Metal Detector Coil Layout for Soil Signal Nulling
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Solution Overview
Problem
Existing metal detector coils face challenges in effectively canceling out spurious signals from magnetic soils, particularly in saturable soils, while maintaining sensitivity to buried targets, due to issues like saturation and sensitivity to surface soil inhomogeneities, which reduce the capability to detect weak targets.
Innovation Solution
The design incorporates a hand-held metal detector coil with separate transmit and receive windings, where the transmit windings are oriented perpendicular to the coil housing bottom plane and spaced further away, and receive windings are positioned to minimize coupling with surface soils, using out-of-phase connections to reduce mutual inductance and enhance target detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the transmitted magnetic field is significantly intense enough to penetrate deeper into the soil, then the detection depth is improved, but soil saturation occurs which produces spurious signals and reduces the capability of locating the weakest detectable targets
Solution Approach 1:
The coil is divided into two separate windings: a transmit winding for generating the magnetic field and a receive winding for detecting signals. This segmentation allows independent optimization of each winding's characteristics, enabling deeper penetration without excessive saturation effects in the receive winding.
Solution Approach 2:
The transmit and receive windings are positioned at different locations within the coil housing, with the receive winding spaced further from the bottom plane. This creates local quality differences in magnetic field intensity, exposing the receive winding to weaker fields that reduce saturation while maintaining detection sensitivity.
2Measurement precision
If the coil is positioned close to the soil surface to detect shallow targets, then the sensitivity to shallow targets is improved, but the sensitivity to surface soil inhomogeneities increases which reduces the capability to detect weak targets
Solution Approach 1:
The receive winding is positioned at a different location (further from the bottom plane) than the transmit winding, creating local quality differences in exposure to surface soil effects. This spatial differentiation reduces the receive winding's sensitivity to surface inhomogeneities while maintaining overall detection capability.
Solution Approach 2:
The receive function is extracted and separated from the transmit function, with the receive winding positioned to minimize coupling with surface soils. This extraction allows the receive winding to operate with reduced sensitivity to surface effects.
3Device complexity
If a single coiled winding is used for both transmit and receive functions, then the device complexity is reduced, but the capability to cancel out magnetic soil signals is insufficient
Solution Approach 1:
The single winding is segmented into two separate windings (transmit and receive), enabling independent optimization of each function. This segmentation provides the structural basis for effective ground balancing while maintaining relatively simple overall device design.
Solution Approach 2:
The transmit and receive windings are combined within a single coil housing structure, maintaining device simplicity while achieving the functional separation needed for effective ground balancing and signal cancellation.
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 configuration reduces soil saturation signals and improves target detection by minimizing sensitivity to surface soil inhomogeneities, allowing for better detection of buried targets in various soil conditions.
Implementation Method 1
inductive coiled windings that act to transmit time-changing magnetic fields and to receive time-changing magnetic fields
Implementation Method 2
inductive coiled windings that act to transmit time-changing magnetic fields and to receive time-changing magnetic fields
Implementation Method 3
The windings are often surrounded by an electrostatic (ES) screen within the coil housing, with the ES screen connected to a 'ground' reference potential of the detector electronics. This acts to screen out external EMI electric fields coupling into the receiver
Implementation Method 4
using out-of-phase connections to reduce mutual inductance and enhance target detection
Implementation Method 5
Magnetic soils contain super-paramagnetic viscous remnant magnetic particles (called VRM) that are highly relevant to metal detectors, namely, single crystal ferrite particles with dimensions about the 30 nm range. Each particle has an associated time-constant that are Arrhenius temperature dependent. Basically, this time-constant determines how frequently the direction of the magnetism of the particle spontaneously randomly changes direction
Implementation Method 6
if the transmitted magnetic field is significantly intense enough, some of these 'X' components may exhibit Rayleigh hysteresis, and this in turn modifies the field non-linearly with transmitted field intensity within the soil applied to the VRM components
Implementation Method 7
yet further, magnetostriction present in some magnetic particles also may respond non-linearly
Data Source
AI summary
A hand-held metal detector coil, including a coil housing which houses aggregate transmit windings and aggregate receive windings. The aggregate transmit windings include a major group of transmit windings that includes a first transmit winding, and the aggregate receive windings include a major group of receive windings that includes a first receive winding; the coil further includes a minor group of windings to null the aggregate receive windings with respect to the aggregate transmit windings. In an absence of external influences, a mutual inductance coupling coefficient between the aggregate receive windings and the aggregate transmit windings, kTR, is <0.03. A mean location of turns of the major group of transmit windings is further from a bottom plane of the coil housing than a mean location of turns of the major group of receive windings; the first transmit winding has at least part of their cross-sectional winding profile with a first cross-sectional axis longer than a second cross-sectional axis by at least a factor of 3; a mutual coupling constant coefficient between the major group of transmit windings and the major group of receive windings, k11, is <0.5; and a mean location of turns of the of the first transmit winding is at least 25 mm or more from a bottom plane of the coil housing.