## Notes on Voice to Skull Patent 6,470,214
by Dr. Allen L. Barker, January 27, 2007

These notes present some details on an improvement in the pulsed microwave voice to skull technology originally demonstrated in 1973 by experimenter Dr. Joseph Sharp. Note that this is a 1994 re-confirmation of voice to skull as a fully demonstrated technology, and NOT "in the future" as some articles mistakenly say.

    [Below are comments on] two of the documents which Sharon Weinberger
    received as a result of a FOIA request for documents
    related to the patent:

        O'Loughlin JP, Loree DL: Method and device for
        implementing the radio frequency hearing effect.
        US patent #6470214, Oct 22, 2002

    One document is an Aug. 2001 letter from O'Loughlin to the Judge
    Advocate handling the patent case, and the other is a draft of the
    patent from 1994 which contains some different information than the
    final patent.

    The scientific principle underlying the invention, and assumed by the
    inventors, is that thermal expansion can convert microwave pulses to
    acoustic signals.  As everyone knows from basic science, when things
    heat up they tend to expand, and when they cool down they tend to
    contract.  Microwave pulses carry energy, and when a pulse is absorbed
    by biological tissue this energy is converted to heat.  This causes
    the tissue to expand very slightly, and then to contract back when it
    cools.  This is basically the standard model for describing and
    analyzing the microwave hearing effect (and has been for several
    decades).  A single microwave pulse causes a click to be heard.  More
    complex signals can be broken down into strings of "clicks" by various
    modulation methods.  The amplitude of the induced acoustic wave is (at
    least roughly) proportional to the power level of the microwave pulse.

    The basic modulation method used in the O'Loughlin patent is an
    amplitude modulation.  In a simple amplitude modulation, the signal is
    broken up into discrete samples in time and then the power level of
    the microwave pulse train is modulated accordingly.  This is "an AM
    modulated envelope over a pulsed RF carrier train."  This method
    unfortunately introduces nonlinear distortion which cannot be
    compensated for by preprocessing.  It works for tones, but not for
    complex signals such as speech.  This is theoretically worked out in
    the draft patent, which also describes experimental verification that
    the simple AM modulation produces barely intelligible speech.  The
    experiments were conducted at "the Air Force Phillips Laboratory
    during the week of 24 Oct 94, using the AM sampled data modulation
    process."  Subjects could recognize the encoded messages, but only if
    they were told what the message was.

    The patent actually makes use of a different form of AM modulation,
    the "AM double sideband suppressed carrier" method, which is linear in
    the amplitude and allows for preprocessing of the audio signal.  They
    state (and show) that "conventional AM modulation ... is not useful
    for the implementation of this invention."

    O'Loughlin points out in his letter that since the power of a
    microwave signal is proportional to the square its the amplitude, and
    since the acoustic signal at the head is roughly proportional to the
    microwave signal's power level, the microwave signal's amplitude
    should be modulated according to the square root of the original audio
    signal's amplitude.  According to O'Loughlin, "This is the basic
    essence of the invention."  It is essentially a preprocessing of the
    input audio signal.  Other preprocessing is also applied, for example
    to decrease the higher frequencies according to a spherical model of a
    human head (which shows "a 40dB per decade slope in favor of the
    higher frequencies").

    In the Washington Post article "Mind Games," Sharon Weinberger writes
    that she obtained "records that note that the patent was based on
    human experimentation in October 1994 at the Air Force lab, where
    scientists were able to transmit phrases into the heads of human
    subjects, albeit with marginal intelligibility."  But these were
    initial experiments, using the simple AM modulation (which would be
    expected to give marginal intelligibility).  Using the actual process
    in the patent "will produce an undistorted subjective sound; which is
    the invention," according to the draft of the patent.  O'Loughlin's
    letter to the Judge Advocate states, "... the fact that when the
    signal is processed by the teachings of the invention the signal is
    intelligible has also been experimentally demonstrated."

    In a calculation in the draft patent, the sound level is calculated
    for a single tone sent via the AM balanced modulator method.  A 1GHz
    RF carrier is used, with a power level of 100mW/sqcm.  The calculation
    yields a sound level of ~50dB, which is said to be at the level of "a
    normal male voice at one meter."  The calculations do not take several
    loss sources into account, though, and the actual sound level would be
    somewhat lower.  It is calculated that the 100mW/sqcm signal could be
    applied for ten seconds and stay within the ANSI exposure level at
    1GHz.

    The suppressed-carrier method only outputs power while a signal is
    present, so power levels would be much less of a problem unless
    someone were really being blasted by a constant auditory stream.  (As
    if any experimenters on nonconsensual subjects would necessarily
    follow the ANSI exposure levels while psychologically manipulating
    involuntary human subjects.)

    Justesen reported in "Microwaves and Behavior," American Psychologist,
    March 1975, that Sharp and Grove had successfully encoded speech (the
    spoken digits from one to ten) in a pulsed microwave signal.  The
    method reported in that article is essentially an FM modulation,
    rather than an AM modulation.  That paper states that "the electrical
    sine-wave analogs of each word were then processed so that each time a
    sine wave crossed zero reference in the negative direction, a brief
    pulse of microwave energy was triggered."  That sounds like they are
    taking a Fourier decomposition of the speech signal and then using a
    frequency modulation on all of the Fourier components, simultaneously.
    The results reported in the O'Loughlin patent for AM modulation do not
    necessarily apply to the FM modulation methods.

    Of course, neither the Justesen article nor the O'Loughlin patent
    discuss the psychological sequelae that would result from testing
    these devices on nonconsensual subjects and/or applying them against
    unwitting citizens.