Monday, September 24, 2012

Hybrid rocket engine with acrylic and gaseous oxygen

I built a small rocket engine for demonstration purposes. The engine is built from a 2" diameter acrylic rod through which I drilled a 0.5" hole. The oxygen at 80 psi or less is passed through the hole and then is forced through a convergent-divergent nozzle at the tail end. The nozzle's throat is about 0.25" and expands to 0.625". I lit the engine by inserting a burning cotton swab (with wooden stick) while a small amount of oxygen was flowing. The acrylic catches fire very easily in a pure oxygen environment. The engine can be throttled and shut off completely, which is a major benefit to hybrid engine designs. Solid-fuel rockets cannot be throttled or shut off, which makes them difficult to control.

Thursday, September 6, 2012

Viewing an active electronic circuit with a scanning electron microscope

I used my DIY scanning electron microscope to view a 555 timer circuit while it was powered. The circuit is a simple oscillator with a very long time constant to make the changes easy to see. My plan was to view the silicon die itself, and hopefully discern changes in its internal circuitry as the oscillations occurred. As it turns out, I was only able to "see" the charge of the electrical wires going to the chip socket. There is likely a clear oxide layer that covers the silicon die, and needs to be removed with hydrofluoric acid in order to use the SEM to inspect the die itself while powered.

Sunday, September 2, 2012

First test with eBay x-ray tube

 I found an X-ray tube on eBay and fired it up with my Spellman high voltage supply. I ran the tube at about 35-40KV at 180uA. This required a filament current of about 1.5A at 2.5V DC.  With the room very dark, I could clearly see the phosphorescent screen glowing green. It wasn't bright enough for my eye to discern details in the X-ray images, but the camera with a 4 second exposure at f/5.6 and ISO400 was perfect. I took some pictures of various electronic components. I also X-rayed a dead, dried-up bumble bee, and it produced no image at all! The X-rays completely penetrated the insect without any visible absorption. I should have turned down the anode voltage, but I didn't think of this until after I threw away the bee.
The tube is a Nago GFH2-0.3-85-60