A new fabrication system for Ionic Polymer Metallic Composites (IPMC) entitled Micro Deposition Method(MDM) is
introduced. The tolerances in prototyping IPMC's using available fabrication techniques does not meet the tight limits
for fabricating the polymer transducer. The MDM overcomes this limitation by using a microfluidic dispersion head that
can deposit 3 to 10 picoliters of the electrode layer dissolved in a solvent at a high throughput. The MDM in its existing
configuration can be used to fabricate micron scale polymer transducers with features 2 microns and above with high
accuracy and repeatability. A commercially available piezoelectric deposition head from an inkjet printer is modified
and used to disperse the electrode material of controlled thickness as a concept demonstration. The physical properties
of the dispersed fluid are adjusted to meet the requirements of the deposition head to fabricate the prototype. The
dispersion fluid used had a viscosity of 3.47 ±0.06 cP, a surface tension of 23.6 ±.1 mNm-1, and a conducting power
volume load set at 10%.
Ionomeric polymer transducers (IPTs) have recently received a great deal of attention.
As actuators, IPT have the ability to generate large bending strain and moderate stress at low applied
voltages. Although the actuation capabilities of IPTs have been studied extensively, the sensing
performance of these transducers has not received much attention. The work presented herein aims to
develop a wall shear stress sensor for aero/hydrodynamic and biomedical applications. Ionic polymers
are generally created by an impregnation-reduction process in an ion exchange membrane, typically
Nafion, and then coated with a flexible electrode. The traditional impregnation-reduction fabrication
technique of IPTs has little control on the electrode thickness. However, the new Direct Assembly
Process (DAP) for fabrication of IPTs allows for experimentation with varying conducting materials
and direct control of electrode architecture. The thickness of the electrode is controlled by altering the
amount of the ionomer/metal mix sprayed on the membrane. Transducers with varied electrode and
membrane thicknesses are fabricated. The sensitivity of the transducer is characterized using two basic
experiments. First, the electric impedance of the transducer is measured and its capacitive properties
are computed. Earlier studies have demonstrated that capacitance has been strongly correlated to
actuation performance in IPTs. Subsequently, the sensing capability of the IPTs in bending is measured
using a fixed-pined cantilever configuration. Finally the shear stress sensing performance in fluid flow
is quantified through a detailed calibration procedure. This is accomplished using two dynamic shear
stress calibration apparatuses. In this study we demonstrate a strong correlation between the electrode
thickness and the sensing performance of an IPT.
Novel designs of skin friction and heat flux sensors have been developed based on advanced materials and processing techniques. These sensors produce dynamic, time-resolved, direct measurements of skin friction and heat flux, especially tailored towards turbulent flows. The skin friction sensors use ionic polymer transducers, which contain no moving parts, directly measure shear, and can be surface mounted with minimal flow intrusion. The sensors exhibit measurement accuracy in fluctuating shear on the order of 4.92% over a range of stresses of +/- 3 Pa and signal-to-noise-ratio on the order of 60 dB. The frequency response of the sensor is on the order of 10 kHz. An approach for automatic recalibration and error compensation based on changes of impedance has been developed. This process allows in-situ recalibration of the sensors under varying temperature conditions. The heat flux sensors are made with thin-film deposition which allows fine arrays to be created. The measured Seebeck coefficient (temperature sensitivity) of the deposited metals is 23.5 μV/oC, which closely matches that of bulk wire.