Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
  • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
  • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
  • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
  • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
  • B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
  • B06B1/0662—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface
  • B06B1/067—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface which is used as, or combined with, an impedance matching layer
• • 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
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/02—Mechanical acoustic impedances; Impedance matching, e.g. by horns; Acoustic resonators

Definitions

• the invention relates to a sound transducer, in particular a
• Ultrasonic transducer with a transducer element, such as a piezoceramic disc, and an adaptation layer, such as a syntactic foam, for operation as a transmitter or receiver of ultrasonic pulses, for example in a gaseous medium, and a method for producing such a sound transducer.
• a transducer element such as a piezoceramic disc
• an adaptation layer such as a syntactic foam
• a piezoceramic transducer element can emit only a small part of the ultrasound power to the surrounding air, since the interface ceramic / air is less permeable thereto, the permeability is the lower, the greater the difference of the acoustic impedance resulting from the product of the density and the speed of sound in the respective material or medium is calculated. From the prior art, the use of one or more matching layers is known, wherein theoretically the matching layer is optimal when the
• Layer thickness is an integer multiple of a quarter of the wavelength of the sound waves in the matching layer and the acoustic
• Resistance in the matching layer is equal to the root of the product of the acoustic impedances in the adjacent media, for example, the piezoceramic disk on the one hand and the air on the other hand.
• At least one scarf labstrahl preparation has a ⁇ / 4-layer whose acoustic impedance has a value which is between the acoustic impedance of the
• ⁇ is the wavelength of the ultrasound generated in the ⁇ / 4 layer.
• the ⁇ / 4 layer is prepared by mixing glass hollow spheres with a diameter of about 0.1 mm with polystyrene varnish. After drying the paint, a foam having a pore size of about 0.1 mm and a density of about 0.3 g / cm 3 is obtained . From DE 10 2008 055 126 A1 an ultrasonic transducer for use in a fluid medium is known in which a matching body is made of a pressed or porous sintered polyimide.
• a piezoelectric or electrostrictive thin-film element is known, which can cause or detect deformations or force in the form of distortions or bending or bending.
• DE 101 35 414 C1 discloses the production of a non-flat membrane for electroacoustic transducers which has a core layer comprising polymethacrylimide foam and at least one covering layer.
• the invention has for its object to provide a sound transducer and an associated manufacturing method, with the simple way an even better adaptation of the transducer element to the
• the object is achieved by a sound transducer in which the matching element at least partially comprises a hardened bismaleimide resin, preferably the resin used consists entirely of a bismaleimide resin.
• Bismaleimide have a high temperature resistance after curing.
• the hollow bodies used for the adaptation element are embedded in the bismaleimide resin and form together with the
• Bismaleimide resin a bismaleimide resin-containing syntactic foam, which provides excellent adjustment of the acoustic impedance of the
• Transducer element such as a piezoelectric lead zirconium titanate (PZT) ceramic having a typical acoustic impedance of 3 x 10 7 kg / (m 2 s), to the acoustic impedance of air at about 4 x 10 2 kg / (m 2 ⁇ s) offers.
• PZT piezoelectric lead zirconium titanate
• the adaptation element produced in this way has significantly better properties than the previously known matching elements or ⁇ / 4 layers.
• the syntactic foam has a density of greater than 110 and less than 220 kg / m 3 , more preferably greater than 130 and less than 200 kg / m 3, and more preferably greater than 150 and less than 180 kg m 3 .
• the adaptation of the acoustic impedances is further improved.
• more than 80% of the hollow bodies, in particular more than 90%, and preferably more than 95%, of the hollow bodies are covered with a layer of the bismaleimide resin in the syntactic foam.
• the layer thickness may be less than 20 ⁇ m, in particular less than 12 ⁇ m and preferably less than 8 ⁇ m.
• the packing density of the hollow body in the foam is less than 20%, in particular less than 1 5% and preferably less than 10% lower than in the starting material of the hollow body.
• the thickness of the matching element is more than three times and less than twenty times the thickness of the matching element
• Transducer element in particular more than five times and less than fifteen times and preferably more than eight times and less than twelve times.
• Transducer element less than 0.6 mm, in particular less than 0.4 mm and preferably less than 0.25 mm.
• a syntactic foam with one or more of the aforementioned parameters leads to a very good sound conduction with a comparatively low specific weight and overall to a very good adaptation of the acoustic impedance.
• the foam and thus the adjustment element is very good heat resistance to at least 200 ° C and therefore also steam sterilizable, as well as chemical resistant and has a high rigidity.
• the adjoining the transducer element first sound coupling surface of the matching element and / or to the the
• the sound transducer according to the invention can in particular for measuring the flow velocity of a fluid, for example a
• Breathing gas mixtures are used.
• ultrasonic pulses are sent both in the direction of the flow and in the opposite direction, and the time that is necessary in each case to pass through a defined path is measured. From the duration difference, the
• Flow rate can be calculated. With operating frequencies between 100 and 500 kHz, a very high accuracy can be achieved. Ultrasound of this frequency can be generated in a simple way with the aid of a slice of piezoceramic, which is provided on the two parallel surfaces with a metallization.
• the transducer element is operated in the region of its resonant frequency, which is essentially determined by the geometric dimensions, in the case of a disc through the diameter and the thickness. If an alternating voltage is applied to the electrodes of the transducer element, this is excited to oscillate and emits sound waves. Conversely, a voltage proportional to the sound pressure can be tapped at the two electrodes when sound waves impinge on the transducer element.
• the sound transducer according to the invention not only has an optimal
• Scarf Iwandmin invention are dispensed with.
• the invention also relates to a process for the preparation of a
• Adaptation element comprising hollow bodies embedded in a bismaleimide resin.
• the bismaleimide resin may be in the form of a powder, a paste or a liquid.
• To reduce the viscosity is slurried the bismaleimide resin with a solvent and then mixed with the hollow bodies. Thereafter, the solvent is largely evaporated and the resulting paste is cured or crosslinked at temperatures of for example between 150 and 180 ° C according to the respective regulations of the resin supplier. It is advantageous if as little additional air in the foam
• the mixture is off
• an as yet uncured green compact of the matching element may be manufactured separately in a mold
• a green compact of the matching element can be placed on the transducer element and cured on this and in particular crosslinked and are simultaneously firmly connected to the transducer element.
• the ratio of the mass of the bismaleimide resin (excluding the proportion of the solvent) to the mass of the hollow bodies is more than 0.8 and less than 1.9, in particular more than 1.0, and less than 1.7 and preferably more than 1, 2 and less than 1, 5. In one embodiment, the ratio of the mass of
• Bismaleimidharz to the mass of the hollow body, which consist of hollow glass spheres, between 1, 0 and 1, 5, in particular between 1, 3 and 1, 4.
• glass hollow spheres it is possible, for example, to use those of the type K1 or K1 1, which are offered by the company 3M as "glass bubbles.”
• the "true density" of these spheres is, for example, 125 or 110 g / cm 3 .
• the packing density is 60%, which is the
• the mass ratio of resin mass to glass ball mass would theoretically have to be about 5.
• the hollow glass spheres are covered with a resin layer of a few ⁇ ⁇ thickness, in particular less than 10 ⁇ , and the packing density of about 60% is maintained, in particular, the packing density is reduced by less than 10% compared to the starting material, preferably less than 5%. If the resin layer is very thin, the attenuation of the sound in the matching element increases; with thicker resin layers, the density of the foam increases.
• the green compact is in contact with a mold element on at least two opposing surfaces. If the green compact is cured directly on the transducer element, the transducer element, in particular its surface facing the adapter element, can form one of the two mold elements. In this way, the thickness of the adjustment element can be reproducibly made very accurate reproducible in a simple manner.
• the composite of transducer element and adapter element is fixed by means of an elastomer in a housing of the sound transducer.
• the housing may for example consist of a polymer plastic, such as polyvinylidene fluoride (PVDF), and / or cup-shaped.
• PVDF polyvinylidene fluoride
• silicone rubber can be used, for example, via an opening in the bottom surface of the housing in a cavity between the bottom surface and the
• Transducer element is injected and during curing and the
• FIG. 1 shows a schematic representation of a section through a
• Fig. 3 shows a section through the inserted into a housing
• Fig. 4 shows an enlarged view of a section IV of the
• FIG. 1 shows a schematic representation of a section through an embodiment of a transducer 1 according to the invention in a not yet completely produced state.
• the sound transducer 1 has a transducer element 10, which in the embodiment by a
• piezoelectric ceramic disc is formed with a diameter of 10 mm and a thickness of 0.2 mm. The essentially of
• Diameter specific oscillation frequency of the transducer element 10 is about 200 kHz.
• an electrically conductive and preferably metallic contact layer 12, 14 is applied to the transducer element 10 in each case.
• the first contact layer 12 is electrically contacted by means of a first connecting line 16, in particular a first connecting wire is soldered.
• a second connecting line 18 can be attached to the opposite second contact layer 14, in particular soldered.
• the matching element 20 is formed of a bismaleimide resin having hollow bodies embedded therein, in particular hollow glass spheres, in the form of a syntactic foam.
• a bismaleimide resin having hollow bodies embedded therein, in particular hollow glass spheres, in the form of a syntactic foam.
• Adjustment element 20 in the state of Figure 1 is still a green, d. H. the bismaleimide resin is not yet crosslinked, so that the adjustment element 20 is not yet cured.
• the bismaleimide resin a bismaleimide adhesive of the type PX-305 from Polymerics GmbH Berlin was used
• the solution thus produced can also be used as an intermediate layer between the second contact layer 12 and the green compact of the adaptation element 20
• Glass bubbles for example "3M type K1 Glass Bubbles" are stirred into the solution, and this slurry can be poured out onto a flat dish, and after evaporation of the solvent, a layer with a thickness of, for example, 2.5 to 3 mm remains , which already has sufficient inherent stability for further processing.
• Adjustment element 20 are made or cut out and then brought into abutment with the transducer element 10.
• FIG. 2 shows a state during the production of the
• Sound transducer 1 in which the adaptation element 20 is already networked and firmly connected to the transducer element 10.
• the adjustment element 20 has two sound coupling surfaces 21, 22, wherein a sound coupling surface 21 is in close contact with the transducer element 10 and the
• Sound coupling surfaces 21, 22 preferably unprocessed.
• Adjustment element 20 in particular the lateral surface of the im
• Substantially cylindrical adapter 20 is convex.
• An electrically insulating hose is laid over the first connection line 16 in order to prevent an electrical short circuit, in particular when installing the sound transducer 1 in a housing 30.
• the housing 30 preferably consists of a Plastic.
• the two connection lines 16, 18 are led to outside of the housing 30 and there electrically contacted.
• the housing 30 is substantially pot-shaped, wherein the sound transducer 1 is inserted so far into the housing that the sound coupling surface 22 of the
• Adjustment element 20 is substantially flush with the edge of the housing 30. On one of the sound coupling surface 22nd,
• the housing 30 openings for the passage of the two connecting lines 16, 18.
• a filling compound 32 can be introduced into the cavity remaining between the transducer element 10 and the bottom surface of the housing 30, by means of which the transducer element 1 can be fixed mechanically and preferably also fluid-tightly in the housing 30.
• filler 32 for example, a silicone rubber can be used.
• the transducer element 10 is spaced from the housing 30. in the
• the arrangement for this purpose an annular gap between the transducer element 10 and the housing 30, which is filled by the filling compound 32.
• the dimension of the annular gap is not to scale in FIG. 3; in particular, the dimension of the annular gap may be smaller than shown in FIG. 3.
• the filling compound 32 is flush with the transducer element 10.
• between the adaptation element 20 and the housing 30 at least
• annular gap may be provided in sections, which is preferably also filled by the filling compound 32.
• Annular gap between the adjustment element 20 and housing 30 and a fitting of a deviating from the cylindrical shape adjustment element 20, in particular a tone shown in FIG. 2 nenförmförm
• Adjustment element 20, carried in the housing 30 with its cylindrical opening. 4 shows an enlarged view of a section IV of the adjustment element 20 in the networked state of FIG. 3.
• the hollow body 34, in the embodiment glass hollow body, are embedded in the Bismaleimidharz 36e.
• the wall 38 of the hollow body 34 is so thin that the density of the adaptation element 20 is sufficiently low in order to ensure optimum acoustic coupling of the transducer element 10 to the medium surrounding the sound transducer 1.
• Outer surface 40 of the wall 38 is covered with a preferably few ⁇ thick layer of Bismaleimidharzes 36, even in the areas in which adjacent hollow body 34 is very close or even abut each other.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Transducers For Ultrasonic Waves (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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• 2012
  • 2012-01-10 DE DE201210000275 patent/DE102012000275A1/de not_active Withdrawn
• 2013
  • 2013-01-10 WO PCT/EP2013/000054 patent/WO2013104538A2/fr not_active Ceased

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