Metal Detector Receive Screen Circuit for Faster Transient Decay
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Solution Overview
Problem
Existing metal detectors face challenges in reducing the decay time of receive signal transients, which affects the sensitivity to short time-constant targets due to higher-order internal resonances caused by inter-winding distributed capacitance and mutual inductance, leading to spurious signals during synchronous demodulation.
Innovation Solution
The implementation of an electrostatic screen connected to an electronic circuit that reduces the effective capacitance presented to the receive winding, utilizing a phase-shifted signal to accelerate the decay of transients and lower the Q factor of higher-order internal resonances, thereby improving the sensitivity and reducing unwanted ringing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an electrostatic screen is added to cover the winding, then shielding effect is improved, but effective capacitance increases causing higher-order internal resonances
Solution Approach 1:
The patent applies feedback by connecting the electrostatic screen to receive phase-shifted signals from the winding through electronic circuits. This feedback connection allows the screen to actively counteract the harmful capacitive effects and reduce higher-order internal resonances while maintaining the shielding benefit
Solution Approach 2:
The patent changes the electrical parameters by introducing phase-shifted signals to the electrostatic screen, which modifies the effective capacitance presentation. This parameter change transforms the screen from a passive capacitive load into an active component that can reduce resonances
2Measurement precision
If decay time of receive signal transients is reduced, then sensitivity to short time-constant targets is improved, but spurious signals increase due to higher-order internal resonances
Solution Approach 1:
The feedback connection to the electrostatic screen with phase-shifted signals actively suppresses higher-order internal resonances, thereby reducing spurious signals while allowing the decay time to be reduced for improved sensitivity
Solution Approach 2:
The electrostatic screen acts as an intermediary element that, when connected to phase-shifted signals, mediates between the winding and the higher-order resonances, filtering out spurious signals while permitting useful signal detection
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 significantly reduces the decay time of receive signal transients and minimizes spurious signals, enhancing the detector's ability to identify short time-constant targets by effectively managing higher-order internal resonances, resulting in improved sensitivity and accuracy.
Implementation Method 1
reduce an effective capacitance presented by the electrostatic screen to the winding
Implementation Method 2
a winding with a plurality of turns, for receiving a magnetic field
Data Source
AI summary
A metal detector for detecting a target, the metal detector including: a transmitter for transmitting a transmitted magnetic field; a receiver, including a winding with a plurality of turns, for receiving a magnetic field; and a receive electronics connected to the winding for receiving signals from the winding. The receiver further includes an electrostatic screen covering at least part of the winding. The electrostatic screen is connected to an electronic circuit to receive signals from the receiver to reduce an effective capacitance presented by the electrostatic screen to the winding.