Hydrodynamic pressure sensing for a biomimetic robotic fish caudal fin integrated with a resistive pressure sensor.

Micro-sensors, such as pressure and flow sensors, are usually adopted to attain actual fluid information around swimming biomimetic robotic fish for hydrodynamic analysis and control. However, most of the reported micro-sensors are mounted discretely on body surfaces of robotic fish and it is impossible to analyzed the the hydrodynamics between the caudal fin and the fluid. In this work, a biomimetic caudal fin integrated with a resistive pressure sensor is designed and fabricated by laser machined conductive carbon fibre composites. To analyze the pressure exerted on the caudal fin during underwater oscillation, the pressure on the caudal fin is measured under different oscillating frequencies and angles. Then a model developed from Bernoulli equation indicates that the maximum pressure difference is linear to the quadratic power of the oscillating frequency and the maximum oscillating angle. The fluid disturbance generated by caudal fin oscillating increases with an increase of oscillating frequency, resulting in the decrease of the efficiency of converting the kinetic energy of the caudal fin oscillation into the pressure difference on both sides of the caudal fin. However, perhaps due to the longer stability time of the disturbed fluid, this conversion efficiency increases with the increase of the maximum oscillating angle. Additionally, the pressure variation of the caudal fin oscillating with continuous different oscillating angles is also demonstrated to be detected effectively. It is suggested that the caudal fin integrated with the pressure sensor could be used for sensing the in situ flow field in real time and analysing the hydrodynamics of biomimetic robotic fish.

Comprehensive stiffness regulation on multi-section snake robot with considering the parasite motion and friction effects.

Snake robots have been widely used in challenging environments, such as confined spaces. However, most existing snake robots with large length/diameter ratios have low stiffness, and this limits their accuracy and utility. To remedy this, a novel 'macro-micro' structure aided by a new comprehensive stiffness regulation strategy is proposed in this paper. This improves the positional accuracy when operating in deep and confined spaces. Subsequently, a comprehensive strategy for regulating the stiffness of the system is then developed, along with a kinetostatic model for error prediction. The internal friction, variation of cable stiffness as a function of tension, and their effects on the structural stiffness of the snake arm under different configurations have been incorporated into the model to increase the modelling accuracy. Finally, the proposed models were validated experimentally on a physical prototype and control system (error: 4.3% and 2.5% for straight and curved configurations, respectively). The improvement in stiffness due to the adjustment of the tension in the driving cables (i.e. average 183.4%) of the snake arm is shown.

A Review of Robotic Fish Based on Smart Materials.

The present study focuses on summarizing the recent advancements in the field of fish swimming mode research and bionic robotic fish prototypes based on smart materials. It has been widely acknowledged that fish exhibit exceptional swimming efficiency and manoeuvrability compared to conventional underwater vehicles. In the pursuit of developing autonomous underwater vehicles (AUVs), conventional experimental methods often prove to be complex and expensive. Hence, the utilization of computer simulations for hydrodynamic modelling provides a cost-effective and efficient approach for analysing the swimming behaviour of bionic robotic fish. Additionally, computer simulations can provide data that are difficult to obtain through experimental methods. Smart materials, which integrate perception, drive, and control functions, are increasingly being applied to bionic robotic fish research. However, the utilization of smart materials in this field is still an area of ongoing research and several challenges remain unresolved. This study provides an overview of the current state of research on fish swimming modes and the development of hydrodynamic modelling. The application of four distinct types of smart materials in bionic robotic fish is then reviewed, with a focus on analysing the advantages and disadvantages of each material in driving swimming behaviour. In conclusion, the paper highlights the key technical challenges that must be addressed for the practical implementation of bionic robotic fish and provides insights into the potential future directions of this field.

Adaptive control of a class of time-varying nonlinear systems via immersion and invariance.

This paper addresses the adaptive control of a class of time-varying nonlinear systems. Under the framework of Immersion and Invariance (I&I) adaptive control, a set of sufficient conditions is obtained to stabilize the concerned time-varying nonlinear systems. It is shown that the presented controller can also be utilized to complete tracking control for a class of nonholonomic constraint systems if the desired trajectories satisfy certain conditions. The effectiveness of the new adaptive controller is demonstrated by some numerical simulations on a nonholonomic mobile robot.

An Adaptive Time-Varying Impedance Controller for Manipulators.

Aiming at the situation that the structural parameters of the general manipulators are uncertain, a time-varying impedance controller based on model reference adaptive control (MRAC) is proposed in this article. The proposed controller does not need to use acceleration-based feedback or to measure external loads and can tolerate considerable structure parameter errors. The global uniform asymptotic stability of the time-varying closed-loop system is analyzed, and a selection approach for control parameters is presented. It is demonstrated that, by using the proposed control parameter selection approach, the closed-loop system under the adaptive controller is equivalent to an existing result. The feasibility of the presented controller for the general manipulators is demonstrated by some numerical simulations.

A highly conductive self-assembled multilayer graphene nanosheet film for electronic tattoos in the applications of human electrophysiology and strain sensing.

Highly conductive, conformable and gel-free electrodes are desirable in human electrophysiology. Besides, intimately coupling with human skin, wearable strain sensors can detect numerous physiological signals, such as wrist pulse and breath. In this study, a multilayer graphene nanosheet film (MGNF) with high conductivity was prepared by the Marangoni self-assembly for using in tattoo dry electrodes (TDEs) and in a graphene tattoo strain sensor (GTSS). Compared to commercial Ag/AgCl gel electrodes, TDEs have lower skin-electrode contact impedance and could detect human electrocardiogram for 24-hour wearing more accurately as well as electromyogram. Through designing a slim serpentine ribbon structure, a resistance-type GTSS, without deterioration even after 2000 cycles, is well demonstrated for human wrist pulse and breath sensing. With the advantages of high conductivity and conformability, MGNF provides support to fabricate low-cost, customizable, and high-performance electronic tattoos for human electrophysiology and strain sensing.

Highly efficient and giant negative electrocaloric effect of a Nb and Sn co-doped lead zirconate titanate antiferroelectric film near room temperature.

Adiabatic temperature variation (ΔT), coefficient of performance (COP) and electrocaloric coefficient (ΔT/ΔE) play important roles in evaluating the comprehensive performance of solid-state cooling technology based on the electrocaloric effect (ECE). A Nb and Sn co-doped lead zirconate titanate antiferroelectric film, Pb0.99Nb0.02(Zr0.85Sn0.13Ti0.02)O3 (PNZST), shows a highly efficient and giant negative ECE. The ΔT, |ΔT/ΔE| and COP are about -9.8 K, 0.0488 K cm kV-1 and 35.53 at around 50 °C, respectively. The full width at half maximum of the ΔT peak is about 37 °C. Phenomenological analysis indicates that the highly efficient and giant negative ECE is associated with the first-order transition that has a discontinuous polarization change with increasing temperature.

Flexible Semitransparent Energy Harvester with High Pressure Sensitivity and Power Density Based on Laterally Aligned PZT Single-Crystal Nanowires.

A flexible semitransparent energy harvester is assembled based on laterally aligned Pb(Zr0.52Ti0.48)O3 (PZT) single-crystal nanowires (NWs). Such a harvester presents the highest open-circuit voltage and a stable area power density of up to 10 V and 0.27 µW/cm2, respectively. A high pressure sensitivity of 0.14 V/kPa is obtained in the dynamic pressure sensing, much larger than the values reported in other energy harvesters based on piezoelectric single-crystal NWs. Furthermore, theoretical and finite element analyses also confirm that the piezoelectric voltage constant g33 of PZT NWs is competitive to the lead-based bulk single crystals and ceramics, and the enhanced pressure sensitivity and power density are substantially linked to the flexible structure with laterally aligned PZT NWs. The energy harvester in this work holds great potential in flexible and transparent sensing and self-powered systems.

Efficient degradation of phenol using iron-montmorillonite as a Fenton catalyst: Importance of visible light irradiation and intermediates.

Iron-montmorillonite (Fe-Mt) with delaminated structures was synthesized via the introduction of iron oxides into Na-montmorillonite. Fe-Mt showed significant increases in the available iron content, surface area and pore volume, along with a slight increase in the basal spacing from d001=1.26 (Na-Mt) to 1.53nm (Fe-Mt). The Fenton process was efficient for phenol removal using Fe-Mt as a catalyst under visible light irradiation, and the process had two-stage pseudo-first order kinetics. The overall reaction had a higher degradation rate even when it was only irradiated with visible light for the first 40min period. Further investigation confirmed that the irradiation increased the presence of certain intermediates. Among them, 1,4-benzoquinone, hydroquinone, and catechol all enhanced the Fenton reaction rates. Either catechol or hydroquinone was added to the Fenton system with Fe-Mt/H2O2 with or without visible light irradiation, and they both accelerated phenol degradation because catechol and hydroquinone are capable of reductively and effectively transforming Fe(III) into Fe(II). The concentrations of dissolved total Fe increased with the increase in the oxalic acid concentration, which can strongly chelate Fe(III). Hence, iron was released from Fe-Mt, and reductive transformation played an important role in promoting the Fenton reaction process for phenol removal.

Decolourization of the azo dye Orange G in aqueous solution via a heterogeneous Fenton-like reaction catalysed by goethite.

Decolourization of the azo dye Orange G (OG) was investigated by using goethite/H2O2 as a heterogeneous Fenton-like reagent. Five principle operational parameters, namely pH, ion strength, concentrations ofgoethite (alpha-FeOOH) and hydrogen peroxide (H2O2), and reaction temperature, were taken into account to investigate how these controlling factors mediated OG decolourization. Goethite surfaces catalysed a Fenton-like reaction responsible for decolourizing OG following pseudo-first-order kinetics (R2 > 0.964). This process was effective but seriously impacted by the medium pH and the dosages of both alpha-FeOOH and H2O2. The decolourization efficiencies of OG increased with the decrease of solution pH and NaCl (chloride ion) concentration and/or the increase of H2O2. The acidic aqueous medium conditions were likely favourable due to the surface adsorption of the negatively charged OG leading to the promotion of decolourizing OG. The apparent activation energy (E) for this reaction was 42.18 kJ mol(-1), a relatively low value. This is consistent with the OG decolourization being enhanced with the reaction temperature increase.