Self-draining sensor chamber

Abstract

A body for an acoustic resonance fluid flow rate sensor or an acoustic resonance fluid flow sensor comprising such a body, the body comprising a reflector surface having at least one portion that is more hydrophilic than surrounding portions of the reflector surface to promote movement of water from the center of the reflector surface to the edge of the reflector surface.

Description

Technical Field

[0001] The present invention relates to a device for measuring the flow velocity of a fluid, and in particular to a device for measuring the movement velocity and movement direction of air and other fluids. Background Art

[0002] Devices for measuring the velocity of a fluid flow are widely used, particularly in meteorology. Such use exposes the measuring devices to a wide range of environmental conditions that may affect the accuracy of the measurements achieved by the devices. It would be desirable to provide a fluid flow measurement device that provides fluid flow velocity measurements with improved accuracy despite changes in the environmental conditions in which the device operates.

[0003] An acoustic resonant cavity is a device that measures the velocity of a fluid flowing through the cavity. The cavity is capable of supporting an acoustic standing wave and also includes at least two acoustic transducers for generating and detecting the acoustic standing wave.

[0004] It is desirable to improve the accuracy of measuring fluid flow velocity under adverse environmental conditions. Summary of the invention

[0005] According to one embodiment, a body for an acoustic resonance fluid flow rate sensor is provided, the body including a reflector surface having at least one portion that is more hydrophilic than surrounding portions of the reflector surface to promote movement of water from a center of the reflector surface to an edge of the reflector surface.

[0006] The surrounding portion may include a hydrophobic coating.

[0007] The at least one portion that is more hydrophilic than surrounding portions of the reflector surface may include fibers arranged on the reflector surface.

[0008] The fibers may be able to wick liquid using capillary action.

[0009] The fibers may comprise a hydrophilic material.

[0010] The fibers may be natural fibers or synthetic fibers or a combination of natural and synthetic fibers.

[0011] The fibers have a diameter of less than 0.2 mm. Alternatively, the fibers may have a diameter of greater than 0.2 mm.

[0012] At least one portion that is more hydrophilic than surrounding portions of the reflector surface may include a hydrophilic surface.

[0013] An ablation process can be used to create a hydrophilic surface.

[0014] An ablation process may be used to etch the hydrophobic coating to expose the hydrophilic material forming the at least one portion that is more hydrophilic than surrounding portions of the reflector surface.

[0015] The width of the at least one portion that is more hydrophilic than surrounding portions of the reflector surface may increase in a direction from the center of the reflector plate toward an edge of the reflector surface.

[0016] The at least one portion that is more hydrophilic than surrounding portions of the reflector surface may include a series of channels having a constant width, a diverging width, or a combination of such constant and diverging widths.

[0017] At least one portion that is more hydrophilic than surrounding portions of the reflector surface includes a plurality of rough features.

[0018] Rough features may be formed on the reflector surface by laser ablation.

[0019] The roughness features may include a plurality of circular pillars or square pillars or hexagonal pillars or a combination of the plurality of circular pillars, square pillars and hexagonal pillars.

[0020] Columns can have different heights.

[0021] The device may be coated with a hydrophobic material, and at least one portion that is more hydrophilic than surrounding portions may be formed on top of the hydrophobic portion, or may be formed by selectively removing the hydrophobic coating.

[0022] The channels may diverge radially from the centre of the reflector towards the edge of the reflector at an angle between 5° and 20°.

[0023] The channels may diverge radially from the center of the reflector toward the edge of the reflector at varying angles.

[0024] The acoustic resonance cavity may be formed by two reflector surfaces separated by a predetermined distance.

[0025] The two reflector surfaces may be spaced apart by a spacer having an outer surface including a hydrophilic portion.

[0026] The outer surface of the body may include a hydrophilic portion.

[0027] According to another aspect of the present invention, an acoustic resonance fluid flow rate sensor is provided, which includes a body as described above. The device can be a complete acoustic resonance fluid flow rate measuring device. In such a complete device, the acoustic resonance cavity is capable of supporting an acoustic standing wave in a direction perpendicular to the direction of fluid flow. However, it is intended that the protection provided by the claims be extended to the original body used for assembly to form such a device. Before the device is fully assembled, because the second surface can be at least partially formed by the acoustic energy emitting surface of the transducer, such an original body may not include a fully formed second reflector surface. However, the reflector surface already formed on the body includes at least one portion that is more hydrophilic than the surrounding portion of the reflector surface to promote the movement of water from the center of the reflector surface to the edge of the reflector surface.

[0028] According to another embodiment, a method of providing a surface on a body for an acoustic resonant fluid flow rate sensor is provided, the surface being a reflector surface of the sensor and being configured to assist drainage of water from the sensor, the method comprising providing at least one portion that is more hydrophilic than surrounding portions of the reflector surface to promote movement of water from a center of the reflector surface toward an edge of the reflector surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The arrangement of the present invention will be more fully understood and appreciated from the following detailed description which is given by way of example only and in conjunction with the accompanying drawings, in which:

[0030] FIG. 1( a ) shows a top view of an acoustic resonance sensor according to one embodiment;

[0031] FIG1( b ) shows a side view of an acoustic resonance sensor according to one embodiment;

[0032] Figure 2 shows a perspective view of an acoustic resonance sensor according to one embodiment;

[0033] Figure 3 The material is shown in threaded form and with various twisted configurations;

[0034] Figure 4 shows a top cross-sectional view through a resonant cavity of an acoustic resonance sensor, showing a reflector surface of a body patterned with hydrophobic and hydrophilic portions;

[0035] Figure 5 shows a side view of an acoustic resonance sensor showing a body patterned with hydrophobic and hydrophilic portions;

[0036] Figure 6 shows an example of a surface pattern used on a reflector surface of an acoustic resonance sensor body;

[0037] Figure 7(a) shows the top view and side cross-section view. Figure 2 The latter shows possible surface pattern geometries using circular pillars;

[0038] Figure 7(b) shows the top view and side cross-section view. Figure 2 The latter shows possible surface pattern geometries using square pillars; and

[0039] Figure 7(c) shows the top view and side cross-section view. Figure 2 A possible surface pattern geometry using hexagonal columns is shown in FIG.

[0040] Figure 8 (a) to (d) show a reflector surface having a surface pattern according to an embodiment;

[0041] Fig. 9 (a) to (d) show surfaces with and without surface features;

[0042] Fig.10 (a) and (b) show height profiles of surface features according to an embodiment;

[0043] Fig.11 (a) shows a hydrophilic channel according to one embodiment;

[0044] Fig.11 (b) shows a graph illustrating surface tension of various embodiments;

[0045] Fig.12 shows a hydrophilic channel according to one embodiment;

[0046] Fig.13 shows the water transport action on the reflector surface according to one embodiment;

[0047] Fig.14 The water transport action on a reflector surface is shown according to one embodiment. DETAILED DESCRIPTION

[0048] A fluid flow velocity measuring device such as an acoustic resonance anemometer is known from EP 0 801 311. In one embodiment, such a fluid flow velocity measuring device comprises a first reflector surface 16 and a second reflector surface 18 which are spaced apart, parallel, circular, and planar, and an acoustic transducer arranged in the first reflector surface 16 for transmitting acoustic energy into a cavity 4, as shown in FIG. 1( a), which cavity 4 is defined by the spaced apart reflector surfaces 16, 18.

[0049] The first reflector 16 and the second reflector 18 define a resonant cavity 4 forming a measuring cavity of the sensor 1 in the space between the first reflector 16 and the second reflector 18. The first reflector surface 16 and the second reflector surface 18 are spaced apart so that an acoustic standing wave is formed between the first reflector surface 16 and the second reflector surface 18 in the cavity 4. In use, a fluid such as air flows through the cavity 4, and the cavity 4 supports the acoustic standing wave in a direction perpendicular to the direction of fluid flow.

[0050] In the embodiment shown in the drawings, the electroacoustic transducer (not shown) may be housed in the first body portion 10 or the second body portion 12. The second body portion 12 is connected to a support rod 14.

[0051] When in operation, the electroacoustic transducers generate sound waves. Any one of the transducers receives an electrical signal generated by an electronic unit (not shown) and excites a proportional acoustic signal; through the action of the acoustic resonance cavity 4, the acoustic signal is applied to other transducers (not shown), which receive the acoustic signal and generate proportional electrical signals, which are fed back to the electronic unit for processing.

[0052] The resonant frequency that supports the standing wave depends on the speed of sound in the fluid and the spacing between the reflectors 16 and 18 (resonator gap), which is an integer multiple of half the wavelength at the resonant frequency. When propagating from one transducer A to another transducer B, the acoustic signal and its differential electrical signal experience a time delay (and equivalent phase shift) that is related to the speed of sound in the fluid medium and the clear distance between the transmitting transducer A and the receiving transducer B.

[0053] In still air, because (a) the distance the signal travels and (b) the speed of sound remain the same whether the signal travels from transmitting transducer A to receiving transducer B or vice versa, the same time delay will be measured when the signal travels in the opposite direction, from receiving transducer B to transmitting transducer A.

[0054] On the other hand, if the air moves, then the air proportionally increases the net speed of sound in the direction of movement. Conversely, the air proportionally decreases the speed of sound in the direction opposite to the direction of movement. Therefore, when the direction of the signal is reversed, the electronic unit measuring the time delay or equivalently the phase shift detects the difference in time delay (and phase shift).

[0055] The magnitude of the difference in time delays and the equivalent difference in phase shift is related to the velocity of the air along the line of abutment between the pair of transducers. Using a second pair of transducers with a line of abutment in the other direction, the velocity in the second direction can be found, from which the velocity and direction of the airflow can be calculated using established trigonometric formulas.

[0056] As discussed, under dry conditions, the resonant frequency of the standing wave depends on the spacing between reflectors 16 and 18. Under adverse weather conditions, the resonant cavity 4 may fill with rainwater. However, under wet conditions, the upper surface of the water accumulated on the reflector surface 16 forms a water-air interface at which at least a portion of the acoustic energy of the standing wave is reflected. This effectively reduces the spacing of the reflectors forming the resonant cavity 4. Therefore, the frequency of the acoustic standing wave supported by the resonant cavity 4 is changed by the presence of the accumulated water in the resonant cavity 4.

[0057] Furthermore, because the air flow in the cavity may continually disturb the ponding water, the air-water interface formed by the ponding water will not remain stationary and maintain a level surface under adverse weather conditions.

[0058] Figure 1(a) and 1(b) A fluid velocity measurement arrangement of the type shown comprises an electronic measuring device which tracks the resonant frequency of an acoustic standing wave within a resonance cavity 4 to adapt to changes in frequency due to changes in environmental conditions such as changes in temperature. Such electronics are able to adapt to changes in the resonant frequency of the acoustic standing wave due to accumulation of water which narrows the resonator gap. As the air-water interface of such accumulated water moves under the influence of air currents, the electronics attempt to track the resulting changes in the resonant frequency of the acoustic standing wave. However, in particularly adverse weather conditions, the air-water interface may move rapidly, resulting in correspondingly rapid changes in the resonant frequency. This can make tracking difficult and / or inaccurate. As a result, the ability of the sensor 1 to evaluate such acoustic waves may be adversely affected due to environmental conditions. It has been recognised that this problem may be mitigated if accumulation of water in the resonance cavity 4 can be avoided or at least reduced.

[0059] It is known to use a homogenous superhydrophobic coating on the lower reflector 16 to reduce the accumulation of water in the resonant cavity 4 of the sensor 1. Additionally or alternatively, in one embodiment, as shown in FIG. 1( a), the fibers 22 are arranged so that the fibers 22 extend from the center of the reflector 16 to the edge of the reflector 16. The fibers 22 can wick the accumulated water from the center of the reflector 16 to the edge, where the water can flow out along the outside of the sensor 1 under the action of gravity. Therefore, the fibers 22 provide an alternative method for draining rainwater from the resonant cavity 4.

[0060] As shown in Fig. 1(a), the fiber 22 is optionally positioned around the spacer 6. In addition, as shown in Fig. 1(b), the fiber 22 may also extend downward along the vertical side wall of the body 2, particularly on the second body portion 12, and be fixed in place by an anchoring ring 24.

[0061] A plurality of spacers 6 are positioned spaced apart around the perimeter of the first reflector 16 and the second reflector 18. As shown, the fibers 22 of FIG. 1( a) may be separated and extend through individual spacers 6 on either side. Alternatively, the fibers 22 may be wrapped around the spacers 6 to ensure that the fibers 22 do not move laterally on the reflector surface 16.

[0062] By arranging the fibers 22 in alignment with the spacers 6, the fibers extend downwardly along the body 12 aligned with the spacers 6. In this manner, water flowing downwardly along the spacers is urged to continue flowing downwardly along the fibers 22.

[0063] The fibers 22 include materials that utilize capillary forces to transport water that contacts the fibers 22. Capillary forces cause liquids to penetrate the void spaces within the hydrophilic walls and displace the liquids through the hydrophilic walls. The void spaces are spaces within the fiber structure and may include pores, or when the fibers 22 are formed from smaller threads, fibers, or non-porous structures, the internal spaces are formed when the smaller threads, fibers, or non-porous structures are entangled together. The capillary forces are controlled by the properties of the liquid (in this case, water), the liquid-medium surface interactions (the level of hydrophilicity), and the geometric configuration of the void spaces in the medium (fibers). Therefore, the fibers 22 have a certain degree of hydrophilicity and a sufficiently permeable structure, which encourages liquids to travel through the fibers 22 using capillary forces. The fibers 22 may be natural fibers (e.g., cotton), synthetic fibers (e.g., polyester), or a combination of natural fibers (e.g., cotton) and synthetic fibers (e.g., polyester). The meniscus formed by the fibers 22 in the void spaces allows capillary forces to draw water out. As Figure 2 As shown, the downward extension of the fibers 22 to the anchor ring 24 facilitates the pumping action under the action of gravity. Figure 3 As shown, the strands making up the bundle of fibers 22 are twisted together to form larger fibers - improving the strength of the fibers 22, increasing surface area, promoting water absorption, and providing void space to enhance fluid transport.

[0064] In one embodiment, for a resonant cavity having a reflection cavity spacing between 5 mm and 10 mm, the effect of fiber 22 on the aerodynamic and acoustic performance of sensor 1 is minimized by keeping the outer diameter of fiber 22 less than 0.2 mm. Alternatively, fibers 22 having larger diameters or braiding other fibers together may provide superior wicking by providing a larger surface for capillary action and may be used without compromising the performance of sensor 1.

[0065] The fibers 22 may be placed radially anywhere on the surface 16 of the reflector to draw water from the cavity 4. However, as shown in FIG1 , preferably, the fibers 22 are wrapped around the spacer 6 of the sensor because during rain, water flows from the top of the sensor to the bottom of the sensor via the spacer 6. It is observed that water tends to preferentially accumulate near the inner surface of the spacer 6 compared to other areas of the reflector surface 16.

[0066] Figure 4 An alternative embodiment is shown in which a pattern of hydrophilic and hydrophobic portions has been formed on the reflector surface 16. The reflector surface 16 is machined from aluminum and treated to form a hard anodized surface. To form the pattern, the sensor body 2 including the reflector surface 16 is coated with a hydrophobic material. The material can be a hydrophobic material, such as a polymer or ceramic. In an embodiment, selected portions of the hydrophobic coating are etched and / or removed to expose the underlying hard anodized aluminum surface. For example, this can be accomplished using a laser texturing or ablation process. The surface of anodized aluminum is naturally hydrophilic; thus, the process creates a hydrophilic portion 26 on the sensor body 2 having the hydrophobic coating. Figure 4 The hydrophilic portion 26 shown in FIG. 4 is in the form of diverging triangular channels to allow water to move from the inside to the outside of the reflector surface and leave the cavity 4 , however, other geometries of the hydrophilic portion 26 are possible.

[0067] The use of laser texturing or ablation on the sensor 1 offers two key advantages: scalability and flexibility to produce any complex geometric pattern or shape to facilitate water transport.

[0068] Figure 5 A side view of the sensor 1 is shown. In this embodiment, the outer surface of the spacer 6 and portions of the side walls of the first and second parts 10, 12 of the sensor body have also been coated and etched. Figure 5 It can be seen that the patterned portion on the upper body portion 10 of the sensor extends around the entire circumference of the upper body portion 10 in the upper part of the figure. Further downward toward the spacer 6, the patterned portion is no longer continuous in the circumferential direction, but includes residual hydrophobic portions positioned circumferentially between multiple portions of the hydrophilic pattern. The portions of the hydrophilic pattern themselves gradually narrow in the circumferential direction as the distance to the spacer 6 decreases. The width of the portions of the hydrophilic pattern at the point where the pattern contacts the spacer 6 is substantially the same as the width of the spacer 6. From Figure 5 It can be seen that in one embodiment, the spacer itself is also patterned to increase the hydrophilicity of the spacer, and in an embodiment, the area of ​​the lower body 12 extending downward from the spacer is also patterned in the area extending downward from the spacer.

[0069] The etched portions of the first body 10 and the second body 12 are such that water traveling from the top surface 24 of the first body 10 under the action of gravity will be directed downward toward each spacer 6, along the outer surface of each spacer 6, and then selectively along the selectively etched areas on the outer surface of the second body portion 12, wherein the top surface 24 is the surface farthest from the support rods 14. Thus, water on the exterior of the sensor body 2 follows a hydrophilic path and bypasses the cavity 4.

[0070] Despite Figure 5 The patterned portion is shown as a triangle, but in Figure 6 In the alternative embodiment shown, the patterned portion can also be formed as a series of channels. The pattern of hydrophilic areas in the form of discrete tracks is Figure 6 shown in and used with reference to Figure 4 The same process described above is used to form the reflector surface 16. The hydrophobic material 28 is located between the channels. In this example, the dispersed hydrophilic channels 26 diverge over a 1.8° sector of the reflector surface 16, and the pattern includes five such channels 26, which diverge radially from the center of the reflector surface 16 over a 15° sector of the reflector surface 16. There may be multiple groups of such channels on the reflector surface 16.

[0071] The use of divergent tracks provides an additional driving force for displacing water by providing a pressure difference from a narrower area to a larger cross-sectional area near the edge of the reflector surface 16. However, as previously shown in Figure 1, the hydrophilic portion in the form of the hydrophilic channel 26 may also have a constant cross-section. The number of hydrophilic channels 26 is not limited to five.

[0072] Alternatively or additionally, laser ablation may be used to create complex roughness features 29, as shown in Figures 7(a) to (c). The features shown include circular posts 30 (Figure 7(a)), square posts 32 (Figure 7(b)), and hexagonal posts 34 (Figure 7(c)). The posts are formed on the exposed hard anodized aluminum surface of the reflector surface 16 to control and enhance the wetting behavior of water. Areas of the reflector plate 16 and / or sensor 1 where complex roughness features 29 are not present may be coated with a hydrophobic coating. The sensor body may be coated with a hydrophobic material such as with respect to Figure 4 and Figure 5 As discussed above, the hard anodized aluminum surface may be selectively etched to expose the underlying hard anodized aluminum surface. For example, this may be accomplished using a laser texturing or ablation process. An etching process may then be applied directly to the exposed hard anodized surface, wherein the laser selectively etches the surface to form, for example, a post.

[0073] The profile of the patterned area including the posts creates a wettability gradient on the reflector surface 16, thereby facilitating fluid transport using a known biomimetic phenomenon, where natural materials are able to directionally drive water by controlling the interaction between their nano / microstructured surfaces and water.

[0074] As mentioned previously, the surface of anodized aluminum has an oxide layer that makes it hydrophilic. Using a laser or similar etching process, pillars can be formed on the surface that hold the hydrophilic oxide surface on its top surface. In general, according to the Cassie-Baxter formula, a water droplet on a microstructured surface will sit on top of the pillars but will not wet the spaces between the pillars. This allows air to remain inside the microstructured pattern surrounding the pillars, thus forming a heterogeneous surface composed of air and solid.

[0075] The result of a textured surface is that the adhesion between water and the solid parts of the surface is lower than the adhesion between water and a continuous solid surface. This is because the water has less surface to adhere to, allowing the water to roll off easily. The hydrophilic upper surface of the pillars means that water preferentially accumulates on this area, and the water droplets that form on these areas grow larger over time as more water arrives. Once the weight of the trapped water drop exceeds the water adhesion to the surface, the droplet rolls off and the process repeats. The result is a "self-cleaning" surface.

[0076] like Figure 4 or Figure 6 As shown, the textured surface including pillars on the reflector surface 16 forms channels with constant width or covers triangular cross-sections that diverge from the center of the reflector surface 16 toward the outside. However, the present disclosure is not limited to these arrangements, and other pillar patterns that achieve the same effect can also be envisioned. By using Figure 4 or Figure 6 The water may move toward the wider portion of the triangular pattern by coating the reflector surface 16 so that the triangular diverging track of the hydrophilic posts comprising anodized aluminum is surrounded by a hydrophobic surface, i.e., a hydrophobic material. Water droplets may form at the narrow portion of the triangular track where gravity and adhesion forces are balanced. As water droplets preferentially form on the hydrophilic portion of the patterned surface area, the size of the water droplets increases and the center of mass of the water droplets moves toward the wider area of ​​the patterned surface. The movement of the droplets is driven by a combination of the surface tension of the droplets and the width of the area available for the growing droplets to overcome the pinning force acting on the droplets.

[0077] As discussed, the pillars may be circular pillars 30, square pillars 32, and hexagonal pillars 34. That is, many different pillar geometries are possible, limited only by the capabilities of the manufacturing process used to form the pillars. The present invention is not limited to the use of the pillar shapes mentioned. Without wishing to be bound by theory, the effect of small-scale features on wetting behavior can be explained by the Cassie-Baxter theory (Cassie and Baxter 1944), which explains that the contact angle of water on a textured surface can be written as:

[0078] cosθ α =f1cosθ1+f2cosθ2 (1)

[0079] θ α , θ1 and θ2 are the apparent contact angles on the heterogeneous surfaces and the intrinsic contact angles on surfaces 1 and 2, respectively. f1 and f2 represent the solid fractions of surfaces 1 and 2, respectively. Figure 6 In the example shown, surfaces 1 and 2 are hard anodized aluminum and air, respectively, and f1+f2=1. For complete wetting of the surfaces, θ2=0. Therefore, the Cassie-Baxter equation 1 becomes:

[0080] cosθ α =1-f1(1-cosθ1) (2)

[0081] f1 can be calculated from the geometry of the microscale roughness features. Figure 6 For the geometry shown, f1 can be written as:

[0082] (Fig. 7(a)) for circular column 30

[0083] (Fig. 7(b)) for square column 32

[0084] (Fig. 7(c)) For hexagonal column 34

[0085] For circular columns, d represents the diameter and P represents the center-to-center distance between features. For square columns, a represents the side length and P represents the center-to-center distance between squares, and for hexagonal components, a represents the side length of the hexagon and t represents the thickness of the hexagon.

[0086] The above geometries are governed by the feature sizes achievable by the laser system, but other geometries are possible using other methods such as 3D printing. Typically, industrial laser systems can provide feature sizes down to 40 μm with a resolution of approximately 80 μm. Using these constraints in the Cassie-Baxter formula (d = 40, p = 80, a = 40, p = 80 and a = 80, t = 40 μm), f1 is 0.196, 0.25, and 0.75 for textures of circular, square, and hexagonal columns, respectively. Therefore, using the common knowledge that the typical contact angle of water on an alumina surface is approximately 50° (Bubois, Fournee, Thiel, and Belin-Ferre 2008 and Moore, Ferraro, Yue, and Estes 2007), the θ for a textured hard anodized surface can be theoretically estimated. α 11°, 24° and 40° respectively. Thus, the pattern of anodized aluminum posts provides a much lower water contact angle than hydrophobic materials (>90°).

[0087] The benefit of texturing the surface is that the structure facilitates the movement of droplets off the surface, and due to the chosen surface chemistry and structure, the water is forced to follow a defined trajectory without the application of any external energy.

[0088] Figure 4 The reflector surface 16 shown comprises a hard anodized surface coated with a commercially available polymer 28. The coating 28 is hydrophobic, having a water contact angle of approximately 100° and a roll-off angle of approximately 15°. Laser ablation is used on the surface 16 to produce the surface features 29. As discussed, it will be appreciated that other suitable means for producing the surface features are also encompassed by the present invention, such as other etching techniques. In one embodiment, the laser ablation process comprises two steps: In a first step, the hydrophobic polymer 28 is selectively removed, thereby exposing portions of the underlying hard anodized surface. As shown in FIG. Figure 4 As shown, laser ablation is selectively applied to the coated surface 16 to produce diverging tracks 26. In a second step, the hard anodized surface is selectively patterned to produce surface roughness features 29, such as cylindrical pillars or square pillars. The surface features 29 are formed on portions of the hard anodized surface, thereby enhancing the hydrophilicity of these areas. It should be understood that throughout this disclosure, the terms diverging channels and diverging tracks can be used interchangeably.

[0089] Figure 8 (a) shows a hard anodized reflector surface 16 coated with a hydrophobic polymer, the reflector surface 16 having a hydrophilic portion including diverging channels 26 with surface features 29. Figure 8The circular inset in (a) shows a magnified image of a surface feature 29, which is a circular pillar 30 having a feature size of 80 μm and a feature pitch of 240 μm, the scale bar in the inset is 100 μm. Throughout this disclosure, "feature pitch" P refers to the center-to-center distance between adjacent surface features. Figure 8 The inset of (b) shows a magnified image of the surface features 29 within the hydrophilic dispersion channel 26, which includes cylindrical pillars 30 having a feature size of 160 μm and a feature spacing of 480 μm, with a scale bar of 100 μm. Figure 8 The inset of (c) shows a magnified image of surface features within the hydrophilic dispersion channel 26, which includes cylindrical pillars 30 having a feature size of 240 μm, a feature spacing of 720 μm, and a scale bar of 200 μm. Figure 8 The inset of (d) shows an enlarged image of the surface features 29 in the hydrophilic dispersion channel 26, which includes square pillars 32 having a feature size of 80 μm and a feature spacing of 240 μm. The scale bar of the inset is 200 μm. Figure 8 As shown, the diverging channels 26 do not converge at the center of the reflector plate 16 .

[0090] Fig. 9 (a)-9(d) show the wetting behavior of the hard anodized surface for water droplets with and without surface features 29. In the absence of surface features 29, the bare hard anodized surface is slightly hydrophilic with a contact angle of about 45°, causing the water droplets to remain at the locations where they are deposited, as shown in FIG. Fig. 9 (a) shown. Fig. 9 The surfaces shown in (b)-(d) have surface features 29 etched on the hard anodized surface. Fig. 9 (b) comprises cylindrical pillars with a feature size of 80 μm and a feature spacing of 240 μm, Fig. 9 (c) has a feature size of 160 μm and a feature pitch of 480 μm, Fig. 9 (d) has a feature size of 240 μm and a feature pitch of 720 μm. Fig. 9 The contact angles on all surfaces of (b), 9(c) and 9(d) are less than 10°. Fig. 9 (b)-9(d) The effect of surface texturing on wetting can be clearly seen. Fig. 9 (b)-9(d) The water droplet spreads on the surface.

[0091] Fig.10Laser microscopy images showing the height profile of a laser ablated hard anodized surface are shown and illustrate that the laser ablation process performed on the hard anodized layer does not sacrifice its integrity. Fig.10 (a) shows an embodiment where the square pillars 32 remain after the ablation process. Fig.10 (b) shows an embodiment where the cylindrical post 30 remains after the ablation process. Fig.10 The graphs provided in (a) and 10(b) show the corresponding height profiles measured along the corresponding lines shown in the top view micrographs of the ablated hard anodized surface. Fig.10 As can be seen from the height profiles of (a) and 10(b), the hard anodized layer still exists in the areas between the surface features. There, the height of the layer is about 15 μm to 20 μm. The height of the hard anodized layer of the surface features / the entire layer before patterning is about 30 μm. Therefore, even in the case of etching the surface features 29, the reflector surface retains the hard anodized coating and is therefore suitable for extreme environments.

[0092] like Figure 4 As shown, the hydrophilic channels 26 diverge over a 15° sector of the reflector surface 16 (i.e., the sector angle Ψ=15°), and there are six such channels 26 that diverge radially from the center of the reflector surface 16. There are 45° sectors of hydrophobic material 40 on the reflector surface 16, which separate the divergent channels. The surface features 29 within the hydrophilic channels 26 can include any suitable geometry. Although the divergent channels 26 shown have an angle of 15°, it should be understood that any suitable divergence angle Ψ is possible. In particular, divergent channels that diverge at an angle Ψ of 5° to 20° are possible, but other channel divergence angles can also be used.

[0093] The angle at which the channels 26 diverge affects the surface tension acting on the water droplets and subsequently pushing the water droplets toward the edge of the reflector surface 16. Fig.11 As shown in (a), the hydrophilic channel diverges from the center of the reflector surface 16 toward the edge of the surface at an angle Ψ. The center of the droplet is shown at a distance d from the left vertex of the hydrophilic channel 26. The droplet contact line touches the hydrophobic boundary / hydrophilic boundary twice: the first contact point makes an angle Φ with the center line of the hydrophilic channel 26 f The second contact point forms an angle Φ with the center line of the hydrophilic channel 26 s .

[0094] As the contact angle changes at the boundary between the surface of the hydrophilic channel 26 and the hydrophobic sector 28, the net surface tension F acting on the water droplet can be estimated from the following formula:

[0095]

[0096] θ p and θ l are the water contact angles on the hydrophobic polymer coated surface 28 and the hydrophilic laser textured surface 26, respectively. γ is the surface tension and R is the radius of the water droplet. Knowing γ (which is a constant of 0.072 N / m for water), the surface tension can be estimated using the above formula to transport a 2 mm sized water droplet along the hydrophilic channel 26. Fig.11 (b) Graph depicting net surface tension (F) as a function of distance from the left vertex of the hydrophilic channel.

[0097] As in Fig.11 As can be seen in (b), F decreases as the distance between the droplet and the center of the reflector surface 16 increases. For the hydrophilic channel, as the value of Ψ decreases, F also decreases. Therefore, as the droplet moves more toward the edge of the reflector surface 16, the net surface tension from the hydrophobic boundary / hydrophilic boundary decreases.

[0098] Diverging channels 26 with higher Ψ (i.e., wider tracks) have higher net surface tension closer to the center of the reflector surface, which decays rapidly as the droplet travels along the hydrophilic channel 26 toward the edge of the reflector 16. Diverging channels 26 with lower Ψ (i.e., narrower tracks) provide lower net surface tension, so the droplet takes longer to travel from the center of the reflector surface 16 toward the edge of the reflector 16. Fig.11 Edge movement in (a).

[0099] In the embodiment shown, Fig.12 The hydrophilic channel in the embodiment includes a varying divergence angle θ. The hydrophilic channel starts with a divergence angle of Ψ=20°, and then the divergence angle Ψ gradually changes to 15°, 10°, and 5°. This geometry maximizes the surface tension on a 2 mm-sized water droplet traveling along the hydrophilic boundary / hydrophobic boundary. Fig.11 (b) shows the approximate surface tension of a hydrophilic channel with variable Ψ.

[0100] Depending on the requirements of the application, the wider hydrophilic channels 26 are used to provide higher surface tension to transport water from the center of the reflector surface 16 to the periphery of the reflector surface 16. However, some embodiments use narrower diverging channels so that less of the reflector surface 16 needs to be laser ablated, thereby minimizing the laser processing time. In addition, because hydrophilic surfaces are more likely to be contaminated when compared to hydrophobic areas, in some embodiments, it is desirable to minimize the hydrophilic areas.

[0101] Fig.13 Shown in Fig.1416. After the droplets are deposited on the reflector surface 16, the droplets form a water meniscus that is shaped like a "tadpole" toward the edge of the reflector surface 16. Since the surface tension varies from the center to the periphery (having a higher value at the center relative to the periphery) along the hydrophilic channel 26 based on the formula shown above, the water meniscus does not have a uniform shape in the hydrophilic channel 26. The droplets are spherical at positions closer to the center and conical meniscus at the periphery, as shown, forming a general "tadpole" shape. Finally, the water accumulates at the edge of the reflector surface 16. The embodiment shown transports a water droplet having the volume of a typical raindrop from the center of the reflector surface 16 to the periphery of the reflector surface 16 in 10 seconds.

[0102] Fig.14 Another way of arranging the diverging hydrophilic channels 26 on the reflector surface 16 is shown. Although in the previous description, the various symmetry axes of the diverging channels 26 converge at a single point in the center of the disk. Fig.14 In the embodiment of the present invention, the axes of symmetry of the different diverging hydrophilic channels 26 do not intersect at a single point in the center of the disk. Instead, one or more or all of the symmetry lines (e.g. Fig.14 (d) intersect each other so that one or more or all of the lines of symmetry define a polygon around a point at the center of the disk. The number of vertices of the polygon corresponds to the number of diverging channels 26 on the disk.

[0103] As in Fig.14 As can be seen in FIG. 1 , the positioning of the diverging channels 26 also improves the efficiency of water transport. In one embodiment, the diverging channels 26 converge at the central portion of the reflector surface. In this configuration, as in FIG. Fig.14 As observed at the time scales shown in FIGS. 14(a), 14(b) and 14(c), the water droplets are radially transported within 7 seconds of deposition. In this embodiment, the transport of water is aided by the additional surface driving tension generated by the hydrophobic islands at the center of the reflector surface 16. It should be understood that although six diverging channels 26 are shown, the number of channels is not limited, and more or fewer diverging channels 26 are also possible.

[0104] although Fig.14 A particular arrangement is shown in which the diverging channels meet at or near the center of the disk, but it should be understood that other arrangements are also contemplated in which the diverging channels meet at or about the center of the disk.

[0105] As described above, water accumulates at the edge of the reflector surface 16. Therefore, it is beneficial to remove the accumulated water. The hydrophilic portion on the outer surface of the sensor body 1 draws water away from the cavity 4. In one embodiment, other external forces such as gravity help to remove water accumulated at the edge of the reflector plate 15. For example, in one embodiment, a bevel is provided at the edge of the reflector surface 16 to allow water to be exposed to gravity. In one embodiment, the bevel angle relative to the reflector surface 16 is approximately 45°.

[0106] In one embodiment, the transducer of the sensor 1 is arranged in the upper body part 10 of the sensor. The upper body part 10 of the sensor is therefore hollow to allow the transducer to be accommodated. After the body of the sensor is manufactured and before the transducer is installed, the surface of the lower reflector 16 can be accessed not only from the side of the sensor 1 through the space defined by the spacer 6, but also through the hollow upper body part 10. The surface of the reflector 16 can be patterned before the transducer is inserted into the body, and it is intended that the sensor body including the surface of the lower reflector arranged in any of the above-mentioned ways, but not including the transducer and / or any other electronic components, falls within the scope of protection provided by the claims.

[0107] The present invention has been described above by way of example only. Within the scope of the appended claims, the present invention may be modified in detail. In addition, it should be understood that the present invention is by no means limited to the combination of features shown in the examples described herein. Features disclosed with respect to one example may be combined with features disclosed with respect to another example.

Claims

1. A main body for an acoustic resonance fluid flow rate sensor, characterized in that: The body includes a reflector surface having at least one portion extending radially from a center of the reflector surface toward an edge of the reflector surface, The at least one portion is more hydrophilic than surrounding portions of the reflector surface extending toward an edge of the reflector surface, providing movement of water along a radial direction from a center of the reflector surface toward an edge of the reflector surface through the at least one more hydrophilic portion.

2. The main body according to claim 1, characterized in that The surrounding portion includes a hydrophobic coating.

3. The main body according to claim 1, characterized in that The at least one portion that is more hydrophilic than surrounding portions of the reflector surface comprises a hydrophilic surface.

4. The main body according to claim 3, characterized in that The hydrophilic surface is formed using an ablation process.

5. The main body according to claim 2, characterized in that The hydrophobic coating is etched using an ablation process to expose the hydrophilic material forming the at least one portion that is more hydrophilic than surrounding portions of the reflector surface.

6. The main body according to claim 1, characterized in that The at least one portion that is more hydrophilic than surrounding portions of the reflector surface includes fibers arranged on the reflector surface.

7. The main body according to claim 6, characterized in that The fibers are capable of wicking liquids using capillary action.

8. The main body according to claim 6, characterized in that The fibers include a hydrophilic material.

9. The main body according to claim 6, characterized in that The fibers are natural fibers or synthetic fibers, or a combination of the natural fibers and synthetic fibers.

10. The main body according to claim 6, characterized in that The fibers have a diameter of less than 0.2 mm.

11. A body according to any one of claims 1 to 10, characterized in that The width of the at least one portion that is more hydrophilic than surrounding portions of the reflector surface increases in a direction from a center of the reflector surface toward an edge of the reflector surface.

12. A body according to any one of claims 1 to 10, characterized in that The at least one portion that is more hydrophilic than surrounding portions of the reflector surface includes a series of channels having a constant width, a diverging width, or a combination of the constant and diverging widths.

13. A body according to any one of claims 1 to 10, characterized in that The at least one portion that is more hydrophilic than surrounding portions of the reflector surface includes a plurality of rough features.

14. The body according to claim 13, characterized in that The rough features are formed on the reflector surface by laser ablation.

15. The body according to claim 13, characterized in that The rough features include a plurality of circular pillars, square pillars, or hexagonal pillars, or a combination of the plurality of circular pillars, square pillars, and hexagonal pillars.

16. The body according to claim 15, characterized in that The columns have different heights.

17. A body according to any one of claims 1 to 10, characterized in that The reflector surface is coated with a hydrophobic material, and the at least one portion that is more hydrophilic than surrounding portions is formed on top of the hydrophobic portion or is formed by selectively removing the hydrophobic coating.

18. The body according to claim 12, characterized in that The channels extend radially from a center of the reflector surface, and wherein the channels overlap each other at a center portion of the reflector surface.

19. The body according to claim 12, characterized in that The channels extend radially from the center of the reflector surface and converge at a single point in the center of the reflector surface.

20. The body according to claim 18, characterized in that The channels diverge radially from a center of the reflector surface toward an edge of the reflector surface.

21. The body according to claim 18, characterized in that The channels diverge radially from a center of the reflector surface towards an edge of the reflector surface at an angle between 5° and 20°.

22. The body according to claim 18, characterized in that The channels diverge radially from a center of the reflector surface toward an edge of the reflector surface at varying angles.

23. The body according to claim 18, characterized in that Each channel has an axis of symmetry, and wherein the axes of symmetry intersect each other and define a polygon around the center of the reflector surface.

24. A body according to any one of claims 1 to 10, characterised in that The acoustic resonance cavity is formed by two reflector surfaces separated by a predetermined distance.

25. The body according to claim 24, characterized in that The two reflector surfaces are spaced apart by a spacer having an outer surface including a hydrophilic portion.

26. A body according to any one of claims 1 to 10, characterised in that The outer surface of the body includes a hydrophilic portion.

27. An acoustic resonance fluid flow velocity sensor, characterized in that: The sensor comprises a body according to any one of claims 1 to 26.

28. A method of providing a surface on a body for an acoustic resonance fluid flow sensor, characterized in that The surface is a reflector surface of the sensor and is configured to assist water drainage from the sensor, and the method includes providing at least one portion that is more hydrophilic than surrounding portions of the reflector surface to provide water movement along a radial direction from a center of the reflector surface to an edge of the reflector surface through the at least one more hydrophilic portion.

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