WO2004016041A1 - Microphone differentiel - Google Patents

Microphone differentiel Download PDF

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Publication number
WO2004016041A1
WO2004016041A1 PCT/US2002/024995 US0224995W WO2004016041A1 WO 2004016041 A1 WO2004016041 A1 WO 2004016041A1 US 0224995 W US0224995 W US 0224995W WO 2004016041 A1 WO2004016041 A1 WO 2004016041A1
Authority
WO
WIPO (PCT)
Prior art keywords
accordance
differential microphone
approximately
membrane
microphone
Prior art date
Application number
PCT/US2002/024995
Other languages
English (en)
Inventor
Ronald Miles
Sanjay Sundermurthy
Colum Gibbons
Ronald Hoy
Daniel Robert
Original Assignee
State University Of Ny Binghamton
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by State University Of Ny Binghamton filed Critical State University Of Ny Binghamton
Priority to PCT/US2002/024995 priority Critical patent/WO2004016041A1/fr
Priority to AU2002332475A priority patent/AU2002332475A1/en
Publication of WO2004016041A1 publication Critical patent/WO2004016041A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
    • H04R25/40—Arrangements for obtaining a desired directivity characteristic
    • H04R25/402—Arrangements for obtaining a desired directivity characteristic using contructional means
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
    • H04R1/38—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means in which sound waves act upon both sides of a diaphragm and incorporating acoustic phase-shifting means, e.g. pressure-gradient microphone

Definitions

  • the present invention relates to microphones and, more particularly, to a new differential microphone having improved frequency response and sensitivity characteristics .
  • the most common approach to constructing a directional microphone is provided by an apparatus comprising sound inlet ports defined by juxtaposed tubes that communicate with a diaphragm.
  • the two sides of the microphone diaphragm receive sound from the two inlet ports.
  • the sound pressure driving the rear of the diaphragm travels through a resistive material that provides a time delay.
  • the dissipative, resistive material must be designed to create a proper time delay in order for the net pressure to have the desired directivity.
  • the net pressure on the directional microphone is proportional to the frequency of the sound, and thus has a 6 dB per octave slope.
  • the net pressure is also diminished in proportion to the distance between the ports. Reducing the overall size of the diaphragm results in a proportional loss of sensitivity. It can be observed that the 6 dB per octave slope and the dependence on the distance dimension remain even in microphones devoid of the resistive material .
  • a microphone without the resistive material is normally called a differential microphone or a pressure gradient microphone.
  • Directional microphones which are commonly used in hearing aids, are normally designed to operate below the resonant frequency of the diaphragm. This causes the response to have roughly the same frequency dependence as the net pressure. As a result, the microphone output is proportional to frequency, as is the net pressure.
  • the uncompensated directional output exhibits a 6 dB per octave high pass filter shape. To correct for this frequency response characteristic, a 6 dB per octave low pass filter is incorporated in the hearing aid device, along with a gain stage. This yields a "flat" response.
  • the microphone package incorporates a switch to allow the user to select between the two response curves.
  • Hearing aid manufacturers have found it necessary to incorporate switches on hearing aids that allow users to switch to a non-directional microphone mode in quiet environments, where the directional microphone noise proves most objectionable .
  • the noise inherent in conventional, directional microphones has caused hearing aid microphone designers to use a relatively large port spacing of approximately 12 mm. This is considered to be the largest port spacing that can be used while still achieving directional response at 5 kHz, the highest frequency for speech signals .
  • Creating small directional microphones is dependent upon the product of frequency and port spacing. The distance factor indicates that sensitivity of the device is reduced as its overall size is reduced.
  • the present invention seeks a new approach to solving the aforementioned problems. It has been discovered that the mechanical structure employed in the directionally sensitive ears of the fly, Ormia ochracea, can act as a model for a hearing aid microphone having sound sensitivity without drastic amounts of frequency compensation. A diaphragm patterned after the Ormia ochracea ears is very well suited to silicon microfabrication technology.
  • the current invention provides a directional microphone having a one micron thick silicon membrane with dimensions of approximately 1mm x 2mm.
  • the directional microphone has improved sensitivity, a reduced noise level, and a frequency response that is comparable to existing high performance miniature microphones.
  • an improved directional microphone or acoustic sensor having greater sensitivity and reduced noise.
  • the directional microphone or acoustic sensor comprises a rigid, one micron thick polysilicon membrane having dimensions of approximately lmm x 2mm. The membrane is supported upon its central axis by beams having torsional and transverse stiffness.
  • the total damped area of the microphone is between approximately 1.5 and 2.5 x 10 "s m 2 .
  • the distance between centers of the two sides of the device is approximately 10 "3 m.
  • the resonant frequency in the rotational mode is in a range of between approximately 700 to 1,000 Hz, and the resonant frequency of the translational mode is in the range of between approximately 40,000 and 45,000 Hz.
  • the total mass of the device is between approximately 2.0 and 3.0 x 10 "8 kg.
  • the mass moment of inertia about an axis through the supports is in a range of between approximately 9.0 and 10 x 10 "15 kgm 2 .
  • the damping constant is in a range of between approximately 9.5 and 10 x 10 "5 N-s/m, and is designed to provide critical damping.
  • the signals from the microphone are filter compensated to achieve a flat frequency response over a range, typically between the 250 and 8,000 Hz octave bands.
  • FIGURE 1 illustrates a schematic, sectional view of a conventional directional microphone
  • FIGURE 2 depicts a graph of a measured directional hearing aid microphone response
  • FIGURES 3a and 3b show schematic, perspective and front views, respectively, of the sensing device of this invention.
  • FIGURE 3c depicts an alternate embodiment of the inventive differential microphone,-
  • FIGURE 3d depicts a perspective front view of the microphone of the invention with stiffeners and masses,-
  • FIGURE 4 illustrates a graph of the frequency response of the inventive differential microphone compared with a conventional differential microphone
  • FIGURE 5 depicts a graph of the compensation filter response of the differential microphone of this invention compared with a conventional differential microphone
  • FIGURE 6 shows a graph of the output noise of the inventive differential microphone compared to a conventional differential microphone.
  • the invention features a new, miniature acoustic sensing device or directional microphone having greater sensitivity and reduced noise.
  • the directional microphone or acoustic sensor comprises a rigid, one micron thick, polysilicon membrane having dimensions of about 1mm x 2mm. The membrane is supported upon its center by beams having torsional and transverse stiffness.
  • FIGURE 1 a schematic of a conventional directional microphone 10 is illustrated.
  • the most common directional microphone 10 has directivity in the approximate shape of a cardioid.
  • the sound inlet ports 12 and 14, respectively, are spaced a distance "d" apart, and are defined by juxtaposed tubes 16 and 18 that communicate with the diaphragm 20.
  • the two sides 22 and 24, respectively, of the microphone diaphragm 20 receive sound from the two respective inlet ports 12 and 14.
  • the sound pressure driving the rear of the diaphragm travels through a resistive material, or damping screen 26, designed to provide a time delay.
  • the dissipative, resistive material must be designed to create a proper time delay in order for the net pressure to have the desired directivity.
  • the ports which are separated by a distance d, as aforementioned, create a net pressure on the diaphragm that may be expressed as:
  • the dissipative material must be designed to create the proper time delay in order for the net pressure to have the desired directivity. If the resistive material 26 is represented by an equivalent low-pass electronic circuit, the transfer function of the material is :
  • Directional microphones are normally designed to operate below the resonant frequency of the diaphragm 20, which causes the response to have roughly the same frequency dependence as the net pressure.
  • the microphone output is proportional to frequency, as in the net pressure in equation (1.6) .
  • FIGURE 2 shows measured response of a commercially available directional microphone for hearing aids.
  • the curve labeled "low cut” corresponds to the uncompensated directional output, and exhibits a 6 dB per octave high pass filter shape.
  • a 6 dB per octave low pass filter is incorporated along with a gain stage to yield the "flat" response curve shown.
  • the microphone 10 incorporates a switch to allow a user to select between the two response curves.
  • the invention solves these problems, by using a new mechanical structure patterned after the directionally sensitive ears of the fly Ormia ochracea.
  • the new mechanical approach reduces the need for drastic amounts of frequency compensation.
  • the new diaphragm design concept is very well suited for silicon microfabrication technology.
  • a directional microphone 30 has dimensions of 1 mm x 2 mm, and has a sensitivity, noise, and frequency response that is comparable to existing high performance miniature microphones.
  • the analysis of the microphone 30 is based on a lumped parameter model in which the parameters of the structure are obtained through a detailed finite element analysis.
  • the microphone 30 has a rigid diaphragm 32 that is supported by flexible hinges 34 and 36, respectively.
  • the diaphragm 32 has two degrees of freedom. Motion can be represented by rotation about the centerline " ⁇ " and the displacement of the midpoint "x" .
  • the equations of motion are:
  • equations (II.2) the right sides of equations (II.1) become:
  • eo- L and ⁇ 2 are the resonant frequencies of the rotational and translational modes, respectively, and ⁇ x and ⁇ 2 are the damping ratios.
  • T he dashpot constant may be related to the properties of the rotational mode by: (II - 8) WW '
  • the total sensitivity is thus roughly proportional to the distance "d”, and the area “s”, and is inversely proportional to the total mass, "m” .
  • the equivalent dBA sound pressure level due to thermal noise in the ' microphone may be computed from:
  • Equation (11.16) shows that the noise is minimized by designing a structure with a low resonant frequency for rotational motion, ⁇ ⁇ .
  • the damping ratio ⁇ x should be as small as possible without resulting in unacceptable transient response. It is reasonable to design the damping in the system so that it is slightly overdamped, giving ⁇ : » 1.
  • the directivity pattern of this microphone is determined by cos ( ⁇ ) , which gives it the shape of a figure eight, as expected for a differential microphone.
  • ⁇ cos ( ⁇ )
  • the diaphragm is fabricated using a "conventional" approach so that it consists of a 1 ⁇ .m silicon membrane having dimensions 1 2 mm.
  • the displacement of the diaphragm can be approximated by:
  • ⁇ 0 is the natural frequency
  • ⁇ 0 is the damping ratio
  • s 0 is the area
  • m 0 is the total mass.
  • equation (III.5) is used to express the integral in terms of ⁇ .
  • equations (III.l) and (III.5) through (III.9) gives :
  • Microphone 30 consists of a fairly rigid diaphragm 32 supported at its center by beams 34 and 36 that have been carefully designed with torsion and transverse stiffnesses.
  • the overall dimensions are 1 mm x 2 mm, and the structure is constructed out of 1 ⁇ m thick polysilicon.
  • the total mass is m « 2.5 x 10 " ⁇ kg.
  • the resonant frequency of the rotational mode is predicted to be 830 Hz and the frequency of the translational mode is 41,722 Hz.
  • the rotational mode is the only mode having a frequency anywhere near the audible frequency range. This realizable structure thus behaves much like the idealized rigid bar depicted at the bottom of FIGURE 1.
  • the diaphragm of the conventional microphone is assumed to be a 1 ⁇ m thick polycrystalline silicon membrane having dimensions 1 x 2 mm. Both microphones thus have the same area.
  • the natural frequency of the membrane estimated using the finite element method was found to be « 10 kHz.
  • the required damping constants are well within the range of what can be achieved with the proper design of the porous back electrode .
  • Another approach to constructing a differential microphone that responds with rotational motion about its centerline is shown in FIGURE 3c.
  • the operating principle is similar to that of the structure depicted in FIGURES 3a and 3b but in this case, the microphone diaphragm 32 is supported around its entire periphery 38 rather than only at flexible hinges 34 and 36.
  • the structure 30 is designed with stiffeners 40 and masses 42, 44 that emphasize motion having a shape as shown in FIGURE 3d.
  • the two ends of the diaphragm 32 move in opposite directions and hence rock about the centerline 45.
  • each microphone 10, 30 will be compensated using a filter in order to achieve a flat frequency response over the 250 Hz through 8 kHz octave bands.
  • the output levels of these filters are adjusted so that they are equal to the maximum output of the inventive microphone at its first resonant frequency, 830 Hz.
  • the two filter responses are shown in FIGURE 5.
  • the low signal level of the conventional microphone 10 at low frequencies causes it to require over 30 dB of gain.
  • FIGURE 6 depicts both conventional and inventive microphones 10, 30 compared with respect to their noise outputs.

Abstract

L'invention concerne un nouveau dispositif de détection acoustique ou un microphone directionnel (10) présentant une sensibilité plus grande et un bruit réduit. Ledit microphone directionnel (10) ou détecteur acoustique présente une membrane (20) rigide, d'épaisseur 1 micron, en polysilicium et présente des dimensions de 1mm x 2mm. Ladite membrane (20) est supportée en son centre par des supports rigides présentant une rigidité transversale et de torsion. Le microphone différentiel (10) est utilisé dans des appareils d'aide auditive, l'équipement pour télécommunications, la technologie de l'information et des applications militaires.
PCT/US2002/024995 2002-08-07 2002-08-07 Microphone differentiel WO2004016041A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/US2002/024995 WO2004016041A1 (fr) 2002-08-07 2002-08-07 Microphone differentiel
AU2002332475A AU2002332475A1 (en) 2002-08-07 2002-08-07 Differential microphone

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2002/024995 WO2004016041A1 (fr) 2002-08-07 2002-08-07 Microphone differentiel

Publications (1)

Publication Number Publication Date
WO2004016041A1 true WO2004016041A1 (fr) 2004-02-19

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WO (1) WO2004016041A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007089505A2 (fr) * 2006-01-31 2007-08-09 The Research Foundation Of State University Of New York Microphone différentiel à micro-usinage de surface
EP1978779A2 (fr) * 2007-04-04 2008-10-08 Funai Electric Advanced Applied Technology Research Institute Inc. Unité de microphone, dispositif d'entrée de voix de proximité, système de traitement des informations et procédé de fabrication de l'unité de microphone
WO2012159217A1 (fr) * 2011-05-23 2012-11-29 Phonak Ag Procédé de traitement d'un signal dans un instrument auditif, et instrument auditif
NO333056B1 (no) * 2009-01-21 2013-02-25 Cisco Systems Int Sarl Direktiv mikrofon
US9554213B2 (en) 2012-10-01 2017-01-24 The Research Foundation For The State University Of New York Hinged MEMS diaphragm
EP3506650A1 (fr) * 2014-10-10 2019-07-03 Harman Becker Automotive Systems GmbH Reseau de microphones
US11418873B2 (en) 2020-11-03 2022-08-16 Edward J. Simon Surveillance microphone

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930560A (en) * 1974-07-15 1976-01-06 Industrial Research Products, Inc. Damping element
US4450930A (en) * 1982-09-03 1984-05-29 Industrial Research Products, Inc. Microphone with stepped response
US5878147A (en) * 1996-12-31 1999-03-02 Etymotic Research, Inc. Directional microphone assembly
US6151399A (en) * 1996-12-31 2000-11-21 Etymotic Research, Inc. Directional microphone system providing for ease of assembly and disassembly

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930560A (en) * 1974-07-15 1976-01-06 Industrial Research Products, Inc. Damping element
US4450930A (en) * 1982-09-03 1984-05-29 Industrial Research Products, Inc. Microphone with stepped response
US5878147A (en) * 1996-12-31 1999-03-02 Etymotic Research, Inc. Directional microphone assembly
US6075869A (en) * 1996-12-31 2000-06-13 Etymotic Research, Inc. Directional microphone assembly
US6134334A (en) * 1996-12-31 2000-10-17 Etymotic Research Inc. Directional microphone assembly
US6151399A (en) * 1996-12-31 2000-11-21 Etymotic Research, Inc. Directional microphone system providing for ease of assembly and disassembly
US6285771B1 (en) * 1996-12-31 2001-09-04 Etymotic Research Inc. Directional microphone assembly

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007089505A2 (fr) * 2006-01-31 2007-08-09 The Research Foundation Of State University Of New York Microphone différentiel à micro-usinage de surface
WO2007089505A3 (fr) * 2006-01-31 2008-07-10 Univ New York State Res Found Microphone différentiel à micro-usinage de surface
US7992283B2 (en) 2006-01-31 2011-08-09 The Research Foundation Of State University Of New York Surface micromachined differential microphone
DE112007000263B4 (de) * 2006-01-31 2014-05-28 The Research Foundation Of State University Of New York Differentialmikrofon, hergestellt in Mikrofertigung
EP1978779A2 (fr) * 2007-04-04 2008-10-08 Funai Electric Advanced Applied Technology Research Institute Inc. Unité de microphone, dispositif d'entrée de voix de proximité, système de traitement des informations et procédé de fabrication de l'unité de microphone
US8437490B2 (en) 2009-01-21 2013-05-07 Cisco Technology, Inc. Ceiling microphone assembly
NO333056B1 (no) * 2009-01-21 2013-02-25 Cisco Systems Int Sarl Direktiv mikrofon
WO2012159217A1 (fr) * 2011-05-23 2012-11-29 Phonak Ag Procédé de traitement d'un signal dans un instrument auditif, et instrument auditif
US9635474B2 (en) 2011-05-23 2017-04-25 Sonova Ag Method of processing a signal in a hearing instrument, and hearing instrument
US9554213B2 (en) 2012-10-01 2017-01-24 The Research Foundation For The State University Of New York Hinged MEMS diaphragm
US9906869B2 (en) 2012-10-01 2018-02-27 The Research Foundation For The State University Of New York Hinged MEMS diaphragm, and method of manufacture thereof
EP3506650A1 (fr) * 2014-10-10 2019-07-03 Harman Becker Automotive Systems GmbH Reseau de microphones
US11418873B2 (en) 2020-11-03 2022-08-16 Edward J. Simon Surveillance microphone

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