Metal detector employing static discrimination
First Claim
Patent Images
1. A method for characterizing a target metal object in ground, comprising:
- (a) characterizing the ground at two distinct sinusoidal frequencies of interrogation;
(b) characterizing the target metal object in the ground at said two frequencies;
(c) characterizing a plurality of reference metal objects apart from the ground at said two frequencies;
(d1) computing a respective first number for each of said reference metal objects using the characterizations of said steps (a) and (c);
(d2) computing a second number for the target, metal object using the characterization of step (b);
(e) comparing said first and second numbers; and
(f) characterizing the target metal object with the result of the comparison of said step (e), wherein the characterizing step (a) provides for determining at least the ratios (Y1ground/Y2ground) and (X1ground/X2ground), where X1ground, Y1ground are reactive and resistive components of the response of the ground to interrogation at a first of said two frequencies, where X2ground, Y2ground are reactive and resistive components of the response of the ground to interrogation at a second of said two frequencies, wherein the characterizing step (c) provides for determining at least the ratios, for each of the objects, (X1object/X2object), (Y1object/Y2object), and (Y2object/X2object), where X1object, Y1object are reactive and resistive components of the response of one of the objects to interrogation apart from the ground at said first frequency, where X2object, Y2object are reactive and resistive components of the response of said one of the objects to interrogation apart from the ground at said second frequency, and wherein said first number is proportional to;
tan−
1 [(Y2object/X2object)·
[(Y1ground/Y2ground)−
(Y1object/Y2object)]/[(X1ground/X2ground)−
(X1object/X2object)]].
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Abstract
A metal detector employing static discrimination. Within the scope of the invention is a two-frequency method and apparatus for discriminating between metal objects and ground. Also within the scope of the invention is a three-frequency method and apparatus for discriminating between ferrous and non-ferrous metal objects. The methods and apparatus do not require movement of the search head of the metal detector.
60 Citations
26 Claims
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1. A method for characterizing a target metal object in ground, comprising:
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(a) characterizing the ground at two distinct sinusoidal frequencies of interrogation;
(b) characterizing the target metal object in the ground at said two frequencies;
(c) characterizing a plurality of reference metal objects apart from the ground at said two frequencies;
(d1) computing a respective first number for each of said reference metal objects using the characterizations of said steps (a) and (c);
(d2) computing a second number for the target, metal object using the characterization of step (b);
(e) comparing said first and second numbers; and
(f) characterizing the target metal object with the result of the comparison of said step (e), wherein the characterizing step (a) provides for determining at least the ratios (Y1ground/Y2ground) and (X1ground/X2ground), where X1ground, Y1ground are reactive and resistive components of the response of the ground to interrogation at a first of said two frequencies, where X2ground, Y2ground are reactive and resistive components of the response of the ground to interrogation at a second of said two frequencies, wherein the characterizing step (c) provides for determining at least the ratios, for each of the objects, (X1object/X2object), (Y1object/Y2object), and (Y2object/X2object), where X1object, Y1object are reactive and resistive components of the response of one of the objects to interrogation apart from the ground at said first frequency, where X2object, Y2object are reactive and resistive components of the response of said one of the objects to interrogation apart from the ground at said second frequency, and wherein said first number is proportional to;
tan−
1 [(Y2object/X2object)·
[(Y1ground/Y2ground)−
(Y1object/Y2object)]/[(X1ground/X2ground)−
(X1object/X2object)]]. - View Dependent Claims (2)
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3. A method for characterizing a target metal object in ground, comprising:
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(a) characterizing the ground at two distinct sinusoidal frequencies of interrogation;
(b) characterizing the target metal object in the ground at said two frequencies;
(c) characterizing a plurality of reference metal objects apart from the ground at said two frequencies;
(d1) computing a respective first number for each of said reference metal objects using the characterizations of said steps (a) and (c);
(d2) computing a second number for the target metal object using the characterization of step (b);
(e) computing said first and second numbers; and
(f) characterizing the target metal object with the result of the comparison of said step (e), wherein the characterizing step (a) provides for defining two ground balanced axes G1 and G2 corresponding to first and second of said two frequencies respectively, wherein the characterizing step (c) provides for determining, for each of the objects, quantities Aobject and Bobject, where Aobject is the magnitude of the response of one of the objects to interrogation apart from the ground at said first frequency projected onto the axis G1, where Bobject is the magnitude of the response of said one of the objects to interrogation apart from the ground at said second frequency projected onto the axis G2, and wherein said first number is proportional to Aobject/Bobject. - View Dependent Claims (4)
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5. A method for characterizing a target metal object in ground, comprising:
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(a) characterizing the ground at two distinct sinusoidal frequencies of interrogation;
(b) characterizing the target metal object in the ground at said two frequencies;
(c) characterizing a plurality of reference metal objects apart from the around at said two frequencies;
(d1) computing a respective first number for each of said reference metal objects using the characterizations of said steps (a) and (c);
(d2) computing a second number for the target metal object using the characterization of step (b);
(e) comparing said first and second numbers;
(f) characterizing the target metal object with the result of the comparison of said step (e);
(g) characterizing the ground at a third sinusoidal frequency of interrogation distinct from said two frequencies;
(h) characterizing the target metal object in the ground at said third frequency;
(i) characterizing the plurality of reference metal objects apart from the ground at said third frequency;
(j) computing a respective third number for each of said reference metal objects using the characterizations of said steps (g) and (i);
(k) computing a fourth number for the target metal object using the characterization of step (h);
(l) comparing said third and fourth numbers;
(m) characterizing the target metal object with the result of the comparison of said step (1); and
(n) comparing the identification of step (m) with the identification of step (f) to determine whether the target object is non-ferrous. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for characterizing a target metal object in ground, comprising:
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an interrogating portion for (a) characterizing the ground at two distinct sinusoidal frequencies of interrogation and for (b) characterizing the target metal object in the ground at said two frequencies;
data characterizing a plurality of reference metal objects apart from the ground at said two frequencies; and
a processing portion for computing a respective first number for each of said reference metal objects using the results of said (a) characterizing and said (b) characterizing, computing a second number for the target metal object using said data, first comparing said first and second numbers; and
first characterizing the target metal object with the results of said first comparing, wherein said interrogating portion is adapted so that said (a) characterizing provides for determining at least the ratios (Y1ground/Y2ground) and (X1ground/X2ground), where X1ground, Y1ground are reactive and resistive components of the response of the ground to interrogation at a first of said two frequencies, where X2ground, Y2ground are reactive and resistive components of the response of the ground to interrogation at a second of said two frequencies, wherein said data provide for determining at least the ratios, for each of the objects, (X1object/X2object), (Y1object/Y2object), and (Y2object/X2object), where X1object, Y1object are reactive and resistive components of the response of one of the objects to interrogation apart from the ground at said first frequency, where X2object, Y2object are reactive and resistive components of the response of said one of the objects to interrogation apart from the ground at said second frequency, and wherein said processing portion is adapted to compute said first number as being proportional to tan−
1 [(Y2object/X2object)·
[(Y1ground/Y2ground)−
(Y1object/Y2object)]/[(X1ground/X2ground)−
(X1object/X2object)]]. - View Dependent Claims (15)
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16. An apparatus for characterizing a target metal object in ground, comprising:
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an interrogating portion for (a) characterizing the ground at two distinct sinusoidal frequencies of interrogation and for (b) characterizing the target metal object in the ground at said two frequencies;
data characterizing a plurality of reference metal objects apart from the ground at said two frequencies; and
a processing portion for computing a respective first number for each of said reference metal objects using the results of said (a) characterizing and said (b) characterizing, computing a second number for the target metal object using said data, first comparing said first and second numbers; and
first characterizing the target metal object with the result of said first comparing, wherein said interrogating portion is adapted so that said (a) characterizing provides for defining two ground balanced axes G1 and G2 corresponding to first and second of said two frequencies respectively, wherein said data provide for determining, for each of the objects, quantities Aobject and Bobject, where Aobject is the magnitude of the response of one of the objects to interrogation apart from the ground at said first frequency projected onto the axis G1, where Bobject is the magnitude of the response of said one of the objects to interrogation apart from the ground at said second frequency projected onto the axis G2, and wherein said processing portion is adapted to compute said first number as being proportional to Aobject/Bobject. - View Dependent Claims (17)
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18. An apparatus for characterizing a target metal object in ground, comprising:
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an interrogating portion for (a) characterizing the ground at two distinct sinusoidal frequencies of interrogation and for (b) characterizing the target metal object in the ground at said two frequencies;
data characterizing a plurality of reference metal objects apart from the ground at said two frequencies; and
a processing portion for computing a respective first number for each of said reference metal objects using the results of said (a) characterizing and said (b) characterizing, computing a second number for the target metal object using said data, first comparing said first and second numbers; and
first characterizing the target metal object with the result of said comparing, wherein said interrogating portion is further adapted for (g) characterizing the ground at a third sinusoidal frequency of interrogation distinct from said two frequencies, and (h) characterizing the target metal object in the ground at said third frequency, wherein said data provide for (i) characterizing the reference metal objects apart from the ground at said third frequency, and wherein said processing portion is further adapted for computing a respective third number for each of the objects using said data, computing a fourth number for the target metal object using the result of said (h) characterizing, second comparing said third and fourth numbers, second characterizing the target metal object with the result of said second comparing, and third comparing the result of said first and second characterizing the target metal object to determine whether the object is non-ferrous. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26)
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Specification