Advanced Materials for Electromagnetic Shielding

Fundamentals, Properties, and Applications

Maciej Jaroszewski, Sabu Thomas, Ajay V. Rane, Maciej Jaroszewski, Sabu Thomas, Ajay V. Rane

• Publisher: Wiley
• Year: 2018
• Print ISBN: 9781119128618
• eBook ISBN: 9781119128632
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

A comprehensive review of the field of materials that shield people and sensitive electronic devices from electromagnetic fields

Advanced Materials for Electromagnetic Shielding offers a thorough review of the most recent advances in the processing and characterization of the electromagnetic shielding materials. In this groundbreaking book, the authors—noted experts in the field—discuss the fundamentals of shielding theory as well as the practice of electromagnetic field measuring techniques and systems. They also explore applications of shielding materials used as absorbers of electromagnetic radiation, or as magnetic shields and explore coverage of new advancedmaterials for EMI shielding in aerospace applications. In addition, the text contains methods of preparation and applicability of metal foams.

This comprehensive text examines the influence of technology on the micro-and macrostructure of polymers enabling their use in screening technology, technologies of shielding materials based on textiles, and analyses of its effectiveness in screening. The book also details the method of producing nanowires and their applications in EM shielding. This important resource:

• Explores the burgeoning market of electromagnetic shielding materials as we create, depend upon, and are exposed to more electronic devices than ever
• Addresses the most comprehensive issues relating to electromagnetic fields
• Contains information on the manufacturing, characterization methods, and properties of materials used to protect against them
• Discusses the important characterization techniques compared with one another, thus allowing scientists to select the best approach to a problem

Written for materials scientists, electrical and electronics engineers, physicists, and industrial researchers, Advanced Materials for Electromagnetic Shielding explores all aspects in the area of electromagnetic shielding materials and examines the current state-of-the-art and new challenges in this rapidly growing area.

1
EMI Shielding Fundamentals

M. K. Aswathi¹, Ajay V. Rane^1,2, A. R. Ajitha¹, Sabu Thomas^1,3, and Maciej Jaroszewski⁴

¹ International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India

² Composite Research Group, Department of Mechanical Engineering, Durban University of Technology, Durban, South Africa

³ School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India

⁴ Faculty of Electrical Engineering, Wrocław University of Science and Technology, Wrocław, Poland

1.1 Fundamentals of EMI Shielding Theory

Electromagnetic shielding is process of reducing the dispersion of electromagnetic waves into a desired space by hindering the waves with a shield made of conductive material. The effective performance of electrical instruments or the working of electrical instruments is interrupted, degraded, obstructed, or limited due to the electromagnetic interference (EMI). In a material the main mechanisms for EMI attenuation are reflection, absorption, and multiple reflection [1, 2]. Reflection is the primary mechanism of EMI shielding. For reflection the material must possess mobile charge carriers such as electrons or holes that interact with the electromagnetic radiation. Metals are the most common material for EMI shielding and the available free electrons in metals interact with the electromagnetic waves [3]. If the material is highly conductive the shielding against EM (electromagnetic) waves will occur through the reflection mechanism. However, conductivity is not a condition for EMI shielding but it does enhance the reflection mechanism of an EMI shielding material.

The secondary mechanism for EMI shielding is absorption, which requires the existence of electric or magnetic dipoles to interact with the electromagnetic radiation. It changes with the thickness of the material. Materials that have a high dielectric constant provide electric dipoles and materials with high magnetic permeability provide magnetic dipoles for the EMI shielding by absorption [1].

The third mechanism is multiple reflections, which is the reflections at different surfaces or at the interface of the material. Materials that have large specific internal surfaces or composites with fillers show a multiple reflection mechanism. Generally, multiple‐reflection decreases the total shielding value if the material is thinner than the skin depth and the value can be neglected if the material has a higher thickness than the skin depth. At higher frequencies electromagnetic radiation penetrates only to the near surface region of the electrical conductor. This is known as the skin effect. The intensity of penetration of an electromagnetic wave decreases exponentially with increasing depth of the conductor [4]. The skin depth is the depth of the conductor at which the intensity of the incident field drops in to 1/e of the incident value and is denoted by δ [5]:

Here f is the frequency, μ is the magnetic permeability, and σ the electrical conductivity in Ω⁻¹ m⁻¹. Skin depth is not directly proportional to frequency, magnetic permeability, and conductivity, i.e. skin depth decreases with increase in frequency, magnetic permeability, or electrical conductivity. Owing to this skin effect, a material that contains a conductive filler with a small unit size of filler is more effective for shielding than a filler with a large unit size. The complete cross section of the filler unit can be used only when the unit size of the filler is less than or comparable with the skin depth.

Shielding effectiveness, which is expressed in dB, is the sum of reflection loss, absorption loss, and multiple reflections [6]. When electromagnetic waves strike the surface of an object they undergo reflection, multiple reflection, absorption, and transmission as shown in Figure 1.1. To be a shield against the EM wave, the material should reflect or absorb the electromagnetic wave. Factors determining shielding effectiveness (SE) are classified in Figure 1.2.

Figure 1.1 Schematic representation showing mechanism of electromagnetic shielding.

Figure 1.2 Factors determining shielding effectiveness [7].

Source: Adapted from Gooch 2007.

1.2 Materials for EMI Shielding

Owing to the increasing use of electronic equipment the shielding of other instruments and of human beings from electromagnetic waves is a very serious issue in the present scenario, which is detailed in Chapter 2. The EM waves harmfully affect both the device performance and human beings. Nowadays, a reduction in the use of electronic equipment is not always practical. What we are able to do is to reduce the penetration of EM waves produced from electronic instruments. To decrease the penetration we must use a shield or block the EM waves from the desired surface.

Metals are common...

Table of contents

• Cover
• Table of Contents
• 1 EMI Shielding Fundamentals
• 2 EM Noise and Its Impact on Human Health and Safety
• 3 Electromagnetic Field Sensors
• 4 Shielding Efficiency Measuring Methods and Systems
• 5 Electrical Characterization of Shielding Materials
• 6 Magnetic Field Shielding
• 7 Recent Progress in Electromagnetic Absorbing Materials
• 8 Flexible and Transparent EMI Shielding Materials
• 9 Polymer‐Based EMI Shielding Materials
• 10 Textile Based Shielding Materials
• 11 Graphene and CNT Based EMI Shielding Materials
• 12 Nanocomposites Based EMI Shielding Materials
• 13 Silver Nanowires as Shielding Materials
• 14 Advanced Carbon Based Foam Materials for EMI Shielding
• 15 Electromagnetic Interference Shielding Materials for Aerospace Application
• 16 Metamaterials as Shielding Materials
• 17 Double Percolating EMI Shielding Materials Based on Polymer Blend Nanocomposites
• 18 Mechanical Performance Characterization of EMI Shielding Materials Using Optical Experimental Techniques
• Index
• End User License Agreement