Interference elimination device of open-end coaxial sensor

Abstract

The utility model provides an interference elimination device for an open-end coaxial sensor, and the device comprises a balance-to-unbalance conversion device which is provided with a signal combination port, an in-phase port, and an anti-phase port. An open-end coaxial sensor; wherein the number of the open-end coaxial sensors is two, one open-end coaxial sensor is connected to the in-phase port, and the other open-end coaxial sensor is connected to the anti-phase port; according to the utility model, the signals of the two sensors are synthesized to one port by using the balance-unbalance conversion device, useful signals are superposed in the same phase at the port, interference signals are superposed in the opposite phase at the port, and the superposed result greatly reduces the interference on the detection signals, thereby avoiding the interference of the detection signals in a non-laboratory environment. And the detection result is seriously influenced by external interference.

Description

Technical Field

[0001] The utility model relates to the technical field of signal processing, in particular to an interference elimination device for an open-ended coaxial sensor of a portable device. Background Art

[0002] Open-ended coaxial sensors are often used to detect the dielectric constant of materials. Before this, waveguides or resonant cavities were often used to measure the dielectric constant of materials. Before testing, the material to be tested needed to be made into a sample of a specific shape so that it could fit into the test frame of the waveguide or resonant cavity. The requirement of "making samples" has limited its application in many fields.

[0003] In the 1970s, Decreton, Tanabe and others proposed a new nondestructive testing method, which is to determine the dielectric constant of the material by measuring the reflection coefficient of the transmission mode of the open-ended waveguide electromagnetic wave on the surface of the material to be tested. The structure and use of the open-ended coaxial sensor can be seen in Figure 1 As shown in Figure 2, this idea has broad application prospects and quickly attracted widespread attention. Figure 2 As shown in the figure, in the analysis of open-ended coaxial sensors, the capacitance equivalent circuit is often used. In this model, the radiation of the interface is not taken into account. A further model equates the end face to a parallel connection of a capacitor and a radiation resistor. This model is called an antenna model. Figure 3 As shown:

[0004] Its port equivalent admittance is:

[0005]

[0006] The last term is proportional to the 5 / 2 power of the dielectric constant of the material to be tested, which is related to the antenna effect. This antenna effect will cause errors in the test.

[0007] The detection end face of the open-ended coaxial sensor has an antenna effect. This means that in a non-laboratory environment, its detection end face may receive external electromagnetic interference signals. External electromagnetic radiation sources may interfere with the sensor's detection process. Such electromagnetic radiation sources include but are not limited to: car spark plugs, motors, small power tools, microwave ovens, electromagnetic switches, etc.

[0008] From the above analysis, we can see that the antenna effect exists on the exposed detection end face of the sensor. The external interference signal sensed by the sensor probe mainly enters the detection system from the exposed end face. In a non-laboratory environment, this interference will seriously affect the detection results.

[0009] Therefore, an interference elimination device for an open-ended coaxial sensor is proposed. Utility Model Content

[0010] In view of this, the embodiments of the present invention hope to provide an interference elimination device for an open-ended coaxial sensor applied to a portable device, so as to solve or alleviate the interference problem existing in the prior art, and at least provide a beneficial choice.

[0011] The technical solution of the embodiment of the utility model is implemented as follows: an interference elimination device for an open-ended coaxial sensor, comprising:

[0012] A balanced-to-unbalanced conversion device having a signal combining port, a common-phase port and an anti-phase port;

[0013] Open-ended coaxial sensor;

[0014] There are two open-ended coaxial sensors, one of which is connected to the in-phase port, and the other is connected to the anti-phase port.

[0015] In a preferred embodiment: the inner and outer conductors of the two open-end coaxial sensor end faces are exposed, and the exposed structure is equivalent to a small antenna. The external interference signal will induce time-varying interference signals n1(t) and n2(t) on the detection end faces of the two open-end coaxial sensors. The time-varying interference signals n1(t) and n2(t) have a phase difference of 180° when they are merged at the signal merging port, and the time-varying interference signals n1(t) and n2(t) cancel each other out.

[0016] Similarly, in the above preferred embodiment: after the high-frequency detection signal generated by the detection device is input into the interference elimination device through the signal merging port, after passing through the balanced-to-unbalanced device and the sensor, a part of the high-frequency signal is reflected at the interface between the detection end face of the open-end coaxial sensor and the substance to be measured, and when the reflected signal is superimposed again at the signal merging port, its phase relationship is an in-phase relationship, that is, the high-frequency detection signal input by the sensor is divided into two branches after entering the above-mentioned balanced-to-unbalanced device, and the phase difference of the two signals at this time is 180°. They will be reflected at the interface where the sensor contacts the substance to be measured, and after the reflected signal passes through the above-mentioned balanced-to-unbalanced device for the second time, the cumulative phase difference when the two signals are combined is 360°, that is, 0°. This means that the high-frequency signal input by the sensor is added in phase when the reflected return is superimposed. After the internal signal of the detection device is input through the signal merging port and passes through the balanced-to-unbalanced device and the sensor, when the part of the signal reflected at the detection end face of the sensor is superimposed again at the signal merging port, the two signals are in phase. (One signal undergoes two 180-degree phase shifts, and the other signal has no phase shift)

[0017] That is to say, the interference elimination device superimposes the useful signal in phase, and counteracts the interference signal, which generally improves the signal carrier-to-noise ratio. The useful signal is a high-frequency detection signal generated by the detection device and input to the open-end coaxial sensor.

[0018] In all embodiments: the insertion loss of a high-frequency detection signal (a high-frequency signal required for detection) passing through the balanced-to-unbalanced device is less than 3 dB.

[0019] The embodiment of the utility model has the following advantages due to the adoption of the above technical solution:

[0020] The utility model synthesizes the signals of two sensors into one port by utilizing a balanced-to-unbalanced conversion device. The useful signal passes through the balanced-to-unbalanced conversion device twice and is superimposed in phase at the signal combining port. Most interference signals pass through the balanced-to-unbalanced conversion device only once and are superimposed in reverse at this port. The superposition result will greatly reduce the interference of the detection signal, avoiding the situation in a non-laboratory environment where such interference will seriously affect the detection result.

[0021] The above summary is for the purpose of description only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the utility model will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 The top view and the side view of the detection end face of the open-ended coaxial sensor in the prior art are also symbolically drawn in the top view and the side view. When the detection end face of the open-ended coaxial sensor contacts the material to be measured, a part of the electric lines will pass through the material to be measured, so that the dielectric properties of the material to be measured will affect the distribution of the end face electric field, thereby affecting the reflection coefficient of the detection end face.

[0024] Figure 2 This is an open-end coaxial capacitance model diagram in the prior art, which treats the detection end face as equivalent to a fixed capacitor Cf and a capacitor C(εr) that changes with the dielectric constant of the material being measured in parallel. This model assumes that the antenna effect of the detection end face can be ignored. It is suitable for situations where the dielectric constant of the material to be measured is not very high and the measurement frequency is not very high.

[0025] Figure 3 For the existing technology Figure 2Schematic diagram of the open-ended coaxial capacitor model being changed to an antenna model. When the dielectric constant of the material being measured is relatively high or the measurement frequency is high, the antenna effect of the detection end face cannot be ignored. If this part is taken into consideration, the above model is improved to an antenna model, and a radiation conductance is used to equivalently expose the antenna radiation effect of the detection end face.

[0026] Figure 4 It is a structural diagram of the connection between the balanced-to-unbalanced conversion device of the utility model and the open-ended coaxial sensor; DETAILED DESCRIPTION

[0027] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0028] It should be noted that the terms "first", "second", "symmetrical", "array", etc. are only used to distinguish between description and position description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the definition of "first", "symmetrical", etc. can explicitly or implicitly include one or more of these features; similarly, when the quantity of certain features is not limited in the form of words such as "two" or "three", it should be noted that this feature also explicitly or implicitly includes one or more feature quantities;

[0029] In the present invention, unless otherwise clearly specified and limited, the terms such as "installation", "connection", "fixation" and the like should be understood in a broad sense; for example, it can be a fixed connection, a detachable connection, or an integral molding; it can be a mechanical connection, a direct connection, welding, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood based on the description and drawings combined with specific circumstances.

[0030] Embodiment 1

[0031] The embodiments of the present utility model are described in detail below with reference to the accompanying drawings.

[0032] like Figure 4 As shown, the embodiment of the utility model provides an interference elimination device for an open-ended coaxial sensor, comprising:

[0033] A balanced-to-unbalanced conversion device 20, which has a signal combining port 23, an in-phase port 22 and an inverting port 21;

[0034] An open-end coaxial sensor 11 and an open-end coaxial sensor housing 19;

[0035] There are two open-end coaxial sensors, one of which is connected to the in-phase port 22 through the adapter 17, and the other is connected to the anti-phase port 21 through the adapter 17; the signal merging port 23 is connected to the output cable of the detection device through the adapter 24.

[0036] That is, the present application utilizes a balanced-to-unbalanced conversion device 20, also known as a balun, to convert a single-ended signal into a double-ended differential signal, the two differential signals have a phase difference of 180°, and uses two open-ended coaxial sensors, one sensor is connected to the in-phase port 22 of the balun, and the other sensor is connected to the inverting port 21 of the balun;

[0037] Two open-ended coaxial sensors are connected to an external antenna, and the interference signals n1 and n2 induced by the external signal on the end face have a phase difference of 180° when combined at the signal combining input port. The input useful signal passes through the balanced-to-unbalanced device twice, and has a phase difference of 360° when superimposed at the signal combining input port. The insertion loss of the signal passing through the balanced-to-unbalanced device is less than 1dB.

[0038] For the interference signals n1(t) and n2(t) generated at the end face, when they are combined at the signal input port, their phases are exactly 180° apart, and the reverse superposition cancels each other out. The useful signal enters from the signal combination input port, and has passed through a balanced-to-unbalanced device once before being reflected back from the interface of the measured material, and the phase has already differed by 180°. The second reflection back passes through the balanced-to-unbalanced device, and when it is superimposed at the signal combination input port, the phase difference is 360°, and the in-phase superposition signal is enhanced. The price paid for this interference cancellation circuit is the use of an extra sensor, and the insertion loss of the signal passing through the balun twice. Generally, this insertion loss can be controlled below 3dB, and the interference cancellation device adopted must be Balun and not other devices. One input and two outputs, the phase difference between the two outputs is 180°. In addition to Balun, there are other structures for this type of structure, such as 180-degree bridges. However, only Balun can achieve an insertion loss of the input signal within 3dB, while others are generally greater than 3dB. In addition, within 3dB is a generally acceptable insertion loss value.

[0039] When the utility model is working, the signals of the two probes are synthesized into one port by utilizing the balanced-unbalanced conversion device, the useful signal is superimposed in phase at this port, and most of the interference signals are superimposed in reverse phase at this port, and the superposition result will greatly reduce the interference of the detection signal.

[0040] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited thereto. Any technician familiar with the technical field can easily think of various changes or substitutions within the technical scope disclosed by the utility model, which should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. An interference elimination device for an open-ended coaxial sensor, characterized in that: include: A balanced-to-unbalanced conversion device having a signal combining input port, a common-phase port and an anti-phase port; Open-ended coaxial sensor; There are two open-ended coaxial sensors, one of which is connected to the in-phase port, and the other is connected to the anti-phase port.

2. The interference elimination device for an open-ended coaxial sensor according to claim 1, characterized in that: The inner and outer conductors of the two open-end coaxial sensor detection end faces are exposed to the outside world, and the external interference signal will induce time-varying interference signals n1(t) and n2(t) at the two open-end coaxial sensor detection end faces. The time-varying interference signals n1(t) and n2(t) have a phase difference of 180° when they are merged at the signal merging port, and the time-varying interference signals n1(t) and n2(t) cancel each other out.

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