http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6470214.PN.&OS=PN/6470214&RS=PN/6470214
United States Patent 6,470,214
O'Loughlin , et al. October 22, 2002
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Method and device for implementing the radio frequency hearing effect
Abstract
A modulation process with a fully suppressed carrier and input
preprocessor filtering to produce an encoded output; for amplitude
modulation (AM) and audio speech preprocessor filtering, intelligible
subjective sound is produced when the encoded signal is demodulated
using the RF Hearing Effect. Suitable forms of carrier suppressed
modulation include single sideband (SSB) and carrier suppressed
amplitude modulation (CSAM), with both sidebands present.
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Inventors: O'Loughlin; James P. (Placitas, NM), Loree; Diana L.
(Albuquerque, NM)
Assignee: The United States of America as represented by the Secretary
of the Air (
(Washington, DC)
Appl. No.: 08/766,687
Filed: December 13, 1996
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Current U.S. Class: 607/56 ; 128/898
Current International Class: A61N 1/08 (20060101); H04B 007/00 ()
Field of Search: 607/55,56 600/559,23,586 128/897,898
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References Cited [Referenced By]
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U.S. Patent Documents
3563246 February 1971 Puharick
3629521 December 1971 Puharick
4835791 May 1989 Daoud
Primary Examiner: Schaetzle; Kennedy
Attorney, Agent or Firm: Skorich; James M. Callahan; Kenneth E.
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for
the Government for governmental purposes without the payment of any
royalty thereon.
BACKGROUND OF THE INVENTION
This invention relates to the modulating of signals on carriers, which
are transmitted and the signals intelligibly recovered, and more
particularly, to the modulation of speech on a carrier and the
intelligible recover of the speech by means of the Radio Frequency
Hearing Effect.
The Radio Frequency ("RF") Hearing Effect was first noticed during
World War II as a subjective "click" produced by a pulsed radar signal
when the transmitted power is above a "threshold" level. Below the
threshold level, the click cannot be heard.
The discovery of the Radio Frequency Hearing Effect suggested that a
pulsed RF carrier could be encoded with an amplitude modulated ("AM")
envelope. In one approach to pulsed carrier modulation, it was assumed
that the "click" of the pulsed carrier was similar to a data sample
and could be used to synthesize both simple and complex tones such as
speech. Although pulsed carrier modulation can induce a subjective
sensation for simple tones, it severely distorts the complex waveforms
of speech, as has been confirmed experimentally.
The presence of this kind of distortion has prevented the click
process for the encoding of intelligible speech. An example is
provided by AM sampled data modulation.
Upon demodulation the perceived speech signal has some of the envelope
characteristics of an audio signal. Consequently a message can be
recognized as speech when a listener is preadvised that speech has
been sent. However, if the listener does not know the content of the
message, the audio signal is unintelligible.
The attempt to use the click process to encode speech has been based
on the assumption that if simple tones can be encoded, speech can be
encoded as well, but this is not so.
A simple tone can contain several distortions and still be perceived
as a tone whereas the same degree of distortion applied to speech
renders it unintelligible.
SUMMARY OF THE INVENTION
In accomplishing the foregoing and related object the invention uses
a. modulation process with a fully suppressed carrier and pre-
processor filtering of the input to produce an encoded output. Where
amplitude modulation (AM) is employed and the pre-processor filtering
is of audio speech input, intelligible subjective sound is produced
when the encoded signal is demodulated by means of the RF Hearing
Effect. Suitable forms of carrier suppressed modulation include single
sideband (SSB) and carrier suppressed amplitude modulation (CSAM),
with both sidebands present.
The invention further provides for analysis of the RF hearing
phenomena based on an RF to acoustic transducer model. Analysis of the
model suggests a new modulation process which permits the RF Hearing
Effect to be used following the transmission of encoded speech.
In accordance with one aspect of the invention the preprocessing of an
input speech signal takes place with a filter that de-emphasizes the
high frequency content of the input speech signal. The de-emphasis can
provide a signal reduction of about 40 dB (decibels) per decade.
Further processing of the speech signal then takes place by adding a
bias level and taking a root of the predistorted waveform. The
resultant signal is used to modulated an RF carrier in the AM fully
suppressed carrier mode, with single or double sidebands.
The modulated RF signal is demodulated by an RF to acoustic
demodulator that produces an intelligible acoustic replication of the
original input speech.
The RF Hearing Effect is explained and analyzed as a thermal to
acoustic demodulating process. Energy absorption in a medium, such as
the head, causes mechanical expansion and contraction, and thus an
acoustic signal.
When the expansion and contraction take place in the head of an
animal, the acoustic signal is passed by conduction to the inner ear
where it is further processed as if it were an acoustic signal from
the outer ear.
The RF to Acoustic Demodulator thus has characteristics which permit
the conversion of the RF energy input to an acoustic output.
Accordingly, it is an object of the invention to provide a novel
technique for the intelligible encoding of signals. A related object
is to provide for the intelligible encoding of speech.
Another object of the invention is to make use of the Radio Frequency
("RF") Hearing Effect in the intelligible demodulation of encoded
signals, including speech.
Still another object of the invention is to suitably encode a pulsed
RF carrier with an amplitude modulated ("AM") envelope such that the
modulation will be intelligibly demodulated by means of the RF Hearing
Effect. A related object is to permit a message to be identified and
understood as speech when a listener does not know beforehand that the
message is speech.
Other aspects of the invention will become apparent after considering
several illustrative embodiments, taken in conjunction with the
drawings.
What is claimed is:
1. A method of encoding an input audio signal a(t) to produce a double
sideband output signal having a .omega..sub.c carrier frequency, which
when transmitted to the head of a receiving subject, will by the radio
frequency hearing effect induce a thermal-acoustic signal in the bone/
tissue material of the head that replicates the input audio signal and
is conducted by the bone/tissue structure of the head to the inner ear
where it is demodulated by the normal processes of the cochlea and
converted to nerve signals which are sent to the brain, thereby
enabling intelligible speech to be perceived by the brain as any other
nerve signal from the cochlea, the method comprising: applying an
input audio signal a(t) to an audio pre-distortion filter with an As
(f) filter function to produce a first output signal a(t)As(f); adding
a very low frequency bias A to the first output signal to produce a
second output signal a(t)As(f)+A; applying the second output signal to
a square root processor to produce a third output signal (a(t)As(f)
+A).sup.1/2 ; applying the third output signal to a balanced modulator
to produce a double sideband output signal (a(t)As(f)+A).sup.1/2 sin
(.omega..sub.c t), where .omega..sub.c is the carrier frequency; and
transmitting the double sideband output signal to the head of the
receiving subject.
2. The method of claim 1, wherein the As(f) filter function step
further comprises the step of de-emphasizing the high frequency
content.
3. The method of claim 1, wherein the further step of suppressing one
of the sidebands of the double sideband output signal is done
resulting in a single sideband modulation transmission.
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