Electrical audio signal processing systems and devices – Hearing aids – electrical – Specified casing or housing
Reexamination Certificate
1999-12-17
2003-07-29
Tran, Sinh (Department: 2643)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Specified casing or housing
C381S330000
Reexamination Certificate
active
06600825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to converters for hearing aids used in the rehabilitation of damaged inner ears. In particular, the present invention relates to such converters for hearing aids which are hermetically sealed.
2. Description of the Related Art
Hearing aids for rehabilitating damaged inner ear typically pick up sound with a microphone and using this microphone, convert the sound into an electrical signal. This signal is processed in analog or digital form by an electronic unit and is amplified. The amplified electrical signal is basically sent to an electroacoustic converter which acts as a loudspeaker and is also called an “earphone”. This electroacoustic earphone radiates the amplified electrical signal into the auditory canal of the pertinent ear. The auditory canal, in many cases, is sealed by an individually produced ear fitting piece (so-called “otoplasty”) in order to first, function as an acoustic pressure chamber which is formed by the residual volume up to the eardrum, and second, to prevent acoustic feedback between the microphone and the earphone at high degrees of amplification. Basically, there are two different designs of these hearing aids. First, in the “behind-the-ear hearing aids” (HdO), the important components of the hearing aid such as the microphone, electronic unit, battery and earphone are located in a common housing which is worn behind the ear. The amplified acoustic signal is decoupled from the earphone by a sound conduction tube and routed via the auricular muscle to the ear fitting piece and supplied through it to the auditory canal. The hearing aid can also be mounted on the frames of glasses. Second, in the “In-the-ear device” (IdO) type of hearing aid, all the aforementioned elements of the hearing aid are located in a common housing which is worn in the auricular muscle in the area of the outer auditory canal. One such in-the-ear device is integrated, for example, into the individual ear fitting piece or represents the ear fitting piece itself by a corresponding outer structure. In the in-the-ear design, the sound feed tube is eliminated since the sound exit opening is located on the side of the hearing aid facing the auditory canal and the earphone radiates the amplified acoustic signal directly into the auditory canal.
Hearing aids of the two aforementioned designs have fundamentally the following disadvantages:
The converters (earphones) of almost all hearing aids operate based on the electromagnetic conversion principle due to reasons of electrical efficiency and the optimization of the battery service life. This results in inevitable occurrence of nonlinear distortions especially at high converter currents and the pertinent output levels which adversely affect sound quality.
In addition, the first mechanical resonant frequency of this converter is generally in the middle of the spectral transmission range. This, and other physical and construction aspects, leads to an uneven frequency response and thus, undulations of the output acoustic pressure level. These resonances within the transmission range also fundamentally cause phase rotations. Both of these aspects contribute to reduced transmission quality.
The converter (earphones) are mechanically “open” on the output side as a result of the acoustic signal to be transmitted, thus, the outside air (except for a few cases where additional flow screens are provided) can penetrate relatively unhindered into the interior of the converter. Thus, the converter is exposed and almost unprotected to all weather and environmental effects, especially atmospheric humidity. These environmental effects are to a largely responsible for frequently occurring performance reductions of the converter operating parameters or even the failure of this component.
Especially in the in-the-ear devices, as a result of the local arrangement of the earphone in the outer (for maximally miniaturized devices) or inner auditory canal, fouling of the acoustic access channel by ear wax which is the product of the natural cleaning process of the auditory canal leads to adverse effects or failures of the earphone and thus, the hearing aid.
SUMMARY OF THE INVENTION
The primary object of this invention is to minimize or eliminate the aforementioned defects of known prior art hearing aid converters.
In accordance with one embodiment of the present invention, this and other objects and advantages are achieved by providing an electroacoustic converter for hearing aids including an electromechanical converter drive unit, a hermetically sealed metallic converter housing for enclosing the drive unit, the converter housing including one wall which is made as a bendable converter membrane, where the output-side of the converter drive unit which vibrates mechanically is coupled to the converter membrane in a manner that the converter membrane is excited in to bending vibrations thereby resulting in sound emission outside of the converter housing. The converter membrane acts as an earphone membrane which radiates sound outside the converter. The electromechanical converter drive unit within the converter may be based and operate on all known converter principles, especially piezoelectric, dielectric, electromagnetic, electrodynamic and magnetostrictive converter principles.
The converter housing is preferably cylindrical, especially circularly cylindrical, and may have a housing part which is open on one side, the open side being hermetically sealed gas tight by the converter membrane.
The housing part and/or the converter membrane can be made of a corrosion resistant, stainless metal, such as high grade steel or other body-compatible metal such as titanium, platinum, niobium, tantalum or their alloys.
Preferably, the housing part is provided with at least one single-pole, a hermetically sealed electrical housing feed through and the ground potential lying on the housing part. The housing feed through can be advantageously provided using metal-ceramic connections soldered gas tight with aluminum oxide ceramic as the insulator and at least one platinum-iridium wire as the electrical feed through lead.
The electromechanical converter drive unit is preferably a piezoelectric ceramic wafer which can be made circular and applied to the inside of the converter membrane as an electromechanically active element which, together with the converter membrane, represents an electromechanically active heteromorph composite element. Here, as in a bimorph element, the piezoelectric transverse effect is used except that the partner of the composite here does not consist of a second piezoelectrically active element, but instead, consists of the passive converter membrane of geometry similar to the piezoelement. The piezoelectric ceramic wafer can be provided with a very thin, electrically conductive coating on both sides which is used as the electrode surface and can consist especially of lead zirconate titanate. If an electrical field is applied to the piezoelectric ceramic wafer, the wafer changes its geometry, preferably in the radial direction, as a result of the transverse piezoeffect. Since extension or radial shortening is prevented by the mechanically strong connection to the passive converter membrane, sagging of the composite element takes place which is maximum in the middle with the corresponding edge support of the converter membrane.
The thickness of the converter membrane and the thickness of the piezoelectric ceramic wafer may be roughly the same and may be in the range of 0.05 mm to 0.15 mm. Furthermore, the converter membrane and the piezoelectric ceramic wafer may have roughly the same E-modulus. One especially simple and reliable structure is obtained when both the converter membrane and the housing part are electrically conductive, the piezoelectric ceramic wafer being connected electrically conductively to the converter membrane by an electrically conductive cement and the housing part forming one of at least two electric converter terminals. The radius of the conver
Nixon & Peabody LLP
Phonak AG
Safran David S.
Tran Sinh
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