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Abstract Liquid‐solid triboelectric nanogenerator (LS‐TENG) harvests energy efficiently while eliminating wear issues associated with solid‐solid TENG. However, the effect of ions or charges in the liquid on output performance needs further examination. In this work, the impact of fluorine and copper ions introduced through deionized water with sodium fluoride (DI‐NaF) and deionized water with copper sulfate (DI‐CuSO4) solution on the output voltage, charge and current of a tubular LS‐TENG with polytetrafluoroethylene (PTFE) and Nylon as solid materials is examined. The results indicate that fluorine and copper ions have opposite effects on PTFE and Nylon LS‐TENG's output. The fluorine (F−) ions enhance the triboelectric effect and charge transfer in Nylon LS‐TENG, increasing output, while they hinder the charge transfer process in PTFE LS‐TENG, consequently decreasing its output. Conversely, the copper (Cu2+) ions have a positive effect on the output of PTFE LS‐TENG and a detrimental effect on Nylon LS‐TENG's output. Moreover, the results indicate that LS TENG's output performance depends on the charges of solid and liquid triboelectric materials. Thus, this study provides insights into material‐ion interaction in LS‐TENG and underscores the importance of triboelectric material selection for optimizing output performance.

Abstract Piezoelectric energy generation is relevant for developing advanced electronics. However, the poor understanding of the influence of triboelectricity as an alternate charge generation mechanism has, in many cases, resulted in the reporting of exaggerated piezoelectric outputs. Herein, the signal output is systematically investigated from a range of organic piezoelectric materials (poled polyvinylidene fluoride (PVDF)), moderately piezoelectric (heat‐treated PVDF), and non‐piezoelectric (non‐poled PVDF), polytetrafluoroelthylene (Teflon) and nylon) under tapping and compression (33 direction) and stretching (31 direction) in both encapsulated and non‐encapsulated forms. This findings reveal that regardless of their piezoelectric properties, all tested materials exhibit substantial voltage outputs (4.2–4.6 V) during tapping, primarily attributed to the triboelectric effect at the contact interface. The triboelectric contribution to the signal is reduced by 99% in compression mode for non‐piezoelectric materials and the piezoelectric signal is the primary contributor in the stretching mode with a high signal output of 7.71 V N−1 for poled PVDF and a negligible signal (0.01–0.12 V N−1) for non‐piezoelectric materials. Moreover, elastomeric encapsulation is demonstrated to markedly increase triboelectric signals in tapping mode. These results have important implications for the future design of piezoelectric‐triboelectric devices and the accurate interpretation of the data obtained from such devices.

Wearable electrode arrays can selectively stimulate muscle groups by modulating their shape, size, and position over a targeted region. They can potentially revolutionize personalized rehabilitation by being noninvasive and allowing easy donning and doffing. Nevertheless, users should feel comfortable using such arrays, as they are typically worn for an extended time period. Additionally, to deliver safe and selective stimulation, these arrays must be tailored to a user’s physiology. Fabricating customizable electrode arrays needs a rapid and economical technique that accommodates scalability. By leveraging a multilayer screen-printing technique, this study aims to develop personalizable electrode arrays by embedding conductive materials into silicone-based elastomers. Accordingly, the conductivity of a silicone-based elastomer was altered by adding carbonaceous material. The 1:8 and 1:9 weight ratio percentages of carbon black (CB) to elastomer achieved conductivities between 0.0021–0.0030 S cm−1 and were suitable for transcutaneous stimulation. Moreover, these ratios maintained their stimulation performance after several stretching cycles of up to 200%. Thus, a soft, conformable electrode array with a customizable design was demonstrated. Lastly, the efficacy of the proposed electrode arrays to stimulate hand function tasks was evaluated by in vivo experiments. The demonstration of such arrays encourages the realization of cost-effective, wearable stimulation systems for hand function restoration.

Sensors as a composite film made from reduced graphene oxide (rGO) structures filled with a silicone elastomer are soft and flexible, making them suitable for wearable applications. The sensors exhibit three distinct conducting regions, denoting different conducting mechanisms when pressure is applied. This article aims to elucidate the conduction mechanisms in these sensors made from this composite film. It was deduced that the conducting mechanisms are dominated by Schottky/thermionic emission and Ohmic conduction.

Soft robotic actuators are highly flexible, compliant, dexterous, and lightweight alternatives that can potentially replace conventional rigid actuators in various human-centric applications. This research aims to develop a soft robotic actuator that leverages body movements to mimic the function of human fingers for gripping and grasping tasks. Unlike the predominantly used chamber-based actuation, this study utilizes actuators made from elastomers embedded with fiber braiding. The Young’s modulus of the elastomer and braiding angles of the fiber highly influenced the bending angle and force generated by these actuators. In this experiment, the bending and force profiles of these actuators were characterized by varying the combinations of elastomeric materials and braiding angles to suit hand manipulation tasks. Additionally, we found that utilizing water, which is relatively more incompressible than air, as the actuation fluid enabled easier actuation of the actuators using body movements. Lastly, we demonstrated a body-powered actuator setup that can provide comfort to patients in terms of portability, standalone capability, and cost effectiveness, potentially allowing them to be used in a wide range of wearable robotic applications.

Soft and flexible strain sensors are becoming popular for many robotic applications. This article presents a stretchable capacitive sensor by combining a conductive filler of carbon black with elastomers and implementing shielding to reduce parasitic interference, applied to an underactuated robotic hand. Sensors with different configurations were explored. The results show that a shield introduced to the sensor does have some mitigation effect on external interference. Two sensor configurations were explored: longitudinal interdigitated capacitive (LIDC) sensor, where the interdigitated fingers lie along the same axis as the strain, and transverse interdigitated capacitive (TIDC) sensor, where the interdigitated fingers are orthogonal to the strain direction. The LIDC configuration had better performance than TIDC. The fabricated two-layered LIDC sensor had a gage factor of 0.15 pF/mm and the rates of capacitive creep of 0.000667 pF/s and 0.001 pF/s at loads of 120 g and 180 g, respectively. The LIDC sensors attached to an underactuated robotic hand demonstrate the sensors’ ability to determine the bending angles of the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints.

This research investigates the design and implementation of elastomer-based piezoresistive strain sensors and applies them to a data glove to demonstrate their application. The piezoresistive strain sensors are made by mixing Ecoflex 00-30 and carbon-black nanoparticles and then using stencil and doctor blading to deposit the piezoresistive traces as a mass fabrication technique. The primary objective is to integrate two sensing piezoresistive elements as one single-piece sensor that detects the bending angles of the metacarpophalangeal and proximal interphalangeal joints of each finger. Using a unique zig-zag pattern allows to selectively mask any unwanted piezoresistive sensing. The sensor has a gage factor of 0.68. Experiments conducted have demonstrated that the use of these soft, flexible, and stretchable piezoresistive sensors is repeatable and viable sensors for data-glove and has the potential for other wearable applications.

Dielectric elastomer (DE) sensors have been widely used in a wide variety of applications, such as in robotic hands, wearable sensors, rehabilitation devices, etc. A unique dielectric elastomer-based multimodal capacitive sensor has been developed to quantify the pressure and the location of any touch simultaneously. This multimodal sensor is a soft, flexible, and stretchable dielectric elastomer (DE) capacitive pressure mat that is composed of a multi-layer soft and stretchy DE sensor. The top layer measures the applied pressure, while the underlying sensor array enables location identification. The sensor is placed on a passive elastomeric substrate in order to increase deformation and optimize the sensor’s sensitivity. This DE multimodal capacitive sensor, with pressure and localization capability, paves the way for further development with potential applications in bio-mechatronics technology and other humanoid devices. The sensor design could be useful for robotic and other applications, such as fruit picking or as a bio-instrument for the diabetic insole.

In this paper, the effect of strain rate on the output signal of highly stretchable interdigitated capacitive (IDC) strain sensors is studied. IDC sensors fabricated with pristine Ecoflex and a composite based on 40 wt% of 200 nm barium titanate (BTO) dispersed in a silicone elastomer (Ecoflex 00-30TM) were subjected to 1000 stretch and relax cycles to study the effect of dynamic loading conditions on the output signal of the IDC sensor. It was observed that the strain rate has no effect on the output signal of IDC sensor. To study the non-linear elastic behaviour of pristine Ecoflex and composites based on 10, 20, 30, 40 wt% of 200 nm BTO filler dispersed in a silicone elastomer, we conducted uniaxial tensile testing to failure at strain rates of ~5, ~50, and ~500 mm/min. An Ogden second-order model was used to fit the uniaxial tensile test data to understand the non-linearity in the stress-strain responses of BTO-Ecoflex composite at different strain rates. The decrease in Ogden parameters (α1 and α2) indicates the decrease in non-linearity of the stress-strain response of the composite with an increase in filler loading. Scanning electronic microscopy analysis was performed on the cryo-fractured pristine Ecoflex and 10, 20, 30, and 40 wt% of BTO-Ecoflex composites, where it was found that 200 nm BTO is more uniformly distributed in Ecoflex at a higher filler loading levels (40 wt% 200 nm BTO). Therefore, an IDC sensor was fabricated based on a 40 wt% 200 nm BTO-Ecoflex composite and mounted on an elastic elbow sleeve with supporting electronics, and successfully functioned as a reliable and robust flexible sensor, demonstrating an application to measure the bending angle of an elbow at slow and fast movement of the arm. A linear relationship with respect to the elbow bending angle was observed between the IDC sensor output signal under a 50% strain and the deflection of the elbow of hand indicating its potential as a stretchable, flexible, and wearable sensor.

Growth in patient acceptance of robotic-assisted surgery has led to increased demand and has stimulated research in many new surgical robotic applications. In some cases, the performance of robotic surgery has proven to surpass that of human surgeons alone. A new research area which uses the inherently force-compliant and back-drivable properties of polymers, ionic polymer–metal composite (IPMC) in this case, has shown potential to undertake precise surgical procedures in the delicate environments related to medical practice. This is because IPMCs have similar actuation characteristics to real biological systems, which can help ensure safety. Despite this, little has been done in developing IPMCs for a rotary joint actuator for functional surgical devices. This research proposes and demonstrates the design of a single degree of freedom (1-DOF) robotic surgical instrument with one skeleton-joint mechanism actuated by IPMC with an embedded strain gauge as a feedback unit. The system performance with a developed gain-schedule PI controller is demonstrated. Despite the simplicity of the system, it was proven to be able to cut to the desired depth using the implemented force control (up to 8 gf cutting force).

Wearable electronics and soft robotics are emerging fields utilizing soft and stretchable sensors for a variety of wearable applications. In this paper, the fabrication of a highly stretchable capacitive sensor with a printed carbon black/Ecoflex interdigital capacitor is presented. The highly stretchable capacitive sensor was fabricated on a substrate made from barium titanate–EcoflexTM 00-30 composite, and could withstand stretching up to 100%. The designed highly stretchable capacitive sensor was robust, and showed good repeatability and consistency when stretched and relaxed for over 1000 cycles.

We present, for the first time, the design, development and testing of a portable ultra-lowvelocity flow sensor with a disposable architecture for use in medical applications. 3Dmicroprintingtechnique was used to fabricate high aspect ratio microscopic hair-like structuresfrom conducting polymers, in particular, poly(3,4-ethylenedioxythiophene):polystyrene-sulfonate(PEDOT:PSS). These high aspect ratio micro-hairs are flexible and conductive that can respond toair flowing over them. A disposable and portable flow sensor with a modular design that allowstuning of measurement range was developed, for integration with an automated neonatalresuscitator to provide closed-loop feedback. The developed portable sensor architecture is capableof real-time indication of the air flow velocity range down to few millimeters/second.

In this paper, the behavior of a piezoelectric stack generator subject to a direct mechanical force, such as that experienced by pedestrian loads, is characterized and modelled. A lumped element model is developed that describes the electrical output of piezoelectric stack generators for quasi-static, off-resonance and random input conditions which are typical of underfloor or supporting structure energy harvesters. This research demonstrates the ability for accurate predictions of output voltage and current based on the material properties and geometry of the piezoelectric stack. The behavior of real-world random loading patterns is incorporated in the model, pairing mechanical input with interfacing circuitry requirements in order to maximize energy transfer. The developed model facilitates time-efficient design by reducing the simulation time to the order of seconds.

Demand for highly compliant mechanical sensors for use in the fields of robotics and wearable electronics has been constantly rising in recent times. Carbon based materials, and especially, carbon nanotubes, have been widely studied as a candidate piezoresistive sensing medium in these devices due to their favorable structural morphology. In this paper three different carbon based materials, namely carbon black, graphene nano-platelets, and multi-walled carbon nanotubes, were utilized as large stretch sensors capable of measuring stretches over 250%. These stretch sensors can be used in robotic hands/arms to determine the angular position of joints. Analysis was also carried out to understand the effect of the morphologies of the carbon particles on the electromechanical response of the sensors. Sensors with gauge factors ranging from one to 1.75 for strain up to 200% were obtained. Among these sensors, the stretch sensors with carbon black/silicone composite were found to have the highest gauge factor while demonstrating acceptable hysteresis in most robotic hand applications. The highly flexible stretch sensors demonstrated in this work show high levels of compliance and conformance making them ideal candidates as sensors for soft robotics.

This paper presents a wireless diaphragm actuator and focuses on a lumped parameter grey-box model capable of simulating actuation displacement. Here, modelling aims to provide further insight into this smart material actuator and help facilitate design into new implantable applications. Model parameters were calibrated to a prototype actuator using experimental data and a genetic algorithm optimisation. The model was validated against experimental data and showed a good ability to simulate both static and dynamic diaphragm displacement.

The excellent compliance and large range of motion of soft actuators controlled by fluid pressure has lead to strong interest in applying devices of this type for biomimetic and human-robot interaction applications. However, in contrast to soft actuators fabricated from stretchable silicone materials, conventional technologies for position sensing are typically rigid or bulky and are not ideal for integration into soft robotic devices. Therefore, in order to facilitate the use of soft pneumatic actuators in applications where position sensing or closed loop control is required, a soft pneumatic bending actuator with an integrated carbon nanotube position sensor has been developed. The integrated carbon nanotube position sensor presented in this work is flexible and well suited to measuring the large displacements frequently encountered in soft robotics. The sensor is produced by a simple soft lithography process during the fabrication of the soft pneumatic actuator, with a greater than 30% resistance change between the relaxed state and the maximum displacement position. It is anticipated that integrated resistive position sensors using a similar design will be useful in a wide range of soft robotic systems.

This letter reports a broadband electret-based vibrational energy harvester (eVEH) targeting at applications in low frequency (4–10 Hz) and low excitation (0.1–0.2 g) scenarios. A soft magneto-sensitive elastomer (SMSE) cantilever with low resonance and strong softening nonlinear behaviour is utilized as the broadband oscillator. A spring suspended end-stopper attached to the electret converts low frequency excitation of the SMSE cantilever to high frequency vibrations of the eVEH for efficiency enhancement. An asymmetrical frequency response profile for the SMSE cantilever is intentionally designed to preserve its softening behaviour for broadband performance when the end-stopper is engaged. A proof-of-concept prototype is fabricated and the experiment shows that within a working frequency range of 4.0–8.2 Hz, the eVEH can harvest the average power output of 40.23 μW under a base excitation of 0.2 g. [ABSTRACT FROM AUTHOR]

In this paper, a broadband vibrational energy harvester (VEH) is developed based on a soft magneto-sensitive elastomer (SMSE). The utilization of SMSE provides the VEH with a strong softening effect when it is subjected to the magnetic field of a permanent magnet. A polyvinylidene fluoride (PVDF) layer is attached to the SMSE to convert vibrational energy into electricity. A magneto-electro-mechanical model based on finite element method is developed and is further reduced using assumed modes. Two prototypes are fabricated with different SMSE thicknesses (3 mm and 5 mm respectively). Frequency sweep experiments are conducted to investigate their broadband behavior. The difference between jumping frequencies are 2.39 and 4.34 Hz at a low acceleration level of 0.3 g. With the broadband characteristics of SMSE, the two prototypes are capable of providing power over a wide frequency range and generating an average power of 0.096 μW and 0.11 μW respectively with a load of 4.7 MΩ. [ABSTRACT FROM AUTHOR]