Thank you for sending me recordings from the three transmitters that failed while implanted.

> 115.1: no signal from the beginning (e.g.: 12.08.2016)

I see a signal in your archive from 12-AUG-16. Reception appears to be 90% or higher. The signal is not EEG, however. Maybe when you say "no signal" you mean "no EEG". The signal you see on No115.1 is you were to drop the transmitter in water. You can get the same effect for an implanted transmitter by breaking one of the EEG leads inside its insluation, so that it is insulated from the animal body. So I think something has gone wrong with your implant.

The frequency response of R115.1 is plotted here:

http://www.opensourceinstruments.com/Electronics/A3028/Data/R114_5mV.png

Here's from my notes about R115.1 "Four have severe cosmetic flaws in the silicone: wrinkles on the battery side. These are R114.9, R115.1, R115.2, and R115.7." We re-coated two of these, but my notes don't say anything about re-coating R115.1. It's possible we shipped you a transmitter that had failed quality assurance. I'm copying Kirsten to see what her notes have to say.

Even if we did ship a transmitter with wrinkles in the silicone, the wrinkles would not cause the effect you are seeing. We have performed accelerated aging tests on many transmitters with flawed silicone, and they perform well.

When you explant that transmitter, do you see 50 Hz when you hold it in your hand near a pick-up antenna? If not, then ship it back to us so we can figure out what went wrong. If it's a faulty transmitter, please accept our apologies, we will send you a replacement.

I see that R115.1 is still implanted and running on 29-OCT-16.

> 106.7: failed before 28.10.2016 0:00:13, had some serious jumps in amplitude over the course of about 3 days

Its battery is almost run down on 17-SEP-16. By 29-OCT-16 it should not be working at all. Only the radio frequency transmission is working. The battery voltage has dropped below 2.1 V. Here's what the average value of X (the EEG input) looks like with battery voltage (scroll down a bit):

http://www.opensourceinstruments.com/Electronics/A3028/M3028.html#Analog%20Inputs

As the battery voltage drops from 4.2 V to 1.2 V in that experiment, we see the average value of X jump down and up again. In August, R106.7's battery was at 2.7 V, in September it's 2.3 V.

We have tested fifty transmitters in hot water in the past year. I can say with confidence: they don't drain their batteries in one month at 37C. So it looks like this one must have been running while it was on the shelf since March. We are now putting warning labels on all our transmitter bags because we have had trouble in the past year with transmitters turning on while they are in storage. At ION/UCL, for example, they were storing transmitters on the floor in a box next to a computer case, which contains a power supply transformer and a hard drive with a big magnet.

> 117.14: loss increased over time (compare: 17.09.2016 to 23.10.2016)

On 17-SEP-16 reception is over 90% and EEG amplitude is around 60 uV. On  29-OCT-16 I see what looks like pulses from your electrical stimulation.    The EEG amplitude is around 200 uV and looks good, but reception has dropped to 70%. The next archive I have is 23-NOV-16 (not 23-OCT-16). Here, reception is poor. At times, it's 95% but at other times it's 0%. This data was recorded with one of your older Octal Data Receivers. Maybe reception would be better from R117.14 with the new ODR. The EEG signal now has amplitude 40 uV and it's no longer EEG. The spectrum is wrong. At time 3132 s in M1479884349.ndf we see 80 uV amplitude 50 Hz. At time 3396 s we see significant power between 100-200 Hz. Both these spectra are symptoms of a broken X- or X+ EEG lead. Here is the spectrum of a transmitter with a broken X- lead:

http://www.opensourceinstruments.com/Electronics/A3028/HTML/Broken_C_Noise.gif

In summary, my best guess as to the causes of failure are:

R115.1: Broken EEG lead.

R106.7: Was running while on shelf, exhausted most of its battery before implantation.

R117.14: Broken EEG lead.


Thanks for your note. At ION, they have been running 16-week experiments
for the past year, and the A3028R is reliable over that period. You are
the first people to plan experiments past week 16. You are the first
people to push the battery life of the A3028R to the limit.

> Transmitter 112.6 had been implanted for 118 days.

We shipped that transmitter in mid-May. It failed on 18th September. You
You implanted as soon as you received it. The typical current
consumption for the R112.6 is 80 uA and the nominal capacity of the
BR2330 battery is 255 mA-hr, so the typical operating life for that
device is 3200 hours, which is 133 days.

On 24th May, I put R113.9 and R113.10 in the oven at 60C. They both
failed this week, after 125 days. Corrosion takes place 10x faster at
60C than 37C. Furthermore, you will always see large artifact in the
A3028R transmitter's EEG recording before it fails from corrosion
damage. I'm going to assume corrosion was not the problem.

The A3028R consumption varies from 77 uA to 85 uA. The Panasonic BR2330
data sheet does not give us a minimum battery capacity, only a "nominal"
capacity. Back in 2008 we measured the capacity of four 120-mA-hr
Panasonic batteries.

http://www.opensourceinstruments.com/Electronics/A3013/M3013.html#Battery%20Life

In our small sample of 4 batteries, capacity varied +-10% around the
nominal value. If we combine this with a +-5% variation in operating
current, we get at +-15% variation in the operating life of the A3028R.
Our nominal operating life is 133 days, but actual operating life could
be as short as 113 days or as long as 152 days.

I have asked my operations manager to look up the actual current
consumption of R112.6. I'm not in the office right now.

> From day 32 to 38 the rat was stimulated...

We have never seen stimulation of the electrodes cause any damage to the
transmitters, so I agree that this cannot be the problem either.

> Transmitter 110.4 had been implanted for 80 days.

That transmitter we shipped to you in late April. It failed at the end
of August, 120 days after you received it.

> I remove one antenna from an enclosure and connect it to the Receiver
> outside the enclosure. I make sure that the activity lamp is silent.
> Then I take each transmitter out of the FedEx box and bring it next to the antenna. If the activity lamp does not turn on, I consider the
> transmitter to be turned off.

I see: that's clever. You are using the antenna activity light.

Of course, that light will turn on and off at random with cross-talk from the neighboring antenna amplifiers, which I assume you have connected to antennas in faraday enclosures.

Your procedure will work most of the time, and has the great advantage that you don't need a separate Octal Data Receiver to test if the transmitters are on or off. Having said that, we are certain the transmitters are turned off when we ship them. So the biggest risk in turning them on is when you move them from the FedEx box to your storage box via your testing procedure location.

Nevertheless, your ambient 902-928 MHz interference is significant, and it is certainly going to vary. In our office, there are times when we place the transmitter next to the antenna and we don't get reception. At other times, we get reception from another transmitter for a moment, turn on the transmitter in our hand because we think we are turning it off, and then set it aside when the activity light goes off. If I turn off twenty transmitters, half the time one is still running at the end.

> The transmitters go back into the box and are stored in another box
> that is not touched until someone takes out a transmitter.

Good.

Nevetheless, the only way to be certain that the transmitters are off when you store them is to move the antenna slowly around the box with the transmitters inside (a cardboard or plastic box, of course), and see if there is any activity.

But this procedure raises a question: how is it possible for you to
perform this check, when you are recording full-time from your two
existing Octal Data Receivers? You are using the antenna activity light,
which will flash from cross-talk even if you have no transmitters turned
in the box. And if you do detect power coming from the box, how are you
going to know which transmitter to take out and turn off?

When we do this check at OSI, we have an Octal Data Receiver dedicated to the task, and when we see a transmitter is on, we know which one to take out, because we have the channel activity lights to look at.

I have not thought this through properly.

> I checked for magnetic sources or the chance of heavy as well.

Good.

If we were certain the transmitters were off when you stored them, we could say for sure that something is wrong with R110.4.

> I explanted one of them yesterday, the other will be explanted next week. I will send them to you then.

Thank you. When I receive them, I will measure current consumption and check the amplifiers. Any transmitters that are faulty, we will replace.

Yours, Kevan
When you explant the transmitters, please look for places where the EEG lead comes out of your head fixture and makes a sudden bend.