Antenna assembly for emitting microwaves and measuring assembly having at least one such antenna assembly

Abstract

The invention relates to an antenna assembly (100) for emitting microwaves, comprising: a dielectric hollow conductor element (110); and a support element (120); wherein: the hollow conductor element has an electrically conductive surface (112) at least along a circumferential side surface, the hollow conductor element (110) has an electrically non-conductive emission surface (118), the hollow conductor element (112) has a coupler socket (112); the support element (140) comprises a material having an elastic modulus of not less than 50 GPa, in particular not less than 150 GPa; the support element (120) surrounds the dielectric hollow conductor element at least along a side surface, the dielectric hollow conductor element (110) is fixed in the support element (120), the support element (120) has an emission opening (122), the emission surface (118) is aligned with the emission opening (122), the hollow conductor element has a dielectric constant of, for example, not less than 8 at 2 GHz, in particular not less than 9.5 at 2 GHz, the hollow conductor element (110) comprises a ceramic material, in particular aluminium oxide, zirconium oxide or titanium dioxide.

Description

Technical Field

[0001] This invention relates to an antenna assembly for emitting microwaves and a measuring assembly having at least one such antenna assembly. It is known from the literature that the complex dielectric constant of a medium can be derived from the propagation time and damping of electromagnetic waves in that material. The complex dielectric constant can also be used to draw conclusions about the properties of a medium, such as its water content. Background Technology

[0002] Therefore, measuring devices for determining dielectric properties—such as the complex dielectric constant of a process medium—are well known. Published patent application DE 30 38 725 A1 discloses an apparatus for determining moisture content. Published patent applications DE 44 26 280 A1 and DE 101 64 107 C1 disclose a device for measuring the load of an airflow with a solid content. Published document US 2016 313 259 A1 discloses a temperature-compensated device for determining the dielectric properties of a medium. WO 1991 005 243 A1 discloses an apparatus for measuring the concentration of two substances. Published patent application DE10 2017 131 269 A1 discloses an apparatus for determining the fat content in milk.

[0003] Patent GB 2 293 014 discloses a measuring assembly with a hollow conductor antenna, which has a stainless steel body and a glass-ceramic filler fused into the cavity of the stainless steel body. This firstly requires complex manufacturing, and secondly, due to the relatively low dielectric constant of the glass-ceramic, the antenna has a large volume. Summary of the Invention

[0004] Therefore, the present invention aims to provide a compact hollow conductor antenna that is resistant to high voltage and high temperature and can be used over a wide frequency range. This objective is achieved by the antenna assembly and measurement assembly according to the present invention.

[0005] The antenna assembly for transmitting microwaves according to the present invention includes:

[0006] Dielectric hollow conductor elements; and

[0007] Support elements;

[0008] The dielectric hollow conductor element has a conductive surface at least along its circumferential side surface.

[0009] The dielectric hollow conductor element has a non-conductive emitting surface.

[0010] The dielectric hollow conductor element has a coupler socket;

[0011] The material of the support element has an elastic modulus of not less than 50 GPa, and in particular not less than 150 GPa.

[0012] The support element surrounds the dielectric hollow conductor element at least along its side surface.

[0013] The dielectric hollow conductor element is fixed in the support element.

[0014] The support element has a firing opening, and the firing surface is aligned with the firing opening.

[0015] In an improvement of the present invention, the dielectric hollow conductor element has a dielectric constant of not less than 8 at 2 GHz, and particularly has a dielectric constant of not less than 9.5 at 2 GHz.

[0016] In an improvement of the invention, the dielectric hollow conductor element has a ceramic material, particularly alumina, zirconium oxide, or titanium dioxide.

[0017] In an improvement of the invention, the dielectric hollow conductor element has a basic shape of a parallelepiped, particularly a basic shape of a rectangle.

[0018] In an improvement of the invention, the conductive surface of the dielectric hollow conductor element includes a metal coating, thereby forming a filled hollow conductor.

[0019] In an improvement of the present invention, the metal coating comprises an active hard solder.

[0020] By using the aforementioned material selection and shape, a compact antenna can be achieved, because the antenna's size is determined by the cutoff frequency f of the filled hollow conductor. c Determined. For the commonly used basic pattern TE10 of a rectangular hollow conductor with rectangular sides a and b, the following applies: a = c d / (2f c ), where the propagation speed c in the dielectric is... d Applicable to c d =c0 / ε r 1 / 2 Therefore, the size of the antenna is inversely proportional to the square root of the dielectric constant of the dielectric filling material. Thus, in terms of dielectric constant... In this case, the cross-section of the hollow conductor in this antenna at the cutoff frequency f c At 2GHz, this would therefore result in a minimum width of approximately 3.3cm. On the other hand, if a dielectric constant ε of at least 8 is used at 2GHz... rThe dielectric material has a minimum width of only 2.7 cm. This is advantageous because the holes in the support element are also limited to this size. Compared to antennas with dielectrics made of glass, the chosen dielectric material also significantly increases the transmittance into the water medium.

[0021] In an improvement of the invention, the coupler socket includes a hole through which a pin-shaped coupler, particularly a coaxial coupler, extends and terminates at a capacitive element.

[0022] In an improvement of the invention, the capacitive element has a capacitor, which is, for example, in the form of a printed circuit board having an integrated capacitor, a coaxial capacitor, or an open-circuit plate.

[0023] In an improvement of the invention, the support element has a conductive surface surrounding the dielectric hollow conductor element.

[0024] In an improvement of the invention, the support element is made of a metallic material, particularly steel.

[0025] In an improvement of the invention, the support element has a hollow conductor cavity for a dielectric hollow conductor element, wherein the hollow conductor cavity has a cross-section extending parallel to the emission surface, and these cross-sections are filled by the dielectric hollow conductor element to at least 90%, particularly 95%, of the cross-sectional area.

[0026] In an improvement of the present invention, the dielectric hollow conductor element is fixed in a hollow conductor chamber using a polymer.

[0027] In an improvement of the invention, the support element has a process connector for connecting the antenna assembly to an antenna opening in a pipe or container, so as to position the transmission opening in the region of the antenna opening.

[0028] The measurement assembly according to the invention comprises: at least one antenna assembly according to the invention; a measurement tube having antenna openings for each antenna assembly, the antenna assemblies being mounted at the respective antenna openings; and a measurement and operation circuit connected to each antenna assembly by means of corresponding signal lines.

[0029] In an improvement of the invention, the measuring tube has two opposing antenna openings, and one of the antenna assemblies according to the invention is mounted at each of the two opposing antenna openings. Attached Figure Description

[0030] The present invention will now be described in more detail with reference to exemplary embodiments shown in the accompanying drawings.

[0031] The attached diagram shows:

[0032] Figure 1 This is a spatial illustration of an exemplary embodiment of an antenna assembly according to the present invention;

[0033] Figure 2 This is a cross-sectional view through an exemplary embodiment of the measuring component according to the present invention; and

[0034] Figure 3 It is a view of the reflection and conduction ratio at the interface between the antenna and the water medium. Detailed Implementation

[0035] Figure 1 An exemplary embodiment of the antenna assembly 100 according to the invention shown includes a dielectric hollow conductor element 110 having a high dielectric constant ceramic material, such as alumina, zirconium dioxide, or titanium dioxide. The hollow conductor element 110 has a generally rectangular basic shape with slightly rounded edges. A continuous coupler hole 112 extends through the hollow conductor element 110 parallel to its maximum principal axis of inertia. The side surfaces of the hollow conductor element 110 around its minimum principal axis of inertia and the rear front surface 114 of the hollow conductor element 110 have a metal coating 116, the surface normal of which extends in the direction of the minimum principal axis of inertia of the hollow conductor element. This metal coating is prepared by active solder. A second front surface, facing away from the first front surface 114 and serving as the transmitting surface 118, does not have a metal coating. Furthermore, the circumferential ends of the side surfaces adjacent to the transmitting surface do not have the metal coating 116.

[0036] The antenna assembly 100 also includes a metal support element 120, specifically made of stainless steel, having a first end having a generally cylindrical shape. The front of the first end has a transmission opening, from which a hollow conductor cavity 122 extends into the support element 120. A hollow conductor element 110 is disposed within the support element 120, wherein the hollow conductor cavity 122 has walls extending substantially parallel to the metallized surface of the hollow conductor element 110. The unmetallized ends of the side surfaces of the hollow conductor element 110 are arranged close to the front of the first end of the support element 120. In the rear front, away from the first front, the support element 120 has a filling opening 124 communicating with the hollow conductor cavity 122. In this configuration, adhesive is forced into the hollow conductor chamber 122 through a filling opening to fill the circumferential gap volume between the surface of the hollow conductor element 110 and the wall of the hollow conductor chamber 122. As a result, the gap volume, including the non-metallized ends of the side surfaces of the hollow conductor element 110, is sealed up to the emission surface 118. This reliably prevents the medium from seeping into the hollow conductor chamber 122 from the first front side of the support element 120, particularly to avoid corrosion of the metal coating 116 on the side surfaces. Even if the adhesive in the gap becomes damaged near the first front side, corrosion still does not occur because the ends of the hollow conductor element 110 are not metallized.

[0037] The support element 120 also has a coaxial coupler hole 126, which is aligned with the coupler hole 112 of the hollow conductor element 110 and extends from the outer surface of the support element 120 into the hollow conductor chamber 122. Furthermore, the support element 120 has a capacitor chamber hole 128, which is similarly aligned with the coupler hole 112 of the hollow conductor element 110 and extends from the surface opposite to the coaxial coupler hole 126 into the hollow conductor chamber 122.

[0038] A perforated metal contact screw 142 is screwed into the coaxial coupler hole 126 and presses against the metal coating 116 with its front side, thereby establishing a defined current contact between the metal coating 116 and the support element 120. A coaxial coupler 130, having an outer conductor 132 and an inner conductor 134, is guided through the hole of the contact screw 142 and the coupler hole 112 of the hollow conductor element 110, wherein the inner conductor 134 extends into the capacitor chamber hole 128. The outer conductor 132 similarly makes electrical contact with the metal coating 116 and the support element 120 via the contact screw 142.

[0039] In particular, because the hollow conductor element has a very large capacitance due to the selected material, the coaxial coupler 130 still needs to be terminated with a suitable capacitance in order for microwaves to be effectively capacitively coupled to the hollow conductor element 110 in a frequency range of, for example, approximately 2 GHz to 8 GHz. For this purpose, the inner conductor 134 of the coaxial coupler is connected to a capacitor 134, which is specifically designed as a printed circuit board capacitor and arranged in a capacitor chamber aperture 128. As described below, the capacitor 134 is axially clamped in the capacitor chamber aperture 128. An annular disc-shaped pressure member 114 rests against the side surface of the hollow conductor element 110 with an annular axial protrusion. The capacitor 134 is supported on the pressure member 114. An insulating disc 148 is arranged on the side of the capacitor 134 opposite to the pressure member 114, and this insulating disc is axially clamped against the capacitor 134 by means of a disc spring lamination 148 and a clamping screw 144 screwed into the capacitor chamber aperture 128. Despite the different coefficients of thermal expansion of the components, the disc spring lamination 146 still causes only slight fluctuations in clamping force. In addition, the pressure member 114 and the contact screw 142 each press the O-rings 166, 164 against the side surface of the hollow conductor element 110, thereby sealing the gap between the capacitor chamber hole 128 and the coaxial coupler hole 126 relative to the walls of the hollow conductor element 110 and the hollow conductor chamber 122.

[0040] The support element 120 is arranged in the antenna opening 212 of the tube wall 210 of the measuring tube 200 via a cylindrical end, wherein a sealing ring 162 is axially clamped between the tube wall 210 and the support element 120. The antenna assembly 100 is covered by an optional protective housing 240, and the signal line 410 between the operating circuit and the coaxial coupler (e.g.) Figure 2 (As shown) is also guided in the protective housing 240.

[0041] The measurement assembly 300 according to the invention includes two antenna assemblies 100 and a measurement tube 200 having two opposing antenna openings 212, with one of the antenna assemblies 100 mounted in each opening. Furthermore, the measurement assembly includes operating and measurement circuitry 400 connected to the two antenna assemblies 100 via two coaxial cables 410. These antenna assemblies and coaxial signal lines are still covered by a metal protective housing 240, which firstly provides additional EMC protection and secondly prevents the antenna assemblies and signal lines from contamination and mechanical damage. The operating and measurement circuitry is configured to radiate signal sequences of different frequencies, for example, in the frequency range of 2 to 8 GHz, into the medium located in the measurement tube 200 via one of the antenna assemblies, and to receive these signal sequences using the other antenna assembly. The propagation time or damping of these signal sequences can be used to determine the complex permittivity, and thereby determine other medium properties, such as solids content.

[0042] For measuring the performance of the component, it is advantageous if the reflection at the emitting surface 118 of the hollow conductor element is as low as possible. This is affected by the material of the hollow conductor element 110. For this purpose, Figure 3 Various materials and calculated reflection components on the emitting surface are shown for this hollow conductor element. Water is assumed to be the medium, and the width of the hollow conductor element is set to 30 mm. If the s-glass of this hollow conductor element has an assumed dielectric constant of 5.1, it would be impossible to propagate waves up to approximately 2.2 GHz, as these frequencies are below the cutoff frequency. Hollow conductor elements made of Al₂O₃ are clearly more suitable than those of the prior art, even though... Reflection within a certain range. Using ZrO2 filler, electromagnetic energy can be continuously and effectively transmitted into water. Therefore, this demonstrates that, with respect to the ceramic hollow conductor element used according to the invention, effective transmission can be achieved in a medium with high water content for a given antenna geometry.

Claims

1. An antenna assembly (100) for transmitting microwaves, the antenna assembly comprising: Dielectric hollow conductor element (110); as well as Support element (120); The dielectric hollow conductor element has a conductive surface at least along its circumferential side surface. The dielectric hollow conductor element (110) has a non-conductive emitting surface (118). The dielectric hollow conductor element (110) has a coupler socket; The material of the support element (120) has an elastic modulus of not less than 50 GPa; The support element (120) surrounds the dielectric hollow conductor element at least along the side surface. The dielectric hollow conductor element (110) is fixed in the support element (120). The support element (120) has a firing opening (122), wherein the firing surface (118) is aligned with the firing opening (122). The coupler socket includes a hole through which a pin-shaped coupler extends and terminates at a capacitive element.

2. The antenna assembly according to claim 1, wherein, The material of the support element (120) has an elastic modulus of not less than 150 GPa.

3. The antenna assembly according to claim 1, wherein, The dielectric hollow conductor element has a dielectric constant of not less than 8 at 2 GHz.

4. The antenna assembly according to claim 3, wherein, The dielectric hollow conductor element has a dielectric constant of not less than 9.5 at 2 GHz.

5. The antenna assembly according to claim 1, wherein, The dielectric hollow conductor element is made of ceramic material.

6. The antenna assembly according to claim 5, wherein, The ceramic material is alumina, zirconium oxide, or titanium dioxide.

7. The antenna assembly according to claim 1, wherein, The dielectric hollow conductor element has a basic parallelepiped shape.

8. The antenna assembly according to claim 7, wherein, The dielectric hollow conductor element has a basic rectangular shape.

9. The antenna assembly according to any one of claims 1-8, wherein, The conductive surface of the dielectric hollow conductor element includes a metal coating.

10. The antenna assembly according to claim 9, wherein, The metal coating includes an active solder.

11. The antenna assembly according to claim 10, wherein, The metal coating includes an active hard solder.

12. The antenna assembly according to any one of claims 1-8, wherein, The coaxial coupler extends through the hole and terminates at the capacitive element.

13. The antenna assembly according to claim 12, wherein, The capacitive element has a capacitor, which is in the form of a printed circuit board chip having an integrated capacitor, a coaxial capacitor, or an open circuit plate.

14. The antenna assembly according to any one of claims 1-8, wherein, The support element has a conductive surface that surrounds the dielectric hollow conductor element.

15. The antenna assembly according to any one of claims 1-8, wherein, The support element is made of metallic material.

16. The antenna assembly according to claim 15, wherein, The support element is made of steel.

17. The antenna assembly according to any one of claims 1-8, wherein, The support element has a hollow conductor cavity for the dielectric hollow conductor element, wherein the hollow conductor cavity has a cross-section extending parallel to the emitting surface, and the cross-section is filled by the dielectric hollow conductor element to at least 90% of the cross-sectional area.

18. The antenna assembly of claim 17, wherein, The cross-section is filled to 95% of its cross-sectional area by the dielectric hollow conductor element.

19. The antenna assembly according to claim 17, wherein, The dielectric hollow conductor element is fixed in the hollow conductor chamber using a polymer.

20. The antenna assembly according to any one of claims 1-8, wherein, The support element has a process connector for connecting the antenna assembly to an antenna opening in a pipe or container, so as to position the transmission opening in the region of the antenna opening.

21. A measuring component, comprising: At least one antenna assembly according to any one of claims 1-20; A measuring tube having at least one antenna opening, wherein the antenna assembly is mounted at the at least one antenna opening; And measurement and operation circuitry, which is connected to each antenna assembly by means of corresponding signal lines.

22. The measurement assembly of claim 21, comprising two antenna assemblies according to any one of claims 1-20, wherein, The measuring tube has two opposing antenna openings, and one of the antenna assemblies is mounted on each of the two opposing antenna openings.

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