Ground Eliminating Metal Detector Using Current Waveform Segmentation
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Solution Overview
Problem
Metal detectors struggle to distinguish between target eddy currents and responses from permeability and viscous magnetic remanence from ferrous components in the ground matrix, leading to interference and inaccurate readings.
Innovation Solution
The solution involves applying a constant low voltage to the inducing coil to eliminate permeability responses and using a fast half sine current to initiate remanent ground responses, which are then differentiated from target eddy currents by extending the target interrogation period and subtracting predetermined remanent ground signals from combined signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional metal detection methods are used, then target detection is achieved, but interference from permeability and remanent ground components reduces measurement precision
Solution Approach 1:
The patent segments the ground response into two distinct components: permeability response and remanent response. By applying different current waveforms (constant current for permeability, decaying current for remanent), the system separately measures and processes each component, allowing for precise elimination of ground interference while maintaining target detection accuracy
Solution Approach 2:
The patent changes the electrical parameters (current waveform, frequency, duration) of the inducing coil to selectively excite different ground components. By varying these parameters between measurement phases, the system can distinguish and eliminate harmful ground responses while preserving target signal integrity
2Measurement precision
If extended interrogation period is used to allow target eddy current settling, then target detection precision is improved, but the complexity of signal processing increases
Solution Approach 1:
The patent performs preliminary measurements of ground components (permeability and remanent responses) before the main target detection phase. By pre-characterizing the ground interference and storing these values, the system simplifies the main detection phase, as the ground components can be subtracted using predetermined values rather than requiring complex real-time processing
Solution Approach 2:
The patent uses periodic interrogation cycles with specific timing: constant current periods for permeability measurement, zero current periods for remanent measurement, and extended periods for target detection. This structured periodic approach organizes complex measurements into manageable phases, reducing overall system complexity
3Measurement precision
If rapid high current is applied to induce remanent ground response, then ground remanence detection is improved, but the time required for current cycling increases
Solution Approach 1:
The patent uses rapid high current pulses to quickly induce remanent ground responses, then immediately transitions to zero current periods for measurement. By rushing through the induction phase and capturing the remanent response during the natural decay period, the system minimizes total cycling time while maintaining accurate remanent detection
Solution Approach 2:
The patent allows the remanent ground response to decay naturally during zero current periods without requiring active measurement during the high current phase. The ground itself provides the measurement signal during its natural decay, eliminating the need for separate active measurement phases and reducing overall cycling time
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 eliminates interference from permeability and remanent ground components, allowing for accurate detection of target eddy currents without the need for nulling or low-frequency filtering, thereby improving the precision of metal detection.
Implementation Method 1
A capacitor is charged with a positive high voltage source. A first switch is closed, discharging the capacitor charge into a transmit coil.
Implementation Method 2
Ground combined remanence and target eddy current signals are received during the constant current periods and the ground remanence signals sensed during zero transmit coil current flow are subtracted from the combined signals.
Implementation Method 3
The permeability component is eliminated during the interrogation period by having a constant low voltage applied to the inducing coil. The remanent component, responding instantly to magnetizing current, but slowly decaying in remanence, is initiated by a fast half sine current that has little effect upon the desired eddy current object energizing time.
Data Source
AI summary
Remanent ground response is induced by rapid high current in a transmit coil. The transmit coil remains at zero current for a sufficient time for the remanent ground response to be sensed in a receive coil. A rapid high voltage and a sustained low voltage establish and maintain a stable current in the transmit coil followed by a zero current period. The sequence is repeated with a stable negative and followed by positive currents and a zero current. The receive coil is repeatedly interrogated at zero current between switch closings connecting in the transmit coil. Combined ground remanence and target eddy current signals are received during the constant current periods, and the ground remanence signals sensed during zero transmit coil current are subtracted from the combined signals.