U.S. patent number 3,594,514 [Application Number 05/000,489] was granted by the patent office on 1971-07-20 for hearing aid with piezoelectric ceramic element.
This patent grant is currently assigned to Medtronic, Inc.. Invention is credited to Robert C. Wingrove.
United States Patent |
3,594,514 |
Wingrove |
July 20, 1971 |
HEARING AID WITH PIEZOELECTRIC CERAMIC ELEMENT
Abstract
Implantable hearing aid apparatus having a piezoelectric ceramic
element mounted adjacent to the auditory conductive system of the
middle ear for imparting vibration thereto. The piezoelectric
element being electrically connected to electrical circuitry for
providing electrical signals representative of sound waves. The
electrical circuitry and the piezoelectric element being properly
encapsulated for implantation within the body.
Inventors: |
Wingrove; Robert C.
(Minneapolis, MN) |
Assignee: |
Medtronic, Inc. (Minneapolis,
MN)
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Family
ID: |
21691735 |
Appl.
No.: |
05/000,489 |
Filed: |
January 2, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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625042 |
Mar 22, 1967 |
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Current U.S.
Class: |
600/25;
381/326 |
Current CPC
Class: |
H04R
25/606 (20130101) |
Current International
Class: |
H04R
25/00 (20060101); H04r 025/00 () |
Field of
Search: |
;179/107 ;128/1R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Conservative Tympanoplasty," October 1, 1966, Geze J. Jako M.D.
and Claus Jensen M.D., A REPORT TO THE AMERICAN ACADEMY OF
OPHTALMOLOGY AND OTOLARYNAOLOGY, Page 54.
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Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Myers; Randall P.
Parent Case Text
This is a continuation of application, Ser. No. 625,042 filed Mar.
22, 1967 and now abandoned.
Claims
I claim:
1. In an implantable hearing aid including means for providing
electrical signals representative of and derived from sound waves,
piezoelectric ceramic means connected to receive the electrical
signals, and further means operatively connected to said
piezoelectric ceramic means and adapted to be mounted to contact a
portion of a middle ear of an animal.
2. The hearing aid of claim 1 in which said piezoelectric ceramic
means comprises a bimorphic element.
3. The hearing aid of claim 1 in which said further means is
adapted to be mounted to contact the auditory ossicles.
4. The hearing aid of claim 1 in which said further means is
adapted to be mounted to contact the oval window.
5. The hearing aid of claim 1 in which said piezoelectric ceramic
means is substantially rectangular and said piezoelectric ceramic
means has one end adapted to be mounted to the mastoid bone in an
ear of an animal, the other end connected to said further means
adapted to extend to contact the portion of the middle ear of an
animal for imparting vibrations thereto.
6. An implantable hearing aid comprising: electrical circuit means
for providing electrical signals representative of sound waves;
piezoelectric ceramic means for converting the electrical signals
to mechanical vibrations; electrically conductive means connecting
said circuit means to said piezoelectric means; all said means
being encapsulated in a substance substantially inert to body
fluids and tissue; said encapsulated piezoelectric ceramic means
adapted to be mounted to contact a portion of the structure of the
ear of an animal for imparting vibrations thereto.
7. The hearing aid of claim 6 in which said encapsulated
piezoelectric ceramic means is operatively connected to further
means adapted to contact a portion of the structure of the ear of
an animal.
8. The hearing aid of claim 6 in which said piezoelectric ceramic
means comprises a bimorphic element.
9. The hearing aid of claim 8 in which said bimorphic element is
substantially rectangular and said bimorphic element has one end
adapted to be mounted to the mastoid bone in an ear of an animal
and the other end adapted to extend to contact a portion of the
middle ear of an animal.
10. The hearing aid of claim 6 in which said electrical circuit
means comprises electrical receiver means for receiving electrical
signals from a transmitter external to the body in which the
hearing aid is implanted.
11. The hearing aid of claim 6 in which said electrical circuit
means includes mechanical-electrical transducer means for
transforming sound waves into electrical signals.
12. The hearing aid of claim 11 in which said transducer means
comprises second piezoelectric ceramic means.
13. The hearing aid of claim 12 in which said second piezoelectric
ceramic means comprises a second bimorphic element.
Description
BACKGROUND OF THE INVENTION
Hearing aids have long been known in the field of
medical-electronics. Generally these known hearing aids are mounted
external to the body and apply a vibration from a device mounted
adjacent the external portion of the ear drum. While satisfactory
for some uses, these known hearing aids are ineffective when the
auditory system of the middle ear has become inoperative or highly
inefficient. Some prior art attempts have been made to provide an
implantable hearing aid by which the inoperative portions of the
auditory system can be bypassed. These prior art systems used the
technique of converting the vibration into air acoustics, and
providing the vibrated air to the inner ear. These systems have the
disadvantages of being inefficient and not capable of overcoming
many common problems of inoperability of the auditory system, such
as when the auditory ossicles are fused as pointed out in the
publication "Conservative Tympanoplasty," G. J. Jako, M.D. and C.
Jansen, M.D., AMERICAN ACADEMY OF OPHTALMOLOGY AND OTOLARYNGOLOGY,
INSTRUCTIONS SECTION, 1966.
To overcome these disadvantages the apparatus of this invention
provides a piezoelectric ceramic element which is suitable for
implantation in the middle ear structure of the body. Thus
mechanical vibrations can be applied directly to the auditory
system, such as the auditory ossicles or the oval window, or the
vibrations can be caused at a predetermined spacing from the
desired element of the auditory system.
SUMMARY OF THE INVENTION
Briefly described, the apparatus of this invention comprises a
piezoelectric ceramic element, described herein in its preferred
embodiment as a bimorphic ceramic element, capable of transducing
electrical signals to mechanical vibrations. The piezoelectric
element is electrically connected to an electrical circuit which
provides electrical signals to the piezoelectrical element
representing the sound waves desired to be heard. The electrical
circuit and the piezoelectric element are encapsulated in a
substance inert to body fluids and tissue to avoid harmful effects
from implantation in the body. The electrical circuit can be a
receiver which receives electric signals from a transmitter located
external to the body, or can be a complete unit which receives the
sound waves through devices totally implanted, for transmission to
the piezoelectric element.
IN THE DRAWINGS
FIG. 1 is a view of an embodiment of the apparatus of this
invention shown completely encapsulated;
FIG. 2 is a sectional view of a portion of the embodiment of FIG. 1
showing an encapsulated piezoelectric ceramic element;
FIG. 3 is a schematic drawing of the circuit of the embodiment of
FIG. 1; and
FIG. 4 is a block diagram of an external transmitter which can be
used with the circuitry of FIG. 3.
DESCRIPTION OF FIGURES
In FIG. 1 there is shown an implantable hearing aid designated
generally as 10. Hearing aid 10 includes a head portion 11, a stem
portion 12, and a tail portion 13. Head 11 contains an electrical
circuit such as a receiver, stem 12 contains electrically
conductive leads, and tail 13 contains a transducer. All elements
are encapsulated in a substance substantially inert to body fluids
and tissue to provide for proper implantation into the body of the
user.
In FIG. 2 there is shown a sectional view of tail 13 and a portion
of stem 12. Within tail 13 there is shown a piezoelectric
transducer 15, here shown as a bimorphic ceramic element, similar
to bimorphic elements used in phonograph pickup apparatus well
known to those skilled in the electrical art. A pair of leads 16
and 17 are each shown connected to piezoelectric element 15, and
extending through stem 12. Element 15 is shown encased in an epoxy
18. Element 15 and epoxy coating 18, as well as leads 16 and 17,
are shown encapsulated in a substance 19 which is substantially
inert to body fluids and tissue, such as silicon rubber.
Preferably, the substance 19 around tail portion 13 is sufficiently
thin so as to allow efficient translation of vibratory motion from
transducer 15 to the auditory system of the middle ear, as more
fully described below.
With respect to FIGS. 1 and 2 it should be understood that for
purposes of clarity the drawings are not dimensionally accurate or
in scale. For example, in one embodiment of this invention which
has been successfully tested, piezoelectric element 15 was 0.3--0.5
inches long; 0.05 inches wide; and 0.025 inches thick (including
both layers of a bimorphic element); epoxy coating 18 around
element 15 was approximately 0.01--0.015 inches thick; and
substance 19 comprised a coating of about 0.01 inches thickness.
The preceding dimensions are approximate.
Referring now to FIG. 3, there is shown a signal receiving coil 20.
Connected in parallel with coil 20 is a capacitor 21. A diode 22
and a resistor 23 are connected in series across capacitor 21. Lead
16 connects from piezoelectric element 15 to a point between diode
22 and one side of resistor 23. Lead 17 connects between element 15
and the other side of resistor 23.
In FIG. 4 there is shown an exemplary block diagram of a
transmitter used to provide signals to coil 20 of FIG. 3. In FIG, 4
there is shown a microphone 24, the output of which enters an audio
preamplifier 25. Preamplifier 25 then provides a signal to a
modulator 26 which in turn presents the modulated signal to an R-F
oscillator 27. The output of oscillator 27 is transmitted through a
transmitting coil 28 to coil 20 of FIG. 3.
OPERATION
In the preferred embodiment disclosed herein, piezoelectric element
15 is a bimorphic element. That is, it is a ceramic element
composed of two layers. When a voltage is applied between the two
layers, that is across the bimorphic element, one of the layers
tends to lengthen while the other tends to contract. Thus a bending
is accomplished. It thus becomes apparent that the application of a
varying voltage signal, such as one representing sound waves, will
cause element 15 to bend or vibrate in response to the varying
voltage signal. Element 15 is chosen to respond, or vibrate, in the
audio frequency range, and is thus uniquely adapted to act as an
electrical-mechanical transducer in an implanted hearing aid.
The mode of vibration or bending is similar to that of a common
diving board when the element used is substantially rectangular, as
that shown in the preferred embodiment. As mentioned above, an
element 15 can be chosen such that the frequency response covers
the audio frequency range. The amount of bending or vibration is
relatively small and is proportional to the amplitude of the
applied signal. The bending force of an element such as element 15
is related to atomic crystal binding forces, and is thus relatively
large and can overcome damping effects such as may be caused by
epoxy coating 18 and silicon rubber coating 19.
It should be noted that epoxy coating 18 is shown here as part of
the preferred embodiment for its function of adding further
protection to the implanted device of this invention, such as added
moisture protection. The apparatus of this invention will operate
without epoxy coating 18. It should further be noted that greater
efficiency of operation of the apparatus of this invention occurs
when the portion of substance 19 encapsulating element 15 and its
coating 18 in tail 13 of the apparatus 10 is relatively thin, to
avoid undue damping effects.
When mounting the apparatus 10 in a body, it is preferable to
firmly mount one end of element 15 (tail 13) in an area that can
provide a stable platform, such as the mastoid bone. The other end
of element 15 is then placed adjacent one of the elements of the
auditory system of the middle ear, such as one of the auditory
ossicles or the oval window. The free or vibrating end of element
15 can actually touch, or can be spaced from, the portion of the
auditory system, as required. Head 11 can be mounted, for example,
in the antrum cell of the mastoid, from which stem 12 can extend to
tail 13 in the middle ear.
Referring to FIGS. 3 and 4, it can be seen that microphone 24 will
transduce sound waves into electrical signals which will be
amplified in preamplifier 25, modulated in modulator 26, and then
passed on to R-F oscillator 27 whence it will be transmitted by
coil 28. The apparatus of FIG. 4 is in this preferred embodiment
intended to be located external to the body. However, as will be
described below, it is possible to incorporate this entire hearing
aid within an implantable device.
Coil 28 will transmit a modulated RF signal which will be picked up
by the circuit comprising receiving coil 20 and capacitor 21. The
resulting voltage drop across capacitor 21 will be felt across
diode 22 and resistor 23. Leads 16 and 17 connect element 15 across
resistor 23. Diode 22 provides rectification or detection of the RF
signal, and the combination of resistor 23 with the inherent
capacitance of element 15 provides filtering of the RF signal
leaving the resultant audio frequency modulation signal applied
across element 15. Thus, as the transmitted signal varies in
accordance with the varying sound waves picked up by microphone 24,
a proportional varying voltage signal will be felt across element
15. This will cause bending or vibration of element 15 which will
be mechanically transmitted directly to the auditory ossicle or
oval window or other member of the auditory system of the middle
ear.
If desired, and completely in keeping with the spirit of this
invention, microphone 24 and amplifier 25 can be mounted within
head 11 of device 10 so that the entire hearing aid is implanted.
This will remove the need for transmission and receiving coils 28
and 20, as well as modulator 26 and oscillator 27 and the
associated electronic components described above, as will be
obvious to those skilled in the art. Also, because a piezoelectric
element such as element 15 can also be used as a microphone,
microphone 24 can comprise another piezoelectric element, such as a
bimorphic element, which transduces from mechanical to electrical
signals.
The apparatus of this invention can also be used when it is
necessary to remove completely the auditory ossicles of the middle
ear. This is a further example of the situation where it may be
desirable to place vibrating element 15 adjacent the oval
window.
In summary, the apparatus of this invention provides a new and
important hearing aid capable of implantation in the body, for
imparting vibrations to one or more members of the auditory system
of the middle ear by means of a piezoelectric element.
* * * * *