JPH079464B2 - Position detection method and system for buried object, and optical fiber cable - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for position finding suitable for underground use.

[0002]

Copper and fiber optic communication cables are very different in the way they transmit information, and even in the form of energy they transfer, but nevertheless have similar installation methods. Use,
Used in much the same way. For example, both cables may be used on the ground or may be directly buried in the ground.

Since copper cables are metallic in nature,
Unlike fiber optic cables, which do not need to include metallic materials, ie all materials may be dielectric, special shielding is often necessary to protect the cable from lightning strikes. Suspended cables and buried cables exposed on the ground are susceptible to lightning strikes. The problem of lightning strikes has been partially overcome by wrapping around the cable and incorporating into the cable a metal shield that extends the length of the cable. The metal shield is often located between the inner and outer jackets of the cable and is grounded at different points along the length of the cable. If a part of the cable is struck by lightning,
The energy is connected into the metal shield and propagates underground, without disturbing the transmission part of the cable arranged in the metal shield.

Fiber optic cables are often reinforced by incorporating metallic reinforcement within their sheath system. Generally, a plurality of reinforcing wires are helically arranged along the length of the cable before the cable is fitted with the final outermost plastic jacket. Because these wires are metallic, they can pull lightning strikes onto the cable. Lightning protection is the method used to protect copper cables for some lightguide cables, namely placing a metal shield around the inside of the cable sheath system during cable installation. It is done by

It would be desirable to be able to locate buried cables, for example, for maintenance and relocation, and for marking cable runs to avoid cutting the cables during future cable installation and excavation operations. Buried cables, wires, pipes and other objects, the structure of which consists of continuous longitudinally extending metal parts such as shields or reinforcements,
It is located by using a device called a cable locator.

This so-called cable position finder consists of two parts, a signal transmitter and a signal receiver. A signal transmitter, which is directly or inductively connected to the metal part of the buried structure and is placed in a fixed position, transmits a so-called tracing tone in the structure. Tracing tones are electrical signals that cause a metallic part of an embedded object to emit a characteristic electromagnetic field. The operator holds the receiver close to the ground and swings left and right over the area where the operator thinks the cable is located. The receiver has an electromagnetic induction pickup
A coil transducer is attached which, when excited by the electromagnetic field produced by the tracing tones, produces a signal which can be interpreted as indicating the relative position of the buried object.

Recently, an optical fiber cable sheath system has been developed which has a strength required for reliability of an optical cable without using a metallic reinforcing portion. US Patent No. 4,
No. 874,219, an optical fiber consisting of an optical fiber core, a tube in which the core is placed, a waterproof tape extending in the longitudinal direction, a plurality of vertically extending non-metallic reinforcing portions wound in a spiral shape, and an outer jacket. • A cable system is disclosed.

One of the advantages of this so-called all-dielectric design is that it does not include a metallic sheath system part, so it can attract lightning strikes or transmit dangerous voltages if inadvertently crossed the power cable. It is something that does not happen.

[0009]

One of the drawbacks of the all-dielectric design is that conventional buried cable location techniques cannot be used. Obviously, if the buried cable does not include a longitudinally extending metal portion, the conventional position locating means of the buried cable described above cannot be used. An apparatus and method for locating an all-dielectric-embedded cable is a necessity and probably not shown anywhere in the prior art.

[0010]

The foregoing problem of locating buried all-dielectric cables is solved by the method and system of the present invention.

For example, an electronic resonant tag consisting of a printed circuit having an inductive portion and a capacitive portion and a diode mounted on the surface is arranged with an embedded object such as an all-dielectric optical cable. The capacitive portion of the electronic resonance tag and the diode are set to values such that the electronic resonance tag will characteristically resonate when excited by an external electromagnetic stimulus.

[0012] In one embodiment, the transceiver of the transmitter portion is configured to generate and transmit electromagnetic energy of energy of at least two frequencies through the high gain antenna. The transmission energy is composed of the first frequency f _a and the second frequency f _b , and the second frequency f a
_b is within 5% of the value of the first frequency f _a . A narrow bandwidth receiver is provided, which has an input connected to a high gain antenna, which may be the same antenna on which the transmitting portion is mounted. This receiver is then effective in receiving the intermodulation generation frequency of the two transmission frequencies.

The fiber optic cable with the electronic resonance tag is buried and therefore hidden from view. In the case of optical cables, electronic resonance tags are included in or between coaxially arranged dielectric sheath portions of the cable. The electronic resonance tags are spaced along the length of the cable,
It is arranged offset in the circumferential direction.

The cable is located by the transceiver device described above. To do this, the operator scans, or swings, the transceiver into the general area where the cable is believed to be buried. The transmitting part consists of energy of at least one frequency, 1
In one embodiment, two frequencies of electromagnetic energy are transmitted. When this is done, the electromagnetic energy generated by the transmitting portion penetrates the surface of the earth, while exciting the electronic resonance tag.

Since the electronic resonance tag has a non-linear response, 2
Radiates the intermodulation generation frequency of two transmission frequencies. The receiver receives the intermodulation signal and converts the signal into an output signal useful for determining the position of the buried cable.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, there is shown a method of performing a cable location probe of the present invention. As seen in FIG. 1, cable 20 is shown buried beneath ground surface 21.
As shown in FIG. 2, the cable 20 includes at least one cable 20 disposed within a longitudinally extending core tube 24.
It comprises a core 22 having one optical fiber 23. In the preferred embodiment, a plurality of reinforcing portions 26-26 are arranged longitudinally or spirally along the length of the core tube 24. In addition, a waterproof material 27 is also placed around the core tube. The waterproof material may be tape, as shown, or, alternatively, waterproof fiber (not shown).

Cable 20 is an all-dielectric cable,
That is, all the materials that make up the cable, for example,
The reinforcement is non-metallic. For obvious reasons, it is important that the cable 20 be localizable despite being buried underground.

Buried non-dielectric cable, ie
If it is desired that the cable with continuous metal elements be located, conventional cable probing methods can be utilized. FIG. 3 shows a conventional method of performing cable position search. As shown in FIG. 3, the cable 30 is
It has a core 31 of copper wires 32-32 and is shown buried beneath a ground surface 33. The signal transmitter 34 allows a so-called tracing tone 3 to the part 37 of the cable 30.
6 is included.

In another embodiment, the signal transmitter 34
Are electrically conductively connected to the cable 30 by wires 38. The tracing tones 36 are in the frequency range of 50 hertz (Hz) to hundreds of kilohertz (kHz). In this frequency range, the tracing tone 36 is A.T. C. In the form of an electric current, it travels along the length of the cable 30 and in between generates a magnetic field 35 around the cable.

An operator is shown with a hand-held detector 39 consisting of a sensor portion 40 having a multi-turn wire loop, a handle portion 41 having a signal strength indicator, and a handle portion 42. During the cable position search, the hand-held detector 39 is held so that the sensor portion 40 is located directly above the ground surface 33, but not in contact with the ground surface 33. The operator attaches the sensor portion 40 to the cable 30.
When swept over the general position of the
Induces a current in a 0 multi-turn wire loop.

The induced current in the wire loop is converted such that its intensity reading is displayed on a meter or audible as a fluctuating volume of sound produced by a sound transducer. Either of these meters or transducers are located in the handle portion of the portable detector 39.
When the handheld detector is swept over a common area on the cable, a relatively high meter reading or volume is indicative, for example, that the sensor portion 40 is directly above the buried cable 30. When the sensor portion is moved sideways, the meter reading or volume is reduced. Therefore, the relative precise position of the cable is determined using a regression process as just described.

The conventional method just described cannot be used to locate the all-dielectric cable 20 of FIG.
To locate the buried all-dielectric cable 20, the cable must be improved by the present invention.

The cable is equipped with an electronic resonance system so that buried cables, such as all-dielectric cables, can be located. To this end, a plurality of electronic resonance tags 44-44 (see FIG. 2) are placed between the core tube 24 and the outer surface 46 of the outer sheath portion 48. 1
In one embodiment, the electronic resonance tags 44-44 are embedded within the plastic material of the sheath portion 48 adjacent the inner surface 50 of the sheath portion.

In the preferred embodiment, the electronic resonance tag 44
˜44 are spaced along the carrier tape 49 (see FIG. 4) not only vertically but also laterally. This is because, for example, when the tape is wrapped around the core tube 24 during the sheathing operation, each successive electron resonance tag is displaced in the direction of rotation by, for example, 120 degrees from the preceding electron resonance tag. is there.

The electronic resonance tags 44-44, which are otherwise incorporated in a sheath that is all dielectric, consist of metal parts. However, these parts are discontinuous in the length direction of the cable, and in fact, about 60c in the cable.
It is arranged at intervals of m. Moreover, the electronic resonance tags 44-44 do not have any kind of path to electrically ground any part of the cable. Therefore, the electronic resonance tags 44-44 do not increase the likelihood of lightning strikes on the cable.

An example of one of the electronic resonance tags 44-44 and the associated equivalent circuit is shown in FIGS. As will be recalled, one method of incorporating an electronic resonant tag within an all-dielectric cable structure is to place the electronic resonant tag between portions of the cable sheath structure, or
It is a method of embedding in it. Therefore, what is desired is that the electronic resonance tag be mostly planar and relatively thin.

A typical electronic resonance tag consists of a foil circuit 51 arranged on the plane of a relatively thin dielectric substrate 52 and a diode 53 mounted on the surface.
The shape of the foil pattern and the placement of its portions on the plane of the dielectric substrate provide the capacitive and inductive elements represented by capacitor 54 and coil 55, respectively, in the equivalent circuit of FIG.

In the preferred embodiment, inductive foil loop 58 is an open loop with endpoints 56-56, approximately 12 mm wide and 90 mm long, which is 1.0 GH.
z equal to the electrical half-wave of the electromagnetic signal. The pair of leads 57-57 of the diode 53 are inductive foil
The end points 56-56 of the loop are soldered and thus the electrically conductive foil loop 58 is electrically closed.

Another inductive foil loop is 5
8, it is arranged electrically in parallel with the diode 53. The inductive foil loop 58 has an inductance value that exactly resonates with the contact capacitance of the diode 53 at the operating frequency of the electronic resonance tag (in the range of 1.0 GHz). This inductance is necessary to prevent the contact capacitance of the diode 53 from shunting the diode. Without this, the effectiveness of the diode as a signal mixer is reduced.

The cable 20 located by the method of the present invention is typically buried at a depth in the range of 0.5 to 1.5 meters. An operator is shown with a portable transceiver 60 (see FIG. 1), and the portable transceiver 6
0 consists of a sensor portion 62 having a transmitting / receiving antenna 63, a transmitter portion 64 and a receiver portion 74 (see FIG. 7). The handle portion 66 has a meter transducer 67 and an audio transducer 68, the function of which is to convert the signal propagated by the sensor portion into an instrument signal and an acoustic signal, respectively. The handle portion 69 connects the handle portion to the sensor portion.

The operator locates the buried cable 20 by first estimating the general location of a portion of the cable. Some evidence of a cable is either the known location of the associated closure, where the cable is terminated or joined to another cable, or the general location dictated by convention, experience or map. . The operator holds the transceiver 60 in its general position so that the sensor portion 62 is held close to, but out of contact with, the ground surface 21. The sensor portion also sweeps a portion of the ground surface, including the portion directly above the buried cable 20.

When an operator sweeps the sensor portion 62 above the ground surface, the sensor portion transmits electromagnetic energy. This electromagnetic energy has an energy of at least two frequencies _{f a} and _{f b, f b} is within about 5% of the _{f a,} is generated by the transmitter portion 64. The electromagnetic energy having at least two frequencies is hereinafter referred to as an electromagnetic signal 71. The electromagnetic signal 71 penetrates the soil 72 and excites the electronic resonance tags 44 to 44 by inducing an alternating current within the range of the electromagnetic signal 71 into the electronic resonance tag.

The diode 53 of the electronic resonance circuit of each electronic resonance tag 44 acts as a mixer for the two frequencies f _a and f _b of the electromagnetic signal 71 transmitted by the transmitter of the sensor portion 62. When the two frequencies are mixed in a non-linear device such as a diode, harmonic and intermodulation products of the two frequency combinations are produced. Therefore, Acos (2πf
2 represented by the formulas _a t) and B cos (2πf _b t)
When the two signals are mixed in the diode 53, one particularly useful intermodulation product is generated, kA ² Bcos [2π
(2f _a −f _b ) t]. However, k is a coefficient related to the conversion efficiency of the circuit.

[0034] When _{f a} and _{f b} is the frequency which is very close, intermodulation frequency components generated from the mixed frequency diode 53 _(2f a -f _b) relatively to the frequency _{f a} and _{f b} near. If f _a , f _b and the intermodulation frequency (2f _a −f _b ) are relatively close, the antenna 6
3, the transmission frequency f _a and f _b, may be a common antenna and receiving the return signal 73 consisting of intermodulation frequency (2f a _{-f b)} emitted by electron resonance tag. Since the output of the return signal 73 is proportional to the square of the output signal f _a, the return signal by providing an extra output only f _a signal is maximized.

The magnitude of the radiation signal 73 received by the sensor portion 62 must be strong enough to obtain an acceptable signal-to-noise ratio at the receiver portion 74. The magnitude of the energy absorbed and emitted by the electronic resonance tag and thus received by the receiver portion 74 of the sensor portion 62 depends, inter alia, on the frequency of the electromagnetic signal 71, the magnitude of the electromagnetic signal incident on the electronic resonance tag, the electronic resonance. It is a function of the effective exposed surface area of the tag and local soil conditions.

The frequency and magnitude of the radiated signal 73 is largely determined by the characteristics of the selected electronic resonance tag, the depth range in which the cable location method and apparatus are effective, and the local soil conditions. Frequency and magnitude
Optimized to meet the required performance.

The effective exposed surface area of the electronic resonance tag is obtained by multiplying the actual surface area of the electronic resonance tag by the sign of the incident angle of the transmission signal to the electronic resonance tag. Therefore, the electromagnetic signal 71
When is perpendicular to the plane of the electronic resonance tag, the effective exposed surface area of the electronic resonance tag is the product of 1 and the actual surface area, which is equal to the actual surface area. Therefore, the amount of energy absorbed and emitted is maximized. When the electromagnetic signal is parallel to the plane of the electronic resonant tag, the effective exposed surface area is the product of zero and the actual surface area, and therefore the energy absorbed is zero. As will be appreciated, the effective exposed surface area of an electronic resonant tag depends on the orientation of the electronic resonant tag with respect to the transmitted signal.

Soil attenuation is a variable that affects not only the electromagnetic signal going to the electronic resonance tag, but also the signal emitted by the electronic resonance tag and received by the receiver portion 74. The attenuation of an electromagnetic signal as it passes through soil is a function of the soil conditions through which the signal passes and the signal frequency. Looking at FIG. 8, it can be seen that for all types of soil conditions, the one-way soil attenuation increases with increasing frequency of the transmitted signal. In addition, unidirectional soil attenuation is also a function of soil moisture content.

For example, the soil attenuation of electromagnetic signals (dB / meter (depth)) for dry soil is from 1 MHz to 1 G
For each of the signal frequencies in Hz, it rises from about 0.5 dB to 2.5 dB / meter (depth). For wet soil, soil attenuation is 1.5 dB to 7.5 dB for electromagnetic signal frequencies of 1 MHz to 1 GHz, respectively.
/ M (soil depth). The graph of FIG. 8 also includes a plot 77 showing the attenuation of electromagnetic frequencies in water as a function of frequency. Electromagnetic signals transmitted in water are 4 dB / meter (depth) and 17.5 dB / for electromagnetic signal frequencies of 1 MHz to 1 GHz, respectively.
Decays at a rate of meters (depth).

For signals propagating from a point radio source, as is the case with signals propagating by the transmitter portion 64 of the present invention, the signal strength at a distance d from the radio source is 1 / d ² . Proportional. For a signal returning the distance d, the strength of the returning signal is proportional to 1 / d ⁴ . 1 / d ⁴ is a well-known relationship of the strength of the returned radar signal and is applied for a large distance compared to the wavelength. For purposes of buried cables, distances are on the order of 1 meter or less. 1
Frequencies with wavelengths on the order of meters or less are 300 MH
Corresponds to frequencies above z. For frequencies below this frequency, the relationship of return signal strength to d is 1 / d ⁴
Changed to 1 / d ⁶ . Therefore, at least 300
It is desirable to operate at system frequencies above MHz.

The choice of operating frequency of 1.0 GHz limits the detection technique used to separate the return signal from the transmitted signal. For example, pulse gating techniques cannot be used. Assuming that the "Q" of the resonant circuit is about 10 (where Q of the system is related to the slope of the decay curve of the resonant circuit when it is de-energized), the energy of the electronic resonance tag is about 10 resonances. It is expected to last only nanoseconds. This time is not enough time to send a signal, switch off the transmitter and switch on the receiver to look for a return signal. Therefore, the other method is to generate a signal having a third frequency.
A signal consisting of three frequencies is used. The third signal is the intermodulation component described above, the detection of which is used to distinguish the transmitted signal from the received signal.

A block diagram of the transceiver 60 is shown in FIG. Transmitter portion 64 includes a pair of stable oscillator 81 and 82 for generating a signal _{f a} and _{f b,} respectively. Each signal _{f a} and _{f b} amplifier 8
Amplified at 3 and 84. For the reasons previously explained, the signal f _a is amplified to a higher level than the signal f _b . Generally, the amplitude of the signal _{f a} is 20dB is higher than the amplitude of the signal _{f b.} The transmitted signal f _b is modulated by the mixer 86 at the output of the oscillator 82 to enhance the signal detection capability of the receiver portion 74.

[0043] After being sufficiently amplified respectively in the amplifier 81 and 82, the signal _{f a} and _{f b} are output coupler 8
The combined signal composed of 8 frequencies and composed of 2 frequencies is sent to the high gain antenna 63 via the directional coupler 92. Output combiner 88 is also used to keep amplifiers 81 and 82 independent of each other and to prevent spurious intermodulation products from occurring in the amplifier.

It should be understood that the transmitted electromagnetic energy consists of two signals, each with its own frequency, and these signals are combined at the electronic resonance tag 44 of interest. The directional coupler 92 allows the common antenna to act as both a transmit and a receive antenna. The directional coupler prevents the transmitted signal from entering the receiver portion 74 of the transceiver 60 directly.

Return signal 73 is received by antenna 63 and via directional coupler 92 a notch filter 93.
Sent to. Notch filter 93 is effective in a portion of the transmitted signal f _a and f _b is prevented from reaching the rest of the receiver portion 74 of the transceiver 60. Without this, it becomes overloaded part of the signal f _a and f _b are relative to other portions of the receiver portion 74, irrespective of the intermodulation with the same frequency and intermodulation components emitted by the electron resonance tag Product may form.

The return signal 73 exits the notch filter 93, is amplified through the at least one band filter 94, a very narrow frequency spectrum desired intermodulation frequency (2f a _{-f b)} is included in the main Only a signal consisting of The detector 96 detects the D.D. as a result of the modulation of the signal f _{b in} the oscillator part. C. Generates a voltage or low frequency acoustic signal. D. C. The voltage is used to drive a meter or other signal level indicating device,
The acoustic signal is sent to a speaker to produce an acoustic output as an indication of the intensity of the radiated signal.

The receiver portion 74 (see again FIG. 7) is tuned to receive only the intermodulation components of the two transmit frequencies. The strength of the return signal 73 depends, inter alia, on the cable 2
It changes depending on the depth at which 0 is buried and the state of the soil 70. When the sensor portion of the transceiver 60 sweeps over the ground and sends and receives signals, the return signals are converted into signals that stimulate the human senses, such as acoustic signals and instrument signals, and these signals are returned. It depends on

For example, when the sensor portion 62 is located directly above the cable, a relatively maximum volume acoustic signal is heard. As the sensor portion 62 moves from this position, the volume of the acoustic signal decreases. The regression process, in which the sensor part is moved left and right with progressively shorter sweeps until the highest indicated signal strength is achieved, allows the operator to accurately locate the position of the cable 20.

It should be understood that the apparatus described above is merely illustrative of the present invention. Those skilled in the art will be able to think of other devices that implement the principles of the present invention and fall within the spirit and scope of the present invention.

[0050]

As described above, an electronic resonance tag is arranged on a buried object, particularly a buried cable, and the electronic resonance tag returns electromagnetic waves transmitted from a transceiver on the ground at another frequency to prevent lightning strikes. According to the method and system of the present invention, even if the buried object is made entirely of non-metal and the conventional position-finding system is unusable, such as a fiber optic cable made entirely of dielectric material for The position of buried objects can be searched.

[Brief description of drawings]

FIG. 1 is a diagram showing execution of a cable position searching method of the present invention.

FIG. 2 is a perspective view of an all-dielectric communication cable with a sheath system having multiple electronic resonance tags.

FIG. 3 is a diagram representing the performance of a conventional cable location method for locating a cable having continuous metal elements.

FIG. 4 is a perspective view of a carrier tape having a plurality of electronic resonance tags disposed thereon.

5 is a plan view of the electronic resonance tag shown in FIG. 2. FIG.

6 is an equivalent circuit diagram of the electronic resonance tag shown in FIG.

FIG. 7 is a block diagram of a transceiver used in performing the location method of the present invention.

FIG. 8 is a graphical representation of one-way soil attenuation of electromagnetic signals.

[Explanation of symbols]

 20 cable 21 ground surface 22 core 23 optical fiber 24 core tube 26 reinforced portion 27 waterproof material 30 cable 31 core 32 copper wire 33 ground surface 34 signal transmitter 35 magnetic field 36 tracing tone 39 portable detector 40 sensor portion 41 handle Part 42 Handle part 44 Electronic resonance tag 48 Outer sheath part 49 Carrier tape 51 Foil circuit 52 Dielectric substrate 53 Diode 54 Capacitor 55 Coil 58 Inductive foil loop 60 Portable transceiver 62 Sensor part 63 Transmit / receive antenna 64 Transmitter part 66 Handle Part 67 Meter converter 68 Voice converter 69 Handle part 74 Receiver part 81 Oscillator 82 Oscillator 83 Amplifier 84 Amplifier 86 Mixer 88 Output coupler 92 Directional coupler 93 Notch filter Capacitor 94 bandpass filter 96 detector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Al Jay. Shepes United States 30092 Norcross, Georgia, Mayapple Court 4230 (72) Inventor Lois A. Turner United States 30080 Georgia, Smyrna South East, Cherokee Trail 920 (56) References JP-A-1-70887 (JP, A) JP-A-60-82881 (JP, A)

Claims (11)

[Claims] 1. A method of locating an embedded object, wherein for at least one electronic resonance tag associated with the embedded object, the source comprising at least two frequencies within said electronic resonance tag and being a remote radiation transmitter. Exciting the electronic resonance tag by inducing an alternating current from the source, the source detecting a radiated electromagnetic field having the excited third frequency and probing the position of the object. A method for exploring the position of an embedded object. 2. The method of claim 1, wherein the alternating current comprises a first frequency and a second frequency, the first frequency being at least about 300 MHz. 3. The method of claim 1, wherein one of the two frequencies is within about 5% of the other of the two frequencies. 4. The method of claim 3, wherein the alternating current comprises a first frequency and a second frequency, and the third frequency is a harmonic of the first or second frequency. 5. The method of claim 3 wherein the alternating current comprises a first frequency and a second frequency, and the third frequency is an intermodulation term for the first and second frequencies. 6. A fiber optic cable having at least one optical fiber and a sheath system having a plurality of resonant tags spaced along the optical fiber, each resonant tag comprising: Comprising an electronic resonance tag associated with the cable, said resonance tag having a built-in resonance loop, receiving energy of two frequencies and generating a signal of a third frequency different from said two frequencies And a fiber optic cable that is capable of radiating. 7. The built-in resonant loop comprises a dielectric substrate on which is disposed a foil circuit effective to form a given capacitive and inductive element, and the resonant tag has a diode element. 7. The fiber optic cable of claim 6, wherein: 8. A system for locating a buried cable having a plurality of electronic resonance tags associated with the buried cable and spaced along the buried cable, the resonance tag having a built-in resonance loop, The resonant tag receives energy from energy transmitted at at least one frequency and generates a signal at another frequency different from the at least one frequency; and the other frequency. A means for transmitting electromagnetic energy having said at least one frequency, and a means for receiving a signal radiated at said another frequency; The means for discriminating and, depending on the valid signal received at said other frequency,
An embedded cable position exploration system, comprising: a means for indicating the presence of the embedded cable. 9. A system for locating a buried object having at least one electronic resonance tag associated with the buried object, wherein the resonance tag has a built-in resonance loop, the resonance tag at at least two frequencies. It is possible to receive energy from the transmitted energy and to generate a signal of at least one other frequency and to radiate a signal at said one other frequency, at least a first and Means for transmitting electromagnetic energy having a second frequency, means for receiving a signal radiated at a third frequency, means for discriminating the transmission energy from a radiated signal, and a valid signal received at the third frequency In accordance with the above, the embedded object position searching system is characterized by comprising an indicating means for indicating the existence of the embedded object. 10. A means for transmitting electromagnetic energy at first and second frequencies, first and second oscillators for generating first and second signals at first and second frequencies, and a first of the oscillators. And a first and second amplifier for amplifying the second signal, and an output combiner for combining the amplified first and second signals into a signal having two frequencies and for making the amplifier independent of each other, 10. The system of claim 9 including a directional coupler for preventing said signal of frequency from entering said signal receiving means, and an antenna for transmitting said signal of frequency 2. 11. The means for receiving a signal transmitted at a third frequency, the antenna absorbing the signal transmitted at the third frequency, and filtering a desired portion of the signal radiated at the third frequency. A narrow band amplifier for amplifying, a notch filter for preventing a portion of the transmitted signal of two frequencies from entering the narrow band amplifier, and receiving a desired portion of the radiated third frequency,
A detector section for producing a signal related to the intensity of the radiated third frequency.