RESEARCH
INTERESTS
Dielectric Materials
- Develop AFE ceramics for Energy Storage Capacitor Applications
- Develop Device Architectures with High Energy Storage Density Characteristics
- Design Linear Dielectrics with High k' @ High field
- Test Discharge Behavior of Materials
Antiferroelectric
compositions offer the potential for high energy storage densities. These
high energy densities are (at least in part) associated with a field-induced
transformation into a ferroelectric state. Unfortunately a large strain
component is associated with this field-induced phase transformation.
It is expected that this behavior may contribute to accelerated mechanical
failure of capacitors during repeated charge – discharge cycles.
However, for materials with more diffuse phase transformations (DPT behavior),
this strain response is spread out over a broader time spectrum, which
may improve capacitor reliability characteristics (i.e., mechanical reliability
associated with microcracking phenomena). Materials with sharp and diffuse
phase transition characteristics are under development in this project
and their electrical and mechanical reliability characteristics are being
determined to investigate the importance of the nature of the phase transformation.
Shaped
jet charges (e.g., rocket propelled grenades; RPG) represents one of the
most significant threats to tanks and other armored vehicles. One armor
system currently under investigation is capacitive armor which enables
flow disruption of the RPG. The basic concept involves using the outer
metallic armor plate as the ground electrode of a parallel plate capacitor.
An insulating layer, biased underlying electrode, and bank of power capacitors
complete the capacitive armor system. The protective effect that capacitive
armor offers is equivalent to carrying an additional 10 – 20 tons
of steel armor.
This program focuses on two aspects of the capacitive armor system. Development of capacitors with higher energy density and the evaluation of new charging system concepts. A pulser circuit capable of measuring fast discharge pulses has also been constructed as part of the program.
This program focuses on two aspects of the capacitive armor system. Development of capacitors with higher energy density and the evaluation of new charging system concepts. A pulser circuit capable of measuring fast discharge pulses has also been constructed as part of the program.
Piezoelectric Materials and Devices
- Characterize and
Model the Local deformation Response of Stress-Biased Thunder Actuators
Stress-biased
piezoelectric actuators offer unique performance characteristics compared
to more traditional unimorph and bimorph devices. The goals of research
efforts in this area are to develop new, higher performance through engineering
of the stress state and stress response of such devices to take better
advantage of domain switching phenomena. sensors and actuators
To develop new, higher performance devices, standard stress-biased actuators have been modified through the inclusion of mechanical preloads. This has resulted in a 10X enhancement in displacement response. Other research efforts have utilized Moire interferometry to study local deformations and gain insight into the balance of intrinsic and extrinsic contributions to response.
To develop new, higher performance devices, standard stress-biased actuators have been modified through the inclusion of mechanical preloads. This has resulted in a 10X enhancement in displacement response. Other research efforts have utilized Moire interferometry to study local deformations and gain insight into the balance of intrinsic and extrinsic contributions to response.
Thin Film Materials
- Transparent Conducting
Oxides for Sensor Protection
Protection
devices are required for a number of military optical sensor systems to
limit damage posed by laser and other threats. One approach is the electrostatic
shutter shown at the left. This system requires highly conductive oxides
that are transparent in the 3 – 5 and 8 – 12
mm bands to minimize
reductions in sensitivity
During work on this program a Drude free electron model has been used to estimate n and k of TCO materials. These results were then used to simulate optical transmission characteristics of various TCO/substrate combinations. The results of these simulations suggested that Zn2SnO4 and ZnSnO3 possessed an attractive balance of electrical and optical properties. Typical results are illustrated at the right showing greater than 50% transmission (with no correction for reflection losses) in the 3 – 5 mm band for films with sheet resistances between 350 and 390 W/square.m.
During work on this program a Drude free electron model has been used to estimate n and k of TCO materials. These results were then used to simulate optical transmission characteristics of various TCO/substrate combinations. The results of these simulations suggested that Zn2SnO4 and ZnSnO3 possessed an attractive balance of electrical and optical properties. Typical results are illustrated at the right showing greater than 50% transmission (with no correction for reflection losses) in the 3 – 5 mm band for films with sheet resistances between 350 and 390 W/square.m.
Modeling
Microstructural Evolution in Thin Films
-
Solution deposition processes have been widely investigated for the fabrication of multicomponent crystalline thin films. To prepare films with optimized properties, control of microstructure and orientation is required. Our group has worked to understand structural evolution in solution derived films. We have focused on the physical and chemical processes associated with the transformation of the solution precursor into the crystalline ceramic phase. Recently, we have also used classical nucleation and growth theory to develop a pixel by pixel model to look to simulate structural evolution. Representative cross-sectional microstructures are shown at various points during the transformation process. Also shown is a typical microstructure of a barium titanate thin film.
