Cochlear Implants & Mobile Telephones
Peter M Solesbury
petros at mda009.win-uk.net
Mon Nov 18 05:39:40 EST 1996
I have been trying to obtain reports of the effects of mobile
telephones on active implants and would be interested to hear from
clinicians/reserchers on safety problems which may arise with
cochlear implants. I am aware of the "noise" problems which can arise
which is a nuisance issue (see recent posting info on hearing aid
users - below). I am concerned about possible damage to the cochlear &
tissue due to induced voltages/currents - I'm also interested in
possible damage to the implant (CMOS components).
Any info or pointers to info would be appreciated.
Peter M Solesbury
Senior Active Implant Specialist
Medical Devices Agency - UK
------------ posting on hearing aids follows ---------------
> >Could anyone provide any feedback on the use of digital cell phones by
> >hearing aid users. I am specifically interested in the new AT&T PCS
> >Digital phones.
> I can't give you any information specific to the AT&T phones, but
> the following information depends more on the hearing aid model than
> on the phone model.
> First, the PCS I'm familiar with is the broadband PCS in the 1.85-1.99
> GHz band, which is, I believe, what is being used for the new digital
> cell phones.
> Many hearing aid users find that they cannot use PCS phones, because
> conversation is drowned out by a hum at 217 Hertz (or 434 Hertz).
> This occurs as follows: the phone transmits at 1.9 GHz. This
> 1.9 GHz signal switches on and then off again 217 times per second.
> In electrical engineering terms, a 217 Hz square wave amplitude-
> modulates a 1.9 GHz carrier. (Good old AM radio is just
> amplitude modulation using carriers in the range of 450 kHz to
> 1500 kHz. The signal doing the modulating would be the audio signal
> to be transmitted, rather than a square wave.)
> The phone is designed (and licensed) to transmit at 1.9 GHz,
> so it's working as intended. Any nearby unshielded electrical
> devices will pick up this signal to a greater or lesser extent.
> Unfortunately, the unshielded circuitry inside most hearing aids
> tends to demodulate the 1.9 GHz carrier, leaving behind the 217 Hertz
> artifact (and/or harmonics of 217 Hz). That audio-frequency artifact
> is amplified and passed along to the hearing aid's output.
> So, a perfectly-designed PCS phone can induce unwanted artifacts in
> less-than-perfect hearing aids. Hearing aid manufacturers are becoming
> increasingly aware of the problem, and I expect that more hearing aids
> will be engineered to be immune to this type of problem. I suspect,
> though, that as of a couple of years ago, almost all hearing aids
> were susceptible to the problem.
> Hope this helps. Note that I'm not speaking for Nortel. Nortel
> happens to be one of the largest manufacturers of PCS phones, but
> that work is done by another division, and so I have no special
> inside knowledge, nor do I have any particular axe to grind,
> except that I've had trouble using PCS phones with my hearing aids.
> Jeff Joslin All opinions mine.
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