Multi-Frequency Metal Detection With Bandstop Signal Separation
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Solution Overview
Problem
Existing metal detection systems struggle to accurately detect metallic objects of varying sizes on or in conductive or dielectric objects with high sensitivity, especially when electrical or dielectric properties interfere with the detection process.
Innovation Solution
A device utilizing a transmitting unit with multiple resonant frequencies, a receiving unit with symmetrically arranged receiving coils, and a filtering unit with bandstop filters to separate and evaluate signals at different frequencies, enhancing sensitivity and resistance to interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bandpass filters are used to separate partial signals at different operating frequencies, then signal separation is achieved, but the filters exhibit high sensitivity to small frequency shifts and temperature drifts, reducing detection reliability
Solution Approach 1:
The patent inverts the conventional filtering approach by using bandstop filters instead of bandpass filters. Rather than passing only the desired frequency range and blocking others, the bandstop filters block the unwanted frequencies while passing the desired signals with minimal phase distortion. This inversion resolves the technical contradiction by achieving signal separation without the high phase sensitivity characteristic of narrowband bandpass filters.
Solution Approach 2:
The patent changes the filter type parameter from bandpass to bandstop, fundamentally altering the frequency response characteristics. This parameter change enables the system to achieve frequency separation while maintaining low sensitivity to frequency shifts and temperature drifts, as bandstop filters have flatter phase responses in their passbands compared to narrowband bandpass filters.
2Adaptability or versatility
If multiple operating frequencies are used to detect metallic objects of varying sizes, then detection coverage is improved, but the system complexity increases due to the need for multiple resonant circuits and filtering mechanisms
Solution Approach 1:
The patent combines multiple operating frequencies into a single detection system using a multiply resonant oscillating circuit. This merging approach allows the system to operate at several frequencies simultaneously or switchably, maintaining versatility for detecting metallic objects of varying sizes while reducing overall system complexity compared to using separate detection systems for each frequency.
Solution Approach 2:
The patent implements a universal filtering mechanism using bandstop filters that can handle multiple frequency components. The same filter structure effectively separates signals at different operating frequencies, making the system multi-functional without requiring separate filtering paths for each frequency, thus reducing device complexity while maintaining adaptability.
3Adaptability or versatility
If the transmitting coil is part of a resonant circuit with switchable capacitor values, then the operating frequency can be optimized for different detection scenarios, but the adjustment complexity and potential for frequency drift increase
Solution Approach 1:
The patent introduces dynamic frequency adjustment capability through switchable capacitor values in the resonant circuit. This allows the operating frequency to be optimized for different detection scenarios by switching between predetermined capacitor values, providing adaptability while maintaining a relatively simple implementation through discrete switching rather than continuous adjustment mechanisms.
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
The device achieves high sensitivity in detecting metallic objects by minimizing interference from conductive or dielectric properties, allowing reliable detection of small metallic objects even on moving objects.
Implementation Method 1
a transmitting unit with a transmitting coil (7) generates an alternating magnetic field having several operating frequencies
Implementation Method 2
A receiving unit of the device detects the alternating field influenced by the moving objects with at least one receiving coil and outputs a received signal dependent on the detected alternating electric field
Implementation Method 3
The filtering unit of the device bandstops each of the partial signals corresponding to one of the operating frequencies with respect to all other operating frequencies
Data Source
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AI summary
The invention relates to a device (1) for detecting metal objects (2) in and on articles (3) moving relative to the device (1), comprising a transmission device (10) for producing a magnetic alternating field at multiple working frequencies using a transmission coil (7), a receiving device (11) for detecting the magnetic alternating field influenced by the moving articles (3) using at least one receiving coil (8, 9) and outputting a received signal based on the detected magnetic alternating field, a filter device (14) for filtering partial signals, each of which is associated with one of the working frequencies, out of the received signal, and an analysis device (13) for analyzing the partial signals. For each of the partial signals associated with one of the working frequencies the filter device (14) carries out a band-stop filtering process with respect to all of the other working frequencies.