Method for adapting the frequency response of a radiofrequency device

Abstract

The present invention relates to a method for adapting the frequency response of a waveguide device obtained by additive manufacturing, the device including a semi-finished metal core comprising side walls having outer and inner surfaces, the inner surfaces defining an inner opening of the device, the method comprising the steps of: a. measuring a frequency response of the device in order to produce a first measurement of the frequency response; b. chemically polishing the metal core by dipping in order to reduce a thickness of the side walls according to the first measurement and to increase a volume of the inner opening; and c. measuring the frequency response of the device in order to produce a second measurement of the frequency response; repeating steps a. to c. until the second measurement is within a determined range of values.

Description

Method for adapting the frequency response of a radiofrequency device Technical field

[0001] The present invention relates to a method for adapting the frequency response of a radiofrequency device. State of the art

[0001] Radio frequency (RF) signals can propagate either in space or in waveguide devices. These waveguide devices are used to channel RF signals or to manipulate them in the spatial or frequency domain.

[0002] The present invention relates in particular to passive RF devices that allow radio frequency signals to be propagated and manipulated without the use of active electronic components. Passive waveguide devices can be divided into three distinct categories: • Devices based on waveguiding inside hollow metal channels, commonly called waveguides. • Devices based on waveguiding inside dielectric substrates. • Devices based on waveguiding by means of surface waves on metal substrates such as PCB printed circuits, microstrips, etc.

[0003] The present invention relates in particular to the manufacture of waveguide devices according to the first category above, collectively referred to hereinafter as waveguide devices. Examples of such devices include waveguides as such, filters, antennas, polarizers, mode converters, etc. They can be used for signal routing, frequency filtering, signal splitting or recombination, transmission or reception of signals in or from free space, etc.

[0004] Conventional waveguides consist of hollow devices, the shape and proportions of which determine the propagation characteristics for a given wavelength of the electromagnetic signal. Conventional waveguides used for radiofrequency signals have internal openings of rectangular or circular cross-section. They allow the propagation of electromagnetic modes corresponding to different electromagnetic field distributions along their cross-section.

[0005] Manufacturing waveguides with complex cross-sections is difficult and expensive. To address this, the patent application US2012 / 0084968 proposes to produce waveguides by 3D printing. To this end, a non-conductive plastic core is printed using an additive method and then covered with a metal immersion plating. The internal surfaces of the waveguide must be electrically conductive to operate. The use of a non-conductive core makes it possible, on the one hand, to reduce the weight and cost of the device and, on the other hand, to implement 3D printing methods adapted to polymers or ceramics and to produce high-precision parts with low wall roughness. The parts described in this document have complex shapes and include, on the one hand, a channel for wave propagation, and on the other hand, fixing holes on one foot of the waveguide, in order to fix it to another element.

[0006] There are several different 3D printing techniques, including selective laser melting (SLM). This is a selective powder bed melting process in which a laser is used to fuse fine metal particles. Following a computer-determined pattern, it melts the metal particles until they fuse together. A powder spreading system then applies a new layer of powder. The laser creates the next layer. These steps continue until the entire object is printed.

[0007] Although SLM printing allows for layer thicknesses ranging from 0.02mm to 0.10mm on the Z axis, the resolution on the X and Y axes depends on the laser beam diameter of the machine. Standard SLM machines work with lasers with diameters of 0.080mm and 0.1mm. The weld pool around the laser beam for aluminum has a diameter of approximately 0.250mm. Ideally, at least 2 vectors are required to produce one waveguide wall, hence a minimum thickness of 0.5mm.

[0008] The metal parts obtained by this process can have, depending on the desired shape, layer thicknesses going well beyond the Z resolution of the machine which are imposed by the aforementioned constraints. This has a direct impact on the weight of the parts produced.

[0009] Selective laser sintering (SLS) 3D printing is also known, particularly for printing plastics. However, it presents the same resolution problems, particularly related to the diameter of the laser beam.

[0010] An important step in the fabrication of waveguide devices is the calibration of the device's frequency response so that it is suitable for the intended function of the device.

[0011] The frequency response is determined in particular by the geometry of the resonant cavity(ies) of the waveguide device, in particularly the internal volume of the device. Adjustment screws inserted into the resonant cavity(ies) allow the frequency response of the device to be adapted from outside the device. This process of adapting the frequency response occurs after the waveguide device itself has been manufactured, once the geometry of the device's resonant cavity can no longer be modified.

[0012] However, adapting the frequency response may require significant adjustments, particularly due to defects or imperfections due to the manufacture of the device. These adjustments do not affect the geometry and internal volume of the device, but rather the external adjustment elements that must be associated with the device.

[0013] There is therefore a need for a method of adapting the frequency response of a waveguide device allowing adjustment of this response during manufacturing. Brief summary of the invention

[0014] An object of the present invention is to provide a method for adapting the frequency response of a waveguide device free from the limitations present in the prior art.

[0015] Another object of the invention is to provide a method for adapting the frequency response of a faster waveguide device.

[0016] Another aim of the invention is to propose a method for adapting the frequency response of a waveguide device making it possible to limit the use of external elements after the manufacture of the waveguide.

[0017] According to the present invention, these aims are achieved in particular by means of a method for adapting the frequency response of a waveguide device obtained by additive manufacturing, the device comprising a semi-finished metal core comprising side walls having external and internal surfaces, the internal surfaces defining an internal opening of the device, comprises the steps of: a. measuring a frequency response of the device in order to produce a first measurement of the frequency response; b. chemically polishing the metal core by dipping in order to reduce a thickness of the side walls according to the first measurement and to increase a volume of the internal opening; c. measuring the frequency response of the device in order to produce a second measurement of the frequency response; iterating steps a. to c. until the second measurement is within a determined range of values.

[0018] Thus, the frequency response of the waveguide device is adapted by modifying the internal volume of the device.

[0019] According to one embodiment, the soaking time is between 45s and 90s.

[0020] According to one embodiment, the thickness of the side walls is reduced by an ablation thickness of between 5 pm and 30 pm, preferably between 10 pm and 20 pm.

[0021] According to one embodiment, a final thickness of the side walls of the device after iteration of steps a. to c. is less than 300 pm, preferably less than 200 pm.

[0022] According to one embodiment, the metal core is produced by powder bed laser fusion (SLM), in order to obtain a semi-finished metal core, said ablation thickness being equal to at least once a powder grain size of said powder bed.

[0023] According to one embodiment, the step of dipping the semi-finished metal core is carried out in an acid bath.

[0024] According to one embodiment, the acid bath comprises a mixture of two acids.

[0025] According to one embodiment, the acid bath comprises orthophosphoric acid and sulfuric acid.

[0026] According to one embodiment, the density of the bath is in a range between 1.5g / cm 3 and 2g / cm 3 , preferably around 1.7g / cm 3 .

[0027] According to one embodiment, the treatment temperature of the acid bath is between 70°C and 120°C.

[0028] According to one embodiment, the acid bath further comprises dissolved aluminum at a concentration of between 20g / l and 50g / l, preferably between 25g / l and 45g / L.

[0029] According to one embodiment, the dipping of the semi-finished metal core is carried out in a basic bath.

[0030] According to one embodiment, the basic bath comprises a caustic solution having a pH greater than 11.5.

[0031] According to one embodiment, the method may comprise a step of: b', dipping the semi-finished metal core in an acid deoxidation bath following dipping in the basic bath, in order to remove the oxidized residues on the surface of the device.

[0032] According to one embodiment, the method may comprise a step of: b", dipping the semi-finished metal core in an acid bath, for example a bath containing nitric acid and ammonium bifluoride, with a pH preferably less than 2.

[0033] According to one embodiment, the method may comprise a step of b'", dipping the semi-finished metal core in a heated acid bath 10 with application of ultrasound to clean it.

[0034] This solution has the particular advantage over the prior art of producing waveguide devices having a frequency response closer to that targeted and requiring less adjustment and tuning after manufacturing.

[0035] In particular, the use of external elements such as adjustment screws to adjust the frequency response can be greatly limited or even completely eliminated. Example(s) of embodiment of the invention

[0036] The waveguide devices according to the present invention comprise a metal core, for example aluminum, titanium, steel, invar or an alloy of these metals.

[0037] The core is manufactured by additive manufacturing, preferably by stereolithography, selective laser melting, selective laser sintering (SLS), binder jetting or direct energy deposition (DED). The wall thickness of the core is, for example, at least 0.5 mm.

[0038] This core delimits an internal opening forming a channel intended for wave guidance. The core therefore has an internal surface and an external surface defining the internal opening which is for example of oblong cross-section.

[0039] A chemical polishing bath works by leveling the microscopic surface roughness of the material, such as aluminum, used to form the core. Polishing is a process that reduces the roughness Ra of the material and allows it to better reflect light (specularity). This is achieved by leveling the peaks and valleys (or hollows) on the surface of the material. Polishing is carried out by dipping the parts in a bath, with constant agitation.

[0040] The roughness Ra of the material or average roughness or arithmetic mean roughness refers to the average deviation between the peaks and valleys of the material at the scale of the particles (or grains) used for additive manufacturing.

[0041] It is known to use chemical or electrochemical polishing steps to reduce the roughness of the material. Surprisingly, the polishing step of the present invention aims, in addition to improving the specularity of the material, to reduce the thickness of the walls of the waveguide device. Such a reduction in the thickness of the walls thus also makes it possible to significantly reduce the weight of the device.

[0042] The frequency response of a waveguide device refers to the device's response to a variable frequency input signal. This frequency response can be characterized by the amplitude of the device's response, measured in decibels, and the phase, measured in radians, as a function of frequency.

[0043] Measuring the frequency response of a waveguide device is essential to ensure the proper operation of the device for the intended application.

[0044] The frequency response depends in particular on the geometry of the waveguide device, more precisely on the internal geometry of the resonant cavities, in particular their volume. A change in the internal volume of a waveguide device will change its frequency response.

[0045] Generally speaking, the measurement of the frequency response of a given radiofrequency device (or waveguide device) is carried out experimentally by propagating an input signal into the device and measuring the characteristics of the output signal, in particular its amplitude and phase. Each type of radiofrequency device (abbreviated as RF device) has an optimal frequency response (or more generally a range of frequency responses) depending on its application. It is therefore advantageous to be able to adapt the frequency response of a manufactured device according to an optimal theoretical frequency response value for this type of device.

[0046] The present method allows iterative adaptation of the frequency response of an RF device by successively polishing the device by dip-polishing and measuring the frequency response after one or more dips. This method can be used as an alternative to traditional frequency adaptation methods or as a complement, as a fine-tuning step during the manufacturing process.

[0047] The various parameters relating to soaking, e.g. soaking duration, number of soaks, composition of the baths, temperature of the baths, agitation of the baths during soaking, application of ultrasound, etc. are thus determined according to the frequency response targeted for a given RF device. In particular, all these parameters vary according to the type of RF device and even from one device to another depending on the intended application.

[0048] Thus, by way of example, one embodiment of the present method comprises producing a first measurement of the frequency response of an RF device using known measuring techniques. Based on this first measurement, determining chemical polishing parameters as mentioned above and chemically polishing the device. The thickness of the device walls is subsequently reduced and the internal volume of the device increased. A second measurement of the frequency response of the RF device is then carried out after polishing. If this second measurement corresponds to an amplitude and / or phase value consistent with the application for which the device is intended, the method stops. If the second measurement does not correspond to an amplitude and / or phase value consistent with the application for which the device is intended, a new set of chemical polishing parameters is determined on the basis of this second measurement and the device is chemically polished again according to these new parameters.These steps are iterated until a measurement of the frequency response after polishing falls within a range of values ​​corresponding to the desired application of the device.

[0049] The expressions "RF device" and "waveguide device" cover in particular the entire class of passive radiofrequency devices: simple waveguides, waveguide networks, antennas, antenna networks, polarizers, in particular septum polarizers, combiners, dividers, transducers, in particular orthomode transducers, beamforming networks, filters, comb filters, evanescent mode filters.

[0050] The term "semi-finished metal core" refers to the state of the metal core obtained by additive manufacturing, but to which additional finishing steps still need to be applied. For example, chemical polishing steps as described above, but also coating, sanding, assembly steps, etc.

[0051] Advantageously, the thickness of the side walls of the RF device after the chemical polishing steps is less than 300 pm, preferably less than 200 pm, or even 150 pm. In this way, the Chemical polishing steps not only allow to adapt the frequency response of the RF device, but also to obtain a wall thickness sufficiently limiting the weight of the device.

[0052] According to one embodiment, the ablation thickness, i.e. the thickness of the portion of material removed by chemical polishing at each stage, depends on the particular additive manufacturing technique used to produce the semi-finished core.

[0053] For example, when the semi-finished metal core is produced by laser powder bed fusion, the ablation thickness is advantageously equal to at least one time a powder bed grain size. In this way, the surface condition after polishing is improved.

[0054] According to one embodiment, each polishing step comprises dipping the RF device into one or more successive baths. These baths may be of different or similar composition. The function of each bath may be the ablation of material, but also cleaning or the application of a surface treatment.

[0055] The soaking time in each of these baths can be different or similar. Typically, the soaking time in a bath is between 20s and 200s depending on the desired ablation thickness and / or the composition of the bath. Preferably, the soaking time is between 30s and 120s, or even between 45s and 90s.

[0056] The use of dipping baths to reduce the thickness of the walls of the waveguide device also makes it possible to combine surface treatment steps (e.g. polishing to reduce internal roughness) necessary for the proper functioning of the device with the frequency response optimization steps. Indeed, an additive manufacturing thickness of the walls of the semi-finished core can be determined according to the desired final surface condition as well than depending on the target frequency response. In this way, it is possible to optimize the manufacturing time, and therefore the cost, of the device since several steps can be carried out simultaneously.

Claims

Claims 1. A method for adapting the frequency response of a waveguide device obtained by additive manufacturing, the device comprising a semi-finished metal core comprising sidewalls having external and internal surfaces, the internal surfaces defining an internal opening of the device, comprising the steps of: a. measuring a frequency response of the device to produce a first measurement of the frequency response; b. chemically polishing the metal core by dip-polishing to reduce a thickness of the sidewalls according to the first measurement and to increase a volume of the internal opening; c. measuring the frequency response of the device to produce a second measurement of the frequency response; d. iterating steps a. to c. until the second measurement is within a determined range of values.

2. Method according to the preceding claim, in which a soaking duration is between 45s and 90s.

3. Method according to one of the preceding claims, in which the thickness of the side walls is reduced by an ablation thickness of between 5 pm and 30 pm, preferably between 10 pm and 20 pm.

4. Method according to one of the preceding claims, in which a final thickness of the side walls of the device after iteration of steps a. to c. is less than 300 pm, preferably less than 200 pm.

5. Method according to one of the preceding claims, in which the metal core is produced by powder bed laser fusion (SLM), in order to obtain a semi-finished metal core, said ablation thickness being equal to at least one times a powder grain size of said powder bed.

6. Method according to one of the preceding claims, in which the step of dipping the semi-finished metal core is carried out in an acid bath.

7. Method according to claim 6, the acid bath comprising a mixture of two acids.

8. Method according to claim 7, the acid bath comprising orthophosphoric acid and sulfuric acid.

9. Method according to the preceding claim, in which a density of the bath is in a range between 1.5g / cm 3 and 2g / cm 3 , preferably around 1.7g / cm 3 .

10. Method according to one of claims 6 to 9, in which a treatment temperature of the acid bath is between 70°C and 120°C.

11. Method according to one of claims 6 to 10, in which the acid bath further comprises dissolved aluminum at a concentration of between 20g / l and 50g / l, preferably between 25g / l and 45g / l.

12. Method according to one of claims 1 to 5, in which the dipping of the semi-finished metal core is carried out in a basic bath.

13. The method of claim 12, wherein the basic bath comprises a caustic solution and having a pH greater than 11.

5.

14. Method according to one of claims 12 or 13, comprising a step of: b', dipping the semi-finished metal core in an acid deoxidation bath following dipping in the basic bath, in order to remove the oxidized residues on the surface of the device.

15. Method according to one of claims 12 to 14, comprising a step of: b", dipping the semi-finished metal core in an acid bath, for example a bath containing nitric acid and ammonium bifluoride, with a pH preferably less than 2.

16. Method according to one of claims 6 to 15, comprising a step of b'", dipping the semi-finished metal core in a heated acid bath 10 with application of ultrasound to clean it.

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