Active Shielding Eddy Current Coil for PCB Magnetic Field Concentration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Eddy Current Testing (ECT) probes on printed circuit boards face challenges in concentrating magnetic fields within the region of interest while avoiding non-relevant features, particularly due to the limitations of magnetic and conductive shielding methods, which are not compatible with PCB manufacturing processes and are ineffective at low frequencies or for overlapping coil configurations.
Innovation Solution
The implementation of an active shielding coil, concentrically arranged with the test coil and connected in series but wound in the opposite direction, generates a nulling field to restrict the magnetic field to the desired area, allowing operation over a broad frequency range without ferromagnetic or thick conductive materials, enabling multiple coil configurations and overlapping layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If magnetic shielding (ferrite ring) is used to concentrate the magnetic field, then the magnetic field is concentrated into a tighter area around the coil, but the shielding is not compatible with PCB manufacturing processes
Solution Approach 1:
The patent replaces the mechanical magnetic shielding structure (ferrite ring) with an electromagnetic field-based solution (active shielding coil). The active shielding coil generates a magnetic field that actively cancels out the magnetic field in unwanted areas, achieving field concentration without requiring physical shielding materials that are incompatible with PCB manufacturing processes.
2Area of stationary object
If conductive shielding (copper ring) is used to concentrate the magnetic field, then the magnetic field is concentrated, but the shielding effectiveness is strongly tied to test frequency and limits use to very high frequencies
Solution Approach 1:
The patent changes the operational parameters of the shielding mechanism by using an active coil that can be driven at any frequency. Unlike passive conductive shields whose effectiveness depends on skin effect at high frequencies, the active shielding coil can generate the necessary counteracting magnetic field at any frequency including DC, enabling versatile operation across the entire frequency spectrum from 0 Hz to 25 MHz and beyond.
3Ease of manufacture
If conventional shields are made thin to enable overlapping coils, then manufacturing becomes easier, but the shield of a first coil interacts with a second overlapped coil causing both coils to fail operation
Solution Approach 1:
The patent introduces an active control mechanism as an intermediary between overlapping coils. Each coil is equipped with an active shielding coil that detects and counteracts the magnetic field from adjacent coils, acting as a mediator that prevents harmful interactions. This allows multiple coils to be stacked or overlapped on the same PCB without mutual interference, maintaining both ease of manufacture and operational reliability.
4Area of stationary object
If conventional shields are used, then magnetic field concentration is achieved, but the shields are unable to operate properly at DC or very low frequency
Solution Approach 1:
The patent transforms the static passive shielding approach into a dynamic active shielding system. The active shielding coil is driven by a controllable current source that can adjust its output in real-time based on the operating frequency. This dynamic capability allows the system to maintain effective magnetic field concentration even at DC and very low frequencies where passive shields fail, as the active coil can generate the precise counteracting field needed regardless of frequency.
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 solution effectively confines the magnetic field to the test coil's footprint, enabling flexible and cost-effective ECT probes suitable for various frequencies, including DC to 25 MHz, and allows for multiple overlapping coils, enhancing the sensitivity and versatility of ECT systems.
Implementation Method 1
The field magnitude generated by the active shielding coil is set to null the field(s) generated by the test coil at a field nulling line, which is located outside the desired test coil(s) sensing area
Implementation Method 2
such systems include field producing means such as a coil connected to an AC source to generate Eddy currents in a part
Implementation Method 3
ECT inspection is commonly used in NDT/NDI applications to detect flaws in surfaces of manufactured components fabricated out of conductive materials
Implementation Method 4
Magnetically shielded probes have their coil surrounded by a ring of ferrite or other material with high permeability and low conductivity. The ferrite creates an area of low magnetic reluctance and the probe's magnetic field is concentrated in this area
Implementation Method 5
The portion of the coil's magnetic field that cuts across the shielding will generate eddy currents in the shielding material rather than in the nonrelevant features outside of the shielded area. The higher the frequency of the current used to drive the probe, the more effective the shielding will be due to the skin effect in the shielding material
Data Source
AI summary
A shielded eddy current coil probe is formed on a printed circuit board and comprises a first coil component forming a test coil and a second coil component forming an active shielding coil. The test coil and the active shielding coil are concentrically arranged and the number of coil windings in the active shielding coil and the field direction thereof are configured to limit the induced field or the sensed field in the test object to the footprint area of the test coil on the test object. Multiple sets of test coils with active shielding coils can be provided on the same or different layers of the printed circuit board to realize different driver, receiver and combined driver/receiver coil configurations.