Indrek Must

Ionic electroactive polymer artificial muscles in space applications

A large-scale effort was carried out to test the performance of seven types of ionic electroactive polymer (IEAP) actuators in space-hazardous environmental factors in laboratory conditions. The results substantiate that the IEAP materials are tolerant to long-term freezing and vacuum environments as well as ionizing Gamma-, X-ray, and UV radiation at the levels corresponding to low Earth orbit (LEO) conditions. The main aim of this material behaviour investigation is to understand and predict device service time for prolonged exposure to space environment.

In situ scanning electron microscopy study of strains of ionic electroactive polymer actuators

We have developed a technique to determine the bending strain of ionic electroactive polymer actuators without the use of the macroscopic bending geometry. In situ comparisons of the scanning electron microscope micrographs from a bending ionic electroactive polymer actuator, using a digital image correction methodology, identify its bi-directional deformation field. The developed technique allows verification of the factual axial and thickness strains of any notional layer of the actuator, including the outer surfaces of the electrodes. Thus, calculation of the bending and thickness strains of the ionic electroactive polymer laminate becomes possible. Moreover, the technique allows the determination of the position of the neutral layer of bending that is an important requirement for the calculation of the second area and bending moments of the beam. The four examples presented demonstrate the potential variations of the bending schemes, in cases where the neutral layer is at the centroid and shifted away from the centroid.

Lifetime measurements of ionic electroactive polymer actuators

This article is focused on proposing a unified methodology for automating the measurement procedures of ionic electroactive polymer actuators. The proposed methodology and large-scale automation would make testing ionic electroactive polymer actuators less labor-intensive and allow analyzing many ionic electroactive polymer actuators simultaneously. Defining a clear framework for testing ionic electroactive polymer actuators performance and reliability would make the testing process reproducible and provide better comparison between ionic electroactive polymer actuators of either different or similar classes. Our methodology separates two types of degradation: degradation during operation and spontaneous self-degradation.

Direct assessment of solid–liquid interface noise in ion sensing using a differential method

This letter presents a microelectrode cell dedicated to direct assessment of the solid–liquid interface noise without recourse to a reference electrode. In the present design, two identical TiN electrodes of various sizes are used for differential measurements in KCl-based electrolytes. Measured noise of the TiN|electrolyte system is found to be of thermal nature. Scaling inversely with electrode area, the noise is concluded to mainly arise from the solid–liquid interface. This noise is comparable to or larger than that of the state-of-the-art MOSFETs. Therefore, its influence cannot be overlooked for the design of future ion sensors.

Linear modeling of elongated bending EAP actuator at large deformations

This paper describes a linear dynamic model of an elongated bending Electroactive Polymer (EAP) actuator applicable with deformations of any magnitude. The model formulates relation of a) voltage applied to the EAP sheet, b) current passing through the EAP sheet, c) force applied by the actuator and d) deformation of the actuator. In this model only the geometry of EAP piece and four empirical parameters of the EAP material: a) bending stiffness, b) electromechanical coupling term, c) electrical impedance and d) initial curvature are considered. The contribution of this paper is introducing a model that can be used to characterize the properties of different EAP materials and compare them. The advantage of the model is its simplicity and ability to provide insights in to the behavior of bending EAPs. Additionally, due to linearity of the model, the real-time control is feasible. Experiments, using Ionomeric Polymer-Metal Composite (IPMC) sheet from Environmental Robotics Inc., where carried out to verify the model. The experimental results confirm the model is valid.

Biomimetic supercontainers for size-selective electrochemical sensing of molecular ions

New ionophores are essential for advancing the art of selective ion sensing. Metal-organic supercontainers (MOSCs), a new family of biomimetic coordination capsules designed using sulfonylcalix[4]arenes as container precursors, are known for their tunable molecular recognition capabilities towards an array of guests. Herein, we demonstrate the use of MOSCs as a new class of size-selective ionophores dedicated to electrochemical sensing of molecular ions. Specifically, a MOSC molecule with its cavities matching the size of methylene blue (MB+), a versatile organic molecule used for bio-recognition, was incorporated into a polymeric mixed-matrix membrane and used as an ion-selective electrode. This MOSC-incorporated electrode showed a near-Nernstian potentiometric response to MB+ in the nano- to micro-molar range. The exceptional size-selectivity was also evident through contrast studies. To demonstrate the practical utility of our approach, a simulated wastewater experiment was conducted using water from the Fyris River (Sweden). It not only showed a near-Nernstian response to MB+ but also revealed a possible method for potentiometric titration of the redox indicator. Our study thus represents a new paradigm for the rational design of ionophores that can rapidly and precisely monitor molecular ions relevant to environmental, biomedical, and other related areas.

Long-term degradation of the ionic electroactive polymer actuators

The research is focused on lifetime and degradation of ionic electroactive polymer actuators (IEAP). The lifetime measurements were carried out using identical methodology upon the different IEAP types. The experiment conducted with large number of samples shows that two types of degradation have serious effect to the IEAPs: degradation during operation and spontaneous self-degradation. Additionally, two ways of occasional damage decrease their overall reliability. In the scope of the current paper we describe degradation of two different types of IEAP actuators: with carbonaceous electrodes and with conducting polymer electrodes. Nevertheless, the common evolutionary trends, rather than the comparative data analysis or formal statistics of all particular samples, are given. Analyzing the electromechanical and electrical impedances of the samples during their whole lifetime, we have found that observing the electric current gives adequate information about the degradation level of any IEAP actuator. Moreover, tracking this electrically measurable parameter enables detecting the occasional damage of an actuator.

Thermal behavior of ionic electroactive polymer actuators

The high spatial, temporal, and thermal resolution of the thermal imaging system Optotherm EL InfraSight 320 is used for investigation of the thermal behavior of the ionic electroactive polymer (IEAP) actuators. The resolution of 10-20 pixels in the direction of their thickness is close to the theoretical limit restrained by the infrared light wavelength registered by the imaging system. The videos, recorded with the frame rate of 30 fps, demonstrate showy the propagation of heat along the membrane. The analysis of the thermal images provides the foundation for precise modeling of the IEAP actuators, taking into account the thermally induced mechanical and electrochemical effects. Experiments conducted with the IEAP actuators of different types (ionic polymer-metal composite, carbon-polymer composite, conducting polymer actuators) allow comparing their efficiencies. The experiments show demonstrable, that the IEAPs, used improperly, overheat to the inadmissible temperatures within seconds only. This, in turn, evaporizes the volatile electrolyte, and shortens the life expectancy of the IEAP devices.

Pulse-width-modulated charging of ionic and capacitive actuators

We report on using a pulse-width-modulated (PWM) signal for driving the ionic electroactive polymer (IEAP) actuators. The traditional approach for driving the IEAP actuators involves generation of complex analog signals. The proposed control method is substantially different: a digital PWM driving waveform is applied using an H-bridge driver. The two outputs of the H-bridge driver are switched between three states - they are either connected to the positive or negative power supply terminal, or disconnected, with a high-impedance output. An H-bridge can also be used for short-circuiting of the actuator, in turn improving the power-efficiency of the IEAP actuator. This control method is particularly beneficial in applying IEAP actuators in soft robotics.

Smart insole sensors for sports and rehabilitation

A light-weight, soft, robust and low cost sensory system integrated into the inner soles of footwear is being developed that channels information to a mobile device, allowing to assess the ergonomics of the technique applied and to achieve improved performance in several fields of sport, to develop orthopedic footwear or monitor elevated plantar pressures for several fields of medicine, including early detection of diabetic foot ulceration. The advantages and disadvantages of several sensory material types were considered in the present work, focusing on signal reproducibility for periodic pressure measurements, response frequency and long-term stability, especially after extended load periods. Promising results were obtained for both capacitive and resistive sensory materials, utilizing virtually the same electronics platform for both types.