WO2020127903A1

WO2020127903A1 - Tuning device

Info

Publication number: WO2020127903A1
Application number: PCT/EP2019/086570
Authority: WO
Inventors: Philippe Thomas; Pierre BATY
Original assignee: Thales
Priority date: 2018-12-20
Filing date: 2019-12-20
Publication date: 2020-06-25
Also published as: FR3091031A1; EP3900062A1; FR3091031B1

Abstract

Tuning device (100) having a tuning inductor (22) designed to be tuned with a capacitor of an assembly consisting of at least one piezoelectric transducer (3) at a frequency of use of the assembly consisting of at least one piezoelectric transducer, the tuning device comprising a toroidal magnetic core (4) which comprises a magnetic portion (5) made of a nanocrystalline ferromagnetic material, an assembly consisting of at least one air gap (7) made of a non-magnetic material and at least one winding of a conductive element wound around the toroidal magnetic core.

Description

Title of the invention: Tuning device

The field of the invention is that of tuning devices. These devices find a utility for supplying piezoelectric transducers, in particular in the field of sonars, for example acoustic wave transmitting antennas.

The capacitive nature of a piezoelectric transducer represents a major difficulty for its power supply. Indeed, some transducers "consume" reactive power which may be more than five times their maximum active power (i.e. what is actually transmitted in water). It is therefore essential to limit the level of reactive power supplied for the supply of one or more piezoelectric transducer (s) in order to avoid oversizing the power stages placed upstream. However, to maximize the power emitted by the transducer, it makes sense to energize it electrically at its mechanical resonant frequency. The addition, upstream of the transducer, of an inductor whose value is matched with the capacity of the transducer at a frequency close to the mechanical resonance of the transducer makes it possible to produce an assembly consuming only active power and thus minimizes the dimensioning converters.

A step-up transformer can also be provided to adapt the voltage level of the source to that of the piezoelectric transducer. The magnetizing inductance of the latter can also serve as a chord inductor.

In the field of sonar transmission antennas, obtaining directional emissions requires being able to adjust the phase and the amplitude for each transducer, hence the need to associate an amplifier with each transducer or group of transducers. A tuning coil must be provided between each amplifier and its transducer (s). Furthermore, in order to limit the distance over which the reactive power circulates, it is preferable to install this tuning device as close as possible to the transducer, but practical considerations may lead to integrate it on the same electronic card as the power stage intended to excite the piezoelectric transducer.

Up to a few tens of kHz, the magnetic circuits of the tuning coils of the prior art are most often standard circuits, such as toroids made of ferromagnetic material of the iron alloy powder type embedded in a matrix. organic, MPP, Sendust etc. or ferrite circuits with an air gap. These magnetic circuits are heavy and bulky, therefore unsuitable for integrating several tuning coils on the same electronic card.

Furthermore, as shown in FIG. 1 representing the magnetic hysteresis curve of the induction B as a function of the magnetic field of a ferromagnetic material of the prior art, the inductance L, corresponding substantially to the slope of the curve shown in FIG. 1, varies with the field H and therefore the current I. This characteristic is unfavorable to the agreement of the inductance with the capacity of the piezoelectric transducer at a predetermined frequency with a wide dynamic range of emitted power.

An object of the invention is to limit at least one of the aforementioned drawbacks.

To this end, the invention relates to a tuning device having a tuning inductor intended to be tuned with a capacity of an assembly of at least one piezoelectric transducer at a frequency of use of l assembly of at least one piezoelectric transducer, the tuning device comprising a toric magnetic core comprising a magnetic part based on a nanocrystalline ferromagnetic material, a set of at least one air gap in non-magnetic material and at least one winding 'a conductive element produced around the toric magnetic core.

Advantageously, the toroidal magnetic core may comprise a single air gap or several air gaps.

Advantageously, each air gap is dimensioned so that the coefficient of lateral development of the magnetic field lines of each air gap is less than or equal to 2. In a first embodiment, the tuning device is a differential mode coil.

In a second embodiment, the tuning device is an adaptation transformer for tuning an input voltage of the transformer with an input voltage of the piezoelectric transducer, the tuning inductor being l magnetizing inductance of the transformer.

Advantageously, the tuning inductor is substantially fixed over an induction range extending from 0 T to 1 T.

Advantageously, the frequency of use is between 4000 Hz and 7000 Hz.

The invention also relates to a piezoelectric device comprising the tuning device according to the invention and the assembly of at least one piezoelectric transducer, the tuning inductor being tuned with a capacity of the assembly at least one piezoelectric transducer at a frequency of use of the assembly of at least one piezoelectric transducer.

The frequency of use is included in a frequency interval comprising the resonant frequency of the assembly of at least one piezoelectric transducer.

In a particular embodiment, the frequency of use is substantially the mechanical resonance frequency of the piezoelectric transducer.

The tuning device can be a differential mode coil mounted in parallel or in series with the assembly of at least one piezoelectric transducer. As a variant, the tuning device is an adaptation transformer making it possible to adapt an input voltage of the transformer with an input voltage of the assembly of at least one piezoelectric transducer, the tuning inductor being the magnetizing inductance of the transformer.

Advantageously, the piezoelectric device comprises a power stage intended to excite at least one piezoelectric transducer via the tuning device. Advantageously, the power stage and the tuning device are mounted on the same electronic card.

The invention also relates to a sonar antenna comprising a piezoelectric device according to the invention. The piezoelectric transducer is an electroacoustic transducer.

[Fig.1] FIG. 1 already described schematically represents a hysteresis curve of a ferromagnetic material of the prior art,

[Fig.2] Figure 2 schematically shows an example of a piezoelectric device according to the invention comprising a tuning device according to the invention,

[Fig. 3] FIG. 3 schematically represents a magnetic core of a tuning device according to the invention,

[Fig. 4] FIG. 4 already described schematically represents a hysteresis curve of a nanocrystalline ferromagnetic material,

[Fig.5] FIG. 5 schematically represents a magnetic core of a tuning device according to the invention,

[Fig.6] Figure 6 schematically shows a second example of a tuning device according to the invention.

In Figure 2, there is shown a piezoelectric device 1 according to the invention comprising an example of tuning device 2 according to the invention.

The piezoelectric device 1 comprises a piezoelectric transducer 3, a power stage 10 intended to form an excitation signal intended to excite the piezoelectric transducer, and a tuning coil 2 mounted in parallel with the piezoelectric transducer 3 The power stage 10 can, for example, comprise an amplifier as in FIG. 2 and / or a power converter, for example an inverter.

Alternatively, the piezoelectric device comprises several piezoelectric transducers.

Preferably, the tuning frequency is the mechanical resonance frequency of the piezoelectric transducer. According to the invention, the tuning coil 2 comprises, as visible in Figure 3, a toric magnetic core 4 comprising a magnetic part 5 based on a nanocrystalline ferromagnetic material and at least one winding 6 of an element conductor formed around the toroidal magnetic core 4.

Figure 4 shows, with the same scale as Figure 1, the magnetic hysteresis of the induction B as a function of the magnetic field H applied to a nanocrystalline material and therefore of the current I passing through. As a reminder, the induction B is given by B = d (<|)) / dt = d (L ^* l) / dt = L ^* dl / dt when L is constant (and H = N ^* I / Le), with "Le" is the length of the magnetic circuit, "N" is the number of turns and "L" is the value of the inductance.

The induction, corresponding substantially to the slope of one of the branches B1, B2 of the hysteresis shown in Figure 4, is fixed and independent of the H field and therefore of the current between the two saturations represented SAT1, SAT2. This characteristic is favorable to the agreement of the inductance of the coil with the capacity of the transducer at a predetermined frequency because the inductance is constant, that is to say fixed, over this area of the curve. Furthermore, since the slope between the saturations is fixed, the saturation occurs suddenly and in a predictable and reproducible manner, which makes it possible to calculate it easily.

The use of a nanocrystalline material makes it possible to obtain tuning circuits of size and reduced mass (there is a factor 2 in volume and in mass compared to toroids in iron alloy powder MPP, Sendust etc.) due to the high level that induction can reach. The saturation of the nanocrystalline material occurs above 1, 2T without the inductance value having varied appreciably, while in this type of applications, the materials used in the prior art must be used in their linear area, ie most often below 0.5T. Another favorable characteristic of nanocrystalline materials is their low level of iron losses.

These characteristics (inductance value independent of current, low losses, reduced mass and volume) make nanocrystalline materials a technology particularly suited to the tuning function, in particular for producing directional sonars which combine a large number of broadcast channels. The nanocrystalline ferromagnetic material can be an iron alloy. It is for example an alloy of FeCuMSiB type composition where M is a transition metal, for example Nb. A widely used composition is of the type: Fe73.5Cu1 Nb3SixB22.5-x and contain 13.5% or 16.5% of silicon. In this family, iron-silicon crystals are embedded in an amorphous residual matrix. The crystals have dimensions of the order of a nanometer. Other materials of FeMB type can be used. They generally contain more than 80% iron, 7% transition metal and the balance of boron. The materials in this family include nano crystals of pure iron.

It should be noted that the ferromagnetic nanocrystalline materials have a relative magnetic permeability which can be in a wide range of values ranging from 200 to 500,000 depending on the material chosen and the treatment undergone by this material. Heat treatments can, for example, reduce the magnetic permeability of a material. However, the tuning coils are intended to store energy, and in the majority of cases the ferromagnetic core should not exceed a relative permeability of 100. Those skilled in the art are therefore diverted from the use of nanocrystalline materials to make tuning coils.

According to the invention, the toric magnetic core 4 comprises a set of at least one air gap 7 made of non-magnetic material. By air gap is meant here localized air gap. This characteristic makes it possible to reduce the total permeability of the magnetic core, which allows energy storage and the use of the coil to achieve tuning despite the significant value of the relative permeability of ferromagnetic nanocrystalline materials.

The toroidal magnetic core 4 is obtained by spiraling a strip of nanocrystalline material which makes it possible to obtain a torus in the form of a spiral of a strip of nanocrystalline material.

The air gap 7 is then obtained by cutting the torus so as to form a free volume 8, visible in FIG. 5. The remainder of the torus forms the magnetic part 5 of the magnetic core 4. The section of the torus is, for example , produced by a diamond disc or a diamond wheel. Preferably, to avoid altering the material, the cutting of the torus is carried out after impregnation and / or coating in an organic resin.

In addition or alternatively, a tool ensures the mechanical maintenance of the spiral during cutting in order to prevent the latter from bursting.

Advantageously, a shim 9 made of non-magnetic material is inserted into the free volume 8 so as to obtain the air gap and to avoid any deformation of the torus and the air gap because it is the precision of the dimensions of this air gap and in particular of its thickness which predominantly determines the value of the inductance. The thickness of the shim 9 is calibrated and corresponds to the thickness e of the air gap that it is desired to obtain.

The free volume 8 may have a thickness slightly less than the thickness e that one wishes to obtain. The shim 9 can be inserted by slightly deforming the free volume 8 during its assembly.

The wedge 9 can completely fill the free volume 8. As a variant, the wedge 9 only partially fills the free volume 8, a non-magnetic filling material is then advantageously inserted into the rest of the free volume so that the magnetic core has a substantially fixed section which prevents the winding from coming into this volume.

Alternatively, a non-magnetic glue is injected into the free volume and is shaped by a mold configured so that the glue completely fills the free volume and so that the magnetic core 4 has a constant section.

Alternatively, the toric magnetic core may include several air gaps.

The method then comprises several cutting steps, simultaneous or not, so as to produce several free volumes intended to form the localized air gaps. The magnetic part of the magnetic core then comprises several sections separated in pairs by a localized air gap.

The presence of several air gaps improves the energy storage capacity of the tuning coil by reducing the magnetic permeability of the magnetic core compared to a single localized air gap of the same volume. This is of considerable interest for the use of ferromagnetic nanocrystalline materials with high magnetic permeability, more standardized. Furthermore, the production of several air gaps of small volume (small thickness or angular sector of reduced size) is more advantageous from the point of view of energy storage than the production of a single air gap of volume corresponding to the sum of the volumes of the air gaps, that is to say whose angular sector (or thickness) is the sum of the angular sectors (or thicknesses) of the plurality of air gaps. Indeed, in the latter case, the value of the lateral development coefficient of the field lines in the air gaps (“fringing factor” in English) increases. Indeed, the increase in the thickness of an air gap leads to an increase in the apparent section of the latter (by blooming of the field lines), according to a logarithmic law; this phenomenon limits the expected reduction in the value of the induction (F = B. S, with F the flux, B the induction and S the section) and increases the losses by proximity effect (the turns at the right of the air gap are taken in the flow which is no longer properly channeled).

Advantageously, in order to optimize the storage of energy, the dimensions of each air gap are defined so that the coefficient of lateral development of the magnetic field lines (called "fringing factor" in English terminology) of each air gap is less than 2.

The air gaps may have the same dimensions or the air gaps may have different dimensions.

Advantageously, the magnetic core 4 comprises a single air gap when the nanocrystalline material has low magnetic permeability and several air gaps when the nanocrystalline material has a higher magnetic permeability. The fact of providing several air gaps makes it possible to use nanocrystalline toroids of high permeability which can remain inexpensive to form the magnetic core by making the air gaps therein.

Those skilled in the art determine the number of air gaps and their dimensions as a function of the magnetic permeability of the nanocrystalline material, of the lateral bloom coefficient of the lines of maximum desired magnetic field and of the desired inductance.

The invention has been described in the context of a coil type tuning device. The coil can be mounted in parallel with the piezoelectric transducer, as in Figure 2, or in series with the latter.

The tuning inductance L is given by: L = 1 / (C ^* œ ² ) where C is an equivalent capacity of the piezoelectric transducer at the tuning frequency and w, expressed in radian per second, the pulsation eigenw at the tuning frequency f, expressed in hertz. The proper pulsation is linked to the tuning frequency by the following formula: w = 2 * TT * L

When the coil is mounted in parallel with the piezoelectric transducer, the capacity C is the equivalent capacity of the transducer in the Rp-Cp type model in which the transducer is modeled by a resistor in parallel with a capacitor.

When the coil is mounted in parallel with the piezoelectric transducer, the equivalent capacity C is the equivalent capacity of the transducer in the Rs-Cs type model in which the transducer is modeled by a resistor in series with a capacitor.

In the case where the coil is mounted in series or parallel with a set of piezoelectric transducers, the equivalent capacity is the capacity of the set of transducers in one of the models.

In a variant of the piezoelectric device 100, shown in FIG. 6, the tuning device is of the adaptation transformer type 20 configured to adapt the input voltage U1 of the power stage 10, the voltage U2 of the piezoelectric transducer, the tuning inductance L being the magnetizing inductance Lm of the matching transformer. The transformer 20 can be modeled by a perfect transformer 21 and a tuning coil 22 mounted in parallel with the piezoelectric transducer 3, as shown in FIG. 6. The tuning device or transformer 20 then has a double tuning function and adaptation.

The transformer can be an autotransformer or include at least two windings made around the magnetic core 4 so as to form the primary and secondary of the transformer. The transformation ratio m of the transformer is defined to allow adaptation between U1 and U2. In the case where the tuning coil 2 is mounted in series, the power stage is advantageously a current generator and in the case where the tuning coil is mounted in parallel, the power stage is a voltage generator, just as in the case where the tuning device is a tuning and adaptation transformer.

Advantageously, the tuning device is configured so that the tuning inductor L is substantially fixed over an induction range extending from 0 Tesla (T) to a maximum value greater than or equal to 1 Tesla (T), that is to say when it is subjected to an induction included in this range. Indeed, the tuning inductor L must be substantially fixed on an undulation of the excitation current of the piezoelectric transducer. This avoids distortions of the signal generated by the piezoelectric transducer as a function of the value of the current and therefore makes it possible to control this signal which is essential for carrying out sonar measurements.

In the field of sonar antennas, tuning is carried out at a frequency of use of between 4000 Hz and 7000 Hz. At these low frequencies, the mass of a magnetic core of the prior art may prove to be very high. Indeed, the need to maintain a linear magnetization curve would mean working very far from saturation, therefore further increasing the mass of magnetic material.

Claims

[Claim 1] Tuning device (2; 20) having a tuning inductor (L) intended to be tuned with a capacity of an assembly of at least one piezoelectric transducer (3) at a frequency of use of the assembly of at least one piezoelectric transducer (3), the tuning device (2; 20) comprising a toric magnetic core (4) comprising a magnetic part (5) based on a nanocrystalline ferromagnetic material, an assembly at least one air gap (7) made of non-magnetic material and at least one winding of a conductive element (6) produced around the toroidal magnetic core (4).

[Claim 2] Tuning device (2, 20) according to claim 1, in which the tuning inductor (L) is substantially fixed over an induction range extending from 0 T to 1 T.

[Claim 3] Tuning device according to any one of the preceding claims, in which the frequency of use is between 4000 Hz and 7000 Hz.

[Claim 4] Tuning device (2; 20) according to any one of the preceding claims, in which the toroidal magnetic core (4) comprises a single air gap (7).

[Claim 5] Tuning device (2; 20) according to any one of claims 1 to 3, in which the toroidal magnetic core (4) has several air gaps.

[Claim 6] Tuning device (2; 20) according to any one of the preceding claims, in which each air gap (7) is dimensioned so that the coefficient of lateral development of the magnetic field lines of each air gap is lower or equal to 2.

[Claim 7] Tuning device (2; 20) according to the preceding claim, in which the tuning device (2) is a differential mode coil.

[Claim 8] Tuning device (20) according to any one of claims 1 to 6, the tuning device being a matching transformer transformer (20) making it possible to adapt an input voltage of the transformer with an input voltage of the piezoelectric transducer, the tuning inductance (L) being the magnetizing inductance of the transformer.

[Claim 9] Piezoelectric device (1; 100) comprising the tuning device (2; 20) according to any one of claims 1 to 6, and the assembly of at least one piezoelectric transducer (3), the tuning inductor (L) being tuned with a capacity of the assembly of at least one piezoelectric transducer (3) at a frequency of use of the assembly of at least one piezoelectric transducer (3).

[Claim 10] Piezoelectric device (1; 100) according to the preceding claim, wherein the frequency of use is substantially the mechanical resonance frequency of the piezoelectric transducer (3).

[Claim 1 1] A piezoelectric device (1) according to any one of claims 9 and 10, in which the tuning device is a differential mode coil (2) mounted in parallel or in series with the set of at least minus a piezoelectric transducer (3).

[Claim 12] Piezoelectric device (100) according to any one of claims 9 and 10, in which the tuning device is an adaptation transformer (20) making it possible to adapt an input voltage of the transformer with a voltage input of the assembly of at least one piezoelectric transducer, the tuning inductance (L) being the magnetizing inductance (Lm) of the transformer.

[Claim 13] Piezoelectric device (1; 100) according to any one of claims 9 to 12, comprising a power stage (10) intended to excite the assembly of at least one piezoelectric transducer, in electrical energy via the device agree (2; 20).

[Claim 14] Piezoelectric device according to the preceding claim wherein the power stage and the tuning device are mounted on the same electronic card.

[Claim 15] Sonar antenna comprising a piezoelectric device according to the preceding claim. )