RESEARCH ARTICLE Frequency spectrum analysis of lightweight foamed concrete using microwave dielectric measurement technique Kim Yee Lee 1 | Yeong-Nan Phua 1 | Siong-Kang Lim 1 | Kok Yeow You 2 | Ee Meng Cheng 3 1 Lee Kong Chian Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Bandar Sungai Long, Selangor, Malaysia 2 Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia 3 School of Mechatronic Engineering, University Malaysia Perlis, Arau, Perlis, Malaysia Correspondence Kim Yee Lee, Lee Kong Chian Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Bandar Sungai Long, Selangor 43000, Malaysia. Email: kylee@utar.edu.my Abstract The dielectric characterization of concrete is a significant parameter to study the microwave signal transmission for the building materials. In this paper, a microwave mea- surement system has been developed using open ended coaxial sensor and vector network analyzer for frequency spectrum analysis of lightweight foamed concrete. The measurement setup is validated prior to make sure the system is working properly. The results of dielectric con- stant and loss factor of different densities lightweight concrete samples are measured and analyzed from 150 kHz to 8 GHz. From the analysis, the lightweight foamed concrete is a frequency spectrum friendly building mate- rial. In addition, the relationship between the dielectric constant and density of the lightweight foamed concrete is found to be interrelated. The empirical modeling of some selected frequencies has been formed. The models are useful for the future application on determining the dielectric constant and characteristic of lightweight con- crete samples. KEYWORDS dielectric measurement, frequency spectrum analysis, lightweight foamed concrete, open ended coaxial sensor 1 | INTRODUCTION Every material has a special set of electrical characteristics that are based on its dielectric properties. Dielectric properties are intrinsic characteristics of a material, when exposing to micro- wave field, it explains the behavior of the wave-matter interac- tion. A dielectric measurement is able to provide crucial design parameter and information for many applications. In micro- wave field, these properties are very significant for instants it can be used to measure the moisture content of a material, 1–3 freshness of a product, 4,5 and concentration of a sample. 6 The frequency spectrum analysis in various fields is become more significant in recent year. 7–10 Among all, the open ended coaxial is one of the popular non-destructive dielectric sensor 11 for frequency spectrum analysis. In open- ended coaxial measurement, the measured effective relative permittivity is highly depending on the sensor dimension and the sample thickness. 12 Several models such as capaci- tance model, admittance model, virtual line model and modi- fied capacitance model have been studied. 13 The complicated mathematical calculation can be eased by using MATLAB algorithms for the dielectric determination. Besides, the dielectric spectroscopy of a sample under test can be interrelated with the important parameters and can be derived using a coaxial sensor inverse model. 14 On the other hand, concrete is one of the most important material among all building materials. 15 Foamed concrete is made by introducing air or other gas into a cement mortar slurry, which air voids are entrapped in mortar by suitable foaming agent. Foamed concrete possesses high flow ability, low self-weight, minimal consumption of aggregate, con- trolled low strength, and excellent thermal insulation. The air voids in foamed concrete are considered as a primary factor which influences the strength and density. The higher strength to density ratio is attributed to the comparatively uni- form distribution of pore in foamed concrete with fine sand, while pores were larger and irregular for mixes with coarse sand. 16 Even though the lightweight foamed concrete is one of the recent advancement of concrete technology in civil Received: 29 July 2018 DOI: 10.1002/mop.31636 Microw Opt Technol Lett. 2018;1–7. wileyonlinelibrary.com/journal/mop © 2018 Wiley Periodicals, Inc. 1