Thursday, March 29, 2012

Why You Should Go Clean Your Room Now, or Just How Much Do Humans Shed?

The "With You in the Room, Bacteria Counts Spike" article discusses an experiment carried out on a ground floor university classroom in use that analyzed bacteria and fungi, surprising results.

The principle investigator was Jordon Peccia, an associate professor at Yale.

Clean-room anyone?  Or maybe a personal high voltage air purifier. 

Monday, March 26, 2012

Single atom working transistor
How cool would it be to have a high voltage diode the size of a single atom?  Is it possible?

Maybe some day....They're already doing it with transistors.  The University of South Wales has created a working single-atom transistor

It isn't in production, probably won't be any time soon, and there are certain design considerations when dealing with high voltage diodes.

But the single-atom transistor may be just the needed break-through needed to keep up with the predictions of Moore's law.

Defense Security and Sensing Conference 2012

Visit VMI and see our new booth 1535 at Defense, Security, and Sensing 2012 Conference will be held 23 - 27 April 2012 at the Baltimore Convention Center, Baltimore, Maryland.

Thursday, March 22, 2012

Multi-junction High Voltage Diodes


VMI Multi-junction High Voltage Diode
 Once in a while we get a customer inquiry about connecting diodes in series to get a higher reverse blocking voltage in their application.

Sometimes they express concern about one diode having a faster Trr than the others. The thought is that when the applied voltage starts to switch negative, the faster diode would hold off the entire PIV until the rest of the diodes in series could catch up. The question is whether it would cause a catastrophic failure by shorting out first one diode, then the next, and the next, and so one, until the whole string failed.

Fortunately, that is rarely the case. For one thing, reverse voltage does not happen instantaneously. There is a slew rate, and if the reverse recoverytime, Trr, of the diode is sufficiently fast for the application, it will block before the full reverse voltage is experienced, thus preventing a cascade of failing diodes.

Secondly, anytime you work with a diode greater than roughly 1200 Vrwm, there is more than one diode junction in the package. A 10kV diode used multiple internal junctions. It is the rough equivalent of connecting ten single junction diodes in series, in a much, much smaller package.

Multi-junction diodes are made from the same wafer and diffusion lot, so variations in Trr are kept to a minimum. With continuous improvements made to the diffusion and manufacturing processes, process variations have been further minimized. All of which goes towards improved product reliability and quality.  And you know that's good for you!

Thursday, March 15, 2012

Great article from IEEE about the brewing controvery over China's export policies on rare earth metals (think magnets), tungsten (think semi-conductors), and molybdenum (think stainless steel, water & food & hospital distribution systems). 

Effected industries include automobile manufacturing, electronics (including semi-conductors), oil & gas production, medical equipment, and more. 

China has the largest Tungsten reserve.  A distant second is Russia, followed by Canada and the U.S.  The last time the US produced Tungsten was in 1994.  The last time the US processed Tungsten concentrates was in 2004*. 

Tungsten is used extensively in making cemented carbide parts (cutting and wear-resistant materials for metalworking, oil & gas production, construction).  It can also be found in lamp filaments, electrodes, electrical and electronic components, tools, alloying metals, chemical catalysts, and pigments.

Of course, the world is busy working on alternative materials and sources.  Time will tell.
  
*Source:  U.S. Geological Survey, Mineral Commodity Summaries, January 1998

Tuesday, March 13, 2012

High Voltage TWT Power Supply Guidelines

I was doing a little research on design considerations for TWT power supplies, and came across this report from NASA.

This is an analysis of an 11kV High Voltage Power Supply that apparently exhibited evidence of a corona-induced short in the high voltage connector. 

Figure 2 - High Voltage Compartment Construction - NASA PD-ED-1202
Included in the report is a photo of a partially de-encapsulated unit.  It's hard to say for sure, but it looks like they used epoxy diodes?! 

You know how the internet is....down the rabbit hole I went, and, well, one thing let to another, and before I knew it, I came across even more design practices from NASA.

As for researching TWT power supplies, I was looking to confirm guidelines for specifying high voltage diodes.  I seem to recall hearing that diodes are susceptible to damage on the high voltage end of the multiplier because of arcs from the tube.  TWT PS typically run hot and fast, and unless a diode has sufficient reverse power capabilities, it could spell trouble. 

Comments anyone?

Wednesday, March 7, 2012

DARPA program - Robot Cheetah Breaks Speed Record

This article provides interesting information on the DARPA funded project to create a free range running robot.  The robot cheetah video shows just how the M3 (Maximum Mobility and Manipulation) researchers were able to achieve speeds of up to 18mph.  That's incredibly fast when you think the fastest human on the planet might run a 3:30 minute mile, or 17mph.

Check out the article to find out where this is going.