Patent Publication Number: US-2021190564-A1

Title: Su-8 micro coriolis mass flow sensor

Description:
FIELD OF THE INVENTION 
     The invention relates to a channel comprising device, a system comprising a Coriolis-type flow measuring device comprising the channel comprising device, use of such system, a method for measuring a property of a fluid, and methods for providing a channel comprising device, and a flow measuring device. 
     BACKGROUND OF THE INVENTION 
     Coriolis mass low sensors are known in the art. US2016363472, e.g, describes a Coriolis flow sensor comprising a housing and at least a Coriolis-tube with at least two ends being fixed in a tube fixation means. The flow sensor comprises excitation means for causing the tube to oscillate, as well as detection means for detecting at least a measure of displacements of parts of the tube during operation. According to the document, the Coriolis flow sensor comprises a reference mass, as well as further excitation means arranged for causing the reference mass to oscillate during operation, as well as further detection means for detecting at least a measure of displacements of the reference mass during operation. Additionally, control means are provided for controlling the excitation means and/or further excitation means based on vibrations measured by the detection means and/or further detection means. This way a Coriolis flow sensor with active vibration isolation is obtained. 
     SUMMARY OF THE INVENTION 
     Microfluidic Lab on a Chip (LOC), integrated microfluidic systems and micro total analysis systems (μ-TAS) have gained an immense interest in the last years for many applications in different fields including (bio)chemistry, medicine and biology. Some of the goals are low cost, fast response, biocompatibility and a reduced use of reagents. Having a strong control over the fluids that are used during the experiments is essential: flow sensors are one of the key components for these types of devices. 
     Up to now, most known micro flow sensors have been based on a thermal measurement principle. These sensors can measure flows down to a few nl/min, however they are highly dependent on temperature and fluid properties, like density and specific heat. As a result, the fluid has to be known, and the sensor either needs to be calibrated for each fluid or the user needs to use conversion parameters to obtain the flow rate. Flow sensors using the Coriolis flow measuring principle directly measure the mass flow, independent of these parameters and thus need no recalibration or conversions and are capable of measuring flows of unknown or un-calibrated (mixtures of) fluids. 
     Commercially available (macro) Coriolis mass flow sensors in the relevant range are available, but suffer from large internal volume and are very expensive. Recently, silicon-based micro Coriolis mass flow sensors with internal volumes in the order of 10-20 nl and a small footprint have been developed successfully for different flow ranges. When designed for low flow applications, one of these sensors is capable of measuring up to 20 μl/min with an accuracy of 20 nl/min, while dedicated versions for higher flow ranges demonstrated to measure up to 300  82  l/min with an accuracy of 0.4 μl/min. The high sensitivity reported is due to the excellent mechanical properties of silicon and silicon nitride and the extremely thin channel wall that can be realized, resulting in a high performance flow sensor. However, the fabrication process intrinsically involves silicon micromachining which makes the sensor expensive to produce and not suitable for applications where the device is going to be used only a few times, or where it is meant to be disposable (lab-on-a-chip, diagnostics, biomedical systems, etc.). 
     Hence, it is an aspect of the invention to provide a channel comprising device, which preferably further at least partly obviates one or more of above-described drawbacks. Further, it is an objective of the invention to provide a system comprising a Coriolis-type flow measuring device comprising the channel comprising device and also preferably at least partly obviates one or more of above-described drawbacks. Yet, it is also an aspect of the invention to provide a method for measuring a property of a fluid, specially using the system comprising the Coriolis-type flow measuring device. Yet, in further aspects the invention provides methods for providing the flow channel comprising device and for providing the flow measuring system that at least partly obviate one or more of the above described drawbacks. 
     Herein, we present a micro Coriolis mass flow sensor fully fabricated in SU-8. Although SU-8 is certainly not an obvious choice for a resonant sensor because of the high damping due to intrinsic material losses, we have shown that it is still possible to use it for a micro Coriolis flow sensor. Trying to find a compromise between costs and accuracy, the micro SU-8 Coriolis mass flow sensor according to the invention benefits from the advantages of Coriolis type mass flow sensors (insensitivity to fluid parameters, flow profile, etc.), while reducing the fabrication costs. Moreover, SU-8 offers other interesting features such as transparency and biocompatibility. All these attractive properties make that the inventive low-cost biocompatible mass flow sensor may have a great potential in biomedical diagnostics and research. 
     Coriolis mass flow sensors may comprise a channel that is arranged in plane of the sensor. Especially, the channel is a continuous channel configured for a fluid flow entering the channel at channel inlet and exiting the channel at a channel outlet. The channel may for instance comprise a curved configuration or a loop configuration in between the channel inlet and the channel outlet. The channel inlet and the channel outlet may be arranged at a same side of the flow sensor. Yet in other embodiments, the channel inlet and the channel outlet may be arranged at opposite sides of the flow sensor. 
     Especially, the channel is configured to vibrate when a fluid flows through the channel. Especially, at least of a part of the channel may vibrate (relative to the remainder of the flow sensor). A vibration of the channel may be related to a mass flow of a fluid flowing through the channel (from the channel inlet to the channel outlet). A vibration may provide an angular velocity of at least a part of the channel. Especially, said part of the channel may also be referred herein as “tube”. 
     A mass flow (Φ m ) through the channel will induce a Coriolis force (F c ) which is proportional to the mass flow through the channel and the angular velocity (ω am ) of the tube (see  FIG. 6 ) according to {right arrow over (F C )}=−2L x {right arrow over ((ω am )}×{right arrow over (Φ m )}). The resulting Coriolis force may induce an (out-of-plane) swing vibration mode, especially in a direction perpendicular to the plane of the sensor, especially orthogonal to the actuation mode, with an amplitude proportional to the mass flow. 
     Hence, in a first aspect, the invention provides a channel comprising device comprising a channel with a channel wall, a channel inlet and a channel outlet, wherein the channel wall comprises a polymer. 
     In embodiments, the polymer comprises a polymer obtainable by a process using a photoresist, especially wherein the polymer comprises an epoxy based polymer, even more especially wherein the polymer comprises SU-8. 
     In further embodiments, at least part of the channel is configured flexible relative to a remainder of the channel comprising device. 
     In embodiments, the channel wall comprises a wall thickness, wherein the channel comprises a cross-sectional area, and the cross-sectional area is selected in the range of 100 μm 2 -10 mm 2 , especially the cross-sectional area is selected in the range 100 μm 2 -1 mm 2 , and even more especially the cross-sectional area is selected in the range 100 μm 2 -0.1 mm 2 , especially wherein the cross sectional area is selected from the group consisting of a round cross sectional area, a rectangular cross-sectional area and a square cross-sectional area, especially wherein the cross-sectional area comprises a substantial rectangular cross-sectional area, even more especially a square cross-sectional area. 
     In embodiments, the wall thickness is selected in the range of 1-500 μm, especially in the range of 1-100 μm, such as 1-50 μm, especially 1-10 μm. In further embodiments the wall thickness is selected in the range of 100-500 μm. 
     Especially, in embodiments the channel comprising device comprises a biocompatible (channel comprising) device. 
     The channel of the invention may especially be applied in a Coriolis-type flow measuring device, even more especially is a disposable flow measuring device. 
     In a further aspect, the invention provides a system comprising a Coriolis-type flow measuring device comprising the channel comprising device described herein, and an actuation system configured to let at least part of the channel vibrate (especially relative to the remainder of the Coriolis-type flow measuring device), thereby especially causing temporary displacements (relative to a basic configuration of the at least part of the channel). 
     In embodiments, especially of the system, the channel wall comprises an electrical track configured to allow an alternating current to flow at the channel, wherein the flow measuring device further comprises a magnetic element configured to provide a magnetic field parallel to a plane comprising a channel axis, and wherein the actuation system comprises the electrical track and the magnetic element. Especially in such a system the channel may comprise a first channel part comprising the channel inlet, a second channel part, and a third channel part comprising the channel outlet, wherein the second channel part is in direct (fluidic) contact with the first channel part and (in direct—fluidic—contact) with the third channel part and especially at least part of the first channel part may be configured parallel to at least part of the third channel part, especially wherein at least part of the second channel part is configured perpendicular to said part of the first channel part and to said part of the third channel part. In embodiments, at least part of the first channel part and at least part of the third channel part are configured parallel, like schematically depicted in  FIG. 1 . However, these channel parts not necessarily are arranged parallel. Especially, part of the first channel part and part of the third channel part are flexible and especially part of the second channel part may move relatively to the first and the third part of the channel. Hence in embodiments, the system is provided, wherein the channel comprises a first channel part comprising the channel inlet, a second channel part, and a third channel part comprising the channel outlet, wherein the second channel part is in direct (fluidic) contact with the first channel part and with the third channel part, wherein at least part of the first channel part and at least part of the third channel part is flexible, and wherein the channel is configured to allow movement of (at least part of) the second channel part, especially relative to the channel inlet and the channel outlet. In further embodiments, especially at least part of the first channel part is configured parallel to at least part of the third channel part. 
     In further embodiments, the second channel part comprises a first extreme, a second extreme and a channel center, and the actuation system is configured to let at least part of the second channel part vibrate, wherein (respectively) the first extreme and the second extreme displace temporarily around (about) the channel center along respectively a first displacement path and a second displacement path, especially wherein a circumference of a circular plane (comprising the first and the second extreme and a center of the circular plane) comprises the first displacement path and the second displacement path. Especially, in such embodiment a line, perpendicular to the circular plane and comprising the center of the circular plane, comprises the channel center. Said line may comprise a rotational axis of the channel comprising device, especially a line about which the channel comprising device may rotate, especially as a result of the actuation system. 
     In further embodiments, the system comprises a support comprising the Coriolis-type flow measuring device, and a fluidic connection configured to connect a fluid flow channel to the channel inlet. The support especially may comprise a printed circuit board (“PCB”). Alternatively or additionally, the support may comprise a plastic support. 
     In further embodiments, the system further comprises electrical connections, the magnetic element may especially comprise a permanent magnet, and the electrical connections may be configured to connect the electrical track to an electric source especially providing an alternating current. 
     The system described herein may especially comprise a fluidic device, even more especially a micro fluidic device. 
     The Coriolis-type flow measuring device described herein may especially be configured for measuring a property of a fluid in the (micro) fluidic device, especially wherein the property of the fluid is at least one property selected form the group consisting of a mass flow rate of the fluid and a density of the fluid. A flow through the (actuated) channel may induce a Coriolis force. 
     Especially, the property of the fluid may be determined from a displacement of (at least part of) the channel, especially (a displacement of at least part of the channel) at a first position at the channel, and (a displacement of at least part of the channel) at a second position at the channel, especially wherein the first position (at the channel) comprises the channel center and the second position (at the channel) comprises an extreme (the (first or second) extreme). In further embodiments, the system further comprises a displacement analyzer configured to analyze a displacement of said at least part of the channel, especially wherein the displacement analyzer is configured to analyze a displacement of the channel center and at least one of the (first and the second) extreme(s). Additionally or alternatively, the displacement analyzer may be configured to analyze a displacement (of said part of the channel) at (at least) two positions (at the part of the channel), especially (each) at a different distance relative to the channel center. 
     In embodiments, the displacement analyzer comprises at least one analyzer selected from the group consisting of an optical and a capacitive sensor. 
     In yet a further aspect, the invention also provides a method for measuring a property of a fluid per se, especially using a flow measuring system as described herein. Hence, the invention (further) provides a method for measuring a property of a fluid, especially wherein the property of the fluid is a property selected form the group consisting of a mass flow rate of the fluid and a density of the fluid, the method (for measuring a property of a fluid) comprising: providing a flow measuring system (as described herein); providing a flow of the fluid to the channel inlet of the flow measuring system, to provide a Coriolis force induced displacement of at least part of the channel; applying the actuation system (comprised by the flow measuring system) to provide an actuated displacement of at least part of the channel; and analyzing a displacement, especially the Coriolis force induced displacement and/or the actuated displacement, more especially the Coriolis force induced displacement and the actuated displacement, of said part of the channel to provide the property of the fluid. Especially the displacement at a location comprising the rotational axis (see further below) may not be provided by the Corolius force. Hence at a location comprising the rotational axis (only) the actuated displacement may be analyzed. At any location especially not comprising the rotational axis the actuated displacement may be analyzed. 
     In embodiments, the method for measuring a property of a fluid (wherein the property of the fluid is a property selected form the group consisting of a mass flow rate of the fluid and a density of the fluid) comprises: (i) providing a flow measuring system as described herein, especially comprising a displacement analyzer; (ii) providing a flow of the fluid to the channel inlet of the flow measuring device and providing an alternating actuation current, comprising an alternating current frequency, to the electrical track of the flow measuring device, wherein the alternating current frequency especially is selected to provide a resonant frequency of the channel; (iii) applying the displacement analyzer, to determine a mid-point amplitude and an edge amplitude, wherein the mid-point amplitude being a maximum displacement of the second channel part at the first position at the channel, especially at the channel center, along a line parallel to the circular plane, and the edge amplitude being a maximum displacement of the second channel part at the second position of the channel, especially at an (the first or second) extreme, along a straight line parallel to the circular plane; and (iv) determining the property of the fluid on the basis of a ratio between the edge amplitude and the mid-point amplitude. 
     Hence, in embodiments, wherein the displacement analyzer is configured to analyze a displacement of at least part of the channel at a first position at the channel and a displacement of at least part of the channel at a second position a of the channel, the method comprises: (a) providing the flow of the fluid to the channel inlet of the flow measuring device and providing an alternating actuation current, comprising an alternating current frequency, to the electrical track of a the flow measuring device, wherein the alternating current frequency is selected to provide a resonant frequency of the channel; and (b) applying the displacement analyzer, to determine a mid-point amplitude and an edge amplitude, wherein the mid-point amplitude being a maximum displacement of the second channel part at the first position at the channel along a line parallel to the circular plane, and the edge amplitude being a maximum displacement of second channel part at the second position of the channel along a straight line parallel to the circular plane; and (c) determining the property of the fluid on the basis of a ratio between the edge amplitude and the mid-point amplitude. 
     Especially, (embodiments of) the flow measuring system according to the invention may be used for measuring a mass flow rate and/or a density of a fluid flowing through the channel, especially in biomedical diagnostics and/or intravenous therapy. 
     In yet a further aspect, the invention provides a method for providing a channel comprising device, especially the channel comprising device described herein, comprising a polymer flow channel. Especially, the method (for providing a channel comprising device) comprises providing the polymer flow channel by lithography. Especially, in such method the channel comprising device may comprises an epoxy based polymer and the method may especially comprise SU-8 based technology. 
     In a further aspect, the invention also provides a method for providing a flow measuring device, especially the flow measuring device described herein, especially (the method) comprising providing the polymer flow channel by lithography, especially wherein the channel comprising device comprises an epoxy based polymer and especially (wherein) the method comprising SU-8 based technology. 
     In embodiments, the method for providing a flow measuring device comprises (i) providing a first layer comprising (at least) a (first) polymer on a first substrate; (ii) providing a pattern in the first layer by one or more photolithography steps; (iii) providing a second layer comprising at least a (second) polymer on a second substrate; (iv) providing a pattern in the second layer by photolithography; (v) aligning the patterned first layer and patterned second layer to provide a channel; (vi) bonding the aligned layers to each other; (vii) removing the first substrate and the second substrate from the bonded and aligned layers to provide a micro-device; and (viii) depositing metal on the micro-device, wherein an electrical track is provided at the channel. Especially in embodiments the first polymer and the second polymer may comprise the same polymer. 
     In embodiments, the method for providing a flow measuring device comprises providing a first layer comprising a (first) polymer; depositing a (continuous) patterned metal layer onto the first layer, providing a layer structure comprising a patterned conductive layer; and providing a third layer comprising a (second) polymer at the layer structure, wherein a channel is configured in the third layer, especially wherein the first polymer and the second polymer are the same polymer. Especially, in embodiments depositing the metal layer onto the first layer comprises one or more techniques selected from the group consisting of an evaporation deposition, a sputter deposition and a chemical vapor deposition, and especially a pattern of the patterned metal layer may be provided by (i) applying a mask during depositing the metal layer or (ii) by applying lithography or etching after depositing the metal layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 
         FIG. 1  schematically depicts an embodiment of a channel comprising device of the invention; 
         FIGS. 2 and 3  schematically depict some aspects of the channel comprising device and the method for measuring a property of a fluid; 
         FIGS. 4A-4C  schematically depict some aspects of a channel according to the invention; 
         FIG. 5  schematically depicts some aspects of the system of the invention; 
         FIG. 6  schematically depicts the operating principle of a Coriolis mass flow sensor actuated using Lorentz force; 
         FIG. 7  schematically depicts an (SU-8) Coriolis mass flow sensor chip design; 
         FIG. 8  schematically depicts an SU-8 based microfluidic chip with the defined electrodes; 
         FIG. 9 : schematically depicts a chip fabrication process comprising the system of the invention; 
         FIG. 10  schematically depicts a presentation of a fabricated chip mounted on a printed circuit board; 
         FIG. 11  schematically depicts a schematic overview of a measurement setup; 
         FIG. 12 : shows a simulated and measured resonance frequency for different densities of the fluid inside the channel of an embodiment of the device; 
         FIG. 13  depict measured ratio between a mid-point amplitude and edge amplitude as a function of a volume flow ( 13 A) and a mass flow ( 13 B) for various fluids; and 
         FIG. 14  schematically depict some alternative configurations of the channel comprising device. 
     
    
    
     The schematic drawings are not necessarily to scale. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  schematically depicts an embodiment of a channel comprising device  1  of the invention. The channel comprising device  1  comprises a channel  10  comprising a channel inlet  11 , a channel outlet  12 , and a channel wall  15 . Especially, at least part of the channel  10  is configured flexible relative to a remainder of the channel comprising device  1 . 
     The channel  10  comprises a first channel part  110  in direct (fluidic) contact with a second channel part  120 , and a third channel part  130  also in direct (fluidic) contact with the second channel part  120 . In embodiments, at least part of the first channel part  110  and at least part of the third channel part  130  are flexible. Especially, the first channel part  110  and the third channel part  130  comprise the channel inlet  11  and respectively the channel outlet  12 . The channel  10  is especially configured to allow movement of the second channel part  120  relative to the channel inlet  11  and the channel outlet  12 . 
     In the depicted embodiment, a part of the first channel part  110  is configured parallel to (at least) a part of the third channel part  130 , and (at least part of) the second channel part  120 , especially comprising a straight channel  125 , is configured perpendicular to said parts of the first channel part  110  and the third channel part  130 . The figure further depicts a first extreme  121 , a second extreme  122 , and the channel center  18  of the second channel part  120 . In addition, a rotational axis  20  comprising the channel center  18  is depicted. 
     The channel wall  15  comprises a polymer  150 . The polymer  150  (especially, the channel  10 ) is in embodiments obtainable by a process using a photoresist. The polymer  150  may comprise an epoxy based polymer, especially SU-8. The channel wall comprises a wall thickness  16 , especially selected in the range of 1-500 μm. In embodiments, the channel  10  comprises a cross-sectional area  17  selected in the range of 100 μm 2 -10 mm 2 , especially 100 μm 2 -1 mm 2 . Such cross sectional area  17 , may e.g. comprises a substantial circular cross-sectional area  17 , or rectangular, such as square, cross-sectional area  17 , see e.g.  FIGS. 4A, 4B, and 4C . 
     The channel comprising device  1  may comprise a biocompatible device. The channel comprising device  1  may advantageously be used in a Coriolis-type flow measuring device  50 . The invention also provides a system  1000  comprising such Coriolis-type flow measuring device  50 , and further comprising an actuation system  450  (such as a Lorentz actuator) configured to let at least part of the channel  10  vibrate, especially thereby causing temporary displacements of parts of the channel  10 . A displacement (such as by the Coriolus force, and especially by the actuation system  450 ) may be provided to at least a part of the second channel part  120 . In  FIGS. 2 and 3  schematically displacements of the channel  10 , especially the straight channel  125 , are depicted. 
     In  FIG. 2  schematically a displacement is depicted, wherein the first extreme  121  and the second extreme  122  displace (especially rotate) temporarily about (around) the channel center  18 . The displacement may be provided along a first displacement path  301  and a second displacement path  302  for the first extreme  121  and respectively the second extreme  122 . These paths  301 ,  302  are comprised by a circumference of a circular plane  300 . The circular plane  300 , further, comprises a center  350  (of the circular plane). The center  350  may especially comprise the channel center  18 . In embodiments, a line comprising the center  350  and arranged perpendicular to the circular plane  300  also comprises the channel center  18 . Said line perpendicular to the circular plane  300  may comprise the rotational axis  20  (see  FIG. 1 ). 
     In further embodiments see  FIGS. 5 and 6 , the flow measuring device  50  further comprises a magnetic element  400  configured to provide a magnetic field  410  parallel to a plane  200  comprising a channel axis, especially the rotational axis  20 . Such embodiments may advantageously be combined with embodiments wherein the channel wall  15  comprises an electrical track  451 , especially configured to allow an alternating current  456  to flow at the channel  10 . Hence, the actuation system  450  may comprise the electrical track  451  and the magnetic element  400 . The embodiment in  FIG. 5  further comprises electrical connections  452  configured to connect the electrical track  451  to an electric source  455  providing an alternating current. In the embodiment the magnetic element  400  comprises a permanent magnet  405 , especially two permanent magnets  405  (especially comprising a north and a south pole). In further embodiments, the magnetic element comprises an electromagnet. 
     By providing the alternating current (i a )  456  to the electrical track  451  in a magnetic field (B)  410 , the channel  10  may vibrate, providing the displacement, especially an actuated displacement, to part of the second channel part  120 , especially the straight channel  125 . As a result of a Coriolus force  490  (F C ) (see also  FIG. 6 ), such displacement may comprise a rotation about the center  18 . The displacement may comprise an angular velocity (ω am )  310 . Especially a translation may be superimposed on the rotation, providing a displacement schematically depicted in  FIG. 3 . In the figure a maximum displacement  470  at a first position  471 , especially comprising the channel center  18 , and a displacement  480  at a second position  481 , especially comprising the second extreme  122  are depicted. The first position  471  and or second position  481  not necessarily comprise respectively the center  18  and the second extreme  122 . The second position  481  may also comprise the first extreme  121 . Alternatively or additionally, the first position  471  and second position  481  may comprise other locations at the channel  10 . Essentially, the first and the second position  471 , 481  do not comprise the same location. Especially, the first position  471  and the second position  481  are arranged at a different distance relative to the channel center  18 . 
       FIG. 6  schematically shows the operation principle of a Coriolis mass flow sensor. An alternating actuation current (i a )  456  will, in the presence of a constant magnetic field (B)  410  cause Lorentz forces (F L ) that will actuate the channel  10  in a torsional (twist) mode about the rotational axis  20  with an angular velocity (ω am )  310 , according to: {right arrow over (F L )}=L y ({right arrow over (l a )}×{right arrow over (B)}) . A mass flow (O m )  25  through the channel  10  will induce a Coriolis force (F c )  490  which is proportional to the mass flow  25  and the angular velocity (ω am )  310  of the channel according to F c =x (D m ), wherein L X  is especially a length  129  of a part of the second channel part  120 , especially of the straight channel  125 . The resulting Coriolis force induces an out-of-plane  200  swing vibration mode orthogonal to the actuation mode, with amplitude proportional to the mass flow  25 . 
     The system  1000  of the invention may comprises a micro fluidic device. In  FIG. 7  schematically a Coriolis mass flow sensor chip design of a channel  10  comprising an electrical track  451  comprising electrical connections  452  is depicted. The design depicts an embodiment having a length  129  of the straight channel  125 . Said length  129  is also referred herein as “L x ”. In the embodiment a part of the third channel part  130  and of the first channel part  110  are configured perpendicular to the straight channel over a second length (“L y ”)  139 . The chip design of  FIG. 7  is used to provide the system  1000  depicted in  FIG. 8 . The depicted embodiment comprises a support  100 , especially an electronic circuit board (“ECB”). The support  100  comprises the Coriolis-type flow measuring device  50 . The support  100  further comprises a fluidic connection  500  configured to connect a fluid flow channel to the channel inlet  11 . The system further comprises an actuation system  450  comprising two magnetic elements  400  and an electrical track  451 . The electrical track  451  may be connected to an electric source  455  (not shown) via the electrical connections  452 . 
     The Coriolis-type flow measuring device  50  may be configured for measuring a property of a fluid in the micro fluidic device, such as a mass flow rate of the fluid or a density of the fluid. 
       FIG. 11  schematically depicts an embodiment of the system further comprising a displacement analyzer  460 . The displacement analyzer  460  may be configured to analyze a displacement  470  of said at least part of the channel  10 . The displacement analyzer  460  may be configured to analyze a displacement  470  of at least part of the channel  10  at the first position  471  at the channel  10  and a displacement  480  of at least part of the channel  10  at a second position  481  a of the channel  10 . In the figure, the first position  471  comprises the center  18  and the second position  481  comprises the second extreme  122 . The displacements  470 , 480  are schematically indicated by the two arrows  470 , 480 . The displacements  470 , 480  may especially comprise a displacement in the circular plane  300 . In the given embodiment, the circular plane  300  may be arranged perpendicular to the rotational axis  20  and to the plane  200 . Hence the displacements  470 , 480  in  FIG. 11  may especially comprise an out-of-plane (out of the drawing) displacement. In embodiments the displacement analyzer  460  comprises an optical sensor. In further embodiments, the displacement analyzer  460  comprises a capacitive sensor. 
     The system  1000  may be applied in the method of the invention for measuring a property of a fluid, such as a mass flow rate  25  of the fluid or a density of the fluid. In the method providing a flow of the fluid is provided to the channel inlet  11  of the flow measuring system  1000  to provide a Coriolis force induced displacement of at least part of the channel  10 . Additionally, the actuation system  450  is applied to provide an actuated displacement of at least part of the channel  10  and the displacement, especially the Coriolis force induced displacement and/or the actuated displacement, the part of the channel  10  is analyzed, especially by the displacement analyzer  450 , to provide the property of the fluid. 
     In embodiments, the method comprises providing an alternating actuation current, comprising an alternating current frequency, to the electrical track  451  of the flow measuring device  50 . Especially the alternating current frequency is selected to provide a resonant frequency of the channel  10 . The method, further comprises applying the displacement analyzer  460 , to determine the displacements, especially a mid-point amplitude  470  and an edge amplitude  480 , wherein the mid-point amplitude  470  is a maximum displacement of the second channel part  120  at the first position  471  at the channel  10  along a line parallel to the circular plane  300 , and the edge amplitude  480  is a maximum displacement of second channel part  120  at the second position  481  of the channel  10  along a straight line parallel to the circular plane  300 . The property of the fluid may then be determined on the basis of the ratio between the edge amplitude  470  and the mid-point amplitude  480 . 
     The methods described herein for providing the flow measuring device  50 , and especially (also) the channel comprising device  1  comprising a polymer (especially an epoxy based polymer) flow channel  10 , may comprise providing the polymer flow channel  10  by lithography. In embodiments said methods comprise SU-8 based technology, see e.g.  FIG. 9 . 
       FIG. 9  schematically depicts a chip fabrication process comprising the system  1000  of the invention; depicting the following stages: (a) kapton film  102  bonding to a pyrex wafer  101 , (b) spinning of a 90 μm thick SU-8 layer  103  and definition, (c) spinning of the layer  103  and definition of microchannel  10 , (d) development of ground and microchannel  10  layers, (e) kapton film  102  bonding to a pyrex wafer,  101  (f) spinning of a 90 μm thick SU-8 layer  103 , and cover definition by photolithography, (g) cover development, (h) SU-8 to SU-8 bonding, (i) SU-8 device  1  release. 
     Especially, the method for providing a flow measuring device  50 , may comprise the next (consecutive) stages: providing a first layer comprising at least a polymer  150  on a first substrate (see, e.g.  FIG. 9   a - b ), providing a pattern in the first layer by one or more photolithography steps ( FIG. 9   c - d ); providing a second layer comprising at least a polymer  150  on a second substrate ( FIG. 9 e   ); providing a pattern in the second layer by photolithography ( FIG. 9 f - g   ); aligning the patterned first layer and patterned second layer to provide a channel  10  ( FIG. 9 h   ); bonding the aligned layers to each other; removing the first substrate and the second substrate from the bonded and aligned layers to provide a micro-device ( FIG. 9   i ); and depositing metal on the micro-device, wherein an electrical track  451  is provided at the channel  10 . 
     In other embodiments, the method for providing a flow measuring device  50  comprises the next (consecutive) stages: providing a first layer comprising a polymer  150 ; depositing a patterned metal layer onto the first layer, providing a layer structure comprising a patterned conductive layer, especially comprising an electrical track  451 ; and providing a third layer comprising a polymer  150  at the layer structure, wherein a channel  10  is configured in the third layer. 
     The metal layer may especially be deposited by an evaporation deposition and/or a sputter deposition, and/or a chemical vapor deposition. A pattern of the patterned metal layer may be provided by applying a mask during depositing the metal layer. Alternatively, said pattern may be provided by applying lithography or etching after depositing the metal layer. 
     A representation of a working chip comprising the channel comprising device  1  can be observed in  FIG. 10 . 
       FIG. 12  shows a simulated and measured resonance frequency for different densities of the fluid inside the channel  10  of an embodiment of the device  50 . In the figure, at the y-axis, the frequency f in Hz is given as a function of the density of the fluid ρ in kg/m 3  given at the x-axis. The two single points (values) represent the measured values, the continuous line represents the simulated values and the dotted lines indicate the simulated values plus or minus an error margin of 5%. 
       FIG. 13  depict measured ratio of the mid-point amplitude  470  over the edge amplitude  480  (at the y-axis) as a function of (at the x-axis) the volume flow (Φ v ) in μl/min ( FIG. 13A ) or mass flow  25  (Φ m ) in mg/min ( FIG. 13B ) for water and IPA (isopropyl alcohol). In the graphs, the open circles relate to water and the closed circles relate to IPA. The continuous line in  FIG. 13B  represents a linear fit for both fluids. In  FIG. 13A  the continuous line represents the linear fit for water, and the dotted line represents the linear fit for IPA. 
     The invention described herein is not limited to a more or less rectangular shaped channels comprising device as depicted in most of the figures. The channel comprising device may also comprise another kind of configuration of Corolis type of mass flow meters known in the In  FIG. 14  some further configurations of the channel comprising device are depicted. 
     EXPERIMENTAL 
     Abstract 
     This work presents the modelling, design, fabrication and test of the first micro Coriolis mass flow sensor fully fabricated in SU-8 by photolithography processes. The sensor consists of a channel with rectangular cross-section with inner opening of 100 μm×100 μm and is actuated at resonance by Lorentz forces. Metal tracks for the actuation current are deposited on top of the chip. The chip has been tested over a flow range of 0-800 μl/min with both water and isopropyl alcohol (IPA) to confirm that the sensor measures true mass flow. 
     Design 
     The basic sensor design has been adapted from the silicon-based micro Coriolis mass flow sensor presented in J. Haneveld et al,  J. Micromech. Microeng.,  2010, 20, 125001. Earlier, we presented a multi-axis flexible body mechanical model using the Matlab package SPACAR to model the mechanical behavior of the silicon micro Coriolis mass flow sensor (J. Groenesteijn et al.,  Thirteenth IEEE Sensors Conference , Nov. 3-5, 2014, pp. 954-957). This model has been adapted for the SU-8 sensor to include the possible channels shapes and the properties of SU-8 to predict the mechanical behavior of the polymer micro device. Taking into account the lower mechanical strength and rigidity of SU-8 and the reduced accuracy of the fabrication process with respect to silicon micromachining, the dimensions of the tube were adapted to compromise between sensor sensitivity and fabrication limitations. A final design of an embodiment wherein the first channel part and the third channel part are arranged parallel to each other is shown in  FIG. 7 . The new microfluidic chip includes a microchannel with a square internal cross-section of 100 μm by 100 μm, and channel walls of 100 μm thick. Relatively thick channel walls compared to the channel diameter where chosen due to the limitations of the SU-8 processing. It is anticipated that improvements in fabrication technology will allow us to reduce the wall thickness to 20 μm or less in the future. The channel window (L x    129  and L y    139  in  FIGS. 6 and 7 ) remained at 4 mm×2.5 mm, while external dimensions were chosen to be 1 cm×1 cm. Compared to the silicon-based sensor, the sensitivity will be reduced due to the increase of wall thickness and lower stiffness compared to silicon. However, the increased inner opening is expected to allow for a much higher mass flow for a given pressure drop across the sensor. 
     Fabrication 
       FIG. 9  shows an outline of the process flow that was used. The process starts with the temporary bonding of a thin Kapton film (125 μm) on top of a Pyrex substrate ( FIG. 9 a   ). Kapton was used because of its low adhesion to SU-8, allowing the easy releasing of the devices from the substrate when their fabrication is finished. Once the Kapton film was fixed to the substrate, a 60 μm thick SU-8-50 layer was deposited on top of it. After every spinning step, a soft-bake treatment was performed. All soft-bake steps were performed by heating the wafer up to 65° C. for 30 minutes, followed by a cooling step down to room temperature. Then, another spinning of a 20 μm thick layer was performed followed by a new soft-bake step. As a result, a 90 μm thick layer was obtained. The increased thickness from the expected 80 μm was caused by the difference in surface friction: the first layer was spun on top of a Kapton film, while the second was spun over SU-8 material, increasing its expected thickness. Next, a 140 mJ/cm 2  exposure dose was used to pattern the first layer of the device using a 365 nm wavelength lamp, followed by a post-bake step ( FIG. 9 b   ). Every post-bake step consists on heating the wafer up to 65° C. for 15 minutes and cooling it down to room temperature. Then, two more SU-8 layers were spun (60 μm and 20 μm layer, respectively) and their corresponding soft-bakes were performed. An exposure of 140 mJ/cm 2  was then applied using the mask which defines the microchannel ( FIG. 9 c   ). Then, a post-bake was performed followed by a development step to remove the unexposed SU-8 material. The development consisted on an immersion of the wafer into a SU-8 developer for 5 minutes, followed by a rinsed in isopropanol, DI H 2 O and a drying step using nitrogen ( FIG. 9 d   ). As a result, an open, freely suspended microchannel was fabricated. To close the microchannel another wafer was processed. First, a 90 μm thick SU-8 layer was processed (spun and soft-baked) on top of another Kapton film temporary bonded to a Pyrex wafer ( FIGS. 9 e  and 9 f   ). Inlets and outlets were patterned by photolithography using the same exposure and baking parameters explained before. The wafer was finally developed ( FIG. 9 g   ). Then, both wafers (the bottom and the cover) were aligned and bonded to each other by applying a pressure of 1 bar and heating up to 90° C. for 15 minutes ( FIG. 9 h   ). Finally, the bonded SU-8 devices were manually released from the Kapton thanks to its low adhesion ( FIG. 9 i   ). 
     The final thickness of the device was sufficient to be rigid enough for its easy handling, even though there is no substrate. 
     Once the fully SU-8 micro device is finished, electrodes are added through a metal deposition at chip level. First of all, the device is exposes to ozone plasma to ensure good adhesion between the metal and the SU-8 surface. Then, the chips are sputtered with Cr (10 nm) and Au (200 nm) using a shadow mask to define the electrodes. A representation of a working chip can be observed in  FIG. 10 . 
     Measurements 
     Mechanical Behavior 
     When changing the density of the fluid passing through the sensor, a change in its resonance frequency is also expected, as it modifies the total mass of the moving structure.  FIG. 12  shows the simulated resonance frequency of the sensor for fluid densities of 0-1000 kg/m 3 . For SU-8, a Young&#39;s modulus of 4.4 GPa and a density of 1233 kg/m 3  were used. The measured resonance frequencies for water and iso-propyl alcohol (IPA) are shown in the figure as well and are within 2.5% of the simulated values, which can be explained by variations in the fabrication process. As a result, liquid density can be characterized by measuring the change in resonance frequency of the sensor. This can be especially relevant when using unknown mixtures of liquids, or chemically active substances which might change their density with time. By measuring the resonance frequency of the sensor, the flow sensor could also be used to measure the density of the fluid. 
     Due to the thick channel wall, the stiffness and mass of the tube will be higher than that of the silicon sensor. Furthermore, the quality factor will be lower due to the much higher material losses in SU-8. As a result, the vibration amplitude will be much lower at equal actuation current. Using a magnetic field strength at the electrical track on the tube of 0.1T and an actuation current of 20 mA, the simulated vibration amplitude of the air-filled tube is 258 nm and measured to be 239 nm at the twist resonance frequency, compared to 54 μm with an actuation current of 5 mA for the silicon sensor. The modelled Coriolis displacement in the specified flow range will be lower by approximately 3 orders of magnitude, which is still well within the measurement accuracy of the used Polytec vibrometer. 
     Mass flow measurements 
     To facilitate mass flow readout using a SU-8 Coriolis sensor, a dedicated printed circuit board (PCB) with 3D printed fluidic connections was designed and fabricated. It allows straightforward fluidic and electrical connection, as well as an easy integration of permanent magnets as can be seen in  FIG. 6 . Once the sensor is mounted, a Harvard Apparatus PHD Ultra syringe pump is connected to the inlet to control the applied flow rate. The outlet was connected to a waste container. 
     To measure the mechanical displacement of the sensor induced by the Coriolis force, a Polytec MSA-400 laser Doppler vibrometer was used as shown schematically in  FIG. 11 . An alternating actuation current is applied to actuate the sensor at the twist mode resonant frequency. The amplitude of the vibration is measured at two points. The mid-point amplitude (denoted with “ 470 ”) is the amplitude measured exactly on the rotational axis, where only the Coriolis induced amplitude is present and not the actuated amplitude. The edge amplitude (denoted with “ 480 ”) is the actuated amplitude. The ratio between these amplitudes is proportional to the Coriolis force and thus the mass flow. 
     Flow measurements have been performed using two liquids with different density: water and IPA. Results are shown in  FIG. 13 , where the reading of the sensor is plotted as a function of the applied flow rate by the syringe pump. A linear relation is observed for both liquids over a range of hundreds of microliters per minute ( FIG. 13 a   ). While both liquids appear to respond with a different slope, once the readout is converted to mass per unit of time, both plots are coincident ( FIG. 13 b   ), showing the clear advantage of using a Coriolis based flow sensor. 
     Discussion 
     The current measurement setup uses a Polytec MSA-400 laser Doppler vibrometer both for actuation and read-out. The sensors resonance frequency is found by applying a frequency sweep and measuring the edge displacement when there is no flow and then actuating the sensor at the frequency with the highest response. For each flow measurement, the edge displacement and midpoint displacement are measured separately and then divided to get the ratio between actuation and Coriolis mode amplitude. These measurements are based on three assumptions: the resonance frequency does not change during measurements; the amplitude of each point remains constant while the other point is measured and the rotational axis does not change during the measurements. 
     Conclusions 
     We have successfully modelled, fabricated and tested a micro Coriolis mass flow sensor fully fabricated in SU-8. The sensor consists of a rectangular loop channel of 4mm×2.5 mm with a square cross section of 300 μm×300 μm and a channel wall thickness of 100 μm. The sensor design was based on the results of a multi-axis flexible body model in Matlab and the measured resonance frequency of the actuation mode was within 2.5% of the modelled value for two different fluids. The sensor was actuated in a resonance mode by Lorentz force actuation and read out using a laser Doppler vibrometer. The sensor showed a linear response up to 800 μl/min. Measurements with two liquids with different densities and viscosities resulted in the same mass-flow sensitivities, showing the true mass-flow sensing principle of a flow sensor of the Coriolis type. 
     Although the material properties of SU-8 may seem far less favourable for resonant sensors than e.g. silicon or silicon nitride, we have shown that it is possible to use it for fabrication of a micro Coriolis mass flow sensor, resulting in a low-cost, biocompatible sensor. Future work may focus on reducing the wall thickness to channel diameter ratio, which is currently limited by the SU-8 fabrication technology. Furthermore, optical or capacitive readout structures may be integrated on-chip, to eliminate the need for a separate vibrometer setup. 
     The term “substantially” herein, such as in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in embodiments refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”. 
     Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. 
     The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
     The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. 
     The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.