Abstract In recent years carbon nanotubes (CNTs) have been widely used for the realization of polymeric matrix nanocomposites for strain monitoring applications in civil, biomedical and aerospace engineering. In fact, by embedding CNTs in an insulated polymer matrix, it is possible to realize a conductive nanocomposite with piezoresistive behaviour which allows to monitor the occurring strains through an electrical resistance change. In this work a conductive coating made of Multi-Walled Carbon Nanotubes (MWNTs) and PolymethylMethacrilate (PMMA) is fabricated and is applied onto a fiberglass structure surface. In order to characterize the electrical behaviour of the coating and its capability to sense strain, an experimental campaign is carried out by applying a voltage to the manufactured coating. Its variations throughout the surface in the longitudinal and transverse directions are then evaluated to identify the electric field distribution and its dependence on strain.

In this work, the arising of stick-slip dissipation as well as the global mechanical response of carbon nanotube (CNT) nanocomposite films are tailored by exploiting a three-phase nanocomposite. The three phases are represented by the CNTs, a polymer coating localized on the CNTs surface and a hosting matrix. In particular, a polystyrene (PS) layer coats multi-walled carbon nanotubes (MWNTs) that are randomly dispersed in a polyimide (PI) matrix. The coating phase is strongly bonded to the CNTs outer sidewalls ensuring the effectiveness of the load transfer mechanism and reducing the material damping capacity. The coating phase can be thermally-activated to modify, and in particular, decrease the CNT-matrix interfacial shear strength (ISS) thus facilitating the stick-slip onset in the nanocomposite. The ISS decrease finds its roots in a partial degradation of the coating phase and, in particular, in the formation of voids. By weakening the CNT/polymer interfacial region, a significant enhancement in the material damping capacity is observed. An extensive experimental campaign consisting of monotonic and cyclic tensile tests proved the effectiveness of this novel multi-phase material design.

Among anode materials for lithium ion batteries, silicon (Si) in known for high theoretical capacity and low cost. Si exhibits over 300% volume change during cycling, potentially providing large displacement. In this paper, we present the design, fabrication and testing of a multifunctional NCM-Si battery that not only stores energy, but also utilizes the volume change of Si for actuation. The battery is transparent, thus allowing the visualization of the actuation process during cycling. This paper shows Si anode design that stores energy and actuates through volume change associated with lithium insertion. Experimental results from a transparent battery show that a Cu current collector single-side coated with Si nanoparticles can store 10.634 mWh (charge)/2.074mWh (discharge) energy and bend laterally with over 40% beam length displacement. The unloaded anode is found to remain circular shape during cycling. Using a unimorph cantilever model, the Si coating layer actuation strain is estimated to be 30% at 100% SOC.

Piezoresistive strain sensors can be manufactured by embedding carbon nanotubes (CNTs) in an insulating polymer matrix, by taking advantage of CNTs superior electromechanical properties. In particular, the electromechanical properties find their roots in the conductive network formed by the randomly dispersed CNTs, through which the current can flow. When a mechanical strain occurs the conductive network configuration varies, changing the overall material conductivity. In this study this concept is being exploited to form a CNTs-based functional paint that allows to monitor ultra-large structural areas, in multiple directions, with an easy to assemble and processing approach. In particular, CNTs are dispersed in a PolymethylMethacrylate (PMMA) matrix following a carefully designed process to achieve a proper viscosity for direct painting onto a large in scale structure. Electromechanical tests are performed to characterize the piezoresistive behaviour of the coating in static and dynamic loading conditions. The results showed the great sensitivity of the coating to strain. The proposed approach to directly paint a sensitive coating onto the structure to be monitored has the advantages of: ultra-low weight, direct contact with the structure to be monitored and an extremely simple installation procedure.

An identification module is designed and studied to detect and evaluate the cracks at the welding joint area using a new smart coating sensor and entropy measurement. A new piezoelectric composite coating is applied at a welding joint to possibly charge the wireless data transmission module as an energy harvester. It also sends warning and dynamic signals for crack evaluation when the crack damage occurs. More specifically, entropy calculation is introduced to quantify the weak perturbations, which is caused by the material nonlinearity and crack breathing at the crack tip and hidden in the signal. In this paper, a finite element model (FEM) of a welded beam experiencing dynamic base motion is established as an example. The effects of material nonlinearity and crack breathing on structural dynamics response are simulated by creating nonlinear material property around the crack area and contact pair of crack walls, respectively. After obtaining the time domain vibration signal, crack severity is quantified using Sample Entropy. It is concluded that, even at very early stages of 5% of the beam thickness for the crack depth, the entropy variation is significant for a damaged beam compared with the healthy one.

This paper presents the development process of an electrically insulating and liquid-impermeable coating for piezoelectric actuators. Against the background of flow investigations of an adaptive airfoil in a water tunnel the adaptive lip including PZT-ceramics for the active lip deformation must be insulated and sealed up against the ingress of moisture. Due to high electric field strength of 2 kV/mm between electrodes of multilayer actuators any ingress of moisture would lead to a reduction of the dielectric strength and may cause a short circuit. In order to prevent failure of the adaptive lip the electrical connections of the actuators have to be insulated by a waterproof coating. A service life of at least 10 7 load cycles at a frequency of 100 Hz is required for the actuators. Therefore the coating should be as ductile as possible otherwise it could crack and water could diffuse into the actuators. That is why the yield strength of the coating has to be higher than of the actuators, which is 0.3 %. For the investigation of the waterproofness several samples are coated with different materials in various processes. First the actuators are moulded in epoxy resin and then a diffusion-resistant PVF-foil is applied. After a screening of different materials, an additional coating with a two-component tar-epoxy resin in combination with a gold coating applied by a PVD process seems to be the most suitable process. Another promising waterproof coating is the atomic layer deposition (ALD). It is a slightly changed chemical vapor deposition (CVD) and referring to the studies of Abdulagatov et al. an ALD of aluminum oxide (Al 2 O 3 ) and titanium dioxide (TiO 2 ) can slow down the corrosion of static copper specimens in water for ∼80 days [1]. Through a redrying procedure during test intermissions an increased underwater service life of the piezoelectric actuators is achieved.

Arthropod animals like scorpions with modular body parts can be an inspiration for a robot’s structure. The design presented here relays on inter-connected origami towers, but could also be easily disassembled. Each origami tower is fully autonomous and at the same time is part of the robot as a whole. The towers are positioned between two platforms that enable modularity. The scorpion’s tale shape is achieved by the varying platform diameter resulting in cone-like form. Each tower is actuated independently to enable multiple degrees of freedom. Maneuvering with separated units, assists in easier reparation as well as replacement. Detaching the towers into separate parts makes this structure develop more precise movements, since every unit will move autonomously. Therefore, having a higher number of separated movements combined leads to a smooth bionic movement. So, the overall hierarchy will be modular contributing to a greater curvature bending of the whole structure. Actuating and maneuvering the robot in the main concept is done by separated electro motors, built in the platform. The basic structure will be built from thick paper with plastic coatings. The thick paper itself is lightweight, but at the same time flexible. To protect the paper towers, double plastic foil is placed as an outer coating which acts as an origami cover. This transparent layer is elastic hence it can follow and support the individual units’ movements. This work is focused on understanding origami towers kinematics and different combinations of inter-connected towers to achieve multiple degrees of freedom. A conceptual model is developed, supported by CAD and mathematical models. At the end a prototype is presented.

The actuation mechanisms of cnt-based materials are still controversially discussed. It is not common sense whether it is a macroscopic volume effect caused by ion intercalation or electrostatic repulsion of equally charged cnts or a nanoscopic effect of filled electron anti-bonding orbitals of the carbon atom or interactions with ions docking on the carbon surface. In the presented paper arrays of highly aligned multi-walled carbon nanotubes (mwcnts) are used which are stabilized by a polypyrrole-coating. The samples are tested along the cnt-orientation and in perpendicular mode to analyze the influence of the structure-ion interaction. The mwcnt-arrays exhibit only a total length of approximately 2.8 mm but by coating with polypyrrole larger geometries can be tested. The actuation is analyzed using an in-plane test and an actuated tensile testing. Free strain can be detected using the first set-up, the second method is carried out to evaluate the mechanical stability of the samples. As might be expected, the material shows a strong anisotropic active behavior with the actuation along the tube axis being only half of the value detected at the perpendicular oriented samples. The findings point out that an intercalation of ions into the charged CNT-architecture seems here to be the dominating mechanism.

In this paper, we have introduced the bandwidth of a Tilted Fiber Bragg Grating (TFBG) as a measurand and combine it with the central Bragg wavelength to address its cross-sensitivity with temperature and strain. We have developed a method for coating the TFBG with a thermochromic material and characterized the coated TFBG sensor under temperature and strain variations. We observed that the spectral bandwidth is sensitive only to the temperature change while the central Bragg wavelength is sensitive to both the strain and temperature. Therefore, we can measure the temperature from the TFBG bandwidth alone and measure the strain from the TFBG central wavelength after compensating for temperature induced wavelength change.

Shape memory alloy (SMA) materials, such as Nickel Titanium (NiTi), can generate stress and strain during phase transformation induced by thermomechanical stimulation. Therefore, they may be used to construct active actuating devices for various biomedical applications such as smart surgical tools. Since temperature rise during the operation of SMA devices may damage the surrounding tissue, it is important to thermally shield such devices. We propose to use polydopamine (PDA) as an insulating coating for NiTi-based smart needles. PDA is a biomolecule (dopamine) derived polymer that can form conformal coating on various materials including NiTi. It is hypothesized that the surface temperature of the PDA coated needle can be reduced by the low thermal conductivity of PDA and the thermal resistance of the PDA/NiTi interface. Our experiments conducted in ambient air at room temperature showed that the coating reduced the surface temperature by as much as 45%. In this paper, we will present the thermal insulating performance of the PDA coating on NiTi wires. An experimental setup where the wire is embedded inside a gel phantom/tissue has been developed to simulate needle-tissue interaction. Effects of the coating thickness (material thermal resistance) and the number of layers (interfacial thermal resistance) will be discussed. 2D finite element analyses (FEA) were performed using ABAQUS to investigate the thermal distribution around the coated NiTi wires and the tissue gel phantom. In addition, using thermal distribution, potential tissue damage was assessed.

Ionic polymer-metal composites (IPMCs) have intrinsic sensing and actuation capabilities. However, IPMCs require ionic hydration to operate. As the most commonly used solvent, water content contained in the polymer changes with the humidity level of the ambient environment, which affects the sensing behavior of an IPMC in air. Motivated by the need to ensure consistent sensing performance of IPMCs under different ambient environments, in this paper we propose thick (up to 10 micrometers) parylene C coating for IPMC sensors, develop effective coating processes, and evaluate the stability of the encapsulated sensors in air. During the process of parylene coating, water molecules would evaporate inside the deposition chamber, resulting in the encapsulated IPMCs’ losing sensing capability. To address this challenge and control the hydration level of an encapsulated IPMC, the proposed fabrication process comprises major steps of parylene deposition, water absorption, and SU-8 seal. The influence of hydration level controlled by the water absorption step is studied to improve the sensitivity of the IPMC sensor. The water impermeability of the proposed encapsulation technique is tested in different media. Experiments have also been conducted to evaluate the performance of the encapsulated IPMC sensor. The sensing consistency and the lifetime of an encapsulated sensor in air are studied in an environment with changing humidity, along with the comparison with an uncoated IPMC sensor. Experimental results show that the proposed thick parylene coating can effectively maintain the water content inside the IPMC and reduce the interference due to the ambient humidity change, which allows IPMC sensors to be used in many practical applications.

Two types of micro-mechanical memory cells are introduced in this paper. The programmable parameters are the resonant frequency of a micro-mechanical bridge and the tip deflection of a micro-mechanical cantilever. For both cases, the actuation was done by laser pulses that locally heated the vanadium dioxide (VO 2 ) thin film coating. Due to the hysteretic behavior of the mechanical properties of the VO 2 film coating across the transition, a different “memory state” was programmed with every pulse. The memory state remained programmed after the pulse ended, as long as the sample was maintained at a specific temperature (programming temperature) by using a Peltier heater. The resetting of the mechanical memory cell was accomplished by driving the temperature to regions outside the hysteretic region.

Polyvinyl alcohol (PVA) films with embedded electrically-responsive liquid crystal (LC) ellipsoids were fabricated to develop a membrane coating featuring tunable roughness. Membranes (∼30 microns thick) were placed between opposing pieces of indium-tin oxide (ITO) glass, creating electrodes for creation of a uniform electric field. Applied voltages ranged from 0V–350 V, as films were observed using an optical microscope. Thin-film interference patterns were observed in various regions of each film and were measured. Contour plots of film displacement were created and showed elevations across the observed region. The area of the first dark fringe regions, assumed to be in contact with the top glass surface, were measured as a function of applied voltage. The maximum displacement of the film was estimated to reach 1.5 microns and the area in contacted with the top glass surface increased 127% between 0–350 V. Finite element modelling results illustrate the influence of polarity on the roughness of the film surface.

Aqueous magnetorheological (MR) suspensions of composite carbonyl iron particles (CCIPs) were prepared with carbonyl iron particles and an organic reagent coating (N-polyether, N, N, N,-acetyloxy) 2, 6-aminion-1, 3, 4-thiadiazole dimer (EAMTD). The properties of the CCIPs, including morphology, structure, and magnetic behaviors, were characterized using scanning electron microscopy (SEM) and a vibrating sample magnetometer (VSM). The MR properties of the aqueous MR suspensions were analyzed via a strain-controlled parallel disk rheometer equipped with a magnetic field source. The results show that the stability and redispersibility of the aqueous MR suspensions were greatly improved, and the yield stress is influenced by the EAMTD coating layer of the CCIPs.

Lately, there has been an increased demand for vehicle manufacturers to incorporate a large number of communication, security, guidance and entertainment devices in their new vehicle models. In recent decades, the list has expanded from the AM and FM radio antennas to include GPS, mobile phone, collision avoidance radar, Digital Radio and Digital TV antennas. In addition, new technologies such as vehicle to vehicle and vehicle to road side communication are being implemented at 5.9 GHz in the next generation of vehicles. In the past the AM/FM antenna was typically a mast antenna protruding from the vehicle’s exterior, recently however, the trend has been to limit the visibility of vehicular antennas as much as possible to improve vehicle design and aerodynamics. This has lead to integration of antennae so that they become a seamless part of the vehicle structure. This paper reports on a parametric study of embedding an antenna in a polymeric composite substrate in relation to several material processing and coating parameters.

This paper describes the sputter deposition and characterization of nickel titanium (NiTi) shape memory alloy thin film onto the surface of an optical fiber Bragg sensor. The NiTi coating uniformity, crystallinity and transformation temperatures are measured using scanning electron microsocopy, x-ray diffraction and differential scanning calorimetry respectively. The strain in the optical fiber is measured using centroid calculation of wavelength shifts. Results show distinct and abrupt changes in the optical fiber signal with the four related transformation temperatures represented by the austenite-martensite forward and reverse phase transformations. These tests demonstrate a coupling present between optical energy and thermal energy, i.e. a modified multiferroic material.