Nonlinear Transducer Research Articles

Acoustic tomography for velocity estimation in high temperature flows

Accurately measuring the temperature of a gas flow is essential for monitoring purposes in many energy conversion applications. Typically, this is achieved using either contact measurement techniques, like thermocouple sensors, or radiation-based methods, like optic pyrometry. In harsh conditions, contact measurement techniques are prone to degradation due to the high oxidizing and high-temperature environment, thus reducing sensor lifespan. Radiation-based methods, on the other hand, rely on expensive and highly non-linear transduction systems. Acoustic pyrometry is attracting an increasing interest as it allows the estimation of the temperature distribution in a section by computing the time of flight of acoustic waves. If two measurement sections, at different axial positions, are considered, the same theoretical approach can be adapted to also compute the velocity map of the flow (acoustic tomography). However, the complexity of the mathematical problem to be solved for such a calculation needs a careful analysis. In this study, starting from a known temperature and velocity profile, a reconstruction algorithm was developed and tuned with a particular focus on velocity estimation. Relevant guidelines for a proper application of this measurement technique were also derived.

Reduced Device Count for Self Balancing Switched-Capacitor Multilevel Inverter Integration with Renewable Energy Source

In this study, a new switched-capacitor-based seven-level inverter topology with a photovoltaic system is presented. The proposed topology requires a smaller number of devices and has the ability to self-balance the voltage across the capacitor. The proposed topology configuration is simple and has the ability to extend to higher levels of voltage. This multilevel inverter topology is suitable for low- and medium-voltage applications with photovoltaic (PV) system integration. To improve the PV system efficiency as an input of a DC–DC boost converter, a Fuzzy logic-based maximum power point controller technique is used. A PV system with a DC–DC boost converter integrates with the proposed seven-level inverter topology. The anti-predatory particle swarm optimization (APSO) technique is used to solve the non-linear transduction equations of the seven-level PV switched-capacitor-based multilevel inverter (7L−PV−SCMLI) topology. The proposed APSO is described to minimize the harmonics in the multilevel inverter (MLIs), which is a complex optimization problem involving a non-linear transcendental equation. Furthermore, APSO can be applied in order to solve non-linear transcendental equations for all symmetrical and asymmetrical MLIs that have equal and non-equal DC sources. The APSO-based selected harmonic elimination (SHE) technique obtained the best switching angle value, and the optimized obtained switching angles reduced the total harmonic distortion (THD) of 7L−PV−SCMLI.

A method to improve the modulation depth servo accuracy of an integrated fiber-optic gyroscope using the Bouc-Wen model

The development of integrated fiber-optic gyroscopes using piezoelectric modulation (PEM) represents a significant advance in the field of fiber-optic gyroscopes. However, the hysteretic creep nonlinearity of Piezoe-lectric Transducer (PZT) affects the modulation depth monitoring and leads to a drift of its resonant frequency. The accuracy of the PEM's closed-loop feedback signal determines the open-loop gyroscope's accuracy. However, the hysteresis deteriorates the controller phase and the gain margin, inducing the fluctuation of the amplitude of each harmonic wave, which undoubtedly increases the difficulty of the closed-loop feedback control of the modulator. This paper proposes a method to quantify the high-frequency hysteresis nonlinearity of PZT, combining the advantages of feedforward compensation and feedback closed-loop. Feedforward compensation is used to reduce the hysteresis nonlinearity of PEM, reduce the interference of the nonlinear phase shift to zero drift, and increase the control accuracy of feedback control to PEM under temperature disturbance.

A simple model of binocular luster.

The dichoptic combination of simple center–surround stimuli showing a contrast difference between eyes can trigger a lustrous impression in the fused percept, particularly when the contrast polarities in the two input images are of opposite sign. Recent developments suggest that the phenomenon of binocular luster results from a neural conflict between ON and OFF visual pathways at an early binocular level. Support for this idea was found in a previous study in which the empirical luster judgments strongly correlated with the predictions of an interocular conflict model which was based on such ON–OFF pairings. However, our original model could not account for the fact that weaker lustrous sensations can also be evoked by stimuli showing contrast polarities of same sign between eyes. In the present study we present an improved model that also includes ON–ON and OFF–OFF pairings. The predictive power of this model was tested in a series of four experiments, using a total of about 500 different center–ring–surround configurations as test stimuli. We found that, overall, our modified version accounts for more than 80% of the variance in the empirical luster judgments and that the former problems could be largely resolved. Our results further suggest a nonlinear transducer function for the binocular conflict signals.

Loudspeaker virtualization–Part I: Digital modeling and implementation of the nonlinear transducer equivalent circuit

This manuscript, the first of a two-part series, presents a methodology for efficiently implementing an equivalent circuit of nonlinear loudspeakers in the discrete-time domain. This is a crucial step that will allow us to design new algorithms for loudspeaker virtualization in part II of this series. The presented implementation, in fact, is based on Wave Digital Filter (WDF) principles, which lead to a fully explicit model, in the sense that no iterative solvers are needed to compute the output signal. The proposed WDF is highly efficient and modular, since the reference circuit is modeled as a computable interconnection of input-output processing blocks. The accuracy of the implementation is confirmed by comparing it to a ground-truth SPICE simulation of the reference circuit and to measurements on real loudspeakers. This confirms that the proposed Wave Digital modeling approach can be reliably used for the rapid simulation of the transduction behavior of a loudspeaker (within the frequency limits of validity of the equivalent circuit), and can be employed to develop the digital preprocessing method for loudspeaker virtualization described in the second manuscript of this two-part series.

Low-Frequency Oscillations in Optical Measurements of Metal-Nanoparticle Vibrations.

Time-resolved optical measurements of vibrating metal nanoparticles have been used extensively to probe the ultrafast mechanical properties of the nanoparticles and of the surrounding liquid, but nearly all investigations so far have been limited to the linear regime. Here, we report the observation of a low-frequency oscillating signal in transient-absorption measurements of nanoparticles with octahedral gold cores and cubic silver shells; the signal appears at the difference of two mechanical vibrational frequencies in the particles, suggesting a nonlinear mixing process. We tentatively attribute this proposed mixing to a nonlinear coupling between a vibrational mode of the nanoparticle and its optical-frequency plasmon resonance. The optimization of this nonlinear transduction may enable high-efficiency opto-mechanical frequency mixing in the GHz-THz frequency regime.

Contributed Session II: Evidence for a dipper effect in the perception of global form: findings from psychophysics and EEG.

Decades of psychophysical experiments have shown that the perception of low luminance contrast violates Webers' law: contrast discrimination is best at low (but non-zero) pedestal intensities. This "dipper effect" is thought to be the product of a sigmoidal neuronal transducer function in the early stages of visual processing which is expansive at low contrasts. Here, we ask 1) whether the transducer that governs the perception of global form is subject to a similar nonlinearity and 2) if sensitivity is biased towards a certain axis of pattern alignment (translational, radial, concentric). Using a combination of psychophysics and steady-state VEPs, we examined observers' sensitivity to global form by manipulating the dipole orientation coherence of Glass patterns. Our psychophysical data indicate a Glass pattern "dipper effect" that is strongest for concentric patterns, while our EEG results show some evidence of nonlinear transduction but do not have the form predicted by psychophysical thresholds. Our findings indicate that, like low-level contrast, mid-level form discrimination is subject to mild facilitation (relative to detection) at low global form coherences, and suggest that this could be driven by neurons with nonlinear transducer functions.

Cavity Optomechanical Sensing in the Nonlinear Saturation Limit

AbstractPhotonic sensors based upon high‐quality microcavities have found a wide variety of applications ranging from inertial sensing, electro‐ and magnetometry to chemical and biological sensing. These sensors have a dynamic range limited by the linewidth of the cavity mode transducing the input. This dynamic range not only determines the range of the signal strength that can be detected, but also affects the resilience of the sensor against large deteriorating external perturbations and shocks in a practical environment. Unfortunately, there is a general trade‐off between the detection sensitivity and the dynamic range, which undermines the performance of all microcavity‐based sensors. Here, an approach is proposed to extend the dynamic range significantly beyond the cavity linewidth limit by exploiting the periodic nature of the modulation signal, making measurements in the nonlinear transduction regime without degrading the detection sensitivity for weak signals. With a cavity optomechanical system, a dynamic range of over six times larger than the cavity linewidth is experimentally demonstrated, far beyond the conventional linear region of operation for such a sensor. This approach will help design microcavity‐based sensors to achieve high detection sensitivity and a large dynamic range at the same time, a crucial property for their use in a practical environment.

Simulation and visualization of the interference phenomena inside DC SQUID with interferometric circuit model

Flux modulated static current-voltage characteristics are the basis of DC SQUID being the flux-to-voltage convertor utilized in high-performance magnetic field measurement systems. Those static behaviors are the results of the internal quantum interference between two Josephson junctions. However, the interferometric working principle and the interference phenomena are difficult to be intuitively visualized, either through simulation with conventional models, or through the in-situ measurement inside DC SQUID. Therefore, we redraw the equivalent circuit of DC SQUID in form of the microwave interferometer, and transform it into a concise dynamic system model to study the interferometric mechanism. The double-slit like interference phenomena inside the DC SQUID are visualized through simulations of the AC oscillation current and voltage along the SQUID washer. The concept that DC SQUID is a microwave integrated circuit working as the microwave interferometer rather than a static nonlinear transducer is demonstrated and emphasized. Those concepts help users and designers improve their understandings of quantum interference mechanism of DC SQUID for both circuit design and the practical application system development.

Nonlinear transduction of emotional facial expression

To create neural representations of external stimuli, the brain performs a number of processing steps that transform its inputs. For fundamental attributes, such as stimulus contrast, this involves one or more nonlinearities that are believed to optimise the neural code to represent features of the natural environment. Here we ask if the same is also true of more complex stimulus dimensions, such as emotional facial expression. We report the results of three experiments combining morphed facial stimuli with electrophysiological and psychophysical methods to measure the function mapping emotional expression intensity to internal response. The results converge on a nonlinearity that accelerates over weak expressions, and then becomes shallower for stronger expressions, similar to the situation for lower level stimulus properties. We further demonstrate that the nonlinearity is not attributable to the morphing procedure used in stimulus generation.

Informational masking of negative masking.

Negative masking (NM) is a ubiquitous finding in near-"threshold" psychophysics in which the detectability of a near-threshold signal improves when added to a copy of itself, i.e., a pedestal or masker. One interpretation of NM suggests that the pedestal acts as an informative cue, thereby reducing uncertainty and improving performance relative to detection in its absence. The purpose of this study was to test this hypothesis. Intensity discrimination thresholds were measured for 100-ms, 1000-Hz near-threshold tones. In the reference condition, thresholds were measured in quiet (no masker other than the pedestal). In comparison conditions, thresholds were measured in the presence of one of two additional maskers: a notched-noise masker or a random-frequency multitone masker. The additional maskers were intended to cause different amounts of uncertainty and, in turn, to differentially influence NM. The results were generally consistent with an uncertainty-based interpretation of NM: NM was found both in quiet and in notched-noise, yet it was eliminated by the multitone masker. A competing interpretation of NM based on nonlinear transduction does not account for all of the results. Profile analysis may have been a factor in performance and this suggests that NM may be attributable to, or influenced by, multiple mechanisms.

Interocular difference thresholds are mediated by binocular differencing, not summing, channels.

Patterns in the two eyes' views that are not identical in hue or contrast often elicit an impression of luster, providing a cue for discriminating them from perfectly matched patterns. Here we attempt to determine the mechanisms for detecting interocular differences in luminance contrast, in particular in relation to the possible contributions of binocular differencing and binocular summing channels. Test patterns were horizontally oriented multi-spatial-frequency luminance-grating patterns subject to variable amounts of interocular difference in grating phase, resulting in varying degrees of local interocular contrast difference. Two types of experiment were conducted. In the first, subjects discriminated between a pedestal with an interocular difference that ranged upward from zero (i.e., binocularly correlated) and a test pattern that contained a bigger interocular difference. In the second type of experiment, subjects discriminated between a pedestal with an interocular difference that ranged downward from a maximum (i.e., binocularly anticorrelated) and a test pattern that contained smaller interocular difference. The two types of task could be mediated by a binocular differencing and a binocular summing channel, respectively. However, we found that the results from both experiments were well described by a simpler model in which a single, linear binocular differencing channel is followed by a standard nonlinear transducer that is expansive for small signals but strongly compressive for large ones. Possible reasons for the lack of involvement of a binocular summing channel are discussed in the context of a model that incorporates the responses of both monocular and binocular channels.

Controlled flight of a microrobot powered by soft artificial muscles.

Flying insects capable of navigating in highly cluttered natural environments can withstand in-flight collisions because of the combination of their low inertia1 and the resilience of their wings2, exoskeletons1 and muscles. Current insect-scale (less than ten centimetres long and weighing less than five grams) aerial robots3-6 use rigid microscale actuators, which are typically fragile under external impact. Biomimetic artificial muscles7-10 that are capable of large deformation offer a promising alternative for actuation because they can endure the stresses caused by such impacts. However, existing soft actuators11-13 have not yet demonstrated sufficient power density to achieve lift-off, and their actuation nonlinearity and limited bandwidth create further challenges for achieving closed-loop (driven by an input control signal that is adjusted based on sensory feedback) flight control. Here we develop heavier-than-air aerial robots powered by soft artificial muscles that demonstrate open-loop (driven by a predetermined signal without feedback), passively stable (upright during flight) ascending flight as well as closed-loop, hovering flight. The robots are driven by multi-layered dielectric elastomer actuators that weigh 100 milligrams each and have a resonance frequency of 500 hertz and power density of 600 watts per kilogram. To increase the mechanical power output of the actuator and to demonstrate flight control, we present ways to overcome challenges unique to soft actuators, such as nonlinear transduction and dynamic buckling. These robots can sense and withstand collisions with surrounding obstacles and can recover from in-flight collisions by exploiting material robustness and vehicle passive stability. We also fly two micro-aerial vehicles simultaneously in a cluttered environment. They collide with the wall and each other without suffering damage. These robots rely on offboard amplifiers and an external motion-capture system to provide power to the dielectric elastomer actuators and to control their flight. Our work demonstrates how soft actuators can achieve sufficient power density and bandwidth to enable controlled flight, illustrating the potential of developing next-generation agile soft robots.

Dynamic Nonlinearity in Piezoelectric Flexural Ultrasonic Transducers

The flexural ultrasonic transducer is a unimorph device which typically comprises a piezoelectric ceramic bonded to a metallic membrane. It is widely applied in industrial applications for metrology and proximity sensing. However, the electromechanical and dynamic characteristics of this class of transducer have only recently been reported, and the influence of different excitation levels on dynamic nonlinearity remains unclear. Dynamic nonlinearity in high-power piezoelectric ultrasonic transducers is familiar, where the performance or dynamic stability of the transducer can significantly reduce under high amplitudes of excitation. Nonlinearity can manifest as measurable phenomena such as resonance frequency drift, influenced by thermomechanical phenomena or structural constraints. There is relatively little reported science of the dynamic nonlinearity in the vibration response of flexural ultrasonic transducers. This study examines the vibration responses of four flexural ultrasonic transducers, showing the existence of dynamic nonlinearity for increases in excitation voltage. An analytical solution of the governing equations of motion for the flexural ultrasonic transducer is presented which complements the experimental investigation, and suggests a close relationship between material properties and nonlinearity. This research demonstrates a detailed dynamic characterization of the flexural ultrasonic transducer, showing the potential for the optimization of dynamic performance in industrial measurement applications.

Detection and intensity discrimination of a sinusoid with and without masker uncertainty

The effect of stimulus-based uncertainty on the shape of the masking function at circa-threshold pedestal levels was investigated. Of particular interest was how uncertainty regarding properties of the masker affects the magnitude of “negative masking” [Raab et al., J. Acoust. Soc. Am. 35, 1053 (1963)] that is obtained under different stimulus configurations. Intensity discrimination thresholds for gated, 100-ms, 1000-Hz sinusoids were measured at three pedestal levels: -9, 0, and 9 dB re: absolute threshold. A two-interval, two-alternative forced-choice procedure was used. Under the reference condition, thresholds were measured in quiet. In comparison conditions, thresholds were measured in the presence of one of two masker types: (1) a notched-noise masker or (2) a random-frequency, multicomponent masker. In the multicomponent masker condition, uncertainty was imposed by roving the frequency components that comprised the masker from interval-to-interval over a block of trials. The data under each condition were fit with psychometric functions and slope estimates were obtained. Results are discussed with respect to the factors that govern, and possible mechanisms underlying, negative masking. Specifically, two possible explanations for the “dip” in the masking function are examined: nonlinear transduction [Hanna et al., J. Acoust. Soc. Am. 80, 1335 (1986)] and observer uncertainty.

Calibrated Phase-Shifting Digital Holographic Microscope Using a Sampling Moiré Technique

A calibrated phase-shifting digital holographic microscope system capable of improving the quality of reconstructed images is proposed. Phase-shifting errors are introduced in phase-shifted holograms for numerous reasons, such as the non-linearity of piezoelectric transducers (PZTs), wavelength fluctuations in lasers, and environmental disturbances, leading to poor-quality reconstructions. In our system, in addition to the camera used to record object information, an extra camera is used to record interferograms, which are used to analyze phase-shifting errors using a sampling Moiré technique. The quality of the reconstructed object images can be improved by the phase-shifting error compensation algorithm. Both the numerical simulation and experiment demonstrate the effectiveness of the proposed system.

Nonlinearity in the Dynamic Response of Flexural Ultrasonic Transducers

Recent studies of the electro-mechanical behavior of flexural ultrasonic transducers have shown that their response can be considered as three distinct characteristic regions, the first building towards a steady state, followed by oscillation at the driving frequency in the steady state, before an exponential decay from the steady state at the transducer's dominant resonance frequency, once the driving force is removed. Despite the widespread industrial use of these transducers as ultrasonic proximity sensors, there is little published information on their vibration characteristics under different operating conditions. Flexual transducers are composed of a piezoelectric ceramic disc bonded to the inner surface of a metallic cap, the membrane of which bends in response to the high-frequency ceramic vibrations of the ceramic. Piezoelectric devices can be subject to nonlinear behavior, but there is no reported detail of the nonlinearity in flexural transducers. Experimental investigation through laser Doppler vibrometry shows strong nonlinearity in the vibration response, where resonance frequency reduces with increasing vibration amplitude.

The Integration of Color-Selective Mechanisms in Symmetry Detection

We studied how the visual system detects multicolor symmetric patterns by manipulating the number of colors in an image in both isoluminance and luminance conditions. With a two-interval forced choice noise masking paradigm, we presented a noise mask in both intervals of each trial. A vertically symmetric target was randomly presented in one interval while a noise control was presented in the other. The task of the observers was to determine which interval contained the target. The target detection threshold was measured at various noise mask densities, which was found to decrease 1.4- to 2.5-fold as the number of colors in the image went up at median to high noise densities across different conditions. In addition, this color facilitation effect was greater in luminance conditions than in isoluminance conditions. Our data cannot be explained by the probability summation theory or simple signal-to-noise ratio. We therefore propose a computational model that incorporates a linear chromatic symmetry register, a nonlinear transducer response, noise manipulation and a multiple channel decision making process. This model suggests that the increment of the number of colors reduces the interference to the symmetry channels produced by noise, and in turn facilitates symmetry detection.

Vocal efficiency of electrolaryngeal speech production

From the perspective of efficiency, this article studied the energy transfer and conversion in the process of electrolaryngeal (EL) speech production. An overall vocal efficiency of EL speech production was defined as the ratio of the acoustic power of the EL speech to the electric power supplied by the battery. The measurements of a commercial EL showed that the actual utilization efficiency of the battery energy was no more than 0.1%. The energy transfer process was divided into three successive stages. The corresponding efficiencies of these stages were defined and estimated to analyze potential power losses and possible impact of two factors (EL cap and vowel) on the vocal efficiency. It was concluded that the non-linear transducer of the EL device and the physiological features of the neck tissue were the main reasons for the high power losses and low vocal efficiency. Furthermore, both EL cap and phonation vowel showed significant effects on the EL vocal efficiency. Thus, improvement of EL linear vibrator and compatible cap will be beneficial to raising the vocal efficiency and improving the EL speech quality.

Dissimilar trend of nonlinearity in ultrasound transducers and systems at resonance and non-resonance frequencies

Several factors can affect performance of an ultrasound system such as quality of excitation signal and ultrasound transducer behaviour. Nonlinearity of piezoelectric ultrasound transducers is a key determinant in designing a proper driving power supply. Although, the nonlinearity of piezoelectric transducer impedance has been discussed in different literatures, the trend of the nonlinearity at different frequencies with respect to excitation voltage variations has not been clearly investigated in practice. In this paper, to demonstrate how the nonlinearity behaves, a sandwich piezoceramic transducer was excited at different frequencies. Different excitation signals were generated using a linear power amplifier and a multilevel converter within a range of 30–200V. Empirical relation was developed to express the resistance of the piezoelectric transducer as a nonlinear function of both excitation voltage and resonance frequency. The impedance measurements revealed that at higher voltage ranges, the piezoelectric transducer can be easily saturated. Also, it was shown that for the developed ultrasound system composed of two transducers (one transmitter and one receiver), the output voltage measured across receiver is a function of a voltage across the resistor in the RLC branches and is related to the resonance frequencies of the ultrasound transducer.