Abstract:
An alert apparatus for a personal communication device includes a mechanically prestressed piezoelectric wafer positioned within the personal communication device and an alternating voltage input line coupled at two points of the wafer where polarity is recognized. The alert apparatus also includes a variable frequency device coupled to the alternating voltage input line, operative to switch the alternating voltage on the alternating voltage input line at least between an alternating voltage having a first frequency and an alternating voltage having a second frequency. The first frequency is preferably sufficiently high so as to cause the wafer to vibrate at a resulting frequency that produces a sound perceptible by a human ear, and the second frequency is preferably sufficiently low so as to cause the wafer to vibrate at a resulting frequency that produces a vibration readily felt by a holder of the personal communication device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of Application Ser. No. 09/344,030, filed Jun. 25, 1999 and also claims priority under 35 U.S.C. §119 from Provisional Application Ser. No. 60/098,658 filed Aug. 31, 1998, the entire disclosure of which is incorporated herein by reference. 
    
    
     ORIGIN OF INVENTION 
     The invention disclosed herein was jointly conceived and made by employees of the United States Government and employees of Projects Unlimited, Inc. under a Space Act Agreement No. MOA#400. 
     BACKGROUND 
     The present invention relates to personal communication devices, and more particularly, to a vibrational and/or acoustic transducer for use with personal communication devices. 
     Vibrating alarms for use with personal communication devices are well known in the art. Many of these alarms comprise conventional motors having an eccentric weight attached to the rotor shaft. Accordingly, when the motor is activated, the rotation of the rotor shaft and corresponding rotation of the eccentric weight causes vibration within the personal communication device that is detected by the holder of the device. Typically, such vibrating alarms are not capable of also producing an acoustic alert signal; or if the vibrating alarm is capable of producing an acoustic alert signal, the design of the combination vibrating/acoustic alarm is complicated—rendering it not feasible for inexpensive mass production. 
     Accordingly, a need exists for a combination vibrating and acoustical alarm mechanism that has a relatively uncomplicated design, is relatively inexpensive to produce, that is substantially durable and is suited (relatively light-weight and small) to be incorporated into a hand-held communication device. 
     SUMMARY 
     One aspect of the present invention is to provide an alert apparatus for a personal communication device that includes: a mechanically prestressed piezoelectric wafer positioned within the personal communication device and an alternating voltage input line coupled at two points of the wafer where polarity is recognized. Preferably the alert apparatus also includes a variable frequency device coupled to the alternating voltage input line, operative to switch the alternating voltage on the alternating voltage input line at least between an alternating voltage having a first frequency and an alternating voltage having a second frequency. The first frequency is preferably sufficiently high so as to cause the wafer to vibrate at a resulting frequency that produces a sound perceptible by a human ear, and the second frequency is preferably sufficiently low so as to cause the wafer to vibrate at a resulting frequency that produces a vibration readily felt by a holder of the personal communication device. 
     It is another aspect of the present invention to provide a personal communication device (such as a wireless telephone or pager) that includes: a housing; a receiver component, mounted within the housing, for receiving messages transmitted to the communications device; a processor, mounted within the housing, operatively coupled to the receiver component for processing messages received by the receiver component; and an alarm apparatus operatively coupled to the processor; where the alarm includes: a mechanically prestressed piezoelectric wafer positioned within the personal communication device and an alternating voltage input line coupled at two points of the wafer where polarity is recognized. Preferably the alarm also includes a variable frequency device coupled to the alternating voltage input line, operative to switch the alternating voltage on the alternating voltage input line at least between an alternating voltage having a first frequency and an alternating voltage having a second frequency. The first frequency is preferably sufficiently high so as to cause the wafer to vibrate at a resulting frequency that produces a sound perceptible by a human ear, and the second frequency is preferably sufficiently low so as to cause the wafer to vibrate at a resulting frequency that produces a vibration readily felt by a holder of the personal communication device. Usually, the frequency of the high frequency supply is approximately 1200 to 20,000 Hz and the frequency of the low frequency supply is less than approximately 300 Hz. 
     It is also preferred that the personal communication device includes a voltage amplifier operatively coupled to the alternating voltage input line to amplify the alternating voltage input to the wafer, producing an amplified, alternating voltage signal, where the amplified, alternating voltage signal is approximately 20 Volts to approximately 120 Volts. However, with some applications of the present invention, the voltage amplifier may amplify the signal up to approximately 300 Volts. 
     It is also preferred that the wafer be clamped to the housing of the personal communication device at one or both ends of the wafer or that the wafer be held within a guide mounted within the housing, where the wafer is not attached to the guide or to the housing. Alternatively, the wafer may be clamped to a sounding board, which is in-turn fixed to the housing of the personal communication device. 
     In an alternate embodiment of the invention, the transducer includes an additional weight or tuning mass attached to the wafer. The additional tuning mass, when combined with the mass of the wafer and the spring constant of the wafer, permits the resonant vibrational frequency of the system to be more definitely tuned to a desired frequency. In another alternate embodiment of the invention, the transducer includes a speaker assembly that provides better impedance matching to the air. This allows a voice frequency range to be produced by the device. Thus the device not only produces an acoustic alert, but may also produce acoustic sounds having a voice range frequency capability. 
     Accordingly, it is an object of the present invention to provide a combination vibrating and acoustical alarm mechanism that has a relatively uncomplicated design, is relatively inexpensive to produce, is substantially durable and is suited (relatively light-weight and small) to be incorporated into a hand-held communication device. These and other objects and advantages of the present invention will be apparent from the following description, the appended claims and the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a schematic, block diagram representation of a personal communication device incorporating the transducer of the present invention; 
     FIG. 1B is a schematic, block diagram representation of an alternate personal communication device incorporating the transducer of the present invention; 
     FIG. 1C is a schematic, block diagram representation of another alternate personal communication device incorporating the transducer of the present invention; 
     FIG. 2 is a schematic, elevational side view of a first embodiment of the transducer device of the present invention; 
     FIG. 3 is a perspective view of the transducer device of FIG. 2; 
     FIG. 4 is a schematic, elevational side view of an example of an alternate clamping arrangement for the transducer device of the present invention; 
     FIG. 5 is a schematic, elevational side view of a second embodiment of a transducer device of the present invention; 
     FIG. 6 is a schematic, elevational, cross-sectional side view of a third embodiment of a transducer device of the present invention; 
     FIG. 7 is a schematic, elevational side view of a fourth embodiment of a transducer device of the present invention; 
     FIG. 8 is a perspective view of the transducer device of FIG. 7; 
     FIG. 9 is a schematic, elevational side view of a fifth embodiment of a transducer device of the present invention; and 
     FIG. 10 is a perspective view of the transducer device of FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1A, a cellular telephone, pager or other typical personal communication device typically includes a central processor  10  such as a micro-processor, micro-controller or other similar processing device; a receiver  22  such as an RF antenna, an infra-red sensor or other related reception device; an output device  24  such as an LCD or LED display component and/or an ear-piece component; and a power supply  26 , such as a battery, a solar cell, or any other known means for providing power to the various components of the personal communication device. Such components are well known to those of ordinary skill in the art and will therefore not be discussed in significant detail herein. Generally, the processor tends to receive information transmitted to the personal communication device from the receiver  22  and relays that information to the user of the personal communication device by controlling the output device  24 . The personal communication device will also include a transducer  28  of the present invention for alerting a user of the device of an incoming message, for example. As will be described in detail below, the transducer is preferably adapted to provide both vibrational and/or acoustic alerts to the user. Accordingly, the processor includes an acoustic signal output  30  and a vibrational signal output  32 . The acoustic signal output transmits an alternating voltage signal at a frequency of approximately 1200 to approximately 20000 Hz; while the vibrational signal output  32  transmits an alternating voltage signal at approximately 300 Hz or less. It is to be understood that an “alternating voltage” signal may be a standard AC signal or a switched DC signal (such as a square wave and the like). 
     The transducer  28  is preferably a piezoelectric wafer  44  (see FIGS. 2-10) formed substantially according to the process described in U.S. Pat. 5,632,841 to Hellbaum, et al., the disclosure of which is incorporated herein by reference. This wafer includes a piezoelectric layer which is bonded to an adhesive layer, such as a polyimide, at elevated temperatures so that the differential thermal compression rates of these two layers imparts a mechanical prestress into the layers. Such a mechanically prestressed piezoelectric device is commercially available from Par Technologies, Newport News, Va. 
     It has been found that upon applying an alternating input voltage having a frequency of approximately 1200 to 20,000 Hz to the wafer  44 , at two sides of the wafer where polarity is recognized, causes the wafer to vibrate at a resulting frequency to produce a sound which is perceptible by the human ear. It has also been found that upon applying an alternating voltage at a low frequency of approximately 300 Hz or less, to the wafer  44  produces a readily perceptible vibration for the transducer  28  which will be perceived by the holder of the personal communication device. The voltage level needed to vibrate the wafer depends upon the thickness of the ceramic material and preferably ranges from 20 to 120 volts (amplified from a 1.5 to 10 volt base supply  26 ), although voltages of up to approximately 300 volts may be necessary. 
     Accordingly, the personal communication device also includes a voltage amplifier  34  for amplifying the voltage from the power supply  26  into an amplified voltage signal  36  as required by the piezoelectric wafer and the given application. These amplified voltage signals  36  are provided to signal combiners  38  which respectively combine the amplified voltage signals  36  with the acoustic output signal  30  or the vibrational output signal  32 . The personal communication device also includes a switch  40  which may be controlled mechanically or electronically by the user. This switch  40  switches the input  42  into the transducer  28  between the amplified acoustic output signal  43  or the amplified vibrational output signal  45 . The switch  40  can be controlled manually by a user or may be controlled by the processor  10 . 
     As shown in FIG. 1B, an alternate configuration of the personal communication device circuit utilizes a voltage amplifier device  41  operatively positioned between the processor  10  and the switch  40  for amplifying the alternating voltage acoustic signal  30  and vibrational signal  32  outputs from the processor to the amplified acoustic output signal  43  and amplified vibrational signal  45 . 
     As shown in FIG. 1C, another alternate configuration of the circuit may include a programmable clock generator device  47  controlled by the microprocessor, via data signal  49 , for generating the desired frequency output  51 , where the single frequency output of this device would be amplified by the amplifier device  41  to provide the input  42  into the transducer  28 . Therefore, in this alternate configuration, the operation of the switch  40  of FIGS. 1A and 1B is replaced by the processor control. 
     As shown in FIGS. 2 and 3, a first embodiment of the transducer  28   a  includes the piezoelectric wafer  44  retained on or to a sounding board  46  by a single clamp  48  which is positioned at a far end of the wafer  44 . The sounding board  46  may be unitary with, or otherwise rigidly attached to the housing of the personal communication device. Preferably the wafer is a planar wafer being substantially rectangularly shaped. However, as will be appreciated by those of ordinary skill in the art, the wafer can take many shapes such as a circular shape. The clamp  48  is rigidly bounded to the case-integral sounding board  46 . Suitable clamps  48  may take a variety of forms. For example, as shown in FIG. 4, a suitable clamp  48  may include a bracket  50  retaining the wafer  44  to the sounding board with a threaded screw  52 . The mass of the wafer  44  combined with the spring constant of the wafer  44  provides a certain resonant frequency of the system that is tuned to the desired frequencies for vibrational and acoustic notification. The resonant frequency of the system is tuned by varying the mass or other physical attributes of the wafer (e.g., size, material constituents, etc.). Furthermore, sizing the wafer to increase the capacitance of the wafer can reduce the current (and power) needed to actuate the wafer; and increasing the wafer size also results in a greater vibratory displacement for lower frequency vibration. 
     As shown in FIG. 5, a second embodiment of the transducer  28   b  includes the piezoelectric wafer  44  retained to the sounding board  46  by a pair of clamps  54 , positioned on opposite ends of the wafer  44 . While the embodiment shown in FIG. 5 will be retained to the housing  46  of the personal communication device more securely than the embodiment shown in FIGS. 2 and 3, the deflection caused by the reception of the input signal  42  will be much less than in the embodiment in FIGS. 2 and 3. 
     As shown in FIG. 6, a third embodiment of the transducer  28   c  includes a box or a guide  56  mounted to the sounding board  46 . The wafer  44  resides within the guide  56 , but is not attached to the guide  56  or the sounding board  46 . Accordingly, when power is applied to the wafer  44 , it will vibrate freely within the guide  56 . 
     As shown in FIGS. 7 and 8, a fourth embodiment of the transducer  28   d  includes an additional weight or tuning mass  58  attached to the wafer  44 . The additional tuning mass  58 , when combined with the mass of the wafer and the spring constant of the wafer, permits the resonant vibrational frequency of the system to be more definitely tuned to a desired frequency. Additionally, the additional tuning mass will allow for a more readily perceptible vibrational signal from the transducer. The resonant frequency of the system is tuned to the desired frequency by varying the mass or physical attributes of the wafer  44  and the tuning mass  58  (e.g., size, material constituents, etc.), and also by varying the position and size of the tuning mass. 
     A prototype of the embodiment illustrated in FIGS. 7 and 8 was constructed on a rectangular wafer  44  having dimensions of 1.75×2.5 inches. The wafer  44  included constituent layers (from bottom to top) of brass, approximately 0.003-0.005 inches thick, a sprayed layer of LaRC SI, PZT, approximately 0.008 inches thick, a sprayed layer of LaRC SI, and a layer of aluminum, approximately 0.001-0.003 inches thick. The wafer  44  was clamped along its width at one end and a mass of approximately 4 to 10 grams was attached to the other end, approximately 2.25 inches from the clamp along the centerline of the wafer. Preliminary testing of the wafer  44  measured frequencies of approximately 61 Hz and 138 Hz for maximum momentum exchange. 
     As shown in FIGS. 9 and 10, a fifth embodiment of the transducer  28   e  includes a speaker assembly  60  that allows better impedance matching to the air. This allows a voice frequency range to be produced by the device, thus providing a means not only to produce an acoustic alert, but to provide acoustic sounds having a voice range frequency capability. The speaker assembly  60  includes a speaker bracket  62  rigidly attached to the sounding board  46 , a speaker cone  64 , and a speaker cone attachment  66  for attaching the narrow end of the speaker cone  64  to the wafer  44 . The open end of the speaker cone  64  is fastened to the speaker bracket  62  to maintain the open end of the speaker cone in a substantially fixed position during operation of the transducer. When the wafer is actuated by applying current to the current input leads  42 , differential movement will be caused between the open and narrow ends of the speaker cone, thus pumping air and causing sound to be produced. 
     Based upon the above, it will be apparent to those of ordinary skill in the art that many different means for mounting the wafer  44  within the personal communication device are available. The more constrained the wafer is mounted, the lower the deflection of the wafer will occur when power is provided by the input signal  42 . It is also within the scope of the invention to attach a diaphragm to the wafer  44  so as to provide a more distinct acoustic signal. 
     Following from the above description, it should be apparent to those of ordinary skill in the art that, while the designs and operations herein described constitutes several embodiments of the present invention, it is to be understood that the invention is not limited to these precise designs and operations, and that changes may be made therein without departing from the scope of the invention.