Square-wave Input Research Articles

Dynamic response of a thermal transistor to time-varying signals

Thermal transistor, the thermal analog of an electronic transistor, is one of the most important thermal devices for microscopic-scale heat manipulating. It is a three-terminal device, and the heat current flowing through two terminals can be largely controlled by the temperature of the third one. Dynamic response plays an important role in the application of electric devices and also thermal devices, which represents the devices’ ability to treat fast varying inputs. In this paper, we systematically study two typical dynamic responses of a thermal transistor, i.e., the response to a step-function input (a switching process) and the response to a square-wave input. The role of the length L of the control segment is carefully studied. It is revealed that when L is increased, the performance of the thermal transistor worsens badly. Both the relaxation time for the former process and the cutoff frequency for the latter one follow the power-law dependence on L quite well, which agrees with our analytical expectation. However, the detailed power exponents deviate from the expected values noticeably. This implies the violation of the conventional assumptions that we adopt.

Two Proposals of a Simple Analog Conditioning Circuit for Remote Resistive Sensors with a Three-Wire Connection.

This article proposes and experimentally characterizes two implementations of a novel front-end circuit for three-wire connected resistive sensors with a wire-resistance compensation. The first implementation relies on two twin diodes, whereas the second on a switch; in both cases, those devices are non-remote (i.e., they are placed at the circuit end). The two circuit proposals have a square-wave input excitation so that a constant current with the two polarities is alternatively generated. Then, depending on that polarity, the current goes through either the sensor and the wire parasitic resistances or just the parasitic resistances. This generates a square-wave bipolar output signal whose average value, which is obtained by a low-pass filter, is proportional to the sensor resistance and only depends on the mismatch between two of the three wire resistances involved. Experimental tests applied to resistances related to a Pt100 thermal sensor show a remarkable linearity. For example, the switch-based front-end circuit offers a non-linearity error lower than 0.01% full-scale span, and this is practically insensitive to both the presence and the mismatch between the wire resistances.

Nematic twist-bend phase of a bent liquid crystal dimer: field-induced deformations of the helical structure and macroscopic polarization

The twist-bend nematic (Ntb) phase is a recent addition to the family of nematic (N) phases of liquid crystals (LCs). A net polar order in the Ntb phase under an external electric field is interesting and it was predicted in several recent theoretical studies. We investigated the field-induced polarization behaviour, dielectric, and electro-optic properties of a bent LC dimer CB7CB in the N and Ntb phases. A threshold-dependent polarization current response was obtained in both the phases under triangular and square-wave input electric fields, existing till frequencies as high as 150 Hz. The polarization switching times were found in ∼1 ms region, especially in the N phase. In the Ntb phase, electric field-induced deformation of the helical structure was observed, like ferroelectric LCs. Dielectric measurements revealed the presence of cybotactic clusters via collective relaxations. The dielectric anisotropy (Δϵ) is negative at the frequencies of polarization measurements. The net polarization resulted from field-induced reorientation of cybotactic clusters and additionally from the field-induced deformation of helical structures in the Ntb phase. We explored the possibility of ionic contributions to the net polarization by synthesizing TiO2 nanoparticles (NPs) dispersed CB7CB LC nanocomposite. Incorporation of the NPs resulted in reduction of the collective order, increase in the ionic impurity content and conductivity, but an extinction of the field-induced polarization response. Our results demonstrate that the net polarization has competing contributions from both ferroelectric-like and ionic origin (up to ∼10 Hz) in the LC phases, but it becomes dominantly ferroelectric-like at higher frequencies.

Impacts of Discretization and Numerical Propagation on the Ability to Follow Challenging Square Wave Commands

This study determines the threshold for the computational rate of actuator motor controllers for unmanned underwater vehicles necessary to accurately follow discontinuous square wave commands. Motors must track challenging square-wave inputs, and identification of key computational rates permit application of deterministic artificial intelligence (D.A.I.) to achieve tracking to a machine-precision degree of accuracy in direct comparison to other state-of-art approaches. All modeling approaches are validated in MATLAB simulations where the motor process is discretized at varying step-sizes (inversely proportional to computational rate). At a large step-size (fast computational rate), discrete D.A.I. shows a mean error more than three times larger than that of a ubiquitous model-following approach. Yet, at a smaller step size (slower computational rate), the mean error decreases by a factor of 10, only three percent larger than that of continuous D.A.I. Hence, the performance of discrete D.A.I. is critically affected by the sampling period for discretization of the system equations and computational rate. Discrete D.A.I. should be avoided when small step-size discretization is unavailable. In fact, continuous D.A.I. has surpassed all modeling approaches, which makes it the safest and most viable solution to future commercial applications in unmanned underwater vehicles.

The voltage and spiking responses of subthreshold resonant neurons to structured and fluctuating inputs: persistence and loss of resonance and variability.

We systematically investigate the response of neurons to oscillatory currents and synaptic-like inputs and we extend our investigation to non-structured synaptic-like spiking inputs with more realistic distributions of presynaptic spike times. We use two types of chirp-like inputs consisting of (i) a sequence of cycles with discretely increasing frequencies over time, and (ii) a sequence having the same cycles arranged in an arbitrary order. We develop and use a number of frequency-dependent voltage response metrics to capture the different aspects of the voltage response, including the standard impedance (Z) and the peak-to-trough amplitude envelope ([Formula: see text]) profiles. We show that Z-resonant cells (cells that exhibit subthreshold resonance in response to sinusoidal inputs) also show [Formula: see text]-resonance in response to sinusoidal inputs, but generally do not (or do it very mildly) in response to square-wave and synaptic-like inputs. In the latter cases the resonant response using Z is not predictive of the preferred frequencies at which the neurons spike when the input amplitude is increased above subthreshold levels. We also show that responses to conductance-based synaptic-like inputs are attenuated as compared to the response to current-based synaptic-like inputs, thus providing an explanation to previous experimental results. These response patterns were strongly dependent on the intrinsic properties of the participating neurons, in particular whether the unperturbed Z-resonant cells had a stable node or a focus. In addition, we show that variability emerges in response to chirp-like inputs with arbitrarily ordered patterns where all signals (trials) in a given protocol have the same frequency content and the only source of uncertainty is the subset of all possible permutations of cycles chosen for a given protocol. This variability is the result of the multiple different ways in which the autonomous transient dynamics is activated across cycles in each signal (different cycle orderings) and across trials. We extend our results to include high-rate Poisson distributed current- and conductance-based synaptic inputs and compare them with similar results using additive Gaussian white noise. We show that the responses to both Poisson-distributed synaptic inputs are attenuated with respect to the responses to Gaussian white noise. For cells that exhibit oscillatory responses to Gaussian white noise (band-pass filters), the response to conductance-based synaptic inputs are low-pass filters, while the response to current-based synaptic inputs may remain band-pass filters, consistent with experimental findings. Our results shed light on the mechanisms of communication of oscillatory activity among neurons in a network via subthreshold oscillations and resonance and the generation of network resonance.

CMOS-compatible synaptic transistor gated by chitosan electrolyte-Ta2O5 hybrid electric double layer

This study proposes a hybrid electric double layer (EDL) with complementary metal-oxide semiconductor (CMOS) process compatibility by stacking a chitosan electrolyte and a Ta2O5 high-k dielectric thin film. Bio-inspired synaptic transistors with excellent electrical stability were fabricated using the proposed hybrid EDL for the gate dielectric layer. The Ta2O5 high-k dielectric layer with high chemical resistance, thermal stability, and mechanical strength enables CMOS-compatible patterning processes on biocompatible organic polymer chitosan electrolytes. This technique achieved ion-conduction from the chitosan electrolyte to the In-Ga-Zn oxide (IGZO) channel layer. The on/off current ratio, subthreshold voltage swing, and the field-effect mobility of the fabricated IGZO EDL transistors (EDLTs) exhibited excellent electrical properties of 1.80 × 107, 96 mV/dec, and 3.73 cm2/V·s, respectively. A resistor-loaded inverter was constructed by connecting an IGZO EDLT with a load resistor (400 MΩ) in series. This demonstrated good inverter action and responded to the square-wave input signals. Synaptic behaviours such as the hysteresis window and excitatory post-synaptic current (EPSC) variations were evaluated for different DC gate voltage sweep ranges and different AC gate spike stimuli, respectively. Therefore, the proposed organic–inorganic hybrid EDL is expected to be useful for implementing an extremely compact neural architecture system.

Time-Domain Dielectric Spectroscopy Using a Miniaturized Contact-Based UWB System

This paper presents a miniaturized contact-based system for dielectric spectroscopy using time-domain (TD) technique in ultrawideband (UWB) frequency range. The system consists of a miniaturized UWB transmitter, a planar sensor having direct contact with a liquid material under test (MUT), and a high-speed oscilloscope receiver. In the transmitter, a baseband (BB) pulse with 3.5-GHz bandwidth is generated from a square-wave input signal by employing a step recovery diode and a short-circuited stub. Then, the BB pulse is upconverted by a UWB mixer with 6.5-GHz local oscillator frequency, creating a 3–10-GHz passband pulse. After being amplified, the passband pulse excites the miniaturized sensor, including two stages of microstrip open-circuited stub between meander inductors. This sensor has a small area, requires only 0.3 $\mu \text{L}$ of liquid MUT for accurate sensing, and responds to both $\epsilon '$ and $\epsilon ''$ properties. The sensor output is captured by the oscilloscope in TD and then converted to frequency domain (FD) by the fast Fourier transform operation. Considering $\epsilon '$ and $\epsilon ''$ of MUT simultaneously affect both phase and magnitude of output signal in FD, the behavior of the system is described by testing 12 reference MUTs. From the behavioral model of the system, three unknown MUTs are characterized with errors less than $0.1|\epsilon ^{*}|$ in both $\epsilon '$ and $\epsilon ''$ from 3.28 to 10 GHz.

Realization and AC modeling of electronic circuits with water-gated field effect transistors (WG-FETs) based on gate probe distance

We present AC modeling of WG-FET devices based on gate probe distance. Small- and large-signal models are proposed. It is shown that unity gain frequency is inversely proportional to gate distance. Also, common source amplifier, inverter, and ring oscillator circuits are fabricated with WG-FET devices, which use 16 nm-thick mono-Si film as channel layer, for the first time. Circuit simulations are performed based on AC models. Results are verified with experimental measurements using de-ionized (DI) water. For common source amplifier, fUG is measured as 21 Hz for 2 mm gate distance, and it is increased to 1.2 kHz when gate distance is decreased to 200 μm. For inverter, rail-to-rail operation is observed with tPLH of 24 ms and tPHL of 58 ms for 1 square-wave input signal at 1 Hz. Gain is measured as −11 V/V at switching threshold. Ring oscillator is realized with five inverters. A square-wave output signal with amplitude of 840 and frequency of 2.6 Hz is obtained. AC modeling of WG-FET enables realization of advanced circuits which are inherently compatible with fluidic systems. Therefore, they can be valuable assets especially in microfluidic applications.

Effect of Waveform on Tactile Perception by Electrovibration Displayed on Touch Screens.

In this study, we investigated the effect of input voltage waveform on our haptic perception of electrovibration on touch screens. Through psychophysical experiments performed with eight subjects, we first measured the detection thresholds of electrovibration stimuli generated by sinusoidal and square voltages at various fundamental frequencies. We observed that the subjects were more sensitive to stimuli generated by square wave voltage than sinusoidal one for frequencies lower than 60 Hz. Using Matlab simulations, we showed that the sensation difference of waveforms in low fundamental frequencies occurred due to the frequency-dependent electrical properties of human skin and human tactile sensitivity. To validate our simulations, we conducted a second experiment with another group of eight subjects. We first actuated the touch screen at the threshold voltages estimated in the first experiment and then measured the contact force and acceleration acting on the index fingers of the subjects moving on the screen with a constant speed. We analyzed the collected data in the frequency domain using the human vibrotactile sensitivity curve. The results suggested that Pacinian channel was the primary psychophysical channel in the detection of the electrovibration stimuli caused by all the square-wave inputs tested in this study. We also observed that the measured force and acceleration data were affected by finger speed in a complex manner suggesting that it may also affect our haptic perception accordingly.

High-speed optical sensor interrogator with a silicon-ring-resonator-based thermally tunable filter.

On-chip optical interrogators employing a silicon-ring-resonator-based thermally tunable filter (SRRTF) offer a promising solution for realizing portable, compact optical sensing systems. However, the slow interrogation speed of conventional SRRTF-based interrogators (less than a few Hz) hinders real-time sensing of dynamic parameters. In this Letter, we report a 100 kHz of high-speed optical interrogation system based on the SRRTF. The speed enhancement is achieved by using the nonlinear transient response of the SRRTF to a square-wave input voltage. The entire spectral range of the SRRTF is scanned twice during its thermal response cycle. The time-domain sensor output signal, which is obtained by scanning the SRRTF over the sensor spectrum, is converted into spectrum domain based on the experimentally characterized, time-dependent resonance wavelength shifts of the SRRTF. With this system, we demonstrate high-speed interrogation of a fiber Bragg grating sensor under dynamic temperature change (200 Hz).

Automated Resonance Matching for CMOS MEMS Micro-Resonators

This paper reports the design and characterization of a phase-locked loop-based control scheme implemented in a complementary metal–oxide–semiconductor process for resonance matching between capacitive micro-resonators. The system-on-chip implementation can be utilized for calibrating individual resonance in a large sensor array or matching the drive and sense modes for micromachined vibratory gyroscopes. The target micro-resonator acts as a voltage-controlled oscillator in the control loop with the resonance being adjusted by the electrostatic spring-softening effect. Sinusoidal test inputs applied to the control loop are shown to provide better resonance matching than square-wave inputs. This paper successfully demonstrates automated matching by pulling the resonance of a target micro-resonator within $2.4\times 10^{-2}$ % of the reference resonance under atmospheric pressure.

Detection of Internal Resistance Change for Photovoltaic Arrays Using Extremum-Seeking Control MPPT Signals

Maximum power point tracking (MPPT) and fault diagnosis are two important aspects of reducing the cost of energy for photovoltaic (PV) systems. Many mechanisms of PV degradation are associated with change in the internal resistance, especially the shunt resistance. This brief proposes a cost-effective scheme for detecting the change of PV internal resistance using the signals available in extremum-seeking control (ESC)-based MPPT. With the square-wave dither inputs, the steady-state trajectories of PV output signals effectively consist of a train of small-amplitude step responses. The transient characteristics of such step responses are affected by the PV internal resistance. A small-signal transfer function analysis is performed for the PV buck system, which justifies the impact of the internal resistance on the transient characteristics. A simulation study is first conducted for single-string PV systems, and the simulation results show that ESC can achieve satisfactory MPPT under a square-wave dither input. The transient characteristics, such as integrated absolute error, show a strong correlation with the internal resistance. The applicability of this scheme to multistring PV is demonstrated with a multi-input ESC based on the total power feedback, with the internal resistance of individual modules detectable from one output signal.

Adaptive Control? But is so Simple!

In a recent paper, a few pioneers of adaptive control review the classical model reference adaptive control (MRAC) concept, where the designer is basically supposed to conceive a model of the same order as the (possibly very large) plant, and then build an adaptive controller such that the plant is stable and ultimately follows the behavior of the model. Basically, adaptive control methods based on model following assume full-state feedback or full-order observers or identifiers. These assumptions, along with supplementary prior knowledge, allowed the first rigorous proofs of stability with adaptive controllers, which at the time was a very important first result. However, in order to obtain this important mathematical result, the developers of classical MRAC took the useful scalar Optimal Control feedback signal and made it into an adaptive gain-vector of basically of the same order as the plant, which again had to multiply the plant state-vector in order to finally end with another scalar adaptive control feedback signal. It is quite known today, however, what happens when this requirement is not satisfied, and when "unmodeled dynamics" distorts the controller based on these ideal assumptions. Even though much effort has been invested to maintain stability in spite of so-called "unmodeled dynamics," in some applications, such as large flexible structures and other real-world applications, even if one can assume that the order of the plant is known, one just cannot implement a controller of the same order as the plant (or even a "nominal" or a "dominant" part of the plant), before even mentioning the complexity of such an adaptive controller. Without entering the argument around their special reserve in relation to claimed efficiency of the particular L1-Adaptive Control methodology, this paper first shows that, after the first successful proof of stability and even under the same basic full-state availability assumption, the adaptive control itself can be reduced to just one adaptive gain (which multiplies one error signal) in single-input-single-output (SISO) systems and, as a straightforward extension, an m*m gain matrix in an m-input-m-output (MIMO) plant. Not only is stability not affected, but actually the simplified scheme also gets rid of most seemingly "inherent" problems of the adaptive control represented by classical MRAC. Moreover, proofs of stability have all been based on the so-called Barbalat's lemma which seems to require very strict uniform continuity of signals. The apparent implications are that any discontinuity, such as square-wave input commands or just some occasionally discontinuous disturbance, may put stability of adaptive control in danger, without even mentioning such things as impulse response. Instead, based on old yet amazingly unknown extensions of LaSalle's Invariance Principle to nonautonomous nonlinear systems, recent developments in stability analysis of nonlinear systems have mitigated or even eliminated most apparently necessary prior conditions, thus adding confidence in the robustness of adaptive scheme in real world situations.

Clawed Miniature Inchworm Robot Driven by Electromagnetic Oscillatory Actuator

In this research we propose a novel inchworm robot, which is composed of an Electromagnetic Oscillatory Actuator (EOA) and claws. The EOA consists of a yoke, a magnet, and a coil. The overall robot size is 12.2 mm × 11 mm × 9 mm (length × height × width). The locomotion of the robot is achieved by different amounts of slips when the robot stretches and contracts its front leg. To realize locomotion, the working conditions were calculated theoretically and the calculated input signal was applied to the robot. The performance of the inchworm robot was evaluated experimentally with varying input voltages and frequencies. A simple op-amps based driving circuit was used to provide a square-wave input. Travel speed, average distance per step of the robot, and moving distance of the leg and body at each step were measured. The maximum travel speed was 36 mm·s−1 at 30 Hz, which validates our simple locomotion strategy experimentally.

Tip trajectory control of a flexible-link manipulator using an intelligent proportional integral (iPI) controller

This paper presents the development, stability analysis and validation of an intelligent proportional integral (iPI) controller for the tip position control of a flexible-link manipulator. A stability analysis included in the paper shows that the iPI controller is equivalent to the proportional integral-squared controller. In order to verify the performance of the iPI controller, several experiments were conducted. In these experiments, step and square-wave inputs and two other trajectories were applied to the flexible-link manipulator. Also, the performance of the iPI controller was compared with those of classical PI and PID controllers. The results obtained from the comparison experiments showed that, the PI and PID controllers produced better performance in step and square-wave inputs, but the iPI controller yielded better trajectory tracking performance. All of the controllers were tested for disturbance and noise rejection capability. The iPI controller eliminated disturbance and noise better than the classical controllers. Considering all of the results, the iPI controller has great potential in trajectory tracking control of flexible-link manipulators.

Design of a Novel Excitation Circuit for Low Perming Error Fluxgate

An effective method for low perming error of fluxgates is to enlarge the peak value of the excitation current, but large amplitude excitation will increase the power consumption. A narrow pulse excitation current with sufficient peak value can reduce perming error with low power consumption while increase the difficulty of the signal processing with low sensitivity. The perfected excitation waveform with high ratio of peak value to RMS value by careful excitation tuning is an efficient solution. This paper presents a novel circuit which can generate an excitation current waveform with high peak value and low RMS value for fluxgates. Different from the tuned excitation circuit, the proposed circuit is a combination of an integrator and a differentiator with the same squarewave input. The excitation signal is the sum of a triangle wave and a sharp narrow pulse signal. It is easy to adjust the peak value of the narrow pulses for perming error study and no careful tune adjusting is needed. Finally, in case of the fixed peak value of the narrow pulses, an improved excitation circuit with only two resistors, two capacitors and one amplifier is also presented in the paper. The experiment results show that 0.5nT perming error can be achieved for 10mT shock.

Nomoto Indices for Constant-Depth Zigzag Manoeuvres of an Autonomous Underwater Vehicle

A two-dimensional simulation code is used to study the characteristics of constant-depth zigzag manoeuvres of the axisymmetric autonomous underwater vehicle (AUV) MUN Explorer. Sea trials data for several manoeuvres with the AUV have been reported during the past four years; however, to obtain a more complete understanding of the vehicle's hydrodynamics, additional towing tank tests and computer simulation were performed. The present work, based on the towing tank test results and sea-trials data, utilizes computer simulations to predict the performance of the MUN Explorer AUV during horizontal zigzag manoeuvres. Next, the Nomoto indices for this AUV during constant-depth zigzag manoeuvres are estimated using the simulation results, and, then, Nomoto's first-order model for the rate of turn of the vehicle during horizontal zigzag manoeuvres in response to a square-wave input for the rudder deflection angle is analytically solved. The paper investigates the validity of the simplified yaw equation to predict a zigzag manoeuvre. Results of this research are a first step to understand the details of zigzag manoeuvres of an AUV such as duration of the first execute, yaw-checking ability, and duration of the overshoot.

Model identification for impact dynamics of a piezoelectric microactuator

A parameterized model for the impact dynamics of a piezoelectric microactuator is proposed, and a system-identification procedure for quantifying model parameters is presented. The proposed model incorporates squeeze-film damping, adhesion and coefficient-of-restitution effects. Following parameter quantification from sample data of bouncing impacts and progressive ramped-square-wave inputs, the model is found to be effective in predicting the time response of the actuator to a range of square-wave and sinusoidal inputs. The main contributions of this paper are to show that the dynamic response to micro-scale contact can be predicted using simple lumped-parameter modeling after a proposed system-identification procedure is performed and that certain small-scale forces can be quantified. For example, for motions where bounce of the cantilever tip may occur, the range of adhesion is found to be time dependent and vary between approximately 20 and 520 nN, while the range of squeeze-film damping is estimated to be between 50 and 130 nN, depending on the input signal frequency and amplitude. The presence, absence and quantity of bounces upon impact are predicted very accurately, while oscillation amplitudes and contact durations are predicted to be between 1% and 30% error for the majority of many test cases of periodic inputs between 5 and 100 Hz.

Lift Response of a Stalled Wing to Pulsatile Disturbances

The transient lift response of a low-Reynolds-number wing subjected to small amplitude pulsatile disturbances is investigated. The wing has a small aspect ratio and a semicircular planform, and it is fully stalled at a 20 deg angle of attack. Microvalve actuators distributed along the leading edge of the wing produce the transient disturbance. It is shown that the lift response to a single pulse increases with increasing actuator supply pressure and that the lift response curves are similar to each other when scaled by the total impulse. Furthermore, for fixed actuator supply pressure, the amplitude and total impulse of the transient lift response curve increases with increasing external flow speed. In this case, the lift response curves are similar when scaled by the dynamic pressure. The lift response to a single pulse can be treated as a filter kernel, and it can be used to predict the lift time history for the arbitrary actuator input signals. The kernel is similar in shape to transient measurements obtained by other investigators on two-dimensional wings and flaps. Comparisons between the model predictions and the experiments using multiple pulse inputs and square-wave modulated input signals at low frequencies are presented.

Fabrication of a peristaltic micro pump with novel cascaded actuators

This paper presents the fabrication of an all-PDMS (polydimethylsiloxane) micro pump with novel cascaded actuators as dynamic valves. The micro pump consists of three pneumatic actuators in series and a micro fluidic channel connecting two fluidic inlet and outlet ports. The three-layer bonded pump structure is fabricated through a typical moulding process of PDMS and a simple heating process for the PDMS-to-PDMS bonding. The total size of the micro pump is 5 mm × 5 mm. The dynamic valve pattern of the single actuator is observed under various operational conditions of the square-wave input signal for the estimation of its volume stroke. The maximum volume stroke of the pneumatic actuator for liquid is about 85% of the volume of the liquid chamber. Three types of liquid-pumping tests are performed for characterization of the micro pump such as backpressure, frequency and viscous liquids. The flow rate of the de-ionized (DI) water is about 73.9 nl min−1 at zero backpressure. As the hydraulic difference between inlet and outlet ports increases, the flow rate gradually decreases. In the case of the frequency responses, the micro pump has the maximum flow rate of the DI water at 2 Hz. The viscosity-dependent flow rate of the working fluids is also observed.