ABSTRACT
An improved protocol is proposed for preparation of a humidity-sensitive soft actuator through the layer-by-layer assembling of weight-ratio-variable composites of sodium alginate (SA) and poly(vinyl alcohol) (PVA) into laminated structures. The design induces nonuniform hygroscopicity in the thickness direction and gives rise to strong interfacial interaction between layers, making the actuator have directional motility. A mathematical model reveals that the directional motion is driven by the chemical potential of humidity, and its energy conversion efficiency from humidity to mechanical work reaches 81.2% at 25 °C. By coating with CoCl2, the composite film of SA@PVA/CoCl2 can act as a warning sign that provides reminder information to prevent people from slipping or falling by a conspicuous red sign during a high-humidity environment. When the film is involved in a bidirectional switch, it is capable of turning on/off light-emitting diodes by humidity, showing promising potential in control over humidity-dependent devices.
ABSTRACT
We for the first time disclose the evolutionary mechanism of solid-to-hollow sodium alginate (SA) hydrogel in an aqueous solution of Cu2+, H2O2 and Tris-HCl elements, where the oxidative degradation and gas bubble assistance result in the hollow structures. This provides a promising concept or method basis for the preparation of hollow hydrogels with sophisticated geometries.
ABSTRACT
Hollow hydrogel tubes that are capable of maintaining their flexibility and structural stability in extreme temperature conditions have potential for use in biomedical scaffolds, carriers, and soft robotics over a wide temperature range. However, the preparation of hollow hydrogel tubes still remains challenging because it normally requires templates or complex devices and it is hard to endow the hollow tubes with antifreezing heat-resistant capabilities. We report a protocol that does not require a template or complex devices, in which sodium alginate film strips are immersed in an aqueous mixture of CaCO3, CaCl2, NaHCO3, and HCl, which results in the manufacture of hollow tubes in 30 min. These hollow tubes are functionalized by glycerol and poly(ethylene glycol), which provides the tubes with antifreezing heat-resistant performances and enables them to keep their flexibility and hollow structures from -70 to 120 °C. This is the first report on antifreezing heat-resistant hollow hydrogel tubes, to the best of our knowledge. Such hollow tubes as carriers can control the sublimation of a mothball at a rate of 1.1 mg/h, which is one-tenth of the sublimating rate of an unloaded mothball. This sublimating rate reduces the hazard to environments along with maintaining the repellent effects. As the tube is a honey carrier, it enables the sustainable release of the honey over 800 min with a high efficacy for tricking and capturing ants. The simple applications demonstrate that the antifreezing heat-resistant hollow tubes might be feasible as carriers for the controlled release in extremely cold/hot environments.
ABSTRACT
It is well-known that incoherent sampling is detrimental for frequency estimation of a real sinusoid, and the estimation errors get worse when the signal lengths are very short. In this paper, a spectrum matching based frequency estimator is proposed as well as evaluated against other four two-step methods developed to suppress the effect of incoherent sampling. The spectral interference introduced by incoherent sampling is eliminated via a spectrum matching process including modulation and spectral analysis. A further error correction based on Fourier transform is conducted to generate the fine frequency estimate. Simulation results are carried out to show that the proposed method can closely approach the Cramér-Rao lower bound without any error floor, and it can outperform the other four methods particularly for short signal lengths.
ABSTRACT
Phase difference estimation is a fundamental problem in numerous applications. However, incoherent sampling (IS) is an inevitable factor which degrades the precision of many correlations or Fourier transform-based approaches. In this paper, IS and the spectral superposition of real signals are both considered. A novel estimator is developed based on modulation and the discrete Fourier transform (DFT). With the estimated frequency, the phase difference can be obtained by calculating four DFT samples of the modulated signals. Simulations and the experimental results have proved their validity as well as their superiority over five other methods designed for IS, particularly at high signal-to-noise ratios. Furthermore, the proposed method can maintain high accuracy even when a significant bias occurs with the frequency estimation.
ABSTRACT
Accurate frequency estimation affects the ranging precision of linear frequency modulated continuous wave (LFMCW) radars significantly. To improve the ranging precision of LFMCW radars, a phase match based frequency estimation method is proposed. To obtain frequency estimation, linear prediction property, autocorrelation, and cross correlation of sinusoidal signals are utilized. The analysis of computational complex shows that the computational load of the proposed method is smaller than those of two-stage autocorrelation (TSA) and maximum likelihood. Simulations and field experiments are performed to validate the proposed method, and the results demonstrate the proposed method has better performance in terms of frequency estimation precision than methods of Pisarenko harmonic decomposition, modified covariance, and TSA, which contribute to improving the precision of LFMCW radars effectively.
ABSTRACT
For the ultralow frequency signals or adjacent Nyquist frequency signals, which widely exist in vibration engineering domain, the traditional discrete time Fourier transform (DTFT) algorithms show poor performance for phase difference measurement. To improve the accuracy of phase difference measurement for these extreme frequency signals, the phase difference measurement error of DTFT algorithm is analyzed, which indicates that the negative frequency contribution is the main cause of the bias. By considering the negative frequency contribution, a new phase difference measurement algorithm for extreme frequency signals is proposed based on DTFT, and the new formulas for phase difference calculation with different windows are derived in detail. The new algorithm has stronger inhibition of spectrum leakage and has a higher accuracy than traditional DTFT algorithms. Simulation and experimental results show that the proposed algorithm has better performance than the other DTFT algorithms.
ABSTRACT
The precision of frequency tracking method and phase difference calculation method affects the measurement precision of Coriolis Mass Flowmeter directly. To improve the accuracy of the mass flowrate, a novel signal processing method for Coriolis Mass Flowmeter is proposed for this time varying signal, which is comprised of a modified adaptive lattice notch filter and a revised sliding recursive discrete-time Fourier transform algorithm. The method cannot only track the change of frequency continuously, but also ensure the calculation accuracy when measuring phase difference. The computational load of the proposed method is small with higher accuracy. Simulation and experiment results show that the proposed method is effective.
