Last week at Hearing International we reviewed the military’s need to jam signals in the operation areas. As we found out it basically saved the lives of soldiers deployed to various areas where hostile action was required. This week Hearing International investigates the 
actual issue of if buzzing is caused in cochlear implants by signal jamming and if so what causes the “Buzzing”.
As discussed last week, the purpose of signal jamming by the military is a practice that is conducted regularly. The physics of jamming a cell phone are actually quite simple. Cell phones operate by sending signals along a range of the electromagnetic spectrum reserved for their use. In the United States most cell phone companies use the CDMA standard that that typically transmits on either 800 or 1,900 megahertz; in Europe most phones use the GSM standard and the frequency usually 900 or 1,800 megahertz.), in other parts of the world it might be another frequency, but most of the world has either adopted the US or the European versions. All a cell phone jamming device needs to do is broadcast a signal on those same frequencies, and it will interfere with any devices trying to transmit in that range. Jamming devices, illegal for civilian use in the US, overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out. Cell phones are designed to add power if they experience low-level interference, so the jammer must also recognize and match the power increase from the phone. The net effect for a hapless cell-phone user is that the phone’s screen will simply indicate that no signal is available. Odds are most people won’t even notice that their phones are being jammed. They’ll just assume that they’re in a dead spot—and feel
annoyed. Or terroists will be frustrated that they cannot remotely activate their explosive devices.
Enter the innocent cochlear implant patient in a military operations area. Click here for a video of how a cochlear implant operates. Normally, their implant operates with a transmitter sending signals from a usually a behind the ear (BTE) processor/transmitter to the implant inside of their head which sends the signal to electrodes that communicate with the cochlea and, subsequently, to the auditory nerve and pathways. Cochlear implants andtheir use with cellphones are 
described at Hub pages.com. Just as the jammer interferes with the signals for cell phone transmission, it interferes with the transmission of the signal from the processor/transmitter. Since the jamming device causes a constant collision with the radio frequency signal, the “buzzing” can be constant as long as the signal continues to be jammed.
In the Middle East, the primary area of current US military operations, the incidence of profound sensori-neural hearing impairment aas well as other exceptionalities is about 25% greater than in other parts of the world due to consaiguous marriage. Cochlear implants are quite popular in the Middle East as they a are beneficial for profound hearing impairment, often a government funded, and offer a relatively cosmetic given the customary attire of the region. Although the potential for problem patients from signal jamming will probably increase as the use of cochlear implants increase, Dr. Tarek El Dousseki, MD, indicates that this issue appears to be difficulty for cochlear implant users isolated to a small geographical area where military operations are found. The answer then to our Hearing International question this week is that jamming really does cause buzzing within cochlear implants in close proximity to the signal jamming devices. For those patients that are plagued with this problem, it is a major issue that affects them routinely. It is best for them to, if possible, to stay out of the range of the jamming devices or to turn off the implant while the jamming is present.
For cochlear implant users interested, Gallaudet University is conducting a study to evaluate interference in cochlear implants from digital cellular telephones. Their study is of cochlear implant patients that experience a “buzzing sound” when using a wireless phone which is caused by electromagnetic interference. This type of research could lead to help for those that are experiences this buzzing as a reault of jamming. Click on the links to get the Gallaudet site and register for their study.
Bob,
In the United States, AT&T and Deutche Telekom (T-Mobile brand) use GSM transmission, while Sprint and Verizon use CD/MA: This is important for hearing aid & CI users because of the structure of the signal: GSM, when demodulated (more on this later) produces tremendous energy in the audio spectrum, many dB greater than CD/MA.
As for CI’s, the FDA is extremely strict about overstimulation, and modern CI’s don’t suffer from this problem due to digital transmission: They shut down, either from the reverse update data (3,000 reverse updates/sec with the Advanced Bionics HiRes 90k system), or the reverse updates not being received, resulting in a loss of lock.
Now, on to what is actually causing that buzzing that can be heard when using a GSM cell phone, especially with older analog hearing aids: It’s Bad Design. Since hearing aid and CI processor cases are made out of plastic, it is difficult to provide the first line of defense against EMI: Shielding.
Remember when I wrote above, when demodulated? Well, as it turns out, what happens when an unshielded electronic circuit is in the presence of a strong modulated RF signal, the N-P junctions in the transistors act as an (unintentional) diode (rectifier), nicely demodulating the RF signal, stripping off the portion of the signal in the audio range… And amplifying it in subsequent stages.
Let me give you a parallel example: Back in the mid-1970’s during the CB radio boom (27mHz 6A3 (AM)), all of a sudden we had a new spate of complaints of “Breaker, Breaker!” being heard on home stereos everywhere. What happened was that the loudspeaker wiring made for a very nice antenna to bring the modulated RF signal right back into the N-P-N transistors in the output power amplifier, where it was rectified (demodulated) on the N-P junctions and sent right back out to the loudspeakers. [A variation of this occurred in the 1930’s & 40’s within a few miles of the new 50,000 watt AM broadcast radio transmitters with telephones.]
Part 15 of the Communications Act of 1933 (which established the FCC) clearly spells out that all electronic devices must not generate interfering (spurious) signals, and must accept any and all RF signals. What this means in the case of hearing aids and CI’s is that it is the responsibility of the device manufacturer to make them immune to any and all RF signals, period.
The solution in the 1930’s, 1970’s, and today is the same: Install RF bypass capacitors. In the case of telephones, these can be in the keyset or at the jacks. For stereos, installing them across the speaker terminals usually did the trick (unless it was a cheap all-in-one made out of pressboard, when the caps had to be on the output PA circuit board). For hearing aids & CI’s, it’s more complex, as the bypass capacitors have to be installed in numerous places, wherever there is an N-P semiconductor junction.
[As a side note, whenever a new AM broadcast transmitter would be commissioned, a team of technicians would go out into the field to install bypass caps on phones, radios and TV’s to stop the unintentional interference. By statute, it was the responsibility of the receiving device to reject it, i.e. it was (and is) the fault of the device; however the radio stations wanted to be a “good neighbor,” hence the dispatch to address complaints.]
So, in summary, as long as the hearing aid or CI processor is properly designed, it should be 100% immune to UHF RF sources, whether these sources are from a mobile phone held up to it, or from a jammer a few yards away.
Footnote: I’m sure you’ve heard the stories from your great Aunt about being able to hear music on her dentures or tooth fillings — In fact, she probably did! As it turns out, rectification from metal in the mouth causing demodulation is quite common~
Dan:
Thanks for your comments. If you would like to present these issues in a Guest Posting by tying your comments to the Jamming articles from a few weeks ago send me a note to [email protected] and we can work out a guest spot. Your comments are very interesting and a nice adjunct to Dr. Terek’s piece and the supplemental material that followed.
Bob
As a footnote to my lengthy comment about a properly designedCI or hearing aid never buzzing, there is still an issue of the RF data and power link for CI’s: Just like a mobile phone, these links can indeed be jammed, by in-band RF signal energy.
In the case of the Advanced Bionics CII/HR90k circuits, this would involve a very powerful 49 mHz signal to jam the forward data/power transmission link and/or a 10.7mHz signal to jam the much weaker reverse data link: When this occurs, the speech processor loses lock with the implant, and the system gracefully shuts down.
I have two cochlear implants, and I have experienced this buzzing problem twice! In fact, yesterday, I began having a hard time understand someone with background noise, because it seems like the noise in the background drowned out the person’s voice that I was talking to! I also experienced headaches, nonstop buzzing, and a little pain in my left ear. Two months ago, this happened to me, but I did not find out the problem until I went to U of M to check it out. It was hard to focus in school with this problem going on, so it is a serious problem. Last time U of M just put one of my electrodes on standby, and after that it seemed better…. But I guess it’s happening again… I hope someone can find a permanent fix to this problem!