Air-Core Coil Thickness Sensing for Banknote Adhesive Detection
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Solution Overview
Problem
Existing devices for detecting thickness variations in flat objects, such as banknotes, struggle to achieve high sensitivity for adhesive strips and lateral resolution, making it difficult to distinguish between single and multiple banknotes or thickness changes caused by adhesive strips.
Innovation Solution
A device utilizing air-core coils and electrically conductive elements that create an alternating magnetic field, where the deflection of guide elements relative to each other influences the resonant frequency and damping of an LC oscillating circuit, allowing for sensitive detection of thickness variations and lateral resolution through a multiplexed signal processing system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thickness measurement devices are used, then the device structure is simple, but the sensitivity for detecting adhesive strips is insufficient
Solution Approach 1:
The patent replaces conventional mechanical thickness measurement systems with an electromagnetic sensing system. Flat air-core coils generate alternating magnetic fields that interact with conductive elements on the banknote, detecting thickness variations through changes in resonant frequency and damping of LC oscillating circuits. This substitution enables high sensitivity detection of adhesive strips while maintaining a relatively simple overall device structure.
Solution Approach 2:
The patent utilizes changes in electromagnetic parameters (resonant frequency and damping) of LC oscillating circuits to detect thickness variations. When the distance between the coil and conductive element changes due to thickness variation, the resonant frequency and damping characteristics change, providing a sensitive measurement mechanism for detecting even small adhesive strip thicknesses.
2Measurement precision
If conventional thickness detection methods are used, then the device is inexpensive, but the lateral resolution is insufficient to distinguish multiple banknotes
Solution Approach 1:
The patent divides the sensing area into multiple discrete flat air-core coils arranged in a matrix or array. Each coil can independently detect thickness variations in its specific region, providing lateral resolution to distinguish between multiple banknotes. This segmentation enables spatially resolved measurements while using simple, inexpensive flat coils that can be manufactured using printed circuit board techniques.
Solution Approach 2:
The patent uses multiple copies of the same simple flat coil structure arranged in different positions. Each coil is identical in design and can be manufactured using the same low-cost printed circuit board process, yet collectively they provide lateral resolution through their spatial arrangement. This copying approach achieves complex sensing capability with simple, repeatable manufacturing.
3Measurement precision
If mechanical roller deflection methods are used, then the device is simple to operate, but the sensitivity for detecting small thickness variations is insufficient
Solution Approach 1:
The patent replaces mechanical roller deflection methods with an electromagnetic field-based sensing system. Flat air-core coils generate alternating magnetic fields that penetrate the banknote and interact with conductive elements, detecting thickness variations through electromagnetic parameter changes rather than mechanical deflection. This substitution maintains ease of operation while dramatically improving sensitivity for detecting small thickness variations caused by adhesive strips.
Solution Approach 2:
The patent employs oscillating electromagnetic fields at resonant frequencies of LC circuits to enhance detection sensitivity. The alternating magnetic field from the flat coils excites resonant oscillations in the LC circuit, and thickness variations cause measurable changes in the resonant frequency and damping. This vibrational approach to electromagnetic sensing provides high sensitivity while keeping the system simple to operate.
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 provides high sensitivity for detecting adhesive strips and thickness variations, enabling accurate differentiation between single and multiple banknotes, with a cost-effective design using printed circuit board coils and conductive materials, and is temperature-independent due to frequency-selective measurement.
Implementation Method 1
a flat air-core coil (6), which generates an alternating magnetic field
Implementation Method 2
The alternating field causes eddy currents in the electrically conductive, i.e. mostly metallic but not ferromagnetic, material of the conductive element (7)
Implementation Method 3
the deflection of a second guide element (2) relative to an opposite first guide element (1) is detected via an electrically conductive element (7) by at least one flat air-core coil (6), which generates an alternating magnetic field
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
The invention relates to a device essentially characterised in that, on transport of a planar object, in particular, a value note, through guide elements (1, 2), the deflection of one or more secondary guide elements (2) relative to a first guide element (1) is recorded by one or more planar air-core coils (6) with an electrically-conducting element (7). A magnetic alternating field is hence generated which is influenced by a change in position of the electrically-conducting element (7). The alternating field generates eddy currents in the electrically-conducting element (7). These in turn affect the alternating field. When the planar coils are each part of an L.C. tuned circuit resonance frequencies and damping of said tuned circuit are affected. With a constant supply frequency the oscillation amplitude is altered.