Metal Detector Transmit Electronics for Magnetic Soil Interference
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Solution Overview
Problem
State-of-the-art metal detectors face challenges in accurately distinguishing metal targets from magnetic soil signals, particularly in environments with ferrimagnetic materials, due to unpredictable reactive voltage components and non-linear behavior in receive electronics, which complicates the cancellation of magnetic soil signals and reduces sensitivity to long time constant targets.
Innovation Solution
The method involves generating a constant reactive transmit coil voltage approximately equal to zero, allowing for improved accuracy and sensitivity by maintaining a non-zero transmit coil current, which reduces environmental magnetic interference and enhances target detection, especially for long time constant targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-zero reactive voltages are transmitted during resistive synchronous demodulation, then metal target detection capability is maintained, but X contamination from magnetic soils causes non-linear behavior in receive electronics and reduces measurement precision
Solution Approach 1:
The patent applies periodic action by transmitting reactive voltage during specific time intervals (first and second periods) and maintaining zero reactive voltage during other intervals (third and fourth periods). This periodic transmission pattern allows the system to achieve both metal target detection during active periods and reduced X contamination during zero-voltage periods, resolving the contradiction between maintaining detection capability and eliminating harmful interference.
Solution Approach 2:
The patent implements preliminary anti-action by pre-establishing a zero reactive voltage condition during the third and fourth periods before metal target signals are demodulated. This preliminary zero-voltage state proactively prevents X contamination from magnetic soils from interfering with the receive electronics, thereby maintaining measurement precision without requiring complex post-processing corrections.
2Reliability
If reactive voltage is transmitted continuously to maintain sensitivity to metal targets, then target detection capability is improved, but power consumption increases and sensitivity to long time constant targets decreases
Solution Approach 1:
The patent uses periodic action to transmit reactive voltage only during necessary intervals (first and second periods) and maintain zero voltage during other intervals (third and fourth periods). This periodic pattern reduces overall power consumption while maintaining sensitivity to long time constant targets during the active transmission periods, resolving the contradiction between continuous transmission benefits and power consumption costs.
Solution Approach 2:
The patent maintains continuity of useful action by ensuring that the transmit coil current remains non-zero during the third and fourth periods even though reactive voltage is zero. This continuous current flow preserves the magnetic field necessary for detecting long time constant targets while eliminating the power-consuming reactive voltage component, thereby maintaining reliability with reduced energy consumption.
3Object-affected harmful factors
If transmit coil current is reduced to minimize magnetic soil interference, then environmental magnetic interference is reduced, but sensitivity to metal targets decreases
Solution Approach 1:
The patent applies local quality by differentiating the function of transmit coil current from reactive voltage. The current is maintained at non-zero levels to preserve target detection sensitivity, while the reactive voltage component is set to zero during specific periods to eliminate magnetic soil interference. This local differentiation of parameters allows the system to independently optimize for both sensitivity and interference reduction.
Solution Approach 2:
The patent segments the transmission waveform into distinct time periods with different characteristics: active periods (first and second) for metal target detection and zero-voltage periods (third and fourth) for interference minimization. This segmentation allows the system to achieve both high sensitivity during active periods and low environmental interference during zero-voltage periods, resolving the contradiction between maintaining current for sensitivity and reducing current for interference mitigation.
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 results in a metal detector system with high power efficiency and improved sensitivity to metal targets while minimizing interference from magnetic soils, achieving better performance compared to pulse induction systems.
Implementation Method 1
a transmit coil which may transmit an alternating magnetic field associated with a reactive transmit coil voltage
Implementation Method 2
receive electronics which may receive a magnetic field and process received signals to produce an indicator output
Data Source
AI summary
An electronic metal detector having, a transmit coil arranged and adapted to transmit an alternating magnetic field associated with a reactive transmit coil voltage, the transmit coil being connected to transmit electronics arranged and adapted to generate a transmit signal, the transmit electronics having at least two power sources, a first power source and a second power source, wherein the first power source is adapted and arranged to connect to the transmit coil for at least a first period, and the second power source is adapted and arranged to connect to tie transmit coil for at least a second period, the said transmit electronics including at least one servo control negative feedback loop, a first servo control negative feedback loop, which is adapted and arranged to monitor a transmit coil current for at least part of the said first period, and to control at least part of the said transmit signal, the transmit electronics being adapted and arranged to control the transmit signal to produce the reactive transmit coil voltage to be approximately constant and approximately equal to zero while the transmit coil current is non-zero and approximately constant for at least part of the first period; and receive electronics which are adapted and arranged to receive and process a receive magnetic field during at least some of the first period to produce an indicator output.