Nonlinear Modes Of Operation Research Articles

Influence of the Nonlinear Operating Mode of Acoustic Liners at High Sound Pressure Levels on Sound Wave Propagation in a Cylindrical Duct with a Flow

Influence of the Nonlinear Operating Mode of Acoustic Liners at High Sound Pressure Levels on Sound Wave Propagation in a Cylindrical Duct with a Flow

Nonlinear regimes of spin wave propagation in a waveguide with a one-dimensional hole array

Purpose. Investigation of spin-wave signal passage in a system of magnetic microwaves separated from each other by a one-dimensional array of holes. Using numerical and experimental methods to show controlled spatial-frequency selection of the signal in linear and nonlinear modes of operation. Methods. Micromagnetic modeling of the spatial intensity distributions of spin waves. Obtaining S-parameters of spin waves propagating in a tangentially magnetized structure using a vector circuit analyzer. Results. The spatially selective properties of the structure in linear and nonlinear modes are demonstrated using micromagnetic modeling. A mechanism for controlling the frequency range of the Bragg zone is revealed using a vector analyzer. Conclusion. The proposed structure can be used as a functional element in planar topologies of magnon networks and parallel signal processing devices based on them.

Current mode of photomultiplier tube operation for the detection of the kinetics of small optical signals

Subject of study. The possibility of using the nonlinear current mode of operation of a photomultiplier tube for measurements of luminescence kinetics was investigated. Aim of study. This study aimed to validate the possibility of using the nonlinear current mode of operation of a photomultiplier tube to determine the kinetic properties of small luminescence signals of condensed media, including the signals that cannot be detected in a linear current mode. Method. The signal arriving at a high-impedance (1 MΩ) input of a digital oscilloscope from a photomultiplier tube via a coaxial cable was measured. This signal is a convolution of a photocurrent pulse with a kinetic instrument function determined by the discharge of capacitance in the measurement circuit of the photomultiplier tube. The bandwidth of the circuit was determined by the lowest frequency of its elements instead of the characteristic time of the instrument function. The real photocurrent signal was reconstructed by the deconvolution of the digital convoluted array. The pulsed cathodoluminescence method was used to detect the kinetics. Main results. A method for measuring the kinetics of small optical signals in the current mode of operation of a photomultiplier tube connected to a high-impedance input of a digital oscilloscope was presented. The results of using this method to measure the kinetics of pulsed cathodoluminescence of impurity and intrinsic centers in ceramic and monocrystalline samples of yttrium aluminum garnet were presented. The direct determination of characteristic decay times by approximating the convoluted curves without deconvolution was demonstrated for an exponential luminescence decay profile. Practical significance. The proposed method for the characteristic time detection of luminescence kinetics enables comprehensive analysis of luminescence that can be applied in various sectors of the national economy.

Enhancing the Dynamic Range of OFDM Radars Using Non-Linear Operation and Symbol-Based Equalization

Due to the increased flexibility in terms of waveform generation, digitally-modulated radar systems are gaining increasing popularity among research and academia. The ability to dynamically allocate frequency and time slots, as well as to employ different coding, enables novel multiplexing techniques for multiple-input-multiple-output radars and sensor networks, compared to state-of-the-art chirp-modulated systems. Another significant benefit is the possibility for joint radar and communication with the same hardware. A popular modulation for digital radar is orthogonal frequency-division multiplexing (OFDM), due to its well-known properties from communication applications. It offers all the above-mentioned possibilities, however OFDM radar has two main drawbacks: high peak-to-average power ratio (PAPR) due to the varying signal envelope which significantly increases the linearity requirements on the analog hardware and reduces the power efficiency, as well as a decoupling of target range and frequency-shift, which eliminates the possibility of using a high-pass filter to suppress close targets and thus decreases the sensor's dynamic range in comparison to conventional frequency-modulated continuous-wave (FMCW). The latter weakness is sometimes also viewed as a positive, due to the fact that range-frequency coupling can lead to undesired effects in some cases. This work addresses both of these problems together, which exist in every real-world OFDM radar sensor, and presents detailed analysis, simulation, characterization and measurement validation results that show how these effects negatively influence the signal quality and the obtained range-Doppler map of an automotive radar. Furthermore, a non-linear operation mode with receiver-sided healing that does not require any additional processing steps or computation power during radar operation is proposed. Its high potential is verified by measurements with a 78 GHz prototype setup in an anechoic chamber with static reflectors, as well as an automotive radar echo generator for dynamic targets and extended ranges.

About theory of hybride TWTO and an amplifire with a complex permittivity

The purpose of this work is to construct a nonlinear theory of a hybrid between travelling wave tube (TWT) and an amplifier with a complex permittivity. Methods. The following model is considered: an ion-compensated one-dimensional electron beam penetrates the input travelling wave tube section, then flies into a medium with a complex permittivity, and then enters the output travelling wave tube section. A linear theory of this hybrid is constructed, and its results are compared with the results of the well-known linear theory of travelling wave tube. A nonlinear theory of this hybrid was constructed by a modified wave method, and the results were compared with the nonlinear travelling wave tube theory obtained by the classical Ovcharov–Solntsev’s wave method. In addition, to test the limits of applicability of the obtained results, a stationary nonlinear theory of the hybrid was constructed, obtained using the large particle method. The results of this theory were also compared with the stationary nonlinear travelling wave tube theory constructed using the large particle method. Results and conclusion. Based on the results of the developed theories, it is shown that, under certain parameters, the linear theory and nonlinear theories (both by the modified Ovcharov–Solntsev’s wave method and by the large particle method) make it possible to obtain comparable results both in the case of a classical travelling wave tube and for the hybrid under study. It is shown that under certain parameters, due to the resistive instability, the bunching of electrons can be noticeably improved and, as a result, the gain of the hybrid can exceed the gain in a classical travelling wave tube with the same parameters and the same total length of the device in the linear mode of operation. In the nonlinear mode of operation, the specified hybrid, with optimal environmental parameters, can have significantly higher values of output power and efficiency than travelling wave tube with the same value of the space charge parameter and the Pierce parameter.

Research of the Sound-Absorbing Structureshape Influence on the SAS Acoustic Efficiency in the Nonlinear Operation Mode

This research is focused on the acoustic efficiency of various shapeHelmholtz resonators on non-linear operating modes, with an acoustic pressure level of 130 dB. In this work physical and mathematical models for predicting the effective acoustic properties of SAS cells are formulated. Numerical studies have been performed to assess the acoustic efficacy of honeycomb and cone-shaped sound-absorbing structures samples in an interferometer with a normal incidence of a sound wave in a nonlinear operation mode. The validation of the developed mathematical models was carried out. A comparison of the numerical calculation results with the results of laboratory studies has been carried out. According to the results of the conducted computing experiments, the most effective resonators were identified, and recommendations on the SAS design based on the most effective resonators were formulated.

Slow 0.1 Hz Breathing and Body Posture Induced Perturbations of RRI and Respiratory Signal Complexity and Cardiorespiratory Coupling.

Objective: We explored the physiological background of the non-linear operating mode of cardiorespiratory oscillators as the fundamental question of cardiorespiratory homeodynamics and as a prerequisite for the understanding of neurocardiovascular diseases. We investigated 20 healthy human subjects for changes using electrocardiac RR interval (RRI) and respiratory signal (Resp) Detrended Fluctuation Analysis (DFA, α1RRI, α2RRI, α1Resp, α2Resp), Multiple Scaling Entropy (MSERRI1−4, MSERRI5−10, MSEResp1−4, MSEResp5−10), spectral coherence (CohRRI−Resp), cross DFA (ρ1 and ρ2) and cross MSE (XMSE1−4 and XMSE5−10) indices in four physiological conditions: supine with spontaneous breathing, standing with spontaneous breathing, supine with 0.1 Hz breathing and standing with 0.1 Hz breathing.Main results: Standing is primarily characterized by the change of RRI parameters, insensitivity to change with respiratory parameters, decrease of CohRRI−Resp and insensitivity to change of in ρ1, ρ2, XMSE1−4, and XMSE5−10. Slow breathing in supine position was characterized by the change of the linear and non-linear parameters of both signals, reflecting the dominant vagal RRI modulation and the impact of slow 0.1 Hz breathing on Resp parameters. CohRRI−Resp did not change with respect to supine position, while ρ1 increased. Slow breathing in standing reflected the qualitatively specific state of autonomic regulation with striking impact on both cardiac and respiratory parameters, with specific patterns of cardiorespiratory coupling.Significance: Our results show that cardiac and respiratory short term and long term complexity parameters have different, state dependent patterns. Sympathovagal non-linear interactions are dependent on the pattern of their activation, having different scaling properties when individually activated with respect to the state of their joint activation. All investigated states induced a change of α1 vs. α2 relationship, which can be accurately expressed by the proposed measure—inter-fractal angle θ. Short scale (α1 vs. MSE1−4) and long scale (α2 vs. MSE5−10) complexity measures had reciprocal interrelation in standing with 0.1 Hz breathing, with specific cardiorespiratory coupling pattern (ρ1 vs. XMSE1−4). These results support the hypothesis of hierarchical organization of cardiorespiratory complexity mechanisms and their recruitment in ascendant manner with respect to the increase of behavioral challenge complexity. Specific and comprehensive cardiorespiratory regulation in standing with 0.1 Hz breathing suggests this state as the potentially most beneficial maneuver for cardiorespiratory conditioning.

Acoustic Resistance of an Orifice at High Sound Pressure Levels

The effect of sound pressure level on acoustic resistance of an orifice in a baffle is investigated based on the measurements in an impedance tube by the two-microphone method. Dependences of the resistance of an orifice on the diameter of the latter are obtained for the case of nonlinear mode of operation. It is shown that, in this case, the resistance of the orifice depends on its diameter. The dependence of the nonlinear resistance on particle velocity in the orifice is approximated by a linear function.

Experimental investigation of nonlinear operation mode of a DP-QPSK 100G link with co-propagating-pump Raman amplification

The nonlinear interference noise in a coherent single-span fibre-optic communication link (FOCL) with co-propagating Raman amplification is investigated at different levels of input Raman pump and channel powers and dispersion. A simple phenomenological expression for calculating the nonlinear noise power at the output of a single-channel FOCL is presented. The merit of using a distributed Raman amplifier with co-propagating pump up to 1 W in a single-span single-channel FOCL is experimentally investigated.

Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules

Chemists have created molecular machines and switches with specific mechanical responses that were typically demonstrated in solution, where mechanically relevant motion is dissipated in the Brownian storm. The next challenge consists of designing specific mechanisms through which the action of individual molecules is transmitted to a supramolecular architecture, with a sense of directionality. Cellular microtubules are capable of meeting such a challenge. While their capacity to generate pushing forces by ratcheting growth is well known, conversely these versatile machines can also pull microscopic objects apart through a burst of their rigid tubular structure. One essential feature of this disassembling mechanism is the accumulation of strain in the tubules, which develops when tubulin dimers change shape, triggered by a hydrolysis event. We envision a strategy toward supramolecular machines generating directional pulling forces by harnessing the mechanically purposeful motion of molecular switches in supramolecular tubules. Here, we report on wholly synthetic, water-soluble, and chiral tubules that incorporate photoswitchable building blocks in their supramolecular architecture. Under illumination, these tubules display a nonlinear operation mode, by which light is transformed into units of strain by the shape changes of individual switches, until a threshold is reached and the tubules unleash the strain energy. The operation of this wholly synthetic and stripped-down system compares to the conformational wave by which cellular microtubules disassemble. Additionally, atomistic simulations provide molecular insight into how strain accumulates to induce destabilization. Our findings pave the way toward supramolecular machines that would photogenerate pulling forces, at the nanoscale and beyond.

Ultimate limits in the gas composition determination within small sealed volumes by quadrupole mass spectrometry

Miniaturization of modern sealed vacuum devices and higher demands for their stable operation require accurate determination of the gas composition in the early stage of their operation as well as after a long operational period. Among a few highly sensitive gas methods, quadrupole mass spectrometry seems to be the most appropriate one for this task as gas amounts are well below 1·10−4 mbar L. In this paper, a new approach, how to prepare a quadrupole mass spectrometer for routine quantitative analysis of small gas amounts, is described. In the first stage, it was calibrated by an innovative in-situ procedure using three different gases: nitrogen, argon and neon. Each gas was admitted into a chamber with a precisely determined volume equipped by a capacitance manometer. By opening the variable leak valve, ion current versus flow rate dependence was determined over three orders of magnitude. Non-linear response at very low flow rates was detected. In the next stage, gas quantities from 3·10−5 mbar L to 6·10−7 mbar L of pure gas were admitted, which proved that by numerical correction of non-linearity, the achieved accuracy of gas quantity determination could be noticeably improved. Rather poor results were on the contrary obtained when synthetic gas mixtures were analysed. Additional calibrations with gas mixtures revealed a strong interference provoked by argon. It enhanced the instrument's sensitivity for nitrogen for a factor of up to 2.3, depending on argon fraction. Considering this effect, further corrections led to a substantially improved accuracy of the nitrogen fraction determination in small gas amount mixtures. In general, quantification of very small gas amounts needs a careful analysis of all contributions influencing the accuracy, as the number of data points is limited and mostly recorded in the non-linear mode of the instrument's operation.

Large Current GaAs PCSS Triggered by a Laser Diode

We have fabricated a 2-mm gap semi-insulating GaAs photoconductive semiconductor switch (PCSS), and obtained a 1.45-kA large current under a bias voltage of 6 kV when the PCSS was triggered by a 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> J commercial laser diode. An RLC transient circuit model was employed to get the electrical properties of the PCSS in the transient discharge process. The reason for the switch exiting from nonlinear operating mode was that the electric field across the switch dropped below the lock-on field. This letter shows the attractive prospect of a low-cost compact high-power pulse source with the GaAs PCSS.

Performance evaluation of transmission of electricity in the sip–lines in electric distribution networks

A method of performance evaluation of electricity transmission through modern electricity transmission SIP-lines of electric distribution networks in conditions of abruptly variable, nonlinear and asymmetric operation mode of electricity consumers was proposed in the paper. The specified operation mode of consumers meet modern operation conditions of the electrical network and is almost not considered in existing calculation methods of the actual electricity losses in the network that does not allow to adequately assess real energy efficiency of electric networks. The proposed evaluation method of electricity losses is based on measuring the current THD and values of harmonic components of currents and voltages in the network that allows to use existing measuring instruments - electricity quality analyzers for evaluation. The relationship between the measured electricity quality parameters and the instantaneous voltage change rate allows to estimate the share of electricity losses, which is caused by abruptly variable, nonlinear and asymmetric operation mode of consumers. Application of the developed method allows to assess the level of additional electricity losses in order to analyze the causes of the deterioration of electricity transmission efficiency, reduce these losses and increase energy efficiency of electricity transmission through the network. It was shown that in the modern electric distribution networks, additional electricity losses are almost 10% due to the presence of higher harmonic components of currents and voltages in the electric network.

Flexure-FET biosensor to break the fundamental sensitivity limits of nanobiosensors using nonlinear electromechanical coupling

In this article, we propose a Flexure-FET (flexure sensitive field effect transistor) ultrasensitive biosensor that utilizes the nonlinear electromechanical coupling to overcome the fundamental sensitivity limits of classical electrical or mechanical nanoscale biosensors. The stiffness of the suspended gate of Flexure-FET changes with the capture of the target biomolecules, and the corresponding change in the gate shape or deflection is reflected in the drain current of FET. The Flexure-FET is configured to operate such that the gate is biased near pull-in instability, and the FET-channel is biased in the subthreshold regime. In this coupled nonlinear operating mode, the sensitivity (S) of Flexure-FET with respect to the captured molecule density (N(s)) is shown to be exponentially higher than that of any other electrical or mechanical biosensor. In other words, while S(Flexure) ~ e(γ1 [square root]Ns-γ2Ns), classical electrical or mechanical biosensors are limited to S(classical) ~ γ(3)N(S) or γ(4) ln(N(S)), where γ(i) are sensor-specific constants. In addition, the proposed sensor can detect both charged and charge-neutral biomolecules, without requiring a reference electrode or any sophisticated instrumentation, making it a potential candidate for various low-cost, point-of-care applications.

First results from plasma density measurements in the FTU tokamak by means of a two-frequency pulsed time-of-flight refractometer

A pulsed time-of-flight refractometer was developed and tested to determine the mean plasma density in the T-11M tokamak by measuring the propagation time of nanosecond microwave pulses in plasma. Later, it was also proposed to use such an instrument to measure and control the mean plasma density in the ITER tokamak by probing the plasma with an extraordinary wave, the electric field of which is perpendicular to the magnetic field in plasma, in the transparency window at frequencies of 50–100 GHz. To avoid the effect of the density profile shape on the measurement results in the nonlinear mode of refractometer operation (near the cutoff), a system operating at two different probing frequencies was developed and tested. Such a system provides two values of the time delay, which can be used to estimate the peaking factor of the density distribution α and correctly determine the linear density 〈Nl〉, regardless of the density profile (assuming a smooth density profile of the form of N(ρ) = N(0)(1 − ρ2)α, where N(0) is the central plasma density and ρ = r/a is the normalized plasma radius). The first experiments on density measurements in the FTU tokamak performed with this refractometer are described, and results from these experiments are presented. The formation of a thin dense plasma layer in the zone of a strong magnetic field (the so-called MARFE layer) at a relatively low (for FTU) plasma density of ∼6 × 1019 m−3 was detected. The thickness of this layer, determined from the refractometry data, agrees well with the data obtained using a digital camera.

Signal reception against the background of strong interference exceeding the dynamic range of a receiver

We analyze nonlinear distortions of a useful signal in an input amplifier of the receiver under the influence of strong interference which switches the input active circuits of the receiver to a nonlinear operation mode. The method of signal reception under the conditions of strong interference is proposed. This method is based on crosstalk correction. The results of experimental testing of this method are presented.

Comparison of measured acoustic power results gained by using three different methods on an ultrasonic low-frequency device

The theme of this work is characterization of an ultrasonic low-frequency device, driven at an excitation frequency of around 25 kHz at different electrical excitation levels by using three different methods as proposed in IEC 61847 and IEC 61088 standards. The first method is based on the electromechanical characterization of the device. It consists of measuring the input electrical impedance around the excitation frequency in the unloaded and loaded conditions at a low level excitation voltage of 1 V. The equivalent RLC electrical circuit parameters of an unloaded and loaded device are determined in an anechoic tank and in a vessel at different immersion depths and tip positions in a complex geometry. The electroacoustic efficiency factor of the method is determined by knowing the real part of the radiation resistance and mechanical loss resistance which are transformed into an equivalent RLC electrical circuit of the transducer. The second method consists of measuring the spatial pressure distribution of an ultrasonic device near pressure release boundary in an anechoic tank. The acoustic reciprocity principle is used to determine the derived acoustic power of an equivalent point source in the form of radially oscillating sphere at the excitation frequency. The third method is based on the measurement of power dissipated in a restricted volume of water by using a calorimetric method. Some of the suggested methods are complicated to apply in the high energy ultrasonic devices whose size is much lower than the wavelength in the loading medium due to the occurrence of strong cavitation activity and influence of the sonotrode tip position in the complex standing wave field. However, the measured acoustic power found by using the three suggested methods is compared by means of the electroacoustic efficiency factor defined for each considered method. In the electromechanical characterization, which is made at low electrical excitation levels (applied electrical power of 1 mW at the series resonance frequency), the calculated maximum electroacoustic efficiency factor is around 48% when the influence of standing waves pattern on the radiation resistance is small. It is approximately the same as the one obtained by measuring the derived acoustic power in an anechoic tank (43%) without cavitation activity in front of the tip. When a strong cavitation activity is present in the loading medium, the bubble cloud has a significant influence on the derived acoustic power which is then dispersed in a broad frequency range and the electroacoustic efficiency factor of the method decreases down to 2%. A significant growth of the input electrical impedance magnitude at the excitation frequency is observed when the cavitation activity is present in front of the tip and when it is compared with the impedance magnitude measured at lower excitation levels without cavitation. The power dissipated in the loading medium almost linearly depends on the applied electrical power, with saturation at higher excitation levels. In the linear operating mode the electroacoustic efficiency factor of the calorimetric method (48%) is comparable with the efficiency factors of two other methods. In the nonlinear operating mode, it is larger (71%) due to a significant amount of heat energy released during the cavitation process.

Measuring derived acoustic power of an ultrasound surgical device in the linear and nonlinear operating modes

Objective and motivation The method for measuring derived acoustic power of an ultrasound point source in the form of a sonotrode tip has been considered in the free acoustic field, according to the IEC 61847 standard. The main objective of this work is measuring averaged pressure magnitude spatial distribution of an sonotrode tip in the free acoustic field conditions at different electrical excitation levels and calculation of the derived acoustic power at excitation frequency ( f 0 ≈ 25 kHz). Finding the derived acoustic power of an ultrasonic surgical device in the strong cavitation regime of working, even in the considered laboratory conditions (anechoic pool), will enable better understanding of the biological effects on the tissue produced during operation with the considered device. Experimental method The pressure magnitude spatial distribution is measured using B&K 8103 hydrophone connected with a B&K 2626 conditioning amplifier, digital storage oscilloscope LeCroy Waverunner 474, where pressure waveforms in the field points are recorded. Using MATLAB with DSP processing toolbox, averaged power spectrum density of recorded pressure signals in different field positions is calculated. The measured pressure magnitude spatial distributions are fitted with the appropriate theoretical models. Theoretical approaches In the linear operating mode, using the acoustic reciprocity principle, the sonotrode tip is theoretically described as radially oscillating sphere (ROS) and transversely oscillating sphere (TOS) in the vicinity of pressure release boundary. The measured pressure magnitude spatial distribution is fitted with theoretical curves, describing the pressure field of the considered theoretical models. The velocity and displacement magnitudes with derived acoustic power of equivalent theoretical sources are found, and the electroacoustic efficiency factor is calculated. When the transmitter is excited at higher electrical power levels, the displacement magnitude of sonotrode tip is increased, and nonlinear behaviour in loading medium appears, with strong cavitation activity produced hydrodynamically. The presence of harmonics, subharmonics and ultraharmonics as a consequence of stable cavitation is evident in the averaged power spectral density. The cavitation noise with continuous frequency components is present as a consequence of transient cavitation. The averaged pressure magnitude at the frequency components of interest (discrete and continous) in the field points is found by calculating average power spectral density of the recorded pressure waveform signal using the welch method. The frequency band of interest where average power spectral density is calculated is in the range from 15 Hz up to 120 kHz due to measurement system restrictions. The novelty in the approach is the application of the acoustic reciprocity principle on the nonlinear system (sonotrode tip and bubble cloud) to find neccessary acoustic power of the equivalent acoustic source to produce the measured pressure magnitude in the field points at the frequency components of interest. Results In the nonlinear operating mode, the ROS model for the considered sonotrode tip is chosen due to the better agreement between measurement results and theoretical considerations. At higher excitation levels, it is shown that the averaged pressure magnitude spatial distribution of discrete frequency components, produced due to stable cavitation, can be fitted in the far field with the inverse distance law. The reduced electroacoustic efficiency factor, calculated at excitation frequency component as ratio of derived acoustic power with applied electrical power, is reduced from 40% in the linear to 3% in the strong nonlinear operating mode. The derived acoustic power at other frequency components (subharmonic, harmonic and ultraharmonic) is negligible in comparison with the derived acoustic power at excitation frequency. Discussion and conclusions The sonotrode tip and loading medium are shown in the strong cavitation regime as the coupled nonlinear dynamical system radiating acoustic power at frequency components appearing in the spectrum. The bubble cloud in the strong nonlinear operating mode decreases the derived acoustic power significantly at the excitation frequency.

The nonequilibrium thermodynamic conditions and properties of materials

The basic principles for classifying the properties of materials, measured under nonequilibrium thermodynamic conditions, are formulated. It is proposed to supplement the nonlinear nonequilibrium thermodynamic mode of operation by new submodes, the area of action of which is determined by the dimensionless criteria introduced. The heat flux relaxation time and the temperature gradient time are considered as new nonlinear properties.

Extrinsic parameter extraction and RF modelling of CMOS

An analytical approach for CMOS parameter extraction which includes the effect of parasitic resistance is presented. The method is based on small-signal equivalent circuit valid in all region of operation to uniquely extract extrinsic resistances, which can be used to extend the industry standard BSIM3v3 MOSFET model for radio frequency applications. The verification of the model was carried out through frequency domain measurements of S-parameters and direct time domain measurement at 2.4 GHz in a large signal non-linear mode of operation.