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Buried object detection sensorBuried object detection sensor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080042892, Buried object detection sensor. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a buried object detection sensor, and in particular to a buried object detection sensor performing a detection of a buried object from the ground by a combined sensor. [0003] 2. Description of the Related Art [0004] A detection device using a metal detector (MD) or a ground penetrating radar (GPR) is used to detect a buried object from the ground. The detection device using the MD has a coil which transmits/receives a magnetism, and is suitable for a detection of an object buried in a relatively shallow depth. Meanwhile, the detection device using the GPR has an antenna which transmits/receives an electromagnetic wave, and is suitable for a detection of an object buried in a deep portion compared to the case when the MD is used. A combined type detection device using both the MD and the GPR is therefore proposed in which both characteristics of the MD and the GPR can be obtained. [0005] As this combined type detection device, an invention according to Japanese Patent publication No. 2001-242263 can be cited. The combined type detection device, disclosed in this Japanese Patent publication No. 2001-242263, has a constitution in which a ring-shaped detection coil to be the MD, and an antenna to be the GPR at a center side of the detection coil, are included. The detection coil generates a magnetic field when a current is supplied, to make a metal object buried underground generate an induced electromotive force. The detection coil senses the magnetic field generated by the induced electromotive force, to thereby probe a presence/absence of a buried object. Besides, the GPR generates an electromagnetic wave from the antenna when the current is supplied. The buried object reflects this electromagnetic wave, and therefore, the antenna senses a reflected electromagnetic wave to probe the presence/absence of the buried object. As stated above, the detection of the buried object is performed by using both sensors in a combined state. [0006] In the combined type detection sensor using the MD and the GPR, when it has a constitution in which a transmission coil of the MD is provided at a center of the GPR and a receiving coil is provided at a periphery of the GPR, an eddy current is generated in the GPR caused by the magnetic field generated at the transmission coil when the current is supplied to the transmission coil. The eddy current forms a loop at all over the GPR, and therefore, a magnetic flux is generated from the GPR, then the magnetic flux works in a direction to deteriorate a performance of the MD. Namely, the magnetic flux generated at the GPR is received by the receiving coil of the MD, and therefore, the receiving coil becomes to have an offset value. The receiving coil has a constant dynamic range, and therefore, an SN ratio may fall if a rate of change of the magnetic field by the buried object is detected under a state having the offset value. A receiving level of the MD in a case of the combined type detection device using the MD and the GPR becomes to be a tenth part or less when the receiving level of the detection device using only the MD is assumed to be one. SUMMARY OF THE INVENTION [0007] An object of the present invention is to provide a combined type buried object detection sensor improving a detectivity by using both a MD and a GPR. [0008] To attain the above object, in the buried object detection sensor according to the present invention, plural antenna elements composing a GPR are arranged on a circumference, and a MD is arranged so that a center portion of the GPR is to be a axis thereof, wherein the GPR has slits separating the respective antenna elements, and the slits between adjacent antenna elements are connected by a metal leaf. In this case, the GPR and the MD are arranged on the same plane. Here, the GPR and the MD are arranged completely on the same plane, or they may be arranged nearly on the same plane if so regarded as on the same when a detection result is processed. Besides, the above MD has a feature of having a coil arranged at a center portion of the GPR and another coil arranged at a periphery of the GPR. [0009] According to the above-stated constitution, the GPR can be divided into plural antenna elements by the slits, and therefore, a small loop of an eddy current is generated at the respective antenna element and a large loop of the eddy current may not be generated at all over the GPR, even when the eddy current is generated at the GPR by a magnetic field generated by the MD. Consequently, it becomes possible to improve a detection performance of the MD because a magnetic flux generated from the small loop of the eddy current is small, and an amount of the magnetic flux generated from the MD to be cancelled by this magnetic flux becomes small. [0010] Besides, the metal leaf does not conduct the eddy current generated at the antenna elements, but it enables to connect the adjacent antenna elements electrically. Consequently, it is possible to make the respective antenna elements to be the same electric potential (ground), and to maintain a detection performance of the GPR even if the slits are provided. [0011] Further, a buried object detection sensor having a constitution in which a GPR and a transmission/receiving coils of a MD are concentrically arranged, can obtain the above-stated effect if slits dividing antenna elements of the GPR individually, and a metal leaf connecting adjacent antenna elements, are provided. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 is a plan view of a sensor portion in a buried object detection sensor according to an embodiment; [0013] FIG. 2 is an exploded perspective view of the sensor portion in the buried object detection sensor according to the embodiment; and [0014] FIG. 3 is an explanatory view of a three element radar antenna system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) [0015] Hereinafter, preferred embodiments of a buried object detection sensor according to the present invention is described. FIG. 1 is a plan view of a sensor portion in the buried object detection sensor. Besides, FIG. 2 is an exploded perspective view of the sensor portion in the buried object detection sensor. A buried object detection sensor 10 is composed of a MD 12 and a GPR 14. [0016] The MD 12 is composed of two coils of an inner coil 16 and an outer coil 18, and these are a transmission coil and a receiving coil. The two coils 16, 18 are formed by respectively winding lead wires (not shown) in circumferential directions, disposed in concentric circles, and formed on the same plane. Incidentally, they do not have to be completely on the same plane, but they may be at positions where they are regarded as the same plane on the process when a detection is performed by using the MD 12. The outer coil 18 is a ring shape, and the inner coil 16 is arranged at a center portion of the ring shape. In such MD 12, the outer coil 18 can be set as the receiving coil and the inner coil 16 is to be the transmission coil, or the outer coil 18 can be set as the transmission coil and the inner coil 16 is to be the receiving coil. [0017] Besides, the GPR 14 composed of plural antenna elements is arranged at a circular ring area between the outer coil 18 and the inner coil 16. The GPR 14 is composed of plain antenna elements, and formed on the same plane with the inner coil 16 and the outer coil 18 of the MD 12. Incidentally, they don't have to be completely on the same plane, but they may be at the positions regarded as the same when the detection is performed by using the MD 12. Namely the position of the GPR 14 may be deviated upward a height where reflected electromagnetic waves from the coils 16, 18 do not affect on the detection, because there is a problem that a detectivity is deteriorated by the reflected electromagnetic waves from the coils 16, 18 of the MD 12. On the contrary, the MD 12 is not able to be set at a height far away from the ground, because a detection depth thereof is originally limited, when the MD 12 is set to be higher than the GPR 14. A deviation in a height direction with the GPR 14 is allowed up to the height in which the MD 12 can secure a sensing of a shallow depth portion unable to be detected by the GPR 14 when the ground is scanned. Substantially, it is not possible to position the MD 12 higher than the GPR 14, and therefore, it is preferable to position them on the same plane. The GPR 14 is a three element radar sensor provided at a periphery of the inner coil 16, and three slits 20 having rectangular wave shapes are formed from the center portion of the GPR 14 toward a side edge direction. The GPR 14 is divided into three GPR antenna elements 22 (antenna element) by the slits 20. The GPR antenna elements 22 are disposed while deviated on a circumference in which a certain point at outside of the GPR antenna elements 22 are set as a reference, and in the present embodiment, they are disposed in a state deviated by 120 degrees in a rotational direction while setting the certain point as the reference. [0018] The GPR antenna element 22 is composed of plural layers, and an antenna base plate 24 is disposed at a bottom layer. Radar antenna elements 26 constituted by placing triangular metal plates at centers thereof as elements and facing vertexes thereof, are provided on the antenna base plate 24. Power feeding terminals 28 are provided at the radar antenna elements 26, and a radio energy is fed from a power feeding module (not shown) provided at the GPR 14 to the radar antenna elements 26 via the power feeding terminals 28. At an upper portion of the antenna base plate 24, an electromagnetic wave absorption material 32 is covered via a spacer 30. The electromagnetic wave absorption material 32 is to absorb electromagnetic wave radiated upward from the radar antenna elements 26. An upper cover 34 is covered at an upper portion of the electromagnetic wave absorption material 32. [0019] Besides, the slits 20 formed between the GPR antenna elements 22 are covered by a metal leaf 36. A cross-sectional area of the metal leaf 36 is adjusted to be thin to have a high resistance value in which the eddy current does not conduct between the antenna elements (GPR antenna elements 22) separated by the slits 20. It is made to be a thin film to have the high resistance, but a conductivity is necessary to make ground potentials of the separated respective antenna elements (GPR antenna elements 22) equal. Namely, the metal leaf 36 has a thickness in which the eddy current generated at the respective GPR antenna elements 22 by the magnetic flux generated at the MD 12 is not conducted, and the thickness in which the grounds of the respective GPR antenna elements 22 to each other are possible. Incidentally, the MD 12 uses a low frequency band of, for example, approximately 1 kHz, the GPR 14 uses a high frequency band of, for example, approximately 2 GHz, and therefore, the thickness of the metal leaf 36 is to be set properly according to the respective frequency bands used by the respective sensor and the material of the metal leaf 36. Herewith, it becomes possible to make a conductive ground of the respective GPR antenna elements 22 to each other even though the eddy current is not conducted through the metal leaf 36. [0020] FIG. 3 is an explanatory view of a three element radar antenna system. A system 40 includes a radar controller 42 performing an overall control by generating a polarized wave switching pulse, a sending circuit 44 transmitting an electromagnetic wave, a receiving circuit 46 demodulating a reflected wave from the underground, a polarized wave switching circuit 48 connecting one of antenna elements 26a, 26b, and 26c to the sending circuit 44 and another antenna to the receiving circuit 46, and a signal processor 50 performing a calculation asking scattering matrix elements based on signals supplied from both the radar controller 42 and the receiving circuit 46. Continue reading about Buried object detection sensor... 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