Monday, March 17, 2008

This is (sort of) a microphone

You are looking at an ultrasound motor drive unit made almost 20 years ago by Diasonics of Milpitas CA. Back in those days I worked for then-young Boston Scientific and we had a joint venture with Diasonics to introduce IVUS, which is catheter-based ultrasound.

Today, IVUS is used all over to look at coronary blockages. I used to fly TWA about every week through St. Louis to get to San Jose then to Milpitas, and racked up a lot of frequent flyer miles.

We have a lot of capacitor microphones with interchangeable heads today. This is actually very similar. That metal "nose" on the left is where the "head" attached. Actually it was a disposable catheter with a coupler based on a familiar ham radio type PL259 antenna connector. Inside is a transformer and a preamp. The transformer is very much like those found in the best mics today, except it is designed to rotate so the catheter can scan the vessel. It was like a speedometer cable from a Schwinn. The catheter has a tip with a small ceramic element on the end, which works exactly like a ceramic microphone, or a bridge pickup for an acoustic guitar. It also can be used to send a sound signal, just like a piezo buzzer in a wristwatch.

Finally, this motor unit, the analog to the mic body, is designed to work at 20 Megahertz. The body is cast urethane plastic, which was a popular way to make short run plastic enclosures. The probe connected to an IVUS console, and if you want to see one, just click here.

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