Equipment shielding

Goals

The objectives of the training Equipment shielding :

Design an electronic box incorporating shielding concepts and optimising protection methods.

The aim of this training course is to:

• Understand shielding theory


• Be able to analyse and deal with openings


• Master the wiring and filtering of input/output interfaces


• Learn case metallisation techniques


• Learn how to measure shielding

Program

1 – Introduction
• EMC characterisation of equipment
• Common mode / Differential mode
• Origins of common mode current
• The two types of electronic radiation
• Impedance of cylindrical conductors
• Roles of a shield
• Definition of shielding effectiveness
• Connecting 0 V to the chassis
• Use of decibels


2 – Shielding: theory
• What is a field?
• Propagation and coupling between E and H fields
• Near field/far field zone
• Modes of operation of a shield
• Impedance of a shield
• Reflection according to field impedance
• Skin depth/absorption
• Cowdell charts
• Shielding: selection criteria
• Magnetic and non-magnetic materials
• Very low frequency fields
• Magnetic field and induction
• Field line deflections
• Risk of saturation


3 – Actual shielding
• Necessity of openings
• Calculation principle
• Shielding attenuation of a slot
• Attenuation of a grid
• Case of multiple openings
• Effectiveness of a guide opening
• Example of a guide / Honeycomb
• Shielding effectiveness of an enclosure
• Baffle effect
• Example of a magnetic screen
• Examples of shielding on a board
• Examples of welded/removable screens
• Use of near-field probes
• Conductive seals


4 – Cable treatment
• Example of internal cabling
• The three methods for preventing HF common mode
• Circulation of HF currents
• Implementation of connectors
• Grouping of inputs/outputs
• Wall-mounted filters
• Filter assembly/examples
• Transfer impedance of shielded cables
• Connection of shielded connectors
• Tubes and textiles for over-shielding


5 – Improving shielding
• General principle
• Hot spots
• Criticality of leaks
• Tinned iron cover
• Cabinet resonance and damping
• Example of absorbent material
• The two topologies for visualization
• Treatment of accessible components
• Shielding accessories: examples
• Effectiveness of a conductive seal
• Effect of pressure/deformation
• Implementation of a conductive seal
• Be careful with adhesive seal glue
• Conductive fingers and springs
• Electrochemical couples
• Use of spring fingers
• Required quality depending on the area
• Electrochemical couples
• Wires are antennas
• Internal wiring
• Coupling near a ground plane
• Electronic/mechanical coordination
• Makeshift filter connectors
• Shielding development stage
• Recurring errors
• Visual inspection
• Industrialized shielded enclosures
• Light bulb method
• Aluminum chrome plating


6 – Plastic enclosures
• Conductive composites
• Conductive paints
• Arc/flame zinc coating
• Vacuum/cathodic metallization
• Chemical/electrolytic deposits
• Metallized plastic enclosures
• Simple shielding in plastic enclosures
• Simple measurement of a coating


7 - Shielding measurements
• Practical attenuation measurement
• Calibration before measurement
• Measurement of a small enclosure
• IEC 61587-3 standard
• IEEE 299 standard
• Recommended measurement procedure