Abstract:
A flexible membrane of piezoelectric material sized to be supported by and to conform to the eardrum. Electrodes on the membrane allow the membrane to function as an audio transducer stimulating the eardrum with an audio signal or detecting audio signals at the eardrum. Applications may include detecting a variety of pathophysiological and biomechanical features of the tissues of the tympanic membrane and regional integrated anatomy, detecting audio, physical and biological signals, and/or delivery a variety of therapeutic modalities.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under FA9550-08-1-0337 awarded by the USAF/AFOSR. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to nanomembrane transducers and in particular to an audio transducer that may be applied directly to the eardrum. 
     Monitoring and characterizing human body conditions, such as perceptions of pain, pressure, fluid sensations and sound perceptions, is an important aspect in many neurotology diagnosis and treatment plans. 
     With respect to hearing, understanding average and peak sound levels that are sensed (e.g., noise dosimeter) may be helpful in many cases for monitoring risks to hearing or changes in hearing and/or treating the ear (e.g., amplification, noise cancellation). An ear drum supported transducer may objectively characterize symptoms to aid diagnosis and guide treatment. For example, tinnitus is the perception of sound in the absence of a corresponding external sound source and may result from a wide range of underlying causes. 
     Objective tinnitus occurs in cases in which an actual sound is produced within the body and is audible to the patient, though practically may not be audible to the clinician. Objective tinnitus may arise, for example, from muscle spasms that cause clicks or crackling around the middle ear, as in “myoclonic tinnitus.” Other forms of objective tinnitus include, for example, “pulsatile tinnitus” in which patients experience a sound that varies with some aspect of the vascular system (arterial or venous) and which may raise concern for a variety of vascular pathologies. 
     Subjective tinnitus, on the other hand, may arise from neural mechanisms in which a perceived sound has no corresponding external or internal mechanical source. 
     Even among experienced clinicians, given the non-specific nature of a broad range of auditory and vestibular symptoms, the absence of clinical instrumentation to objectively monitor and characterize symptoms represents a fundamental barrier to accurate diagnosis and improved treatment. In other cases, understanding audio conditions may be helpful in monitoring and/or treating other disorders of the head, neck and/or other parts of the body (e.g., pulse oximeter, sleep monitor, bioassay, electrical stimulation for otalgia or headache). 
     Clinic based tests of neurotological conditions have considerable limitations, including sensitivity, specificity and reliability, and presently offer limited and temporally constrained information about physiological and non-physiological function of the auditory and vestibular system in real word conditions. As a result, discrepancies between objective findings and subjective complaints are common. The inability to correlate objective measures of physiological states, including changes in environmental and internal conditions, with subjective symptoms in real world conditions limits advances in the characterization and management of a broad range of neurotological conditions. 
     SUMMARY OF THE INVENTION 
     The present invention provides a small and lightweight audio transducer or “audio-lens” membrane at a micro or nano scale that may be placed directly on the eardrum to stimulate and sense an audio environment. The membrane may be sized to minimize interference with the normal physical properties of the conductive hearing system and to allow intimate connection with the structure that it is measuring. In particular, the membrane may be a flexible piezoelectric material that naturally generates electricity when vibrated and produces vibrations when stimulated with electricity and/or electromagnetic radiation. The membrane may operate wirelessly, or wired electrodes may be directly attached. The membrane may be sized to adhere to a portion or the whole tympanic membrane. 
     In one embodiment the invention provides an audio transducer having a piezoelectric membrane sized to be supported by and to conform to the eardrum. At least two electrodes are attached to the piezoelectric membrane to exchange audio frequency electrical energy with the piezoelectric membrane corresponding to audio vibrations of the eardrum. 
     It is thus a feature of at least one embodiment of the invention to provide an audio transducer that may intimately contact the eardrum for precise measurements of the audio environment of the eardrum. 
     The electrodes may be in an interdigitated pattern. 
     It is thus a feature of at least one embodiment of the invention to provide a simple electrode structure applied to one side of the membrane that may serve as an interface to the piezoelectric material. 
     The audio transducer may further include an antenna coupled to the membrane and the electrodes for exchanging electrical energy with the electrodes. 
     It is thus a feature of at least one embodiment of the invention to allow wireless communication with the membrane, which may avoid connecting wires or the like and possible unintended pressure from attachment of those wires. 
     The membrane may be a semiconductor and may be doped to provide for an active semiconductor device incorporated into the membrane. 
     It is thus a feature of at least one embodiment of the invention to provide a membrane that may both serve as a transducer and as a substrate for integrated circuits that may be placed on the membrane. 
     The audio transducer may further include at least one of a temperature sensor and pressure sensor supported by the membrane. 
     It is thus a feature of at least one embodiment of the invention to provide for supplemental measurements of the environment of the eardrum that may enhance diagnosis or treatment of ear related conditions. 
     The audio transducer may further include a releasable mechanical carrier attached to a periphery of the membrane for supporting the membrane during placement of the membrane on the eardrum and subsequent removal. 
     It is thus a feature of at least one embodiment of the invention to permit the membrane to be light and flexible without risk of folding over during installation. 
     The membrane may be coated with a biocompatible coating. 
     It is thus a feature of at least one embodiment of the invention to permit the membrane to be constructed of electrically desirable materials while still maintaining biocompatibility. 
     When the membrane includes an antenna, the invention may be practiced with the steps of exchanging electrical energy with the electrodes from a remote source. This energy may be radiofrequency energy which is down converted on the membrane to an audio signal to be applied to the electrodes. 
     It is thus an object of the invention to provide a simple method of electrically stimulating the membrane with an external radiofrequency source. 
     In one embodiment, radiofrequency energy may be “scavenged” and converted to DC power from the radiofrequency energy to retransmit radiofrequency energy from the membrane indicating a membrane state. 
     It is thus a feature of at least one embodiment of the invention to permit sophisticated radiofrequency communication between the membrane and external device not limited to passive electrical field detection. 
     The membrane further includes a projection extending from a broad surface of the membrane used to grasp the projection with a placement tool to locate the membrane on the eardrum and then release the same, and again grasp the projection with the placement tool to remove the membrane from the eardrum. 
     These and other objects, advantages and aspects of the invention will become apparent from the following description. The particular objects and advantages described herein may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made, therefore, to the claims herein for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective simplified view of the eardrum and ear canal showing an audio transducer of the present invention attached to the eardrum; 
         FIG. 2  is a cross-section along lines  2 - 2  of  FIG. 1  showing a piezoelectric membrane of the audio transducer having doping, surface metallization, a biocompatible coating, a removal handle, and a support ring used in various embodiments of the invention; 
         FIG. 3  is a simplified block diagram of a diagnostic system including a membrane of the present invention and an external radiofrequency transceiver for exchanging electrical energy and signals with the membrane; and 
         FIG. 4  is a block diagram of the components of some embodiments of the membrane implemented in a semiconductor in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a human eardrum  10  (the “tympanic membrane”) may span the end of an ear canal  14  for the receipt and detection of airborne audio signals through the ear canal  14  impinging on an outer surface  16  of the eardrum  10 . A rear surface  18  of the eardrum  10  may contract a malleus bone  20  for communication of vibratory signals from the eardrum  10  to an inner ear structure that may sense those signals. 
     An audio transducer  22  of the present invention provides for a thin and flexible membrane  24  that may attach directly to an outer surface  16  of the eardrum  10 , for example, through cohesive forces between a rear surface of the membrane  24  abutting the outer surface  16  of the eardrum  10 , for example, promoted by moisture or oils on the outer surface  16  of the eardrum  10 . As contacting the outer surface  16  of the eardrum  10 , the membrane  24  maintains close conformance to the eardrum  10  resulting from its substantial flexibility to vibrate with the eardrum  10  without substantial modification to the acoustic properties of the eardrum  10 . Alternative embodiments may provide other mechanisms for attachment, including micro- or nano-suction cups, or arrangements of hooks and loops. 
     In this regard, the membrane  24  may in one embodiment be a substantially circular disk having a diameter generally within the range of 0.5 millimeter to 10 millimeters, and in one embodiment substantially one millimeter, so that it may be placed on the outer surface  16  close to a center of the eardrum  10  (such as lateral to the umbo, being the most depressed part of the tympanic membrane, or draping over a substantial portion of the tympanic membrane) to experience substantial vibration while on a relatively smooth area of the eardrum outer surface  16  to which the flexible membrane  24  adheres. The membrane  24  may have a thickness of less than 1 μm and, in a preferred embodiment, a thickness of substantially 100 nm. It will be appreciated that other configurations than a circular disk may also be employed, for example a rectangular, square, trapezoidal, etc. shape, which may also advantageously reduce unwanted acoustical reflections with the membrane. 
     Referring now also to  FIG. 2 , the membrane  24  may comprise an internal piezoelectric core  26  which, for example, may be a semiconductor, such as Silicon (“Si”) or, in a preferred embodiment, may be a combination of a group III element with a group V element, such as the semiconductor compounds GaAs, InP, GaP and GaN, or a material such as PMN-PT as described in “Giant Piezoelectricity on Si for Hyperactive MEMS,” S. H. Baek, J. Park, D. M. Kim, V. Aksyuk, R. R. Das, S. D. Bu, D. A. Felker, J. Lettieri, V. Vaithyanathan, S. S. N. Bharadwaja, N. Bassiri-Gharb, Y. B. Chen, H. P. Sun, C. M. Folkman, H. W. Jang, D. J. Kreft, S. K. Streiffer, R. Ramesh, X. Q. Pan, S. Trolier-McKinstry, D. G. Schlom, M. S. Rzchowski, R. H. Blick, C. B. Eom, Science 334, 958-961 (2011); DOI: 10.1126/science.1207186, hereby incorporated by reference. Methods of fabricating thin a piezoelectric core  26  of silicon are described, for example, in U.S. Pat. Application No. 2011/0170180 to Turner et al. citing U.S. Pat. No. 6,372,609 to Aga et al, all hereby incorporated by reference. Fabricating a piezoelectric core  26  of other semiconductors is enabled by U.S. Pat. No. 7,812,353 to Yuan et a., also hereby incorporated by reference. 
     Piezoelectricity refers to the charge that accumulates in certain solid materials, such as crystals, in response to applied mechanical stress. The piezoelectric effect is a reversible process in which substrates exhibiting the direct piezoelectric effect, such as internal generation of electrical charge resulting from an applied mechanical force, also exhibit the reverse piezoelectric effect, that is, internal generation of a mechanical strain that results from an applied electrical field. 
     The piezoelectric core  26  may be doped, for example, in regions  28  and may have metallization layers  30  together to fabricate electrical components such as resistors, transistors, diodes, small inductors, capacitors and memristors in the manner of an integrated circuit using standard integration circuit fabrication techniques. The metallization layers  30  may also provide for electrodes in contact with the piezoelectric core  26  for stimulating the core as will be described to produce mechanical flexure or detecting electrical fields caused by mechanical flexure of the piezoelectric core  26 . 
     A handle  32  extending outward from a front surface of the audio transducer  22  may be attached to the piezoelectric core  26  for placement of the membrane  24  on the eardrum  10  has will be described. The piezoelectric core  26 , doped regions  28 , metallization electrodes  30  and portions of the handle  32  may all be conformably coated with a bio compatible coating  34  such as a Parylene coating preventing direct contact between non-biocompatible materials of the membrane  24  and tissue of the eardrum  10 . Alternatively this coating may be applied solely on a rear face of the piezoelectric core  26  in contact with the outer surface  16  of the eardrum  10 . 
     A carrier ring  36  may be optionally attached around a periphery of a front surface of the audio transducer  22  by a releasable adhesive to hold the otherwise flexible piezoelectric core  26  substantially flat without folding over onto itself during storage and installation. 
     Referring again to  FIG. 1 , the audio transducer  22  may be installed by grasping the handle  32  with forceps  38  (for example alligator forceps) while the carrier ring  36  is in place. Once the membrane  24  is attached to the surface of the eardrum  10 , the carrier ring  36  may be removed by outwardly peeling away extending tabs  39  on a portion of the carrier ring  36 . 
     Referring now to  FIG. 3 , in one embodiment, the metallization electrodes  30  may form a set of interdigitated but electrically separate electrodes  40  extending along a surface of the piezoelectric core  26 . Such electrodes may form one or both of an antenna structure and sensing electrodes for sensing piezoelectric activity of the piezoelectric core  26  for stimulating electrodes for stimulating piezoelectric activity of the piezoelectric core  26 . In this latter capacity, the interdigitated electrodes  40  may implement a surface acoustic wave device (“SAW”). A surface acoustic wave may be considered an acoustic wave traveling along the surface of a material exhibiting elasticity with an amplitude that typically decays exponentially with depth into the substrate. Surface acoustic waves produced in piezoelectric substrates in nano scale electromechanical systems are described in “Acoustic Waves—From Microdevices to Helioseismology,” Chapter 28 (“Surface Acoustic Waves and Nano-Electromechanical Systems,” D. J. Kreft and R. H. Blick), edited by Prof. M. G. Beghi, November 2011, which material is expressly incorporated by reference. 
     Mechanical stimulation of the piezoelectric core  26  from conducted audio vibrations energy from the eardrum  10 , in this case, may produce electrical waveforms providing outgoing radio frequency energy  42  that may be detected by a sensitive radio transceiver  44 , for example, positioned adjacent to the outer ear of the patient. Conversely, ingoing radio frequency energy  46  from the transceiver  44  may be received by the periodic structure of the interdigitated electrodes  40  to impress corresponding signals on the piezoelectric core  26  stimulating it into mechanical vibration. In this way the acoustic environment of the eardrum may be measured by audio output signals  48  received from the transceiver  44  derived from outgoing radiofrequency energy  42 , and the audio environment of the eardrum may be affected by audio waveforms  50  provided to the transceiver  44  to produce the ingoing radio frequency energy  46 . 
     Up conversion or down conversion between the outgoing radiofrequency energy  42  and  46  and the stimulation applied to the piezoelectric core  26  may be implemented by circuitry implemented on the piezoelectric core  26 . This can allow the antenna  52  to operate in the megahertz or gigahertz range, reducing antenna size while producing audible stimulation to the electrodes  54  in the range of 20 hertz to 20 kilohertz. Conversely audio stimulation of the piezoelectric core  26  may be up converted allowing transmission of such audio signals through the antenna  52  in the megahertz or gigahertz range. Such up conversion and down conversion may make use of a nonlinear element to produce frequency harmonics or standard mixing or heterodyne technology. More advanced digital techniques such as pulse code modulation and frequency modulation may also be used. 
     Referring now to  FIG. 4 , with respect to these more sophisticated signal processing techniques, it will be appreciated that the piezoelectric core  26  may support a variety of different elements including an arbitrarily designed antenna  52  produced using metallization electrodes  30  communicating with separately fabricated piezoelectric interface electrodes  54  which may be placed to produce desired modes of vibration or to detect desired modes of vibration of the piezoelectric core  26 . Active circuitry  56  may, for example, scavenge power from the antenna  52  in the manner of an RFID (radiofrequency identification) tag to power heterodyne or mixing circuitry, and/or amplifiers to mediate between the antenna  52  and the electrodes  54 . The active circuitry  56  may further include digital circuitry including analog to digital and digital to analog converting circuitry that may allow for digital communication over antenna  52  with the transceiver  44 , small amounts of computer type memory and computer processing circuitry. In this regard additional sensor circuits  58  may be placed on the piezoelectric core  26  including, for example, pressure sensors, temperature sensors, accelerometers, optical electronics and the like. Some signal processing may be provided on the piezoelectric core  26  and multiplexing capabilities to transmit or receive different signals from the ear. 
     The antenna  52  may be augmented or replaced with a photoelectric detector which may also be used to provide a source of power. Micro-Electromechanical Systems (MEMS) technology supported on the piezoelectric core may be used to produce micro sampling circuitry or drug delivery circuitry, all activated by signals received over the antenna  52 . 
     While the invention contemplates linkage using optical or radiofrequency signals, it will be appreciated that in a simplest embodiment, alternatively thin wires or conductive threads may be attached strictly to the electrodes  54  for similar purpose. 
     Together with or instead of fabricating circuitry directly on the piezoelectric core  26 , the piezoelectric core  26  may communicate with a local circuit system  60 , for example, supported by or otherwise in close proximity with the audio transducer  22  to effect additional processing and communication tasks. For example, the piezoelectric core  26  may communicate with the conventional RFID circuit resting within the ear canal  14 . 
     Generally, the present invention may operate to detect vibrations of the eardrum, which may help to diagnose tinnitus subtypes or other conditions in patients, which may help to monitor the ear and diagnose patients. Alternatively, the invention may operate to provide direct excitations of the eardrum, which may help to relieve patients of pain. In some applications the invention may replace external ear probes, such as for otoacoustic emission testing, auditory brainstem response testing, electro-cochleaography, vestibular evoked myogenic responses, and others applications. As set forth above, various embodiments of the invention may include amplifying external sounds to the ear, as in an improved hearing aid, canceling undesirable sounds to the ear, as in a treatment for tinnitus or somatosensory disturbances, pain management, or improved “earplugs,” and/or discreetly communicating with a person from a remote location, such as for military and/or security applications. Further embodiments may provide actuating elements for intelligent delivery of small medication doses to the eardrum, micro-sampling of blood, micro-sampling for drug testing and/or vital sign monitoring. 
     One or more specific embodiments of the present invention have been described above. It is specifically intended that the present invention not be limited to the embodiments and/or illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the present invention unless explicitly indicated as being “critical” or “essential.” 
     Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper,” “lower,” “above,” and “below” refer to directions in the drawings to which reference is made. Terms such as “front,” “back,” “rear,” “bottom,” “side,” “left” and “right” describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first,” “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
     When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a,” “an,” “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising,” “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     References to “a microcontroller” or “the microcontroller” can be understood to include one or more microcontrollers that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more microcontroller-readable and accessible memory elements and/or components that can be internal to the microcontroller-controlled device, external to the microcontroller-controlled device, and can be accessed via a wired or wireless network. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as coming within the scope of the following claims. All of the publications described herein including patents and non-patent publications are hereby incorporated herein by reference in their entireties.