# Vibration Reduction of an Existing Glass Window through a Viscoelastic Material-Based Retrofit
## 1 Introduction  
Windows, the interface between the indoor and outdoor environments, play highly important roles in creating comfort for residents. A glass window has important functions, such as allowing natural lighting, providing thermal insulation, and providing sound isolation [1]. Since the damping ratio of a window glass panel is relatively low, when subjected to mechanical excitations, such as those induced by a passing train [2], window glass often generates considerable noise, lowering residential comfort. In some cases, large vibrations can even result in broken glass and the injury of people. Over the past several decades, research on the vibration control of civil structures and mechanical systems attracted much attention. Various control methods were developed and implemented to attenuate vibration [3]. Tuned mass dampers (TMDs) [4], which are effective and reliable for suppressing undesirable vibrations induced by winds and earthquake loads, were extensively utilized in tall buildings and towers. Recently, bounding-tuned mass dampers [5; 6; 7] and eddy-current-tunedmass dampers [8; 9] were proposed for structural vibration control. As a passive device, particle dampers were studied for the vibration control of various systems [10; 11; 12; 13]. In addition, vibration isolation was researched for structural vibration reduction [14; 15; 16]. In recent years, semi-active devices received attention for vibration control. Semi-stiffness control devices were adopted to control the stiffness of structures in an effort to establish a non-resonant condition during earthquakes [17; 18]. Electrorheological (ER) dampers [19; 20; 21] with controllable damping forces were reported for the vibration control of civil structures. Magnetorheological (MR) dampers [22; 23; 24; 25; 26; 27] are essentially the magnetic equivalent of ER dampers, where the control effect is governed by a magnetic field, instead of an electric field. With much larger control forces, MR fluid dampers were applied in structural vibration control [28; 29; 30]. Due to their advantages regarding efficient energy dissipation, viscous dampers [31; 32; 33; 34; 35; 36] were widely utilized in civil structures to control seismic, wind-induced, and thermally induced vibration. In addition, viscoelastic damping materials found many applications in automobile and aerospace structures [37]. Viscoelastic dampers (VEDs) were demonstrated as effective in providing structures with considerable damping to reduce vibration due to wind-induced, seismic, and other excitations [38; 39; 40; 41; 42; 43; 44]. However, all these devices are mechanical systems with many parts, and they are not suitable for glass window panels due to their aesthetic, weight, and dimension requirements. For the vibration reduction of a glass window, the damper should be lightweight, and have a minimal dimension intrusion, and aesthetic appeal. For the vibration reduction of a glass panel, there are few reported papers and patents. [PERSON] [45] used an experimental set-up consisting of microphones and a two-dimensional (2D) vibrometer to measure local amplitudes and phases of out-of-plane glass motion, in which the vibration and noise transfer characteristics were measured. Various methods that can help improve the damping of a glass window are listed below. 1. The use of both air-film damping technology and viscoelastic material. [PERSON] and [PERSON] developed a window damping system that employs both air-film damping technology and viscoelastic damping materials to improve mechanical and/or acoustic vibration damping in window structures [46]. 2. The use of laminates with a viscoelastic layer. [PERSON] et al. [47] proposed an experiment showing that the use of a two-phase adhesive applied via a co-extrusion method with a low-viscosity core can dramatically lower the overall level of vibrations in window glass by 30-50 percent, and in particular, can bring about a flattening of the resonance peaks in the all-important roll vibration range between 100 Hz and 500 Hz. [PERSON] et al.