Ionic polymer-metal composites (IPMCs) have inherent underwater sensing and actuation properties. They can be used as sensors to collect ﬂow information. Inspired by the hair-cell mediated receptor in the lateral line system of ﬁsh, the impact of a ﬂexible, cupula-like structure on the performance of IPMC ﬂow sensors is experimentally explored. The fabrication method to create a silicone-capped IPMC sensor is reported. Experiments are conducted to compare the sensing performance of the IPMC ﬂow sensor before and after the PDMS coating under the periodic ﬂow stimulus generated by a dipole source in still water and the laminar ﬂow stimulus generated in a ﬂow tank. Experimental results show that the performance of IPMC ﬂow sensors is signiﬁcantly improved under the stimulus of both periodic ﬂow and laminar ﬂow by the proposed silicone-capping.
Ionic polymer-metal composites (IPMCs) have intrinsic sensing and actuation properties. An IPMC sensor typically has the beam shape and responds to bending deﬂections only. Recently tubular IPMCs have been proposed for omnidirectional sensing of bending stimuli. In this paper we report, to our best knowledge, the ﬁrst study on torsion sensing with tubular IPMCs. In particular, a dynamic, physics-based model is presented for a tubular IPMC sensor under pure torsional stimulus. With the symmetric tubular structure and the pure torsion condition, the stress distribution inside the polymer only varies along the radial direction, resulting in a one-dimensional model. The dynamic model is derived by analytically solving the governing partial diﬀerential equation, accommodating the assumed boundary condition that the charge density is proportional to the mechanically induced stress. Experiments are further conducted to estimate the physical parameters of the proposed model.
Ionic polymer-metal composites (IPMCs) have intrinsic actuation and sensing capabilities, and they need hydration
to operate. For an IPMC sensor operating in air, the water content in the polymer varies with the humidity
level of the ambient environment, which leads to its strong humidity-dependent sensing behavior. However, the
study of this behavior has been very limited. In this paper, the influence of environmental humidity on IPMC
sensors is characterized and modeled from a physical perspective. Specifically, a cantilevered IPMC beam is excited
mechanically at its base inside a custom-built humidity chamber, where the humidity is feedback-controlled
by activating/deactivating a humidifier or a dehumidifier properly. We first obtain the empirical frequency responses
of the sensor under different humidity levels, with the IPMC base displacement as input and the tip
displacement and short-circuit current as outputs. Based on physics-based model for a given humidity level, we
then curve-fit the measured frequency responses to identify the humidity-dependent physical parameters, including
Young’s modulus and strain-rate damping coefficient for the mechanical properties, and ionic diffusivity for
the mechanoelectrical dynamics. These parameters show a clear trend of change with the humidity. By fitting
the identified parameters at a set of test humidity levels, the humidity-dependence of the physical parameters
is captured with polynomial functions, which are then plugged into the physics-based model for IPMC sensors
to predict the sensing output under other humidity conditions. The latter humidity-dependent model is further
validated with experiments.
Ionic polymer-metal composites (IPMCs) have inherent sensing and actuation properties. An IPMC sensor typically
consists of a thin ion-exchange membrane, chemically plated with electrodes on both surfaces. Such IPMC
sensors respond to deflections in the beam-bending directions only and thus are considered one-dimensional. In
this paper, a novel IPMC sensor capable of two-dimensional sensing is proposed by plating two pairs of electrodes
on orthogonal surfaces of a Nafion beam that has comparable thickness and width. The fabrication method is
reported along with the characterization of the fabricated sensor. Experimental results show that the proposed
IPMC sensor can be used for 2D flow sensing with promising applications in artificial lateral line systems. In
the fabrication process Nafion solution is first cast and solidified, and the resulting structure is then cut to form
beams with square cross-sections. In particular, the sample we fabricated has cross section of 1mm by 1mm and
length of 15mm. Platinum electrodes are then plated on four side surfaces of the Nafion beam, insulated from
each other. The fabricated IPMC sensor is shown to respond to 2D mechanical stimuli, and separate sensor
signals are collected from the two pairs of electrodes. The responses (short-circuit currents) of the fabricated
IPMC sensor are characterized both in air and in water, to verify the 2D sensing capability and examine the
correlation between the two sensor signals.
In this paper a dynamic, physics-based model is studied analytically and experimentally for an ionic polymermetal
composite (IPMC) sensor that is excited at the base. This work is motivated by structural monitoring and
energy-harvesting applications of IPMCs. The model combines the vibration dynamics of a flexible beam under
base excitation and the ion transport dynamics within the IPMCs. The vibration dynamics of a base-excited IPMC beam is obtained from the Euler-Bernoulli beam equation incorporating damping and accommodating
suitable boundary conditions. The charge dynamics is derived by analytically solving the governing partial differential equation, which captures electrostatic interactions, ionic diffusion and ionic migration along the thickness direction. The derived model relating short-circuit sensing current to the base excitation is expressed
as an infinite-dimensional transfer function, in terms of physical and geometric parameters, and is thus scalable. The model is then reduced to a finite-dimensional one for real-time signal processing. In particular, we present an inversion scheme for reconstructing the mechanical stimuli given the sensor output. Experimental results show that the proposed model captures well both the beam dynamics and the overall sensing dynamics. Simulation results are also presented to illustrate the inversion algorithm.
As the primary flow sensing organ for fishes, the lateral line system plays a critical role in fish behavior. Analogous
to its biological counterpart, an artificial lateral line system, consisting of arrays of micro flow sensors, is
expected to be instrumental in the navigation and control of underwater robots. In this paper we investigate the
microfabrication of ionic polymer-metal composite (IPMC) cilia for the purpose of flow sensing. While existing
macro- and microfabrication methods for IPMCs have predominantly focused on planar structures, we propose
a device where micro IPMC beams stand upright on a substrate to effectively interact with the flow. Challenges
in the casting of 3D Nafion structure and selective formation of electrodes are discussed, and potential solutions
for addressing these challenges are presented together with preliminary microfabrication results.