U.S. patent number 3,870,832 [Application Number 05/492,675] was granted by the patent office on 1975-03-11 for implantable electromagnetic hearing aid.
Invention is credited to John M. Fredrickson.
United States Patent |
3,870,832 |
Fredrickson |
March 11, 1975 |
IMPLANTABLE ELECTROMAGNETIC HEARING AID
Abstract
Problems of conventional hearing aids (low fidelity, poor
frequency response and feedback) and of hearing aids employing
implanted piezoelectric elements (high power requirements and
microtrauma) are eliminated or attenuated by implanting a coil and
magnet in the ear after removal of the incus, the magnet being
fastened to the head of the stapes and the coil being energized by
electrical signals from a sound transducer and producing a magnetic
field which, interacting with the magnetic field of the magnet,
causes movement of the stapes in the same manner as it normally is
moved by the incus.
Inventors: |
Fredrickson; John M. (Toronto,
Ontario, CA) |
Family
ID: |
27448808 |
Appl.
No.: |
05/492,675 |
Filed: |
July 29, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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364938 |
May 29, 1973 |
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Foreign Application Priority Data
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Jul 18, 1972 [GB] |
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33476/72 |
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Current U.S.
Class: |
600/25;
381/326 |
Current CPC
Class: |
H04R
25/606 (20130101); A61B 5/076 (20130101); A61F
2002/183 (20130101); H04R 2225/67 (20130101) |
Current International
Class: |
A61F
11/04 (20060101); A61F 11/00 (20060101); A61F
2/18 (20060101); A61B 5/07 (20060101); H04R
25/00 (20060101); H04r 025/00 () |
Field of
Search: |
;179/17R,17E,17BC |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Course Lecture Material, p. 54, FIG. 65, American Academy of
Opthamology and Otolarynaology, Course 319, "Conservative
Tympanoplasty," Oct. 1, 1966..
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Primary Examiner: Blakeslee; Ralph D.
Attorney, Agent or Firm: Sim & McBurney
Parent Case Text
This application is a continuation-in-part of Ser. No. 364,938
filed May 29, 1973, now abandoned.
Claims
What I claim as my invention is:
1. A hearing aid having certain components thereof that are
implanted in the ear of the user, said hearing aid comprising sound
transducer means for converting audio signals to electrical signals
and electromagnetic transducer means for receiving said electrical
signals and converting said electrical signals into mechanical
movement of the stapes bone of the ear of the user, said
electromagnetic transducer means being implantable in the ear of
the user and comprising a magnet, means for firmly securing said
magnet to the head of the stapes bone of the user such that said
magnet and said stapes bone move as a unit without relative
movement therebetween when said magnet is attracted by a magnetic
field and a coil of a size that permits it to be implanted in the
middle ear space of the user, said coil being adapted to be
implanted in the middle ear space of the ear of the user in close
proximity to said magnet, said coil when energized by said
electrical signals producing a magnetic field in which said magnet
is located, said coil and said magnet being positioned with respect
to each other such that upon energization of said coil said stapes
bone moves as a result of the interaction between the magnetic
field of said magnet and said magnetic field of said coil in the
same manner as said stapes bone normally is moved by the incus
bone, said hearing aid also including implantable support means for
said coil, said support means being adapted to be secured to a bone
that holds said coil in a fixed position in said middle ear
space.
2. A hearing aid according to claim 1 wherein said sound transducer
means comprises a microphone, an amplifier and a battery.
3. A hearing aid according to claim 2 further including a socket
having electrical terminals therein, means electrically connecting
said sound transducer means and said coil, said means electrically
connecting said sound transducer means and said coil including
implantable conductors connected to said terminals and to said coil
for supplying said electrical signals to said coil, said socket
being adapted to be located behind the ear of the user and secured
to bone of the user thereat, a housing for said microphone,
amplifier and battery, said housing having output terminals for
said electrical signals, said housing being adapted for reception
by said socket with said terminals of said socket electrically
contacting said output terminals of said housing.
4. A hearing aid according to claim 3 wherein said socket is
externally threaded to threadably engage in a tapped opening in
said bone behind the ear of the user.
5. A hearing aid according to claim 1 wherein said means for
securing said magnet to the head of the stapes bone of the user
comprises a non tissue toxic cement.
6. A hearing aid according to claim 1 wherein said means for
securing said magnet to the head of the stapes bones comprises a
holder for said magnet, said holder being adapted for attachment to
the head of the stapes bone of the user.
7. A hearing aid according to claim 1 including means for securing
said support means to a bone that holds said coil in a fixed
position in said middle ear space.
8. A hearing aid according to claim 7 wherein said means for
securing said support means comprises a non tissue toxic
cement.
9. A hearing aid having certain components thereof implanted in an
ear of the user from which the incus has been removed, said hearing
aid comprising sound transducer means for converting audio signals
to electrical signals and electromechanical transducer means
adapted to receive said electrical signals and convert said
electrical signals into mechanical movement of the stapes bone of
said ear of said user, said electromechanical transducer means
being implanted in said ear of said user and comprising a magnet,
means for firmly securing said magnet to the head of said stapes
bone such that said magnet and said stapes bone move as a unit
without relative movement therebetween when said magnet is
attracted by a magnetic field and a coil implanted in the middle
ear space of said ear in close proximity to said magnet, said coil
when energized by said electrical signals producing a magnetic
field in which said magnet is located, said coil and said magnet
being positioned with respect to each other such that upon
energization of said coil said stapes bone is moved as a result of
the interaction between the magnetic field of said magnet and said
magnetic field of said coil in the same manner as said stapes bone
normally is moved by the incus bone, said hearing aid also
including implanted support means for said coil for holding said
coil in a fixed position in said middle ear space, and means for
securing said support means to a bone of said user that holds said
coil in a fixed position in said middle ear space.
10. A hearing aid according to claim 9 further including a socket
having electrical terminals therein, said socket being implanted in
bone behind the ear of said user, implanted conductors connected to
said terminals and to said coil for supplying said electrical
signals to said coil, and a housing for said sound transducer, said
housing having output terminals for said electrical signals and
being received by said socket with said terminals of said socket
electrically connecting said output terminals of said housing.
Description
BACKGROUND OF THE INVENTION
This invention relates to hearing aids. More particularly, this
invention relates to hearing aids that operate electromagnetically
and some of the components of which are implantable.
A conventional hearing aid consists of a microphone, an amplifier,
batteries and a loudspeaker. All of these components are mounted
externally on the user, and various attempts have been made to
disguise of hide them, as by building them into the earpieces of
eyeglasses for example.
There is a considerable number of people with severe sensorineural
hearing losses who are not adequately served by the most modern
hearing aids that are available. The reasons for this revolve
around the distortion inherent in the individual's hearing loss as
well as the superadded distortion in the hearing aid which may
include low fidelity, poor low frequency response and feedback.
Many conventional hearing aids require an ear mould and ear tubing.
These components must be custom made, which is expensive. Moreover,
if they are not made perfectly, feedback and consequent distortion
problems are likely to arise.
A number of attempts have been made to solve the aforesaid
problems. Thus it is known to place a magnet on the eardrum with a
coil in an externally located earpiece and energize the coil via a
microphone and amplifier. A hearing aid of this type suffers from
low efficiency because the coil is located too far from the magnet.
In addition, such a system does not provide a permanent solution
for hearing loss because the magnet on the eardrum will be
displaced in a short time by migration of the epithelium.
Epithelial migration commences at the eardrum. Only about six weeks
is required for the epithelium to leave the eardrum, and only about
five months is required for it to come out of the ear canal.
Another disadvantage of this system is its high power requirements.
This is due not only to the large distance between the externally
located coil and implanted magnet, but also to the large mass
(eardrum and ossicles) that must be moved, taking into
consideration that all that really is required is movement of the
stapes, and the area ratio of eardrum to stapes footplate is about
15:1.
In U.S. Pat. No. 3,594,514 dated July 20, 1971, Robert C. Wingrove,
and U.S. Pat. No. 3,712,962 dated Jan. 23, 1973, J.M. Epley, there
are described implantable hearing aids that utilize piezoelectric
ceramic elements. From an electrical point of view such systems, as
compared to the electromagnetic system to be disclosed herein, have
a higher impedance and higher voltage requirements. In fact such
systems probably will require about a 15 volt battery, which would
be about 1 inch .times. 1 inch .times. 1/2 inch in size and hence
not readily disquised or hidden. on the other hand the
electromagnetic system to be disclosed herein will require only
about 1.5 volts to operate it. A battery of this size would be
about 10 mm. in diameter and 5 mm. thick, and a battery of this
size can be hidden readily. What is even more serious, however, is
the fact that the piezoelectric ceramic element will, as a result
of its continually striking the bone (one of the ossicles) with
which it cooperates, create microtrauma and erosion of that
bone.
In accordance with my invention there is provided a hearing aid
which eliminates or attenuates many of the disadvantages of
conventional hearing aids of the type noted previously as well as
those of hearing aids of the types noted in the two preceding
paragraphs.
SUMMARY OF THE INVENTION
A hearing aid embodying my invention may include a microphone,
amplifier and a battery or batteries (or other suitable sound
transducer), as is conventional, all of which may be located in a
small housing that may be hidden behind one ear of the individual
and which may plug into a receptacle and socket implated in the
temporal bone behind the ear. The hearing aid further includes an
implanted electromagnetic device that replaces the loudspeaker,
tubing and earmould of a conventional hearing aid. This device
consists of a magnet that is permanently attached to the stapes
(one of the three auditory ossicles) and an implanted coil that is
located in close proximity to the magnet and which receives
electrical signals from the sound transducer. Also provided is a
suitable support for the coil.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will become more apparent from the following detailed
description, taken in conjunction with the appended drawings, in
which:
FIG. 1 is a perspective view showing the aforesaid housing located
behind the ear of an individual;
FIG. 2 is a horizontal section through a normal human ear but with
the outer tissue folded over on itself;
FIG. 3 is a view similar to that of FIG. 2 but with the incus
removed, a necessary step in the operative procedure for implanting
certain components of a hearing aid embodying my invention;
FIG. 4 is a view similar to that of FIG. 2 but showing these
components in place;
FIG. 5 is a side view of an individual's right ear with the tissue
removed and showing the same components as are seen in FIG. 4;
FIGS. 6 and 7 are top and side views respectively showing the
stapes and the components illustrated in FIGS. 4 and 5;
FIG. 8 is a view similar to that of FIG. 7 but with the coil and
its support removed;
FIG. 9 is a view similar to FIG. 8 but showing another embodiment
of my invention;
FIG. 10 is an exploded view of certain components of a hearing aid
embodying my invention; and
FIG. 11 is a schematic diagram of a hearing aid embodying my
invention.
Referring to FIG. 1, a hearing aid embodying my invention includes
a housing 10 (see also FIG. 10) in which, as shown in FIG. 11, may
be located a microphone 30, an amplifier 31 and a battery 32. This
housing is very small and can be located behind the ear tissue of
an individual. It has three male terminals 33 (FIG. 10) projecting
therefrom adapted to plug into three female terminals 34 in a
receptacle 11 (FIGS. 6 and 10). As best shown in FIG. 10,
receptacle 11 fits into and externally threaded socket 35. The
lower part 36 of socket 35 is permanently implanted by an operative
procedure into the temporal bone of the patient. This procedure
requires tapping a hole in the temporal bone immediately behind the
ear to accommodate the lower part 36 of socket 35, this part being
screwed into the tapped opening. Once housing 10 has been plugged
into receptacle 11, an internally threaded cap 37 (FIGS. 1 and 10)
is threadably engaged with the upper part 38 of socket 35 to hold
housing 10 and receptacle 11 in position. A cap (not shown) similar
to cap 37 but with its top end closed may be provided and used in
place of cap 37 when the individual is showering or swimming.
Illustratively socket 35 may be about 1 cm. long and have a maximum
diameter of about 1.3 cm.
Housing 10, receptacle 11 and socket 35 are fabricated of a
material that is non tissue toxic. One suitable material is
"TEFLON" (trade mark). Cap 37 also may be fabricated of this
material or stainless steel, for example.
Two of the three terminals 33 are, in fact, the output terminals of
amplifier 31, the latter being powered by battery 32 and serving to
amplify sounds picked up by microphone 30. The third terminal is
for stability and locating. The microphone, amplifier and battery
may be of a conventional type. A suitable microphone is a condensor
microphone model No. BL1680 made by Knowles Electronics Inc.,
Franklin Park, Illinois. Amplifier 31 preferably is a logarithmic
amplifier. Two suitable amplifiers both manufactured by Robert
Bosch Electronic Company of Berlin, West Germany are "STAR 6"
(trade mark) dynamic range compression (DRC) amplifier and
"OMNITRON II" (trade mark) DRC amplifier. The battery may be an
"EVEREADY" (trade mark) model E675 1.4 volt mercury battery.
Terminals 33 and 34 preferably are gold plated.
It should be understood, of course, that microphone 30, amplifier
31 and battery 32 individually or in total may be located elsewhere
than behind the ear.
The other part of a hearing aid embodying my invention consists of
a magnet 12 (FIGS. 5, 6, 8 and 12), which, in the embodiment shown,
is cylindrical in configuration, and which is secured to the stapes
13; a coil 14 located in close proximity to magnet 12; a support or
holder 15 for the coil; and two lead-in conductors 16 connected
between terminals 34 of receptacle 11 and coil 14. All of these
components are surgically implanted.
As shown in FIGS. 4, 6, 7 and 8, a holder 17 for magnet 12 is
provided. This holder may be fabricated of "TEFLON" (trade mark),
for example, and is designed so as to be readily attached to stapes
13. Magnet 12 may be encased in the material of the holder. In
another embodiment of the invention shown in FIG. 9 magnet 12 is
firmly secured to the head of stapes 13 by a non tissue toxic
cement such as "SILASTIC" (trade mark) or "CRANIOPLAST" (trade
mark). In this embodiment, unless magnet 12 is encapsulated in a
non tissue toxic material, it itself must be non tissue toxic.
Thus, it may be made of "VITALLIUM" (trade mark), for example.
However, a superior magnet is one made of cobalt symareum and
available from the General Electric Company, Schenectady, New York.
Such a magnet requires encapsulation in a non tissue toxic
material.
Regardless of how magnet 12 is secured to stapes 13, it must be
firmly fastened thereto so that the magnet and stapes move as a
unit without relative movement there-between in order to avoid
microtrauma. This poses no problem where cement is used. Where
holder 17 is mechanically secured to the stapes without cement, the
inherent springiness of the holder material may be relied upon to
provide the required connection or, depending on the holder
material, it may be crimped in position.
Magnet 12 is very small, typically about 1 mm. in diameter and 1
mm. long. Coil 14 must be sufficiently small to fit in the middle
ear space and should have an input impedance that matches the
output impedance of amplifier 31. Strictly by way of example, coil
14 may consist of 1,600 turns of insulated 50 gauge copper wire
embedded in a suitable non tissue toxic material such as "SILASTIC"
(trade mark). It may be about 1.5 mm. internal diameter (core), 4
mm. outside diameter and 1 mm. long.
In order to implant components 12 and 15 to 17 a maistoidectomy is
performed, the "facial triangle" bone is removed from the posterior
bony ear canal wall and the incus 18 (FIG. 2) is removed. Magnet 12
then is firmly secured to stapes 13. In the embodiment shown in
FIGS. 4, 7 and 8 this is accomplished by fastening holder 17 to
stapes 13, but it also may be accomplished by cementing the magnet
or its encapsulating material to the stapes using a suitable cement
as shown in FIG. 9. By means of a tool 19 (FIG. 4) which threadably
engages a connector 20 (FIG. 4) secured to holder 15, coil 14 and
holder 15 are positioned in place and holder 15 is permanently
cemented in position using a suitable non tissue toxic cement 40
(FIG. 4) such as "CRANIOPLAST" (trade mark). This operation is
performed using a suitable micromanipulator. Tool 19 then is
removed.
Coil 14 is located in close proximity to magnet 12. In the
embodiment of the invention shown in FIGS. 4, 6 and 7 it is
positioned just above magnet 12 with the core of the coil and the
magnet arranged coaxially. The coil could be arranged to surround
holder 17 if desired. In other words, magnet 12 then would be in
the core of the coil. The important thing, however, is that coil 14
and magnet 12 are so arranged that the interaction of the magnetic
field of the magnet and that of the coil when energized results in
movement of the stapes in the same manner as it normally would be
moved by the incus.
Holder 15 performs the important function of supporting coil 14 in
a fixed position in the middle ear space. It may be a silver wire
approximately 0.2 mm. in diameter. It may be flattened at one end
and this flattened end then wrapped around coil 14, the flattening
being for the purpose of providing a greater surface area of
contact. The other end of holder 15 is cemented to bone within the
mastoid bowl.
After tool 19 has been removed, wires 16, which preferably are made
of gold, are led into socket 35 through a small opening in the
bottom wall thereof, are passed through and out of the socket and
then are soldered to terminals 34. Socket 35 than may be screwed
into the previously tapped opening in the mastoid tip of the
temporal bone behind the patient's ear and components 11, 10 and 37
located in position as previously explained herein.
When coil 14 is energized by electrical signals from amplifier 31,
the interaction of the magnetic field of coil 14 thereby created
and the magnetic field of magnet 12 causes stapes 13 to function in
its normal way like a piston causing vibration of the inner ear
fluids in response to sound pick up by microphone 30.
It should be understood that my invention also may be practised
using an implanted receiver and an external microphone and
transmitter as disclosed in aforementioned U.S. Pat. No. 3,712,962,
the piezoelectric element disclosed in this patent being replaced
with the electromagnetic system disclosed herein.
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