Biasing device for implantable hearing devices

An implantable hearing device is coupled to a tympanic membrane and an oval window of a human subject's ear. The implantable hearing device includes an amplifier, a first transducer electrically coupled to the amplifier, and a second transducer also electrically coupled to the amplifier. A first compliant connecting member elastically couples the tympanic membrane to the first transducer. A second compliant connecting member elastically couples the second transducer to the oval window. Ambient sounds are transmitted from the tympanic membrane to the first transducer by the first compliant connecting member, thus generating an audio signal. The audio signal is amplified by the amplifier, which drives the second transducer. The second compliant connecting member transmits the amplified sounds to the oval window, possibly via one or more ossicles or prostheses. The hearing of the human subject is thus improved.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for improving the 
impaired hearing of a human subject using an implantable hearing aid 
device. More specifically, the present invention relates to a method and 
apparatus for improving the performance of implantable hearing aid 
devices. 
The human hearing mechanism is a complex system of levers, membranes, fluid 
reservoirs, neurons, and hair cells which must work in concert to deliver 
nervous stimuli to the brain where this information is compiled into what 
we perceive as sound. Because the human hearing system encompasses a 
complicated mix of acoustic, mechanical, and neurological systems, there 
is ample opportunity for its impairment. Unfortunately, this is often the 
case. 
Attempts to remedy such deficiencies have a long history. The first 
electronic hearing aids began making their debut in the early 1900's. The 
development of the transistor led to smaller, more power-efficient aids 
that began to appear in the 1950's. In the 1960's and 70's, the hearing 
aid enjoyed a period of accelerated development. 
The hearing impaired patient now has a wide variety of hearing devices to 
choose from. Devices having improved circuits, now permit a hearing aid's 
frequency response to be customized to a patient's individual hearing 
loss. New devices located completely in the patient's ear canal are 
available that are cosmetically superior to the large, bulky devices of 
years past. 
A number of auditory system defects are now known to impair or prevent 
hearing. To illustrate such defects, a schematic representation of part of 
the human auditory system is shown in FIG. 1. The auditory system is 
generally comprised of an external ear AA, a middle ear JJ, and an 
internal ear FF. External ear AA includes ear canal BB and tympanic 
membrane CC, and internal ear FF includes an oval window EE and a 
vestibule GG (a passageway to the cochlea (not shown)). Middle ear JJ is 
positioned between external ear AA and internal ear FF, and includes 
eustachian tube KK and three bones called ossicles DD. Ossicles DD include 
a malleus LL, an incus MM, and a stapes HH, which are positioned between 
and connected to tympanic membrane CC and oval window EE. 
In a person with normal hearing, sound enters the external ear AA where it 
is slightly amplified by the resonant characteristics of ear canal BB. The 
sound waves produce vibrations in tympanic membrane CC, the part of 
external ear AA that is positioned at the distal end of ear canal BB. The 
force of these vibrations is magnified by ossicles DD. 
Upon vibration of ossicles DD, oval window EE, which is part of internal 
ear FF, conducts the vibrations to cochlear fluid (not shown) in inner ear 
FF thereby stimulating receptor cells, or hairs, within the cochlea (not 
shown). Vibrations in the cochlear fluid also conduct vibrations to the 
round window (not shown). In response to the stimulation, the hairs 
generate an electrochemical signal which is delivered to the brain via one 
of the cranial nerves, causing the brain to perceive sound. 
The vibratory structures of the ear include the tympanic membrane, ossicles 
(malleus, incus, and stapes), oval window, round window, and cochlea. Each 
of the vibratory structures of the ear vibrates to some degree when a 
person with normal hearing hears sound waves. However, hearing loss in a 
person may be evidenced by one or more vibratory structures vibrating less 
than normal or not at all. Some patients with hearing loss have ossicles 
that lack the resiliency necessary to increase the force of vibrations to 
a level that will adequately stimulate the receptor cells in the cochlea. 
Other patients have ossicles that are broken, and which therefore do not 
conduct sound vibrations to the oval window. 
Various types of hearing aids have been developed to restore or improve 
hearing for the hearing impaired. With conventional hearing aids, sound is 
detected by a microphone, amplified using amplification circuitry, and 
transmitted in the form of acoustical energy by a speaker or another type 
of transducer into the middle ear by way of the tympanic membrane. Often, 
the acoustical energy delivered by the speaker is detected by the 
microphone, causing a high-pitched feedback whistle. Moreover, the 
amplified sound produced by conventional hearing aids normally includes a 
significant amount of distortion. 
An interesting implementation concerns implantable hearing aids configured 
for disposition principally within the middle ear space. For example, such 
an approach could provide a transducer capable of converting mechanical 
vibration within the ossicular chain into an output voltage (e.g., a 
piezoelectric transducer). That output voltage could be converted to 
mechanical vibrations (e.g., again, by a piezoelectric transducer) and 
applied to the area of the oval window to stimulate it. Alternatively, the 
output voltage could be used to electrically stimulate the auditory nerve. 
As an alternative, the stapes may be removed and the hearing aid 
physically located in its stead, conditions permitting. Under 
circumstances where the stapes is removed, the end of the incus is 
free-standing and the hearing aid may be physically associated with it, 
such as by means of crimpable rings or the like. Thus the hearing aid 
serves as an integral part of the mechanical linkage in the transmission 
of forces from the eardrum to the oval window in all events, whether or 
not the integrity or continuity of the ossicular chain remains unimpaired. 
That being the case, however, unwanted mechanical feedback through the 
ossicular chain is a possibility, diminishing the overall efficacy of this 
approach. 
Methods have been devised to avoid this unwanted feedback, and so improve 
the hearing of patients using such devices. For example, such an invention 
is described in "IMPLANTABLE HEARING AID AND METHOD OF IMPROVING HEARING" 
by D. W. Schaefer (U.S. Pat. No. 4,729,366), which is hereby incorporated 
by reference in its entirety. Schaefer describes a method and apparatus 
for improving the impaired hearing of a subject utilizing a device which 
receives vibrations from one of the subject's ossicles or the subject's 
eardrum, and provides an amplified version of those vibrations to the 
subject's inner ear. 
Referring to FIG. 2, one embodiment of an implantable hearing device 10 
according to Schaefer is shown disposed in an antrum 12 surgically 
developed in the mastoid bone of a subject's skull 14. Antrum 12 
communicates with a middle ear space 16 of the subject. Device 10 may 
include, for example, a power source 18, an amplifier 20, an input 
transducer 22, and an output transducer 24. Input transducer 22 converts 
mechanical vibrations to electrical signals, while output transducer 24 
converts electrical signals to mechanical vibrations. 
Input transducer 22 and output transducer 24 may, for example, each include 
a piezoelectric element cooperating with a resilient diaphragm. A 
connecting member 25, mounted on a diaphragm (not shown), is operatively 
coupled to piezoelectric element (also not shown). Schaefer indicates that 
connecting member 25 is preferably a rigid stainless steel wire. (The 
respective connecting members 25 associated with input transducer 22 and 
output transducer 24 will be referenced as wires 25A and 25B, 
respectively.) 
Input transducer 22 converts vibrations of a tympanic membrane 26 into 
electrical signals. Input transducer 22 is mechanically coupled to 
tympanic membrane 26 by wire 25A to a malleus 30 of the subject. Wire 25A 
must have an acceptable degree of stiffness and may be affixed to malleus 
30 utilizing surgical techniques similar to those used in ossicular 
reconstructive surgery, for example. Tympanic membrane 26 vibrates in 
response to sound waves 32. The vibrations are transmitted to malleus 30, 
through wire 25A to input transducer 22. These vibrations are converted to 
electrical signals by a first piezoelectric element within input 
transducer 22 (not shown). The electrical signals are then applied to 
amplifier 20. Amplifier 20 amplifies these input signals in a manner 
sufficient to drive output transducer 24, compensating for deficiencies in 
the frequency response of the subject's hearing. 
Output transducer 24 converts the amplified electrical signals representing 
the tympanic vibrations into mechanical vibrations for application to an 
inner ear 28 of the subject. The amplified electrical signals are 
converted into corresponding mechanical vibrations by a second 
piezoelectric element within output transducer 24 (also not shown). The 
vibrations are communicated to inner ear 28 by a mechanical connection 
between wire 25B and a stapes 34. Stapes 34 then transmits these 
vibrations to an oval window 36 of inner ear 28. In this manner, the 
vibrations are transmitted to a cochlea 40 of the subject. The connection 
between wire 25B and inner ear 28 can be made in a manner similar to 
techniques employed in reconstructive surgery using passive mechanical 
prosthetic devices, for example. 
Implantable hearing devices such as those in Schaefer have been used with 
the ossicular chain intact. However, Schaefer prefers that the ossicular 
chain be broken to prevent positive feedback of the amplified vibrations 
to input transducer 22 (e.g., via the incus). A break would typically be 
effected by removing at least one of the component parts of the ossicular 
chain, typically the incus. It is desirable to maintain the malleus and 
stapes in normal anatomical position with muscle and tendon intact to 
maintain the subject's natural defense mechanism against acoustic trauma. 
The hearing aid then becomes an integral piece of the ossicular chain. 
As noted, wires 25A and 25B are preferably made of a substantially rigid 
material such as stainless steel. Such materials are used in the interest 
of accurately transmitting the mechanical vibrations correspond to sound 
waves 32, thereby providing faithful reproduction of the sounds received 
at the eardrum. Schaefer discusses several methods of attaching the distal 
ends of these wires to the ossicles or other structures. 
For an implantable hearing aid such as that described in Schaefer to 
provide acceptable fidelity over the long term, however, the tension on 
the wires used to input and output mechanical vibrations preferably 
remains constant. While a simple attachment, such as is described in 
Schaefer, may provide acceptable performance in the near term, aging of 
the various auditory structures involved may cause these attachments to 
loosen or otherwise cause wires 25A and 25B to lose tension, impairing the 
hearing aid's performance. 
SUMMARY OF THE INVENTION 
The present invention solves at least some of the problems associated with 
the prior art by providing an improved implantable hearing device that 
employs one or more connecting members adapted to elastically couple the 
device to a component or else between components of the middle ear. The 
coupling preferably maintains a tensive (or compressive) force on 
mechanical couplings between the hearing device and structures of the 
subject's ear. Use of such connecting members at least partly accommodates 
post-implantation changes in the positional relationship between the 
hearing device and the subject's anatomy, which in the absence of the 
coupling, would impair the fidelity of sound reproduction. Such positional 
changes may be due to aging (of either the hearing aid or the auditory 
structures), changes in pressure (e.g., scuba diving or flying in an 
airplane), physical forces (e.g., a helmet or motion of the subject's 
head), and other reasons. Tension provided by a connecting member may also 
maintain the dampening necessary for acceptable sound reproduction over 
the long term. A tympanic membrane which is not dampened or is poorly 
dampened will have an increased probability of delivering erratic or 
distorted mechanical stimuli to the hearing aid's input transducer. 
The connecting member of the present invention comprises an elastic 
(extensible and/or compressible) mechanism or material, and so is 
described as being "compliant," the term being further defined below. 
The desired adaptability and dampening can be achieved by positioning one 
or more compliant connecting members at any point or points within the 
mechanical linkage between the native components of the ear. 
In one embodiment, an implantable hearing device is described, which is 
adapted to being coupled between a tympanic membrane and an oval window of 
a human subject's ear. The implantable hearing device includes an 
amplifier, a first transducer electrically coupled to the amplifier, and a 
second transducer also electrically coupled to the amplifier. A first 
compliant connecting member is capable of elastically coupling the 
tympanic membrane to the first transducer. A second compliant connecting 
member is capable of elastically coupling the second transducer to the 
oval window. The compliant connecting members may be, for example, springs 
or urethane strips. Ambient sounds are transmitted from the tympanic 
membrane to the first transducer by the first compliant connecting member, 
thus generating an audio signal. The audio signal is amplified by the 
amplifier, which drives the second transducer. The second compliant 
connecting member transmits the amplified sounds from the second 
transducer to the oval window, optionally via one or more ossicles or 
prostheses. 
In another embodiment, an implantable hearing device, adapted to couple one 
or more ossicles of an inner ear of a human subject, includes a housing 
and an electromagnetic unit. The electromagnetic unit includes a magnet, 
disposed inside the housing, and a coil, surrounding a portion of the 
housing. A diaphragm is mechanically coupled to the electromagnetic unit. 
The motion of the diaphragm is proportional to movement of the magnet 
caused by an electrical signal applied to the electromagnetic unit. A 
compliant connecting member elastically couples the diaphragm to one or 
more ossicles of the human ear. The diaphragm is preferred since it can 
capture the mechanical energy of the magnet, and evenly translate the 
mechanical motion of the magnet to the connecting member, regardless of 
the internal geometry of the electromagnetic unit or the shape of the 
magnet. 
In yet another embodiment, an implantable hearing device, adapted to be 
coupled to one or more ossicles of an inner ear of a human subject, 
includes a coil and a compliant connecting member. The compliant coupling 
member elastically couples the coil to a magnet. The magnet is, in turn, 
coupled to one or more ossicles of the human ear. The coil, when 
electrically driven by signals applied thereto, induces a motion in the 
magnet. The magnet responds in proportion to the applied signals and 
causes movement to one or more ossicles of the inner ear. 
In another aspect of the invention, a method of improving hearing in a 
human subject using an improved implantable hearing device coupled to a 
component of an ear of the human subject is described. The method includes 
implanting an implantable hearing device into a mastoid bone of the human 
subject and elastically coupling the implantable hearing device to the 
component of the ear usually using a compliant connecting member. By 
providing tensive (or compressive) force, the compliant connecting member 
maintains consistent connection between the implantable hearing device and 
the component of the ear. 
In yet another aspect of the invention, a method of improving hearing in a 
human subject, where an ear of the human subject has a middle ear 
structure, comprises implanting an implantable hearing device in a mastoid 
bone of the human subject. The implantable hearing device includes an 
electromagnetic unit having a diaphragm which is mechanically driven by 
the electromagnetic unit. The method also includes elastically coupling 
the diaphragm to a component of the middle ear structure, using a 
compliant connecting member. 
In yet another aspect of the present invention, a method of improving 
hearing in a human subject where the human subject has an ear with a 
middle ear structure is described. The method includes implanting a magnet 
on a component of the middle ear structure; elastically coupling the 
magnet to a first portion of a compliant connecting member; and 
elastically coupling a coil device to a second portion of the compliant 
connecting member. 
A further understanding of the nature and advantages of the present 
invention may be realized by reference to the remaining portions of the 
specification and the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As used herein, a "compliant" connecting member transmits acoustic energy 
above 100 Hz, such that the acoustic signal is not significantly degraded. 
At the same time, the compliant connecting member provides a constant bias 
on to the component or components to which it may be attached, allowing 
for small displacements that may occur, for example, during shifting. As 
can be better understood from FIG. 3, the compliant connecting member of 
the present invention, by way of example, can be modeled as a mechanical 
circuit 42. The compliant connecting member is made to combine in series 
the physical properties of a resistance or damper 44 (viscous) and a 
spring 46 (elasticity). Thus, as illustrated in graph 48 of FIG. 3A, the 
compliant connecting member responds by compensating for relatively slow 
physical movements (i.e., have relatively high dampening at low 
frequencies) 50, while transmitting audible vibrations that are relatively 
high in frequency (i.e., have relatively low dampening at audio 
frequencies) 52. Acceptable sound reproduction is thus maintained. 
The spring force in the compliant connecting member is determined using 
clinical data. In any event, the magnitude of the spring force is low 
enough to avoid damaging the components to which it is attached or other 
items which may be connected to the component. Also, the spring force does 
not alter the acoustic characteristics of the outer, middle, or inner ear. 
After determining the spring force, the resistance value is tuned such that 
the system as a whole has the desired characteristic of transmitting a 
complete signal above 100 Hz. At frequencies below 100 Hz the signal drops 
off steeply in magnitude. In one example, when the spring force is equal 
to 1 N/m, the resistance value may be as high as 100 N/m. 
This set of properties for the compliant connecting member can be, but are 
not limited to, being created through a combination of various material 
properties, material shapes, and/or mechanical components. 
FIG. 4 illustrates implantable hearing device 10 having improvements 
according to the present invention. According to the present invention, 
wires 25A and 25B are replaced with compliant connecting members 225A and 
225B. Compliant connecting members 225A and 225B are shown in FIG. 4 as 
including springs 228A and 228B. Spring 228A is connected to input 
transducer 22 by a connecting wire 226A and to malleus 30 by a connecting 
wire 227A. Spring 228B is connected to output transducer 24 by a 
connecting wire 226B and to stapes 34 by a connecting wire 227B. 
Preferably, compliant connecting members 225A and 225B are each fabricated 
from a single wire, but may also be constructed from separate parts if the 
design of compliant connecting members 225A and 225B so mandates. The use 
of stainless steel is preferable in the fabrication of connecting members 
225A and 225B, but other biocompatible materials such as gold or titanium 
may be used. Springs 228A and 228B are shown in FIG. 4 as being coil-type 
springs. 
Springs 228A and 228B thus supply a constant tension to their respective 
connecting wires. This tension permits implantable hearing device 10 to 
provide improved sound reproduction over the long term, despite aging, 
pressure changes, physical force, and the like. For example, in the prior 
art, vibrations could loosen the mechanical coupling connecting wires 25A 
and 25B to elements of middle ear JJ, especially over the long term. 
Variations in ambient pressure such as those that occur during commercial 
airline flights and when scuba diving also cause mechanical stress in the 
components of such systems, loosening their mechanical couplings. Springs 
228A and 228B maintain tension, and so acceptable sound reproduction, 
while allowing the mechanism to compensate for such conditions. 
Although the characteristics of a compliant connecting member may vary 
widely while still providing acceptable performance, certain materials and 
parameters are preferable in the design of an implantable hearing aid 
according to the present invention. While compliant connecting members are 
preferably fabricated from stainless steel, other biocompatible materials 
such as gold or titanium may be used, as may other materials. Certain of 
these materials are preferably coated with biocompatible materials (e.g., 
coated with gold, silicone, polyamide, titanium, or the like) by various 
methods (e.g., sputtering, electroplating, or the like). Such compliant 
connecting members may also be fabricated from strips of plastic material 
such as urethane or even some types of foam material. If compliant 
connecting member uses a spring, the spring's resonant frequency should 
preferably be below about 500 hertz (Hz), and most preferably below 200 
Hz. For most applications, the spring should readily transmit voice 
frequencies (i.e., about 1500 Hz to 3500 Hz), and exhibit a flat response 
curve in this range. A broader frequency range may also be desirable, such 
as between about 500 Hz and 10,000 Hz. Normally, such a spring will 
exhibit a reduced response to frequencies outside these ranges. The free 
length of such a spring will be determined by the configuration of the 
hearing aid's mechanism and the subject's middle ear volume, among other 
factors. 
FIG. 5 illustrates another possible configuration using compliant 
connecting members 325A and 325B. Compliant connecting members 325A and 
325B employ a loop-type spring. Again, compliant connecting members 325A 
and 325B provide the tension necessary to permit the transmission of 
normal sound pressure levels (SPLs) to stapes 34. For normal sound 
pressure-induced modes to be harnessed by the tympanic membrane and 
transferred to input transducer 22, the maintenance of such tension is 
important. A tympanic membrane such as tympanic membrane 26 which is not 
dampened or is poorly dampened will face an increased probability of 
delivering erratic or distorted mechanical stimuli to input transducer 22. 
By providing a tensioning device such as compliant connecting member 325A, 
such problems are avoided. 
Several other types of compliant devices may serve as compliant connecting 
members in the present invention. FIGS. 6A and 6B illustrate bow-tie 
spring designs which may be employed in the present invention. A bow-tie 
spring 400 is shown in FIG. 6A and includes a first loop 410 and a second 
loop 420. Bow-tie spring 400 is shown in FIG. 6B with the addition of a 
sleeve 430 coupling loop 410 and loop 420. A urethane strip could also 
serve as a compliant connecting member. Such a strip could be attached to 
a respective transducer and auditory component by stainless steel wires, 
for example. The use of other such materials and designs will be obvious 
to those skilled in the art. 
FIG. 6C illustrates a compliant connecting member 400 with a bended 
segment, configured to provide a surgeon with an improved view of the 
surgical field during implantation. Most implantable devices are imbedded 
in the mastoid bone and tend to block or obscure a portion of the surgical 
field during system implantation. Preferably, a set of dual right-angle 
bends 460, 470 are added to compliant connecting member wire 455. The 
bended feature of compliant member wire 455 is meant to be used with any 
of the several types of biasing mechanisms 450 described herein, but is 
not so limited. The bent compliant connecting wire makes it possible for 
the surgeon to maneuver the implantable device out of the surgical field 
of view, while reducing disturbance to both the placement and the 
attachment of the compliant member to components of the inner ear. 
However, the compliant connecting member of the present invention need not 
be restricted to providing tensive force between implantable hearing 
device 10 and structures of the inner ear. The present invention may also 
employ spring designs which provide compressive force. For example, the 
compliant connecting members shown in FIGS. 7 and 8 are capable of 
providing either compressive or tensive force in connecting implantable 
hearing device 10 (or other such device) to the ear's structures. 
FIG. 7 illustrates a compliant connecting member 600. Compliant connecting 
member 600 includes a formed wire 610 made of a material such as stainless 
steel and having a compressible section 620 with a first arm 621 and a 
second arm 622. A spring 630 is connected at a first end to arm 621 by a 
connector 631 and at a second end to arm 622 by a connector 632. 
In operation, compliant connecting member 600 can provide either tensive or 
compressive force, depending on the state of spring 630. If, for the 
nominal length of compliant connecting member 600, spring 630 is stretched 
beyond its resting length, spring 630 tends to force first arm 621 and 
second arm 622 together. In that case, compliant connecting member 600 
provides tensive force. If spring 630 is compressed, spring 630 tends to 
force first arm 621 and second arm 622 apart, with compliant connecting 
member 600 thus providing compressive force. 
FIG. 8 illustrates yet another compliant connecting member 700 which 
includes a first wire 710 and a second wire 720. First wire 710 is 
connected at a first end to a point on second wire 720 by a coupling 730. 
Similarly, second wire 720 is connected at a first end to a point on first 
wire 710 by a coupling 735. A spring 740 is connected at a first end to a 
point on first wire 710 midway between couplings 730 and 735 by a coupling 
750. Similarly, spring 740 is connected at a second end to second wire 720 
at a point midway between couplings 730 and 735 by a coupling 760. 
Compliant connecting member 700 is also capable of providing either tensive 
or compressive force. In a manner similar to compliant connecting member 
600, this depends on the state of spring 740. If, for the nominal length 
of compliant connecting member 700, spring 740 is stretched beyond its 
resting length, spring 740 tends to force first wire 710 and second wire 
720 together. In that case, compliant connecting member 700 provides 
compressive force. If spring 740 is compressed, spring 740 tends to force 
first wire 710 and second wire 720 apart, with compliant connecting member 
700 thus providing a tensive force. 
The present invention is not limited to being used with an implantable 
hearing device such as implantable hearing device 10. For example, 
implantable hearing devices, such as those shown in FIGS. 9, 10A-B and 
11A-B, and described herein below, can also benefit from the present 
invention. 
In FIG. 9, an implantable hearing device 500 employs a lever arrangement 
capable of actuating oval window EE, or one or more of ossicles DD (e.g., 
stapes HH). A bimorphic lever 510 is connected to the mastoid bone of a 
subject's skull by anchor pins 520 and 530. Bimorphic lever 510 is 
preferably fabricated from two different piezoelectric materials, shown in 
FIG. 9 as piezoelectric strips 540 and 545. Piezoelectric strips 540 and 
545 are connected, at a first end of each, to an amplifier (not shown) by 
wires 550 and 555. 
In operation, piezoelectric strips 540 and 545 expand and contract 
different amounts upon the application of a given signal voltage. Thus, in 
a manner similar to the bimorphic strips used in thermostats, bimorphic 
lever 510 bends in response to the signals applied to piezoelectric strips 
540 and 545. In this way, the motion of a distal end of bimorphic lever 
510 (i.e., a second end of each of piezoelectric strips 540 and 545) is 
substantially proportional to the signal applied to piezoelectric strips 
540 and 545 by the amplifier. The amplifier may take as its input 
electronic signals from a sound pickup (also not shown). The sound pickup 
receives ambient sounds and provides them to the amplifier by way of an 
electromagnetic coupling, for example. (Other alternatives such as 
directly wiring the sound pickup to the amplifier are, of course, also 
available.) However, if a simple wire is used to connect the distal end of 
bimorphic lever 510 to stapes HH, the design can be expected to suffer the 
previously-mentioned infirmities. 
To address such limitations, a compliant connecting member 560 according to 
the present invention is used to couple the distal end of bimorphic lever 
510 to stapes HH. Alternatively, compliant connecting member 560 could be 
attached directly to oval window EE. A mechanical coupling 570 attaches 
compliant connecting member 560 to the distal end of bimorphic lever 510. 
A mechanical coupling 580 attaches compliant connecting member 560 to 
stapes HH. As before, the benefits of the present invention are provided, 
including compensation for loosening of mechanical couplings 570 and 580, 
and other phenomena which may impair coupling between the distal end of 
bimorphic lever 510 and stapes HH. 
In FIG. 10A, an implantable hearing device 800 is shown which employs an 
electromagnetic drive unit 820 capable of imparting vibrational energy 
typically through a rigid connection to one or more ossicles of the inner 
ear. Electromagnetic drive unit 820 is a conventional drive unit having an 
internal set of magnets 815 coupled to diaphragm 830. Magnets 815 are 
induced into motion which corresponds to a signal applied to drive unit 
820. The motion of magnets 815 causes diaphragm 830 to vibrate, which 
drives a rigid rod connected to one or more of the bones of the inner ear. 
In an alternative device, shown in FIG. 10B, the implantable hearing device 
900 is an improved coil floating mass unit. Floating mass drive unit 910 
is typically rigidly connected to one or more of the inner ear ossicles 
and is designed to be hermetically encapsulated. The encapsulation 
isolates key components of the unit to ensure long term stability and 
performance of the implant. Floating mass electromagnetic drive unit 910 
has a mass, typically a magnet 920, disposed within hermetically sealed 
housing 930. Preferably housing 930 is made of titanium or other 
biocompatible material. Coils 940 made of, for example, gold, are wrapped 
on the outside of housing 930 and add strength and protection to the 
housing, among other things. Protective coating 980 is also disposed on 
the outside of the housing to provide strength and protection, as well. 
Diaphragm 950, preferably made of titanium and laser welded to housing 
930, is in contact with one end of internal magnet 920 through connecting 
member 960. On the end of housing 930 opposed to diaphragm 950 is a spring 
mechanism 970 coupled to another end of magnet 920 and suspends magnet 
920, allowing it to float within housing 930. The motion of magnet 920 is 
induced by a current traveling through coils 940. The resonance of the 
system is tuned by adjusting the durometers and/or vibratory parameters of 
silicone spring 970, diaphragm 950, and connecting member 960 (as a system 
or individually). Ideally, electromagnetic unit 910 resonates at around 
1500 Hz to mimic the vibratory motion of a human ear. 
In either of the above described electromagnetic driver designs 820 or 910, 
the diaphragm is made to vibrate upon application of a given input signal 
in a manner similar to an acoustic speaker. In this way, the motion of the 
diaphragm is proportional to the signal applied to the electromagnetic 
unit. The rigid connection of the hearing device to the inner ear is made 
using a strut of a rigid material in the interest of accurately 
transmitting mechanical vibrations to the ossicles and faithfully 
reproducing sound waves. However, by using a rigid strut to connect the 
diaphragm to one or more bones of the inner ear, the driver designs 820 
and 910 can be expected to suffer the previously mentioned weaknesses. 
To address such weaknesses, a compliant connecting member according to the 
present invention is used with either electromagnetic device described 
above. For example, FIG. 10A shows compliant member 810, according to the 
present invention, being used to couple diaphragm 810 to malleus 30. 
Alternatively, compliant connecting member 810 could be attached directly 
to any of the other bones of the middle ear. Moreover, FIG. 10B shows the 
floating mass electromagnetic unit being similarly connected to an ossicle 
bone using the compliant member of the present invention. 
In a preferred embodiment, magnetic coupling devices are used to attach the 
compliant connecting member to the diaphragm and to the ossicle bones. As 
shown in FIG. 10A, for example, single magnets 855, 865 are coupled on to 
diaphragm 830 and target ossicle bone 30, respectively. Single magnets 
850, 860, having an opposing charge are coupled to the ends of compliant 
member 810. To secure compliant member 830 into the system, the magnets 
are brought into contact and hold member 810 in place. As before, the 
benefits of the present invention are provided, including holding the 
tensioning unit in its proper location, facilitating surgical placement, 
rendering the device reversible and other phenomena which may impair 
coupling between the diaphragm and the compliant member and the compliant 
member and the bones of the inner ear. 
Another potential implantable hearing device, as shown in FIG. 11A, is a 
coil-magnet implantable device. FIG. 11A illustrates an embodiment of the 
present invention used with the coil-magnet configuration. Coil-magnet 
device 981 has a coil 988 in a housing and is brought into close proximity 
with magnet 986, which is coupled to on one or more ossicle bones of the 
inner DD. When coil 988 is energized, motion is induced in magnet 986. 
Compliant member 982 provides a compliant connection between coil device 
988 and magnet 986. Preferably the compliant member is a keeper/spring 
982, as shown in FIG. 11A, and is made from a soft pliable material, such 
as silicone or rubber. Keeper/spring 982 has a first open end 984 adapted 
to receive coil device 988. The second open end 986 is adapted to receive 
magnet 986 and center the magnet's position with coil device 988. The 
motion of magnet 986 is proportional to the signal applied to coil device 
988. The compliant connection of coil device 988 to the inner ear is made 
to accurately transmit mechanical vibrations to the ossicles and 
faithfully reproduce sound waves. The compliant member or keeper/spring 
982 is further designed to tune the resonance of the system and ease the 
method of implantation of the coil device. To ease the implantation 
process, magnet 986, with keeper/spring 982 coupled to one side, is 
coupled to a bone of the inner ear. After magnet 986 is secured in 
position, coil device 988 is moved into position and coupled to compliant 
keeper/spring 982. 
FIG. 11B, illustrates yet another embodiment of the present invention. 
Compliant member 994 is coupled on a perimeter of magnet 990 and resembles 
a gasket. Coil 992 is then positioned to surround the portion of magnet 
990 having the gasket-like compliant member 994 disposed thereon. 
It is to be understood that the above description is intended to be 
illustrative and not restrictive. Many embodiments will be apparent to 
those of skill in the art upon reviewing the above description. By way of 
example, the inventions herein have been illustrated primarily with regard 
to the type of implantable hearing devices shown in Schaefer, as well as 
others, but they are not so limited. Those skilled in the art will 
recognize other equivalent or alternative methods of maintaining tension 
in the mechanical couplings of an implantable hearing device while 
remaining within the scope of the claims of the present invention. 
Although the above description discusses the use of stainless steel in 
particular, other materials may be used for the compliant connecting 
members of the present invention. The scope of the invention should, 
therefore, be determined not with reference to the above description, but 
should instead be determined with reference to the appended claims, along 
with the full scope of equivalents to which such claims are entitled.