Boy have we been busy! We have had our heads down and have been so focused on solving the valve issues we last reported, that months have gone by and in the blink of an eye. In our last technical update we promised to share more of the details of our development efforts, so here is an update on where we stand. In debugging the valve issues, we have focused on two areas.
There are several material properties that can affect the operation of the micro valves in the micro-blowers. The two primary properties we have been investigating are surface roughness and residual stress [in the film].
Surface roughness – When the valves in the micro-blower move, they slide between two surfaces. It is imperative that the valves slide smoothly back and forth between an open and a closed position. This is how they perform the “input” and “output” valve functions. If their travel is interrupted or altered, then their functions no longer work. We have evidence that this is happening and we believe that it is due, in part, to how rough the surfaces are. Using a laser microscope, we have characterized how rough these surfaces are; rougher than we had imagined. We also discovered that it is common to make the films with “roughening” additives to make the films easier to handle; good for handling, bad for valve sliding. We have found an alternative film that is less rough and are investigating it as a replacement. We’ll keep you posted.
Residual stress – This is a property that can affect how the films move or how they might change their dimensions once they are machined by the laser during micro fabrication. If there is significant stress in the film, it makes the film stiffer and therefore requires more force (energy) to bend. Depending on the magnitude and direction of these stresses, it is possible that the machined micro structures could distort; bow or twist. The valves are designed to operate in a very specific way and their dimensions are very important. Any such distortions could impact their movement quite negatively and render them inoperable. We have evidence that there is residual stress in our films and we are in the process of characterizing it to determine if it is sufficiently large enough to create a problem. Again, we’ll keep you posted.
2. Valve design
In our last technical update, we told you that one of our valves was not moving correctly. So, since one of our valves appears to be moving as designed, we have been analyzing the other valve (the one that isn’t moving well) to try and determine if there might be a geometric issue that could be affecting the aerodynamics of its movement. First, we made some geometry changes around the valve to alter the flow path of the air. We hoped that these might cause it to move as designed, but the changes did not have much effect. Next, we re-designed the valve to a different geometry that more closely resembles the properly moving valve. We have fabricated test devices and are in the process of characterizing this new valve. While we like what we have seen so far, it is too early to tell whether this new geometry will perform as designed. We will keep you posted.