EP4645584A1

EP4645584A1 - Method for manufacturing an electromagnetic resonator

Info

Publication number: EP4645584A1
Application number: EP24305703.1A
Authority: EP
Inventors: Matthieu LABOUSSE; Joshua MCGRAW; Samuel HIDALGO-CABALLERO; Grégoire CLEMENT; Mathieu OLERON; Finn BOX
Original assignee: Centre National de la Recherche Scientifique CNRS; Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI; Universite Paris Sciences et Lettres
Current assignee: Centre National de la Recherche Scientifique CNRS; Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI; Universite Paris Sciences et Lettres
Priority date: 2024-05-02
Filing date: 2024-05-02
Publication date: 2025-11-05
Also published as: WO2025229058A1

Abstract

A method for manufacturing an electromagnetic resonator comprising:
- placing a polymer phase in a first channel (104) and a continuous phase (40) in a second channel (108) orthogonal to the first channel, the first channel having a junction with the second channel,
- providing a flow (114),
- placing a conductive fiber inside a third channel (3), the third channel opening into the first channel, a projection of the third channel on the flow being located upstream of the junction, the third channel presenting an axis of extension, the axis passing continuously through the third channel (3), the first channel (104) and the second channel (108),
- moving the fiber inside the second channel (108),
- ejecting a single droplet from the polymer phase into the continuous phase (40) and bring the droplet into contact with the fiber (118), and
- curing the single droplet.

Description

FIELD OF THE INVENTION

The presentation relates to the field of manufacturing electromagnetic resonators and in particular electromagnetic resonators with a resonance frequency comprised between 50 GHz and 10 THz, the resonators having a characteristic dimension superior or equal to 10 µm and inferior or equal to 500 µm.

STATE OF THE ART

The functional operation of electromagnetic devices and sensors is classically based on the principle of electromagnetic resonance. Plasmon-based technologies, antenna arrays or meta-atoms can be used. Electromagnetic devices configured to operate in the electromagnetic wavelength bands around the millimeter and the centimeter, are usually Split Ring Resonators (SRRs). Depending on the intended application, the size of these resonators ranges from millimeters to centimeters. An electromagnetic resonance device based on a network of SRRs is thus a large device in the case of these wavelengths around the millimeter and the centimeter.
There is a need for a method for manufacturing electromagnetic resonators that present a resonance frequency superior or equal to 50 GHz and inferior or equal to 10 THz and a dimension inferior or equal to 500 µm.

DISCLOSURE OF THE INVENTION

It is an object of this presentation to provide a method for manufacturing electromagnetic resonators that produces resonators presenting a dimension inferior or equal to 500 µm.
To that end, it is provided a method for manufacturing an electromagnetic resonator, the method comprising the following steps:

placing a polymer phase in a first channel and a continuous phase in a second channel orthogonal to the first channel, the first channel having a junction with the second channel,
providing a flow along a direction of the second channel,
placing a conductive fiber inside a third channel, the third channel opening into the first channel, a projection of the third channel on the direction being located upstream of the junction with respect to the flow, the third channel presenting an axis of extension, the axis passing continuously through the third channel, the first channel and the second channel,
moving the fiber along an axis of extension of the third channel out of the third channel, across the first channel and inside the second channel, and
ejecting a single droplet from the polymer phase into the continuous phase so as to bring the droplet into contact with the fiber at the junction, and
curing the single droplet.

Such method is advantageously and optionally completed by the following features taken singly or in combination:

the electromagnetic resonator has a dimension superior or equal to 10 µm and inferior or equal to 500 µm;
a step of detecting an entry of the fiber in the second channel and a step of triggering the ejection of the droplet once the fiber entry is detected;
a step of monitoring an interface between the polymer phase and the continuous phase and a step of adjusting a pressure of the polymer phase and a pressure of the continuous phase so as to stabilize the interface;
a step of generating the conductive fiber that comprises the following sub steps:
- generating a single conductive droplet containing light-curing polymers, moving the conductive droplet in a first portion of the third channel, the first portion having a funnel shape so that a dimension of the third channel in the first portion continuously decreases along the axis in a transport direction of the droplet, moving the conductive droplet in a second portion of the third channel, the second portion being contiguous to the first portion,
- the dimension of the third channel being constant in the second portion, exposing in the second portion the conductive droplet to a light radiation so as to at least partially cure the conductive droplet into the conductive fiber, and moving the conductive fiber in a third portion of the third channel, the third portion being contiguous to the second portion, the third portion having a funnel shape so that the dimension of the channel in the third portion continuously increases along the transport axis;
generating the single conductive droplet comprises: forming an interface between a conductive polymer phase and a continuous phase in a microfluidic junction device, such as a flow-focusing or T-junction, the polymer phase containing light-curing polymers, and applying a pressure pulse to the conductive polymer phase so as to eject the conductive droplet from the conductive polymer phase into the continuous phase; and
generating the single conductive droplet comprises extracting the single conductive droplet from a conductive polymer phase, the method further comprising a step of generating the conductive polymer phase that comprises the following sub steps: a first sub step of mixing a liquid phase of light-curing polymers with a conductive material comprising carbon nanotubes, a second sub step of adding a solvent to the liquid phase, the solvent preferably being dimethylformamide, a third sub step of exposing the liquid phase to ultrasound waves, advantageously for a duration superior or equal to 30 minutes and inferior or equal to 6 hours, and a fourth sub step of evaporating the polar solvent out of the liquid phase.

It is also provided a device for manufacturing an electromagnetic resonator, the device comprising a droplet generator comprising:

-- a first channel configured to contain a polymer phase, and
-- a second channel orthogonal to the first channel, the first channel having a junction with the second channel, the droplet generator being configured to provide a flow along a direction in the second channel,

Such device is advantageously and optionally completed by the following features taken singly or in combination:

the droplet generator is configured to produce a single droplet having a dimension superior or equal to 10 µm and inferior or equal to 500 µm;
the device comprising a sensor configured to monitor the junction, a treatment unit configured to receive a sensor signal and detect a conductive fiber in the junction based on the sensor signal, and a command unit configured to control the droplet generator so as to generate a droplet if a conductive fiber is detected in the junction;
the sensor is configured to monitor an interface between the polymer phase and the continuous phase, the droplet generator comprising pressure actuators configured to adjust a pressure of the polymer phase and a pressure of the continuous phase, the device comprising a command unit configured to command the droplet generator to adjust the pressures so as to stabilize the interface; and
the device comprising a conductive droplet generator configured to generate a single conductive droplet, the third channel comprising a first portion having a funnel shape, a dimension of the third channel continuously decreasing in the first portion along the axis, a second portion contiguous to the first portion, the dimension of the third channel being constant in the second portion, and a third portion contiguous to the second portion, the third portion having a funnel shape, the dimension of the third channel continuously increasing in the third portion along the axis, the device comprising a light source configured to expose the second portion to a light radiation.

It is further provided an electromagnetic resonator comprising a cured-polymer non-conductive or magnetic core and a conductive fiber wound around the core, the electromagnetic resonator having a dimension superior or equal to 10 µm and inferior or equal to 500 µm.
Such electromagnetic resonator is advantageously and optionally completed by the following features taken singly or in combination:

the conductive fiber presents a length along a main extension direction, a width along a first transverse direction orthogonal to the main extension direction and a height along a second transverse direction orthogonal to the main extension direction and the first transverse direction, the length being superior to the height, the height being superior to the width, the fiber having a rectangular cross-section in a plane defined by the first transverse direction and the second transverse direction, a transverse aspect ratio corresponding to a ratio of the height above the width being superior or equal to 1.25 and inferior or equal to 30;
the length is inferior to a perimeter of the polymer core and the conductive fiber partially surrounds the core; and
the electromagnetic resonator being manufactured by a method as described above.

It is finally provided an electromagnetic resonance device comprising a plurality of electromagnetic resonators as described above.

DESCRIPTION OF THE FIGURES

Further features and advantages will be apparent from the following description, which is purely illustrative and non-limiting, and should be read in conjunction with the appended drawings on which :

figure 1 is a schematic representation of a device for manufacturing a fiber;
figure 2 is a schematic representation of a fluidic channel of the device;
figure 3 is a schematic representation of a droplet generator of the device;
figure 4 is a schematic representation of a pressure pulse applied to the droplet generator;
figure 5 is a schematic representation of a droplet generation;
figure 6 is a schematic representation of a fiber generation;
figure 7 is a schematic representation of a phase diagram of a fiber generation;
figure 8 is a schematic representation of a process for manufacturing a fiber;
figure 9 is a schematic representation of a phase diagram of a droplet generation;
figure 10 is a schematic representation of a device for manufacturing an electromagnetic resonator;
figures 11 to 14 are schematic representations of different steps of an electromagnetic resonator generation;
figure 15 is a schematic representation of a process for manufacturing an electromagnetic resonator; and
figure 16 is a schematic representation of an electromagnetic resonator.

DETAILED DESCRIPTION OF THE INVENTION

In correspondence with figures 10 and 11, a device 100 for manufacturing an electromagnetic resonator comprises a main droplet generator 102.
The main droplet generator 102 comprises a first main channel 104, a second main channel 108 and a T-junction 116 formed by the first main channel 104 and the second main channel 108.
The first main channel 102 comprises a first main inlet 105 that is configured to receive a non-conductive polymer phase 115 or non-conductive dispersed phase that comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and 10% of water. Other photopolymerisable formulations may be used instead of PEGDA such as PVA,PEGDVE, PEGDMA, etc.The non-conductive polymer phase comprises light-curing polymers such as UV-curing polymers. In addition to light-curing polymers, the non-conductive polymer phase may advantageously comprise the photo-initiator 2-hydroxy-2-methylpropiophenone. Other photo-initiators such as ethylanthraquinone, ferrocene, hydroxybenzophenone, acetophenone, etc., can also be used.
The main droplet generator 102 comprises a non-conductive polymer phase reservoir that is fluidically connected to the first main inlet 105.
The main droplet generator 102 comprises a first main pressure actuator 106 fluidically connected to the first main inlet 105 through a first main provider channel 107. The first main pressure actuator 106 is configured to apply a pressure Pd2 to the non-conductive polymer phase contained in the first main inlet 105. The first main pressure actuator 106 may be a syringe pump or advantageously a pressure controller. The first main pressure actuator 106 is fluidically connected to the non-conductive polymer phase reservoir so as to provide the non-conductive polymer phase to the first main inlet 105.
The device 100 for manufacturing an electromagnetic resonator comprises a command unit 64 that is configured to control the first main pressure actuator 106.
From the junction 116, the first main channel 104 extends towards the first main inlet 105 along a Yc direction.
The second main channel 108 comprises a second main inlet 109 that is configured to receive a continuous phase 140 that comprises advantageously Krytox oil and 1% of surfactant. Other types of oil can be used in place of Krytox oil, such as mineral oils or hydrocarbon derivatives. The surfactant may be advantageously PFPE-COOH. Other types of surfactants such as polysorbate 20 , sorbitan monooleate, sodium dodecyl sulfate (SDS), etc., may also be used. The main droplet generator 102 comprises a continuous phase reservoir that is fluidically connected to the second main inlet 109.
The main droplet generator 102 comprises a second main pressure actuator 110 fluidically connected to the second main inlet 109 through a second main provider channel 111. The second main pressure actuator 110 is configured to apply a pressure Pc2 to the continuous phase contained in the second main inlet 109. The second main pressure actuator 110 may be a syringe pump or pressure controller. The second main pressure actuator 110 is fluidically connected to the continuous phase reservoir so as to provide the continuous phase to the second main inlet 109.
The command unit 64 is configured to control the second main pressure actuator 110.
The second main channel 108 extends along a main direction of extension 117 through the junction 116 along a Xc direction orthogonal to the Yc direction.
In a zone Z that surrounds and includes the junction 116, the second main channel 108 is orthogonal to the first main channel 104.
The zone Z is illustrated with more details in figures 11 to 14.
The first main channel 104 extends only on one side of the T-junction 116, or in other words, the first main channel extends only on one side of the second main channel 108.
The main droplet generator 100 is configured to provide a main flow 114 along the main direction of extension 117 in the second channel.
The main droplet generator 100 comprises a third main channel 3 that opens into the first main channel 104. The third main channel 3 extends only on one side of the first main channel 104. The junction 137 between the third main channel 3 and the first main channel 104 is located in the zone Z, so that the junction 137 between with the third main channel 3 and the first main channel 104 is close to the junction 116 first main channel 104 and second main channel 108. The third main channel 3 advantageously enters the first main channel 104 within a distance of the second main channel 108 equal to one width 135 of the first main channel 104. In other words, the distance 134 from the second main channel 108 and the junction 137 between the third main channel 3 and the first channel 104 is inferior or equal to the width 135 of the first main channel 104.
In correspondence with figure 11, the width 135 of the first main channel 104 and the width 136 of the second main channel 108 are both superior or equal to 20 µm and inferior or equal to 500 µm. The lengths of these channels 104 and 108 are in the range from 1000 µm to 4000 µm.
A projection of the third main channel 3 on the main direction of extension 117 of the second channel 108 is located upstream of the junction 116 with respect to the main flow 114. The third main channel 3 has an axis of extension 9 that is, in the zone Z, not parallel or orthogonal to both directions Xc and Yc. The third main channel 3 extends obliquely with respect to both the first main channel 104 and the second main channel 108.
The angle 133 between the axis of extension 9 of the third main channel 3 and the main direction of extension 117 is strictly superior to 0°and strictly inferior to 90°.
The main droplet generator 100 is configured so that when the third main channel 3 approaches the first main channel 104, the third main channel 3 approaches also the second main channel 108.
More particularly, and as illustrated in figure 11, the axis of extension 9 of the third main channel 3 passes continuously through the third channel 3, the first channel 104 and the second channel 108. In other words, the axis of extension 9 does not cross the walls of the first main channel 104 and crosses only one wall of the second main channel 108. The axis of extension 9 is centered in the third main channel 3.
The main droplet generator 100 is configured so that the third main channel 3 transports along the axis of extension 9 a conductive fiber 118 from the third channel across the first channel and inside the second channel.

T-junction

In operation, the first main inlet 105 is provided with the non-conductive polymer phase 115 and the second main outlet is provided with the continuous phase 40, the main droplet generator 102 is configured to create an interface 123 between the continuous phase and the non-conductive polymer phase at the cross junction 80.
More specifically, the interface 123 is located within the first main channel 104. Advantageously, the junction 137 between the third main channel 3 and the first channel 104 is located between the interface (or meniscus) 123 and the second main channel 108. The interface (or meniscus) 123 is separated from the junction 137 between the third main channel 3 and the first channel 104 by a distance inferior or equal to the width 136 of the second main channel 108.
The main droplet generator 102 comprises a sensor 120 located close to the T-junction 116, the sensor 120 being configured to monitor the interface 123. For instance, the sensor 120 is a camera configured to image the interface 123 and the T-junction 116. In another instance, the sensor 123 can be any physical device configured to detect an interface between two liquids, for example, a local refractive index probe, a capacitance probe or a dielectric probe.
The sensor 123 is connected to the command unit 64. The command unit 64 is configured to control the first main pressure actuator 106 and the second main pressure actuator 110 possibly based on a signal provided by the sensor 123. In particular, the command unit 64 is configured to control the pressure actuators 106 and 110 so as to stabilize the interface 123. This stabilization may correspond to a steady or a quasi-|steady signal provided by the sensor 123.
The sensor 123 may in addition be sensitive to conductive materials. The sensor 123 may then deliver a signal that also depends on the presence of a conductive fiber 118 in the junction 116 and in particular in the second channel 108. The sensor may alternatively produce a complementary signal that depends on the presence of a conductive fiber 118 in the junction 116 and in particular in the second channel 108. The command unit 64 may further comprise a treatment unit 121 configured to receive the sensor signal or the complementary signal and detect a conductive fiber in the junction based on this signal. The command unit 64 may then trigger a droplet generation in the main droplet generator 102 based on the detection of a conductive fiber 118 in junction 116.
Further with respect to the T-junction in the second main channel 108 following the main flow 114, the device 100 for manufacturing an electromagnetic resonator comprises a curing device 112. The curing device 112 is configured to bring to objects formed by non-conductive polymer phase 115 and located in the second main channel 108 enough energy to reticulate. The curing device 112 may bring energy under a light form or a thermal form.
Further with respect to the curing device 112 in the second main channel 108 following the main flow 114, the device 100 for manufacturing an electromagnetic resonator comprises a main outlet 113.

Fiber

The fiber is conductive. For instance, the fiber is loaded with a fraction of conductive materials such as carbon nanotubes, metallic nanoparticles, metallic nanowires, reduced graphene oxide or PEDOT:PSS (polymer mixture of polystyrene sulfonate and poly(3,4-ethylenedioxythi ophene).).
A fiber presents an elongated shape along a main extension direction X. The fiber presents a length L along the main extension direction X and a width W along a Y direction orthogonal to X, and a height H along a Z-direction orthogonal to both X and Y directions. The width corresponds to the smallest dimension of the fiber. When the fiber has a circular cross-section orthogonally to the main extension direction X, the width corresponds to the diameter of the fiber. The fiber presents an elongated shape along the main extension direction X, which means that a first aspect ratio L/W and a second aspect ratio L/H are significantly superior to 1. In other words, the dimension of an elongated fiber along its main extension direction is much larger than the dimension of the fiber in a transverse plane orthogonal to the main extension direction. A third aspect ratio, H/W is also variable and can be much larger than 1. When the third aspect ratio H/W is significantly different from 1, the fiber presents a ribbon shape.
The fiber may be a thin fiber presenting a width inferior or equal to 12 µm, 10 µm, 8 µm, 6 µm and even 4 µm.
The fiber may be a larger fiber presenting a width superior or equal to 15 µm, 20 µm, 25 µm, 50 µm and even 100 µm.
The length of the fiber may be superior or equal to 25 µm and inferior or equal to 10 mm.
The height of the fiber may be superior or equal to 10 µm and inferior or equal to 200 µm.
The fiber may present a rectangular cross-section. The fiber is, in this case, a ribbon.
The fiber has a rectangular cross-section when the shape of the fiber is rectangular in a plane Y Z orthogonal to the main extension direction X. The transverse aspect ratio of the fiber corresponds to the ratio H/W. When the third aspect ratio H/W is different from 1, the fiber presents a ribbon shape.
The aspect ratio H/W of the fiber may be comprised between 1.25 and 30. For instance the aspect ratio H/W is equal to 1.5, 2, 3, 3.5, 4, 4.5, 5, 7, 10 ,15, 20, 25 or 30
The third main channel 3 advantageously presents a shape that is adapted to the shape of the conductive fiber transported. For instance, when the fiber is a ribbon with a transverse aspect ratio of the fiber equal to 5, the third main channel may also present a section orthogonally to the axis of extension 9 which presents a rectangular shape and a transverse aspect ratio close to 5. In particular, the third main channel may have transverse dimensions with respect to the axis of extension 9 that are sufficiently adjusted to the width and the height of the fiber so that the fiber cannot rotate inside the third main channel with respect to axis of extension 9.
For instance, a width of the third main channel 3 may be two times or three times bigger than the width of the fiber and a height of the third main channel 3 may be less than two times bigger than the height of the fiber.
The conductive fiber may be produced out of the main droplet generator 100 and inserted into the third main channel 3.
The conductive fiber may alternatively be produced in the main droplet generator 100. This second option may be implemented using a device 1 for manufacturing a fiber that comprises a droplet generator 2 and a fluidic channel 3.
The device 1 for manufacturing a fiber is illustrated in figures 1 to 3.
Advantageously, the device 1 comprises a microfluidic circuit 5 that includes both the droplet generator 2 and the fluidic channel 3.

Droplet generator

In correspondence with figure 3, the droplet generator 2 comprises a microfluidic pathway 29 that comprises two inlets 30 and 32 and one outlet 34. The microfluidic pathway 29 extends in a plane defined by orthogonal directions Xa and Ya.
A first inlet 30 of the droplet generator is configured to receive a flow of continuous phase 40 that comprises advantageously Krytox oil and 1% of surfactant. Other types of oil can be used in place of Krytox oil, such as mineral oils or hydrocarbon derivatives. The surfactant may be advantageously PFPE- COOH. Other types of surfactants such as polysorbate 20, sorbitan monooleate, Sodium dodecyl sulfate (SDS), etc... may also used.
The droplet generator 2 comprises a continuous phase reservoir that is fluidically connected to the first inlet 30.
The droplet generator 2 comprises a first pressure actuator 56 fluidically connected to the first inlet 30 through a first provider channel 58. The first pressure actuator 56 is configured to apply a pressure Pc to the continuous phase contained in the first inlet 30. The first pressure actuator 56 is fluidically connected to the continuous phase reservoir so as to provide the continuous phase to the first inlet 30.
A second inlet 32 of the droplet generator is configured to receive a conductive polymer phase 42 or, also generally called conductive dispersed phase that comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and a proportion of water superior or equal to 10% and inferior or equal to 30%. Other types of photopolymerisable polymer formulation may be used instead of PEGDA such as PVA, PEGDVE, PEGDMA, etc.... The conductive polymer phase comprises light-curing polymers such as UV-curing polymers. In addition to light-curing polymers, the conductive polymer phase may advantageously comprise a photo-initiator 2-hydroxy-2-methylpropiophenone Other photo-initiators such as Ethylanthraquinone, Ferrocene, Hydroxybenzophenone, acetophenone, etc., can also be used.
The conductive polymer phase and the continuous phase correspond to non-miscible fluids. The droplet generator 2 comprises a conductive polymer phase reservoir that is fluidically connected to the second inlet 32.
The droplet generator 2 comprises a second pressure actuator 57 fluidically connected to the second inlet 32 through a second provider channel 59. The second pressure actuator 57 is configured to apply a pressure Pd to the continuous phase contained in the second inlet 32. The second pressure actuator 57 is fluidically connected to the conductive polymer phase reservoir so as to provide the conductive polymer phase to the second inlet 32.
The command unit 64 is configured to control the pressure actuators 56 and 57.
The first pressure actuator 56 and the second pressure actuator 57 may be syringe pumps, pressure controllers or any device which is either pressure-controlled or flow-controlled....
The microfluidic pathway 29 comprises a first inlet channel 39 that connects fluidically the inlet 30 to the rest of the microfluidic pathway 29. The first inlet channel 39 has a main extension direction parallel to the direction Xa and presents a length 31 along this main extension direction. The length 31 is advantageously comprised between 900 µm and 1000 µm, for instance equal to 970 µm.
The microfluic pathway presents a height measured in an orthogonal to directions Xa and Ya that is superior or equal to 10 µm and inferior or equal to 50 µm, for instance the height is equal to 28.5 µm.
The height of the microfluic pathway corresponds to the height of each channel comprised in the microfluic pathway, such as the first inlet channel 39.
The first inlet channel 39 extends up to an upper channel 43 and a lower channel 44 of the microfluidic pathway 29 and opens into both the upper channel 43 and the lower channel 44.
The upper channel 43 comprises :

a first portion 43A extending from the first inlet channel 39 along the direction Ya and presenting a length 33 along the direction Ya,
a second portion 43B extending from the first portion 43A along the direction Xa and presenting a length 35 along the direction Xa, and
a third portion 43C extending from the second portion 43B in the opposite direction to the direction Ya and presenting a length equal to the length 33 along the direction Ya.

The lower channel 44 comprises :

a first portion 44A extending from the first inlet channel 39 in the opposite direction of the direction Ya and presenting a length equal to the length 33 along the direction Ya,
a second portion 44B extending from the first portion 44A along the direction Xa and presenting a length equal to the length 35 along the direction Xa, and
a third portion 44C extending from the second portion 44B along the direction Ya and presenting a length equal to the length 33 along the direction Ya.

The third portion 44C of the lower channel 44 and the third portion 43C of the upper channel 43 presents the same width 49 measured along the Xa direction.
The length 33 is advantageously comprised between 100 µm and 4000 µm, for instance equal to 1700 µm
The length 35 is advantageously comprised between 2000 µm and 20000 µm, for instance equal to 7665 µm
The width 49 is advantageously comprised between 50 µm and 500 µm, for instance equal to 150 µm.
The upper channel 43 and the lower channel 44 are arranged symmetrically with respect to the direction Xa.
The upper channel 43 and the lower channel 44 define between them a rectangular area 45. The second inlet 32 is located in the rectangular area 45. The second inlet 32 is located in the center of the rectangular area 45 with respect to the Ya direction.
The microfluidic pathway 29 comprises a second inlet channel 46 that connects fluidically the second inlet 32 to the rest of the microfluidic pathway 29. The second inlet channel 46 extends from the second inlet 32 along the direction Xa. The second inlet channel may alternatively comprise a central part that presents a sinuous shape, the central part being located between two straight parts that both extend along a main extension direction parallel to Xa. The second inlet channel 46 presents a length 36 along this main extension direction which is the direction Xa or alternatively a variable direction in the case of sinuous central part. The second inlet channel 46 presents a width 47 measured along the Ya direction.
The length 36 is advantageously comprised between 1000 µm and 20000 µm, for instance equal to 9225 µm.
The width 47 is advantageously comprised between 50 µm and 500 µm, for instance equal to 150 µm.
The first inlet channel 39 and the second inlet channel 46 have the same main extension direction so that the first inlet channel 39 and the second inlet channel 46 are aligned. The second inlet channel 46 extends from the second inlet 32 along the direction Xa up to the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
The second inlet channel 46 opens into both the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
The microfluidic pathway 29 comprises an outlet channel 53 that connects fluidically the outlet 34 to the rest of the microfluidic pathway 29. The outlet channel 53 extends from the outlet 32 in the opposite direction to Xa and presents a length 37 along this main extension direction.
The first inlet channel 39, the second inlet channel 46 and the outlet channel 53 have the same main extension direction so that they are all aligned.
The outlet channel 53 extends from the outlet 32 in the opposite direction to Xa up to the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44. The outlet channel 53 opens into both the third portion 43C of the upper channel 43 and the third portion 44C of the upper channel 44.
The outlet channel 53 comprises a collar 51 that connects the third portion 43C and the third portion 44C to the rest of the outlet channel. The collar 51 presents a width 54 along the direction Ya that is smaller than a width 55 of the rest of the outlet channel 53 along the direction Ya.
The length 37 is advantageously comprised between 5000 µm and 20000 µm, for instance equal to 8000 µm.
The width 55 is advantageously comprised between 50 µm and 300 µm, for instance equal to 200 µm.
The width 54 is advantageously comprised between 20 µm and 70 µm, for instance equal to 50 µm.

Cross-junction

The microfluidic pathway 29 defines a cross junction 80 where the second inlet channel 46, the third portion 43C of the upper channel 43, the third portion 44C of the upper channel 44 and the collar 51 of the outlet channel 53 meet.
In the cross junction the third portion 43C and the third portion 44C are facing each other and aligned on the Ya direction, and the second inlet channel 46 and the collar 51 of the outlet channel 53 are facing each other and aligned on the Xa direction.
In operation, the first inlet 30 is provided with the continuous phase 40 and the second inlet 32 is provided with the conductive polymer phase 42, the droplet generator 2 is configured to create an interface 60 between the continuous phase and the polymer at the cross junction 80.
More specifically, the interface 60 is located within the second inlet channel 46 so as to define a flow focusing junction.
The droplet generator 2 comprises a sensor 62 located close to the cross junction 80, the sensor 62 being configured to monitor the interface 60. For instance, the sensor 62 is a camera configured to image the interface 60 and the cross junction 80. In another instance, the sensor 62 is a conductivity sensor configured to perform a conductivity measurement across the microchannel in the Ya direction at the meniscus 60. Another option is to use a capacitance sensor configured to perform a capacitance measurement along the same direction. Another possible option is to use an optical sensor configured to perform a local measurement of the optical density. Such an optical sensor may be different from a camera. The sensor 62 is connected to the command unit 64. The command unit 64 is configured to control the pressure actuators 56 and 57 possibly based on a signal provided by the sensor 62. An option of control consists in varying a set value of the first pressure actuator 56 while a command signal of the second pressure actuator 57 is maintained constant. Alternatively, the operator may vary a set value of the second pressure actuator 57 while a command signal of the first pressure actuator 56 is maintained constant. In particular, the command unit 64 is configured to control the pressure actuators 56 and 57 so as to stabilize the interface 60. This stabilization may correspond to a constant or a quasi-contant signal provided by the sensor 62.

Droplet generation

For a given pressure Pc of the continuous phase, there exists a pressure Pd of the dispersed phase or conductive polymer phase at which the interface 60 is at equilibrium close to the cross junction 80. Then, in steady conditions, if Pd is below this value, there is some backflow inside the second inlet channel 46. Conversely, if Pd exceeds this equilibrium value, the dispersed phase is pushed towards the collar 51 of the outlet channel 53.
When Pd is above this equilibrium value and below a second threshold, the dispersed phase is squeezed by the flow of continuous phase and breaks into droplets. Different regimes exist in the microfluidic literature (dripping, squeezing, jetting...) depending on the mechanism responsible for the pinch-off of the neck. In the illustrated configuration of figure 3, droplet production occurs in the squeezing regime. In that case, the dispersed phase clogs the channel which gives rise to a pressure gradient inside the film of continuous phase in between the wall and the dispersed phase. When the latter fills the exit channel over a sufficient length, the pressure gradient becomes strong enough to deform and break the dispersed phase. When Pd exceeds the second threshold, the dispersed phase forms a jet inside the outlet channel 53: this is commonly referred to as the jetting regime in microfluidic literature Note that in the illustrated configuration of figure 3, the jet remains stable over the whole length of the exit channel.
The droplet generator 2 as described above can be used to implement a step S2 of generating a single droplet. The step S2 is a step of a fiber generation process P which is described further in the description.
To realize this step S2 and generate a single droplet, the following substeps can be implemented :

T1 : providing the continuous phase 40 from the first inlet 30 of the droplet generator and providing the conductive polymer phase 42 from the second inlet 32,
T2 : setting a given pressure Pc to the continuous phase,
T3 : forming an interface between a conductive polymer phase and a continuous phase, for instance by setting a given pressure Pd to the conductive polymer phase, the given pressure corresponding to the equilibrium value so as to create an interface 60 in the cross junction 80,
T6 : applying a pressure pulse in the polymer (or dispersed) phase so as to increase Pd by an amount ΔP for a duration Δt.

Optionally, when the droplet generator 2 comprises the sensor 62, the process P can comprise the optional steps :

T4, during which the sensor 62 monitors the interface 60, and
T5, during which the command unit 64 controls the pressure actuators to adjust the pressure of the conductive polymer phase and the pressure of the continuous phase and stabilize the interface.

Such monitoring and adjustment greatly improve the stability of the interface 60 and enable to generate single droplet in a much more efficient way.
Figure 4 illustrates this temporal sequence wherein curve 66 corresponds to the pressure applied to the continuous phase and curve 68 corresponds to the pressure applied to the conductive polymer phase.
To generate a single droplet, different pressure pulse parameters corresponding to pressure Pc, pressure Pc, amplitude ΔP and duration Δt, can be applied.
Figure 6 illustrates the generation of a single droplet obtained thanks to such a pressure pulse application. Image 71 of figure 5 corresponds to the situation before the application of the pulse: the conductive polymer phase is located inside the second input channel 46 and the interface 60 is stable. Image 72 of figure 5 corresponds to the situation during the application of the pulse: the conductive polymer phase is projected out of the second input channel 46 up to the outlet channel 53. The conductive polymer phase forms a liquid neck between the second inlet channel 46 and the collar 51 and further in the outlet channel the conductive polymer phase forms a curved volume. The curved volume, the liquid neck and the rest of the conductive polymer phase inside the second input channel 46 form a continuous conductive polymer phase.
At the end of the pressure pulse, the liquid neck stops and is compressed by the continuous phase, the curved volume is separated from the rest of the conductive polymer phase inside the second input channel 46 so as to generate a single droplet 38.
The step T6 leads to a step T7 of extracting a single droplet from the conductive polymer phase.
The volume of the droplet is controlled by the pulse amplitude ΔP, its duration Δt and the pressures Pc and Pd.
Larger single droplets may be obtained by increasing the amplitude ΔP or the duration Δt.
Smaller single droplets may be obtained by decreasing the amplitude ΔP or the duration Δt.

Calibration of the droplet generator

In order to generate a single droplet, the microfluidic droplet generator may first be calibrated. A basic calibration method C may be implemented before the implementation of the step S2.
The basic calibration method C comprises the following steps:

C1: selecting a value of the pressure Pc of the continuous phase,
C2: determining the corresponding equilibrium value of Pd,
C3: selecting a value of the pulse amplitude ΔP and a set of candidate values of the pulse duration Δt,
C4: for each candidate value of the pulse duration Δt, applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd, the value of the pulse amplitude ΔP and the candidate value of the pulse duration Δt,
C5: for each candidate value of the pulse duration Δt, determining if a single droplet is generated
C6: validating a candidate value of the pulse length Δt if a single droplet of conductive polymer phase is generated.

Step C2 may be achieved by a balance of pressures based on the following equality: the difference in pressure between the first inlet 30 and the pressure at junction 48 is equal to the difference in pressure between the second inlet 32 and the Laplace pressure at the meniscus 60. The Laplace pressure Pl depends on the surface tension between the continuous phase 42 and the dispersed phase 42, the channel height and the width 47 of the second inlet channel 46.
Step C5 may be achieved by optical observation. To that end, the sensor 62 may advantageously comprise a camera.
This basic calibration method may advantageously comprise the complementary steps :

C7: determining a lower threshold of Δt1 so that applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd, the value of the pulse amplitude ΔP and any value of Δt inferior or equal to Δt1 does not generate a single droplet of conductive polymer phase, and
C8: determining an upper threshold of Δt2 so that applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd, the value of the pulse amplitude ΔP and any value of Δt superior or equal to Δt2 does not generate multiple droplets of conductive polymer phase; Δt2 can be estimated during the calibration phase by holding the second pressure actuator 57 at the combined value Pd+ΔP and observing the time elapsed between successive droplet formation events.

These complementary steps are based on the following trends that have been generally observed. There are a lower threshold Δt1 and an upper threshold Δt2, so that:

below Δt1, the pulse is too short to generate a droplet, and
above Δt2, either the droplet takes the shape of a plug or the droplet gets separated into a plurality of smaller droplets; a plug corresponds to a droplet that entirely fills

The microfluidic droplet generator may be further calibrated by :

C9: selecting a set of candidate values of Pc and
C10: applying the basic calibration method for each candidate value of Pc.

Based on these different method steps, phase diagrams may be built. A phase diagram may be associated with each candidate value of Pc, and represent schematically the determined values of the pulse amplitude ΔP and of determined values of the pulse length Δt that lead to the generation of a single droplet of the conductive polymer phase.
The following trends have been generally observed. Long pulses (Δt > Δt2) generate plugs at high amplitude ΔPh (that is the set of values Pc and Pd+ ΔPh corresponds to the jet regime ; in other words Pd+ ΔPh is above the second threshold of Pd for which the dispersed phase forms a stable jet inside the outlet channel 53 when the pressure is applied continuously at Pd+ ΔPh) and several drops at low amplitude ΔPl (that is the set of values Pc and Pd+ ΔPl corresponds to the dripping regime ; in other words Pd+ ΔPl is below the second threshold of Pd for which the dispersed phase breaks into droplets inside the outlet channel 53 when the pressure is applied continuously at Pd+ ΔPl).
An example of a phase diagram is given in figure 9, for four different sets of values of pressure of the continuous phase Pc and pulse amplitude ΔP, figure 9 illustrates values of pulse length Δt (x-axis) for which a single droplet is generated. The volume of the droplet is given on the y-axis. This diagram shows additionally that the volume increases when the pulse amplitude ΔP increases and/or when the pulse length Δt increases.
The control of the pressure actuators so as to stabilize the interface is stopped during the pressure pulse.
It is to be noted that alternative microfluidic droplet generating devices may be used, for instance a device based on a T-junction. Pressure pulses as previously described may be used to generate a single droplet in these alternative microfluidic droplet generating devices. Analogous calibration methods may also be implemented to identify pressure pulse parameters that lead to a single droplet generation.

Conductive polymer phase

The conductive polymer phase may be generated during a first step S1 of the process P.
The conductive polymer phase 42 comprises advantageously a mixture of light-curing polymers such as PEGDA (Polyethylene glycol diacrylate) and 10% of water. Other types of photopolymers may be used instead of PEGDA such as PVA, PEGDVE, PEGDMA, etc ... The conductive polymer phase comprises light-curing polymers such as UV-curing polymers. In addition to light-curing polymers, the conductive polymer phase may advantageously comprise a photo-initiator 2-hydroxy-2-methylpropiophenone. Other photo-initiators such as Ethylanthraquinone, Ferrocene, Hydroxybenzophenone, acetophenone, etc., can also be used. In the case of 2-hydroxy-2-methylpropiophenone, 5% is placed in the mixture.
The conductive polymer phase comprise, in addition to light-curing polymers and water, a conductive material.
In a first substep G1 of the step S1, the conductive material is mixed with light-curing polymers.
The conductive material may comprise carbon nanotubes, Silver Nanoparticles, reduced graphene oxide or PEDOT:PSS (polymer mixture of polystyrene sulfonate and poly(3,4-ethylenedioxythiophene) ). Carbon nanotubes (CNT) may be single walled CNT or multiwalled CNTs.
In the case of carbon nanotubes, graphene oxide or PEDOT:PSS, the generation of the conductive polymer phase may comprise:

the first substep G1 that comprises mixing the functional material with light-curing polymers in a liquid phase,
a second substep G2 that comprises adding a polar solvent to the liquid phase, the polar solvent preferably being dimethylformamide,
a third substep G3 that comprises exposing the liquid phase to ultrasound waves advantageously for a duration superior or equal to 30 minutes and inferior or equal to 6 hours, and
a fourth substep G4 that comprises evaporating the polar solvent out of the liquid phase. The substep G3 of exposing the liquid phase to ultrasound, also known as a ultrasonication step, enables to supply mechanical energy to debundle CNTs (or graphene oxide or PEDOT:PSS) and create percolated suspensions in the liquid phase.

In order to obtain even more homogeneous dispersions in the liquid phase, an optional previous step of adding a polar solvent to the liquid phase can be implemented. In this case, a further step after the ultrasonication step of removing the polar solvent by evaporation is necessary to obtain a liquid phase that fulfills the initial polymer solution conditions.

Fluidic channel

The third main channel 3 may also be designated by the term "fluidic channel 3" in the description.
In correspondence with figure 2, the third main channel fluidic channel 3 extends along a transport axis 9 from an inlet 6 of the fluidic channel 3 to an outlet 15 of the fluidic channel 3.
The fluidic channel comprises advantageously walls in PDMS (Polydimethylsiloxane).
The fluidic channel 3 extends in a main plane defined by orthogonal directions Xb and Yb. The transport axis 9 is parallel to the direction Xb.
The fluidic channel 3 presents a height measured in an orthogonal to directions Xb and Yb that is superior or equal to 10 µm and inferior or equal to 200 µm, for instance the height is equal to 28.5 µm.
The height of the fluidic channel is the same as channel 3 and it is superior or equal to 10 µm and inferior or equal to 200 µm.
The inlet 6 of the fluidic channel may be advantageously fluidically connected to the outlet 34 of the droplet generating device 2.
The fluidic channel 3 presents a width (or more generally a dimension) measured along the direction Yb and orthogonally to the transport axis 9. The width (or dimension) of the fluidic channel is variable along the transport axis 9.
The inlet 6 and the outlet 15 of the channel correspond to straight channel so that in the main plane walls of the inlet 6 and the outlet 15 of the fluidic channel 3 are parallel to the transport axis 9. The width of the fluidic channel 3 is constant in the inlet 6 and the outlet 15. For example, the width of the fluidic channel 3 in the inlet 6 and the outlet 15 is inferior or equal to 500µm.
The fluidic channel 3 comprises three different portions located along the direction defined by the transport axis between the inlet 6 and the outlet 15.
The fluidic channel 3 comprises a first portion 7 that is contiguous to the inlet 6. The first portion 7 is contiguous to the inlet 6 means that the wall of the fluidic channel is continuous from the inlet 6 to the first portion 7. The same meaning of the term "contiguous" is used further in the description.
The first portion 7 has a funnel shape so that the dimension 8 of the channel in the first portion continuously decreases along the transport axis 9.
The first portion 7 extends on a length 20 superior or equal to 200 µm and inferior or equal to 1000 µm measured along the transport axis 9.
The fluidic channel 3 comprises a second portion 10 that is contiguous to the first portion 7. The second portion 10 has a straight shape so that the dimension 11 of the channel in the second portion 10 is constant along the transport axis 9. The second portion 10 extends on a length 22 superior or equal to 400 µm and inferior or equal to 4000 µm measured along the transport axis 9.
The dimension 11 is superior or equal to 2 µm and inferior or equal to 100 µm. The dimension may take any value between 2 µm and 100 µm, for instance 15 µm, 20 µm, 25 µm, 30 µm, 35 µm, 40 µm, 45 µm, 50µm. Advantageously the dimension 11 inferior or equal to 12µm and even more advantageously inferior or equal to 10µm. The dimension 11 may take any value between 2 µm and 12 µm, for instance 4 µm, 5µm, 6µm, 7µm, 8 µm, 9µm, 10µm and 11µm. The fluidic channel 3 comprises a third portion 12 that is contiguous to the second portion 10. The third portion 12 has a funnel shape, the dimension 13 of the channel continuously increasing along the transport axis 9. The third portion 12 extends on a length 24 superior or equal to 200 µm and inferior or equal to 1000 µm measured along the transport axis 9.
The fluidic channel may be centered on the transport axis 9.
In this case, the first portion 7 presents a funnel shape so that an angle 16 of a wall of the first portion 7 with respect to the transport axis 9 is inferior or equal to 30°, and advantageously inferior or equal to 7°. In other words, a ratio (R1) of a decrease (Δw1) of the dimension (width) of the channel in the first portion over a distance (ΔL1) along the transport axis so that R1=Δw1/ΔL1 is inferior or equal to 1 and advantageously inferior or equal to 0.24. R1 is equal to twice the tangent of the angle 16.
The decrease (Δw1) of the dimension (width) of the channel is determined between two points of the wall of the fluidic channel in the first portion before entering the zone of constant dimension 11. The two points are separated along the transport axis 9 by a distance ΔL1. At the first point the fluidic channel presents a first width wA and at the second point the fluidic channel presents a second width wB. If the second point is closer to the outlet 15 and the first point closer to the inlet 6, then wB<wA and R is equal to the ratio (wA-wB)/ΔL1. The angle 16 of a wall of the first portion 7 with respect to the transport axis 9 can be superior or equal to 2° and advantageously superior or equal to 4°. In other words, the ratio (R1) of the decrease (Δw1) of the dimension (width) of the channel in the first portion over the distance (ΔL1) along the transport axis is superior or equal to 0.07 and advantageously superior or equal to 0.14.
In this same case, the third portion 12 presents a funnel shape so that an angle 18 of a wall of the third portion 12 with respect to the transport axis 9 is inferior or equal to 32°.
In other words, a ratio (R2) of an increase (Δw2) of the dimension (width) of the channel in the third portion 12 over a distance (ΔL2) along the transport axis so that R2=Δw2/ΔL2 is inferior or equal to 1 and advantageously inferior or equal to 1.2. R2 is equal to twice the tangent of the angle 18.
The increase (Δw2) of the dimension (width) of the channel is determined between two points of the wall of the fluidic channel in the third portion. The two points are separated along the transport axis 9 by a distance ΔL2. At the first point the fluidic channel presents a first width wC and at the second point the fluidic channel presents a second width wD. If the second point is closer to the outlet 15 and the first point closer to the inlet 6, then wD>wC and R2 is equal to the ratio (wD-wC)/ΔL2.
The angle 18 of a wall of the third portion 12 with respect to the transport axis 9 can be superior or equal to 2° and advantageously superior or equal to 4°. In other words, the ratio (R2) of the increase (Δw2) of the dimension (width) of the channel in the third portion 12 over the distance (ΔL2) along the transport axis is superior or equal to 0.07 and advantageously superior or equal to 0.14.
The angle of a wall of the second portion 10 with respect to the transport axis 9 is equal to zero as the second portion is a straight portion. Advantageously, the angle presents a continuous variation in the first portion 7, the second portion 10 and the third portion 12. In other words, the angle of a wall of the fluidic channel with respect to the transport axis 9 is equal to zero in the second portion 10 and takes continuously positive values from the second portion to the first portion or from the second portion to the third portion.
The device 1 for manufacturing a fiber comprises also a light source 14 configured to expose the second portion to a light radiation. In particular, the light source 14 may be a UV light source.
The light source emits light in a specific band width and provides a light energy density in the second portion 10.
The light source is configured to not emit light towards the first portion or the third portion.
Optionally, the device 1 for manufacturing a fiber may comprise complementary channels 80 and 82 that open into the fluidic channel at a transition between the second portion 10 and the third portion 13. The complementary channels are parallelly disposed with respect to the transport axis 9. The complementary channels are curved so that the main direction of extension of each complementary is variable in the plane defined by directions Xb and Yb. In particular, the main direction of extension of each complementary channel becomes more and more parallel to the transport axis 9 as the complementary channel approaches the fluidic channel 3. Advantageously an angle between the transport axis 9 and the main direction of extension of a complementary channel at the transition of the complementary channel and the fluidic channel 3 is inferior or equal to 5° and preferably between 0° and 4°.
These complementary channels are configured to be filled with continuous phase and to carry complementary flows 81, 83. For each complementary channel 80, 82, the complementary flow 81, 83 is directed along the main direction of extension of the complementary channel and directed to enter the fluidic channel and flow from the second portion towards the third portion.

Fiber generation

The device 1 for manufacturing a fiber can be used to implement a process P to manufacture a fiber. In correspondence with figure 8, we now present the process P.
The first step S1 and the second step S2 of the process P are evoked previsously in the description and correspond respectively to the generation of the conductive polymer phase and the generation of a single droplet. The first step S1 may be preceded by the steps of the calibration method C of the droplet generator.
A third step S3 of the process P comprises moving the single droplet 38 containing light-curing polymers from the outlet 34 of the droplet generator 2 to the inlet 6 of the fluidic channel 3, for instance through the microfluidic circuit 5 that may include both the droplet generator 2 and the fluidic channel 3.
In order to implement this transport, a main flow 70 can be provided, during a sub-step S3A, along the transport axis 9 in the continuous phase through the fluidic channel 3 which is filled with the continuous phase 40.
The third step S3 may be preceded by the steps of the calibration method F of the fluidic channel which is presented further in the description.
A fourth step S4 of the process P comprises moving the single droplet 38 in the first portion 7 of the fluidic channel 3 along the transport axis.
As the single droplet 38 progresses in the first portion towards the second portion, the width of the fluidic channel continuously decreases and the shape of the droplet continuously changes. In particular, the width of the droplet decreases in the direction Yb and the length of the droplet expands in the direction Xb.
Moving the single droplet 38 in the first portion 7 leads to the sub-step S4A of decreasing continuously a dimension of the droplet measured along a transverse direction orthogonal to the transport axis.
Thanks to the funnel shape of the first portion, the shape of the droplet is progressively modified when it travels from the first portion towards the second portion along the transport axis 9. The funnel shape enables to avoid fragmentation of the droplet into multiple smaller droplets.
In order to implement this transport, a main flow 70 can be provided along the transport axis 9 in the continuous phase through the fluidic channel 3 which is filled with the continuous phase 40.
During a fifth step S5, the droplet 38 is transported in the second portion 10 of the channel 3. As the single droplet 38 progresses in the second portion the width of the fluidic channel reaches a minimum value. The width of the droplet decreases and reaches a minimum value. Steps S4 and S5 are schematically illustrated in parts 74 and 75 of figure 6.
During a sixth step S6, the light source 14 provides light to the second portion 10 so as to at least partially cure the droplet into a fiber.
The wavelength of the light source and the density of light energy provided in the second junction are adapted to the type of light-curing polymers contained in the droplet and the density of light-curing polymers contained in the droplet, so as to cure the droplet.
In particular, the wavelength of the light source can be in the UV range, for example around 365 nm.
The polymer solution reticulates and solidifies when exposed to the light of the light source 14. The polymer solution retains the shape of the second portion 10.
In the second section of the channel, the size and shape of the droplet are controlled by the geometry of the channel. As the droplet is cured in the second portion, the size and shape of the droplet in the second section is retained. By controlling the size and shape of the second section, it is thus possible to manufacture fibers presenting a width inferior or equal to 10 µm and/or a rectangular cross-section.
The droplet 38 is surrounded in the second portion by a thin, continuous-phase layer of that facilitates the movement of the droplet and once cured, the movement of the fiber.
When the walls of the fluidic channel 3 are made of PDMS, the presence of the thin continuous-phase layer is promoted by a molecular oxygen diffusion through the PDMS. This diffusion leaves around the droplet/fiber an unpolymerized oxygen inhibition layer. Adding 10% of deionized water to the polymer solution prevents further wetting. 10% of deionized water was used for the experiments. 5% of deionized water corresponds to a minimum amount of water to prevent wetting issues. 30% of deionized water corresponds to a maximum value above which no polymerization is achievable.
Thanks to the continuous-phase layer, the fiber does not stop in the second portion and keeps moving along the transport axis 9.
Exposing the droplet to the light radiation may comprise advantageously providing a light energy density to the droplet superior or equal to a predetermined energy density threshold, and maintaining the droplet in the second portion during a duration superior or equal to a predetermined duration threshold.
There is a light exposure threshold for the cross-linking of each polymer solution. The elastic properties of the obtained fiber appear to depend directly on the energy density of the light and the exposure time.
The elastic properties thus depend on the speed at which the droplet crosses the light-illuminated zone. The speed can be controlled by the pressures applied to the continuous phase.
In order to establish the optimal parameters to generate a fiber, the fluidic channel 3 can be calibrated previously to implement the method P.
For instance, one can elaborate phase diagrams as a function of the width of the second portion, the power of the light source, the pressures applied to the continuous phase and conductive polymer phase during the droplet generation.
For a set of pressure pulse parameters corresponding to pressure Pc, pressure Pc, amplitude ΔP and duration Δt, one can run a fiber generation process with different values of the width of the second portion and different values of power of the light source and evaluate in each case if a fiber is efficiently manufactured. An optical validation, for instance using a camera, can be implemented to verify the presence of a fiber. A calibration method F of the fluidic channel is presented further in the description.
During a seventh step S7, one can move the droplet 38 from the second portion 10 to the third portion 12. This fifth step corresponds to the extraction of the fiber from the thin second portion. The funnel shape of the third portion enables to prevent clogging of the fluidic channel 5 and breakage of the fiber. To the contrary, an abrupt transition will lead to a sudden deceleration of the head of the fiber when it exits the second portion, so that the rest of the fiber is also slowed down. The rest of the fiber will consequently spend more time in the light-exposed second portion. The rest of the fiber may reach a level of curation significantly higher than the head of the fiber, leading to an inhomogeneous fiber and possibly to a clogging of the second portion. The funnel shape of the third portion enables a more progressive deceleration that prevents clogging and the production of more homogeneous fibers.
In other words, as the fiber exits the second section, it experiences slower velocities that can lead to channel clogging, especially in the case of a thin fiber. The funnel shape of the third portion prevents clogging as it limits this slowdown and simplifies the extraction of the rest of the fiber out of the second section.
Advantageously and when the device for manufacturing a fiber comprises complementary channels 80, 82, the step S7 of the process P comprises a substep S7A of adding complementary continuous-phase flows in the third portion so as to align the fiber with the transport axis. The complementary continuous phase flows 81 and 83 help the soft fiber to exit the second portion 10 without deforming and speed up the step S7 of moving the single droplet 38 in the third portion 12, that is extracting the fiber from the second portion 10.
During an optional eighth step S8 implemented once the fiber is reticulated and extracted from the second portion, one can cover the fiber with active molecules. Active molecules may include enzymes, conductive dispersions of nanoparticles, magnetic materials, piezoelectric materials, catalytic materials, electrets, fluorophore etc., ... Covering the fiber with active molecules can be realized thanks to the initial mixture preparation. Preferably, a homogeneous dispersion of the initial mixture preparation helps to locate the active molecules at the surface of the extruded fiber.A homogeneous dispersion may be obtained using an ultrasonication of the mixture in the dispersed phase 42, or using surface chemical modifications of the conductive phase. This latter can be, for example, grafted polymer chains.

Calibration method of the fiber channel

A method F for calibrating the fiber channel may comprise the following steps.
During a first step F1, the operator selects a set of pressure pulse parameters (values of Pc, corresponding equilibrium value of Pd, pulse amplitude ΔP and pulse duration Δt), for which a single droplet is obtained using the droplet generator 2.
During a second step F2, the operator selects a set of candidate values of the width 11 of the second portion 10. The operator will thus need to dispose of different fluidic channels that each presents one of the candidate values of the width 11. Each fluidic channel may be fluidically connected to the droplet generator as previously mentioned.
During a third step F3, the operator selects a set of candidate values of power of the light source. The operator will thus need to dispose means to modify the power of the light source so as to be able to provide the second portion of the channel with each candidate value. For instance, the light source may be naturally controlled in power thanks to a variator, or alternatively calibrated attenuator windows may be disposed between the light source and the second portion. Other means to modify the power of the light source may include pulse width modulation via an electronic trigger and spectral filters.
During a fourth step F4 and for each fluidic channels, the operator implements a droplet generation and a fiber generation by connecting the outlet of the droplet generator to the inlet of the fluidic channel, generating in the droplet generator a single droplet based on the set of pressure pulse parameters, moving the single droplet through the fluidic channel from the first portion to the second portion, exposing the droplet in the second portion to a candidate power of the light source, and evaluating if a fiber is efficiently manufactured at the output of the fluidic channel.
During a fifth step F5, the operator may repeat steps F4 for different sets of pressure pulse parameters.
During a sixth step F6, the operator determines each case an exposure time of the droplet to the light source and a light energy density at which the droplet was exposed to the light source. The exposure time depends on the velocity of the droplet inside the second portion, this velocity depending itself on the pressure Pc and the geometry of the fluidic channel. The light energy density depends on the power of the light source and the geometry of the second portion of the fluidic channel.
During a seventh step F7, the operator determines a minimum exposure time above which fibers can be obtained. This determination may be limited to a specific geometry of the fluidic channel, for instance to a specific width of the second portion.
During a seventh step F8, the operator determines a minimum light energy density above which fibers can be obtained. This determination may be limited to a specific geometry of the fluidic channel, for instance to a specific width of the second portion.
This calibration may lead to a phase diagram as examplified in figure 7. This phase diagram corresponds to a fixed geometry of the fluidic channel for which the parameters of exposure time (y-axis) and energy density (x-axis) have been scanned. Situations for which a fiber is obtained are illustrated as inclined squares, other situations correspond to right squares. This calibration enables to identify a minimum exposure time above which fibers can be obtained. This minimum exposure time can then be used in the process to maintain the droplet in the second portion during a duration superior or equal to this minimum exposure time, corresponding then to a predetermined duration threshold.
This calibration enables also to identify a minimum light energy density above which fibers can be obtained. This minimum light energy density can then be used in the process to provide a light energy density superior or equal to this minimum light energy density corresponding then to a predetermined energy density threshold.
If the calibration method is perfomed, substeps S6A and S6B may be advantageously to step S6 of exposing the droplet to the curing light provide by the light source.
During the substep S6A, the light source provides a light energy density to the droplet superior or equal to the predetermined energy density threshold.
During the substep S6B, the droplet is maintained in the second portion during a duration superior or equal to the predetermined duration threshold.

Manufactured fiber

The manufacturing device 1 and the manufacturing method P enables to manufacture fibers comprising curing polymers and in particular light-curing material.
The width of the fiber is given by the width of the second portion 10 of the fluidic channel 3. As the width of the second portion 10 may be as small as 2 microns, thin fibers may be manufactured, and in particular fibers presenting a width inferior or equal to 12 µm, 10 µm, 8 µm, 6 µm and even 4 µm.
In addition, larger widths may also be manufactured, for instance fibers presenting a width superior or equal to 15 µm, 20 µm, 25 µm, 50 µm and even 100 µm can be manufactured.
Another advantage of the manufacturing device 1 and the manufacturing method P is the possibility to control the shape of the fiber produced. In particular, it is possible to manufacture fibers that present a rectangular cross-section. The fiber is, in this case, a ribbon.
The fiber presents a length L along the main extension direction X and a width W along a Y direction orthogonal to X, and a height H along a Z-direction orthogonal to both X and Y directions. The fiber has a rectangular cross-section when the shape of the fiber is rectangular in a plane Y Z orthogonal to the main extension direction X. The transverse aspect ratio of the fiber corresponds to the ratio H/W. When the third aspect ratio H/W is different from 1, the fiber presents a ribbon shape.
The fiber presents a transverse rectangular cross-section when the second portion 10 presents a rectangular cross-section.
The cross section of the second portion 10 is the section of the second portion 10 in a plane defined by the direction Yb and the direction orthogonal to both directions Xb and Yb.
The cross section of the second portion is given by the ratio of the width 11 of the second portion 10 by the height of the second portion 10. The height of the second portion 10 corresponds to the height of the fluidic channel and is measured in the direction orthogonal to both directions Xb and Yb. The second portion 10 presents a height superior or equal to 10 µm and inferior or equal to 200 µm, for instance the height is equal to 28.5 µm.
The height of the second portion 10 may be equal to 20 µm, 30 µm, 40 µm, 50 µm, 60µm, 80µm, 100µm, 120µm,
The aspect ratio of the rectangular cross-section of the second portion 10 may be comprised between 1.25 and 20. For instance the aspect ratio H/W is equal to 1.5, 2, 3, 3.5, 4, 4.5, 5, 7, 10, 15, 20, 25 or 30.
The aspect ratio of the rectangular cross-section of the second portion 10 gives the aspect ratio H/W of the fiber.
The aspect ratio H/W of the fiber may be comprised between 1.25 and 30. For instance the aspect ratio H/W is equal to 1.5, 2, 3, 3.5, 4, 4.5, 5, 7, 10, 15, 20, 25 or 30.
The manufacturing device 1 and the manufacturing method P enables to manufacture fibers comprising light-curing material that presents a very wide range of lengths and a very wide range of widths. The length of the fiber is given by the volume of the single droplet and the width of the fiber is given by the width of the second portion 10.
The length of the fiber may be as small as 25µm and as large as 1cm.
An important advantage of the manufacturing device 1 and the manufacturing method P is the high repeatability of the fibers produced. Once a set of manufacturing parameters is chosen (pressure pulse parameters and dimensions of the second portion 10 of the fluidic channel), the manufacturing method leads to single droplets generated that have a very regular volume and to fibers generated that have a very regular length, width and height. Thanks to the precision of microfluidic technologies, the statistic distribution of the length, (respectively the width and the height) of the fibers produced with a fixed set of manufacturing parameters is a very narrow peak so that the distribution can be qualified as monodisperse.
Fibers with precise and repeatable geometry can be fabricated based on the manufacturing device 1 and/or the manufacturing method P.

Electromagnetic resonator generation

The electromagnetic resonator generator 100 is configured to generate an electromagnetic resonator according to a method A for manufacturing an electromagnetic resonator.
We now present the steps of the method A in correspondence with figure 15.
In a first step A1, an operator generates a non-conductive polymer phase 115.
In a second step A2, an operator places the non-conductive polymer phase 115 in the first main channel 104 and the continuous phase 40 in the second main channel 108.
In a third step A3, the operator provides the main flow 114 of the continuous phase 40 along the direction of extension 117. To this end, the operator may set a pressure Pc of the continuous phase 40 in inlet 109. Advantageously, a forward flow of the continuous phases in the third main channel 3 is also provided. The forward flow corresponds to a flow from the third main channel 3 into the second main channel 108. Fluidic resistances of the second main channels 108 from inlet 109 to zone Z and further to outlet 113 and fluidic resistances of the third main channel 3 and from inlet 30 to zone Z and further to outlet 113 may be evaluated theoretically and the pressures applied to inlets 109 and 30 may be chosen in order to establish a forward flow of the continuous phases in the third main channel 3 taken into account the fluidic resistances.
In a fourth step A4, the main droplet generator 102 may be set to establish an interface 123 between the non-conductive polymer phase 115 and the continuous phase 40.
For a given pressure Pc of the continuous phase 40, there exists an equilibrium pressure of the non-conductive polymer phase 115 at which the interface 123 is at equilibrium close to the T-junction 116. Then, in steady conditions, if Pd2 is below this value, there is some backflow inside the first main channel 104. Conversely, if Pd2 exceeds this equilibrium value, the dispersed phase is pushed towards the second main channel 108.
Such equilibrium may be found through carrying a calibration method M similar as the one presented for the droplet generator. A calibration method M of the main droplet generator 102 is presented further in the description.
The interface 123 may be formed between the non-conductive polymer phase 115 and the continuous phase 40, for instance by setting the pressure Pd2 of the non-conductive polymer phase 115 equal to the equilibrium pressure.
The fourth step A4 may advantageously comprise the following sub steps to create a stable interface 123.
In a first sub step A41, the sensor 120 monitors the interface 123. A monitoring signal is provided to command unit 64.
In a second sub step A42, the command unit 64 adjusts the pressure Pd2 of the non-conductive polymer phase and the pressure Pc of the continuous phase so as to stabilize the interface. The command unit may control the pressure actuators 106 and 110 to that end.
Such monitoring and adjustment greatly improve the stability of the interface 123 and enables single droplets of the same size to be generated much more efficiently.
During the fifth step A5, a conductive fiber 118 is placed inside the third channel 3. This placement may correspond to a generation of the fiber within the device 1 for manufacturing an electromagnetic resonator following the method P previously described.
The situation of the fifth step A5 is illustrated in figure 11.
During a sixth step A6, the conductive fiber 118 is moved out of the third channel 3 into the second channel 108. The motion velocity is set by the pressure values set in the calibration of the pressure controllers 56 and 57.
As the axis 9 of the third channel 3 passes continuously through the third channel, the first channel and the second channel, the conductive fiber 118 does not come up against an obstacle before entering the second channel 108.
The situation of the sixth step A6 is illustrated in figure 12.
During a seventh step A7, the presence of the fiber 118 is detected inside the second main channel 108. This detection is for instance enabled by the sensor 120 that detects a signal different when the fiber 118 enters the second channel 108.
During an eighth step, the command unit 64 triggers the ejection of a droplet from the non-conductive polymer phase 115 into the continuous phase 40. The command unit controls the main droplet generator 102 to generate a single droplet. The delay between the detection of the fiber 118 in the second main channel and this triggering is chosen superior or equal to half of the time required for the fiber to travel from the detection point to the main channel 108 and inferior or equal to the time required for the fiber to move two widths of channel 104. Controlling the delay enables to obtain in a much more efficient way a contact between the singe droplet and the fiber.
During a ninth step, the main droplet generator 102 generates a single droplet.
The single droplet may be generated by applying, during a sub step A91, a pressure pulse to the non-conductive polymer phase, the continuous phase pressure PC remaining constant. In a very similar way as described for the conductive droplet generator 1, optimal parameters to generate efficiently a single droplet may be found for the main droplet generator 102 using similar calibration methods.
The pressure pulse pushes the non-conductive polymer phase 115 inside the second main channel as illustrated in figure 13. At the end of the pulse, the non-conductive polymer phase 115 flows back into the first main channel 104. A part of the non-conductive polymer phase 115 remains in the second main channel 108. This part forms a single droplet 122 that is extracted from the non-conductive polymer phase 115 into the continuous phase 40. The situation is illustrated in figure 14.
The single droplet 122 presents a dimension superior or equal to 10 µm and inferior or equal to 500 µm. The size of the droplet is given by the pressure pulse parameters in a similar way as presented with respect to the conductive droplet generator.
The height of the droplet 122 depends on the height of the channels, and notably the height of the second main channel 108. In particular, the height of the droplet 122 can be equal or inferior to the height of the second main channel 108. In this way, the droplet advantageously presents a circular shape in the X-Y plane, or if the pressure pulse is long enough the droplet may become elongated along the second main channel 108.
Once the single droplet 122 is generated, the conductive fiber 118 is in contact with the single droplet 122 and a spontaneous coiling of the conductive fiber 118 around the single droplet occurs. Thanks to the controlled triggering of the droplet generation, it is possible to ensure in a much more efficient way a contact and merging between the conductive fiber 118 and the single droplet 122.
Such a contact enables to obtain the spontaneous coiling effect.
This effect is obtained in a reproductible way when the droplet presents a size above a critical droplet size. This critical droplet size appears to be proportional to an electrocapillary length (L_BC ). This length depends on the fiber's Young modulus (E), the liquid-liquid surface tension (γ), the fiber width (w): $L_{BC} = \sqrt{\frac{{Ew}^{3}}{γ}}$ .
The liquid-liquid surface tension γ corresponds to an interface between the non-conductive polymer droplet 122 and the continuous phase 40.
The electromagnetic resonator device may be calibrated to determine the critical droplet size as a function of the size of the fiber and the physical parameters E and γ. To determine during the calibration method, when a spontaneous coiling does occur, optical monitoring the conductive fiber 118 and the single droplet 122 may be achieved for instance using an optical microscope connected to a camera.
During a tenth step A10, the droplet is cured so as to solidify the wound droplet into an electromagnetic resonator. The curing may be light curing or thermal curing and be implemented using the curing device 112.
The cured electromagnetic resonator is moved onto the outlet 113 and may be retrieved out of the electromagnetic resonator generator device 100.
The process for manufacturing an electromagnetic resonator and the device for manufacturing an electromagnetic resonator as presented above enable to manufacture electromagnetic resonators that present a dimension superior or equal to 10 µm and inferior or equal to 500 µm. The electromagnetic resonators are formed by a cured-polymer non-conductive core and a conductive fiber wound around the core 124 and given the dimension of the resonator, the resonance frequency is superior or equal to 50 GHz and inferior or equal to 10 THz.
Such a resonator is obtained thanks to a spontaneous winding of the conductive fiber around a polymer droplet, the winding requiring the fiber and droplet to encounter one another under controlled conditions. In particular, the winding can occur when the fiber and the droplet are provided in a channel, the droplet being in contact with the fiber. Thanks to this method and this spontaneous winding step, electromagnetic resonators as small as 10 µm in size may be obtained.
The process for manufacturing an electromagnetic resonator and the device for manufacturing an electromagnetic resonator as presented above enable to manufacture electromagnetic resonators whose geometric parameters and resonance parameters may be finely controlled. The size of the non-conductive droplet depends on the pressure pulse parameters applied to the non-conductive polymer phase and the size of the conductive fiber depends on the pressure pulse parameters applied to the conductive polymer phase and the geometry of the second portion of the third channel. The resonance parameters of the electromagnetic resonator depend on the geometric parameters of the electromagnetic resonator and the electrical resistivity of the conductive fiber.
The process for manufacturing an electromagnetic resonator and the device for manufacturing an electromagnetic resonator as presented above enable to manufacture electromagnetic resonators in a highly reproductible way. Once optimal pulse parameters are identified to obtain a single non-conductive droplet and a conductive fiber, once triggering delay has been optimized to obtain spontaneous coiling, applying those parameters will lead to manufacturing resonators that have a regular geometric parameters and resonance parameters. Thanks to the precision of microfluidic technologies, the statistical distribution of these parameters is narrowly peaked as compared to other droplet-production methods, so that the distribution can be qualified as monodisperse.
The process for manufacturing an electromagnetic resonator and the device for manufacturing an electromagnetic resonator as presented above enable to manufacture electromagnetic resonators in an automated way. Once optimal pulse parameters and triggering delay are identified, it is possible to program the command unit a set of commands to automatically generate resonators.

Calibration of the main droplet generator

In order to generate a single droplet, the main droplet generator 102 may first be calibrated. A basic calibration method M may be implemented before the implementation of the step A2 of the process A.
A single droplet may be generated by applying a pressure pulse in the non-conductive polymer phase 115 at the inlet 105 so as to increase Pd2 by an amount ΔP2 for a duration Δu. The width of the third main channel 3 may be chosen small enough with respect to the widths of the first main channel 104 and the second main channel 108 so that the influence of the third main channel 3 in the single droplet generation from the non-conductive polymer phase may be neglected.
The basic calibration method M comprises the following steps:

M1: selecting a value of the pressure Pc of the continuous phase,
M2: determining the corresponding equilibrium value of Pd2,
M3: selecting a value of the pulse amplitude ΔP2 and a set of candidate values of the pulse duration Δu,
M4: for each candidate value of the pulse duration Δu, applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd2, the value of the pulse amplitude ΔP2 and the candidate value of the pulse duration Δu,
M5: for each candidate value of the pulse duration Δu, determining if a single droplet is generated,
M6: validating a candidate value of the pulse length Δu if a single droplet of polymer phase is generated.

Step M2 may be achieved by a balance of pressures based on the following equality: the difference in pressure between the second main inlet 109 and the pressure at junction 116 is equal to the difference in pressure between the first main inlet 105 and the Laplace pressure at the meniscus 123. The Laplace pressure Pl depends on the surface tension between the continuous phase 40 and the dispersed phase 115, the channel height and the width 135 of the first main channel 104.
Step M5 may be achieved by optical observation. To that end, the sensor 120 may advantageously comprise a camera.
This basic calibration method may advantageously comprise the complementary steps:

M7: determining a lower threshold of Δu1 so that applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd2, the value of the pulse amplitude ΔP2 and any value of Δu inferior or equal to Δu1 does not generate a single droplet of polymer phase, and
M8: determining an upper threshold of Δu2 so that applying a pressure pulse based on the value of Pc, the corresponding equilibrium value of Pd2, the value of the pulse amplitude ΔP2 and any value of Δu superior or equal to Δu2 does not generate multiple droplets or a jet of polymer phase.

These complementary steps are based on the following trends that have been generally observed. There are a lower threshold Δu1 and an upper threshold Δu2, so that:

below Δu1, the pulse is too short to generate a droplet, and
above Δu2, either the droplet takes the shape of a continuous jet or the droplet gets separated into a plurality of smaller droplets.

The basic calibration method may advantageously be implemented for a plurality of different values of the pulse amplitude ΔP2.
The microfluidic droplet generator may be further calibrated by:

M9: selecting a set of candidate values of Pc and
M10: applying the basic calibration method for each candidate value of Pc.

Based on these different method steps, phase diagrams may be built. A phase diagram may be associated with each candidate value of Pc and represent schematically the determined values of the pulse amplitude ΔP2 and of determined values of the pulse length Δu that lead to the generation of a single droplet of the polymer phase.
The control of the pressure actuators so as to stabilize the interface is stopped during the pressure pulse.
The volume of the droplet depends on the pulse amplitude ΔP2 and on the pulse length Δu. The volume of the single droplet increases when the pulse amplitude ΔP2 increases and/or when the pulse length Δu increases.

Electromagnetic Resonator

In correspondence with figure 16, an electromagnetic resonator 124 comprises a cured-polymer core 125 and a conductive fiber 118 wound around the core 124.
The core 125 is a non-conductive material and presents a dimension 126, for instance a diameter 126 if the core 125 has a spherical shape.
The dimension of the core 125 is superior or equal to 10 µm and inferior or equal to 500 µm. For instance, the dimension of the core 125 is equal to 12 µm, 15 µm, 20 µm, 25 µm, 50 µm, 100 µm, 200 µm, 300 µm,
As the dimension of the resonator 124 is inferior or equal to 500 µm and given the specific composition of a polymer core surrounded by a conductive fiber, the resonator 124 presents a resonance frequency superior or equal to 50 GHz and inferior or equal to 10 THz.
When the resonator is manufactured by the manufacturing device 100 previously presented, the dimension of the core 125 is given by the pressure pulse parameters of the pressure pulse that generates the non-conductive polymer single droplet.
The conductive fiber 118 presents a length along a main extension direction 129 that is a orthoradial (or circumferential) direction around the sphere in figure 16. The length is measured from a first extremity 131 up to a second extremity 132.
The main direction 129 describes a circle around the sphere. The direction z is orthogonal to the circle and constantly orthogonal to the main direction 129.
The length may be inferior to a full perimeter of the sphere so that a gap 130 remains between the extremities 131 and 132.
However, longer fibers may be used so that the fiber surrounds the polymer core on a complete perimeter or even on more than a perimeter, for instance two or three or four or five perimeters.
The conductive fiber 118 presents a width 127 along a first transverse direction orthogonal to the main extension direction 127. The first transverse direction corresponds here to a radial direction.
The conductive fiber 118 presents a height 128 along the direction z. The length is superior to the height 128 and the height 128 is superior to the width 127.
In this situation, the parameters that control the resonance frequency of the electromagnetic resonator 124 are, for short fibers that do not completely surround the drop, the dimension of the gap 130, the height 128, the width 12 and the drop radius 126. Alternatively, for fibers that completely surround the drop, the resonance of the electromagnetic resonator 124 are determined by the number of times the fiber winds the drop, the height 128, the width 12 and the drop radius 126.
As the dimensions of the fiber 118 may be controlled thanks to the geometry of the second portion of the fluidic channel 3, it is possible to obtain a resonator which resonance parameters may be finely controlled.
As previously mentioned, the fiber may have a rectangular cross-section in a plane defined by the first transverse direction and the second transverse direction, a transverse aspect ratio corresponding to a ratio of the height above the width being superior or equal to 1.25 and inferior or equal to 30. When the fiber presents this transverse aspect ratio, the fiber spontaneously winds around the droplet so that the width 127 of the fiber aligns with a radial direction of the droplet. That leads to more reproductible resonator manufacturing.
The resonators manufactured may be collected to create a metamaterial by placing them on a solid or a soft substrate. Such a metamaterial would be an electromagnetic resonance device comprising a plurality of electromagnetic resonators. If the resonators present very close resonance frequencies, the electromagnetic resonance device would then present a precise resonance frequency and a narrow bandwidth.

Claims

A method for manufacturing an electromagnetic resonator, the method comprising the following steps:
- (A2) placing a polymer phase (115) in a first channel (104) and a continuous phase (40) in a second channel (108) orthogonal to the first channel, the first channel having a junction (116) with the second channel,

- (A3) providing a flow (114) along a direction (117) of the second channel,

- (A5) placing a conductive fiber (118) inside a third channel (3), the third channel opening into the first channel, a projection of the third channel on the direction (117) being located upstream of the junction (116) with respect to the flow (114), the third channel presenting an axis of extension (9), the axis (9) passing continuously through the third channel (3), the first channel (104) and the second channel (108),

- (A6) moving the fiber (118) along the axis (9) out of the third channel (3), across the first channel (104) and inside the second channel (108),

- (A8) ejecting a single droplet (122) from the polymer phase (115) into the continuous phase (40) so as to bring the droplet (122) into contact with the fiber (118) at the junction (116), and

- (A10) curing the single droplet (122).
The method according to claim 1 wherein the electromagnetic resonator has a dimension superior or equal to 10 µm and inferior or equal to 500 µm.
The method according to any of claims 1 and 2 comprising a step of (A7) detecting an entry of the fiber in the second channel and a step of (A8) triggering the ejection of the droplet once the fiber entry is detected.
The method according to any of claims 1 and 3, comprising a step of (A41) monitoring an interface (123) between the polymer phase and the continuous phase and a step of (A42) adjusting a pressure of the polymer phase and a pressure of the continuous phase so as to stabilize the interface.
The method according to any of claims 1 to 4, comprising a step of generating the conductive fiber that comprises the following sub steps:
- (S2) generating a single conductive droplet (38) containing light-curing polymers,

- (S4) moving the conductive droplet (38) in a first portion (7) of the third channel (3), the first portion having a funnel shape so that a dimension of the third channel in the first portion continuously decreases along the axis (9) in a transport direction of the droplet,

- (S5) moving the conductive droplet (38) in a second portion (10) of the third channel, the second portion being contiguous to the first portion, the dimension of the third channel being constant in the second portion,

- (S6) exposing in the second portion the conductive droplet to a light radiation so as to at least partially cure the conductive droplet into the conductive fiber, and

- (S7) moving the conductive fiber in a third portion (12) of the third channel, the third portion being contiguous to the second portion, the third portion having a funnel shape so that the dimension of the channel in the third portion continuously increases along the transport axis.
The method according to claim 5 wherein generating the single conductive droplet comprises:
- (T3) forming an interface (60) between a conductive polymer phase (42) and a continuous phase (40) in a microfluidic junction device (29), such as a flow-focusing or T-junction, the polymer phase containing light-curing polymers, and

- (T6) applying a pressure pulse to the conductive polymer phase so as to eject the conductive droplet (38) from the conductive polymer phase into the continuous phase.
The method according to any of claims 1 to 6, wherein generating the single conductive droplet comprises (T7) extracting the single conductive droplet from a conductive polymer phase, the method further comprising a step of (S1) generating the conductive polymer phase that comprises the following sub steps:
- a first sub step of (G1) mixing a liquid phase of light-curing polymers with a conductive material comprising carbon nanotubes,

- a second sub step of (G2) adding a solvent to the liquid phase, the solvent preferably being dimethylformamide,

- a third sub step of (G3) exposing the liquid phase to ultrasound waves, advantageously for a duration superior or equal to 30 minutes and inferior or equal to 6 hours, and

- a fourth sub step of (G4) evaporating the polar solvent out of the liquid phase.
A device (100) for manufacturing an electromagnetic resonator, the device comprising a droplet generator (102) comprising:
-- a first channel (104) configured to contain a polymer phase (115), and

-- a second channel (108) orthogonal to the first channel, the first channel (104) having a junction (116) with the second channel, the droplet generator being configured to provide a flow (114) along a direction (117) in the second channel,
the device further comprising a curing device (112) configured to cure polymers and a third channel (3) opening into the first channel, a projection of the third channel on the direction (117) being located upstream of the junction (116) with respect to the flow (117), the third channel (3) presenting an axis of extension (9), the axis passing continuously through the third channel, the first channel and the second channel, the device being configured to transport along the axis (9) a conductive fiber (118) from the third channel across the first channel and inside the second channel.
The device according to claim 8 wherein the droplet generator (102) is configured to produce a single droplet (122) having a dimension superior or equal to 10 µm and inferior or equal to 500 µm.
The device according to any of claims 8 and 9 comprising:
- a sensor (120) configured to monitor the junction (116),

- a treatment unit (121) configured to receive a sensor signal and detect a conductive fiber in the junction based on the sensor signal, and

- a command unit (64) configured to control the droplet generator (102) so as to generate a droplet (122) if a conductive fiber (118) is detected in the junction (116).
The device according to claim 10 wherein the sensor (120) is configured to monitor an interface (123) between a polymer phase (115) and a continuous phase (40), the droplet generator comprising pressure actuators (106, 110) configured to adjust a pressure of the polymer phase (115) and a pressure of the continuous phase (40), the device (100) comprising a command unit (64) configured to command the droplet generator (102) to adjust the pressures so as to stabilize the interface (123).
The device according to any of claims 8 to 11, further comprising a conductive droplet generator (2) configured to generate a single conductive droplet (38), the third channel (3) comprising:
--a first portion (7) having a funnel shape, a dimension of the third channel continuously decreasing in the first portion along the axis (9),

-- a second portion (10) contiguous to the first portion, the dimension of the third channel being constant in the second portion,

-- a third portion (12) contiguous to the second portion, the third portion having a funnel shape, the dimension of the third channel continuously increasing in the third portion along the axis, and

- a light source (14) configured to expose the second portion to a light radiation.
Electromagnetic resonator comprising a cured-polymer non-conductive core (125) and a conductive fiber (118) wound around the core, the electromagnetic resonator having a dimension (126) superior or equal to 10 µm and inferior or equal to 500 µm.
Electromagnetic resonator (124) according to claim 13, wherein the conductive fiber (118) presents a length along a main extension direction (129), a width (127) along a first transverse direction orthogonal to the main extension direction and a height (128) along a second transverse direction orthogonal to the main extension direction and the first transverse direction, the length being superior to the height, the height being superior to the width, the fiber having a rectangular cross-section in a plane defined by the first transverse direction and the second transverse direction, a transverse aspect ratio corresponding to a ratio of the height above the width being superior or equal to 1.25 and inferior or equal to 30.
Electromagnetic resonator according to claim 14, wherein the length is inferior to a perimeter of the polymer core and the conductive fiber partially surrounds the core.
Electromagnetic resonator according to any claims 13 to 15 manufactured by a method according to any of claims 1 to 7.
Electromagnetic resonance device comprising a plurality of electromagnetic resonators according to any of claims 13 to 16.