In this paper, we cover our studies on accelerating the molding process of a polymer by applying
acoustic stress-wave time reversal. Tests carried out on an epoxy polymer mixed with a curing
agent have shown evidence that the introduction of unfocused acoustic energy during the molding
process will accelerate that process. The effects of focusing acoustic energy at a mold discontinuity
while curing are explored. We also detail our investigations on focusing acoustic energy at a crack
location by iteratively applying time reversal. Multiple types of media were tested.
We consider the effects of acoustic pressure on the curing of a two-part epoxy, which can be considered
analogous to the polymer healing process. An epoxy sample is loaded into a tube and monitored
throughout the curing process by measuring the amplitudes of its natural frequencies in response to
periodic mechanical impulses. The progress of the curing process can be quantified by tracing the
natural frequencies and temperature of the epoxy-tube system. Studies described in our last report
continue and work completed in this reporting period has sought and achieved repeatable test results
by making slight modifications to existing procedures and protocol.
We consider the effects of acoustic pressure on the curing of a two-part epoxy, which can be considered analogous
to the polymer healing process. An epoxy sample is loaded into a tube and monitored throughout the early stages
of curing by measuring its vibrational response upon periodic impulses. By tracing the natural frequencies of the
epoxy-tube system and cross-checking the temperature of the epoxy, the progress of the curing can be quantified. Acoustic stimulation at three different frequencies is investigated and compared to the unstimulated case. We find that external acoustic pressure does seem to affect the curing, though much work remains to be completed.
This paper reports on the development and testing of electrostatically actuated deformable mirrors for optical correction.
The system considered here is limited to the lower modes of aberration; namely, focus/defocus and tip/tilt. The main
problem with using electrostatics is due to the nonlinear relationship between force and distance in such a system.
Accordingly, this work uses a nonlinear control system in order to obtain greater deflection for a given voltage. The
paper describes recent experimental results with closed loop control.