Abstract:
A bone conduction microphone and speaker mountable in contact with a user&#39;s head or head area, each utilize a strategically mounted audio transducer that is preferably a piezoelectric ceramic bender. In the case of the speaker, the bender is coupled to an audio transformer which may or may not be potted with the bender within the same housing. Additionally, the speaker bender is mounted on a foam layer either with or without a supporting shelf depending on the desired application. The microphone bender is potted within the housing and includes a JFET and resistor mounted directly to the elements of the bender. The present microphone is designed to create the largest possible acoustic mismatch with air while nearly matching the acoustic impedance to the human skill structure. This attenuates the amount of ambient air noise coupled sound receivable into the microphone by greater than 80 dB. The speaker is designed with acoustic impedance matched for bone conduction sound.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional U.S. patent application based upon provisional U.S. patent application Ser. No. 60/103,205, filed Oct. 6, 1998, entitled “BONE CONDUCTION ACOUSTIC COMMUNICATION”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to bone conduction audio communication systems and, more particularly, to bone conduction audio speakers and microphones. 
     2. Description of the Related Art 
     Most conventional audio listening and/or communication systems do not use bone conduction. Instead, such conventional systems provide sound to the listener utilizing normal air conduction via the ear canal. Such conventional systems are used in a variety of applications or activities. One type of well known air conduction system is the headphone or earphone that is placed over the ear and transmits sound to the user via the ear canal. As well, conventional microphones utilize air vibration transducers to translate incoming air movement (sound/audio) into electrical pulses. 
     In contrast, it is also known to provide bone conduction microphones that utilize energy generated by auditory vibrations of the bones of the head. Generally, these types of microphones utilize an inertial-type or low mass accelerometer transducer which is placed in intimate contact with the head to detect bone vibrations and then generate output signals responsive to the vibrations. 
     However, these types of microphones are adversely affected by ambient noise transmitted through the air as well as through mounting equipment. Also, the audio quality is generally poor because the transducer cannot be held in intimate contact with the head with a sufficient, but comfortable, pressure so as to pick up or detect all frequencies of sound, especially high frequencies. 
     What is therefore needed in the art is a bone conduction audio communication system having both a microphone and speaker that overcomes the deficiencies of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a bone conduction microphone and speaker which comprise separately and together a communication system. Both the speaker and microphone are designed to be in contact with the head, head area, or on the mastoid of a user. 
     The present microphone is constructed with materials and geometries such that the acoustic impedance thereof is nearly matched to the human skull structure. Additionally, the present microphone is designed to create the largest possible acoustic mismatch with air, attenuating ambient air coupled sound by greater than 80 dB, thereby almost completely eliminating air coupled sound reception. Further, the present microphone is specific to vibrations which exist in the human flesh and is specifically not sensitive to ambient air coupled vibrations, while at the same time being constructed with simple and inexpensive components. 
     In one form thereof, the microphone comprises an audio transducer potted within a low profile plastic housing and including a transistor and resistor mounted directly to the audio transducer. 
     The audio transducer is preferably a piezoelectric ceramic bender having a ceramic element disposed on a metallic vibration element and of appropriate operating characteristics. A Junction Field Effect Transistor (JFET) has the gate thereof electrically coupled to the ceramic element, the source thereof electrically coupled to the metallic vibration element, and the drain electrically coupled to the output conductor. The resistor has one end electrically coupled to the ceramic element and the other end coupled to the metallic vibration element. 
     The present speaker is a bone conduction transduction device with acoustic impedance matched for bone conduction sound. The speaker is placed in intimate contact with the head or head area of the user such that sound generated thereby is injected directly into the skull creating a minimum of ambient air excitation. 
     In one form thereof, the present speaker comprises an audio transducer and audio transducer potted within a plastic housing. The audio transducer is supported on a foam layer disposed between the audio transducer and audio transformer. Depending on the application, the audio transducer may also be supported on a shelf of the housing. 
     The audio transducer is preferably a piezoelectric ceramic bender having a ceramic element disposed onto a metallic vibration element and of appropriate operating characteristics. The ceramic element is preferably disposed adjacent a protective polyurethane layer. 
     In another form thereof, the present speaker comprises an audio transducer potted within a plastic housing and disposed adjacent a foam layer, and electrically coupled via a cable to an audio transducer potted within a separate plastic housing. The audio transducer is supported on a foam layer disposed between the audio transducer and audio transformer. Depending on the application, the audio transducer may also be supported on a shelf of the housing. 
     It is an advantage of the present invention that the specific microphone and speaker designs can be independent of the application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a front, partial section, perspective view of an embodiment of a speaker in accordance with the principles present invention; 
     FIG. 2 is a front perspective view of another embodiment of a speaker in accordance with the principles of the present invention, showing the speaker and transformer therefor in partial section; and 
     FIG. 3 is a front, partial section, perspective view of a microphone in accordance with the principles of the present invention. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, in several forms, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to FIG. 1, there is shown high profile speaker or high profile integral speaker  10 . High profile speaker  10  has housing  12  made of a machined or thermoformed plastic such as ABS or another thermoplastic or thermoset polymer. Disposed within housing  12  is audio transformer  14  comprised of primary winding  15  and secondary winding  16  preferably having a turns ratio of approximately 10:1 and a peak performance at approximately 25-2000 Hz. One type of audio transformer that may be used is a Radio Shack® P/N 273-1380. Surrounding transformer  14  is epoxy potting  18  which provides protection and electrical insulation. One type of epoxy that may be used is known as 20-3060, a 100% reactive potting and encapsulating epoxy resin from Epoxies, Etc. Inc. of Greenville, R.I. Surrounding epoxy potting  18  is the plastic of housing  12  except for the upper portion thereof. 
     Wired to the high voltage side of transformer  14  is audio transducer  20 . Audio transducer  20  is preferably a piezo ceramic bender such as standard piezo ceramic bender part number KBI 3526 from Projects Unlimited, Inc. in Dayton, Ohio that has a resonant frequency of 2600 Hz. Bender  20  has annular piezo ceramic element  21  and non-ceramic or metal substrate vibration element  22 . In the case of the KBI 3526, piezo ceramic element  22  has a diameter of 25 mm (0.984″) and a thickness of 0.28 mm (0.011″), while non-ceramic vibration element  21  is brass and has a diameter of 35 mm (1.378″) and a thickness of 0.25 mm (0.010″) for an overall bender  20  thickness of 0.53 mm (0.021″). Of course, other bender configurations or audio transducers may be used according to the principles of the present invention. 
     Depending on the application, either above or below water applications, bender  20  is situated within housing  12  in one of two ways. In above water or non-diving applications, non-ceramic vibration element  22  of bender  20  is supported on its outside diameter by annular or other configuration shelf  24 , that is preferably only approximately 0.050 inches wide around its circumference. Disposed between bender  20  and transformer  14  is closed cell foam layer  26  that provides support for bender  20  in case of compression. This helps prevent cracking piezo ceramic element  21  of bender  20 . For underwater applications, however, non-ceramic vibration element  22  of bender  20  is not supported by a shelf but is directly supported on closed cell foam layer  26 . This allows for near uniform forces to be exerted over the entire surface area of bender  20  during such submersed applications. Again, this helps prevent cracking of piezo ceramic element  21 . 
     Disposed onto the top of bender  20  is polyurethane layer  28 , preferably of a 40-60 shore A or high viscosity resin polyurethane. The profile of polyurethane layer  28  is preferably nominally hemispherical and does not extend beyond the diameter of housing  12 . Electrical connection of transformer  14  and bender  20  is achieved by two or three conductor cable  30  that extends through housing  12  and is retained within housing  12  by epoxy potting  18  to provide protection, electrical insulation, and a secure structure. Preferably, cable  30  is a PVC or polyurethane jacketed material with conductor sizes nominally at least 26 gauge, but no larger than 20 gauge. 
     With reference now to FIG. 2, there is shown low profile speaker assembly  32 . Speaker assembly  32  comprises separate speaker  34  and separate transformer  36 . Speaker  34  has housing  38  of a machined or thermoformed plastic such as ABS or another thermoplastic or thermoset polymer and includes an audio transducer  40 . Audio transducer  40  is preferably a piezo ceramic bender such as standard piezo ceramic bender part number KBI 3526 from Projects Unlimited, Inc. of Dayton, Ohio that has a resonant frequency of 2600 Hz. Bender  40  has annular piezo ceramic element  41  and non-ceramic or metal substrate vibration element  42 . In the case of the KBI 3526, piezo ceramic element  41  has a diameter of 25 mm (0.984″) and a thickness of 0.28 mm (0.011″), while non-ceramic vibration element  42  is brass and has a diameter of 35 mm (1.378″) and a thickness of 0.25 mm (0.010″) for an overall bender  40  thickness of 0.53 mm (0.021″). Of course, other bender configurations or audio transducers may be used according to the principles of the present invention. 
     Depending on the application, either above or below water applications, bender  40  is situated within housing  34  in one of two ways. In above water or non-diving applications, non-ceramic element  42  is supported on its outside diameter by annular or s other configuration shelf  44 , that is preferably only approximately 0.050 inches wide around its circumference. Disposed under non-ceramic portion  42  of bender  40  is closed cell foam layer  46  that provides support for bender  40  in case of compression. This helps prevent cracking the piezo ceramic element  41  of bender  40 . For underwater applications, however, bender  40  is not supported by a shelf but is directly supported on closed cell foam layer  46 . This allows for near uniform forces to be exerted over the entire surface area of bender  40  during such submersed applications. Again, this helps prevent cracking of piezo ceramic element  41 . Disposed onto the top of bender  40  is polyurethane layer  47 , preferably of a 40-60 shore A or high viscosity resin polyurethane. The profile of polyurethane layer  47  is preferably nominally hemispherical and does not extend beyond the diameter of housing  38 . Cable  54 , which may be a two or three conductor cable, has one end which extends into housing  38  to directly couple with bender  40 . 
     Transformer assembly  36  includes upper housing  48   a  and lower housing  48   b  again made of a machined or thermoformed plastic such as ABS or another thermoplastic or thermoset polymer. While upper and lower housings  48   a  and  48   b  together form a football shaped housing, other shaped housings may be used such as rectangular or spherical. Disposed within housings  48   a  and  48   b  is audio transformer  70  comprised of primary winding  71  and secondary winding  72  preferably having a turns ratio of approximately 10:1 and a peak performance at approximately 25-2000 Hz. One type of audio transformer that may be used is a Radio Shack® P/N 273-1380. Surrounding transformer  70  is encapsulation potting  73  which provides protection and electrical insulation. One type of encapsulation material is an epoxy such as 20-3060, a 100% reactive potting and encapsulating epoxy resin from Epoxies, Etc. Inc. of Greenville, R. I. Other encapsulation materials may be used such as silicone or polyurethane. The other end of cable  74  extends into one side of housings  48   a  and  48   b  of transformer assembly  36  to couple with secondary winding  72 . One end of cable  75 , which may be a two or three conductor cable, extends into another side of housings  48   a  and  48   b  to couple with primary winding  71 . Cable  75  couples at the other end with a source of electric audio signal (not shown). For strength, cables  74  and  75  may be constructed with an integral string of Kevlar® or other synthetic high tensile strength material to enhance the tensile properties of the cable construction. 
     With reference now to FIG. 3, there is shown bone conduction microphone  50 . Microphone  50  has cup-shaped housing  52  of a machined or thermoformed plastic such as ABS or another thermoplastic or thermoset polymer. Disposed in housing  52  is audio transducer  54  for the active element which is preferably a piezo ceramic bender such as standard piezo ceramic bender part number KBI 2720 from Projects Unlimited, Inc. of Dayton, Ohio that has a resonant frequency of 2000 Hz. Bender  54  has annular piezo ceramic element  55  and non-ceramic or metal substrate vibration element  56 . In the case of the KBI 2720, piezo ceramic element  55  has a diameter of 20 mm (0.787″) and a thickness of 0.13 mm (0.005″), while non-ceramic vibration element  56  is brass and has a diameter of 27 mm (1.063″) and a thickness of 0.10 mm (0.004″) for an overall bender  54  thickness of 0.23 mm (0.009″). Of course, other bender configurations or audio transducers may be used according to the principles of the present invention. 
     Attached to bender  54  is Junction Field Effect Transistor (JFET)  62  with a SOT  23  configuration such as a J201 from National Semiconductor (or a Siliconix sst201). Gate  63  of JFET  62  is electrically coupled as by soldering to the silvered coating of piezo ceramic element  55  of bender  54 . Source  64  of JFET  62  is electrically coupled as by soldering to metal substrate vibration element  56  acting as electrical ground. Drain  65  of JFET  62  is electrically coupled as by soldering to output conductor  66  of cable  58 . The purpose of JFET  62  is to provide current and voltage amplification as close to the source as possible. This dramatically reduces noise introduction through cable  58 . A ground conductor (not shown) or cable shield if used (not shown) of cable  58  which extends through housing  52 , is electrically coupled as by soldering to metal substrate vibration element  56 . Cable  58  preferably has a polyurethane, PVC, or other insulating jacket which will provide at least two conductors in an overall diameter of less than 0.100 inches. 
     Resistor  68 , preferably with a value of 1 to 10 megaohms, is electrically coupled as by soldering at one end to piezo ceramic element  55  and at another end to metal substrate vibration element  56 , thus draining the predominately direct current bias from the active piezoelectric ceramic element  55 . Resistor  68  bleeds off DC current from active piezoelectric ceramic element  55  to maintain gate  63  of JFET  62  at a voltage whereby the small AC signals from audio received by bender  50  are amplified in the linear range of JFET  62 . Disposed onto the top of bender  54  is polyurethane layer  60 , preferably of a 40-60 shore A or high viscosity resin polyurethane. The profile of polyurethane layer  60  is preferably nominally hemispherical and does not extend beyond the diameter of housing  52 . 
     It is preferred to place bender  54  within housing  52  such that the piezo ceramic element  55  side is at the bottom and in intimate connection with the housing bottom. In any case, housing  52  is filled with a hard curing epoxy, preferably the 20-3060 epoxy as mentioned above from Epoxies, Etc. Inc., with the absence of air anywhere around bender  54  and is filled only until bender  54  is completely covered and the portion of cable  58  that extends into housing  52  is covered. Preferably, microphone  50  is less than 0.100 inches thick with a total thickness around bender  54  at 0.075 inches. This can be accomplished by placing the cable attachment and any strain relief to the side of the housing but mechanically attached by means of connective moldings or appropriate adhesives. It is also desired to attach a small conductor such as wire (not shown) to electrical ground within the housing and which protrudes therefrom and is connected to a thin metallic sheath that completely covers the microphone. This aids in the elimination of electromotive. interferences such as 60 cycle hum interference, radio signal interference, or other electromagnetic disturbances. 
     In use, either high profile speaker  10  or low profile speaker  32  and microphone  50 , or a single speaker  10  or  32 , or a multiple number and combinations of speakers  10  and  32 , or using only microphone  50  alone, may be placed into a supporting device, such as a helmet, to be placed in contact with a user&#39;s head. The preferred configuration is to use either high profile speaker  10  or low profile speaker  32  such that one or more of them are placed in contact with the user&#39;s head near the top or crown thereof. The speakers are preferably embedded into a soft, comfortable strap or cushioning material inside a hat, helmet or head covering such that intimate contact of the speaker is maintained against the head. The material around the speaker is best placed such that it forms a seal around the speaker and against the head without unloading pressure from the speaker against the user&#39;s head. The use of sound deadening material is most advantageous as this will result in attenuation of sounds being heard outside of the head covering, such as by a person in close proximity to the user. This is especially useful in applications such as the military or police activities where the user prefers to hear audio without that audio being detected by a bystander or by surveillance equipment. Any cables from the speakers would be routed beneath the soft comfortable material in the head covering, hat, or helmet to provide the best comfort for the user. 
     Microphone  50  is preferably placed into the head covering, hat or helmet such that it is maintained in intimate contact with the user&#39;s head, and most preferably on the forehead. Other locations, however, may be used such as near the rear of the head, the side of the head, near the mandibular joint, on the jaw, around or on the throat area, or near the mastoid. The microphone is maintained in contact with the chosen location by whatever means, such as elastic, or by a mechanical structure such that during normal movement, the microphone does not separate from the chosen location. Also, unwanted noise is reduced when the microphone is place in one location and maintained there without substantial movement. 
     Another application of microphone  50  is the use of more than one microphone in separate locations on the head, such as, without being exhaustive, two microphones place against the forehead, or one microphone on the forehead and another microphone on the back of the head. The output of the two microphones can be compared almost instantaneously by electronic means and audio/sound which is not present in both microphones concurrently (i.e. noise) can be removed. This technique completely eliminates unwanted noise. 
     Another system which is made from the incorporation of both the speaker and microphone of the present invention can use a single cable which connects to both the microphone(s) and speaker(s). This configuration allows for the system to be adapted to a portable single or two way radio or telephone. 
     Thus, the present microphone and speaker system has many uses or applications. These may include army helmets, headbands, directly taped to the head, application with Velcro®, chin straps, football helmets, bicycle helmets, race car drivers, helmet or non-helmet related sports with various attachment means, rollerblading, hard hats, goggle straps, eyeglasses, hoods, face masks, face shields, hats, baseball caps, direct hand held, fire/police helmets, mountain climbing, cellular phones, game or toy related head gear, virtual reality head gear or helmets, fetal heartbeat monitors, stethoscopes, and mechanical troubleshooting such as for engine diagnostics, only to name a few without being an exhaustive list. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.