Systems and methods for generating damped electromagnetically actuated planar motion for audio-frequency vibrations

Abstract

A vibration module for applying vibrational tractions to a wearer's skin is presented. Use of the vibration module in headphones is illustrated for providing tactile sensations of low frequency for music, for massage, and for electrical recording and stimulation of the wearer. Damped, planar, electromagnetically-actuated vibration modules of the moving magnet type are presented in theory and reduced to practice, and shown to provide a substantially uniform frequency response over the range 40-200 Hz with a minimum of unwanted audio.

1 . (canceled) 
     
     
         2 . An apparatus for imparting motion to the skin of a user, the apparatus comprising:
 a housing;   a plurality of coils capable of carrying electrical current;   a plurality of magnets arranged in operative proximity to the plurality of coils, wherein said magnets are thin relative to their length and width, and are polarized through their thinnest dimension;   a moving portion comprising an inertial mass and the plurality of magnets;   a suspension comprising a plurality of flexures that guides the moving portion in a planar motion with respect to the housing and the plurality of coils;   wherein movement of the moving portion is damped by a ferrofluid in physical contact with at least the moving portion; and   wherein the ferrofluid reduces at least a mechanical resonance within a frequency range of 40-200 Hz in response to electrical signals applied to the plurality of coils.   
     
     
         3 . The apparatus of  claim 2  wherein said housing comprises a plurality of generally flat surfaces, wherein each of said surfaces is generally parallel to another of said surfaces, and wherein at least some of said surfaces meet a plurality of adjacent surfaces at substantially right angles. 
     
     
         4 . The apparatus of  claim 3  wherein at least one pair of substantially parallel surfaces is substantially smaller than at least another pair of substantially parallel surfaces. 
     
     
         5 . The apparatus of  claim 2  wherein the housing has a length dimension in a general direction of motion of the moving portion, a thickness and a width, wherein said thickness is less than the width and less than one-third of a length, where a thickness and width are both orthogonal to a general direction of motion of the moving portion. 
     
     
         6 . The apparatus of  claim 2  wherein the housing has a length dimension in a general direction of motion of the moving portion, and a thickness dimension perpendicular to the length dimension, wherein a thickness dimension is less than one-third of a length dimension, and a thickness is less than a width. 
     
     
         7 . The apparatus of  claim 2  wherein a portion of said housing comprises at least one magnetic flux guide that is coupled to at least one coil and acts as a heat sink for said at least one coil. 
     
     
         8 . The apparatus of  claim 2  wherein said housing comprises at least one magnetic flux guide comprising a ferromagnetic material. 
     
     
         9 . The apparatus of  claim 8  wherein each said magnetic flux guide is coupled to a plurality of coils. 
     
     
         10 . The apparatus of  claim 2  wherein said housing comprises an upper magnetic flux guide and a lower magnetic flux guide. 
     
     
         11 . The apparatus of  claim 2  wherein each of said coils is an elongated oval with substantially flat sides. 
     
     
         12 . The apparatus of  claim 2  wherein each of said flexures is thinner along a motion axis of the moving portion than it is in at least a direction orthogonal to a motion axis of the moving portion. 
     
     
         13 . The apparatus of  claim 2  wherein each of said flexures is more resistant to motion transverse to a plane of the moving portion than it is to linear motion in the plane of and along a motion axis of the moving portion. 
     
     
         14 . The apparatus of  claim 2  wherein said moving portion includes at least a pocket that provides space for at least a magnet. 
     
     
         15 . The apparatus of  claim 2  wherein said apparatus is capable of producing audio frequency vibrations in response to electrical signals applied to the plurality of coils. 
     
     
         16 . The apparatus of  claim 2  wherein each of said plurality of magnets is mounted so that it has a polarity that is an opposite of the polarity of the magnet or magnets adjacent to it. 
     
     
         17 . The apparatus of  claim 2  wherein said moving portion moves relative to said plurality of coils along a plane that is orthogonal to a thickness dimension of the housing, wherein said thickness dimension is smaller than a length dimension and a width dimension. 
     
     
         18 . An apparatus for imparting motion to the skin of a user, the apparatus comprising:
 a housing or frame;   one or more conductive coils capable of carrying electrical current;   a plurality of magnets arranged in operative proximity to the one or more of the conductive coils, wherein said magnets are polarized through their thinnest dimension;   a moving portion comprising an inertial mass and the plurality of magnets;   a suspension comprising a plurality of flexures that guides the moving portion in a planar motion with respect to the housing and the one or more conductive coils;   wherein said moving portion includes at least one pocket that provides space for at least a magnet;   wherein movement of the moving portion is damped by a ferrofluid in physical contact with at least the moving portion; and   wherein the ferrofluid reduces at least a mechanical resonance within a frequency range of 40-200 Hz in response to electrical signals applied to the one or more conductive coils;   wherein the housing or frame has a thickness of less than one-third of a length dimension, where the thickness and width are both orthogonal to a direction of motion of the moving portion, and a length dimension is in a general direction of motion of the moving portion;   wherein each of said one or more conductive coils is an elongated oval with substantially flat sides; and   wherein each of said flexures is more resistant to motion transverse to a plane of the moving portion than it is to linear motion in the plane of and along a direction of motion of the moving portion.   
     
     
         19 . The apparatus of  claim 18  wherein said mechanical resonance is reduced by shearing of the ferrofluid. 
     
     
         20 . An apparatus for generating damped electromagnetically actuated planar motion, the apparatus comprising at least one vibration module, said vibration module comprising:
 a housing;   one or more coils capable of carrying electrical current;   a plurality of magnets arranged in operative proximity to the one or more coils;   a moving portion comprising an inertial mass and the plurality of magnets;   a suspension comprising a plurality of flexures that guides the moving portion in a planar motion with respect to the housing and the one or more coils;   wherein movement of the moving portion is damped by a ferrofluid in physical contact with at least the moving portion; and   wherein the ferrofluid reduces the Q-Factor of the response of the apparatus over at least a portion of a frequency range of 40-200 Hz in response to signals applied to the coil.   
     
     
         21 . The apparatus of  claim 20  wherein:
 the apparatus comprises a headphone set, said headphone set comprising a headphone bow with ear cups at opposite ends; 
 at least one vibration module coupled to at least one of the headphone bow or ear cups; and 
 the at least one vibration module guides motion of the moving portion in a plane substantially parallel to a surface of a user's head contacted by at least one of said headphone bow and said ear cups; and 
 at least one of said ear cups comprises a window that provides a view of the motion inside moving portion inside the vibration module.