You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Variable impedance actuators: A review 
Chapter Title:  Eddy Current Dampers 
1. Abstract of Cited Paper (BIB001):  We describe the design of an eddy current brake for use as programmable viscous damper for haptic interfaces. Unlike other types of programmable brakes, eddy current brakes can provide linear, programmable physical damping that can be modulated at high frequency. These properties makes them well suited as dissipative actuators for haptic interfaces. We overview the governing physical relationships, and describe design optimization for inertial constraints. A prototype haptic interface is described, and experimental results are shown that illustrate the improvement in stability when simulating a stiff wall that is made possible using programmable eddy current dampers. 
2. Abstract of Cited Paper (BIB002):  A novel eddy current damper is developed and its damping characteristics are studied analytically and experimentally. The proposed eddy current damper consists of a conductor as an outer tube, and an array of axially magnetized ring-shaped permanent magnets separated by iron pole pieces as a mover. The relative movement of the magnets and the conductor causes the conductor to undergo motional eddy currents. Since the eddy currents produce a repulsive force that is proportional to the velocity of the conductor, the moving magnet and the conductor behave as a viscous damper. The eddy current generation causes the vibration to dissipate through the Joule heating generated in the conductor part.An accurate, analytical model of the system is obtained by applying electromagnetic theory to estimate the damping properties of the proposed eddy current damper. A prototype eddy current damper is fabricated, and experiments are carried out to verify the accuracy of the theoretical model. The experimental test bed consists of a one-degree-of-freedom vibration isolation system and is used for the frequency and transient time response analysis of the system. The eddy current damper model has a 0.1 m s−2 (4.8%) RMS error in the estimation of the mass acceleration. A damping coefficient as high as 53 Ns m−1 is achievable with the fabricated prototype.This novel eddy current damper is an oil-free, inexpensive damper that is applicable in various vibration isolation systems such as precision machinery, micro-mechanical suspension systems and structure vibration isolation. 
3. Abstract of Cited Paper (BIB003):  Electromagnetic drives are subjected to an inherent inertia-torque tradeoff that fundamentally limits transparency: the higher the torque, the higher the inertia. We describe a dual-stage design that is not subjected to this tradeoff and that is able to approach perfect transparency for human users. It comprises a large, proximal motor and a small, distal motor to reproduce the transients. The two stages are coupled by a viscous clutch based on eddy currents that, without contact, accurately transforms slip velocity into torque. Such a system can, in general, be controlled to achieve a variety of objectives. Here, we show that an advanced, discrete-time, RST polynomial pole-placement controller can achieve near-perfect transparency. Experimental validation evaluated the human ability to detect small haptic details when using this drive and compared it with when using a conventional, single-motor interface.

Literature Review:
Eddy Current Dampers (ECDs, see Fig. 11d ) are magnetic devices composed of a conductive material moving through a magnetic field. Eddy currents are induced and create a damping force that is proportional to the relative velocityq r between the material and the magnetic field: The coefficient D depends, ultimately, on the geometry of the conductor, represented by r, and of the magnet, denoted by d, their gap, h, the magnetic flux, B and the specific conductivity of the conductor σ. These devices can be realized with both permanent magnets or electromagnets. In both cases there is the possibility to design a device whose damping can be adjusted BIB003 BIB002 [97] BIB004 . In one case, the damping coefficient can be controlled by varying the intensity of the magnetic field, in the other case, by modifying the geometry of the conductor, or the gap between the conductor and the magnets (the effectiveness is shown in BIB001 ). Albeit electromagnetic ECD are not composed of mobile parts, they have the disadvantage of consuming power while maintaining a fixed damping value. This class of devices, being fluid-free and contact-free, is not affected by typical troubles due to oil (e.g., the need of seals against leakage), and by frictional wear. Still, they present the disadvantage of requiring a gearbox because of their low damping torque.