WO2005085902A1

WO2005085902A1 - Apparatus and method for detecting a buried objetc using solitary wave.

Info

Publication number: WO2005085902A1
Application number: PCT/KR2005/000661
Authority: WO
Inventors: Do-Young Kim
Original assignee: Do-Young Kim
Priority date: 2004-03-10
Filing date: 2005-03-09
Publication date: 2005-09-15
Also published as: KR100671266B1; KR20050090870A; JP2007528498A

Abstract

The present invention discloses an apparatus for detecting a buried object using solitary waves comprising: an acoustic source for emitting a solitary wave; at least one first acoustic sensor for generating a first reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; at least one second acoustic sensor for generating a second reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the first and the second reflected wave signals from the first acoustic sensor and the second acoustic sensor, respectively, and determining the existence of the buried object in the medium based on the first and the second reflected wave signals.

Description

APPARATUS AND METHOD FOR DETECTING A BURIED OBJECT USING SOLITARY WAVE

Technical Field The present invention relates to an apparatus and a method for detecting a buried object. More specifically, the present invention relates to an apparatus and a method for detecting a buried object using solitary waves.

Background Art Generally, a natural and/or an artificial buried object(s) may be buried in a medium in which the natural and/or the artificial buried object(s) may have different physical and/or chemical properties from those of the medium. There are many occasions necessary for determining existence of a buried object and/or the type of the buried object itself, such as a typical example of a land mine buried under ground. It is simple to bury mines. However, it is extremely difficult to find and remove the mines which are buried over a wide area because it is not easy to determine exact points where the mines are buried, and more importantly the points of the buried mines may be changed due to various environmental factors as well. Some mine detection methods in prior art may determine the buried points of mines by using animals having a keen sense of smell, or by a prodding and excavation method. However, it is very inefficient in terms of time to find mines buried over a very wide area through the prior art mine detection methods. In addition, metal detectors have been used as a detection method for detecting metal mines in prior art. However, because the prior art metal detectors respond to all the metals buried in a medium, it is very hard to detect only the metal mines and more importantly it is impossible to detect plastic mines which are currently widely used. In another prior art, a method for detecting a nitrogen component which is buried under ground has been proposed and used, based on the fact that a nitrogen component is included in gunpowder contained in a mine.

More specifically, this prior art method detects gamma-rays emitted from a nitrogen component included in gunpowder and determines whether a mine is buried or not. However, this prior art method has a problem in terms of a practical use because it requires a huge sized oscillator in order to excite nitrogen included in gunpowder and a further problem arises in particular in terms of portability due to the use of a huge sized oscillator. Other prior art detection methods for detecting a mine and/or a buried object may be classified depending on a source wave such as X-ray, ultrasonic wave, microwave, and electromagnetic wave, etc., which is used for detecting a buried object. Recently, a general developing trend in detection methods for detecting a mine and/or a buried object has been evolved toward a direction of developing a new source wave capable of determining a mine and/or a buried object more exactly and enhancing the exactness of determination in case of using the new source wave. However, the prior art detection methods for detecting a mine and/or a buried object described above have some limits in detecting metal mines exactly and are also very difficult to exactly detect a mine and/or a buried object made of a plastic material which is currently widely used.

Disclosure of Invention An object of the present invention is to solve the prior art problems by providing a novel apparatus and a method for detecting a buried object which improves reliability and exactness in detecting a mine and/or a buried object by using solitary waves as a new source wave and processing effectively a reflected wave of the solitary waves by means of highly sensitive sensors. To achieve the above object, an apparatus for detecting a buried object using solitary waves according to a first aspect of the present invention comprises an acoustic source for emitting a solitary wave; at least one first acoustic sensor for generating a first reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; at least one second acoustic sensor for generating a second reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the first and the second reflected wave signals from the first acoustic sensor and the second acoustic sensor, respectively, and determining the existence of the buried object in the medium based on the first and the second reflected wave signals. According to a second aspect of the present invention, an apparatus for detecting a buried object using solitary waves comprises an acoustic source for emitting a solitary wave; at least one acoustic sensor for generating a reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the reflected wave signal from the acoustic sensor, and determining the existence of the buried object in the medium based on the reflected wave signal. According to a third aspect of the present invention, a detector for detecting a buried object having an apparatus for detecting a buried object using solitary waves, wherein the apparatus for detecting a buried object comprises an acoustic source for emitting a solitary wave; at least one first acoustic sensor for generating a first reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; at least one second acoustic sensor for generating a second reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the first and the second reflected wave signals from the first acoustic sensor and the second acoustic sensor, respectively, and determining the existence of the buried object in the medium based on the first and the second reflected wave signals; wherein the detector for detecting a buried object comprises a lower body for mounting the acoustic source and the first and the second acoustic sensors; a connection bar extending from the lower body; a fixing device mounted to the connection bar for fixing a part of a user's body; and a display device installed to a part of the connection bar. According to a fourth aspect of the present invention, a method for detecting a buried object using solitary waves comprises the steps of emitting a solitary wave toward a medium; generating a first reflected wave signal corresponding to a reflected wave of the solitary wave; generating a second reflected wave signal corresponding to a reflected wave of the solitary wave; calculating a first characteristic frequency for the first reflected wave signal; calculating a second characteristic frequency for the second reflected wave signal; determining the existence of the first characteristic frequency in a first predetermined frequency range; determining the existence of the second characteristic frequency in a second predetermined frequency range; and determining that a known buried object corresponding to both the first and the second predetermined frequency ranges exists in the medium, when the first and the second characteristic frequencies respectively exist in the first and the second predetermined frequency ranges.

Advantageous Effect In accordance with the apparatus and the method of the present invention, since a solitary wave as a source wave is used for detecting a buried object, reliability and exactness for detecting a buried object are enhanced and the apparatus for detecting a buried object can be made in a compact size. Brief Description of the Drawings Fig. 1 is a block diagram of an apparatus for detecting a buried object in accordance with an embodiment of the present invention. Fig. 2 shows a side view and a plan view of a structure for a GMI sensor which is applied to an apparatus for detecting a buried object in accordance with an embodiment of the present invention. Fig. 3 is a graph showing frequency characteristics in a reflected wave of solitary waves received by a GMI sensor in accordance with the present invention. Fig. 4 shows a side view and a plan view of a structure for an SCM sensor which is applied to an apparatus for detecting a buried object in accordance with one embodiment of the present invention. Fig. 5 is a graph showing frequency characteristics in a reflected wave in accordance with the present invention. Fig. 6 is a perspective view of a detector for detecting a buried object in accordance with an embodiment of the present invention. Fig. 7 is a view of a lower body of a detector for detecting a buried object seen from "A" direction as illustrated in Fig. 6. Fig. 8 is a flow chart showing a method for detecting a buried object using solitary waves in accordance with an embodiment of the present invention.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments in accordance with the present invention are described in more detail with reference to the appended drawings. Fig. 1 illustrates a block diagram of an apparatus 10 for detecting a buried object in accordance with an embodiment of the present invention. As illustrated in Fig. 1 , the apparatus 10 for detecting a buried object in accordance with an embodiment of the present invention comprises an acoustic source 130 for emitting a solitary wave; at least one first acoustic sensor 160 for generating a first reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source 130; at least one second acoustic sensor 165 for generating a second reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source 130; and a control unit 100 for driving the acoustic source 130 to emit the solitary wave toward a medium 190 expected to have the buried object, receiving the first and the second reflected wave signals from the first acoustic sensor 160 and the second acoustic sensor 165, respectively, and determining the existence of the buried object 195 in the medium 190 based on the first and the second reflected wave signals. A structure of the control unit 100 included in the apparatus 10 for detecting a buried object in accordance with an embodiment of the present invention is described in detail below. As illustrated in Fig. 1 , the control unit 100 includes an electronic control unit 110 (hereinafter referred to "ECU") which controls overall functions of the control unit 100. ECU 110 may be embodied by one or more microprocessors operated by predetermined programs, and the predetermined programs may include a series of instructions for performing respective steps of a method for detecting a buried object in accordance with an embodiment of the present invention as illustrated in Fig. 8. The control unit 100 has a memory 115 which stores various data used for performing the functions of ECU 110. For example, the memory 115 pre-stores a first characteristic frequency to be searched by a first acoustic sensor 160 and a second characteristic frequency to be searched by a second acoustic sensor 165 for respective buried objects to be detected, and the error scopes for the first characteristic frequency and the second characteristic frequency. That is, when it is required to find plastic mines, the memory 115 stores, as its first frequency range, a peak frequency range measured by the first acoustic sensor 160 embodied by a Giant Magnetic Impedance sensor (hereinafter referred to "GMI sensor") for reflected waves of solitary waves which are reflected from the plastic mines, and also stores, as its second frequency range, a peak frequency range measured by the second acoustic sensor 165 embodied by a Micro Electro-Mechanical Systems sensor (hereinafter referred to "MEMS sensor") having a cantilever for the reflected waves of the solitary waves which are reflected from the plastic mines. More specifically, the MEMS sensor described above may be embodied by Silicon Cantilever Magnetometer sensor (hereinafter referred to "SCM sensor"). Thus, ECU 110 is possible to determine the existence of burial of plastic mines by comparing real peak frequencies measured by the first and the second acoustic sensors 160,165, respectively, for unknown buried objects with pre-stored peak frequency ranges for known buried objects as described above. The control unit 100 also includes a function generator 120 for acoustic source which receives a signal for driving the acoustic source 130 from the ECU 110 and generates a signal for driving the acoustic source 130; and an amplifier 125 for amplifying the signal from the function generator 120 for acoustic source and transferring it to the acoustic source 130. The acoustic source 130 applied to the present invention may be embodied by, for example, an electrically drivable speaker and is controlled to generate solitary waves by the control unit 100. Typically, solitary waves have a propagation characteristic without any interference and dispersion between waves during superposition, unlike a general characteristic of a wave. Thus, solitary waves maintain its original wavelength even when passing through a medium which has a buried object or when reflected by a buried object. In addition, solitary waves cannot pass through a medium having a natural frequency identical to a characteristic frequency of the solitary waves, and rather are reflected from the medium (frequency characteristic). Accordingly, if the acoustic source 130 emits solitary waves toward a certain medium 190 expected to have an unknown buried object 195 to be detected by using the control unit 100, the emitted solitary waves are reflected from the medium 190 and the unknown buried object 195. The control unit 100 detects the reflected waves and searches frequency components thereof and therefore it is possible to determine the existence of the unknown buried object and the type thereof. In the meanwhile, the control unit 100 includes a function generator 140 for sensor which drives the first and the second acoustic sensors 160,165. The first and the second acoustic sensors 160,165 are respectively embodied by a GMI sensor (see Fig. 2) and SCM sensor (see Fig. 4), and operation performances thereof depend on the characteristics of an external electric power. Typically, a frequency range of 100kHz~10MHz may be used for driving a GMI sensor and especially a GMI sensor operates most sensitively to a change of magnetic field near about 1 MHz. Thus, the function generator 140 for sensor according to the present invention generates a frequency of about 1 MHz and a voltage signal of about 1V (hereinafter referred to "driving signal") and feeds them to the first and the second acoustic sensors 160,165. However, although the driving signal generated by the function generator 140 for sensor is described to be about 1 MHz, the scope of the present invention is not limited to this range of frequency. In addition, it is obvious by a skilled person in the art that optimal operations of the first and the second acoustic sensors 160,165 may be variably set up depending on the different specifications thereof. As described above, although the function generator 140 for sensor is to be one, the scope of the present invention shall not be limited thereto. As one example, the function generator 140 for sensor may be provided separately for driving the first acoustic sensor 160 embodied by a GMI sensor and for driving the second acoustic sensor 165 embodied by a SCM sensor. Also, since the output value from a SCM sensor to be used for the second acoustic sensor 165 is related to capacitance thereof, the control unit 100 is provided with a capacitance bridge circuit 167 in order to obtain a reduced value from the output value. From the above description, the function generator 140 for sensor is described to feed a driving signal to the second acoustic sensor 165. However, if the capacitance bridge circuit 167 is used, then the second acoustic sensor 165 embodied by an SCM sensor may operate regardless of the driving signal fed from the function generator

140 for sensor, due to the characteristics of the SCM sensor. Therefore, it is optional in the present invention whether to feed a driving signal to the second acoustic sensor 165 by the function generator 140 for sensor. The reason why the present invention uses the first and the second acoustic sensors 160,165 is to enhance exactness in detection performance of the apparatus 100 for detecting a buried object in accordance with the present invention. That is, the first acoustic sensor 160 embodied by a GMI sensor and the second acoustic sensor 165 embodied by an SCM sensor respectively have different peak values in a natural frequency for a same buried object (see Figs. 3 and 5). Thus, it is necessary to firstly analyze peak values of a natural frequency for an unknown buried object by using the first and the second acoustic sensors 160,165, and then compare the analyzed peak values of the natural frequency for the unknown buried object with the pre-stored peak values of the natural frequency for a known buried object. If the comparison result turns out that the two peak values for the natural frequency for the unknown buried object are the same as the pre-stored peak values of the natural frequency for the known buried object, it is possible to determine the type of the unknown buried object exactly. However, it should be fully understood by a skilled person in the art that any apparatus 10 for detecting a buried object using either one only from the first and the second acoustic sensors 160, 165 should fall upon the scope of the present invention. Meanwhile, the control unit 100 further comprises a first lock-in amplifier and a second lock-in amplifier. The first lock-in amplifier 170 receives a signal generated from the first and the second acoustic sensors 160, 165 (hereinafter referred to "generated signal") and also receives a driving signal outputted from the function generator 140 for sensor. Then, the first lock-in amplifier 170 compares the driving signal with the generated signal and outputs a deviation between the generated signal and the driving signal to the second lock-in amplifier 150. A detection signal indicating the deviation between the generated signal and the driving signal by the first lock-in amplifier 170 directly shows an intensity of a received reflected wave of a solitary wave emitted from the acoustic source 130. The detection signal of the first lock-in amplifier 170 is also transmitted to a display device 105. Further, the signal outputted from the amplifier 125 is transmitted to the acoustic source 130 and is also transmitted to the second lock-in amplifier 150 and the display device 105 simultaneously. Thus, the second lock-in amplifier 150 can determine a specific frequency of the solitary wave emitted from the acoustic source 130 by using a signal received from the amplifier 125 (hereinafter referred to "reference signal"). The second lock-in amplifier 150 searches whether the detection signal received from the first lock-in amplifier 170 contains the specific frequency component of a reflected wave of the solitary wave from the reference signal. Then the second lock-in amplifier 150 calculates the intensity of the reflected wave of the solitary wave (seen Fig. 5), and transmits the calculated intensity to the ECU 110. From a method described above, it is possible to know an intensity of the received reflected wave of the solitary wave for a specific frequency. Thus, by emitting solitary waves having various frequencies through the acoustic source 130 and calculating the intensities of the received reflected waves of the respective solitary waves, it is possible to obtain a graph of frequency characteristics (Figs. 3 and 5) where the medium 190 and the buried object 195 respectively reflect corresponding solitary waves. Therefore, based on the peak frequencies obtained from the graph of frequency characteristics, it is ultimately possible to determine the existence of a buried object and the type thereof. Fig. 2 shows a side view and a plan view of a structure for a GMI sensor 160 which is applied to an apparatus 10 for detecting a buried object in accordance with an embodiment of the present invention. As illustrated in Fig. 2, the GMI sensor 160 includes a membrane 210 which responds to external vibrations. When the membrane 210 receives an external vibration, a change of high-frequency impedance occurs in the membrane 210 and is detected by electrodes 220 connected to the membrane 210 by lead lines. In this circumstance, since the change of high-frequency impedance depends on a magnetic field around the GMI sensor 160, the GMI sensor 160 is typically used for measuring a fine magnetic field. The GMI sensor 160 described above causes a vibration of the membrane 210 when a solitary wave is incident onto the membrane 210 of the GMI sensor 160, and thus can be used for measuring an incident solitary wave. Thus, a GMI sensor typically used for measuring a fine magnetic field may be used as the first acoustic sensor 160 of the apparatus 10 for detecting a buried object in order to measure a solitary wave. More specifically, the membrane 210 of the GMI sensor 160 used in an embodiment of the present invention may include a material showing an impedance valve phenomenon formed by a method disclosed in Korean laid- open patent publication No. 2001-86630 (Patent No. 383564 entitled "a method for forming an impedance valve type material and a magnetic sensor using the same"). The GMI sensor 160 disclosed in Korean laid-open patent publication No. 2001-86630 is incorporated by reference herein. The detailed description of a specific structure and its function of the GMI sensor 160 is disclosed in Korean laid-open patent publication No. 2001-86630 in detail and thus may be omitted herein. Fig. 3 is a graph showing frequency characteristics in a reflected wave of solitary waves received by a GMI sensor in accordance with the present invention. The graph in Fig. 3 shows a scanned drawing by a GMI sensor at 10Hz unit regarding frequency intervals for a case that steel is buried in a medium and for a case that plastic is buried in the medium, respectively. As illustrated in Fig. 3, the reflected wave of a solitary wave shows a very high peak value at around 725 Hz when plastic is buried in the medium 190, while the reflected wave of a solitary wave shows a very high peak value at around 780 Hz when steel is buried in the medium 190. Accordingly, it is possible to determine the type of an unknown buried object when determining a substance corresponding to the unknown buried object, by checking a frequency characteristic of a reflected wave of a solitary wave reflected from a known buried object in a certain medium through the first acoustic sensor 160, pre-storing a peak frequency calculated for the corresponding buried object into the memory 115, and detecting the peak frequency of a reflected wave of a solitary wave for an unknown buried object in a certain medium through the first acoustic sensor 160 and comparing it with the pre-calculated peak frequency. Fig. 4 shows a side view and a plan view of a structure for an SCM sensor used as the second acoustic sensor 165 of the apparatus 10 for detecting a buried object in accordance with one embodiment of the present invention. As illustrated in Fig. 4, the SCM sensor 165 includes a cantilever 310 which responds to external vibrations. As an example for a SCM sensor having the cantilever 310, there is a MEMS sensor disclosed in US Patent No. 5,925,822 issued to Michael J. Naughton. The MEMS sensor disclosed in US Patent No. 5,925,822 is incorporated by reference herein. The detailed description of a specific structure and its functions of the SCM sensor 165 is disclosed in US Patent No. 5,925,822 in detail and thus may be omitted herein. Fig. 5 is a graph showing frequency characteristics in a reflected wave in accordance with the present invention. More specifically, Fig. 5 shows a frequency characteristic (dot line graph) of a reflected wave of a solitary wave obtained from sand which is filled in a box with a dimension of 1.5mx1.5mx1.5m and a frequency characteristic (solid line graph) of a reflected wave of a solitary wave obtained from a plastic mine made of FRP (Fiberglass-Reinforced Plastic) material which is buried with a depth of 10cm from the sand surface, respectively. In Fig. 5, a high level of the reflected wave shown in a low frequency range below 300Hz is an effect due to a wall of the sand box, which resulted from an experimental condition in a laboratory. Thus, it is easily understood by a skilled person in the art that the level of a reflected wave is expected to be very low in a low frequency range if a search is made to detect a buried object in a wide area. As depicted in Fig. 5, when comparing a case that a plastic mine is buried in a medium with a case that the plastic mine is not buried in the medium, the result shows that the frequency-based characteristics of a reflected wave of a solitary wave for a plastic mine is quite different. These different frequency-based characteristics depend on the types of buried objects in a medium. Accordingly, it is possible to determine the type of an unknown buried object in a certain medium by the following steps of: checking the frequency-based characteristics of reflected waves of a solitary wave for a certain medium and the unknown buried object therein detected through the second acoustic sensor 165; calculating a peak frequency for the unknown buried object which shows a substantial difference from a standard data value for the certain medium; comparing the calculated peak frequency with a peak frequency for a known substance pre-stored in the memory 115 as illustrated in Fig. 1 ; and determining a substance corresponding to the unknown buried object. Here, the standard data value of a medium is initialized by building a database after measuring a reflected wave of a solitary wave under the same medium environment where a buried object does not exist and checking a wave form of the reflected wave. Herein, it should be understood that different peak frequencies of a reflected wave signal of a solitary wave detected by the first acoustic sensor 160 and the second acoustic sensor 165 for a same buried object in a medium may be obtained. This result comes from different characteristics between a GMI sensor and an SCM sensor which are used for the first acoustic sensor 160 and the second acoustic sensor 165, respectively. Thus, when detecting the unknown buried object 195, it is possible to confirm the existence of the unknown buried object and the type thereof by pre-storing the peak frequencies by first acoustic sensor 160 and the peak frequencies by the second acoustic sensor 165 into the memory 115 and then comparing the pre-stored peak frequencies with the measured peak frequencies by the first acoustic sensor 160 and the second acoustic sensor 165 for the unknown buried object. Fig. 6 is a perspective view of a detector 600 for detecting a buried object in accordance with an embodiment of the present invention. As illustrated in Fig. 6, the detector 600 for detecting a buried object in accordance with an embodiment of the present invention comprises a lower body 610 for mounting the first acoustic sensor 160, the second acoustic sensor 165, and the acoustic source 130 shown in Fig. 1 ; a connection bar 620 extending from the lower body 610; a fixing device 630 mounted to the connection bar 620 for fixing a part of a user's body such as arm, etc.; and a display device 105 installed to a part of the connection bar 620. The display device illustrated in Fig. 6 is to display the existence or not of an unknown buried object, in accordance with a determination result by the control unit 100 shown in Fig. 1 on whether the unknown buried object exists in a certain medium or not. For this purpose, the display device 105 may include a lighting lamp. In addition, the display device 105 may include a display panel 640 for visually displaying the measured result obtained from the first acoustic sensor 160 and the second acoustic sensor 165 using, for example, graphics. The display panel 64 may be embodied by a flat panel display device such as, for example, an LCD panel, etc. Fig. 7 is a view of a lower body 610 of a detector 600 for detecting a buried object seen from "A" direction as illustrated in Fig. 6. That is, Fig. 7 shows an arrangement relationship on how the acoustic source 130, the first acoustic sensor 160 and the second acoustic sensor 165 used for the detector 600 are arranged in the lower body 610. More specifically, in the detector 600 of the present invention depicted in Fig. 7, the acoustic source 130 is placed in the center of the lower body 610, while the first acoustic sensor 160 and the second acoustic sensor 165 are placed alternately along the circumference of the lower body 610. Thus, the first acoustic sensor 160 and the second acoustic sensor 165 respectively receive a reflected wave of a solitary wave emitted from the acoustic source 130 with same conditions. Below, a method for detecting a buried object using a solitary wave in accordance with the present invention is described in detail by reference to Figs. 1 and 8. Fig. 8 is a flow chart showing a method for detecting a buried object using solitary waves in accordance with an embodiment of the present invention. As illustrated in Fig. 8, ECU 110 drives the function generator 140 for senor and transmits the driving signal described above to the first acoustic sensor 160 and the second acoustic sensor 165, and the first lock- in amplifier 170 (S810). Therefore, the first acoustic sensor 160 and the second acoustic sensor 165 are in a waiting state for detecting a reflected wave of a solitary wave. At this moment, when a generated signal is transmitted to the first lock-in amplifier 170 from the first acoustic sensor 160 and the second acoustic sensor 165, then the first lock-in amplifier 170 is in a waiting state for comparing the generated signal with the driving signal and transmitting a detection signal equivalent to a deviation therebetween to the second lock-in amplifier 150. In such a waiting state for detecting a reflected wave, ECU 110 sets up a specific frequency and transmits a solitary wave generation signal corresponding to the specific frequency to the function generator 120 for acoustic source (S815). Then, the function generator 120 for acoustic source generates a solitary wave signal corresponding to the specific frequency which is transmitted to the amplifier 125 (S820). The amplifier 125 transmits a reference signal which is an amplified signal of the received solitary wave signal to the acoustic source 130 (S822), and the acoustic source 130 emits a solitary wave signal toward a medium (S825). In the meanwhile, the reference signal of the solitary wave outputted from the amplifier 125 is inputted into the second lock-in amplifier 150 (S827). The solitary wave emitted from the acoustic source 130 is reflected from a buried object 195 in the medium 190 (S830). Then, the reflected wave is detected by the first acoustic sensor 160 and the second acoustic sensor 165. That is, the first acoustic sensor 160 generates a first reflected wave signal corresponding to the reflected wave of the solitary wave (S835) and the second acoustic sensor 165 generates a second reflected wave signal corresponding to the reflected wave of the solitary wave (S837). Then, the generated first and second reflected wave signals are inputted into the first lock-in amplifier 170 (S840). Thereafter, the first and the second reflected wave signals are modulated by the first lock-in amplifier 170 and then transmitted to the second lock-in amplifier 150. That is, the first lock-in amplifier 170 calculates a deviation (i.e., a modulated first reflected wave signal) between the first reflected wave signal and a driving signal from the function generator 140 for sensor (S845) and simultaneously calculates a deviation (i.e., a modulated second reflected wave signal) between the second reflected wave signal and a driving signal from the function generator 140 for sensor (S847). Then, the second lock-in amplifier 150 extracts, from the first and the second reflected wave signals, frequency components (i.e., reflection intensities of the reflected wave relating to the specific frequency described above) corresponding to the reference signal inputted from the amplifier 125 and transmits the frequency components to ECU 110 (S850). Therefore, ECU 110 receives the frequency components by the first acoustic sensor 160 and the frequency components by the second acoustic sensor 165 of the reflected waves from the medium 190 and the buried object 195 for the specific frequency used for driving the function generator 120 for acoustic source (S855). ECU 110 performs repeatedly the steps (S815-S855) for detecting the reflection intensities of reflected waves relating to a variety of specific frequency by varying the specific frequency. As an example, it is possible to detect the reflection intensities of reflected waves for various specific frequencies with a unit interval of 10Hz over a frequency range of 10Hz~10KHz. However, it is easily understood by a skilled person in the art that the unit interval between specific frequencies may be adjusted to be a narrower range (e.g., 5Hz) or to be a wider range (e.g., 20Hz) on a necessity basis. More specifically, ECU 110 which completed the steps (S815-S855) for detecting the reflection intensities of a reflected wave relating to one specific frequency determines whether further steps for detecting the reflection intensities of reflected waves relating to all specific frequencies having a unit interval of 10Hz over the frequency range of 10Hz~10KHz (S860). If the determination in step S860 is "No," then the method for detecting a buried object of the present invention proceeds to step S815. If the determination in step S860 is "Yes," then ECU 110 calculates a first characteristic frequency for the first reflected wave signal (S862) and calculates a second characteristic frequency for the second reflected wave signal (S864). The first and the second characteristic frequencies are calculated as peak frequencies for the first and the second reflected wave signals. Then, ECU 110 determines whether both the first and the second characteristic frequencies exist in a first predetermined frequency range and a second predetermined frequency range (S870). That is, ECU 110 determines whether both the first predetermined frequency range covering the first characteristic frequency and the second predetermined frequency range covering the second characteristic frequency exist among a plurality of frequency ranges. Here, it is not necessarily required that the first predetermined frequency range covering the first characteristic frequency should be identical to the second predetermined frequency range covering the second characteristic frequency. The reason is that the first characteristic frequency and the second characteristic frequency may vary depending on the characteristics of sensors to be used as described above. If it turns out that both the first and the second predetermined frequency ranges exists in step S870, ECU 110 warns that a buried object exists by lighting a lighting lamp included in the display device 105 (S875).

Then, ECU 110 determines the type of the buried object corresponding to both the first and the second predetermined frequency ranges (S880). That is, ECU 110 retrieves the type of the buried object, corresponding to both the first and the second predetermined frequency ranges, which is pre-stored in the memory 115. Once the type of the buried object is determined, ECU 110 displays the determined type on the display device 105 (S885). Thus, it is displayed that a predetermined substance corresponding to both the first predetermined frequency range for the first acoustic sensor and the second predetermined frequency range for the second acoustic sensor is buried in the medium. If either one of the first and the second predetermined frequency ranges does not exist in step S870, step S870 proceeds to the initial step and performs detection processes continuously for the unknown buried object. Although the present invention is described by referring to embodiments described and illustrated in the detailed description and the drawings, the scope of present invention should not be limited to the embodiments. Rather, it is obvious that any modifications and their equivalents conceivable by a skilled person in the art from the disclosed embodiments should fall upon the scope of the present invention.

Industrial Applicability The apparatus and the method for detecting a buried object of the present invention can detect the existence of a buried object and the type thereof reliably and exactly and the apparatus for detecting a buried object can be made in a compact size by using with compact sized sensors having high performance.

Claims

What is claimed is:

1. An apparatus for detecting a buried object using solitary waves comprising: an acoustic source for emitting a solitary wave; at least one first acoustic sensor for generating a first reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; at least one second acoustic sensor for generating a second reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the first and the second reflected wave signals from the first acoustic sensor and the second acoustic sensor, respectively, and determining the existence of the buried object in the medium based on the first and the second reflected wave signals.

2. The apparatus according to Claim 1 , wherein the first acoustic sensor is a GMI sensor having a membrane responsive to the reflected wave of the solitary wave, and wherein the second acoustic sensor is a MEMS sensor comprising a cantilever responsive to the reflected wave of the solitary wave. 3. The apparatus according to Claim 1 or 2, wherein the control unit calculates a first and a second characteristic frequencies for the first and second reflected wave signals, respectively, and determines the existence of the buried object and the type thereof based on the first and the second characteristic frequencies.

The apparatus according to Claim 3, wherein the control unit determines the existence of a first frequency range including the first characteristic frequency among a plurality of predetermined frequency ranges; wherein the control unit determines the existence of a second frequency range including the second characteristic frequency among the plurality of predetermined frequency ranges; and wherein the control unit determines that the buried object corresponding to the first and the second frequency ranges exists, when both the first and the second frequency ranges exist.

5. The apparatus according to Claim 3, wherein the first and the second characteristic frequencies are calculated as peak frequencies corresponding to the reflected wave signals, respectively. 6. The apparatus according to Claim 4, wherein the first and the second characteristic frequencies are calculated as peak frequencies corresponding to the reflected wave signals, respectively.

7. The apparatus according to Claim 1 , wherein the control unit comprising: a function generator for acoustic source; an amplifier for amplifying a signal from the function generator for acoustic source and feeding the amplified signal to the acoustic source as a driving signal; a function generator for sensor for driving the first and the second acoustic sensors; a first lock-in amplifier for comparing the signals outputted from the first and the second acoustic sensors driven by the function generator for sensor with the signal outputted from the function generator for sensor; a second lock-in amplifier for comparing a signal outputted from the first lock-in amplifier and the driving signal fed to the acoustic source; and at least one processor for controlling the function generator for acoustic source and the function generator for sensor, and determining the existence of the buried object in the medium based on the signal outputted from the second lock-in amplifier.

8. The apparatus according to Claim 7, wherein the at least one processor processes a series of instructions for performing the steps of: a) calculating a first characteristic frequency for the first reflected wave signal; b) calculating a second characteristic frequency for the second reflected wave signal; c) determining whether the first characteristic frequency exists in a first predetermined frequency range; d) determining whether the second characteristic frequency exists in a second predetermined frequency range; and e) when meeting both conditions in the steps c) and d), displaying that a predetermined substance corresponding to both the first predetermined frequency range for the first acoustic sensor and the second predetermined frequency range for the second acoustic sensor is buried in the medium.

9. The apparatus according to Claim 8, wherein the first and the second characteristic frequencies are calculated as peak frequencies corresponding to the reflected wave signals, respectively.

10. An apparatus for detecting a buried object using solitary waves comprising: an acoustic source for emitting a solitary wave; at least one acoustic sensor for generating a reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the reflected wave signal from the acoustic sensor, and determining the existence of the buried object in the medium based on the reflected wave signal.

11. The apparatus according to Claim 10, wherein the acoustic sensor comprises either a GMI sensor or a MEMS sensor.

12. A detector for detecting a buried object having an apparatus for detecting a buried object using solitary waves, wherein the apparatus for detecting a buried object comprising: an acoustic source for emitting a solitary wave; at least one first acoustic sensor for generating a first reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; at least one second acoustic sensor for generating a second reflected wave signal corresponding to a reflected wave of the solitary wave emitted from the acoustic source; and a control unit for driving the acoustic source to emit the solitary wave toward a medium expected to have the buried object, receiving the first and the second reflected wave signals from the first acoustic sensor and the second acoustic sensor, respectively, and determining the existence of the buried object in the medium based on the first and the second reflected wave signals; wherein the detector for detecting a buried object comprising: a lower body for mounting the acoustic source and the first and the second acoustic sensors; a connection bar extending from the lower body; a fixing device mounted to the connection bar for fixing a part of a user's body; and a display device installed to a part of the connection bar.

13. The detector according to Claim 12, wherein the detector is provided with a plurality of the first acoustic sensors and a plurality of the second acoustic sensors, respectively.

14. The detector according to Claim 13, wherein the acoustic source is placed in the center of the lower body, while the first acoustic sensor and the second acoustic sensor are placed alternately along the circumference of the lower body.

15. A method for detecting a buried object using solitary waves comprising the steps of: emitting a solitary wave toward a medium; generating a first reflected wave signal corresponding to a reflected wave of the solitary wave; generating a second reflected wave signal corresponding to a reflected wave of the solitary wave; calculating a first characteristic frequency for the first reflected wave signal; calculating a second characteristic frequency for the second reflected wave signal; determining the existence of the first characteristic frequency in a first predetermined frequency range; determining the existence of the second characteristic frequency in a second predetermined frequency range; and determining that a known buried object corresponding to both the first and the second predetermined frequency ranges exists in the medium, when the first and the second characteristic frequencies respectively exist in the first and the second predetermined frequency ranges.

16. The method according to Claim 15, wherein the first and the second characteristic frequencies are calculated as peak frequencies corresponding to the reflected wave signals, respectively.

17. The method according to Claim 16, wherein the method further comprises a step of displaying that the known buried object in the medium when the first and the second characteristic frequencies respectively exist in the first and the second predetermined frequency ranges.