Metal Detector Signal Processing for Soil Interference Reduction
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Solution Overview
Problem
Existing metal detectors face challenges in accurately detecting targets in soils due to interfering signals from soil components, which can vary significantly, making it difficult to distinguish between signals from the soil and the target, especially in cases of 'hot rocks' with different compositions than the surrounding soil.
Innovation Solution
A method that involves generating a transmit magnetic field, receiving and processing the induced magnetic field to determine a model of soil components, subtracting this model from the receive signal to reduce soil interference, and producing an indicator output signal for target detection, using techniques such as demodulation, singular value decomposition, and eigendecomposition to enhance sensitivity to metallic objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If synchronous demodulation with pre synchronous demodulation band-pass and/or low-pass filtering is used, then soil signal reduction is improved, but measurement precision deteriorates due to inability to distinguish hot rock signals from soil signals
Solution Approach 1:
The patent segments the soil signal into multiple independent components (typically two or more) based on their different temporal decay characteristics. By modeling each component separately with different time constants, the system can distinguish between soil components and target signals, thereby maintaining measurement precision while reducing soil interference.
Solution Approach 2:
The patent employs dynamic signal processing by using time-dependent decay models where each soil component is characterized by its own time constant. The processing adapts to the varying decay rates of different soil components, allowing dynamic separation of soil signals from target signals based on their distinct temporal behaviors.
2Device complexity
If simple signal recording and comparison is used, then device complexity is reduced, but measurement precision deteriorates due to unrepresentative environmental signals
Solution Approach 1:
The patent performs preliminary characterization of the soil signal by recording and analyzing the environmental signal before target detection. This preliminary action allows the system to establish accurate models of soil components and their decay characteristics, which are then used to improve subsequent target detection precision without significantly increasing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces soil signal interference, improving the accuracy of target detection and identification by isolating residual signals sensitive to target characteristics, thereby enhancing the signal-to-noise ratio and detection depth.
Implementation Method 1
transmit electronics generating a repeating transmit signal cycle of a fundamental period, which is applied to an inductor, for example a transmit coil, which transmits a resulting varying magnetic field
Implementation Method 2
receive electronics that processes a receive signal from a measured receive magnetic field
Data Source
AI summary
A method for detecting a target in a soil using a metal detector, including: generating a transmit magnetic field for transmission into the soil based on a transmit signal; receiving a receive magnetic field; providing a receive signal induced by the receive magnetic field; determining, based on the receive signal, a model of at least two independent components of the receive signal which are due to signals from the soil; processing the receive signal to produce a set of data which is with effects of the signals from the soil reduced therein or removed therefrom by fitting the model to the receive signal, then subtracting the fitted model from the receive signal; and producing, based on the set of data, an indicator output signal for indicating a presence and/or identity of the target.