Energy-saving glass is becoming very popular in building design due to their effective shielding of building interior against heat entering the building with infrared (IR) waves. This is obtained by depositing a thin layer of metallic-oxide on the glass surface using special sputtering processes. This layer attenuates IR waves and hence keeps buildings cooler in summer and warmer in winter. However, this resistive coating also attenuates useful microwave/RF signals required for mobile phone, GPS and personal communication systems etc. by as much as 30 dB. To overcome this drawback, a bandpass aperture type cross-dipole frequency selective surface (FSS) is designed and etched in the coatings of energy-saving glass to improve the transmission of useful signals while preserving IR attenuation as much as possible. With this FSS, 15-18 dB peak transmission improvement can be achieved, for waves incident with ±45° from normal for both TE and TM polarizations. Theoretical and measured results are presented.

Cross-Dipole Bandpass Frequency Selective Surface for Energy-Saving Glass Used in Buildings

This paper presents a dual-bandpass (DBP) frequency selective surface (FSS) based on hard-coating energy saving glass (ESG). The objective of this study is to generate a novel design of FSS on ESG, which is to be used for future energy smart buildings at Edith Cowan University (ECU). The ESG is made of a transparent coating of conducting layer on glass substrate, which attenuates infrared (IR) radiations for energy saving purpose. However the coating also attenuates useful UMTS and Wi-Fi signals which are necessary for the communication systems within the University. FSS technique is used to improve transmission of RF/MW signals through ESG by generating an array of patterns in the hard coating layer. The design of the DBP-FSS presented here has achieved transmission requirements for two specific frequency bands, with stable frequency response for both transverse electric (TE) and transverse magnetic (TM) polarization at normal and oblique incidence angles up to 60°. The double square loop (DSL)-FSS sustains 92.7% efficiency of ESG by attenuating IR radiations. This design methodology can be adapted as a general reference, which is suitable for applications under similar circumstances. Optimized design and theoretical results are presented.

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Transmission improvement of UMTS and Wi-Fi signals through energy saving glass using FSS

This paper outlines problems that cellular network operators will face as energy-efficient housing becomes more popular. We report measurement results from houses made of modern construction materials that are required to achieve sufficient level of energy-efficiency, but that impact heavily also on radio signal propagation. Energy-efficiency is especially important in northern countries, where houses need to be properly isolated as heating generates a big share of the total energy consumption of households. However, the energy-efficiency trend will also reach rest of the Europe and other warmer countries as the tightening energy-efficiency requirements concern also cooling the houses. The measurement results indicate severe problems originating from radio signal attenuation as it increases up to 35 dB for individual construction materials for cellular frequencies around 2 GHz. From the perspective of actual building penetration losses in modern, energy-efficient houses, average attenuation values even up to 30 dB have been measured. Additional attenuation is very sensitive to buildings materials, but could jeopardize cellular coverage in the future.

Radio signal propagation and attenuation measurements for modern residential buildings

A bandpass FSS design is presented for dual-layer energy saving glass panels, with the aim to improve RF communication in modern buildings. The proposed FSS design provides satisfactory transmission from 0.5 to 2 GHz. This design has several advantages over recently proposed dual-band FSSs: (a) its transmission bandwidth is significantly wider; (b) it does not block important communication signals such as GSM around 1800 MHz; and (c) it secures 2.45 GHz WLAN signals by confining them to the interior of the building.

Design of a bandpass FSS on dual layer energy saving glass for improved RF communication in modern buildings

Glass windows have undergone an energy saving evolution over the past three, four decades, from single panes till today's ultralow-emission windows. While the earliest energy saving windows were constructed as a sandwich of clear glass panes using the vacuum-flask principle, modern low-emission windows includes panes with coatings of metal and/or metal oxides. This coating has caused radio propagation problems for communication systems; something that may be utilized to protect a building from intentional electromagnetic interference (IEMI) attacks and to help protecting against information leakage. In this paper measurements of the shielding performance of different generations of windows and qualities of window panes are presented. The intention is to include the results in a guide-line for IEMI protection of critical infrastructures. Measurements are made using two complementary methods; in a nested reverberation chamber and in a semi-anechoic chamber, both over the range 1 – 18 GHz. The results show a clear generation dependency where the energy saving windows largely do not attenuate RF signals at all and low-emission windows offer shielding effectiveness values between 10 and 45 dB with potentially as much as around 60 dB in the upper half of the spectrum.

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Measurement of radio signal propagation through window panes and energy saving windows

This paper reports initial work on creating frequency selective surfaces (FSS) on modern day glass windows to improve the transmission of wireless/mobile/cellular communication signals through the glass. The manufacturers of these glass windows apply very thin layers of metallic oxides on one side of glass to provide extra thermal insulation. These coatings block the infrared and ultraviolet waves to provide thermal insulation, but they also attenuate communication signlas such as GSM 900, GSM 1800/1900, UMTS and 3G mobile signals. This creates a major communication problem when buildings are constructed using mostly such type of glass. A bandpass FSS can provide a solution to increase the transmission of useful bands through the coated glass. In order to design an appropriate FSS, the relative permittivity and conductivity of glass should be measured accurately. Moreover, electrical properties of the coated layer must also be known in order to obtain a resonance in the desired band. In this work, we used two different methods of measuring the permittivity and conductivity of glass. Electrical properties of one of the common glass windows (Optithermtrade SN) are presented. Simulations of Optitherm glass shows about 35 dB transmission loss over 900-2200 MHz frequency band.

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C.I. Kiani

Papers

Glass Characterization for Designing Frequency Selective Surfaces to Improve Transmission through Energy Saving Glass Windows