measuring in the conditions of different wall thickness of steel containers. The significance of research is determined by the possibilities of a multiple increase in the measuring accuracy. Acoustic methods and level measuring devices are considered; the advantage of time-pulse (time-of-flight, TOF) methods over interferometric (including swept-frequency acoustic interferometry, SFAI) and other measuring methods in large containers is shown. A method of level measuring using the correlation-phase reception of compound signals and a scheme for calculating the broadband impulse signal transmission through an elastic wall (and building the amplitude-frequency and phase-frequency characteristics) taking into account the longitudinal and shear waves of thickness wall vibrations and standing waves of its resonant vibrations along the length (diameter) are proposed. A method for selecting the probing signal frequency range according to an amplitude-frequency characteristic of elastic wall which provide the low phase structure distortions when transmitting through a wall is suggested. The achievable accuracy estimates of measuring the sound velocity and the fluid level in rail tank wagons are obtained. Experimental works carried out on a thin-walled (0.8 mm) barrel with signals of the frequency range of 250-750 kHz (i.e. frequencies below the first thickness resonance frequency of barrel bottom) are confirmed the small phase structure distortion of signals when transmitting through the bottom and the high efficiency of the correlation-phase reception. With a signal-to-noise ratio of 0.4, a high time measuring accuracy of ~0.15 μs corresponding to a level measuring accuracy of ~0.1 mm is obtained. For signals of frequency range 250-750 kHz the interval of wall thickness is defined as 0.3-3.6 mm at which the efficiency of the correlation-phase reception and the level measuring accuracy should be high. The results showed that the use of correlation-phase reception of compound signals when measuring a fluid level through the bottom of a thin-walled steel barrel is possible and provides both high operating efficiency in the noise conditions and high measuring accuracy. It can be expected that the same accuracy factors and operating efficiency will be kept in a bottom thicknesses range at which the probing signal frequencies will be less than the first bottom thickness resonance frequency. In cases of large bottom thicknesses, if the first bottom thickness resonance frequency is low, the probing signal spectrum may include frequency regions between the thickness resonance frequencies. In this case, it becomes possible to use the correlation-phase reception for the level measuring in containers with a wide range of bottom thicknesses. Ref. 20, tab. 1, fig. 7.

Parameter optimization for the three-frequency feed for the mirror antenna of the non-linear radar

Analyzed below is a radiating structure represented by a flat self-complementary three-sector structure fed by three segments of the microstrip line and located above the stepped metal screen, and to be used as an exciter for the non-linear radar antenna. When proper matching with the feeding coaxial cable is achieved, results of the numerical simulation proved that the antenna can provide near-circular polarization of radiation at the probing signal frequency, and linear polarization at the second and third harmonics of this signal.

Direct Observation of CdCl2 Treatment Induced Grain Boundary Carrier Depletion in CdTe Solar Cells Using Scanning Probe Microwave Reflectivity Based Capacitance Measurements

Device grade polycrystalline CdTe films, grown by rf-sputtering (yielding up to 13% efficient devices) and close-spaced sublimation (CSS) (yielding up to 16% efficient devices), have been analyzed using scanning microwave impedance microscopy (sMIM). In order to study the effect of Cl on the electronic properties of grain boundaries in CdTe, sMIM based capacitance measurements were performed on the surfaces of as-deposited and CdCl2 annealed CdTe films. The measurements were performed with an sMIM instrument operating at ∼3 GHz probe signal frequency in conjunction with a combination of ac and dc voltage biases applied to the tip. It was found that CdCl2 annealed CdTe samples deposited using both CSS and sputtering exhibit carrier depletion along the grain boundaries as compared to the grain bulk. The grain boundary carrier depletion was not observed in samples that have not been CdCl2 annealed and hence have no incorporated Cl.

All-optical tunable photonic crystal nor gate based on the nonlinear Kerr effect in a silicon nanocavity

A tunable nor gate based on the Kerr effect in silicon-rod-based photonic crystals is presented. The proposed gate consists of two-dimensional photonic crystal add–drop filters with wavelength-selective reflector cavities, which are aligned in series with each other. The main feature of this structure is the enhancement of nonlinear phenomena caused by strong light localization in the photonic crystal nanocavities. Because of this feature, the designed nor gate can control the amount of dropped probe signal light and change the gate output. The operation of the proposed gate is investigated numerically by using the finite-difference time domain method. The results reveal that the power levels of 0, 1, and uncertain states can be changed by appropriate adjustment of the probe signal frequency.

ASPECT-SENSITIVE SCATTERING OF HF RADIO WAVES BY FIELD-ALIGNED IRREGULARITIES OF A PLANE-STRATIFIED IONOSPHERE

Directions and radar cross-sections are calculated for aspect sensitive scattering of HF radio waves by random field-aligned irregularities of a plane-stratified (on average) ionosphere. In the calculations, the probe signal frequency is assumed to be greatly in excess of the electron gyrofrequency of the plasma layer, while lower than its critical frequency. This has allowed investigating the effect of refraction bend in the direct and reflected components of the incident and scattered electromagnetic waves neglecting the geomagnetic field effect to a process of their propagation. The suggested calculation algorithms are illustrated by the example of zenith radiation. It is shown for this geometry that with scattering height the direction of aspect scattered signal leaving the ionospheric layer approaches a vertical line, while the radar cross-section increases. It has been found that simultaneous recordings of radar cross-sections of aspect sensitive scattering from heights of critical reflection for several probe frequencies in the case of vertical incidence allow recovering the height profile of the normalization factor of the spatial spectrum of ionospheric irregularities.

Negative capacitance in forward biased hydrogenated amorphous silicon p+-i-n+ diodes

We present experimental results and a physical explanation for the negative values of the small-signal capacitance of forward biased hydrogenated amorphous silicon (a-Si:H) p+-i-n+ diodes. The device capacitance varies with the probe signal frequency. In the low frequency range the measured capacitance shows large negative values if the diode is sufficiently forward biased. Higher forward bias voltages shift this effect to higher frequencies. Time domain response of the device to a small voltage step and a Fourier transform of the resulting transient current provide a verification of the results. The time domain data also suggest the physical mechanism responsible for the overall dispersive behavior: separate and delayed trapping processes for holes and electrons at the interfaces with the two doped layers.

Effect of parasitics on electrochemical capacitance-voltage profiling of pseudomorphic high electron mobility transistor structures

The effect of parasitic series resistances on electrochemical capacitance-voltage (EC-V) profiling is simulated numerically for AlxGaj1-xAs/InyGa1-yAs pseudomorphic high electron mobility transistor (p-HEMT) structures. The actual EC-V measurement is simulated numerically by reconstructing the charge distribution from an intrinsic distribution calculated from a self-consistent k p model. The calculated charge distribution then forms the basis for examining the possible profiles an EC-V measurement would produce when parasitics are taken into account. From a simple lumped-circuit model, it is shown that parasitic resistances distort the shape of the charge distribution by changing the relative heights of the 5-layer and channel charges. Hysteresis effects may also occur and may be accompanied by a change in material type from n to p even though the material is known to be n-type over the entire range of measurement. Additionally, an undesirable dependence of the charge profile on the probe signal frequency is found.

Cylindrical capacitor and its application to measurements on cylindrical gas discharges

The measurement of high electron densities within a plasma is often conveniently performed using microwave techniques, requiring a probing-signal frequency of the same order as the electron-plasma frequency. If the electron density is high, considerable cost and expertise are associated with this form of measurement.The device described is able to evaluate the electron density at a probing frequency much lower than the plasma frequency, and thus eases the measurement considerably. For example, a tube of 10 cm bore, whose wall is 2 mm thick and is composed of material whose relative permittivity is 6, will enable electron densities at plasma frequencies of 12.5 GHz to be checked using a probing signal of only 1 GHz.