Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R7/00—Diaphragms for electromechanical transducers; Cones
  • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K13/00—Cones, diaphragms, or the like, for emitting or receiving sound in general

Definitions

• the invention relates to an acoustic transducer for broadband loudspeakers or magnetless, electrodynamic headphones for sound generation, in particular for use in the homogeneous and / or inhomogeneous magnetic field of a magnetic resonance tomograph.
• Brain performance and cardiac dysfunction are limited in their use and clinical distribution due to their high sound emissions, which can only be inadequately countered by passive measures in the low-frequency range (Journal "British Journal of Radiology”, Volume 1994, Issue 67, pages 413 to 415; Journal “Radiology”, year 1994, issue 191, pages 91 to 93 in connection with the "Recommendation of the Radiation Protection Commission, adopted in the 131st session on June 22, 1995 ", page 17). Even below the legal limits, noise emissions represent a reduction in patient comfort and communication options and thus patient safety.
• anti-noise Active noise abatement
• MRT systems Journal "Radiology”, 1989, Issue 173, pages 549 to 550 and “Proceedings of the Society of Magnetic Resonance", 1995, Issue 2, Page 1223).
• Effective noise suppression is only possible for frequencies up to about 1 kHz if the anti-noise speaker is very close to the noise source (the gradient tube inside the MRI magnet) and the anti-noise speaker can mirror the acoustic field of the interference source.
• Speakers previously designed for noise control directly in the tomograph which use the inhomogeneous part of the magnetic field for electrodynamic coupling, are only suitable up to pitches of approx. 1 kHz due to their design and can also not be installed in the homogeneous area of the magnetic field (DE 197 27 657 Cl ).
• Arrangements for canceling sound waves based on the principle of generating a signal that is phase-shifted by 180 °, have often been described outside of magnetic resonance tomography (DE 195 28 888 A 1), but can be used in the field of magnetic resonance tomography because of the existing ones Conditions are not used.
• the displacement principle on which the invention is based has already been described elsewhere, in particular by reducing the effective mass Formation of air pockets (DE 2003 950, US 4039044, US 4160883).
• the effective mass is reduced by the use of a membrane, which is suitably driven and displaces the air present in the air pockets formed.
• the desired large ratio of width to depth of the air pockets is limited here by the relatively small spatial expansion of the magnetic field.
• An important aim of the invention is to reduce the noise pollution caused by the MRI system during the examination.
• the noise insulation with passive systems e.g. earplugs
• passive systems e.g. earplugs
• Active systems consisting of a headphone system and soundproof capsules, achieve the same damping and no psychoacoustic effect weakening - on the contrary, loud music lowers the sensitivity ("Noise Covering", effect enhancement) and the ability to communicate with music is perceived as pleasant and increases comfort and lowers Dropout rate and the patient does not lose track of time when listening to music.
• Combined systems consisting of soundproof capsules and headphone systems are known and described in MRI.
• Head uterine system This system is robust and inexpensive, but it is not able to transmit low tones (below 300 Hz).
• Systems with piezo loudspeakers are also described; the above applies to these combinations, only the lower cut-off frequency is even higher here (design requires 500-800 Hz).
• Combinations with electrostatic headphones are also described and are commercially available. These systems have a frequency response that extends sufficiently deep - their acoustic properties are very good. However, you have several disadvantages.
• the combination of headphone system (capacitance) and cable (inductance) can constitute a resonant circuit that absorbs high-frequency energy from the MRI transmitter. With the usual transmission powers, the system could quickly become very hot and there is a risk of burns.
• the object of the invention is to create an acoustic transducer for broadband loudspeakers or headphones which can be used safely and reliably in the magnetic field of a magnetic resonance tomograph without interfering with the imaging, satisfies high quality requirements in a wide frequency range, enables active noise abatement and Can be produced easily and inexpensively and can be combined in the form of headphones with an earmuff.
• This object is achieved by the features in claim 1.
• Useful embodiments of the invention are contained in the subclaims.
• the invention in the form of implementation as a loudspeaker is based on the problem that the high noise levels of MRI systems can be effectively reduced by active noise abatement if a powerful antisound generator can be installed in the gradient tube of the MRI system.
• a powerful antisound generator can be installed in the gradient tube of the MRI system.
• the fact must be taken into account that the handling of magnetic materials in magnetic field flux densities used today (1 T to 3 T in clinical operation) represents an extremely great potential hazard.
• the advantages achieved by the invention are that sound with defined properties can be generated in high quality and with high efficiency within the strong magnetic field of a magnetic resonance tomograph. In addition to music and speech, this also includes the generation of sound for active noise abatement, which cannot be achieved with hose line systems and other electrodynamic transducers only in the inhomogeneous area of the magnetic field and in lower quality.
• the installation of loudspeakers can be anywhere in the magnetic resonance tomograph and thus optimally adapted to the respective purpose. This aspect is essential for use as an anti-noise speaker.
• the loudspeaker has a broad frequency band and tones above a frequency of 1 kHz can be generated.
• the principle applied of a drive that acts uniformly and uniformly on all parts of the loudspeaker membrane ensures that the bending vibrations and distortions that occur with conventional, local cone drives do not occur.
• An unprecedented large ratio of pleat depth to pleat height can be realized in magnetic resonance tomography.
• the effective mass of the loudspeaker diaphragm is therefore very low.
• the effective mass of the membrane is reduced by a factor of 420 compared to the actual mass.
• This in turn means that the acoustic rigidity of the membrane is very high and almost independent of its mechanical properties. This enables distortion-free sound radiation even at high sound pressures.
• the efficiency of sound generation is also increased since the losses due to positive and negative acceleration of the effective membrane mass are low.
• an unprecedentedly large ratio of pleat depth to pleat height can also be achieved with headphones.
• the effective mass of the transducer membrane is also very low here and the acoustic rigidity of the membrane is very high and almost independent of its mechanical properties.
• a large fold area enables the application of many electrically conductive elements, preferably flat wires, arranged in parallel.
• the conductive elements are also electrically connected in parallel and thus result in a very low ohmic resistance of the arrangement.
• the electrical losses are minimized and there is no heat development in the individual elements. This considerably increases the operational safety and the lifespan of the sound generator.
• the arrangement has the advantage over the metal strips described (DE 2003 950) that only very low eddy currents can be generated in the conductive elements by the strong alternating magnetic fields generated by an MRI scanner with a frequency of up to 1500 Hz. This in turn prevents the conductive elements from heating up and, in particular, has no disruptive influences on the magnetic gradient fields of the magnetic resonance tomograph.
• the magnetic field strengths (up to 3T) of an MRI scanner which are atypical for acoustic transducers, transmit a large driving force (Lorentz force) to the membrane firmly connected to them, even at low, auditory currents through the electrically conductive elements. This enables effective sound radiation even at low currents.
• the magnetic fields generated by these currents are correspondingly low and do not impair the homogeneity of the main field, that is, they have no disruptive influence on the imaging.
• Fig. lb the change in the membrane according to FIG. la when a current flows through the conductor tracks
• 3a a membrane with a conductor block
• 3b the change in the membrane of FIG. 3a when a current flows through the conductor tracks
• 3c shows the ratio of air pocket width to air pocket depth.
• Fig. La shows a possible embodiment in which the membrane 1, consisting of elastic, not or only weakly magnetic material, such as paper, fleece or plastic along an orthogonal or almost orthogonal axis orthogonal to the magnetic field B of the magnetic resonance tomograph in one or more folds or waves is arranged, or a corresponding arrangement is formed by several movably connected individual membranes.
• the membrane 1 consisting of elastic, not or only weakly magnetic material, such as paper, fleece or plastic along an orthogonal or almost orthogonal axis orthogonal to the magnetic field B of the magnetic resonance tomograph in one or more folds or waves is arranged, or a corresponding arrangement is formed by several movably connected individual membranes.
• one or more conductor tracks 2 are in each case connected to the membrane 1 over their entire surface and in such a manner that the direction of the conductor tracks runs parallel or almost parallel to the folding or bending axes.
• FIG. 1b shows the arrangement shown in FIG. 1a when a current I flows through the conductor tracks 2.
• the external magnetic field B of the magnetic resonance tomograph transmits a deflecting force on the conductor tracks 2, the orientation of which is determined by the direction of the current flowing through.
• a ladder arrangement as described causes the air pockets on a Side of the folded or corrugated membrane surface 4 are narrowed by conductor tracks 2 to be moved towards one another, while the air pockets located on the other side of the folded membrane are expanded.
• a hearing-frequency current leads to a simultaneous and common opening or closing of the air pockets on both sides of the folded or corrugated membrane 1.
• the pressure fluctuations caused by these movements within the swept air volume are emitted as sound waves on both sides perpendicular to the total membrane area.
• the efficiency of this arrangement is optimal if the magnetic field B of the magnetic resonance tomograph is oriented perpendicular to the folded or corrugated total membrane surface. Deviating from this geometry, whether due to the curvature or twisting of the entire arrangement or of parts thereof, reduces the efficiency without, however, questioning the functionality.
• the headphones can then be operated with an electrical power which is usually provided by headphone outputs of audio devices.
• the membrane is inserted into the earmuffs in such a way that it is almost parallel to the main field of the MRI scanner when worn.
• the remaining space in the earmuffs is filled with acoustic insulation material so that passive attenuation is retained.
• FIG. 2a shows an exemplary embodiment in which the membrane 1 is arranged in one or more folds or waves along an axis parallel or almost parallel to the magnetic field B of the magnetic resonance tomograph, or a corresponding arrangement by means of a plurality of individual membranes which are movably connected to one another is formed.
• One or more flexible conductor tracks 2 are connected flatly and firmly to the membrane 1 in such a way that the direction of the conductor tracks 2 is orthogonal or almost orthogonal to the folding or bending axes 5.
• the conductor tracks 2 attached in this way are electrically connected in parallel.
• FIG. 2b shows the arrangement shown in FIG. 2a when a current I flows through the conductor tracks 2.
• the external magnetic field B of the magnetic resonance tomograph transmits a deforming force on the conductor tracks 2, the orientation of which is determined by the direction of the current flowing through.
• a ladder arrangement as described has the effect that the air pockets on one side of the folded or corrugated membrane 1 are narrowed, while the air pockets on the other side of the folded membrane 1 are expanded.
• a hearing-frequency current leads to a simultaneous and common opening and closing of the air pockets on both sides of the folded or corrugated membrane 1. The pressure fluctuations caused by these movements within the swept air volume are emitted as sound waves on both sides perpendicular to the entire membrane range.
• the efficiency of this arrangement is optimal if the magnetic field B of the magnetic resonance tomograph is oriented perpendicular to the conductor tracks 2. Deviating from this geometry, whether due to curvature or twisting of the entire arrangement or of parts thereof, reduces the effectiveness degree of efficiency, but without questioning the functionality.
• 3a shows the effective part of an exemplary embodiment (without holder) in which the membrane 1 is arranged in one or more folds or waves along an axis orthogonal or almost orthogonal to the magnetic field B of the magnetic resonance tomograph, or a corresponding arrangement by several individual membranes which are movably connected to one another are formed.
• One or more conductors serving as supply lines 2b are connected flatly and firmly to the membrane 1 in such a way that the direction of the conductors is orthogonal or almost orthogonal to the folding or bending axes.
• one or more conductor tracks 2a are connected flatly and firmly to the membrane 1 parallel or almost parallel to the folding axis and thus orthogonally or almost orthogonally to the direction of the magnetic field B of the magnetic resonance tomograph.
• the conductor tracks 2a are electrically connected in parallel with the leads 2b on both sides of the air pocket formed by the membrane 1. The current must be supplied in such a way that one and the same electrical current flows through the conductor tracks 2a on opposite sides of the air pocket in the opposite orientation.
• a plurality of conductor tracks 2a are interconnected to form conductor track blocks 6 by means of leads 2b.
• FIG. 3b shows such an arrangement when a current I flows through.
• a force imparted by the magnetic field B when the current flows through the conductor tracks 2 causes the air pocket formed by the folded membrane 1 to be widened or narrowed.
• a hearing frequency current causes within the swept air volumens a pressure fluctuation in the same direction, which is emitted as a sound wave.
• FIGS. 3a and 3b enable a large-area and eddy current-free drive of the membrane 1 by the application of several parallel effective conductor tracks 2a. If one takes into account the large spatial expansion of the magnetic field B of the magnetic resonance tomograph compared to the dimensions of a transducer, this makes it possible to design a transducer with an additionally increased efficiency, since the efficiency-determining ratio of air pocket width a to air pocket depth b (see FIG. 3 c) can be reduced by increasing the depth b.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Magnetic Resonance Imaging Apparatus (AREA)
• Details Of Audible-Bandwidth Transducers (AREA)
• Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
• Headphones And Earphones (AREA)
• Stereophonic System (AREA)
• Diaphragms For Electromechanical Transducers (AREA)

Applications Claiming Priority (5)

Publications (2)

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• 2001
  • 2001-04-02 AT AT01929489T patent/ATE273604T1/de not_active IP Right Cessation
  • 2001-04-02 WO PCT/EP2001/003720 patent/WO2001076320A2/fr not_active Ceased
  • 2001-04-02 DE DE50103233T patent/DE50103233D1/de not_active Expired - Fee Related
  • 2001-04-02 EP EP01929489A patent/EP1273204B1/fr not_active Expired - Lifetime
  • 2001-04-02 CA CA002405436A patent/CA2405436A1/fr not_active Abandoned
  • 2001-04-02 AU AU2001256247A patent/AU2001256247A1/en not_active Abandoned
  • 2001-04-02 US US10/240,665 patent/US20030161494A1/en not_active Abandoned
  • 2001-04-02 JP JP2001573858A patent/JP2004516690A/ja active Pending

Non-Patent Citations (1)

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