Transient electromagnetic field detection apparatus having dynamic emission source in combination with static emission source and transient electromagnetic field detection method for discovering unexploded ordnance

Patent metadata

Field	Value
Publication number	US-11768058-B2
Application number	US-202017000263-A
Country	US
Kind code	B2
Filing date	Aug 21, 2020
Priority date	Aug 23, 2019
Publication date	Sep 26, 2023
Grant date	Sep 26, 2023

Abstract

A detection method for discovering an unexploded ordnance includes: surrounding a detection region with a transmitting coil and surrounding a detection site with a second receiving coil; conducting the transmitting coil with a second electric current; respectively acquiring a plurality of second feedback signals at a plurality of second feedback time points; partitioning the transmitting coil into a plurality of dipoles, and acquiring a plurality of distance values r respectively between the plurality of dipoles and the detection site; respectively calculating feedback depths according to feedback time periods; respectively calculating apparent resistivity values corresponding to the feedback depths; obtaining an apparent resistivity distribution in depth at the detection site according to the apparent resistivity values and the feedback depths; and judging whether there is any unexploded ordnance at the detection site according to the apparent resistivity distribution in depth.

First claim

What is claimed is:

1. A detection method for discovering an unexploded ordnance, comprising:
surrounding a detection region with a transmitting coil and surrounding a detection site in the detection region with a second receiving coil;
conducting the transmitting coil with a second electric current to transmit a second detecting signal to the detection region;
respectively acquiring a plurality of second feedback signals at a plurality of second feedback time points, the second feedback signals being second induced electromotive force signals of the second receiving coil;
partitioning the transmitting coil into a plurality of dipoles, and acquiring a plurality of distance values r respectively between the plurality of dipoles and the detection site;
respectively calculating feedback depths according to feedback time periods, the feedback time periods being periods of time between the second feedback time points and an initial time point of the conducting the transmitting coil with the second electric current;
respectively calculating apparent resistivity values corresponding to the feedback depths on the basis of the second feedback signals, the feedback time periods, the distance values r, and the second electric current;
obtaining an apparent resistivity distribution in depth at the detection site according to the apparent resistivity values and the feedback depths; and
judging whether there is any unexploded ordnance at the detection site according to the apparent resistivity distribution in depth.

2. The detection method of claim 1 , further comprising:
surrounding the detection region with the transmitting coil and a first receiving coil;
conducting the transmitting coil with a first electric current to transmit a first detecting signal to the detection region;
respectively acquiring a plurality of first feedback signals at a plurality of first feedback time points, the first feedback signals being first induced electromotive force signals of the first receiving coil;
plotting a first curve of the first feedback signals corresponding to the first feedback time points; and
judging whether the first curve is an abnormal curve, and determining the detection region as an abnormal region when the first curve being the abnormal curve.

3. The method of claim 1 , wherein the acquiring the plurality of distance values r respectively between the plurality of dipoles and the detection site comprises:
respectively acquiring relative coordinates (x, y) of the dipoles with respect to the detection site, and calculating the distance value r according to r=(x 2 +y 2 ) 1/2 ,
wherein y is a perpendicular distance from the detection site to the dipole, and x is a perpendicular distance from the detection site to a perpendicular bisector of the dipole.

4. The method of claim 1 , wherein each feedback depth is calculated according to the following formula (I):

D
TD

=

t

μ
D

⁢

σ
D

(
I
)

wherein D TD is the feedback depth, t is the feedback time period, μ D is a magnetic conductivity of geologic body, and σ D is an electric conductivity of geologic body.

5. The method of claim 3 , wherein the plurality of dipoles have a substantially same length.

6. The method of claim 5 , wherein each apparent resistivity value corresponding to a specific feedback depth is obtained by:
S 610 , assigning an assumed value to electrical resistivity;
S 620 , calculating a calculated induced electromotive force on the basis of the assumed value of the electrical resistivity, the feedback time period corresponding to the specific feedback depth, the length of the dipoles, the relative coordinates (x, y) of the dipoles, and the second electric current;
S 630 , comparing the calculated induced electromotive force and the second feedback signal corresponding to the feedback depth; and
S 640 , determining the assumed value of the apparent resistivity as a true value of the apparent resistivity corresponding to the specific feedback depth when a difference between the calculated second induced electromotive force and the second feedback signal is equal to or smaller than a threshold value; and returning back to S 610 to assign another assumed value to the apparent resistivity and repeating S 620 to S 640 when the difference is larger than the threshold value.

7. The method of claim 6 , wherein the assumed value of the apparent resistivity is selected from apparent resistivity values of metals.

8. The method of claim 6 , wherein the calculated induced electromotive force is calculated by:
calculating a secondary magnetic field generated in response to a primary magnetic field created by each dipole according to the following equations (2) and (3):

h
z

(

x
,
y

)

=

I
×
dl
×
y

4
⁢
π
⁢

r
3

×

[

(

1
-

3

2
⁢

u
2

)

⁢

erf
⁡
(
u
)

+

Assignees

• Univ Tsinghua
• Beijing Inst Of Satellite Environmental Engineering

Inventors

• Zheng xiao-ping
• Sun zhen-yuan
• Geng Hua
• Deng xiao-jiao
• Wang Bin

Classifications

• F41H11/136 Primary

  Magnetic, electromagnetic, acoustic or radiation systems, e.g. ground penetrating radars or metal-detectors · CPC title

• G01V3/10 Primary

  using induction coils · CPC title