Subject: Stretched Antennas From: Kevan Hashemi Date: Fri, 27 May 2011 11:05:29 -0400 To: Alexander Rotenberg, Sameer Dhamne Gentlemen, I have a hypothesis that might explain some of the problems you have been having with transmitters. I'm copying our UCL colleagues so they can tell us if they have had similar problems. So far, you have returned 3 transmitters to us with their antennas sticking out of their tubes. The most recent was No2, which failed after one week in an animal. It would not turn on. At the same time, you returned No1 with both leads broken at the base. There was no sign of a cut in the silicone insulation. Transmitter No1 stopped picking up EEG, and for a while was picking up strong 18-Hz noise. In the end it settled down to a 1-Hz square wave, which we have seen twice at UCL. The protruding antennas penetrated their silicone tubes roughly half-way along the tube length. The hole was only just large enough to accommodate the antenna. It's as if the tube were punctured by a needle, but only on one side. In order to move the tip of the steel antenna to a point half-way along the tube length, we must stretch the tube to double its initial length, which I am able to do by hanging a 500-g weight from the loop. When I remove the weight, the tube and antenna look like this. http://www.opensourceinstruments.com/Electronics/A3019/HTML/Antenna_Stretched.jpg And here is a close-up of the tip of the antenna: http://www.opensourceinstruments.com/Electronics/A3019/HTML/Antenna_Breach.jpg You can see that the antenna in my experiment has already punctured the tube, because one strand broke out from the rest and pierced the silicone. The 500-g force is carried by both ends of the antenna tube, and transferred to the base of the electrode leads. The silicone around the bases of these leads is thick, but the springs can uncoil within the silicone and stretch. In this way we can break both leads at the base, or deform them so that fatigue will later cause them to break. When the antenna pierces its sheath, it immediately begins to generate noise that is picked up by the analog inputs. I have a transmitter in water with cut-off electrode leads and no antenna sheath. Here's what I see on the inputs. http://www.opensourceinstruments.com/Electronics/A3019/HTML/Antenna_Noise.gif If the electrodes are far away, in the head of an animal, while the protruding antenna is in the belly, we will see far less noise, like your No6 here: http://www.opensourceinstruments.com/Electronics/A3019/HTML/CHB_No6_No7.gif Also in the above picture you see the trace from No7, which looks as if both the electrodes have broken off at the base. If the antenna is protruding and the transmitter is turned on, it is easy to touch the antenna with a metal tool. Touching a metal tool to a live antenna is almost certain to destroy the RF transmitter, as we describe here. http://www.opensourceinstruments.com/Electronics/A3013/M3013.html#Damaged%20Transmitters I don't think it's possible for a rat's body to exert a 500-g force upon a transmitter, but I may be wrong. I suspect that you are pulling so hard on the transmitters during implantation and explantation that the antennas break out of their tubes and the electrode leads are damaged at the base. The moment your No6 antenna broke out through its tube was 3098 s into archive M1306224760, which was Tue May 24 05:04:18 EDT 2011. I'd like to inspect your No7 to see if the leads are broken, and to take a look at No6 to see if the antenna has indeed popped out. Yours, Kevan -- Kevan Hashemi, President Open Source Instruments Inc. www.opensourceinstruments.com