Metal Detector Double-D Coil Nulling Conductive Soil Interference
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Solution Overview
Problem
Conductive soils, such as those found near salt-water beaches or areas with high salt content, interfere significantly with metal detectors, causing false signals and reducing the ability to detect buried metal targets due to eddy currents, which existing methods fail to adequately null out.
Innovation Solution
A method using a metal detector with a transmit winding and a receive winding forming a Double-D coil configuration, where the parameters of both windings are selected to process signals in a way that reduces or nulls out unwanted signals from conductive soils through synchronous demodulation, by applying different gains to the signals from each winding and subtracting the receive signal from the transmit signal to eliminate interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-winding metal detectors are used, then the device structure is simple, but false signals from conductive soils cannot be adequately nulled out
Solution Approach 1:
The detector winding is segmented into two distinct windings: a transmit winding for generating the magnetic field and a receive winding for detecting signals. This segmentation allows independent optimization of transmit and receive functions, enabling effective nulling of conductive soil signals while maintaining detection capability.
Solution Approach 2:
A nulling signal is introduced as an intermediary element that mediates between the transmit and receive windings. This nulling signal, derived from the transmit signal and adjusted in phase and amplitude, cancels out the unwanted eddy current signals from conductive soils before they reach the receive winding output.
2Measurement precision
If conventional signal processing is used, then the processing is simple, but false signals from eddy currents interfere with metal target detection
Solution Approach 1:
A nulling signal is introduced as an intermediary element that mediates between the transmit and receive windings. This nulling signal, derived from the transmit signal and adjusted in phase and amplitude, cancels out the unwanted eddy current signals from conductive soils before they reach the receive winding output.
Solution Approach 2:
The system dynamically adjusts parameters including the phase and amplitude of the nulling signal, as well as the timing of the receive window, to optimize cancellation of conductive soil signals while preserving metal target detection capability across varying soil conditions.
3Reliability
If the receive winding is placed close to the transmit winding, then the coupling is strong, but the received signal from soil eddy currents is too strong to null out
Solution Approach 1:
The detector winding is segmented into two distinct windings: a transmit winding for generating the magnetic field and a receive winding for detecting signals. This segmentation allows independent optimization of transmit and receive functions, enabling effective nulling of conductive soil signals while maintaining detection capability.
Solution Approach 2:
The transmit and receive windings are configured with asymmetric characteristics including different orientations, effective areas, and spatial positions. This asymmetry allows the receive winding to be optimized for detecting metal targets while the nulling process compensates for the reduced coupling with the transmit winding.
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 interference from conductive soils, enhancing the detection of metal targets by minimizing false signals and improving the sensitivity to both shallow and medium-depth targets, leading to increased accuracy and reliability in gold prospecting and other applications.
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 winding, which transmits a resulting varying magnetic field
Implementation Method 2
receiving a first receive magnetic field using the transmit winding during a receive period to produce a first receive signal; receiving a second receive magnetic field using a receive winding during the receive period to produce a second receive signal
Implementation Method 3
reduce or null detected signals within the indicator output signal due to received soil eddy currents from conducting soil components manifested in the first receive signal and the second receive signal
Data Source
AI summary
Provided is a method for detecting a metal target in soil using a metal detector including the steps of generating a transmit magnetic field for transmission into the soil using a transmit winding based on a transmit signal; receiving a first receive magnetic field using the transmit winding during a receive period to produce a first receive signal; and receiving a second receive magnetic field using a receive winding during the receive period to produce a second receive signal. The transmit winding and the receive winding are separated spatially; and producing an indicator output signal based on the first receive signal, the second receive signal and at least one synchronous demodulation function. The first receive signal includes first parameters that define a first transfer function transforming the first receive magnetic field into the first receive signal. The first parameters include an effective number of turns, a geometry of the transmit winding, and first electronic amplification transfer functions between the transmit winding and first receive signal. The second receive signal includes second parameters that define a second transfer function transforming the second receive magnetic field into the second receive signal. The second parameters include an effective number of turns, a geometry and a relative orientation of the receive winding with respect to the transmit winding, and second electronic amplification transfer functions between the receive winding and second receive signal. The first parameters and the second parameters are selected such that the first receive signal and the second receive signal are processed together to reduce or null detected signals within the indicator output signal due to received soil eddy currents from conducting soil components manifested in the first receive signal and the second receive signal; and where the selection of the first parameters relative to the second parameters are dependent on the synchronous demodulation function.