JP3927688B2 - Antenna for leak detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water leakage detection device that detects the presence or absence of water leakage from piping buried in the ground using electromagnetic waves, and in particular for a water leakage detection device suitable for detecting water leakage using the Doppler effect of a water leakage portion. Regarding antennas.
[0002]
[Prior art]
Conventionally, when water leakage from a water pipe buried in the ground is detected, a microphone is pressed against the ground surface and the sound of water leaking from the water pipe is expanded and heard. However, this method of listening to the sound of water leaking with a microphone requires high skill to judge the presence or absence of water leakage, and the noise and vibration of vehicles traveling on the road are obstructions. There wasn't. Therefore, the applicant of the present application radiates electromagnetic waves having a single frequency into the ground, receives the reflected waves, detects the Doppler frequency due to the flow of the leaked portion from the received reflected waves, and leaks water from underground water pipes. An apparatus for detecting the presence or absence of the above has been developed (Japanese Patent Laid-Open No. 9-5200). FIG. 5 is a block diagram of a water leakage detection device using electromagnetic waves.
[0003]
In FIG. 5, the water leakage detection device 10 includes a transmission antenna 12 that radiates a transmission signal that is an electromagnetic wave in the ground, and a reception antenna 14 that receives a reflected wave of the transmission signal radiated from the transmission antenna 12. The transmission antenna 12 is connected to a signal generator 16 including an oscillator that generates a high-frequency transmission signal, and radiates the transmission signal output from the signal generator 16 into the ground.
[0004]
On the other hand, a high frequency amplifier (RF amplifier) 18 that amplifies the reflected signal received by the receiving antenna 14 is connected to the receiving antenna 14, and the output signal of the RF amplifier 18 is input to the output side of the RF amplifier 18 as an input signal. A demodulator 20 is connected. Further, the reference signal output from the reference signal generator 24 is input to the demodulator 20 via the phase shifter 22. The reference signal generator 24 is connected to the signal generator 16, receives a part of the transmission signal output from the signal generator 16, and outputs a signal having the same frequency as the transmission signal as a reference signal.
[0005]
The demodulator 20 mixes the reflected wave (received signal) received by the receiving antenna 14 and the reference signal input via the phase shifter 22, removes the component of the transmitted signal from the received signal, and causes a phase shift with respect to the transmitted signal. The corresponding signal is output to the low-pass filter 26 and the amplifier 28. The low-pass filter 26 transmits a signal component (a constant phase shift component with respect to the transmission signal, that is, a direct current component) from a fixed object such as a buried pipe or a hollow in the ground, and outputs the signal component to the oscilloscope 30 for display. The amplifier 28 amplifies and outputs the output signal of the demodulator 20. Then, an operator (not shown) adjusts the output of the phase shifter 22 via the knob of the phase shifter 22, and the signal component reflected from a fixed one such as a buried pipe or a cavity among the output signals of the demodulator 20. To be zero. Thereby, the demodulator 20 outputs only a signal based on the Doppler frequency due to the flow of the water leakage part, and this signal is amplified by the amplifier 28.
[0006]
In this way, by detecting the Doppler frequency due to the Doppler effect from the water leakage part using electromagnetic waves, whether or not there is water leakage from the buried water pipe is affected by the level of skill of the operator, the vehicle passing through the road, etc. It can detect without receiving.
[0007]
[Problems to be solved by the invention]
However, in the above-described conventional leak detection apparatus using electromagnetic waves, since the transmitting antenna 12 and the receiving antenna 14 are used for a general underground exploration radar, sufficient detection accuracy can be obtained. could not. That is, the antenna of the conventional water leak detection apparatus is as shown in FIG.
[0008]
This antenna 32 is an antenna for underground exploration radar, and the antenna element 34 is a so-called bow tie antenna having a bow tie shape, and a metal antenna box 36 is provided so as to cover one side of the antenna element 34. . The width a, length b, and height c of the antenna box 36 are generally set based on the center frequency of the sweep frequency. An electromagnetic wave absorbing material 38 made of ferrite, carbon urethane, or the like is provided inside the antenna box 36 so as to flatten the amplitude characteristics with respect to the frequency and prevent multiple reflections in the antenna box 36. . For this reason, the antenna 32 for exploring underground objects has a wide antenna gain (frequency characteristic) with respect to frequency as shown in FIG.
[0009]
This is because in the case of underground exploration radar, the frequency is swept up to several tens of MHz to 1 GHz, and from fixed foreign objects (natural things such as artificial things such as pipes, cavities, and changes in the formation). This is because the phase change of the reflected signal is artificially caused, and the phase change is analyzed to detect the foreign matter in the ground and determine the distance from the ground surface to the foreign matter. Therefore, as shown in FIG. 7, the conventional antenna 32 has excellent broadband characteristics and can transmit and receive electromagnetic waves in a wide frequency band at a relatively constant level. This is not suitable for an antenna of a water leakage detection device that detects a Doppler frequency by radiating an electromagnetic wave of a specific single frequency into the ground, and hinders improvement in detection accuracy.
[0010]
That is, when the antenna 32 is used as the transmitting antenna 12 to radiate an electromagnetic wave having a specific frequency, an electromagnetic wave having a sufficient strength cannot be radiated. Therefore, various noises other than the specific frequency are received, and it is not easy to extract a weak reflected signal from the water leakage part.
The present invention has been made in order to eliminate the drawbacks of the prior art, and it is therefore an object of the present invention to easily detect the Doppler frequency and improve the accuracy of water leakage detection.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the antenna for a water leakage detection device according to the present invention radiates electromagnetic waves into the ground, receives the reflected waves, detects the Doppler frequency, and detects the presence or absence of water leakage from underground pipes. A planar dipole antenna element having a width and a length formed to ½ the wavelength of the electromagnetic wave radiated into the ground, and a resonant cavity covering one side of the antenna element It has the structure which has the housing | casing which forms. It is desirable to provide a dielectric resonator in the transmission path of the planar dipole antenna element.
[0012]
[Action]
The present invention configured as described above is a so-called half-wave antenna in which the dimension of the length and width of the planar dipole antenna element is formed to be half of the wavelength (λ) of the electromagnetic wave radiated into the ground. Since it is a cavity resonance type, a large resonance characteristic can be obtained, a gain for a frequency f corresponding to the wavelength λ of the antenna can be increased, a strong electromagnetic wave of a specific frequency can be radiated, and reflection with less noise Waves can be received, Doppler frequency can be easily detected, and the accuracy of water leakage detection from water pipes buried in the ground can be improved.
[0013]
In addition, if a dielectric resonator made of ceramic or the like is provided in the transmission path connected to the antenna element, the Q value representing the sharpness of resonance can be increased, and the resonance characteristics at a desired frequency can be improved to improve the transmission signal. The band can be narrowed, the influence of incoming noise can be further reduced, and the transmission / reception gain can be improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of an antenna for a water leakage detection device according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an explanatory diagram of an antenna for a water leakage detection device according to an embodiment of the present invention, where (1) is a perspective view of the antenna and (2) is a plan view of the antenna element. In FIG. 1, the antenna 40 has an antenna box 42 that is a casing made of metal, and an antenna element 44 is provided on the lower surface of the antenna box 42. The antenna 40 is a so-called bow tie antenna, and the antenna element 44 is a planar dipole in which the tops of one pair of triangular element pieces 44a and 44b are opposed to each other as shown in FIG. It is an antenna element. In addition, the antenna element 44 has a length d in the vertical direction in FIG. 1B and a length e in the element pieces 44a and 44b in the half length of the wavelength λ of the electromagnetic wave radiated into the ground. That is, λ / 2, which constitutes a so-called half-wave dipole antenna.
[0015]
On the other hand, the antenna box 42 has a size (λ / 2 + α) obtained by adding a fixing margin α for fixing the antenna element 44 to λ / 2 whose two sides l and m are half the wavelength λ. The height h is λ / 4, λ / 2, or λ which is an integral multiple of λ / 4, and is a so-called cavity resonance type having a basic dimension of λ / 2, and a resonance cavity is formed inside. Yes.
[0016]
The antenna 40 configured in this manner resonates at a predetermined frequency f ₀ = c / λ ₀ (c is the speed of light), and the frequency characteristic, that is, the antenna gain with respect to the frequency, as shown in FIG. A Gaussian curve centered at ₀ . Therefore, by emitting from the transmission antenna including a transmission signal of the resonance frequency f ₀ from the antenna 40, with the possible radiation in the ground strong electromagnetic waves when a large antenna gain can be obtained, resonance receiving antenna consisting of antenna 40 frequency f ₀ Because the reflected signal is selectively received, the reflected signal with less noise can be received, the Doppler frequency due to water leakage from the buried water pipe can be reliably detected, and the accuracy of water leakage detection is improved. it can. Further, the antenna 40 according to the embodiment does not need to have a flat amplitude characteristic, and it is not necessary to provide a radio wave absorber inside the antenna box 42, so that it can be made inexpensive.
[0017]
FIG. 3 is an explanatory diagram of a main part of another embodiment. In FIG. 3, a dielectric resonator 48 made of ceramic or the like is provided on a coaxial cable 46 serving as a transmission line inside an antenna box 42 not shown in the figure. A balun 50, which is a transformer for impedance conversion, is connected to the tip of the coaxial cable 46, and the tip of the balun 50 is connected to the element pieces 44a and 44b of the antenna element 44.
[0018]
In the present embodiment configured as described above, by providing the dielectric resonator 48 in the coaxial cable 46, the Q value indicating the sharpness of resonance can be increased as shown in FIG. it can. Therefore, it is possible to resonate at a desired frequency, narrow the transmission signal, reduce the influence of noise such as TV radio waves and mobile phone radio waves reaching the receiving antenna, and further improve the transmission and reception gain. The detection accuracy of water leakage can be further increased.
[0019]
【The invention's effect】
As described above, according to the present invention, a planar dipole antenna element is a so-called half-wave antenna in which the length and width dimensions are formed to ½ of the wavelength λ of electromagnetic waves radiated into the ground. Since the body is of a cavity resonance type, a large resonance characteristic can be obtained, the gain for the frequency corresponding to the wavelength λ of the antenna can be increased, a strong electromagnetic wave with a specific frequency can be radiated, and there is little noise The reflected wave can be received, the Doppler frequency can be easily detected, and the accuracy of detecting water leakage from a water pipe buried in the ground can be improved.
[0020]
In addition, if a dielectric resonator made of ceramic or the like is provided in the transmission path connected to the antenna element, the Q value representing the sharpness of resonance can be increased, and the resonance characteristics at a desired frequency can be improved to improve the transmission signal. The band can be narrowed, the influence of incoming noise can be reduced, and the transmission / reception gain can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an antenna for a water leakage detection device according to an embodiment of the present invention, wherein (1) is a perspective view of the antenna, and (2) is a plan view of the antenna element.
FIG. 2 is a frequency characteristic diagram of an antenna gain according to the embodiment;
FIG. 3 is an explanatory diagram of a main part of another embodiment.
FIG. 4 is a frequency characteristic diagram of the gain of an antenna according to another embodiment.
FIG. 5 is a block diagram of a water leakage detection device using electromagnetic waves.
FIG. 6 is a perspective view of an antenna used in a conventional water leak detection device.
FIG. 7 is a frequency characteristic diagram of the gain of a conventional antenna for a water leakage detection device.
[Explanation of symbols]
40 Antenna 42 Case (antenna box)
44 Planar dipole antenna element (antenna element)
46 Transmission path (coaxial cable)
48 Dielectric Resonator

Claims (2)

An antenna of a leak detection device that radiates electromagnetic waves into the ground, receives the reflected waves, detects the Doppler frequency, and detects the presence or absence of water leaks from underground pipes. An antenna for a water leakage detection device, comprising: a planar dipole antenna element formed at a half of the wavelength of the electromagnetic wave to be radiated; and a casing that covers one side surface of the antenna element to form a resonance cavity. 2. The antenna for a water leakage detection device according to claim 1, wherein a dielectric resonator is provided in a transmission path to which the planar dipole antenna element is connected.

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