In this paper, we propose a new design configuration for a carbon nanotube (CNT) array based pulsed field
emission device to stabilize the field emission current. In the new design, we consider a pointed height distribution
of the carbon nanotube array under a diode configuration with two side gates maintained at a negative potential
to obtain a highly intense beam of electrons localized at the center of the array. The randomly oriented CNTs are
assumed to be grown on a metallic substrate in the form of a thin film. A model of field emission from an array of
CNTs under diode configuration was proposed and validated by experiments. Despite high output, the current in
such a thin film device often decays drastically. The present paper is focused on understanding this problem. The
random orientation of the CNTs and the electromechanical interaction are modeled to explain the self-assembly.
The degraded state of the CNTs and the electromechanical force are employed to update the orientation of the
CNTs. Pulsed field emission current at the device scale is finally obtained by using the Fowler-Nordheim equation
by considering a dynamic electric field across the cathode and the anode and integration of current densities
over the computational cell surfaces on the anode side. Furthermore we compare the subsequent performance of
the pointed array with the conventionally used random and uniform arrays and show that the proposed design
outperforms the conventional designs by several orders of magnitude. Based on the developed model, numerical
simulations aimed at understanding the effects of various geometric parameters and their statistical features on
the device current history are reported.
Ionic polymer-metal composites (IPMC), piezoelectric polymer composites and nematic elastomer composites
are materials, which exhibit characteristics of both sensors and actuators. Large deformation and curvature are
observed in these systems when electric potential is applied. Effects of geometric non-linearity due to the chargeinduced
motion in these materials are poorly understood. In this paper, a coupled model for understanding the
behavior of an ionic polymer beam undergoing large deformation and large curvature is presented. Maxwell's
equations and charge transport equations are considered which couple the distribution of the ion concentration
and the pressure gradient along length of a cantilever beam with interdigital electrodes. A nonlinear constitutive
model is derived accounting for the visco-elasto-plastic behavior of these polymers and based on the hypothesis
that the presence of electrical charge stretches/contracts bonds, which give rise to electrical field dependent
softening/hardening. Polymer chain orientation in statistical sense plays a role on such softening or hardening.
Elementary beam kinematics with large curvature is considered. A model for understanding the deformation
due to electrostatic repulsion between asymmetrical charge distributions across the cross-sections is presented.
Experimental evidence that Silver(Ag) nanoparticle coated IPMCs can be used for energy harvesting is reported.
An IPMC strip is vibrated in different environments and the electric power against a resistive load is measured.
The electrical power generated was observed to vary with the environment with maximum power being generated
when the strip is in wet state. IPMC based energy harvesting systems have potential applications in tidal wave
energy harvesting, residual environmental energy harvesting to power MEMS and NEMS devices.
Cobalt and iron nanoparticles are doped in carbon nanotube (CNT)/polymer matrix composites and studied
for strain and magnetic field sensing properties. Characterization of these samples is done for various volume
fractions of each constituent (Co and Fe nanoparticles and CNTs) and also for cases when only either of the
metallic components is present. The relation between the magnetic field and polarization-induced strain are
exploited. The electronic bandgap change in the CNTs is obtained by a simplified tight-binding formulation in
terms of strain and magnetic field. A nonlinear constitutive model of glassy polymer is employed to account for
(1) electric bias field dependent softening/hardening (2) CNT orientations as a statistical ensemble and (3) CNT
volume fraction. An effective medium theory is then employed where the CNTs and nanoparticles are treated
as inclusions. The intensity of the applied magnetic field is read indirectly as the change in resistance of the
sample. Very small magnetic fields can be detected using this technique since the resistance is highly sensitive to
strain. Its sensitivity due to the CNT volume fraction is also discussed. The advantage of this sensor lies in the
fact that it can be molded into desirable shape and can be used in fabrication of embedded sensors where the
material can detect external magnetic fields on its own. Besides, the stress-controlled hysteresis of the sample
can be used in designing memory devices. These composites have potential for use in magnetic encoders, which
are made of a magnetic field sensor and a barcode.