Intermediate and low radiofrequency electromagnetic field transmission properties in case of common building materials

摘要

Controlling exposure to the electromagnetic fields (EMFs) may serve many causes: to protect sensitive electronic equipment from outside interference; to protect the environment from the high radiation generating equipment; to protect humans from excess radiation etc. Strong EMFs may be encountered in public domain but especially in occupational settings, where the process and technology of work requires the EMFs. Technical measures to manage risks may include using construction materials. In this study the intermediate and low radiofrequency transmission characteristics in case of building materials were investigated. The measurements are called for to determine the amplitude of the electric and magnetic field at the close proximity to the material. A set of common building materials was selected, widely used in modern constructions. The included materials can broadly be divided into three groups: load bearing materials, thermal insulation materials and cover materials. Altogether 17 building materials were tested, forming an overview of some most common materials in construction of houses. The testing was done at 2, 20 and 200 kHz frequencies. The measurement point was in close proximity (10mm) to the material under testing. The electromagnetic irradiator point was on the other side of the material, 150 mm from the measurement sensor. Somewhat frequency dependent variation in the amplification could be observed only in few cases: gypsum panel, aerated concrete, LECA, gypsum board and solid wood. The highest electric field amplification was measured for some materials, up to 5.6 dB increase: custom made gypsum panel, aerated concrete, LECA, gypsum board, high performance concrete plate, solid wood. The results show for the selected samples that semiconductive materials which cannot be grounded due to the high resistance, electric fields may be amplified several folds in close proximity to the material.