Plural frequency method and system for identifying metal objects in a background environment using a target model
First Claim
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1. In a metal detector, a method for identifying a target comprising:
- transmitting from the detector two or more signals at different frequencies in the direction of the target;
receiving signal responses for the two or more signals that at least in part are attributable to the target;
measuring first and second components from the received signal responses; and
deriving data representing skin effect of the target from the first and second components, and the frequencies of the two or more signals, wherein the data representing skin effect is data computed from the first and second components that characterizes target type of the target.
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Abstract
A system for detecting metal targets located in a background environment such as the ground evaluates metal targets by processing components of signals at two or more different frequencies. A component of the received signal induced by the ground can be eliminated by subtracting signal components measured at two different frequencies. The received signal can be processed to account for changes in the background response with frequency. The type of an unknown target can be identified by processing background excluded components to produce data characterizing the target type.
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Citations
14 Claims
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1. In a metal detector, a method for identifying a target comprising:
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transmitting from the detector two or more signals at different frequencies in the direction of the target; receiving signal responses for the two or more signals that at least in part are attributable to the target; measuring first and second components from the received signal responses; and deriving data representing skin effect of the target from the first and second components, and the frequencies of the two or more signals, wherein the data representing skin effect is data computed from the first and second components that characterizes target type of the target. - View Dependent Claims (2, 3, 4, 5)
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6. In a metal detector, a method for generating target data comprising:
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transmitting from the detector at least two signals of different frequencies including a first signal at a first frequency, a second signal at a second frequency, and a third signal at a third frequency; receiving responses to the first, second, and third signals; measuring the response to the first signal at a first and second phase to determine first and second signal components of the response to the first signal; measuring the response to the second signal at a first and second phase to determine first and second signal components of the response to the second signal; measuring the response to the third signal at a first and second phase to determine first and second signal components of the response to the third signal; processing the first and second signal components of the responses to the first, second, and third signals to remove a background response, the processing step including removing the background response from the first and second signal components of the responses to the first, second and third signals by subtracting first or second signal components measured at different frequencies from each other to find background excluded components; and processing the background excluded components using a target model that models a target based at least in part on the skin effect produced by the target when subjected to the transmitted signals from the detector to generate target specific data to evaluate a target. - View Dependent Claims (7, 14)
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8. A metal detector comprising:
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a coil assembly for transmitting at least first, second, and third signals from the detector at first, second and third frequencies, respectively, in the direction of a background environment including a metal target, and for receiving at least first, second, and third response signals at the first, second, and third frequencies, respectively, wherein the response signals include a background response due to the background environment and a response due to the target; at least first and second phase detectors coupled to the coil assembly for measuring first and second signal components at first and second phases, respectively, of the first, second, and third response signals; and a signal processor coupled to the at least first and second phase detectors for receiving the first and second signal components of the first, second, and third response signals, for processing the first and second signal components of the first, second, and third response signals to remove the background response by subtracting signal components measured at different frequencies from each other to generate background excluded response data, and for processing the background excluded response data to compute data representing skin effect of the target, wherein the data representing skin effect of the target characterizes target type of the target.
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9. In a metal detector, a method for identifying target type of a target in a background environment, the method comprising:
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transmitting from the detector at least two signals of different frequencies including a first signal at a first frequency, and a second signal at a second frequency; receiving responses to the first, and second signals, wherein the responses include a background response due to the background environment and a response due to the target; measuring the response to the first signal at a first and second phase to determine first and second signal components of the response to the first signal; measuring the response to the second signal at a first and second phase to determine first and second signal components of the response to the second signal; generating filtered resistive and reactive component data from the first and second signal components of the responses to the first and second signals; and computing data representing skin effect of the target from the filtered resistive and reactive component data, wherein the data representing skin effect of the target characterizes target type of the target.
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10. A metal detector comprising:
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a coil assembly for transmitting at least first, and second signals from the detector at first, and second frequencies, respectively, in the direction of a background environment including a metal target, and for receiving at least first and second response signals at first and second frequencies, respectively, wherein the response signals include a background response due to the background environment and a response due to the target; at least first and second phase detectors coupled to the coil assembly for measuring first and second signal components at first and second phases, respectively, of the first and second response signals; and a signal processor coupled to the first and second phase detectors, the signal processor operable to evaluate a target type of a target in a background environment by deriving data representing skin effect of the target from the first and second signal components of the first and second response signals, wherein the data representing skin effect of the target characterizes target type of the target. - View Dependent Claims (11, 12, 13)
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Specification