Ionic Polymer-metal Composite Sensor Research Articles

Fabrication and application of wearable ionic polymer metal composite sensors for sports science

Ionic polymer-metal composite (IPMC) sensors were fabricated and investigated for quantifying impact energy in sports applications. Nafion membranes were roughened and electroless plated with gold-platinum electrodes to form IPMCs. When subjected to impacts of varying energies, the IPMCs generated transient voltage spikes whose peak amplitudes and slopes showed exponential relationships with the impact energies. Empirical models were developed correlating the IPMC voltage response features to the impact energies, achieving measurement accuracy within ±10 % RMS error over the tested dynamic range from 0.005 J to 1 J. The IPMC voltage profile was found to depend primarily on the impact energy and resultant strain rate, rather than impactor properties or contact geometry. Proper calibration procedures for each IPMC sensor before deployment were required to account for device-to-device variations. The results demonstrate the potential of IPMC sensors for continuous monitoring of athletes' impacts during sports activities. Further optimization is needed to improve the robustness, repeatability, and stability of the IPMC sensors under realistic sports conditions for reliable field performance.

Possible design/fabrication of a soft biomimetic magic (flying) carpet made with Ionic Polymer Metal Composites (IPMCs)

A novel design of an artificial soft robot similar to the motions of a magic carpet is presented. Reported in the planning, designing, and fabricating of a biomimetic magic (flying) carpet made with ionic polymer metal composites (IPMCs). A new family of IPMC sensors and actuators is proposed to be used as a flexible plate and a flexible carpet to form a biomimetic flexible soft sensor and actuator system. The magic carpets made with IPMCs will be experimentally capable of bending, rolling, turning, twisting, and simultaneous sensing. However, their sensing characteristics as a soft biomimetic magic carpet feedback sensor are shown to have great potential for ubiquitous robot-human interactions (RHI). Upon various types of deformation, they are shown to generate unique output voltage signals and transient currents to be correlated to the actual magic carpet feedback force. Furthermore, a flexible sheet of IPMC can be actuated simultaneously on the fly by a small power supply embedded in the magic carpet. The magic carpet version of IPMC can be applied as smart skin to develop human-like dexterous and soft manipulation.

Kirigami-inspired self-powered pressure sensor based on shape fixation treatment in IPMC material

Rapid advances in sensing technologies have brought about the fast development of wearable electronics for biomedical applications. Since its conception, over the years, the ionic polymer metal composite (IPMC) is a new man-made material that has demonstrated its great potential for wearable devices due to self-powered sensing capabilities. Here, for the first time, a novel Kirigami technique with unique cut patterns has been employed for designing a stretchable IPMC sensor with enhanced performance. As Nafion itself exhibits the characteristic of shape memory polymer, the Kirigami structure that is built using the IPMC can be buckled up by loading and heating the IPMC above the deformation temperature, T def. To further enhance the memory effect, the Kirigami structure has further been locked by immersing it in potassium hydroxide for the formation of deprotonated Nafion. The voltage output of the proposed IPMC with Kirigami shows a superior performance with 3 times improvement over the conventionally planar electrodes. Dynamic tests with a range of displacements have been performed to validate the sensor design and the robustness of the Kirigami structure. This novel Kirigami-based IPMC sensor has been successfully demonstrated for braille sensing by designing 7 independent electrodes.

The effects of ethanol content on the electrical response of IPMC for drinking perception

Ionic polymer metal composite (IPMC) is a kind of smart material that integrates functions of actuating and sensing. In this paper, we demonstrated a new sensing function of IPMC to detect the concentration of ethanol by investigating the effects of ethanol content on the electrical response of IPMC. Benefiting from the ion migration effect in the Nafion matrix, the voltage of IPMC varies with different ethanol concentrations. It was found that the response process of IPMC to ethanol solution can be divided into a rapid response stage caused by concentration difference and a slow response stage caused by uneven mechanical stress. The voltage change caused by the concentration difference was defined as the response voltage, and the sensitivity of the IPMC sensor to ethanol concentration was 4.39 mV. We have demonstrated the good cyclability and stability of IPMC to ethanol by experiments. Furthermore, the IPMC sensor was applied to respiratory monitoring after drinking. It has been proven that the IPMC sensor can monitor the changes in alcohol concentration after drinking, which is of great significance for the prevention of stroke after drinking.

Physics-based irrational transfer function of IPMC sensor output voltage⋆

Ionic Polymer-Metal Composite (IPMC) sensors are a kind of soft and wet polymeric sensors and are expected to be used in soft robotics. Zhu's model is one of the most promising physical models for IPMC sensors and is represented by a set of partial differential equations for cation concentration, water concentration, and potential. This paper first derives the exact solution of Zhu's sensor voltage model using the Laplace transform. Specifically, this paper derives irrational (infinite-dimensional) transfer functions from the deformation curvature to the outputs such as the cation concentration, the water concentration, the electric potential, and the sensor output voltage. The obtained frequency response of the sensor voltage is confirmed to be consistent with that of the finite element method in a previous study. Furthermore, this paper derives the DC gain and the peak gain of the transfer function of the open-circuit sensor voltage.

Highly Sensitive and Stable Encapsulated Ionic Polymer–Metal Composite Sensor Under the Optimal Water Content

Sensitivity and stability are crucial for sensors in practical applications. For ionic polymer–metal composite (IPMC) sensors, these properties are closely related to inner water molecules, due to the unique composite structure. In this article, a technique for encapsulating IPMC sensors under the optimal water content is proposed for the first time. First, by means of gravimetric analysis, the amount of water removed from the saturated IPMC sensor by evaporation was measured to acquire the optimal water content. Second, IPMC sensors were encapsulated by polyolefin (POF) shrink film under the optimal water content (denoted as IPMC-OE). The results manifest that the sensing property obviously increased after quantitative removal of water molecules (i.e., the ratios of water lost range from 1.8 to 3.6). The sensitivity of IPMC-OE is 4–6 times higher than that of the naked IPMC sensor not encapsulated by a polymer film (denoted as IPMC-N). Besides, the stability of IPMC-OE has also been evidently enhanced. The proposed method is a simple, low-cost, and facile strategy. The IPMC-OE sensors maintain high signal strength and stable output signal after up to 19000 deformation cycles. Moreover, apart from underwater detection of biomimetic robotic fish and UUV, the monitoring of wrist pulse, breathing, and finger bending has also been accomplished in the air by IPMC-OE sensors. It is also proved that sensing in media ranging from water to air and a physical quantity ranging from displacement to water flow velocity can be realized. The article guides the performance optimization and practical application of IPMC sensors.

The effects of contact area on pressure sensing of ionic polymer metal composite sensor with a soft substrate

Ionic polymer metal composite (IPMC) has been extensively studied as a pressure sensor. Nevertheless, few works have focused on the size effects of external loadings on IPMC pressure sensing. Herein, we investigated the effects of contact area on pressure sensing of an IPMC sensor. By placing a soft substrate behind the IPMC, we enlarged the strain zone when IPMC was deformed. A series of experiments were carried out by changing the radius of loading. And the experimental results revealed that the signal generation of IPMC sensor depends on the compression and bending coupling effects, which even performed a reversal from negative to positive (from −0.184 mV to 0.102 mV) with the increase of the radius of loadings (from 1 mm to 4 mm). Combining the compression model and finite element simulation, we calculated the theoretical voltage and quantitatively compared the experimental results, which showed good consistency. It may provide a new and effective way to simplify the measurement of the contact area.

Hierarchical Structure Fabrication of IPMC Strain Sensor With High Sensitivity

In this paper, a biological template method is introduced and investigated to fabricate ionic polymer-metal composite (IPMC) strain sensor with bionic hierarchical structures. We utilized the multi-level structure of reed leaf surface, which can improve the contact area between the substrate and the electrode layers. Hierarchical structures were observed on the IPMC samples, including pyramid strips with the width in the range of 60–80 μm as well as synaptic scatters with diameter around 10 μm. In addition, five kinds of sensors with different interface structures were obtained by combining the traditional microneedle roller roughening and chemical plating processes. It was found that the IPMC sensor with reed-leaf and microneedle structure on each side presented the best performance, along with a high linearity, a sensitivity of 62.5 mV/1% and a large generated voltage peak under given mechanical stimuli, which is 3.7 times that of the sample fabricated without roughening.

A hyperelastic porous media framework for ionic polymer-metal composite actuators and sensors: thermodynamically consistent formulation and nondimensionalization of the field equations

Ionic polymer-metal composites (IPMCs) are smart materials that exhibit large deformation in response to small applied voltages, and conversely generate detectable electrical signals in response to mechanical deformations. The study of IPMC materials is a rich field of research, and an interesting intersection of material science, electrochemistry, continuum mechanics, and thermodynamics. Due to their electromechanical and mechanoelectrical transduction capabilities, IPMCs find many applications in robotics, soft robotics, artificial muscles, and biomimetics. The current literature is sparce in multiphysics models that account for large deformations, coupled ion-solvent transport, the porous structure of the membrane, and lossy electrodes under finite-strains. This study addresses this by developing a new, hyperelastic porous media modeling framework for IPMCs using the principles of continuum thermodynamics and multiphasic materials. This framework compactly captures the broadest strokes of IPMC modeling methodologies, summarizing them in the form of general constitutive requirements placed on thermodynamic potential describing the polymer skeleton. A simple IPMC model is derived under this framework which captures the finite-strain deformation of a hyperelastic material, accounting for the coupled ion-solvent transport through the porous polymer, and resistive electrodes deforming with the skeleton. The resulting governing equations are further cast into a generalized nondimensional formulation, and an expansive set of unique dimensionless -groups are derived for IPMC actuator and sensor devices. This new framework and the nondimensional formulation lay the groundwork for future research and an expansive characterization of IPMC transduction phenomena via dimensional analysis.

Symbolic finite element discretization and model order reduction of a multiphysics model for IPMC sensors

The multiphysics model of ionic polymer-metal composite (IPMC) sensors proposed by Zhu has a significant advantage of being able to describe the dynamic sensor response, which highly depends on humidity, by explicitly considering solvent dynamics. However, it is difficult to perform analysis and simulation because Zhu’s model is represented by complex non-linear partial differential equations. This paper describes the symbolic finite element discretization of Zhu’s model and further discusses the essential dynamics of the reduced-order model extracted from the finite element model. The obtained linear ordinary differential equations, or the state equation, can be easily implemented in simulators via common programming languages. The simulation results of an in-house simulator implemented by MATLAB code show good agreement with those of direct numerical simulation by using commercial software, COMSOL. To further simplify the model, the minimum order required for an appropriate approximation is numerically investigated by using a model order reduction technique. This paper reveals that the dynamic response of an IPMC sensor can be consequently approximated by a first-order or second-order linear time-invariant system.

Developing next generation ionic polymer–metal composite materials: perspectives for enabling robotics and biomimetics

AbstractIn this article, we present recent advancements in Ionic Polymer‐Metal Composite (IPMC) technology. The current trajectory of the research shows immense promise for a future with highly capable IPMC actuators and sensors being used in a wide range of robotic, soft‐robotic, and biomimetic technologies.. © 2020 Society of Industrial Chemistry

Analysis on enhancing the sensing behavior of ionic polymer metal composite based sensors

In this paper, an in-depth analysis of IPMC (ionic polymer metal composite) as sensors is performed, motivated by application to flapping wing micro air vehicles. The effect of water uptake for different IPMC samples reveals a correlation between IPMC metal content and water uptake. The effect of introducing a mass to the end of High-frequency IPMC (HFI ∼ 20.9 Hz) sensor shows an improvement in the IPMC sensing behavior, whereas, for the Low-frequency IPMC (LFI ∼ 8.9 Hz) sensor, there is a reverse trend. Gold (Au) coating on an HFI sensor results in a decrease in resonant frequency. Different mass loaded on the Au coated HFI beams reveals that the pre-bending by adding end mass to HFI sensor is beneficial up to a specific mass level, after which the sensing voltage decreases. The optimized mass loading for the Au coated HFI is determined.

Asymptotic analysis of compression sensing in ionic polymer metal composites: The role of interphase regions with variable properties

Ionic Polymer Metal Composites (IPMCs) consist of two noble metal electrodes plating an electroactive polymeric membrane, referred to as ionomer, which is electroneutralised by a solvent including mobile ions. The IPMC manufacturing leads to thin interphase regions next to the electrodes, the so-called Composite Layers (CLs), in which metal atoms occupy interstitial sites within the ionomer. In this work we extend previous efforts of our group on IPMC compression sensing to include the important effect of CLs, where large variations of the electrochemical properties occur. In IPMC compression sensing the application of a through-the-thickness displacement leads to a shortcircuit electric response, here assumed to be governed by a linearised <i>modified</i> Poisson-Nernst-Planck (PNP) system of partial differential equations (PDEs), to be solved for the time-evolving electric potential and mobile ions concentration as functions of the displacement field evaluated through the linear momentum balance. The variation of material properties in the CLs requires the simultaneous integration of the governing system of PDEs in three regions: the membrane and the two CLs. To this purpose, we resort to the perturbative method of matched asymptotic expansions. Except for a numerical inverse Laplace transform, this allows us to obtain an analytical solution through which we establish an equivalent circuit model elucidating the main features of the IPMC sensing behaviour. We validate and discuss the analytical solution through comparison with finite element analyses, whereby we also numerically solve the nonlinear modified PNP systems fully coupled with the linear momentum balance accounting for the electrochemical stresses. We finally provide some insight into the role of CLs in the IPMC sensing behaviour, by assessing its sensitivity to some key parameters. We expect the obtained results to aid the design of optimised IPMC sensors.

A theoretical model for analysis of ionic polymer metal composite sensors in fluid environments

By the past two decades IPMCs have been intensively studied because of their special capabilities for actuation and sensing.This paper presents a theoretical physics based model for analyzing the behavior of IPMC sensors in fluid environments. The mechanical vibration of the IPMC strip is described by the classical Euler–Bernoulli beam theory. The model also takes in to account the physical properties of the surrounding fluid. The resulting model is an infinite-dimensional transfer function that relates the input tip displacement to the output sensing current. Further the original model is reduced to a finite-dimensional one, for pure sensing applications of IPMC sensors such as structural health monitoring. The proposed model is verified using existing experimental data. Then the effect of various parameters is investigated. The acoustics physics interface in COMSOL Multiphysics software is used for coupled modal analysis of the IPMC strip. It is shown that the effect of surrounding fluid cannot be neglected.

Electrochemical viscoelastic modeling to predict quasi-static and dynamic response of IPMC actuators

A nonlinear dynamic viscoelastic model of an ionic polymer metal composite (IPMC) actuator is presented based on the viscoelastic constitutive equations and an energy-based variational approach to acquire dynamic and quasi-static response. For this purpose, the equation of motion of an IPMC actuator is obtained by considering the actuator as a cantilever viscoelastic beam and utlizing continuum mechanic relations, Euler-Bernoulli beam theory, Hamilton's principle, and electrochemical properties of ionomer. This new model can simulate time-dependent tip displacement of the IPMC actuators and predict the back-relaxation that occurs in the Nafion-based IPMC actuator under an imposed step voltage. The transfer function derived from the proposed model provides a good frequency response prediction in comparison to the experimental results.This model also can be utilized to obtain mechanical response and vibration analysis of the IPMC sensors.

IPMC Sensor Integrated Smart Glove for Pulse Diagnosis, Braille Recognition, and Human–Computer Interaction

AbstractFlexible sensors, which can meet human ergonomics requirements by virtue of compliance, are widely used in smart wearable electronics. Compared with existing piezoresistive, capacitive, and piezoelectric sensors, flexible ionic polymer metal composite (IPMC) sensors are promising for wearable applications toward monitoring diverse human activities, due to their advanced characteristics of passive, and direction identification. Here, a fluid‐bed‐like reactor is developed for batch preparation of the IPMC sensors, which can overcome those problems including time consuming, and poor batch stability of the devices prepared by the conventional electroless plating method. By the new method, a large number of sensors with good batch stability can be produced in one‐off preparation and in a very short‐time process. Sensitivity of the sensors can reach as high as 2.99 mV in strain range below 1% and high stability above 98.2% over 8000 bending cycles can be achieved. Based on the above, these sensors are successfully integrated into a smart glove, which can diagnose the subtle pulse, perceive the precise braille, and control the robot hand timely. This work presents a practical strategy for large‐scale production of advanced IPMC sensors and will accelerate the wide application in smart wearable systems.

Large-Scale Fabrication of High-Performance Ionic Polymer-Metal Composite Flexible Sensors by in Situ Plasma Etching and Magnetron Sputtering.

Flexible electronics has received widespread concern and research. As a most-fundamental step and component, polymer metallization to introduce conductive electrode is crucial in successful establishment and application of flexible and stretchable electronic system. Ionic polymer–metal composite (IPMC) is such an attractive flexible mechanical sensor with significant advantages of passive and space-discriminative capability. Generally, the IPMC sensor is fabricated by the electroless plating method to form structure of ionic polymer membrane sandwiched with two metallic electrodes. In order to obtain high-quality interface adhesion and conductivity between polymer and metal, the plating process for IPMC sensor is usually time-consuming and uncontrollable and has low reproducibility, which make it difficult to use in practice and in large-scale. Here, a manufacturable method and equipment with short processing time and high reproducibility for fabricating IPMC sensors by in situ plasma etching and magnetron sputtering depositing on flexible substrates is developed. First, the new method shortens the fabrication period greatly from 2 weeks to 2 h to obtain IPMC sensors with sizes up to 9 cm × 9 cm or arrays in various patterns. Second, the integrated operation ensures all sample batch stability and performance repeatability. In a typical IPMC sensor, nearly 200 mV potential signal due to ion redistribution induced by bending strain under 1.6% can be produced without any external power supply, which is much higher than the traditional electroless plating sensor. This work verified that the in situ plasma etching and magnetron sputtering deposition could significantly increase the interface and surface conductivity of the flexible devices, resulting in the present high sensitivity as well as linear correlation with strain of the IPMC sensor. Therefore, this introduced method is scalable and believed to be used to metalize flexible substrates with different metals, providing a new route to large-scale fabrication of flexible devices for potential wearable applications in real-time monitoring human motion and human–machine interaction.

Ionic polymer-metal composite torsional sensor: physics-based modeling and experimental validation

Ionic polymer-metal composites (IPMCs) have intrinsic sensing and actuation properties. Typical IPMC sensors are in the shape of beams and only respond to stimuli acting along beam-bending directions. Rod or tube-shaped IPMCs have been explored as omnidirectional bending actuators or sensors. In this paper, physics-based modeling is studied for a tubular IPMC sensor under pure torsional stimulus. The Poisson–Nernst–Planck model is used to describe the fundamental physics within the IPMC, where it is hypothesized that the anion concentration is coupled to the sum of shear strains induced by the torsional stimulus. Finite element simulation is conducted to solve for the torsional sensing response, where some of the key parameters are identified based on experimental measurements using an artificial neural network. Additional experimental results suggest that the proposed model is able to capture the torsional sensing dynamics for different amplitudes and rates of the torsional stimulus.

Fabrication and characterization of an ionic polymer-metal composite bending sensor

A bending sensor was fabricated with ionic polymer-metal composite (IPMC) and its characteristics as a sensor was studied. The IPMC senor, made by stacking a few Nafion films and water-proofed by Parylene coating, was robust and stable enough to be operated over 5 h in the air. Through the experiments examining the relation between the sensor signal and the deformation of the sensor, the output voltage of the sensor appeared to be linearly proportional to the curvature of the sensor. The proportional relation was maintained in the more realistic conditions like when the sensor is surface-mounted on the static and dynamic fingerjoint. The sensor signal was not affected by the sensor size change in length, width and thickness within the range we tested. Through the reliability tests the IPMC sensor was characterized to be inferior to mechanical sensors in accuracy and precision, and superior in sensitivity and resolution.

Compression and shear mode ionic polymer-metal composite (IPMC) pressure sensors

In this work, two types of dynamic pressure sensors based on ionic polymer-metal composites (IPMCs) in compression and shear deformation modes are designed, prototyped, and tested in a shock pressure tube. Although IPMCs offer appropriate properties such as flexibility, light weight, easy processing, resilience and high sensitivity to be used as sensors, there are only limited studies on applicable IPMC sensors and almost all of these devices were developed based on bending deformation. For a better understanding of the electromechanical sensing performance of the IPMCs, the charge current generation mechanisms due to external pressure in both compression and shear modes are developed based on the streaming potential hypothesis. The direct assembly process (DAP) is applied to fabricate some pressure sensor samples of each type for experimental evaluation. An equivalent circuit with parallel resistance and capacitance of the IMPCs samples, estimated by an impedance analyzer, is used to design an appropriate signal conditioner. A shock pressure tube setup is then utilized for performance evaluation of the fabricated devices. The results demonstrate that IPMCs as dynamic pressure sensors represent an appropriate linearity, sensitivity and consistency in both compression and shear modes. It is found that IPMC sensors in shear mode have a higher sensitivity compared with its compression mode counterpart.