Acoustic resonant anemometer

Abstract

An acoustic resonant fluid motion sensor comprising: a housing comprising a first reflective surface, a second reflective surface, and four struts, wherein the second reflective surface is parallel to the first reflective surface to define a resonant cavity between the reflective surfaces, wherein the resonant cavity is open along a fluid motion direction, and wherein the first reflective surface and the second reflective surface are spaced apart by the four struts. Three electro-acoustic transducers are arranged within the first reflective surface.

Description

Technical Field

[0001] This disclosure relates to the configuration of an acoustic resonance fluid sensor. Background Technology

[0002] An acoustic resonance fluid sensor comprises a resonant cavity located between two parallel reflective surfaces, capable of measuring the velocity and direction of fluid flow. During operation, a transducer present in the resonant cavity of the sensor emits sound waves at the resonant frequency of the cavity, thereby generating a standing wave within the cavity. The transducers are switched such that in one switching state, the first transducer emits an ultrasonic signal, while the second transducer acts as a receiver. In a second switching state, the second transducer emits an ultrasonic signal, while the first transducer acts as a receiver. The signals measured in the respective switching states are processed, and the phase difference between them is determined. Measuring this phase difference helps determine the velocity of the fluid flowing through the cavity. By using more than one transducer pairing, the direction of fluid flow within the cavity can be determined. These paired transducers are arranged in a 2D plane to allow measurement of fluid flow velocities in more than one direction.

[0003] Time-of-flight sensors are also known in the art, which consist of only a reflective surface and measure the time it takes for an ultrasonic pulse emitted by one transducer to be received at another transducer. The transducers are angled approximately 45 degrees relative to the normal, such that the emitted ultrasonic pulse first strikes the reflective surface and is then reflected to be received at a second transducer. Time-of-flight sensors differ substantially from acoustic resonance sensors, especially because they do not use standing waves during the measurement process. Summary of the Invention

[0004] An acoustic resonant fluid motion sensor includes: a housing comprising a first reflective surface, a second reflective surface, and four pillars, wherein the second reflective surface is parallel to the first reflective surface to define a resonant cavity between the reflective surfaces, wherein the resonant cavity opens along a fluid motion direction, and wherein the first reflective surface and the second reflective surface are spaced apart by the four pillars. Three electroacoustic transducers are arranged within the first reflective surface.

[0005] In one embodiment, the housing is at least partially or entirely formed of plastic, metal, or composite material.

[0006] In one embodiment, the housing is formed by injection molding.

[0007] In one embodiment, the four pillars are positioned at equal angles around the periphery of the resonant cavity.

[0008] In another embodiment, a housing for an acoustic resonant fluid motion sensor is provided, comprising: a first reflective surface, a second reflective surface, and four supports. The second reflective surface is parallel to the first reflective surface to define a resonant cavity between the reflective surfaces. The resonant cavity opens along the direction of fluid motion. The first reflective surface and the second reflective surface are spaced apart by the four supports. Mounting elements for three electroacoustic transducers are arranged within the first reflective surface.

[0009] In another embodiment, a computer program instruction is provided for execution by an additive manufacturing apparatus, wherein, when executed by the additive manufacturing apparatus, the computer program instruction causes the additive manufacturing apparatus to manufacture the housing as described above. Attached Figure Description

[0010] Figure 1 A high-level view of the components of the acoustic resonance wind sensor is shown.

[0011] Figure 2 An external view of a conventional acoustic resonance wind sensor is shown.

[0012] Figure 3 A view of the first reflective surface of a conventional acoustic resonance wind sensor is shown.

[0013] Figure 4 shows a set of graphs showing the directional error results for an acoustic resonance wind sensor with three pillars.

[0014] Figure 5 An external view of an acoustic resonance wind sensor with four pillars according to an embodiment is shown.

[0015] Figure 6 A view of the first reflective surface of an acoustic resonance wind sensor with four pillars according to an embodiment is shown.

[0016] Figure 7 shows a set of graphs showing the directional error results of the acoustic resonance wind sensor according to an embodiment. Detailed Implementation

[0017] Figure 1 A high-level view of an acoustic resonant fluid sensor 100 is shown. The acoustic resonant fluid sensor typically includes a first reflective surface 110 and a second reflective surface 120, spaced apart by a perpendicular distance and substantially parallel to each other. The first and second reflective surfaces are typically circular and substantially the same size. A resonant cavity 130 is defined by the space between the first and second reflective surfaces. The resonant cavity 130 has openings around its periphery for fluid to move through the cavity in a plane parallel to the first and second reflective surfaces.

[0018] A plurality of electroacoustic transducers are held in the first reflective surface 110, and these electroacoustic transducers are connected to the electronic unit 150. Each electroacoustic transducer is configured to convert an electrical signal from the electronic unit 150 into a corresponding acoustic signal. Each transducer is also configured to convert a received acoustic signal into a corresponding electrical signal and send it to the electronic unit 150.

[0019] In operation, the first electroacoustic transducer 141 receives a transmitted electronic signal from the electronic unit 150 and converts it into an emitted acoustic signal. The electronic signal driving the transducer 141 has a bandwidth that includes the intended resonant frequency of the resonant cavity 130. The emitted acoustic signal is incident on the second reflective surface 120 and reflected back towards the first reflective surface 110, thereby generating a standing wave inside the cavity 130.

[0020] At least one other electroacoustic transducer 142 in the cavity is configured to receive an acoustic signal and convert it into an electronic signal for transmission to the electronic unit 150. Thus, the second electroacoustic transducer 142 receives the acoustic standing wave formed by the first electroacoustic transducer 141 and converts it into a corresponding received electronic signal. This received electronic signal can be compared with the transmitted electronic signal at the electronic unit 150. The received electronic signal will have a phase shift relative to the transmitted electronic signal, which depends on the time it takes for the sound wave to propagate between the transmitting transducer 141 and the receiving transducer 142. When the roles of the transducers are reversed (i.e., the signal is emitted by the second transducer 142 and received by the first transducer 141), another phase difference can be determined. Using the difference between the first and second phase differences, the velocity of the fluid flowing along the axis defined by the positions of the transmitting and receiving transducers in the first reflective surface 110 can be determined.

[0021] Third electroacoustic transducer 143 ( Figure 1 (Not shown) is held by the first reflective surface 110. The third electroacoustic transducer 143 is positioned outside the axis defined by the positions of the first and second electroacoustic transducers. The third electroacoustic transducer 143 can also receive acoustic standing waves present in the resonant cavity 130, whose phase differs from the transmitted signal. By repeating the above process between different pairs of transducers present in the resonant cavity 130, the overall velocity of the fluid flowing through the cavity 130 can be determined using the velocity components along each axis.

[0022] The embodiments discussed herein use air as an example medium through which signals propagate to determine wind speed and direction. However, the invention is not limited to wind sensors.

[0023] Figure 2An external view of a known embodiment of the sensor 100 described above is shown. The sensor is housed by a first housing portion 101 and a second housing portion 102. The first housing portion 101 holds electroacoustic transducers 141, 142, 143 and electronic unit 150, as well as a first reflective surface 110. Figure 2 (Not shown in the image). The second housing portion 102 holds the second reflective surface ( Figure 2 (Not shown in the image), and is mounted on support member 105. The resonant cavity 130 is defined around its periphery by support column 160. Figure 2 In the illustrated embodiment, the acoustic resonance wind sensor 100 has six pillars 160, which are positioned at equal angles around the periphery of the first and second reflective surfaces. However, the resonant cavity 130 remains substantially open for fluid flow parallel to the first and second reflective surfaces. The electronic unit 150... Figure 2 It is shown in the first housing portion, but may also be located in the second housing portion.

[0024] Figure 3 The layout of the components held by the first reflective surface 110 is shown. The first reflective surface 110 holds electroacoustic transducers 141, 142, and 143. These transducers are symmetrically positioned around the center of the reflective surface in a triangular configuration. As discussed above, by positioning the third transducer 143 outside the axis defined by the positions of the first two transducers 141 and 142, the overall velocity and direction of the wind passing through the cavity 130 can be determined. Furthermore, six geometrically identical struts 160 are distributed at equal angles around the periphery of the first reflective surface 110. Known acoustic resonance wind sensors 100 use six struts 160 to provide symmetry for the system (six struts 160 is a multiple of three transducers).

[0025] For some applications of the acoustic resonance wind sensor 100, it is advantageous to manufacture the first housing portion 101, the second housing portion 102, and the support column 106 using plastic. Manufacturing the sensor using plastic reduces the overall cost of the sensor 100 because the plastic used is much cheaper than the metals conventionally used to manufacture sensor housings. However, to manufacture the sensor 100 using plastic, the design of the parts must be adjusted to ensure sufficient robustness of the sensor. For example, the diameter of the sensor and the dimensions of the support column must be increased to ensure the structural stability of the sensor. In some embodiments, the sensor can be manufactured using injection molding, in which case adjustments must be made to facilitate this manufacturing method. These adjustments include a constant thickness of the parts to allow for uniform cooling, a draft wall, and allowance for movement of the injection mold tooling portion. In another embodiment, additive manufacturing is used to manufacture the sensor.

[0026] The wind sensor, designed to be made of plastic, has a larger diameter than conventional sensors and uses larger struts in its housing than those found in conventional sensors. Testing determined that the number of struts separating the first housing portion 101 from the second housing portion 102 should be reduced to prevent the larger struts from affecting the airflow entering the resonant cavity 130. It has been previously thought that alignment between the struts and the transducer layout is necessary. For an anemometer comprising three transducers, this necessarily means using three struts to maintain this alignment with the transducer positions.

[0027] Typically, a wind sensor is tested by mounting it to a robotic arm via support member 105 and placing it in a wind tunnel. During a constant wind speed and direction through the wind tunnel, the wind sensor can be rotated from 0 degrees to 360 degrees via the robotic arm over the entire test interval. The wind direction measured from the wind sensor can be compared with the known amount of rotation of the robotic arm over the entire test interval, and based on this comparison, a record of the direction measurement error during the entire rotation can be determined.

[0028] Figure 4A This diagram shows a record taken at a constant wind speed of 30 m / s. The direction measurement error (in degrees) is shown on the Y-axis, while the amount of rotation experienced by the wind sensor is shown on the X-axis. The shaded area in the figure represents the angle of rotation of the sensor when it is blocked by the support column at 160 degrees.

[0029] After testing, the data is processed to calibrate measurement errors. This is done by comparing velocity and direction data during testing at various wind speeds (e.g., 15 m / s, 30 m / s, and 65 m / s) and comparing these measurements to known wind speeds and arm rotation angles. The measurements are averaged every few rotation angles to reduce noise, resulting in a smooth error curve for each tested wind speed. These error curves are then interpolated and extrapolated to produce a continuous three-dimensional error curve across a wider speed range. Discrete points are found for the direction error at each speed, and a function is applied to "zero" the direction at these points, generating a calibration table. This method is called "Advanced Yaw Calibration for Direction" (AYC-D). After wind tunnel processing, these calibration tables are written to the wind sensors to correct their wind direction output. Figure 4B This shows the result after AYC-D calibration. Figure 4A The same measurements recorded in the document.

[0030] Figure 4C and Figure 4D Corresponding to Figure 4A and Figure 4BHowever, the X-axis encircles a circle. In this way, the layout of the components in the first reflective surface 110 (as shown in the figures) can be visually visualized. Figure 4A and Figure 4B The results are shown below. Figure 4C and Figure 4D The hollow circle shown represents the transducer, while Figure 4C and Figure 4D The shaded circles shown represent support pillars. Ideally, for a wind sensor to perform correctly, its direction data should be calibrated so that the final result is a flat straight line on a rectangular coordinate graph and a circle on a polar coordinate graph.

[0031] Figure 4A and Figure 4B The results of the aforementioned test procedure, obtained for a wind sensor design with three pillars intended for production in plastic, are shown. It can be seen that, contrary to the expected behavior, the orientation error is instead unstable, abruptly switching from high positive to high negative errors at various points throughout the rotation. These jumps are too large and abrupt to be eliminated by calibration when these data are calibrated. Therefore, they appear as spikes in the calibrated results. Figure 4C and Figure 4D For visual purposes, the X-axis is shown to be wrapped around a circle. Figure 4A and Figure 4B The curve graph.

[0032] Therefore, the sensor geometry needed to be corrected to enable its manufacture in plastic without introducing significant errors in orientation measurements. After extensive testing on many different geometries, a new sensor configuration was determined that minimized this calibration problem.

[0033] Figure 5 An embodiment of a new configuration of sensor 600 is shown. It can be seen that this configuration has four pillars 660 separating the first housing portion 601 and the second housing portion 602, rather than... Figure 2 The diagram shows six pillars, and Figure 4 shows the three pillars being tested. Using four pillars results in a disruption of the rotational symmetry in the layout between the transducers and pillars used in the known six-pillar configuration. By reducing the number of pillars 660 from six, the influence of the larger pillars on the airflow through sensor 600 is reduced. Surprisingly, by using four pillars instead of three, the error present in the direction measurement is reduced, which will be discussed further below.

[0034] Figure 6The arrangement of components on / in a first reflective surface 610 according to one embodiment is shown. The first reflective surface 610 still maintains the three electroacoustic transducers 641, 642, 643 in a generally triangular arrangement, but now four struts 660 are located around the periphery of the surface. In Figure 7, the struts 660 are distributed approximately at equal angles around the periphery of the surface 610. Although not strictly necessary, in this embodiment, one of the transducers 643 is located on an axis defined by two of the struts, while the other transducers 641 and 642 are not.

[0035] According to the test method disclosed above, the wind sensor according to an embodiment of the present invention was tested, and the results shown in Figure 7 were obtained. It can be seen that, compared with... Figure 4A and Figure 4B Unlike the drastic shifts in orientation error shown, the orientation error exhibits a significantly smoother performance throughout the rotation (e.g.) Figure 7A As shown), this allows for more successful sensor calibration (such as...). Figure 7B (As shown). Figure 7C and Figure 7D It was shown again with Figure 7A and Figure 7B The corresponding polar coordinate graph.

[0036] Therefore, it can be seen that the configuration according to the invention provides an improvement in the sensor's directional error, a surprising and unexpected result. Prior to this invention, it was anticipated in the art that acoustic resonance anemometers required symmetry in the transducer configuration. Therefore, it was expected that three supports would be chosen in an attempt to reduce the number of supports. Surprisingly, the measurement error, as described above... Figures 4A to 4D The discussed approach is as follows. Even more surprisingly, after conducting extensive experiments, the following findings were made: by abandoning the expectation of symmetrical arrangement of the supports and transducers, and choosing four supports instead of three, these measurement errors are significantly reduced.

[0037] Although this invention was made in the context of developing acoustic resonance anemometers that can be manufactured from plastic, it should be understood that the fact that four pillars can be used in combination with three transducers is not limited to sensors made of plastic. Alternatively, sensors with this geometry can also be made of other materials, such as metals (including aluminum), ceramics, or composite materials.

[0038] While certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. In fact, the novel methods, apparatuses, and systems described herein can be embodied in many forms; furthermore, various omissions, substitutions, and changes can be made to the forms of the methods and systems described herein without departing from the spirit of the invention. The appended claims and their equivalents are intended to cover these forms or modifications that fall within the scope and spirit of the invention.

Claims

1. An acoustic resonance fluid motion sensor, comprising: A housing comprising a first reflective surface, a second reflective surface, and four pillars, wherein the second reflective surface is parallel to the first reflective surface to define a resonant cavity between the reflective surfaces, wherein the resonant cavity opens along the direction of fluid movement, and wherein the first reflective surface and the second reflective surface are spaced apart by the four pillars. Three electroacoustic transducers are arranged within the first reflective surface.

2. The sensor according to claim 1, wherein, The shell is at least partially or entirely formed of plastic, metal or composite material.

3. The sensor according to claim 2, wherein, The shell is formed by injection molding.

4. The sensor according to claim 1, wherein, The four pillars are positioned at equal angles around the periphery of the resonant cavity.

5. A housing for an acoustic resonance fluid motion sensor, comprising: A first reflective surface, a second reflective surface, and four pillars, wherein the second reflective surface is parallel to the first reflective surface to define a resonant cavity between the reflective surfaces, wherein the resonant cavity opens along the direction of fluid movement, and wherein the first reflective surface and the second reflective surface are spaced apart by the four pillars. Mounting and positioning elements are used to arrange three electroacoustic transducers within the first reflective surface.

6. A computer program instruction, said computer program instruction being executed by additive manufacturing equipment, wherein, When executed by the additive manufacturing equipment, the computer program instructions cause the additive manufacturing equipment to manufacture the housing according to claim 5.

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