An Inter-Disciplinary Resource Website to Effects on Human Electrodynamic Physiology
www.uncg.edu/~t_hunter/sound.html |
Site Map |
Patent No. 4858612 Hearing device (multi-channel microwave voice to skull device) (Stocklin, Aug 22, 1989)
Abstract
A method and apparatus for simulation of hearing in mammals by introduction of a plurality of microwaves into the region of the auditory cortex is shown and described. A microphone is used to transform sound signals into electrical signals which are in turn analyzed and processed to provide controls for generating a plurality of microwave signals at different frequencies. The multifrequency microwaves are then applied to the brain in the region of the auditory cortex. By this method sounds are perceived by the mammal which are representative of the original sound received by the microphone.
Notes:
What
is claimed is:
1. A sound perception device for providing induced perception of sound into
a mammalian brain comprising in combination:
means for generating microwave radiation which is representative of a sound
to be perceived, said means for generating including means for generating a
simultaneous plurality of microwave radiation frequencies and means for adjusting
the amplitude of said microwave radiation frequencies in accordance with the
sound to be perceived; and
antenna means located in the region of the auditory cortex of said mammalian
brain for transmitting said microwave energy into the auditory cortex region
of said brain.
2. A hearing device for perception of sounds comprising in combination:
means for generating a signal representative of sounds;
means for analyzing said signal representative of said sounds having an output;
means for generating a plurality of microwave signals having different frequencies
having a input connected to said output of said means for analyzing said signals,
having an output;
means for applying said plurality of microwave signals to the head of a subject,
and
whereby the subject perceives sounds which are representative of said sounds.
3. The apparatus in accordance with claim 2 wherein said means for generating
a signal is a microphone for detecting sound waves.
4. The apparatus in accordance with claim 2 wherein said means for applying
said plurality of microwave signals is an antenna.
5. The apparatus in accordance with claim 4 wherein said antenna is placed in
the region of the auditory cortex of the subject.
6. The apparatus in accordance with claim 2 wherein the subject is a human being.
7. The apparatus in accordance with claim 2 wherein said means for analyzing
said signal comprises:
an acoustic filter bank for dividing said sounds into a plurality of component
frequencies; and
a mode control matrix means for providing control signals which are weighted
in accordance with said plurality of component frequencies, having an output
connected to said means for generating a plurality of microwave signal inputs.
8. The apparatus in accordance with claim 7 wherein said acoustic filter bank
includes a plurality of audio frequency filters.
9. The apparatus in accordance with claim 8 wherein said audio frequency filters
provide a plurality of output frequencies having amplitudes which are a function
of said signal representative of sounds.
10. The apparatus in accordance with claim 9 wherein said amplitudes are the
weighted in accordance with transform function of the signal representative
of sounds.
11. The apparatus in accordance with claim 7 wherein said mode control matrix
device includes a voltage divider connected to each of said plurality of said
audio frequency filters.
12. The apparatus in accordance with claim 11 wherein each of said voltage dividers
has a plurality of outputs which are connected in circuit to said means for
generating a plurality of microwave signals.
13. The apparatus in accordance with claim 2 wherein said means for generating
a plurality of microwave signals comprises a plurality of microwave generators
each having a different frequency and means for controlling the output amplitude
of each of said generators.
14. The apparatus in accordance with claims 2 wherein said means for generating
a plurality of microwave signals comprises a broad band microwave source and
a plurality of filters.
15. The apparatus in accordance with claim 13 wherein said generators each comprise
a microwave signal source and a gain controlled microwave amplifier.
16. The apparatus in accordance with claim 13 wherein said means for analyzing
output is connected to said means for controlling microwave amplifier output
amplitudes.
17. The apparatus in accordance with claim 13 wherein analyzing includes K audio
frequency filters.
18. The apparatus in accordance with claim 17 wherein there are N microwave
generators.
19. The apparatus in accordance with claim 18 including a mode partitioning
means which provides N outputs for each of said K audio frequency filters.
20. The apparatus in accordance with claim 19 wherein said N amplifiers each
have K inputs from said mode partitioning means.
21. The apparatus in accordance with claim 20 wherein said N amplifiers have
K inputs less the mode partitioning means outputs which are so small that they
may be omitted.
22. The apparatus in accordance with claim 20 wherein said mode partitioning
output device outputs each include a diode connected to each microwave amplifier
gain control to provide isolation between all outputs.
23. The apparatus in accordance with claim 20 wherein said K audio frequency
filters are chosen to correspond to the critical bandwidths of the human ear.
24. The apparatus in accordance with claim 20 wherein said N microwave generators
are each adjustable in frequency output.
25. The apparatus in accordance with claim 18 wherein the frequency of each
N microwave generators is determined by anatomical estimation.
26. The apparatus in accordance with claim 18 wherein the frequency of the lowest
frequency microwave generator is chosen by determination of the effect of external
microwave generation on the EEG of the subject.
27. The apparatus in accordance with claim 18 wherein the frequency of each
of said N microwave generators corresponds to the subject's microwave modal
frequencies.
28. The apparatus in accordance with claim 27 wherein the subject's modal frequencies
are determined by measurement of the subject's cephalic index and the lateral
dimensions of the skull.
29. The apparatus in accordance with claim 28 wherein the subject's lowest modal
frequency is determined by varying the frequency of the lowest frequency microwave
generator about the estimated value until a maximum acoustic perception is obtained
by the subject.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to devices for aiding of hearing in mammals. The invention
is based upon the perception of sounds which is experienced in the brain when
the brain is subjected to certain microwave radiation signals.
2. Description of the Prior Art
In prior art hearing devices for human beings, it is well known to amplify sounds
to be heard and to apply the amplified sound signal to the ear of the person
wearing the hearing aid. Hearing devices of this type are however limited to
hearing disfunctions where there is no damage to the auditory nerve or to the
auditory cortex. In the prior art, if there is damage to the auditory cortex
or the auditory nerve, it cannot be corrected by the use of a hearing aid.
During World War II, individuals in the radiation path of certain radar installations
observed clicks and buzzing sounds in response to the microwave radiation. It
was through this early observation that it became known to the art that microwaves
could cause a direct perception of sound within a human brain. These buzzing
or clicking sounds however were not meaningful, and were not perception of sounds
which could otherwise be heard by the receiver. This type of microwave radiation
was not representative of any intelligible sound to be perceived. In such radar
installations, there was never a sound which was generated which resulted in
subsequent generation of microwave signals representative of that sound.
Since the early perception of buzzing and clicking, further research has been
conducted into the microwave reaction of the brain. In an article entitled "Possible
Microwave Mechanisms of the Mammalian Nervous System" by Philip L. Stocklin
and Brain F. Stocklin, published in the TIT Journal of Life Sciences, Tower
International Technomedical Institute, Inc. P.O. Box 4594, Philadelphia, Pa.
(1979) there is disclosed a hypothesis that the mammalian brain generates and
uses electro magnetic waves in the lower microwave frequency region as an integral
part of the functioning of the central and peripheral nervous systems. This
analysis is based primarily upon the potential energy of a protein integral
in the neural membrane.
In an article by W. Bise entitled "Low Power Radio-Frequency and Microwave
Effects On Human Electroencephalogram and Behavior", Physiol. Chemistry
Phys. 10, 387 (1978), it is reported that there are significant effects upon
the alert human EEG during radiation by low intensity CW microwave electromagnetic
energy. Bise observed significant repeatable EEG effects for a subject during
radiation at specific microwave frequencies.
SUMMARY
OF THE INVENTION
Results of theoretical analysis of the physics of brain tissue and the brain/skull
cavity, combined with experimentally-determined electromagnetic properties of
mammalian brain tissue, indicate the physical necessity for the existence of
electromagnetic standing waves, called modes in the living mammalian brain.
The mode characteristics may be determined by two geometric properties of the
brain; these are the cephalic index of the brain (its shape in prolate spheroidal
coordinates) and the semifocal distance of the brain (a measure of its size).
It was concluded that estimation of brain cephalic index and semifocal distance
using external skull measurements on subjects permits estimation of the subject's
characteristic mode frequencies, which in turn will permit a mode by mode treatment
of the data to simulate hearing.
This invention provides for sound perception by individuals who have impaired
hearing resulting from ear damage, auditory nerve damage, and damage to the
auditory cortex. This invention provides for simulation of microwave radiation
which is normally produced by the auditory cortex. The simulated brain waves
are introduced into the region of the auditory cortex and provide for perceived
sounds on the part of the subject.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the acoustic filter bank and mode control matrix portions of the
hearing device of this invention.
FIG. 2 shows the microwave generation and antenna portion of the hearing device
of this invention.
FIG. 3 shows a typical voltage divider network which may be used to provide
mode partition.
FIG. 4 shows another voltage divider device which may be used to provide mode
partition.
FIG. 5 shows a voltage divider to be used as a mode partition wherein each of
the resistors is variable in order to provide adjustment of the voltage outputs.
FIG. 6 shows a modified hearing device which includes adjustable mode partitioning,
and which is used to provide initial calibration of the hearing device.
FIG. 7 shows a group of variable oscillators and variable gain controls which
are used to determine hearing characteristics of a particular subject.
FIG. 8 shows a top view of a human skull showing the lateral dimension.
FIG. 9 shows the relationship of the prolate spherical coordinate system to
the cartesian system.
FIG. 10 shows a side view of a skull showing the medial plane of the head, section
A--A.
FIG. 11 shows a plot of the transverse electric field amplitude versus primary
mode number M.
FIG. 12 shows a left side view of the brain and auditory cortex.
FIG. 13 shows the total modal field versus angle for source location.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT
This invention is based upon observations of the physical mechanism the mammalian
brain uses to perceive acoustic vibrations. This observation is based in part
upon neuro anatomical and other experimental evidence which relates to microwave
brain stimulation and the perception of sounds.
It is has been observed that monochromatic acoustic stimuli (acoustic tones,
or single tones) of different frequencies uniquely stimulate different regions
of the cochlea. It has also been observed that there is a corresponding one
to one relationship between the frequency of a monochromatic acoustic stimulus
and the region of the auditory cortex neurally stimulated by the cochlear nerve
under the physiologically normal conditions (tonotopicity).
It is has been observed that for an acoustic tone of a frequency which is at
the lower end of the entire acoustical range perceivable by a person, that a
thin lateral region ("Line") parallel to the medial axis of the brain and toward
the inferior portion of the primary auditory cortex is stimulated. For an acoustic
tone whose frequency is toward the high end of the entire perceivable acoustic
range, a thin lateral region parallel to the medial axis and toward the superior
portion of the primary auditory cortex is stimulated.
Neural stimulation results in the generation of a broad band of microwave photons
by the change in rotational energy state of protons integral to the neuron membrane
of the auditory cortex. The physical size and shape of the brain/skull cavity,
together with the (semi-conductor) properties (conductivity and dielectric constant)
of the brain tissue provide an electromagnetic resonant cavity. Specific single
frequencies are constructively reinforced so that a number of standing electromagnetic
waves, each at its own single electromagnetic frequency in the microwave frequency
region, are generated in the brain. Each such standing electromagnetic wave
is called a characteristic mode of the brain/skull cavity.
Analysis in terms of prolate spheroidal wave functions indicates that transverse
electric field components of these modes have maxima in the region of the auditory
cortex. This analysis further shows that transverse electric field possess a
variation of amplitude with angle in the angular plane (along the vertical dimension
of the auditory cortex) and that is dependent only upon the primary mode number.
The auditory cortex in the normally functioning mammalian brain is a source
of microwave modes. The auditory cortex generates these modes in accordance
with the neural stimulation of the auditory cortex by the cochlear nerve. Mode
weighting for any one acoustic tone stimulus is given by the amplitude of each
mode along the line region of the auditory cortex which is neurally stimulated
by that acoustic tone stimulus. A listing of mode weighting versus frequency
of acoustic stimulus is called the mode matrix.
In this invention, the functions of the ear, the cochlear nerve, and the auditory
cortex are simulated. Microwaves simulating the mode matrix are inserted directly
into the region of the auditory cortex. By this insertion of simulated microwave
modes, the normal operation of the entire natural hearing mechanism is simulated.
Referring now to FIG. 1 and FIG. 2 there is shown an apparatus which provides
for induced perception of sound into a mammalian brain. This hearing device
includes a microphone 10 which receives sounds, an acoustic filter bank 12 which
separates the signals from the microphone into component frequencies, and a
mode control matrix 14 which generates the mode signals which are used to control
the intensity of microwave radiations which are injected into the skull cavity
in the region of the auditory. cortex.
The acoustic filter bank 12 consists of a bank of acoustic filters F1 through
Fk which span the audible acoustic spectrum. These filters may be built from
standard resistance, inductance, and capacitance components in accordance with
well established practice. In the preferred embodiment there are 24 filters
which correspond to the observed critical bandwidths of the human ear. In this
preferred embodiment a typical list of filter parameters is given by Table 1
below:
TABLE I ______________________________________ Filter No. Center Frequency (Hz)
Bandwidth (Hz) ______________________________________ 1 50 less than 100 2 150
100 3 250 100 4 350 100 5 450 110 6 570 120 7 700 140 8 840 150 9 1,000 160
10 1,170 190 11 1,370 210 12 1,600 240 13 1,850 280 14 2,150 320 15 2,500 380
16 2,900 450 17 3,400 550 18 4,000 700 19 4,800 900 20 5,800 1,100 21 7,000
1,300 22 8,500 1,800 23 10,500 2,500 24 13,500 3,500 ______________________________________
The rectifier outputs one through K are feed to K mode partition devices. The
mode partitioning devices each have N outputs wherein N is the number of microwave
oscillators used to generate the microwave radiation. The outputs 1 through
N of each mode partition device is applied respectively to the inputs of each
gain controlled amplifier of the microwave radiation generator. The function
of the mode control matrix 14 is the control of the microwave amplifiers in
the microwave amplifier bank 18. In the preferred embodiment thus will be 24
outputs and 24 microwave frequency oscillators.
Connected to each microwave amplifier gain control line is a mode simulation
device 16 which receives weighted mode signals from the mode partition devices
14. Each mode simulation device consists of one through k lines and diodes 17
which are each connected to summing junction 19. The diodes 17 provide for isolation
from one mode partition device to the next. The diodes 17 prevent signals from
one mode partition device from returning to the other mode partition devices
which are also connected to the same summing junction of the mode summation
device 16. The diodes also serve a second function which is the rectification
of the signals received from the acoustic filter bank by way of the mode partition
devices. In this way each mode partition device output is rectified to produce
a varying DC voltage with major frequency components of the order of 15 milliseconds
or less. The voltage at the summation junction 19 is thus a slowly varying DC
voltage.
The example mode partition devices are shown in greater detail in FIGS. 3, 4,
and 5. The mode partition devices are merely resistance networks which produce
1 through N output voltages which are predetermined divisions of the input signal
from the acoustic filter associated with the mode partition device. FIG. 3 shows
a mode partitioning device wherein several outputs are associated with each
series resistor 30. In the embodiment depicted in FIG. 4 there is an output
associated with each series resistor only, and thus there are N series resistors,
or the same number of series resistors as there are outputs. The values of the
resistors in the mode partition resistor network are determined in accordance
with the magnitudes of the frequency component from the acoustic filter bank
12 which is required at the summation point 19 or the gain control line for
amplifiers 20.
The microwave amplifier bank 18 consists of a plurality of microwave oscillators
1 through N each of which is connected to an amplifier 20. Since the amplifiers
20 are gain controlled by the signals at summation junction 19, the magnitude
of the microwave output is controlled by the mode control matrix outputs F1
through F.sub.n. In the preferred embodiment there are 24 amplifiers.
The leads from the microwave oscillators 1 through N to the amplifiers 20 are
shielded to prevent cross talk from one oscillator to the next, and to prevent
stray signals from reaching the user of the hearing device. The output impedance
of amplifiers 20 should be 1000 ohms and this is indicated by resistor 21. The
outputs of amplifiers 20 are all connected to a summing junction 22. The summing
junction 22 is connected to a summing impedance 23 which is approximately 50
ohms. The relatively high amplifier output impedance 21 as compared to the relatively
low summing impedance 23 provides minimization of cross talk between the amplifiers.
Since the amplitude of the microwave signal needed at the antenna 24 is relatively
small, there is no need to match the antenna and summing junction impedances
to the amplifier 20 output impedances. Efficiency of the amplifiers 20 is not
critical.
Level control of the signal at antenna 24 is controlled by pick off 25 which
is connected to the summing impedance 23. In this manner, the signal at antenna
24 can be varied from 0 (ground) to a value which is acceptable to the individual.
The antenna 24 is placed next to the subject's head and in the region of the
subject's auditory cortex 26. By placement of the antenna 24 in the region of
the auditory cortex 26, the microwave field which is generated simulates the
microwave field which would be generated if the acoustic sounds were perceived
with normal hearing and the auditory cortex was functioning normally.
In FIG. 2A there is shown a second embodiment of the microwave radiation and
generator portion of the hearing device. In this embodiment a broad band microwave
source 50 generates microwave signals which are feed to filters 52 through 58
which select from the broad band radiation particular frequencies to be transmitted
to the person. As in FIG. 2, the amplifiers 20 receive signals on lines 19 from
the mode control matrix. The signals on lines 19 provide the gain control for
amplifiers 20.
In FIG. 6 there is shown a modified microwave hearing generator 60 which includes
a mode partition resistor divider network as depicted in FIG. 5. Each of the
mode partition voltage divider networks in this embodiment are individually
adjustable for all of the resistances in the resistance network. FIG. 5 depicts
a voltage division system wherein adjustment of the voltage partition resistors
is provided for.
In FIG. 6, the sound source 62 generates audible sounds which are received by
the microphone of the microwave hearing generator 60. In accordance with the
operation described with respect to FIGS. 1 and 2, microwave signals are generated
at the antenna 10 in accordance with the redistribution provided by the mode
control matrix as set forth in FIG. 5.
The sound source 62 also produces a signal on line 64 which is received by a
head phone 66. The apparatus depicted in FIG. 6 is used to calibrate or fit
a microwave hearing generator to a particular individual. Once the hearing generator
is adjusted to the particular individual by adjustment of the variable resistors
in the adjustable mode partition portion of the hearing generator, a second
generator may be built using fixed value resistors in accordance with the adjusted
values achieved in fitting the device to the particular subject. The sound produced
by headphone 66 should be the same as a sound from the sound source 62 which
is received by the microphone 10 in the microwave hearing generator 60. In this
way, the subject can make comparisons between the perceived sound from the hearing
generator 60, and the sound which is heard from headphone 66. Sound source 62
also produces a signal on 68 which is feed to cue light 69. Cue light 69 comes
on whenever a sound is emitted from sound source 62 to the microwave generator
60. In this manner, if the subject hears nothing, he will still be informed
that a sound has been omitted and hence that he is indeed perceiving no sound
from the microwave hearing generator 60.
In FIG. 7 there is shown a modified microwave hearing generator which may be
used to determine a subject's microwave mode frequencies. In this device, the
acoustic filter bank and the mode control matrix have been removed and replaced
by voltage level signal generated by potentiometers 70. Also included are a
plurality of variable frequency oscillators 72 which feed microwave amplifiers
74 which are gain controlled from the signal generated by potentiometers 70
and pick off arm 76.
This modified microwave hearing generator is used to provide signals using one
oscillator at a time. When an oscillator is turned on, the frequency is varied
about the estimated value until a maximum acoustic perception by the subject
is perceived. This perception however may consist of a buzzing or hissing sound
rather than a tone because only one microwave frequency is being received. The
first test of perception is to determine the subject's lowest modal frequency
for audition (M=1). Once this modal frequency is obtained, the process is repeated
for several higher modal frequencies and continued until no maximum acoustic
perception occurs.
Another method of determination of a subject's modal frequencies is through
anatomical estimation. This procedure is by measurement of the subject's cephalic
index and the lateral dimensions of the skull. In this method, the shape is
determined in prolate spheroidal coordinance.
Purely anatomical estimation of subject's modal frequencies is performed by
first measuring the maximum lateral dimension (breadth) L FIG. 8, of the subject's
head together with the maximum dimension D (anterior to posterior) in the medial
plane of the subject's head. D is the distance along Z axis as shown in FIG.
10. The ratio L/D, called in anthropology the cephalic index, is monotonically
related to the boundary value .xi..sub.o defining the ellipsoidal surface approximating
the interface between the brain and the skull in the prolate spheroidal coordinate
system. .xi..sub.o defines the shape of this interface; .xi..sub.o and D together
give an estimate of a, the semi-focal distance of the defining ellipsoid. Using
.xi..sub.o and a, together with known values of the conductivity and dielectric
constants of brain tissue, those wavelengths are found for which the radial
component of the electric field satisfies the boundary condition that it is
zero at .xi..sub.o. These wavelengths are the wavelengths associated with the
standing waves or modes; the corresponding frequencies are found by dividing
the phase velocity of microwaves in brain tissue by each of the wavelengths.
A subject's microwave modal frequencies may also be determined by observing
the effect of external microwave radiation upon the EEG. The frequency of the
M equal 1 mode may then be used as a base point to estimate all other modal
frequencies.
A typical example of such an estimation is where the subject is laterally irradiated
with a monochromatic microwave field simultaneous with EEG measurement and the
microwave frequency altered until a significant change occurs in the EEG, the
lowest such frequency causing a significant EEG change is found. This is identified
as the frequency of the M=1 mode, the lowest mode of importance in auditory
perception. The purely anatomical estimation procedure (FIGS. 8, 9, 10) is then
performed and the ratio of each modal frequency to the M=1 modal frequency obtained.
These ratios together with the experimentally-determined M=1 frequency are then
used to estimate the frequencies of the mode numbers higher than 1. The prolate
spheroidal coordinate system is shown in FIG. 9. Along the lateral plane containing
the x and y coordinates of FIG. 9, the prolate spheroidal coordinate variable
.phi. (angle) lies FIGS. 9 and 10. Plots of the transverse electric field amplitude
versus primary mode number m are shown in FIG. 11. The equation is
The "elevation view" FIG. 12, of the brain from the left side, shows the primary
auditory cortex 10. The iso-tone lines and the high frequency region are toward
the top of 100 and the low frequency region toward the bottom of 100.
The formula I, set forth below is the formula for combining modes from an iso-tone
line at .phi.=.phi.j being excited to obtain the total modal field at some other
angular location .phi.. For this formula, if we let J=1 (just one iso-tone single
frequency acoustic stimulus line), then it can be shown that ALL modes (in general)
must be used for any ONE tone. ##EQU1## .phi.=ANGLE (0.degree. LATERAL) .phi..sub.j
=LOCATION OF j-TH SOURCE (TOTAL NUMBER J)
.DELTA..phi..sub.m =ATTENUATION LENGTH (IN ANGLE) OF m-TH MODE
m=PRIMARY MODE NUMBER (HIGHEST MODE M)
FIG. 13 shows the resulting total modal field versus angle .phi. for source
location .phi. at 5.25.degree., 12.5.degree., etc. With reference to the set
of curves at the left top of this figure. A spacing of approximately 7.25.degree.
in .phi. corresponds to a tonal difference of about 1 octave. This conclusion
is based on the side-lobes of pattern coming from .phi.=5.25.degree., etc. The
total filed (value on y-axis) falls considerably below the top curves for source
locations well below 5.25.degree. (toward the high acoustic stimulus end) and
also as the source of frequency goes well above 30.degree. (low frequency end).
.phi. is plotted positive downward from 0.degree. at lateral location as indicates
in FIG. 11.
Resistor weightings are obtained from the .vertline.sin (m[.phi.-.phi.j]).vertline.,
Formula I. The scale between acoustic frequency and .phi. must be set or estimated
from experiment. Approximately 5.25.+-.1.degree. corresponds to a tonal stimulus
at about 2 kHz (the most sensitive region of the ear) since this source location
gives the highest electric field amplitude.
The apparatus of FIG. 7 may also be used to determine values for a hearing device
which are required for a particular subject. Once the modal frequencies have
been estimated, the device of FIG. 7 which includes variable microwave oscillators
may be used to determine values for the oscillators which match the subject,
and to determine resistance values associated with the mode partition devices
of the mode control matrix.
In FIG. 7 manual control of the amplifier gain is achieved by potentiometers
76. In this manner the amplifier gains are varied about the estimated settings
for an acoustic tone stimulus in the region of two thousand Hertz (2 kHz) until
maximum acoustic perception and a purest tone are achieved together. The term
purest tone may also be described as the most pleasing acoustic perception by
the subject. This process may be repeated at selected frequencies above and
below 2 kHz. The selected frequencies correspond to regions of other acoustic
filter center frequencies of the subject. When modal frequency (oscillator frequency)
and gain set values (setting a potentiometer 76) are noted, it is then possible
to calculate fixed oscillator frequencies and control resistor values for the
adjusted hearing device for this particular subject.
In the event the subject has no prior acoustic experience, that is deaf from
birth, estimated resistor values must be used. Also, a complex acoustic stimulation
test including language articulation and pairs of harmonically related tones
may be developed to maximize the match of the hearing device parameters for
those of this particular subject.
Typical components for use in this invention include commercially available
high fidelity microphones which have a range of 50 Hz to 15 kHz with plus or
minus 3 dB variation.
The audio filters to be used with the acoustic filter bank 12 are constructed
in a conventional manner, and have Q values of about 6. The filters may also
be designed with 3 dB down points (1/2 the bandwidth away from the center frequency)
occurring at adjacent center frequency locations.
The diodes 17 in the mode control matrix which provide isolation between the
mode partition circuits are commercially available diodes in the audio range.
The microwave oscillators 1 through N and the microwave amplifiers 20 are constructed
with available microwave transistors which can be configured either as oscillators
or amplifiers. Examples of the transistors are GaAsFET field effect transistors
by Hewlitt Packard known as the HFET series or silicone bipolar transistors
by Hewlitt Packard known as the HXTR series.
All the cable between the oscillators, the microwave amplifiers, and the antenna
should be constructed with either single or double shielded coaxial cable.
The antenna 24 for directing microwave signals to the audio cortex 26 should
be approximately the size of the auditory cortex. A typical size would be one
and one half CM high and one half to one CM wide. The antenna as shown is located
over the left auditory cortex, but the right may also be used. Since the characteristic
impedance of the brain tissue at these microwave frequencies is close to 50
ohms, efficient transmission by commercially available standard 50 ohm coax
is possible.
------------------------------------------------------------------------
The invention has been described in reference to the preferred embodiments.
It is, however, to be understood that other advantages, features, and embodiments
may be within the scope of this invention as defined in the appended claims.