Paul Colby said:No, why would one think so? The normal component of ##D=\epsilon(r)E## and the tangent component of ##E## are continuous across dielectric (actually all) material boundaries.
Not if as much ##D## flux exits as enters the volume as leaves which is actually the case. My suggestion is work a 1-D problem that's simple to solve completely. Try a 3 layer parallel plate capacitor with a void layer inside where you ignore fringing fields. Continuity of normal ##D## along with the total voltage drop yields an answer. You will find an ##E\ne0## in the air gap.Leonardo Machado said:But if i close a surface within the hole, there woud not be any charge inside, so ∫ D ⋅ dS = 0 and D = 0.
A cavity in a dielectric material is a void or empty space within the material that is surrounded by the dielectric material itself. It can also be referred to as a defect or imperfection in the material.
Cavities in dielectric materials can form through various processes, such as air bubbles during the manufacturing process, chemical reactions, or mechanical damage. They can also form over time due to environmental factors or stress on the material.
Cavities in dielectric materials can have a significant impact on the material's properties, such as reducing its strength, increasing its susceptibility to electrical breakdown, and altering its dielectric constant. They can also affect the material's overall performance and reliability.
There are various methods for detecting cavities in dielectric materials, including visual inspection, X-ray imaging, ultrasound testing, and electrical measurements. The most suitable method will depend on the size and location of the cavity, as well as the type of material.
In most cases, it is not possible to repair cavities in dielectric materials. However, depending on the material and the severity of the cavity, it may be possible to fill the void with a suitable material or seal it to prevent further damage. In some cases, the affected area may need to be replaced entirely.