Filled polymeric materials are often used to control absorb EMI in electronic devices. The diagram on this slide shows an example where the incident wave (highlighted in blue) penetrates the material; the shield material will absorb, reflect, and transmit the energy from the incident wave. As can be seen from the diagram, the transmitted wave will be lesser with the reflection loss and absorption loss. Typically, the shielding effectiveness of the material is defined in decibels as a log function of the ratio between the transmitted wave and the incident wave. The reflected and transmitted waves can be measured with the proper equipment (typically a vector network analyzer or VNA).