US 3594514 A
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United States Patent  Inventor Robert C. Wingrove Minneapolis, Minn.  Appl. No. 489  Filed Jan. 2,1970  Patented July 20, I971  Assignee Medtronic, Inc. I
Minneapolis, Minn. Continuation of application Ser. No. 625,042, Mar. 22, 1967, now abandoned.
[541 HEARING AID WITH PIEZOELECTRIC CERAMIC ELEMENT 13 Claims, 4 Drawing Figs.
 US. Cl 179/107 R, 128/1 R  Int. Cl H04r 25/00  Field oISearch 179/107; 128/1 R  References Cited UNITED STATES PATENTS 2,339,148 [/1944 Carlisle I79/107 2,995,633 8/1961 Puharich et a1 179/107 3,156,787 11/1964 Puharich et a1 3,170,993 2/1965 Puharich et al.... 179/107 3,209,081 9/ 1 965 Ducote et al. 179/ 107 3,346,704 10/ I 967 Mahoney 179/107 FOREIGN PATENTS 788,099 12/ I 957 England 179/107 OTHER REFERENCES Conservative Tympanoplasty," October 1, 1966, Geze J. Jako MD. and Claus Jensen M.D., A REPORT TO THE AMERICAN ACADEMY OF OPHTALMOLOGY AND OTOLARYNAOLOGY, Page 54 1 Primary Examiner-Kathleen H. Clat'fy Assistant Examiner-Randall P. Myers Attorneyl.'ew Schwartz ABSTRACT: Implantable hearing aid apparatus having a piezoelectric ceramic element mounted adjacent to the auditory conductive system of the middle ear for imparting vibra HEARING AID WITH PIEZOELECTRIC CERAMIC ELEMENT This is a continuation of application, Ser. No. 625,042 filed Mar. 22, I967 andnow abandoned.
BACKGROUND OF THE INVENTION Hearing aids have long been known in the field of medicalelectronics. 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. .I. .lako, MD. and C. Jansen, M.D., AMERICAN ACADEMY OF OPHTALMOLOGY AND OTOLARYNGOLOGY, IN STRUCTIONS 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. I showing an encapsulated piezoelectric ceramic element;
FIG. 3 is a schematic drawing of the circuit of the embodiment of FIG. I; 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. 2 there is shown a sectional view of tall 13 and a portion of stem I2. 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 I6 and I7 are each shown connected to piezoelectric element 15, and extending through stem 12. Element I5 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 I3 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. I 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 in vention 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 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 electricalmechanical 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 I5 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 is relatively thin, to avoid undue damping ef fects.
When mounting the apparatus 10 in a body, it is preferable to firmly mount one end of element (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 [5 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 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 ofdevice 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 car. This is a further example of the situation where it may be desirable to place vibrating element 15 adjacent the oval window.
ln 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 car by means ofa piezoelectric element.
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 ofa 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 ol'claim l 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 cir cuit 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.
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