Rashi Tiwari

The state of understanding of ionic polymer metal composite architecture: a review

Ionic polymer metal composites (IPMCs) are electroactive polymers (EAPs) that are used as soft actuators and sensors. Various mechanical or chemical manufacturing techniques, used for manufacturing IPMC, impart a layered structure that plays a significant role in transduction. These layers comprise of the polymer that constitutes the bulk of the IPMC (polymer layer), the metal used for electroding (electrode layer) and the composite consisting of dispersed metal particles in the polymer matrix (intermediate layer). While ionic pendent chains in the polymer layer are responsible for the charge transport in IPMCs, the metal particles in the intermediate and electrode layers act as conductive pathways for current transmission. At the same time the layered structure imparts a capacitive nature to the IPMC, which positively affects the ionic transduction in the IPMC. The role of each layer and the coupling between them is important for improving IPMC properties and, hence, transduction. The aim of this article is to review the research conducted on IPMC fabrication and layered architecture and study their role in IPMC transduction.

Hydraulic artificial muscles

This article presents hydraulic artificial muscles as a viable alternative to pneumatic artificial muscles. Despite the actuation mechanism being similar to its pneumatic counterpart, hydraulic artificial muscles have not been widely studied. Hydraulic artificial muscles offer all the same advantages of pneumatic artificial muscles, such as compliance, light weight, low maintenance, and low cost, when compared to traditional fluidic cylinder actuators. Muscle characterization in isometric and isobaric conditions are discussed and compared to pneumatic artificial muscles. A quasi-static model incorporating the effect of mesh angle, friction, and muscle volume change throughout actuation is presented. This article also discusses the use of hydraulic artificial muscles for low-pressure hydraulic mesoscale robotic leg.

Effect of metal diffusion on mechanoelectric property of ionic polymer-metal composite

Ionic polymer-metal composite (IPMC) manufactured through electroless deposition has distinct electrode intermediate and polymer layers. Models typically study the ion motion inside the polymer layer, neglecting the electrode and intermediate layers. However, it must be noted that IPMC properties are affected by the physics of each layer and the coupling between them. In this paper, a physical phenomenological model explicitly describing the role of each layer is developed. The model predicts (i) the mechanoelectric behavior, (ii) the frequency response, and (iii) the geometric scalability effect on IPMC.

Passive multi-source energy harvesting schemes

Mobile electronics have continually decreased in size; however, mobile power sources have not had comparable increases in energy density or specific energy. Researchers are considering energy harvesting technologies to reduce dependence on batteries, providing alternate sources of power. Combining multiple energy harvesters onto a single platform is a logical and practical method to increase energy output and system robustness. This study explored the dynamics of two passive, multi-source energy harvesting schemes: disparate sources of piezoelectric and photovoltaic, as well as an array of piezoelectrics. A series and a parallel topology were explored for each scheme. For both the schemes, the series topology lends itself to high-level, low-duty cycle load characteristics as it is able to achieve greater amounts of energy on a storage capacitor. The parallel topology lends itself to low-level, high-duty cycle load characteristics due to increased maximum power levels. Both the parallel and the series topologies of the array of piezoelectrics effectively combine the power from the two harvesters in the absence of differences between the two signals. The series topology is insensitive to amplitude differences, and the parallel topology is insensitive to a phase angle or a frequency difference.

A Novel Ionic Polymer Metal ZnO Composite (IPMZC)

The presented research introduces a new Ionic Polymer-Metal-ZnO Composite (IPMZC) demonstrating photoluminescence (PL)-quenching on mechanical bending or application of an electric field. The newly fabricated IPMZC integrates the optical properties of ZnO and the electroactive nature of Ionic Polymer Metal Composites (IPMC) to enable a non-contact read-out of IPMC response. The electro-mechano-optical response of the IPMZC was measured by observing the PL spectra under mechanical bending and electrical regimes. The working range was measured to be 375–475 nm. It was noted that the PL-quenching increased proportionally with the increase in curvature and applied field at 384 and 468 nm. The maximum quenching of 53.4% was achieved with the membrane curvature of 78.74/m and 3.01% when electric field (12.5 × 103 V/m) is applied. Coating IPMC with crystalline ZnO was observed to improve IPMC transduction.

Mechanoelectric Transduction in Ionic Polymer-Metal Composite

The ability of ionic polymer-metal composite (IPMC) to generate current on mechanical deformation, defined as mechanoelectric transduction, can be exploited for design and development of numerous sensors and energy harvesters. However, sensor application of IPMC is currently limited due to the lack of understanding of the transduction mechanism. This paper presents a physics-based mechanoelectric model that takes into account material properties, electrostatic phenomenon, and ion transport in the IPMC. Experimental verification of the model predictions is also reported.

Energy balance for peak detection method in piezoelectric energy harvester

Numerous methodologies using switching circuits for harvesting vibrational energy via piezoelectric materials have been put forth. These methods generally require knowledge of the occurrence of peak deflections in the vibrations, so that the amount of harvested energy can be maximized. Below, a method of peak detection is outlined that satisfies the missing link between mechanical vibrations and systems that harvest energy from those vibrations. The system employs passive differentiation to initially identify peak positions in the time domain, followed by an active zero-crossing detector coupled with a latch circuit to record the peak detection. A microprocessor is used to check the state of the latch and begin harvesting when a peak is identified. The method requires low power for its operation and has wide bandwidth of operation.

Ionic polymer–metal composite mechanoelectric transduction: effect of impedance

Ionic polymer–metal composites (IPMCs) are commonly used as soft actuators due to their electromechanical response. However, the reverse phenomenon, i.e. IPMCs ability to generate charge on application of mechanical strain (mechanoelectric response), is not very well understood. The concept of mechanoelectric transduction and its dependence on complex IPMC architecture comprising of electrode, polymer and composite layer is illustrated with a phenomenological model. The impedance model takes into account the charge transport inside the polymer and layer properties in terms of their impedances. The model lucidly indicates the significance of capacitance in IPMC transduction. The impedance model is used for studying IPMC step and frequency response and the effect of IPMC capacitance on its application as energy harvester.

Hydraulically actuated artificial muscles

Hydraulic Artificial Muscles (HAMs) consisting of a polymer tube constrained by a nylon mesh are presented in this paper. Despite the actuation mechanism being similar to its popular counterpart, which are pneumatically actuated (PAM), HAMs have not been studied in depth. HAMs offer the advantage of compliance, large force to weight ratio, low maintenance, and low cost over traditional hydraulic cylinders. Muscle characterization for isometric and isobaric tests are discussed and compared to PAMs. A model incorporating the effect of mesh angle and friction have also been developed. In addition, differential swelling of the muscle on actuation has also been included in the model. An application of lab fabricated HAMs for a meso-scale robotic system is also presented.

Variable Thickness IPMC: Capacitance Effect on Energy Harvesting

Ionic Polymer Metal Composites (IPMCs) are manufactured by electroless deposition of metal on Nafion. This deposition method results in the IPMCs with thickness between 0.17mm to 0.20mm with the electrode thickness of around a few m each. It is now generally accepted that on mechanical deformation IPMC produces charge thus making these materials potentially suitable for energy harvesting applications. Due to thin metal plating and inherited flexibility of the Nafion film the IPMCs suffer in stiffness that may be required for some energy harvesting applications. Also earlier works have shown that 0.20mm thick IPMC produce better battery charging than 0.17mm thick one. Hot pressing, using metal mold, Nafion films was employed to produce thicker and comparatively stiffer IPMCs electroded with Palladium metal. Palladium was used because of shorter manufacturing time. This IPMC shows improved energy harvesting. Due to the increased thickness these IPMCs also function as better capacitors than their conventional counterparts. On application of voltage, these IPMCs show charging and discharging effects of a capacitor. This property of IPMC may be useful for storing charge.