Planar Coil Spin Resonance Sensor for Banknote Eddy Current Suppression
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Solution Overview
Problem
Existing banknote authentication systems using spin resonance features face challenges with conflicting objectives of maximizing magnetic field strengths while minimizing coil size and eddy current induction, leading to reduced signal strength and operational inefficiencies, especially in high-speed processing.
Innovation Solution
A sensor element with a planar coil positioned in the air gap of a magnetic core, generating a modulation field, which suppresses eddy currents and allows for a compact design, enabling high signal strength and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If cylindrical coils are arranged in the air gap for generating the modulation field, then the field strength of the modulation field can be increased, but the overall size of the cylindrical coils increases and eddy currents are induced in the magnetic core
Solution Approach 1:
The patent transitions from cylindrical coils (three-dimensional arrangement around the magnetic core) to planar coils (two-dimensional arrangement in the air gap plane). This dimensional change allows the modulation field to be generated directly in the air gap without inducing eddy currents in the magnetic core, while maintaining sufficient field strength for spin resonance excitation.
Solution Approach 2:
The modulation field generation is extracted from the magnetic core structure (cylindrical coils wrapped around) and relocated to the air gap region (planar coils placed in the air gap). This separation removes the source of eddy current induction from the magnetic core while preserving the modulation field generation function in the air gap.
2Power
If the number of turns of cylindrical coils is increased to maximize modulation field strength, then the field strength increases, but the overall size of the coils increases
Solution Approach 1:
By changing from cylindrical to planar coil geometry, the patent achieves efficient use of space. Planar coils with multiple turns can be arranged in a compact two-dimensional pattern within the air gap, providing strong modulation fields without the volumetric constraints of cylindrical coils.
Solution Approach 2:
The planar coil design concentrates the magnetic field generation locally within the air gap region where it is needed for spin resonance excitation. This localized field generation eliminates the need for large cylindrical coils extending beyond the air gap boundaries.
3Power
If cylindrical coils are wound around the magnetic circuit, then the modulation field can be generated, but eddy currents are induced that weaken the modulation field and cause signal reduction
Solution Approach 1:
The modulation field generation function is extracted from the magnetic core and relocated to the air gap. Planar coils are positioned in the air gap to generate the modulation field directly where spin resonance excitation occurs, eliminating the intermediate step that induces eddy currents in the magnetic core.
Solution Approach 2:
The patent eliminates the harmful eddy current effect by changing the coil geometry and position. The planar coil configuration in the air gap generates the modulation field without inducing eddy currents, thereby converting the problematic cylindrical coil arrangement into a beneficial planar arrangement that enhances signal strength.
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 planar coil design achieves enhanced signal strength and reduced eddy current induction, facilitating reliable authenticity checks even at high speeds by optimizing magnetic field distribution and minimizing space requirements.
Implementation Method 1
a modulation device for generating a temporally varying magnetic modulation field in the air gap... the modulation device is formed by at least one planar coil arranged in the air gap
Implementation Method 2
a resonator for exciting the spin resonance feature of the data carrier to be checked... to detect the spin resonance signatures
Implementation Method 3
a magnetic core with an air gap into which the planar data carrier can be inserted... a polarization device for generating a static magnetic flux in the air gap
Implementation Method 4
the modulation field Bmod induces more eddy currents there... the magnetic field generated by the eddy currents has a polarity opposite to its cause, according to Lenz's law
Data Source
AI summary
A sensor element for checking the authenticity of a planar data carrier, in particular a banknote, has a spin resonance feature. The sensor element contains a magnetic core having an air gap, into which the planar data carrier can be inserted for authentication and which defines an axial direction extending between the adjoining surfaces of the magnetic core, a polarization device for generating a static magnetic flux in the air gap, a modulation device for generating a time-varying magnetic modulation field in the air gap, and a resonator for exciting the spin resonance feature of the data carrier to be checked. The modulation device is formed by at least one planar coil arranged in the air gap, which planar coil has one or more turns about the axial direction of the air gap in one plane. The disclosure also relates to a checking device having such a sensor element.