## 1 Introduction  
Preventing damage or discomfort resulting from any sort of external kinetic energy (impact or vibration) is an omnipresent problem in our society. On one hand, impacts and vibrations are responsible for several health problems. According to the European Injury Data Base (IDB), injuries due to accidents are killing one EU citizen every two minutes and disabling many more [1]. Additionally, the European Agency for Safety and Health at Work reported in 2008 that one European worker in three is exposed to vibrations at work and up to 63% of the workers in some sectors such as construction [2]. This can result in Whole Body Vibration (WBV) and Hand-Arm Vibration (HAV) syndromes and vibration-related injuries [34]. Many of these impact-related and vibration-related injuries could be prevented or minimized by wearing adequate personal protection equipment, e.g. helmets or anti-vibration gloves [1]. On the other hand, impacts and vibrations can induce malfunctioning in equipment or devices, and its prevention has generated huge and expanding markets. Just to give a couple of examples about its importance, the expected global market revenue of protective cases for smartphones will rise up to US$ \(\sim\)25,000 Mn by 2025 [5], while the global market for automotive anti-vibration products, such as engine mounts or dampers, accounted for US$ \(\sim\)1,600 Mn in 2013 [6]. Therefore, there is no doubt that developing new advanced energy dissipating systems, able to give the most effective response under external dynamic loads, is an unavoidable global need. The use of fluid in damping systems is a rather common strategy to turn unwanted kinetic energy into heat energy, which is dissipated through the fluid itself. The classical example given is a hydraulic shock absorber [7], universally employed in automotive vehicles, where the damper is mounted in parallel with the springs to damp the accelerations applied to the frame from the wheel in order to provide a smooth ride. Traditionally, the fluid used in damping systems has been Newtonian, mainly air or oil. A Newtonian fluid provides a linear relationship between stress and strain-rate, being the viscosity of the fluid the constant of proportionality. Thus, as the amount of dissipated energy is proportional to the viscosity of the fluid, once selected a Newtonian fluid, the amount of energy dissipated in the system is determined and limited by the viscosity of the fluid. Then, damping systems using a Newtonian fluid are unable to damp external loads in a selective way. Non-Newtonian fluids offer an opportunity to overcome these limitations and allow enhanced selectivity, either by external field activation or the passive response to critical amplitude (stress or strain-rate) and/or transient timescales (frequencies), as they relationship between stress and strain-rate is non-linear [8]. While the Newtonian fluid dissipates more energy at higher velocity (strain rate), this is a linear relationship between stress and strain-rate. ACTIVE, field-responsive systems can change by many orders of magnitude (e.g., yield stress of magneto-rheological fluids changing by many order of magnitude), even under equivalent forcing conditions. This is clearly selective. Similarly, but less dramatically, shear-thickening and viscoelastic materials also change their stress response by orders of magnitude as a function of amplitude and driving frequency, respectively. Energy dissipating systems can be understood as isolators. Their final aim is essentially protecting by minimizing displacements or transmitted forces. Within the frame of this publication, and also quite accepted in the literature, an isolation system is considered active if it requires external power supplies (electric or magnetic field), or passive if it does not [9]. In this article, a revision of the state-of-the-art of the main applications of complex fluids in energy dissipating systems is presented.