The present invention relates to implantable auditory stimulation systems, and more particularly, to an improved bone anchored actuator/transducer that is operative to transmit sound by direct conduction through bone to the inner ear.
The utilization of implanted hearing instruments continues to increase with improving technology. Such implantable hearing instruments provide operative and cosmetic utilitarian features relative to conventional ear canal hearing devices. For example, implantable hearing devices offer operative utilitarian features in relation to patients having certain types of conductive or sensorineural hearing loss (e.g., mixed hearing loss comprising a conductive loss component of 45 dB or more with sensorineural hearing loss component of 40 dB or more). These patients are generally known to perform poorly with conventional hearing aids because their conductive and sensorineural hearing loss components are additive and these patients require substantial amounts of gain and output for proper speech recognition.
Conductive hearing loss can happen when there is a problem conducting sound waves anywhere along the route through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles) and is sometimes termed middle ear hearing loss. Sensorineural hearing loss occurs in the inner ear and/or neural pathways. In patients with sensorineural hearing loss, the external and middle ear can function normally (e.g., sound vibrations are transmitted undisturbed through the eardrum and ossicles where fluid waves are created in the cochlea). However, due to damage to the pathway for sound impulses from the hair cells of the inner ear to the auditory nerve and the brain, the inner ear cannot detect the full intensity and quality of the sound. Sometimes conductive hearing loss occurs in combination with sensorineural hearing loss. In other words, there can be damage in the outer or middle ear and in the inner ear or auditory nerve. When this occurs, the hearing loss is sometimes referred to as a mixed hearing loss.
In instances of middle ear or mixed hearing loss, bone conduction devices, such as bone anchored hearing instruments, provide an option for patients in addition to standard hearing instruments or middle and inner ear hearing instruments. Bone anchored hearing instruments utilize a surgically implanted abutment to transmit sound by direct conduction through bone to the inner ear, bypassing the external auditory canal and middle ear. Accordingly, in cases where the middle ear is damaged or deformed, bone anchored hearing instruments provide a viable hearing solution that is typically less invasive than either a middle ear hearing instrument or a cochlear implant.
Some types of bone anchored hearing instruments have a bone screw surgically embedded into the skull with a small abutment exposed though the overlying tissue/skin. An external sound processor connects onto this abutment and transmits vibrations in response to a sound signal to the abutment and hence the bone screw. The implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, thus providing hearing.
There have been attempts to produce an implantable actuator for generating the necessary vibrations where the implantable actuator can be wirelessly coupled to an external sound processor. However, to date, these attempts have resulted in actuators that provide the vibration of frequency and/or amplitude to stimulate hearing in a manner that has limited utility. For instance, provision of adequate stimulation in these systems can require excitation of a large mass to generate vibration of a magnitude necessary to simulate hearing. This is especially true at low frequencies. Displacement of such a large mass has further complicated efforts due to the high power demands of these devices. That is, as implantable devices typically require a rechargeable battery for energy storage, the power consumption demands of devices utilizing large masses has resulted in devices that do not, inter alia, have an adequate operating duration between charges.
In view of the foregoing a bone conduction actuator/transducer (BCT) (also herein referred to as a bone conduction device) which can be implantable (e.g., such as used in a active transcutaneous bone conduction device) and/or can be applied to the outside of the skin (e.g., such as used in a passive transcutaneous bone conduction device) is provided that can generate large vibrational forces while using a relatively compact mass and relatively low power consumption. In one exemplary arrangement the BCT utilizes a mechanical advantage to convert a low displacement, high force output of an actuator to a high displacement, low force output. This generates utilitarian momentum to generate an increased force without use of a relatively large mass.
An exemplary embodiment provides an implantable and/or externally attachable electromechanical transducer which can improve coupling, reduces infection, and cosmetics. At least some exemplary embodiments provide a transducer that generates a relatively large force output, and does so with relatively low power consumption. It is noted at this time that while the embodiments detailed herein are often described in terms of an implantable device, other embodiments include devices that are applied externally to the recipient. It is further noted that while embodiments detailed herein are described in terms of vibratory apparatuses that vibrate when an electrical signal is applied thereto, the teachings detailed herein and or variations thereof are applicable to apparatuses that detect vibration and output a signal indicative of the detected vibrations. Still further, it is noted that the teachings detailed herein and or variations thereof can be applicable to any device system or method that utilizes piezoelectric transducers.
According to an exemplary aspect, an implantable vibratory actuator is provided for use in a bone conduction transducer that utilizes a lever arrangement to convert a low displacement high force output of an actuator into a high displacement low force output. Specifically, the implantable vibratory actuator includes a housing having a hermetically sealed internal chamber. Disposed within the internal chamber is a lever having a first end and a second free end. The first end of the lever connects to the housing via a hinge or is fixedly interconnected thereto. In the latter regard, the lever can be a cantilever. A piezoelectric element is disposed within the internal chamber that is adapted to deform in response to an applied voltage. The deformation of the piezoelectric element is applied to the lever such that this deformation displaces the second free end of the lever. To provide a mechanical advantage/amplification, the displacement of the free end of the lever can be greater than a deformation displacement of the piezoelectric element. Further, the displacement of the free end of the lever within the internal chamber imparts a vibration to the housing.
In various arrangements, the free end of the lever can support a mass in order to provide a utilitarian momentum. Further, it will be appreciated that the length of the lever can be adjusted to increase displacement and/or velocity of the free end of the lever. In one arrangement, the displacement of the free end of the lever is at least five times the deformation displacement of the piezoelectric element. In a further arrangement, displacement of the free end is at least ten times the deformation displacement of the piezoelectric element.
In further arrangements, the free end of the lever and/or a mass supported thereon, can be designed to have a predetermined resonance frequency. In one arrangement, the resonant frequency of the free end of the lever is between about 500 Hz and 1 KHz. In a further arrangement, the resonant frequency is between about 700 Hz and about 800 Hz. It will be appreciated that in addition to such resonant frequencies, the lever can have additional resonant frequencies (e.g., harmonic frequencies).
In one arrangement, the lever is adapted to translate movement of the actuator from a first direction to a second direction. For instance, in one arrangement, the piezoelectric element can have a long axis that can be aligned with a surface (e.g., base surface and/or top surface) of the implant housing. In such an arrangement, movement of the second free end of the lever can have a component that is normal to this surface. In this regard, the lever can be a nonlinear lever (e.g., right angle or other nonlinear element) that translates movement from the first direction to a second direction. In one arrangement, movement of the free second end has a primary component that is transverse to the direction of axial expansion of the piezoelectric element. In this regard, a majority of the movement of the free second end is transverse to an axial deformation/displacement of the piezoelectric element.
In an arrangement where the first end of the lever is fixedly attached to the housing such that the lever is a cantilever, the lever can further include a flexible portion disposed between its first and second ends. In this arrangement, such a flexible portion can be defined by a connection having a reduced cross-sectional area in relation to adjacent cross-sectional areas to the lever and/or housing. In this regard, flexible portion can define a flexural hinge. In a further arrangement, this flexible portion is disposed between the interconnection of the lever to the housing and a location where the piezoelectric element applies a force to the lever. In a further arrangement, the lever includes at least a second flexible portion along its length. The second flexible portion can be disposed at a location along the length of the lever beyond the location where the piezoelectric element applies a force to the lever. The second flexible portion can define one or more resonant frequencies for the second free end of the lever. In such an arrangement, the second free end of the lever and/or any supported mass thereon can form a resonator.
In another arrangement, the piezoelectric element is interconnected to the lever such that displacement of the free second end of the lever displaces at least a portion of the piezoelectric element. In such an arrangement, a length of the lever can, in a static position, be substantially aligned with the base surface of the internal chamber. Accordingly, movement of the free second end of the lever can have a component that is normal to the base surface. In such an arrangement, the piezoelectric element can form a portion of the mass that is utilized to impart vibrations to the implant housing for hearing augmentation purposes. Accordingly, by utilizing the piezoelectric element as a portion of the mass, the overall size of the vibratory actuator can be reduced. Where the piezoelectric element is connected to the lever, the piezoelectric element can be compliantly engaged to the lever at first and second ends to permit movement between these elements.
In one arrangement, the housing, lever and piezoelectric element are all nonmagnetic materials. In this regard, an implantable bone conduction transducer incorporating these elements can be safe for magnetic resonance imaging procedures.
According to another aspect, a transverse vibratory actuator is provided that allows for translating axial motion of the piezoelectric element from a first direction to a second direction while permitting, but not requiring, amplifying that deformation. The actuator includes a housing having a base surface and a hermetically sealed internal chamber. This base surface can define a reference plane and can be adapted for positioning against a skull surface of a patient. Disposed within the internal chamber is a lever having a first end fixedly connected to the housing and a second free end. The second free end of the lever supports a mass. A piezoelectric element is disposed within the internal surface and is adapted to deform in a direction substantially aligned with the base surface in response to an applied voltage. In this regard, the deformation axis of the piezoelectric element can be substantially parallel to the base surface. The deformation displacement of the piezoelectric element applies a force to the lever to displace the second free end of the lever and the mass in a direction that is primarily normal to the base surface. In this regard, movement of the second free end of the lever has a component of movement in the normal direction that can be greater than a component of movement that is parallel to the base. The displacement of the second free end of the lever and the mass imparts a vibration to the housing.
In one arrangement, an elongated rod is interconnected to an outside surface of the housing. Accordingly, vibrations imparted on the housing can be transmitted through to this elongated rod. Specifically, such vibrations can be transmitted through the rod where it interconnects to the housing to a second free end of the rod which can be selectively positioned relative to a patient's skull. As will be appreciated, this rod or vibration extension need not necessarily be a straight shaft. In one arrangement, the elongated rod is integrally formed with the portion of the housing where it connects. Accordingly, such integral formation can enhance vibration transmissions there between.
According to another aspect, a method is provided for use in an implantable actuator of a bone conduction hearing instrument. The method includes receiving a drive signal at an implanted housing. In response to the drive signal, a voltage can be applied to a piezoelectric element within the housing to deform the piezoelectric element in a first direction. A force associated with the deformation of the piezoelectric element is utilized to displace a free end of a lever supporting a mass within the housing. The displacement of the mass is greater than the deformation displacement of the piezoelectric element. Furthermore, the displacement of the free end of the lever and the mass within the internal chamber imparts a vibration to the implanted housing. In one arrangement, the displacement of the free end of the lever and the mass is at least ten times the deformation displacement of the piezoelectric element. In a further arrangement, displacing the free end of the lever includes displacing the lever and mass in a direction that is primarily transverse to the deformation direction of the piezoelectric element. In one particular arrangement, the piezoelectric element can be adapted to deform in a direction that is substantially aligned with the surface of the skull such that the displacement of the free end of the lever and supported mass is in a direction that is primarily transverse to this movement and substantially normal to the surface of the skull.
Receiving the drive signal can include receiving a transcutaneously transmitted signal from an external speech processing unit. In such an arrangement, the drive signal can be received at an implanted coil or RF receiver. In another arrangement, the step for receiving a drive signal can include receiving a drive signal from an implanted speech processing system.
In according to another aspect, an implantable bone conduction hearing instrument is provided. The instrument includes a speech processing system that is adapted to receive acoustic signals and generate a drive signal representative of the acoustic signals. The system further includes an implantable bone conduction transducer adapted for positioning relative to a patient's skull (e.g., on a skull surface and/or within the skull). The bone conduction transducer includes a biocompatible housing that defines a hermetically sealed internal chamber. Disposed within the internal chamber is a piezoelectric element that is adapted to deform in response to the drive signal as received from the speech processing unit. In response to the drive signal, the piezoelectric element deforms and displaces a lever within the internal chamber that supports a resonant mass. In one arrangement, the displacement of the lever and mass is at least ten times the displacement of the piezoelectric element. In another arrangement, the piezoelectric element can be disposed within the internal housing such that it is aligned with the base surface of the housing, which can be adapted for positioning on, within or against the surface of the skull. In such an arrangement, the displacement of the free end of the lever and mass can be in a direction that is substantially normal to the base surface and hence normal to the skull.
Numerous additional features and utilitarian aspects of at least some embodiments of the present invention will become apparent to those skilled in the art upon consideration of the embodiment descriptions provided hereinbelow.
Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the present invention. In this regard, the following description of a hearing instrument is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention.
Implantable Bone Conduction Hearing Instrument
The housing of the BCT 200 is firmly connected to the skull as excess compliance between the BCT 200 and the skull will reduce the force to the skull, and can introduce undesirable resonances. The mounting structure will typically have at least 3 points of connection. For instance, the housing of the BCT 200 can include three or more mounting holes (not shown). Alternatively, a bracket can be utilized to affix the BCT against the surface of the skull. In any arrangement, it is typically desirable that the bottom of the BCT housing be thinly in contact with the skull at least at one point. Such firm contact provides improved vibration conduction to underlying bone.
The implantable BCT 200 can be utilized in different configurations. For instance, the BCT 200 can be incorporated into a semi-implantable bone conduction hearing instrument (BCHI) as illustrated in
The configuration of the speech processing unit depends upon the configuration of the BCHI. For instance, in the case of the semi-implantable BCHI illustrated in
processing unit that is connected (e.g., wired) to a behind the ear transmitting coil (not shown). In either case, the transmitting coil 122 of the external unit will typically include one or more magnets for retentive positioning with a receiver/transmitter (e.g., coil) 202 of the BCT 200. Typically, one magnet is located under the skin near the receiver/transmitter 202 of the BCT 200 and the other in the center of the transmitting coil 122. In any case, the coils 122 and 202 are aligned across the skin 170 of a patient for transcutaneous communication.
The microphone 120 performs the function of the outer ear. That is, the microphone 120 picks up ambient sounds for processing. The speech processor 150, based on previous fittings (e.g., drive logic 156) selects the sounds most useful for understanding speech and codes them electronically. The electronic codes or drive signals are sent back to the transmitting coil 122. The external transmitting coil 122 sends the drive signals through the skin via inductive coupling to a receiving coil 202 of the BCT. The receiver coil 202 converts the drive signals into electrical signals that are utilized by the BCT 200 to generate vibrations. It will be appreciated that each coil is capable of inductively transmitting and receiving signals and that the terms ‘receiving coil’ and ‘transmitting coil’ can be utilized for purposes of clarity and not by way of limitation. Further, it will be appreciated that the external unit can in some instances provide power to the implanted BCT 200. In such arrangements, a power management module 142 can interface with internal battery 140 and/or external battery 144 of the speech processing unit 100 to provide operating power to the BCT 200. In other arrangements, the BCT can include an implanted power storage device (e.g., battery) 244. In such an arrangement, the BCT can be periodically recharged (e.g., at night) via an external source.
An external unit 160, which includes a coil 162 for inductively coupling with the receiving coil 118 of the hearing unit 110, can be utilized to provide energy to the hearing unit 110 and/or BCT for use in recharging the battery or batteries of the hearing unit 110 or BCT, respectively. Further, the external unit can also be operative to provide programming instructions and or control instructions to the hearing unit. In this regard, the communications processor 152, which can in other embodiments be incorporated into the common processor with the signal processor 150, is operative to receive program instructions from external unit 160 as well as provide responses to the external unit 160. Various additional or different processing logic and/or circuitry components can be included in the implant housing 110 as a matter of design choice.
During operation, acoustic signals are received at the implanted microphone 122 and the microphone provides audio signals to the implantable hearing unit. The signal processor 150 processes the received audio signals to provide a processed audio signal (e.g., a drive signal) for transmission to the BCT 200. As will be appreciated, the implantable hearing unit can utilize digital processing techniques to provide frequency shaping, amplification, compression, and other signal conditioning, including conditioning based on patient-specific fitting parameters in a manner substantially similar to an external speech processing unit (e.g., 220 of
Bone Conduction Transducer Exemplary Features
As noted, the bone conductor transducer (BCT) 200 is designed to stimulate the cochlea via bone conduction. Specifically, the BCT does this by forcing the skull to shake slightly. In this regard, the BCT is a mechanical vibrator that imparts a vibration caused by controlled movement of an inertial mass within the BCT. Moving such an inertial mass (e.g., back and forth) generates a reactive force (e.g., vibration) on the case/housing of the BCT 200. Once the BCT 200 is secured to the skull of the patient, these vibrations are likewise transmitted to and through the skull to the cochlea.
A practical vibrator for use in an implantable housing in the subject to a number of real world constraints. One constraint can be that the vibrations applied to the skull need to have a minimum amplitude to induce a hearing response. Further, the size of the implant housing in which the inertial mass/vibrator is disposed is limited. That is, for subcutaneous implant positioning, it is often desirable that the thickness of the housing be less than 1 cm and more typically that the thickness be less than about 5 mm. This reduces the protuberance of the housing thereby protecting the implant from external contact and reducing cosmetic effects. Stated otherwise, the height of the implant housing above an underlying bone to which it is mounted (e.g., measured in a direction normal to a surface of the underlying bone) is limited. This limits the amplitude of movement of an inertial mass in a direction normal to the skull. In addition, the overall size if an implant housing is limited as it must mount onto and/or within a skull of a patient. Thus the size of a practical inertial mass is likewise limited.
Further complicating generation of a practical implantable bone conduction vibrator is that empirical studies show that, in bone conduction hearing, vibrations applied in a direction normal to the skull provide improved hearing response. That is, it has been observed that the normal excitation (i.e., vibrations moving perpendicular to the surface of the skull) can be more utilitarian (e.g., providing more efficiency of operation) than tangential excitation (i.e., vibrations moving across the surface of the skull). More specifically, it has been determined that vibration that is applied primarily normal to the skull (e.g., proximate to the mastoid) results in 5 to 10 dB greater patient sensitivity in comparison with vibration that is applied primarily tangential to the skull. While normal excitation is most desirable due to the improvement of 5-10 dB in patient sensitivity, measured sensitivity curves of normal and tangential excitation modes show differing peaks and notches (e.g., over a hearing frequency range) due to the different responses of the skull and/or inner/middle ear to these different vibration modes. These peaks and notches do not necessarily occur at the same frequency for normal and tangential modes. Therefore, a vibrator which simultaneously generates both normal and tangential modes will show fewer and less pronounced notches (e.g. frequencies ranges of lowered hearing response) than an implant that generates each one singly. This can be used to help flatten the frequency response of a patient so that the sound perceived is more natural-sounding. There is, therefore, no need to eliminate the tangential vibration modes, so long as the normal vibration mode is of sufficient amplitude.
An exemplary embodiment of a bone conduction vibrator generates a frequency between 700 Hz and 800 Hz with a magnitude of 7 dBN. In an exemplary embodiment, without sufficient power in this range, patients (recipients) report voices as being thin and having little perceived volume, in spite of the fact that most of the information is carried in the so-called “intelligence band” of 1-4 kHz. Thus, as a base line, it can be utilitarian to generate at least a 7 dBN force with the vibrator at low frequencies for hearing stimulation.
A mechanical vibrator often works against an inertial mass to generate a utilitarian force (e.g., reactance force) within the confines of the implant housing. Per Newton's law, the reaction force is:
In order to generate a large force, the momentum p=m*v of the inertial mass must be large. The size constraint on the mass ‘m’ means the velocity ‘v’ of the inertial mass must be large in the device. Assuming the displacement of an actuator (e.g., motor) of the mechanical vibrator is sinusoidal, the displacement can be expressed as x=xo sin(ωt+θo), where xo is the amplitude, ω=2πf, t is time and θo is the phase. Substituting this into the above, the magnitude of force is:
|F|=(2Π)2f2|mx| Eq. (2)
Accordingly, the higher the frequency for a given amplitude of an actuator or motor, the more force that can be generated. Conversely, at low frequencies, it becomes difficult to generate sufficient force unless using a large amplitude of motion and/or a large mass. Because the implant must go onto, and in some cases into, the skull of a patient, there is only a finite volume available for the mass and limited amplitude at least in a direction normal to the skull. Given that the device might be only 1 cm3 in volume, of which potentially ¼ could be utilized by a dynamic/inertial mass (that is, mass that is actively moving and generating force), the ability to generate 0 dBN=1N of force at 700 Hz, even with a tungsten mass (p=19.3 cm3; one of the densest easily available materials), can require an amplitude on the order of approximately 10 μm. In another example, in an implant housing having a diameter of 25 mm and a height of 5 mm (which is large for an implant), an inertial mass composed of tungsten filling the entire available volume would weigh 47 gm. To generate a typical target RMS force of 7 dBN (=3.1 N pk) at 700 Hz with this mass can require xo to be 3.5 μm peak displacement.
Such information can be utilitarian with respect to selecting a motor/actuator for the device in that the motor must in some embodiments generate high forces and/or significant displacement. Further, for an implantable device it can be utilitarian that the energy consumption be low to allow for rechargeable use of adequate duration. Based on these considerations, the inventor determined that generating the necessary forces electromagnetically with good efficiency led to linearity and mechanical stability problems. That is, for the force to be large with small power consumption, the gap spaces between the working spaces of a motor need to be very small utilizing previous technology. Unfortunately, large forces and ranges of motion between the working surfaces of an electromagnetic motor imply to some in the art nonlinear performance. This can give rise to a number of characteristics, such as a nonlinear spring rate due to the magnetic field that at least sometimes must be mechanically compensated. Such compensation can be difficult or impossible without sacrificing performance. Thus, most electromagnetic devices require a choice of making the motion relatively small compared to the total gap, which enforces linearity but sacrifices force, and then increase the force by reducing the electrical impedance, thus, increasing power consumption. Though use of an electromagnetic motor is feasible if power is available, it has been determined a more linear actuator is utilitarian from at least a power consumption standpoint. Some exemplary embodiments of the devices systems and methods detailed herein and/or variations thereof address or otherwise alleviate these issues in whole and/or in part.
Exemplary actuators/motors with increased linear response include magnetic shape memory alloys (MSMA), (e.g., NiMgGa) with variable magnetic fields as well as Piezoelectric transducers (PETs). Piezoelectric transducers are quite linear over their normal input voltage range, and thus free of the difficulties of nonlinear spring rates. They operate by changes in the charge distribution in their crystal lattice, and can be considered a motor module without the magnetic and alignment issues of an electromagnetic motor. An aspect with PETs is that, while the devices produce large forces, their displacements are quite small. An exemplary single layer device 3 mm high can produce a displacement amplitude of 3 μm per 150V, or 20 nm with 1V of excitation which represents a more realistic voltage in an implantable device. At 700 Hz, using such a limited displacement a device would require a mass of 2 kg to generate 1N of force. Such a size can be considered by some practicing the art, in at least some circumstances, impractical in an implanted device. So, even using an unreasonably large theoretical mass with a conventional piezoelectric transducer produces unacceptable results. Some exemplary embodiments of the devices systems and methods detailed herein and/or variations thereof address or otherwise alleviate these issues in whole and/or in part.
In order to effectively use a piezoelectric transducer, it has been determined that it is necessary to convert the very low displacement, high force output of the PET to a high displacement, lower force output. One approach is to use a stack of thin piezoelectric layers, each of which has, for example, 1V across it, but, giving a very large voltage gradient on the stack material. These devices are stacks of thin slices of PZT (piezoelectric material) One utilitarian feature of stacking is that each slice is thin, and thereby a larger V/m on the material, and hence a larger percentage strain for a given voltage per slice. When the slices are stacked, these percentage strains add up. For instance, a stack having dimensions of 5 mm×5 mm (e.g., a diameter allowing placement in an implant housing) and 20 mm in length provides a displacement of 40 μm per 200V, or 200 nm with one volt of excitation. This is 10 times what is achievable in a non-stacked device, but still might require a 200 gm mass, which is unacceptably large due to space limitations. Additionally, the PET would be approximately 20 mm long, which is too long to be accommodated in a direction normal to the skull in an implant. That is, as the direction of displacement in a piezoelectric stack is axial and a utilitarian direction of force is normal to the skull, a normally aligned PZT stack is too long to fit in a practical housing. Some exemplary embodiments of the devices systems and methods detailed herein and/or variations thereof address or otherwise alleviate these issues in whole and/or in part.
In summary, it has been determined that existing actuators including piezoelectric actuators fail to provide utilitarian displacement or, if providing the necessary displacement, are too large to be utilized in an implantable housing. Some exemplary embodiments of the devices systems and methods detailed herein and/or variations thereof address or otherwise alleviate these issues in whole and/or in part.
Bone Conduction Transducer
At least some exemplary bone conduction transducers detailed herein and/or variations thereof utilize the principle that displacement of an actuator/motor used to move an inertial mass is mechanically amplified and that this amplification can be redirected from a first direction (e.g., tangential to the skull) to a second direction (e.g., normal to the skull).
It is noted at this time that the arrangement of
While the increased displacement improves acceleration of the mass and thereby maintains a utilitarian momentum utilizing a smaller mass, use of such a leveraged displacement typically requires a hinge or a pivot 316 as illustrated in
As shown, the actuator 310 is configured to apply an axial force to the lever at a location beyond the flexural hinge 320. Stated otherwise, the flexural hinge 320 is disposed between where the proximal end 318 is fixedly interconnected to a supporting surface (e.g., implant housing etc.) and a point along the length of the lever 312 where the actuator 312 applies force to the lever 312. Such an arrangement eliminates a mechanical joint such as a multi-piece mechanical pivot or hinge and thereby provides improved focusing of the movement in a utilitarian direction and/or amplification with minimal energy losses.
While reducing the compliance of the mechanical chain (e.g., hinge/pivot) delivering force to the mass, it is utilitarian to optimize the force over a large frequency range. That is, it can be utilitarian to shape the force versus a utilitarian frequency transfer function. For instance, as noted above, increasing the force response around the 700-800 hertz frequency band can utilitarian in that it can improve patient perceived loudness. This can be accomplished by adding compliance to the mechanical chain such that the compliance reactants cancel the inertial reactants at the desired frequency. Due to the impedance transformation properties of a lever arm, the very small compliance of the piezoelectric device and its transition layers to the lever and supporting structure can be used to resonate with the inertial mass of the system. A similar approach is to place a compliant component between the pivot or flexural hinge 318 and the inertial mass 314. Such a compliant component (e.g., a second flexural hinge) can be designed to be resonant at a desired frequency. Referring to
During operation, the force (e.g., torque) generated by the actuator 310 is then delivered to the resonator, consisting of a spring (e.g., flexural hinge) and mass (mass and lever). While the PET actuator itself is not capable of generating the needed displacement of a large mass, as noted previously, it is not necessary to generate the maximum displacement at all frequencies. By using a resonator, the displacement can be maximized at around 700 Hz-1 kHz, as is consistent with the requirements for low frequency hearing intelligibility. The amplitude is optimized by designing the resonant frequency to equal frequency of maximum amplitude, and damping the resonator appropriately.
The mechanical resonance of the structure according to some exemplary embodiments can be controlled to have increased utilitarian value. It is also utilitarian to control the width of the resonance. This can be done according to at least some of the embodiments detailed herein and/or variations thereof by several mechanisms, all of which damp the resonance by dissipating some of the energy stored in the resonant mode. Other mechanisms can be utilized in other embodiments. An exemplary mechanism can include viscous damping by fluids (liquids or gases) or gels, use of “dead” materials such as malleable metals such as silver and plastic, laminated construction, constrained layers (e.g., “damping tape”), filled materials, and magnetic eddy dampers. Further the resonances of a bending beam can be controlled by shaping the end of the beam, effectively making the beam into a continuum of beams of various lengths. Additionally, mass loading the end or surface of the beam, as well as using constrained layer damping applied in patterns on the surface, can be used to deliberately damp or promote certain modes, thereby shaping the frequency response.
Finite element modeling can allow, in some embodiments, the modes to be relatively well-defined for an implant envelope. By using nonlinear fitting, a particular set of resonator qualities can be designed to fit an implant shape. This allows the outline of the implant to be conformal to a desired anatomical structure, for instance, the curvature of the skull.
An exemplary embodiment, such as the embodiment according to
As shown, a proximal end of the transverse lever arm 280 defines a footplate 282 that is interconnected to a first end of the frame by a first flexural hinge 284. In the illustrated embodiment, the transverse lever arm 280 is formed in the shape of an “L” and the piezoelectric transducer 270 applies a force to the foot plate 282 of the L-shaped lever arm. The PET 270 has a first end 272 that solidly abuts against the frame 260 of the housing 210, although in other embodiments, an end cap can be positioned therebetween. A second end 274 of the piezoelectric transducer 274 supports an end cap 276 which contacts the foot plate 282 of the L-shaped lever arm 280. In the embodiment depicted in
The tip of the end cap 276 and mating pivot recess 286 are located on the foot plate 282 at a position above the flexural hinge 284, which interconnects the foot plate 282 to the frame 260. In this regard, when the PET 270 expands upon the application or removal of an applied voltage and/or variation of the applied voltage, the end cap 276 applies a force to the end plate 282 which displaces the free end of the lever 288 and resonant mass 290 upward in relation to a bottom surface of the housing. Likewise, upon the PET 270 contracting, the free end of the lever 288 and mass 290 are permitted to move downward. In this regard, the movement of the PET 270 which is directed in a direction that is substantially aligned with the top surface 214 of the housing 210, is translated into a motion that has a primary movement direction that is normal to the top surface 214 of the housing 210.
In addition to the flexural hinge 284 disposed between the foot plate 282 and the frame 260, the long leg of the L-shaped lever arm 280 can likewise include one or more resonator hinges. These resonator hinges 292 are relatively compliant locations along the length of the lever arm that allow for generating a utilitarian resonance of the free end of the lever 288 and supported mass 290. Though shown as including a single resonator hinge 292, it will be appreciated that two or more resonator hinges or other compliant portions along the length of the lever can be incorporated into the lever arm to tailor a desired frequency response(s).
Further in this regard, a proximal end of the transverse lever arm 281 defines a footplate 285 that is interconnected to a first end of the frame by a first flexural hinge 284. In the illustrated embodiment, the transverse lever arm 281 is formed in the shape of an “L” and the piezoelectric transducer 270 applies a force to the foot plate 285 of the L-shaped lever arm. However, different from the PET 270 of the embodiment of
As can be seen from
An exemplary embodiment of an anti-backlash system utilized in the embodiment of
As can be seen from
With the above configuration in mind, in an exemplary embodiment, the piezoelectric transducer 270 is compressed during the manufacturer of the bone conduction device 800, and at least a portion of that compression is retained in the manufactured device such that the potential for backlash between the components associated with the piezoelectric transducer (the drive components) and the components associated with the transverse lever arm (the driven components) is reduced and/or eliminated. More particularly, referring back to
In an exemplary embodiment, the above results in the elimination of all backlash in the system that might otherwise be present during normal and/or abnormal expected operating environments (e.g. dropping the bone conduction device 800 from a given height, etc.) and/or the effective accommodation for any misalignment between the drive components and the driven components. For example, during all normal and/or abnormal expected operating environments, the piezoelectric transducer 270 always remains in compression (e.g. regardless of whether a voltage is applied thereto which causes the piezoelectric transducer 270 to expand and/or contract, depending on the embodiment). Still further by example, for all normal and/or abnormal expected operating environments, no part of the driven components and/or the drive components is not in contact with its adjacent component.
In an exemplary embodiment, this pre-stress imparted onto the drive components compresses the piezoelectric transducer farther than any expected displacement due to, for example, thermal expansion and/or displacement due to application of and/or removal of and/or variation of the applied voltages as detailed herein and/or variations thereof. Also, this pre-stress imparted onto the drive components compresses the piezoelectric transducer a sufficient amount such that the piezoelectric transducer always remands under effective compression during expected abnormal events such as, by way of example and not by way of limitation, the high acceleration resulting from the device being dropped from a reasonable height etc.
In an exemplary embodiment, this pre-stress is a bit more than the force developed by the piezoelectric actuator 270 during operation (e.g., about 1.01, 1.02, 1.05, 1.08, 1.1, 1.15, 1.2, 1.25, 1.4, 1.5, 1.75, or about 2 or more or any value or range of values in between any of these values). It is noted that in some embodiments, this pre-stress feature, along with the methods detailed herein and/or variations thereof, can account for tolerance issues regarding the piezoelectric transducer 270, which in some embodiments comprises a stack of piezoelectric elements.
As noted above, in an exemplary embodiment, the teachings associated with
Further along these lines,
Any device, system or method that can be used to eliminate or otherwise compensate for the moments and/or tension and/or the relief of compression applied to the piezoelectric element 270, which in some embodiments is made out of a ceramic which might be brittle, can be used in some embodiments and/or variations thereof. Further in this regard, as noted above, alternate embodiments include other devices, methods and/or systems of eliminating or reducing the effects of backlash. For example, instead of utilization of the spherical bearing and corresponding female component regime of
In yet an alternative embodiment, still referring back to
With the above teachings in mind,
It is noted that the teachings detailed herein respect to reduction and/or elimination of backlash have been presented as applied to a bone conduction device utilizing the features of the lever. Other embodiments include utilization of these teachings as applied to devices that utilize piezoelectric transducer elements that do not have the features of the lever as detailed herein and/or variations thereof. That is, in some embodiments, the anti-backlash features detailed herein can be applied to for example a bone conduction device, or other device for that matter, where the displacement of the piezoelectric element 270 results in a corresponding displacement of a mass in a 1:1 ratio or less.
As can be seen from the
Along these lines,
It is noted that the methods detailed herein and or variations thereof can include method actions prior to and or during and/or after the method actions delineated herein.
It is noted that the pre-stress detailed above can have in some embodiments the effect of increasing the resonant frequency by, for example, increasing stiffness, which can have the effect of lowering and output force at lower frequencies. In some embodiments, this may affect the utilitarian value of the resulting bone conduction device. Along these lines, this can be countered (eliminated and/or reduced) by tuning the arm. In this regard, referring to
The side arms 378A and 378B have a reduced cross section as shown in
As shown, in this embodiment, the PET 370 itself forms a portion of the mass that is utilized to apply vibrations to the housing in which such a transducer is disposed. In this regard, as the mass of the PET form part of the overall vibrating mass, the size of an inertial mass can be reduced and overall size of the transducer can be reduced.
At least some exemplary embodiments of the BCT 400 are based upon the recognition that it can be utilitarian to provide vibrations to bone structure more proximately located to the cochlea. In this regard, it has been recognized that various middle ear implant systems have been devised that allow for positioning a transducer element proximate to, for example, the ossicular chain of a patient. In such arrangements, a hole is typically formed through the mastoid of the patient in order to position to the transducer element within the tympanic cavity. One such positioning and retention apparatus is disclosed in U.S. Pat. No. 7,273,447.
In the present embodiment, the BCT 400 is adapted to be received within the interior of a positioning device 416 such that the vibration extension 410 can extend from the bottom surface of the housing 402 into the tympanic cavity and be disposed against bone structure proximate to the cochlea 250. As will be appreciated, by positioning the distal end 412 of the extension 410 against bone structure proximate to the cochlea, the magnitude of the vibrations necessary to generate adequate hearing can be significantly reduced. That is, in contrast to
The distal end 412 of the extension 410 can include a rounded engagement head for positioning against the bone surface. Alternatively, the distal end can be engaged within a pocket formed in the bone. In any arrangement, the retention apparatus 416 allows for advancing and/or retracting the BCT 400 to correctly position the distal end. Once so positioned, the retention apparatus 416 can be locked and thereby maintain the distal end 412 of the BCT 400 in contact with the patient bone proximate to the cochlea 250. Though illustrated as utilizing a long, straight extension 410, it will be appreciated that extension need not be straight. That is, the extension can have any shape that allows for desired placement proximate to the cochlea. In this regard, the distal end 410 can be applied to any appropriate location within the tympanic cavity while still reducing the distance between where the vibrations are applied to the skull and received by the cochlea.
According to at least some embodiments of the embodiment of
Power Considerations
Another consideration in the case of utilizing a PET with an implantable device is that the electrical input impedance of a PET is highly capacitive. In at least some embodiments, the amount of power it takes to generate a given force can be minimized to zero (theoretically) by making sure that the energy stored in the electrical reactances presented to the driver/actuator are recovered by the driver/actuator. This can be done with electromagnetic transducers by using a switching amplifier and recovering the energy stored in the inductance of the drive coil by returning it back to the power supply. That is, in electromagnetic drive systems, operation is inductive and as the amplifier switches between different rails and power proceeding through the actuator is recovered on opposite rails.
Accordingly, these systems can be made with near 100% efficiency. With a conventional switching amplifier, capacitive loads dissipate power with every switching cycle equal to the energy stored in the capacitance. That is, the electrical reactance of a piezoelectric motor is different from that of an electromagnetic motor. Rather than looking inductive, the piezoelectric motor looks capacitive. Likewise, previous attempt to utilize piezoelectric actuators has resulted in problems of low electrical efficiency as the piezoelectric actuator looks like a capacitor electrically.
The power loss of not recovering the stored energy is easily computed as the energy stored in the capacitance, times the number of times the capacitance is charged to that energy per second:
where E is the energy lost, f is the mean frequency of the switching amplifier charging to a supply, C is the capacitance, and V is the voltage of the supply, assuming the capacitor is charged from ground to the supply. In most implantable devices, V is around 1.25 VDC. The supply current is then:
For a switching amplifier with f=1.28 MHz, C=650 nF, Vss=1.25 VDC, I is 0.532 A, which in some circumstances can be less than utilitarian for use in an implantable device. Likewise, E could be, in some circumstances, approximately 0.5 W of power dissipation with 11 μF piezoelectric motor/actuator. Again, this power loss is too large for use in an implantable device.
Unfortunately, the phase of the current and voltage of a conventional switching power supply are not in the correct direction to recover energy stored in the capacitors, and therefore this power would be lost even using the type of switching amplifier commonly used to drive electromagnetic motors. The inventor has recognized one solution for this problem: make the piezoelectric motor look like an electromagnetic motor, at least at high frequencies. This can be done by placing a (suitably damped) inductor in series with the piezoelectric motor. At frequencies above the resonant frequency f0:
(where L is the inductance and C is the capacitance of the motor), the circuit will look inductive. The piezoelectric motor will no longer have Vss on it, but the much lower average voltage being demanded by the switching power supply. At high frequencies, the energy stored in the inductor will be returned to the power supply as in an electromagnetic motor, since it will look inductive and the current and voltages will be in the correct phase for recovery. If the inductance is selected to resonate at 8 kHz, it would have a value of
or 600 μH, a very modest-sized inductor. A simple estimate of the worst-case power loss can be estimated as about 1.28 MHz/8 kHz smaller, or 3.3 mA. This would occur only when the output is being driven at 8 kHz to maximum output, with no power at any other frequency. In practice, this number is considerably smaller when computed over the long term average speech spectrum (LTASS), although the estimate above doesn't include the switching amplifier losses or the critical damping resistor. A critical damping resistor would be
or R=30Ω for this example. This is also the minimum impedance for a series LRC circuit, with the impedance being dominated by the capacitor C at low frequencies, and the inductance L at high frequencies. For instance, at 3 kHz, the impedance will be √{square root over (81.62+30.62)}=87Ω, which is an acceptable impedance.
In summary, by putting an inductor in series with the motor, the switching amplifier sees an inductive load at high frequencies, and the change in the stored energy in the capacitance of the motor, and subsequent dissipation, is greatly reduced. Essentially, the inductance in combination with the motor capacitance form a filter which reduces the change in voltage from Vss every 640 kHz to a maximum of Vss every 16 kHz or so, a 40:1 reduction in power. This power reduction makes use of the PET actuator with an implantable device a feasible alternative to an electromagnetic actuator.
In an exemplary embodiment, the displacement of the free end of the lever is greater than a deformation displacement of the piezoelectric element by at least about two times the deformation displacement of the piezoelectric element.
In an exemplary embodiment there is an implantable vibratory actuator for use in a bone conduction hearing instrument, comprising a housing having a hermetically sealed internal chamber, wherein the internal chamber includes a lever having a first end and a free second end, a piezoelectric element adapted to deform in response to an applied voltage, wherein deformation of the piezoelectric element displaces the free second end of the lever, wherein the displacement of the free end of the lever is greater than a deformation displacement of the piezoelectric element; and wherein displacement of the free end of the lever within the internal chamber imparts a vibration to the housing.
According to an exemplary embodiment of an apparatus as detailed above and/or below, the displacement of the free end is at least five times and/or tent times and/or two times the deformation displacement of the piezoelectric element
According to an exemplary embodiment of an apparatus as detailed above and/or below, a force associated with the deformation of said piezoelectric element is mechanically applied to the lever between the first and second ends of the lever. According to an exemplary embodiment of an apparatus as detailed above and/or below, the piezoelectric element is disposed between the lever and an inside surface of the internal chamber of the housing. According to an exemplary embodiment of an apparatus as detailed above and/or below, the piezoelectric element comprises a stack of piezoelectric elements. According to an exemplary embodiment of an apparatus as detailed above and/or below, at least a portion of the piezoelectric element is displaced in conjunction with the displacement of the free end of the lever. According to an exemplary embodiment of an apparatus as detailed above and/or below, a first end of the piezoelectric element compliantly engages the lever proximate to the free second end. According to an exemplary embodiment of an apparatus as detailed above and/or below, a second end of the piezoelectric element compliantly engages a substantially non-compliant surface. According to an exemplary embodiment of an apparatus as detailed above and/or below, the first and second ends are compliantly attached to the lever and the non-compliant surface, respectively. According to an exemplary embodiment of an apparatus as detailed above and/or below, the first and second ends pivotally engage the lever and the non-compliant surface, respectively. According to an exemplary embodiment of an apparatus as detailed above and/or below, wherein the first end of the lever is connected to the substantially non-compliant surface. According to an exemplary embodiment of an apparatus as detailed above and/or below, the lever further comprises a flexible portion disposed between the first end and second end of the lever. According to an exemplary embodiment of an apparatus as detailed above and/or below, the flexible portion of the lever comprises a reduced cross-sectional area in relation to a cross-sectional area of an adjacent portion of the lever. According to an exemplary embodiment of an apparatus as detailed above and/or below, the piezoelectric element forms a portion of a vibrating mass of the vibratory actuator. According to an exemplary embodiment of an apparatus as detailed above and/or below, the housing, lever and piezoelectric element are non-magnetic materials. According to an exemplary embodiment of an apparatus as detailed above and/or below, wherein the free end of the lever arm has a resonant frequency of between 500 Hz and 1 kHz.
In an exemplary embodiment, there is an implantable vibratory actuator for use in a bone conduction hearing instrument, comprising: a housing having a base surface and a hermetically sealed internal chamber, the internal chamber including a lever having a first end fixedly connected to said housing and a free second end, wherein said second free end supports a mass, a piezoelectric element adapted to deform in a direction substantially aligned with said base surface in response to an applied voltage, wherein deformation displacement of the piezoelectric element applies a force to the lever to displace the free second end of the lever and said mass in a direction that is primarily normal to the base surface, wherein displacement of the mass within the internal chamber imparts a vibration to the housing.
According to an exemplary embodiment of an apparatus as detailed above and/or below, the apparatus further comprises an elongated rod having a first end attached to an outside surface of said housing, wherein the vibration imparted on said housing is transmitted through said rod to a free second end of said rod. According to an exemplary embodiment of an apparatus as detailed above and/or below, the displacement of said mass is greater than the deformation displacement of the piezoelectric element. According to an exemplary embodiment of an apparatus as detailed above and/or below, displacement of the mass is at least about two times the deformation displacement of the piezoelectric element.
In an exemplary embodiment, there is an implantable vibratory actuator for use in a bone conduction hearing instrument, comprising a housing having a hermetically sealed internal chamber, wherein the internal chamber includes a lever having a first end and a free second end, a piezoelectric element connected to said lever proximate to said second free end, wherein said piezoelectric element is adapted to deform in response to an applied voltage and wherein a deformation displacement of the piezoelectric element displaces the free second end of the lever and said piezoelectric element, and wherein displacement of the free end of the lever and said piezoelectric element within the internal chamber imparts a vibration to the housing.
According to an exemplary embodiment of an apparatus as detailed above and/or below, wherein the displacement of the free end of the lever is greater than the deformation displacement of the piezoelectric element. According to an exemplary embodiment of an apparatus as detailed above and/or below, in a static position, a length of the lever is substantially aligned with a base surface of said internal chamber, wherein upon displacement a direction of movement of the free second end of the lever has a primary component that is normal to the base surface. According to an exemplary embodiment of an apparatus as detailed above and/or below, a first end of the piezoelectric element compliantly engages a non-compliant surface within said housing and a second end of the piezoelectric element compliantly engages said lever.
In an exemplary embodiment, there is a method for use in implantable vibratory actuator of a bone conduction hearing instrument, comprising receiving a drive signal at an implanted housing, applying a voltage to a piezoelectric element within said housing in accordance with said drive signal to deform said piezoelectric element in a first direction, using a force associated with the deformation of said piezoelectric element to displace a free end of a lever supporting a mass within the housing, wherein the displacement of the mass is greater than deformation displacement of said piezoelectric element, wherein displacement of the free end of the lever and the mass within the internal chamber imparts a vibration to the implanted housing.
According to an exemplary embodiment of a method as detailed above and/or below, displacing the free end of the lever further comprises displacing the piezoelectric element. According to an exemplary embodiment of a method as detailed above and/or below, said drive signal represents an acoustic sound signal, wherein said imparted vibration is in accordance with said acoustic sound signal. According to an exemplary embodiment of a method as detailed above and/or below, the method further comprises receiving an acoustic signal at a sound input element, and generating said drive signal in response to said acoustic signal. According to an exemplary embodiment of a method as detailed above and/or below, said acoustic sound signal is received transcutaneously. According to an exemplary embodiment of a method as detailed above and/or below, transmitting said signal comprises transcutaneously receiving said drive signal from an external source.
In an exemplary embodiment, there is a bone conduction hearing instrument, comprising a speech processing unit operative to receive acoustic signals and generate a transducer drive signal, and an implantable bone conduction transducer operatively interconnected to said speech processing unit for receipt of said drive signal, said implantable bone conduction transducer including a housing having a hermetically sealed internal chamber, a lever, disposed within said internal chamber, having a first end and a free second end, said lever disposed in said internal chamber, a piezoelectric element, disposed within said internal chamber, adapted to deform in response to said drive signal, wherein deformation of the piezoelectric element displaces the free second end of the lever, wherein the displacement of the free end of the lever is greater than a deformation displacement of the piezoelectric element, wherein displacement of the free end of the lever within the internal chamber imparts a vibration to the housing.
According to an exemplary embodiment of a method as detailed above and/or below, said speech processing unit further comprises: a bio-inert housing, wherein said speech processing unit is adapted for subcutaneous implantation. According to an exemplary embodiment of a method as detailed above and/or below, said speech processing unit and said bone conduction transducer are operatively connected by a signal line. According to an exemplary embodiment of a method as detailed above and/or below, said speech processing unit further comprises a first coil and said bone conduction transducer further comprises a second coil, wherein said first and second coil are adapted for transcutaneous communication. According to an exemplary embodiment of a method as detailed above and/or below, said bone conduction transducer further comprises an energy storage device wherein said energy storage device provides energy to said piezoelectric element.
The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain known modes of practicing the invention and to enable others skilled in the art to utilize the invention in such or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
The present application claims priority to U.S. Provisional Patent Application No. 61/567,846, entitled Implantable Electromechanical Transducer With Mechanical Advantage, filed on Dec. 7, 2011, naming Scott Miller, Travis Andrews, Robert McCullogh and Farid Moumane as inventors. The entire contents of this application is incorporated herein by reference in its entirety.
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Number | Date | Country | |
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20130197298 A1 | Aug 2013 | US |
Number | Date | Country | |
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61567846 | Dec 2011 | US |