as) United States
`a2) Patent Application Publication o) Pub. No.: US 2008/0001484 Al
`
` Fuller et al. (43) Pub. Date: Jan. 3, 2008
`
`
`US 20080001484A1
`
`(54) LINEAR ELECTROMECHANICAL
`VIBRATOR WITH AXIALLY MOVABLE
`MAGNET
`
`(76)
`
`Inventors:
`
`Chris Fuller, Virginia Beach, VA
`(US); Steve Booth, Blacksburg, VA
`(US); George Osborne, Fairview
`Park (AU)
`
`Correspondence Address:
`WHITHAM, CURTIS & CHRISTOFFERSON &
`COOK,P.C.
`11491 SUNSET HILLS ROAD, SUITE 340
`RESTON, VA 20190
`(21) Appl. No.:
`11/428,460
`
`(22)
`
`Filed:
`
`Jul. 3, 2006
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`HO2K 33/00
`H02K 35/00
`
`(2006.01)
`(2006.01)
`
`(52) U.S. Ch. ec cececeecneteceeceesenenececeeeeenees 310/15
`
`(57)
`ABSTRACT
`An electromagnetic vibrator has a movable magnet that can
`:
`°
`eae
`.
`movelinearly in an axial direction. A field coil surrounds the
`movable magnet. Magnetic bumpers are disposed on oppo-
`site ends of the vibrator, and are oriented to repel
`the
`movable magnet. Whenan alternating current is provided in
`the field coil, the movable magnetoscillates linearly in the
`axial direction, bumping against the magnetic field of the
`bumper magnets and thereby creating vibration. The mov-
`able magnet may havea toroidal shape and be disposed on
`an axialshaft to linearly constrain the motion ofthe movable
`magnet. Two field coils can be provided to simultaneously
`create push and pull forces on the movable magnet. The
`bumper magnets can be replaced with compression springs.
`The electromagnetic vibrator can be very small and energy
`efficient;
`it
`is well suited for use in portable electronic
`devices, cell phones, toys, industrial mixers, and massage
`devices.
`
` field cai driver|
`
`APPLE 1041
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`.
`ibumpercoil driver}
`ver
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`etree
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`Held col
`i driver
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`ee
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`Fig. 6
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`US 2008/0001484 Al
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`Jan. 3, 2008
`
`LINEAR ELECTROMECHANICAL
`VIBRATOR WITH AXIALLY MOVABLE
`MAGNET
`
`FIELD OF THE INVENTION
`
`[0001] The present invention relates generally to linear
`electromagnetic vibrators, and, more particularly, to a non-
`rotary electromagnetic vibrator having a movable magnet
`that oscillates axially under the influence of an axial field
`coil.
`
`BACKGROUND OF THE INVENTION
`
`[0002] Electromagnetic shakers and vibrators are com-
`monly used in cellular telephones and other portable elec-
`tronic devices. Such vibrators are activated in order to
`
`silently alert a user of an incoming message.
`[0003] Conventional cell phone vibrators typically have a
`miniature rotary motor with an eccentric mass attached to
`the rotor. The eccentric mass produces oscillating accelera-
`tion forces when the motor is activated. Such rotary vibra-
`tors are relatively expensive and complicated to manufacture
`because the motor requires assembly of many small parts.
`Also, rotary vibrators tend to be energy inefficient.
`In
`portable electronic devices such as cell phones, energy
`efficiency is critical.
`[0004] Accordingly, there is a need for an inexpensive,
`simple and energy efficient miniature vibrator. Such a vibra-
`tor could be widely used in portable electronic devices such
`as cell phones. Also, such a vibrator could be scaled up in
`size and widely used in other applications such as in
`personal massage devices,
`industrial shaking or mixing
`devices and the like.
`
`SUMMARY
`
`[0005] The present invention provides an electromagnetic
`vibrator having a movable magnet. The magnet moves in an
`axial direction (linearly or along a curved path). The mov-
`able magnet
`is magnetized in the axial direction. Two
`bumper magnets are disposed axially in-line with the mov-
`able magnet. The bumper magnets are oriented such that
`they magnetically repel the movable magnet. In operation,
`the movable magnet is not always required to “bump” up
`against the bumper magnets (although this may be beneficial
`in some applications); rather, movement of the movable
`magnetin a first direction under the influence of an exter-
`nally applied electric field followed by a repelling force of
`a bumper magnetat the end of the pathwayfor travel results
`in a “vibration” that emanates from the housing in which the
`moveable magnet is located, This process is repeated at the
`other end of the pathway traveled by the moveable magnet.
`That is, the mass of the moveable magnet, andits oscillatory
`movement from one end to another along an axial pathway
`results in vibrations being transmitted from the housing or
`other support to an external environment. The vibrator can
`be small in size (e.g., prototypes the size of a quarter have
`been prepared and tested, but smaller sizes would be pos-
`sible), and may be used in a variety of different electronic
`devices such as providing a “silent ringer”vibration in a cell
`phoneor other communicating device, providing a vibratory
`sensation in a toy or massaging device, etc. Also,
`the
`vibrator can be used for mixing in laboratory or industrial
`applications. The vibrator may be used in combination with
`other vibrators in an array. Virtually any application where
`
`a vibrator is required can be fulfilled by this invention. In
`addition, the vibrator described herein has the advantage of
`being simple to construct, does not require a large number of
`parts, and does not require significant amounts of powerto
`operate. The vibrator can also accurately replay a drive
`signal time history similar to a loud speaker in contrast to a
`rotating eccentric mass vibrator which can only modulate its
`speed of rotation.
`[0006]
`In its simplest construction, the movable magnetis
`disposed between the bumper magnets andtravels along a
`linear or curved axial pathway. The vibrator has at least one
`field coil for causing the movable magnet to move in the
`axial direction. When excited by the field coil, the movable
`magnet will oscillate between the bumper magnets and
`create vibrations.
`can be replaced with
`[0007] The bumper magnets
`mechanical compression springs or electromagnetic bumper
`coils. The bumpercoils can be activated to repel the movable
`magnet each time the moveable magnet approaches.
`[0008] The movable magnet can have a toroidal shape,
`with a hole in the center. Also, the vibrator can have an axial
`shaft. The axial shaft can extend through the hole in the
`toroidal movable magnet. The axial shaft can extend the full
`length of the vibrator, and can be straight or curved.
`[0009] The movable magnet can be disposed within a
`hollow enclosure (e.g. having a cylindrical shape). The
`bumper magnets can be disposed at opposite ends of the
`enclosure. The enclosure can have one or more air holes to
`
`allow air to enter and escape as the movable magnetoscil-
`lates.
`
`[0010] Also, the bumper magnets can have air vents to
`allow air to enter and escape as the movable magnetoscil-
`lates.
`
`[0011] The vibrator can have two spaced apart field coils
`to excite the movable magnet. Thefield coils can be operated
`to apply both push and pull forces to the movable magnet.
`[0012] Also, a pickup coil can be disposed between the
`field coils. The pickup coil can be used in a feedback circuit
`to resonantly control the motion of the movable magnet.
`[0013] The stiffness and thus resonance of the vibratory
`actuatorof this invention can by adjusted by changing either
`the magnetic strength of the bumper magnets at the end of
`the pathway traveled by the moveable magnet, or by chang-
`ing thesize of the air vents in either the housing or end caps
`(i.e., large venting of air (or other fluid ) within the housing
`provides for higher resonance, while smaller venting results
`in lower resonance). In some applications, it may be desir-
`able to allow for adjusting the strength of the bumper
`magnets (e.g., by using electronmagnets as the bumper
`magnets and by permitting adjustmentofthe electric power
`to the electromagnets) or to allow for adjusting the air
`venting (e.g., by providing a valve mechanism that can be
`mechanically or electronically controlled) so that the reso-
`nance can beset to levels preferred by a user(e.g., the user
`sets the degree of vibration provided by his cell phone) or
`which are optimized for a particular application (e.g., dif-
`ferent levels of vibration may be preferred for viscous fluids
`and non-viscous fluids).
`
`DESCRIPTION OF THE FIGURES
`
`FIG. 1 showsa perspective view of an electrome-
`[0014]
`chanical vibrator.
`[0015]
`FIG. 2 shows a cross sectional view of an electro-
`mechanical vibrator.
`
`7
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`US 2008/0001484 Al
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`Jan. 3, 2008
`
`FIG. 3 showsa cross sectional view of an embodi-
`[0016]
`ment that does not have an axial shaft 22.
`
`FIG. 3a is an end view of the movable magnet
`[0017]
`shown in FIG.3.
`
`FIG. 4 shows a cross sectional view of an embodi-
`[0018]
`ment having a single field coil.
`[0019]
`FIG. 5 showsa cross sectional view of an embodi-
`ment having bumpercoils.
`[0020]
`FIG. 6 showsa cross sectional view of an embodi-
`menthavingfield coils disposed at axial ends ofthe vibrator.
`[0021]
`FIG. 7 showsa cross sectional view of an embodi-
`ment having a hollow axial shaft.
`[0022]
`FIG. 8 showsa cross sectional view of an embodi-
`ment having mechanical bumper springs attached to end
`caps of the vibrator.
`[0023]
`FIG. 9 showsa cross sectional view of an embodi-
`ment having mechanical bumper springs attached to the
`movable magnet.
`[0024]
`FIG. 10 shows a cross sectional view of an embodi-
`ment with a curved shape.
`
`
`
`DETAILED DESCRIPTION
`
`bumper magnets 26 are oriented such that they magnetically
`repel the movable magnet 20 (1.e., they are oppositely poled
`to the end surface of the moveable magnet whichis closest
`to the bumper magnet 26a or 265); orientation of the
`magnets 20 26 is shown by the N andS indicia.
`[0028]
`FIG. 2 shows a schematic cross sectional view of
`the vibrator device. FIG. 2 includes the optional tubular
`hollow enclosure 30. The enclosure can be cylindrical as
`illustrated, or can be square or can have othercross sectional
`shape. Preferably, the enclosure 30 is made of a lightweight
`polymeric material such as polycarbonate. Also preferably,
`the tubular enclosure hasat least one air hole 32 for allowing
`air to escape and enter the enclosure as the movable magnet
`20 oscillates. The enclosure 30 can be perforated with many
`holes. The air holes 32 reduce viscous friction losses that
`would otherwise cause damping of the magnet motion.
`However, in some applications, a valve, e.g., a plate which
`covers a portion of the air holes 32, may be provided to
`regulate the resonance of the vibrator wherein higher reso-
`nance is achieved with more open air holes and lower
`resonance is achieved with air holes being partially closed.
`Further, in some applications the movable magnetwill travel
`along the axial path in a fluid other than air where the fluid
`fills the housing 30.
`[0029]
`In addition to the air holes 32 or as an alternative,
`the bumper magnets 26 can haveair vents 40 to allow air to
`escape and enter the enclosure as the movable magnet 20
`oscillates. These air vents 40 could also be equipped with a
`valve mechanism for controlling vibratory resonance. Also
`the movable magnet can have air vents in its body orat its
`sideto let air pass from one side of the moveable magnet to
`the other has it vibrates.
`
`[0025] The present invention provides an electromagnetic
`vibratorparticularly well suited for use in portable electronic
`devices such as cell phones, toys, games, personal massage
`devices and the like. The electromagnetic vibrator has a
`movable magnet that can move in an axial direction. One or
`more electromagnetic field coils surround the movable mag-
`net. Bumper magnets are disposed on opposite ends of the
`vibrator, and constrain the axial motion of the movable
`magnet. Whenan alternating current is provided in the field
`coil,
`the movable magnet oscillates lincarly in the axial
`[0030] The total axial length of the vibrator can be about
`direction. The movable magnet rebounds from the bumper
`% inch to 1 inch, 2 inches, 10 inches or larger. Preferably,
`magnets, thereby creating vibration. This rebounding can be
`the magnets 20 26 are high strength rare earth magnets, but
`with or without actual touching of the bumper magnets
`the magnets can be made of any magnetic material or
`which are poled to repel the oncoming moveable magnet.
`magnetizable material. The shaft 22 is preferably made of a
`The movable magnet may have a toroidal shape (other
`nonferrous metal or plastic. The shaft 22 can have a solid
`shapes being possible in different applications) and may be
`cylindrical construction, or can have an I-beam, hollow
`disposed onastraight rod to linearly constrain the motion of
`tubular, or cross (i.e. +) shape. Also, the vibrator can have
`the movable magnet. The bumper magnets can be replaced
`multiple shafts positioned in parallel.
`with electromagnetic bumper coils or mechanical coil
`[0031] The field coils 28 can comprise conventional cop-
`springs.
`per wire windings; however, other metal or metal alloy
`[0026] The present vibrator is capable of reproducing
`windings may be employed. Preferably, two coaxial field
`complex applied electrical signals and frequencies, and so
`coils 28 are spaced apart, as illustrated in FIGS. 1 and 2.
`can reproduce sound and function as a loudspeaker. In
`Preferably, the field coils 28 are spaced apart by a distance
`contrast, conventional rotary-eccentric mass vibrators can
`at least as great as an axial length 29 of the movable magnet
`only modulate the output frequency by varying the rotational
`20. The field coils can be connected in series or parallel. If
`speed of the eccentric mass. Also, the current vibrator is
`the field coils are connected in series, then they should be
`simpler in construction than rotary vibrators.
`wound in opposite directions so that they produce anti-
`[0027]
`FIG. 1 showsa perspective view of an electromag-
`parallel magnetic fields.
`netic vibrator according to the present invention.Forclarity,
`[0032] A lowviscosity lubricant such assilicone oil can be
`an optional tubular enclosure is omitted from FIG. 1 and
`provided on the shaft 22 to minimize friction between the
`only the main functional components are illustrated. The
`movable magnet 20 and the shaft 22. Ferrofluid adhered to
`electromagnetic vibrator has a toroidal movable magnet 20
`the movable magnet 20 can also be used to reduce friction.
`disposed on an axial shaft 22. The axial shaft 22 extends
`Alternatively, small ball bearings or graphite particles can be
`through a central hole 23 in the movable magnet 20. The
`used to reduce friction.
`movable magnetis free to slide in an axial direction 24. Field
`coils 28a 286 wrap around the vibrator device. The field
`coils 28 have an inner diameter that is large enough to
`accommodate the movable magnet 20. Bumper magnets 26a
`265 are fixedly disposed at opposite ends of the axial shaft
`22. The bumper magnets 26 are fixed in place and are not
`free to slide on the shaft 22. All the magnets are magnetized
`in the axial direction (i.e. parallel with the shaft 22). The
`
`[0033] The vibrator can have a pickup coil 29 for moni-
`toring the position of the movable magnet 20. Electrical
`signals induced in the pickup coil by the movable magnet 20
`are detected by a sensor circuit and used to control the
`operation of a field coil driver circuit. The field coil driver
`circuit can be a conventional amplifier circuit or switching
`circuit or the like.
`
`8
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`

`

`US 2008/0001484 Al
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`Jan. 3, 2008
`
`[0034] The vibrator can be attached to a circuit board 34
`or other support with adhesive 36, as illustrated in FIG. 2.
`Also, fasteners such as bolts or screws can be used.
`[0035]
`In operation, an alternating current is provided in
`the field coils 28a 28b. Preferably, the field coils 28 are
`oriented such that they apply push and pull forces to the
`movable magnet 20. In order to provide push andpull forces,
`the field coils 28 must have anti-parallel magneticfields (e.g.
`field coils can be wound in opposite directions, as noted
`above). As the movable magnet 20 oscillates under the
`influence of the field coils 28, it repeatedly rebounds from
`the magnetic field of the bumper magnets 26. The movable
`magnet will oscillate the frequencies of the alternating
`currents applied to the field coils 28.
`[0036]
`Preferably, the alternating current applied to the
`field coils 28 has a frequency selected to match a mechanical
`resonance frequency of the movable magnet 20. Alterna-
`tively, the alternating current applied to the field coils has a
`range of frequencies that includes the mechanical resonance
`frequency of the movable magnet. Typically the resonant
`frequency and operating frequency will be in the range of
`about 10-200 Hertz. Resonant operation will tend to increase
`the amplitude of the vibrations produced by the movable
`magnet, and increase the energy efficiency and force output
`of the vibrator. The proper resonant frequency for the
`alternating current can be provided by a feedback control
`scheme employing the pickup coil 29. The movable magnet
`induces a current in the pickup coil 29, which is detected by
`a sensor and used to control the alternating current flowing
`in the field coils 28. Alternatively, the frequency of the
`alternating current can be fixed to a value matching or close
`to a known resonant frequency of the movable magnet.
`[0037] The resonant frequency of the movable magnet 20
`depends mainly on the field strength and mass of the
`movable magnet 20 and the field strength of the bumper
`magnets 26. Also, as discussed above, air within the enclo-
`sure 30 will function as an air spring in embodiments where
`the air holes 32 are not provided and the movable magnet 20
`has a close-tolerance fit inside the enclosure 30. The air
`spring will tend to increase the resonant frequency of the
`movable magnet 20.
`[0038] Also, it is noted that the electromagnetic vibrator
`can be operated such that it has a flat frequency response.
`This can be accomplished by feeding back the sensorsignal
`through an electrical control compensator that adjusts the
`alternating current amplitude to producea flat response over
`a broad frequency range. In this case, less power can be
`providedto the field coils 28 at frequencies near the resonant
`frequency. With applied power adjusted according to oper-
`ating frequency, the present vibrator can have a relatively
`flat frequency response and can be usedto provide constant-
`amplitude vibrations over a wide range of frequencies. In
`other words, the present vibrator can function essentially as
`a speaker.
`[0039]
`Preferably, the movable magnet 20 is heavier than
`the enclosure and other vibrator components. Minimizing
`the weight of the enclosure 30 and other componentsrelative
`to the movable magnet 20 will tend to increase the vibration
`forces that can be transferred, which is desirable.
`[0040] The field coils 28 are preferably driven by a
`squarewave signal. A sinusoidal waveform or triangular
`waveform or any other waveform can also be used. Pulse
`width modulated signals can also be used to drive the field
`coils.
`
`FIG. 3 shows across sectional view of an embodi-
`[0041]
`ment in which the axial shaft 22 is not present. In this case,
`the movable magnet can optionally be a solid cylindrical
`magnet (instead of a toroidal magnet), as shown. Also, in
`FIG.3 the bumper magnets 26 are toroidal, with air vents 40.
`The air vents 40 perform the same function as the air holes
`32;
`the air vents 40 allow air to enter and escape the
`enclosure 30 as the movable magnet 20 oscillates.
`[0042]
`FIG. 3a shows a cross sectional view 44 taken
`along line 42. The movable magnet 20 has tabs 38 for
`maintaining the movable magnet 20 in a central position
`within the enclosure 30. The tabs 38 tend to reducesliding
`friction between the movable magnet 20 and the enclosure
`30. The tabs 38 can be made of a fluoropolymer (e.g.
`polytetrafluoroethylene) or other low friction material. Pref-
`erably,
`in embodiments lacking the axial shaft 22,
`the
`movable magnet 20 will have 3 or 4 tabs 38 attached. Ina
`preferred implementation,the tabs 38 are peripheral portions
`of a thin, monolithic disc 39.
`In this embodiment,
`the
`movable magnet 20 can comprise two magnets. The disc 39
`will be squeezed between the magnets comprising the mov-
`able magnet 20. The disc 39 can have a central hole to
`accommodate the axial shaft 22 if the shaft 22 is present.
`Also, the tabs 38 can have a spherical shape so that they
`make point contact with the enclosure 30. Additionally, the
`tabs 38 can be replaced with ball bearings.
`[0043]
`FIG. 4 shows another embodiment having a single
`field coil 28a. The single field coil 28a can be operated so
`thatit applies both pushing andpulling forces to the movable
`magnet 20. Also, the movable magnet 20 of FIG. 4 has an
`air vent 41 for allowing air to flow past the magnet20 asit
`oscillates.
`
`In another embodiment of the present invention,
`[0044]
`the enclosure 30 is hermetically sealed and evacuated (i.e.
`the enclosure contains a vacuum or reducedair pressure). In
`this case, the energy efficiency of the vibrator will tend to be
`higher due to the reduction of viscousfriction from moving
`air.
`
`FIG. 5 shows another embodiment having bumper
`[0045]
`coils 50a 506. The bumpercoils 50 are operated to provide
`the combined functions of both the field coils 28 and the
`
`bumper magnets 26. The bumpercoils 50 are operated such
`that they apply push and pull forces to the movable magnet
`20 and cause it to oscillate. Also, the bumper coils 50 are
`powered when the movable magnet approaches so that the
`movable magnet is repelled from the field of the bumper
`coils 50. Consequently, the movable magnet 20 rebounds
`from the bumper coils 50. The bumpercoils are preferably
`operated in responseto signals received from the pickup coil
`29, as illustrated in FIG. 5. Also, it is noted that ferromag-
`netic yokes (not shown) can be used to concentrate the
`magnetic field from the bumpercoils.
`[0046]
`FIG. 6 shows another embodiment in which the
`vibrator has field coils 28a 28 and bumper magnets 26
`disposed at the axial ends of the vibrator. In this embodi-
`ment, the field coils 28 apply push and pull forces to the
`movable magnet 20, and the bumper magnets 26 repel the
`movable magnet. The operation of the vibrator of FIG.6 is
`essentially the sameas the operation of the vibrator of FIGS.
`2 or 3. The movable magnet 20 reboundsfrom the repelling
`force of the bumper magnets 26.
`[0047]
`FIG. 7 shows another embodiment in which the
`axial shaft 22 is hollow (and has hole 52). The hollow shaft
`extends completely through the entire length of the vibrator.
`
`9
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`US 2008/0001484 Al
`
`Jan. 3, 2008
`
`Thehole in the shaft 22 can be used for mounting the present
`vibrator. For example, a bolt, screw or wire can extend
`through the hole 52 for bolting or otherwise attaching the
`vibrator to a circuitboard, chassis or other fixture. The
`vibrator can be attached to objects designed to be vibrated.
`[0048]
`FIG. 8 shows another embodiment
`in which
`mechanical compression springs 60a 60b are used in place
`of the bumper magnets 26. The springs 60 can be made of
`stainless steel, phosphor bronze, resilient plastic or other
`resilient material. The springs 60 are bonded to end caps 62
`of the vibrator. Preferably, the compression springs 60 are
`nonferromagnetic. In FIG.8, the repelling force of “bumper
`magnets”is replaced by the spring force of the springs 60a
`and 608. As with the designs discussed above, the moveable
`magnetis driven towards the end caps 62 by the externally
`applied electric field. Upon impacting with the springs 60a
`or 60b,
`the springs mechanically store energy from the
`impact and then release the energy to send the moveable
`magnetic 20 in the opposite direction.
`[0049]
`FIG. 9 shows an embodiment in which compres-
`sion springs 64a 640 are attached to the movable magnet20.
`In this embodiment,
`the compression springs 64 can be
`ferromagnetic. In operation, the springs 64 cause the mov-
`able magnet to reboundafter being compressed between the
`magnet 20 and end cap 62.
`[0050] The embodiments of FIGS. 8 and 9 can also
`include an axial shaft 22. In this case,
`the compression
`springs 60 64 will be wrapped around and coaxial with the
`shaft 22.
`
`FIG. 10 shows another embodimentof the inven-
`[0051]
`tion in which the vibrator has a curved shape. The vibrator
`operates in the same manner as the linear embodiments.
`Preferably, the shaft 22 is curved.In certain applications, the
`curved embodiment of FIG. 10 may be preferred. This is
`because the curved embodimentwill producerotating vibra-
`tions in two directions. By comparison, the linear embodi-
`ments of FIG. 1-9 will produce linear vibrations in only one
`direction. ‘lwo dimensionalvibrations are preferred in appli-
`cations such as mixing anisotropic heterogeneous materials
`having properties that vary with direction.
`[0052] Also, it is noted that the curved embodiment can
`alternately have compression springs 60 64, pickup coil 29,
`bumpercoils 50, air holes 32 and other features described
`above.
`
`[0053] The present invention provides an energy efficient
`vibrator useful in many applications. The vibrations pro-
`duced by the present vibrator can be accurately oriented due
`to the linear geometry, or planar, curved geometry of the
`device. Also, the present vibrator can be scaled to very small
`or very large sizes. For example, the vibrator can be less than
`Y% or Y inch in length. Alternatively, the present vibrator can
`be 10 or 20 inches in length and produce very powerful
`vibrations. Also, the present vibrator can produce vibrations
`over a wide range of frequencies, for example in the range
`of about 1-3000 hertz.
`
`[0054] The present vibrator can be varied in many ways
`within the scope of the present invention and appended
`claims. For example, more than one movable magnet can be
`present in the vibrator. The movable magnet can comprise a
`single, monolithic magnet, or can comprise two or more
`magnets bonded or glued together. Also, a non-magnetic
`mass can be attached to the movable magnet, to increase the
`mass of the magnetand reduce the resonant frequency of the
`
`vibrator. Also, each bumper magnet can comprise multiple
`magnets or ferromagnetic yokes.
`[0055] Also, the air holes can be designed to provide an
`optimum amount of mechanical damping. Thepresentvibra-
`tor can be underdamped or overdamped, for example.
`[0056]
`It will be clear to one skilled in the art that the
`above embodiment maybe altered in many ways without
`departing from the scope of the invention. Accordingly, the
`scope of the invention should be determined by the follow-
`ing claims andtheir legal equivalents.
`1. An electromagnetic vibrator comprising:
`a) at least one movable magnet, able to move in an axial
`direction, wherein the movable magnet is magnetized
`in the axial direction;
`b) two bumper magnets disposed axially in-line with the
`movable magnet, wherein the bumper magnets are
`oriented such that they magnetically repel the movable
`magnet, and wherein the movable magnet is disposed
`between the bumper magnets; and
`c) at least one ficld coil for causing the movable magnet
`to move in the axial direction.
`
`2. The electromagnetic vibrator of claim 1, further com-
`prising at least one axial shaft, wherein the movable magnet
`has a toroidal shape with a hole, and the at least one axial
`shaft extends through the hole in the movable magnet.
`3. The electromagnetic vibrator of claim 2, wherein the at
`least one axial shaft is hollow and extends between said two
`bumper magnets.
`4. The electromagnetic vibrator of claim 1, further com-
`prising a hollow enclosure, wherein the movable magnetis
`disposed inside the hollow enclosure, and the at least one
`field coil is disposed outside the enclosure.
`5. The electromagnetic vibrator of claim 4, wherein the
`hollow enclosure has at least one air hole.
`6. The electromagnetic vibrator of claim 1, wherein the
`bumper magnets or end caps associated with said bumper
`magnets have air vents.
`7. The electromagnetic vibrator of claim 1, wherein the
`vibrator has at least two spaced apart field coils.
`8. The electromagnetic vibrator of claim 7, further com-
`prising:
`a pickup coil disposed between the at least two spaced
`apart field coils, and
`a field coil driver circuit for driving theat least two spaced
`apart field coils in response to signals from the pickup
`coil.
`
`9. The electromagnetic vibrator of claim 1, wherein the at
`least one movable magnet moves along a pathwaythat has
`a curved shape.
`10. The electromagnetic vibrator of claim 1, wherein the
`movable magnethas a toroidal shape with a hole that permits
`air flow in an axial direction.
`
`11. An electromagnetic vibrator comprising:
`a) at least one movable magnet, able to move in an axial
`direction, wherein the movable magnet is magnetized
`in the axial direction;
`b) two coils for causing the movable magnet to move in
`the axial direction, wherein the movable magnet is
`disposed between the coils.
`12. The electromagnetic vibrator of claim 11, further
`comprising at least one axial shaft, wherein the movable
`magnethas a toroidal shape with a hole, and theat least one
`axial shaft extends through the hole in the at least one
`movable magnet.
`
`10
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`10
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`

`US 2008/0001484 Al
`
`Jan. 3, 2008
`
`13. The electromagnetic vibrator of claim 12, wherein the
`axial shaft is hollow and extends to end caps at the opposite
`ends of a pathway along which said at least one moveable
`magnet is moved in said axial direction.
`14. The electromagnetic vibrator of claim 11, further
`comprising a hollow enclosure, wherein the at least one
`movable magnet is disposed inside the enclosure.
`15. The electromagnetic vibrator of claim 14, wherein the
`hollow enclosure hasat least one air hole.
`
`16. The electromagnetic vibrator of claim 11, wherein the
`ends of the hollow enclosure have air vents.
`
`17. The electromagnetic vibrator of claim 11, further
`comprising:
`a pickup coil,
`a coil driver circuit for driving the two coils in response
`to signals from the pickup coil.
`18. The electromagnetic vibrator of claim 11, wherein the
`at least one movable magnethas a toroidal shape with a hole
`that permits air flow in an axial direction.
`19. An electromagnetic vibrator comprising:
`a) at least one movable magnet, able to move in an axial
`direction, wherein the at least one movable magnetis
`magnetized in the axial direction;
`b) two compression springs disposed axially in-line with
`the movable magnet, wherein the movable magnet is
`disposed between the compression springs;
`
`c) at least one field coil for causing the movable magnet
`to move in the axial direction.
`
`20. The electromagnetic vibrator of claim 19, further
`comprising an axial shaft, wherein the at least one movable
`magnet has a toroidal shape with a hole, and the axial shaft
`extends through the holein the at least one movable magnet.
`21. The electromagnetic vibrator of claim 19, further
`comprising a hollow enclosure, wherein the movable mag-
`net is disposed inside the hollow enclosure, and theat least
`one field coil is disposed outside the hollow enclosure.
`22. The electromagnetic vibrator of claim 19, wherein the
`vibrator has at least two spaced apart field coils.
`23. The electromagnetic vibrator of claim 22, further
`comprising:
`a pickup coil disposed between the two spaced apart field
`coils, and
`a field coil driver circuit for driving the two spaced apart
`field coils in response to signals from the pickup coil.
`24. The electromagnetic vibrator of claim 19, wherein the
`movable magnethas a toroidal shape with a hole that permits
`air flow in an axial direction.
`
`11
`
`11
`
`