Patent Publication Number: US-6658126-B1

Title: Hearing aid compatible piezoelectric speaker

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to piezoelectric speakers and more particularly to piezoelectric speakers suitable for use in radiotelephones. 
     BACKGROUND OF THE INVENTION 
     Radiotelephones which are hearing aid compatible conventionally rely on leakage from the magnetic field which drives a conventional speaker to provide hearing aid compatibility. Such compatibility is provided by a coil in the hearing aid which is coupled to the leakage field such that the time varying magnetic field of the leakage field induces a current in the coil. Thus, the hearing aid may be provided with the audio from the speaker without requiring amplification of the background noise, such a road noise, or the like. 
     Recently, however, radiotelephones have been produced utilizing piezoelectric speakers. Piezoelectric speakers are desirable because of their small size and low power consumption. A piezoelectric speaker utilizes one or more piezoelectric elements to drive the speaker. Piezoelectric elements operate such that the element moves in response to a voltage being applied to the element. However, the piezoelectric speaker does not produce significant magnetic fields. Accordingly, piezoelectric speakers are typically not hearing aid compatible as there is not a suitable time varying magnetic field which may induce a current in the hearing aid coil. Thus, radiotelephones utilizing piezoelectric speakers are typically not hearing aid compatible. 
     In light of the above discussion, a need exists for improved piezoelectric speakers. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a piezoelectric speaker suitable for use in a radiotelephone. 
     A further object of the present invention is to provide a piezoelectric speaker which is compatible with hearing aids. 
     These and other objects of the present invention are provided by a piezoelectric speaker which provides a magnetic field to couple to a hearing aid coil. The magnetic field induces a current in the hearing aid coil as it appears as a time varying magnetic field to the coil. The time varying magnetic field is preferably proportional to the movement of a piezoelectric member of the piezoelectric speaker so as to induce a current in the hearing aid coil proportional to this movement. Thus, the piezoelectric speaker may provide hearing aid compatibility. 
     In a particular embodiment of the present invention, a piezoelectric speaker is provided in which a portion of the piezoelectric speaker moves in response to the application of electrical energy to the piezoelectric speaker. A means is provided for generating a time varying magnetic field responsive to movement of the moving portion of the piezoelectric speaker such that a time varying magnetic field is generated when the moving portion of the piezoelectric speaker moves. The means for generating a time varying magnetic field may be a magnetic element coupled to the moving portion of the piezoelectric speaker so as to move responsive to movement of the moving portion of the piezoelectric speaker. In one embodiment, the moving portion of the piezoelectric speaker is a diaphragm and the magnetic element is a magnetic film applied to the moving portion of the piezoelectric speaker. The magnetic element may be made from a magnetic material such as NdFeB. 
     In another embodiment of the present invention, the magnetic element is coupled to a maximum displacement location of the moving portion of the piezoelectric speaker. The hearing aid compatible acoustic device may be used as a speaker in a radiotelephone. 
     In a further aspect of the present invention, a method is provided for a hearing aid compatible piezoelectric speaker including generating a time varying magnetic field responsive to motion of the piezoelectric speaker. In one embodiment of the method aspects of the present invention, the generating step includes connecting a magnetic material to the piezoelectric speaker such that motion of the piezoelectric speaker results in motion of the magnetic material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a radiotelephone utilizing a piezoelectric speaker according to the present invention; 
     FIG. 2 is a schematic representation of a piezoelectric speaker according to one embodiment of the present invention; and 
     FIG.  3 A and FIG. 3B are drawings illustrating operation of a piezoelectric speaker according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. As will be appreciated by those of skill in the art, the present invention may be embodied as methods or devices. 
     An embodiment of a radiotelephone  10  which includes a piezoelectric speaker  15  according to the present invention is depicted in the block diagram of FIG.  1 . As shown in FIG. 1, radiotelephone  10  typically includes a transmitter  12 , a receiver  14 , a user interface  16  and an antenna system  18 . The antenna system  18  may include an antenna feed structure  22  and an antenna  20 . As is well known to those of skill in the art, transmitter  12  converts the information which is to be transmitted by radiotelephone  10  into an electromagnetic signal suitable for radio communications. 
     Receiver  14  demodulates electromagnetic signals which are received by radiotelephone  10  so as to provide the information contained in the signals to user interface  16  in a format which may be made understandable to the user. In particular, the user interface  16  includes a piezoelectric speaker  15  according to the present invention for transforming the received signal into an audio signal to be heard by a user. 
     A wide variety of transmitters  12 , receivers  14 , user interfaces  16  (e.g., microphones, keypads, rotary dials) which are suitable for use with handheld radiotelephones are known to those of skill in the art, and such devices may be implemented in radiotelephone  10 . The design of these aspects of radiotelephone  10  are well known to those of skill in the art and will not be further described herein. 
     FIG. 2 depicts a piezoelectric speaker  15  according to an embodiment of the present invention. As seen in FIG. 2, a piezoelectric material  30  has associated with the material a magnetic material  32 . The magnetic material  32  may be a magnetic film and may be attached to the piezoelectric element or a diaphragm or cone of a piezoelectric speaker. The piezoelectric material should be attached to the piezoelectric speaker  15  in such a manner such that motion of the speaker causes motion of the magnetic material  32 . Thus, for a given point in space, motion of the magnetic material generates a time varying magnetic flux. 
     The present invention may be utilized with any number of known piezoelectric speakers. Suitable piezoelectric speakers which may be modified to be utilized according to the present invention are known to those of skill in the art and, therefore, will not be described in detail herein. Any piezoelectric speaker which allows for inclusion of a magnetic material which may move in proportion to the audio sounds generated by the piezoelectric speaker may be utilized. Such motion may result from connection to the speaker or the diaphragm either acoustically or physically. However, preferably, the magnetic material is positioned at the point of maximum displacement of the speaker such that the magnetic material moves through the largest range of motion. Thus, the magnetic material motion may generate the maximum differential flux for a given point in space. 
     Materials which are suitable for use with the present invention include and light weight high density magnetic material such as NdFeB. Furthermore, the material may be provided as a magnetic element including discrete elements such as discs or a film applied to the moving portion of the piezoelectric speaker. However, the magnetic material should not interfere with the operation of the piezoelectric speaker. Accordingly, flexible, smaller, and lighter materials are preferred. 
     Operation of the present invention will now be described with reference to FIG.  3 A and FIG.  3 B. As seen in FIG. 3A, when the piezoelectric material  30  is in a first position, a first amount of the magnetic flux from the magnetic material  32 , as illustrated by flux lines  40 , is coupled to the coil  34  of a hearing aid. As the piezoelectric material  30  moves, as illustrated in FIG. 3B, so does the magnetic material  32 . However, the coil  34  remains in approximately the same position. Thus, when the magnetic material  32  moves farther away from the coil  34  fewer of the magnetic flux lines  40  intersect the coil  34 , thus indicating that the amount of magnetic flux coupled to the coil  34  has decreased. 
     As is seen in FIG.  3 A and FIG. 3B, as the piezoelectric speaker  15  moves, so does the magnetic material  32  and thus, coil  34  sees a time varying magnetic field which induces a current in coil  34 . This current is proportional to the motion of the magnetic material  32  and, therefore, reflects the audio produced by the speaker  15 . Accordingly, the inclusion of the magnetic material  32  in piezoelectric speaker  15  allows for use of the piezoelectric speaker with hearing aids. In particular, such a speaker may be utilized in radiotelephones as described above. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.