Electrical audio signal processing systems and devices – Hearing aids – electrical – Specified casing or housing
Reexamination Certificate
1998-11-12
2001-03-27
Woo, Stella (Department: 2643)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Specified casing or housing
C381S322000, C381S324000, C381S328000, C181S130000, C181S135000
Reexamination Certificate
active
06208741
ABSTRACT:
BACKGROUND OF THE INVENTION
a. Technical Field
The present invention relates to hearing devices, and, more particularly, to hearing devices that are deeply positioned in the ear canal with improved energy efficiency, sound fidelity and inconspicuous wear.
b. Description of the Prior Art
(1) Brief Description of Ear Canal Anatomy and Physiology
The external acoustic meatus (ear canal) is generally narrow and tortuous as shown in the coronal view in FIG.
1
. The ear canal
10
is approximately 23-29 mm long from the canal aperture
17
to the tympanic membrane
18
(eardrum). The lateral part, a cartilaginous region
11
, is relatively soft due to the underlying cartilaginous tissue. The cartilaginous region
11
of the ear canal
10
moves in response to the jaw motions, which occur during talking, yawning, eating, etc. Cerumen (earwax, not shown) production and hair growth occur primarily in the lateral end of the ear canal within the cartilaginous region. The medial part, a bony region
13
proximal to the tympanic membrane, is rigid due to the underlying bony tissue. The skin
14
in the bony region
13
is thin (relative to the skin
16
in the cartilaginous region) and is sensitive to touch or pressure. There is a characteristic bend
15
that roughly occurs at the bony-cartilaginous junction
19
. The magnitude of this bend varies significantly among individuals. There is no earwax production or hair in the bony part of the ear canal. The ear canal
10
terminates at the tympanic membrane
18
.
A cross-sectional view of the typical ear canal
10
(
FIG. 2
) reveals generally an oval shape with a long diameter (D
L
) in the vertical axis and a short diameter (D
S
) in the horizontal axis. The canal dimensions vary significantly among individuals as shown below in the section titled Experiment-A.
(2) The Challenges of Deep Canal Fittings
The benefits of placing a hearing device deep in the ear canal are many. They include improved high frequency response, less distortion, reduction of feedback and improved telephone use (Chasin, M.
CIC [Completely In the Canal] Handbook,
Singular Publishing, pp 10-11, 1997, referred to hereinafter as “Chasin”). A major benefit for “an invisible hearing device” for the user is cosmetic in nature since hearing aid use is often associated with aging and disability.
A conventional deep canal hearing device
50
, shown in
FIG. 3
, typically includes a battery
52
, a microphone
53
, an amplifier
54
and a receiver
55
(speaker), among other components (not shown), all of which are housed within an outer shell
51
composed of acrylic or plastic material. The battery enclosure, comprising battery door
56
, battery compartment with contacts (not shown), and outer shell
51
, is conventionally positioned in the lateral end of the hearing device
50
occupying the lateral end of the ear canal as shown in FIG.
3
. The most lateral structure of a hearing device is referred to in the hearing aid industry as the “face-plate”
57
which is attached to the shell
51
and houses the battery door for access to the battery compartment and the battery within (for example, see U.S. Pat. No. 4,272,591 to Brander, U.S. Pat. No. 4,803,458 to Trine et al., and U.S. Pat. No. 5,675,657 to Giannetti).
Since the battery enclosure is a permanent component of a conventional hearing device, the enclosure must be durable to last the life of the hearing device. For this reason alone, the thickness of shells in conventional canal hearing devices typically ranges between 0.5 to 0.7 millimeter (mm).
With continued improvements in miniaturization of hearing aid components, the battery has emerged as the largest single component in miniature hearing devices. For this reason, among others, the battery is typically positioned laterally within the cartilaginous region
11
of the ear canal, a region with relatively larger dimensions as compared with medial regions of the ear canal.
Unfortunately, fitting a hearing device deeper with prior art battery enclosures is virtually impossible for most hearing impaired individuals due to space limitations in the deeper areas of the ear canal. As demonstrated in Experiment-A (described below) employing measurements of ear impressions from human cadavers, the dimensions of the typical ear canal prohibit placement of batteries with conventional enclosures in the vicinity of the bony-cartilaginous junction
19
.
Resorting to smaller batteries, and thus a smaller enclosure, to reduce the overall size of the device is not practical for most users who expect a prolonged use of their batteries prior to depletion and replacement.
Another problem associated with battery enclosure in conventional hearing aid designs is caused by the occlusion of the ear canal by the housing of the device. Occlusion related problems include:
(i) Discomfort, irritation and even pain may occur attributable to canal abrasion caused by frequent insertion and removal of an occluding hearing device. Due to canal discomfort and abrasion, hearing devices are frequently returned to the manufacture in order to improve the custom fit and comfort (Chasin, pp. 43-44). “The long term effects of the hearing aid are generally known, and consist of atrophy of the skin and a gradual remodeling of the bony canal. Chronic pressure on the skin lining the ear canal causes a thinning of this layer, possibly with some loss of skin appendages” (Chasin, p. 58).
(ii) The occlusion effect is a common acoustic problem caused by the occluding hearing device. It is manifested by the perception of a person's own-voice (“self-voice”) being loud and unnatural compared to that with the open ear canal. This phenomenon is sometimes referred to as the “barrel effect” since it resembles the experience of talking into a barrel. The occlusion effect, which may be experienced by plugging the ears with fingers while talking, is generally related to self-voice resonating within the ear canal. In the ear canal occluded by a conventional hearing device
10
(FIG.
3
), a large portion of the self-voice
20
, originating from the larynx (voice-box) and conducted upward by various body structures, is directed at the tympanic membrane
18
, as shown by arrow
21
. Some of the sound energy escapes to the outside through the occluded hearing device as shown by arrow
22
. The residual “trapped” sound energy
21
is perceived by the individual wearing the device as loud or unnatural. In the open (non-occluded) ear canal, a relatively larger amount of self-voice
22
is allowed to escape, and the residual sound
21
directed at the tympanic membrane
18
is relatively smaller. This represents what is perceived as natural self-voice. For hearing aid users, the occlusion effect is inversely proportional to the residual volume of air between the occluding hearing device and the tympanic membrane. Therefore, the occlusion effect is considerably alleviated by a deeper insertion of a device within the ear canal.
(3) State of the art in Battery Enclosure in Hearing Devices
As mentioned above, prior art hearing devices typically comprise a battery compartment within an outer shell having an attached face-plate. The shell and the attached face-plate are typically composed of rigid acrylic or plastic material. The shell typically occludes the ear canal.
U.S. Pat. No. 5,201,008 to Arndt et al. describes an open-topped battery compartment (24 in
FIG. 1
) that is first contained within a first housing (22 in
FIG. 1
) and subsequently contained in a second housing (12 in
FIG. 1
, where the Figure numbers mentioned with respect to the patent refer to those in the patent itself). U.S. Pat. No. 5,701,348 to Shennib et al. also describes a battery compartment (15 in
FIG. 3
) contained in outer housing (13 in
FIG. 3
) made of rigid non-resilient material. In the above mentioned inventions, the outer housing, containing the battery compartment, is too large to fit in the deeper portion of the ear canal, especially when considering other components (i.e. the microphone) which also reside in the same outer housi
Shennib Adnan
Urso Richard C.
Insonus Medical, Inc.
Ni Suhan
Woo Stella
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