FR2618283A1 - ACOUSTIC PRESSURE SENSOR INSENSITIVE TO THE EFFECTS OF THE WIND. - Google Patents

Abstract

The sensor 1C comprises a detection member 2C sensitive to pressure and connected to electrical means 3 for delivering an electrical signal indicative of the pressure sensed by the detection member 2C, the assembly consisting of the detection member and the electrical means being housed in a body 4C aerodynamically profiled along at least one privileged axis XX 'of said body and the detection member 2C having an axis of symmetry YY' substantially perpendicular to said privileged axis. The detection member 2C is separate from the electrical means 3, the latter being housed next to the latter inside the aerodynamic body 4C and in that the thickness of the body measured along the axis of symmetry YY 'of the detection member does not substantially exceed the height of this member. Application to the measurement of noise in a free field.

Description

The present invention relates to an acoustic pressure sensor

including means of protection

against the effects of the wind.

  The invention also relates to an acoustic antenna produced by means of a sensor mentioned above. The Applicant has been confronted with the need to measure, in a free field, relatively low acoustic pressures, corresponding to a noise of the order of 50 dB. The first experiments carried out showed the strong influence of the wind on these measurements. In view of this first observation, the Applicant has carried out additional measurements in the laboratory consisting in shouting around a sound pressure sensor a silent air flow of infinite speed. These experiments revealed two causes of parasitic signals emitted by the sensor, namely: on the one hand the pressure due to the flow of air around the sensor and on the other hand the vibrations induced by this flow on the sensor support and on the sensor itself. These spurious signals correspond to a parasitic noise of about 90 dB for a wind of 16m / s. It is therefore necessary to eliminate these disturbing effects. Wind sensor protections are already known. It is a rollover surrounding the sensor and whose conformation depends on the direction of the wind. If this direction is known, for example parallel to a fixed plane, the cowling tends to improve the aerodynamics of the sensor in the form of a cone or a disk. If the wind direction is a priori any, an absorbent material is placed around the sensor to reduce the wind speed in the vicinity of the sensitive region of its

detection organ.

  Furthermore, known sensors mounted in a cowling of the aforementioned type comprise a detection member such as a diaphragm cooperating with a piezoelectric element and electrical circuits, these elements being superimposed in a single block placed in the center of the cowling. This arrangement is disadvantageous because it involves a thick rollover offering greater wind resistance and generating a large torque master. In addition, the high inertia of the assembly formed by the sensing element and the associated circuits generates parasitic vibrations which disturb

  the measurements made by the sensor.

  The parasitic noise generated by a flow of air or wind on a profiled aerodynamic body comprises three components: a principal component called dipole, generated by the stresses exerted by the fluid on the body and still called load noise, a so-called secondary component monopolar, due to the displacement of a certain volume of fluid bypassing the body and still called thickness noise, and a negligible component called quadrupole, located in the air streams surrounding the body and caused by their sectional variation. The above-mentioned cowlings do not make it possible to reduce load and thickness noises effectively.

supra.

  Other tests have shown that the wind generates vibrations inside the sensor which move the constituent elements of this sensor in relation to each other and thereby cause mechanical stresses on the sensitive element of this sensor. This results in the appearance of additional noise. This phenomenon is all the more important since the freedom of movement of said constituent elements is large and the inertia of the assembly constituted by the sensing element of the sensor and the mechanically integral elements of this sensitive element is close to inertia.

  elements connected elastically to said assembly.

  The object of the present invention is to propose an acoustic pressure sensor whose free-field measurements are not influenced by the effects of the wind or of an air flow, that is to say for which the sounds of load and thickness and the effects of wind-induced vibration on its constituent elements are

reduced to a minimum.

  The invention thus aims at an acoustic pressure sensor comprising a pressure-sensitive sensing element and connected to electrical means for delivering an electrical signal indicative of the pressure sensed by the sensing element, the assembly consisting of detection member and the electrical means being housed in a streamlined body aerodynamically along at least one preferred axis of said body and the sensing member having an axis of symmetry substantially perpendicular to said preferred axis. According to the invention, this sensor is characterized in that the detection member is separated from the electrical means. the latter being housed next to it inside the aerodynamic body and in that the thickness of the body measured along the axis of symmetry of the detection member does not substantially exceed the height of this body. Because the electrical means of the sensor are separated from its sensor member and housed inside the aerodynamic body, next to this detection member. this significantly reduces the volume of the aerodynamic body which significantly reduces the noise of

  charge while substantially reducing the sound of thickness.

  Indeed, the aerodynamic profile of the body is optimized by minimizing its drag and lift, so that it is also less sensitive to wind-induced vibrations. Furthermore, by mechanically decoupling the electrical means of the detection member, the mechanical stresses imposed by the first on the second are avoided. According to an advantageous characteristic of the invention, the conductors connecting the detection member to the electrical means are metal conductors

flexible or optical fibers.

  This minimizes the mechanical forces exerted

2618 2 8 3

  by the aforementioned conductors on the sensing element.

  According to another advantageous characteristic of the invention, the material constituting the aerodynamic body is a good vibration damping material in the frequency range measured by the sensor, such as a

polycarbonate resin.

  This prevents the formation of a parasitic noise due to the vibrations induced by the action of the wind on the sensor. Preferably, the aerodynamic body is shaped as a tapered cylinder at least one of its ends in a known wind direction, parallel to a given axis, or in a saucer whose edges are profiled in a known wind direction parallel to a

determined plan.

  This contributes to the reduction of parasitic noise mentioned in the introduction of this

  description thanks to a profile optimization

aerodynamic sensor.

  Other features and benefits of

  the invention will emerge again from the description which will

  to follow. In the accompanying drawings given by way of nonlimiting examples: FIG. 1 is a diagrammatic view in longitudinal section of a first embodiment of the invention, FIG. 2 is a schematic view from above of a second form. 3 is a diagrammatic longitudinal sectional view of a third embodiment of the invention, FIG. 4 is a longitudinal section of an industrial embodiment of the invention, FIG. Fig. 6 is a sectional view of the embodiment of Fig. 4; Fig. 6 is a section on the plane VI-VI of the CA-A axel ap UOTlqadJp el suep asJino es quelTwT

  ue 9 aue-qwaw el ap soo40 xne amue; sTsgJ el asTjo ^ e-

  ToiJed el V sgTJdoJdde suaAow sno4 jed a9xT + lsa Tnb 8 aseqwao, Sú anbTuoz awjo. ap 4uawale6 'sanOioeue No. anbTq; UAS aJqT4ew ua' 8 aseqwa aun Jins anddes 9 aueJqwaw a4a3 sdjo b = np L toejwd el suep Quej ^ No; a, A-A zaAe npuo * UO 4SA axis ,; uop anbiuom awJo + ap 9 uoimagp p ap aueJqwaw aun puaJdwao II -anbiilalgazgd adAq np lsa z uoi4zaqp ap o0 aue6jo ,! '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' ' , ap a3nep la ded de ssao SZ luelq siaiujap sao e sanbxjmsalg suaAow sap giedgs 3sa z uo $ T33ap Sp ap auejojo 'uox; uaAu1e; uawewJo + uo3 X- X axel V aJxelnmtpuadJad - o js, AA axJqgwAs ap axis uos anb iz ap [[[a a a a a a a a a a a axe axe axe axe axe axe axe axe 93 [[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93 93uasgidad aTdwaxal suea b 'sdJo am ap 9T69'y ^ $ Jd axis a uae uwanbiweuApoige 9Tx + ojd b sdJioa IF a suep 96ol lsa ú sanbij- = alg suaAow sal the z uoi4maqp ap aue6oo Jed gnrlrsuoz alqwasuaj Z uomzaqp ap aue6do. ! jed a; dez uoissaud el ap + x; emipui anbTJ;, alg Teu6is a 'sanuuom awgw-alla ua a. qxuew ap dSaj ^ xlep.nod snouuom ú sanbiJ; 4mal suaAow sap V1l1a; aIsawl uiissaid OT and the aiqisuas z uorz) a; p ap aue6o a puaidwoD) Jna4dem ame aJn6F el q; uawanbt; ewgqms a; Juow ' qua ^ ux uo $ a; uasgid el 4UE ins ^ r $ anb lsnome uoissaid ap Jnaldem a, p uo; w4esle9J awJo ap + adxwaid aun Sueo uoluaAut, 1 V awJoijuo anbi4sno> e auuaue S

  aunp anbx; ewgqms an ^ aun 4sa 8 aJn6x el -

a b aJn6ii. el

  ap IFe; 4p unp eapuei6e an ^ aun% its e aJn6t + el -

  eb aJn6i + ap ap S verte of the conical base 8 transmits the deformations of the membrane 6 to a beam 9 transmission of forces disposed along the axis YY 'and it-mime bears on an element 10 of piezoelectric material. The element 10 is mounted in support on a support 11, for example annular if the element 10 is a circular pellet, integral with the wall 7 and providing between the element 10 and the wall 7 a cavity 11a connected to the free air through a channel 12. The cavity 11a and the channel 12 and allow the deformation of the piezoelectric element 10 during the displacement of the membrane 6, the latter generating an electrical signal indicative of this deformation and therefore the

  pressure applied to the membrane 6.

  The detection member 2 is composed of the conical elements 6 and 8, the beam 9 and the piezoelectric element 10. This assembly is housed in a cylindrical cavity 2a of the body 4. The thickness E of the body 4 hardly exceeds the height of the sensing element 2 measured

the Y-Y axis.

  The element 10 is connected to the electrical means 3 by flexible conductors 13 such as metal conductors or optical fibers, for example running in channels 14 formed in the wall 7 of the body 4. These channels 14 and connect the element 10 and cavities 15 formed in the body 4 on either side of the sensing member 2. After placing the means 3, these cavities are filled with a dense material and good damping vibrations such as epoxy resin which immobilizes the means 3. The electrical means 3 are for example electronic circuits adapters or charge amplifiers known in themselves and connected to an external signal processing circuit (not shown) by conductors 16 through the wall 7 by a channel 17 arranged

in this one.

  The circuits 3 make it possible to measure and amplify the electrical voltage generated by the deformation undergone by the piezoelectric element 10 under

  the effect of the pressure exerted on the membrane 6.

  The body 4 itself is preferably made of a dense material and good vibration damper such as lead or polycarbonate. The detection member 2 may be of the capacitive, film-like or

  with optical fibers instead of being of the piezoelectric type.

  The sensor 1 described in FIG. 1 is intended to be placed in an air flow of known direction parallel to the axis XX 'of this sensor and indicated by the arrow F or F' in FIG. the electronic circuits 3 on either side of the sensing element 2 makes it possible to reduce the thickness E of the sensor 1 and consequently to produce a body 4 whose aerodynamic profile is optimized. The tapered ends 5 of the body 4 also contribute to this optimization so that the parasitic load and thickness noises induced by the effects of an air flow such as wind are minimized. The choice of dense materials and shock absorbers for the design of the aerodynamic body also optimally reduces the vibrations induced by the flow of air on the sensor 1 and thereby reduce any additional noise. The flexible electrical connections between the circuits 3 and the piezoelectric element 10 contribute to the immunity of the sensor i by reducing the internal stresses likely to distort the measurements. For the same purpose, the detection unit 2 will be selected for

low inertia components.

  In Figure 1i the support of the sensor 1 has not been repesented. The realization of this support will not pose any difficulties for the skilled person. However, care should be taken to avoid that this support transmits vibrations to the sensor by interposing for example between the latter and the support an element of absorbent material. It will also be noted in FIG. 1 that the sensitivity of the sensor 1 has been optimized by choosing a membrane diameter at least equal to twice the thickness E of the body 4. It is of course important, in use, that the membrane 6 of the sensor 1 has its axis YY 'perpendicular to the

  direction F or F 'wind ecoupling.

  In Figure 2, there is shown schematically from above a sensor 1A for use in an air flow which is known that the direction remains parallel to a given plane (marked by P in Figure 2). This sensor has the shape of a saucer, the detection member 2 being disposed in the center of the saucer. Thus, when using this sensor, the edges 21 of the saucer are arranged parallel to the wind direction in the plane P, which reduces drag and lift the aerodynamic body 4A used and therefore obtain a sensor with good immunity

  noise caused by the effects of wind.

  In the case of the body 4A shaped saucer, the preferred axes XA-X'A correspond to the axes perpendicular to the minor axis of revolution of the saucer confused with Y-Y 'and joining the edges 21 of the saucer. The internal design of the sensor of FIG. 2 is moreover identical to that of the sensor of FIG.

  1 and its description is not repeated. The references

  corresponding figures appear in Figure 2.

  The sensor 1B shown in FIG. 3, which may be of identical design to that of FIG. 1 or that of FIG. 2, is intended to be placed in a

  airflow (or wind) of undetermined direction.

  Thus, the body 4 of this sensor is made integral, opposite its detection member 2, a support member 22, for example of good vibration damping material, conformation adapted to that of the body 4 which can be shaped in cylinder or saucer as already described, and attached thereto by any appropriate means. For the realization of body 4, preferably use a good vibration damping material but lighter than

  lead such as expanded polystyrene.

  On the opposite side of the body 4, the element 22 has an angle of 6 mm to 6 mm, and the element 22 has a positive effect on the extent to which it is used. qTew ua amuaJgmgJd ap 4sa Tnb 9Z alzJa ^ name a3 (L aJn6x.TOA ^) eot 4uaw9l, l ap L ToJed el suep gJlsemua 4uawallalxJed agiJJe aldwaxa Jed awJo * ap 9Z almJa ^ name unp s; gq = sap xnap; uawJo + SZ s : eldgw sap qsz saseq sa7 JnaxJ9xa ,! sJa ^ .Ja ^ no 4uawa6Jel soJi apqFp a uewjoi; aot sdjom ap 4uawglgI ap qg 'e5 qWqJXxa O anbe4q V; uawalqlsuas sgnI; s luos Sz slawwos sal 4uop (G ainti JiOA ^) aJelin6uesJ4 awJo + ap gz s4eld9w xnap aquasgjd eot sdJom ap; uawglgl ap qo0 ame + Jns el 'awsw-alla ua anuuoi uozxdanuoa ap auoMdJmtw a lsa 94uasgidas aldwaxa, 1 suep $ nb 31 Jnade i nP; aap naap aue6ioc, gx + qsa Sjenbnp nai $ lw n', XX axis. p ianbiJpuilAm aleJigu6 uoqm; as ap 'eot ledxuzJd sdJom ap; uawglg a puaJdwoD 3I Jnaldem np 3t sdJo, anb al; IOA UO' 9 + f saJn6i xnVi the ain6bx el ua amuaJggJ V s; 4Joep erap squawgll xne sgqla ++ e luos amuaJg + g oz ap sojgwnu sawiw sal S sagqigjd saJn6i + xnW -uoua ^ uAuT, [ue ^ At 3 Anaqdem unpalled uoiqesileg ap awjo * au r ua4uasgJdaJ L a b saJn6Oz sal * s .. jn6Tj, JTO ^>, a n0 a Uo0_zaiTp a: al aJTeInDnpuadJad; uawalqTsuas aqsaJ z uoyTqaqgp ap aue6Jo uos ap ii aTJ; wis ap ax.! anb; a Aie! ap quawalnozql ap, a uoiaaJTp and 4uawalltleed sq; uaTJo lua $ os; uawanbiweuApoige 9IF + ojd lsa t ina4dem ap sdjoo al slanbsa! uolas (adnomnos ap awJd nod u u u nadod n), X s -X ^ $ 69glT AJD saxony sal No. (anbiJputlAo aledjug6 awJo ap + O0 inardem a Jnod) cX X-9T6b9T $ ^ jd axis. anb ajmuew ap awgw -Tnl ap auuo4lxsod as gI jna; dei al z l.oddns uos.ns IF initiate a ginmTlJe a6eluow ne amgJg Jxep 4uawaInoog qam suep auaJu ++ TpuT aJqxuew ap 94TlJd SI Jnaldem al asodsip uo diJoiid e anuuoo u ou uomtqajp pa xp ep uawaIlnomq a suep; xnJq np ainsaw to a jaszIegiJ 4op uonbsiol 6isusu "ja4o ^ Td Inad z; 4oddns luawgl, l allanbel ap Jno1ne the gz ina4dem ap lioddns unp adjep3Tos bZ aInqod to an insb sdiom np uoixelnmi: Jel qawiad Fnb SúZ anbsJg4dsTwgq uawapT ^ a

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  Under this grid 29 is formed a recess 30 of the body member 40a. In this recess 30, extends perpendicular to the axis X-X 'of the element 40a the

  2C microphone whose membrane extends under the grid 29.

  As in previous embodiments, the thickness of the sensor is practically reduced to the height of the microphone. In the recess 30, a caté of the axis of symmetry YY 'of the microphone 2C, is also housed an amplifier circuit 3 connected to the microphone 2C by a flexible electrical connection 13. The assembly formed by the microphone 2C and the Circuit 3 is surrounded by a flexible metal shield 31 serving as protection against external electrical disturbances. The recess 30 is filled with epoxy resin making integral with the wall 7 of the element 40a the microphone 2C and the circuit 3 thus embedded.

in the resin.

  One end 5a of the element 40a has a threaded end 32 of axis X-X 'integral with this element 40a, on which is screwed a member 33 in the form of a tip or cnene for optimizing the aerodynamic profile of the

  1C sensor for the reasons explained above.

  The opposite end 5b also has a threaded end 34 of X-X 'axis integral with the element 40a and allowing the attachment of the sensor 1 to a support (not shown), for example of the type ball as described with reference to the

figure 3.

  Inside a channel 35 which passes axially through the end piece 34 and connects the recess 30 to the outside, an electrical connection 36 connects the circuit 3 to a circuit for processing the circuit.

  external signal (not shown).

  The solid regions of the body member 40a are preferably made of polycarbonate resin while the element 33 in the shape of a tip or cne is made of synthetic material such as plexiglass

(polymethylmethacrylate).

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Claims (6)

  1. An acoustic pressure sensor comprising a detection member (2, 2C) sensitive to pressure and connected to electrical means (3) for delivering an electrical signal indicative of the pressure sensed by the sensing element, the assembly consisting of by the detection member and the electrical means being housed in a body (4, 4A, 4C) profiled aerodynamically along at least one preferred axis (X-X ', XA-X'A) of said body and the detection member (2, 2C) having an axis of symmetry (Y-Y ') substantially perpendicular to said preferred axis, characterized in that the detection member (2, 2C) is separated from the electrical means (3), the latter being housed at its side within the aerodynamic body (4, 4A, 4C), and in that the thickness (E) of the body (4, 4A, 4C), measured along the axis of symmetry (Y- Y ') of the sensing element (2, 2C) does not substantially exceed the height of this organ (2, 2C).   2. Sensor according to claim 1, characterized in that the conductors (13) connecting the detection member (2, 2C) to the electrical means (3) are designed to minimize the mechanical forces exerted on   this detection member (2, 2C) by said conductors.   3. Sensor according to claim 2, characterized in that said conductors (13) are   flexible metal conductors or optical fibers.   4. Sensor according to one of claims 1   at 3, characterized in that the electrical means (3) are made integral with the material constituting the body aerodynamic (4, 4A, 4C).   5. Sensor according to one of the claims   Previous, characterized in that the material constituting the aerodynamic body (4, 4A, 4C) is a good vibration damping material in the frequency domain measured by the sensor.   6. Sensor according to claim 5, characterized in that the aerodynamic body (4, 4A, 4C) X-4uapipmg-to-suoT; eoTpua ^ aJ sap aunj V sawjo [fuo (úOT Zol 'TOI 001T) sanbT; snoze It is important to note that this is not the case with the Alanb as well as the fact that (SQ) is an exception to SOT1 (tZ & Z) alnlt2j 1? umi4lnminox) e aunp uaAow ne (qZ) Jna; dem ap 4joddns a gxT * qsa (t) anbiweuApoige sdjom al anb am ua gsTi; aeJez 'sa; uapgmgjd suoT; emTpuAaJ sap at 1 awjo + uom jnaqdeM 6 (V ) adnomnos alaa ap aJ4uam ne 01 oa 4u * (Z) uoTx; = a; p ap aue6JoTl 'adnomnos ua gwJo + uo = sa (<b) anbTweuApoige sdJom alanb amua eSTJ ") eJen 9 VT suoT; eTpuaa ^ aJ sap aunI V awJo + uoz Jnalde3 8 (qS 'eS i) S9; Tmw9Jxa sas ap aunI suiowne e 91T ++ has aJpuTTI = ua gwJo + uoz; his (3t') anbTweuApoige sdjon anb am ua gsxjgqeem IsaluapogmJd suoTlempuaa ^ aJ sap aun,! V awio + uom Jna; de3 'L auxspi aun suep siou; uos. (ú) sanbTJ) = alg suaAow saet anb am ua la asuap neTJljew un; sa