**4. Active heatsink technologies**

During the last decade, unprecedented technological developments imposed tremendous flows of information (data or multimedia), implying an *ever-growing need for fast data transfers* (Bluetooth, Wi-Fi) and for *larger computing and storage capacities*. In addition, the advent of 5G and the *Internet of Things* means that the number of connected devices is constantly increasing [19]. Moreover, *onboard electronics* and *mobile telephony* created new ergonomics and space (volume) constraints. From a systems engineering perspective, this implies that *larger power circuits have to be integrated in smaller volumes*.

Under such conditions, the amounts of energy generated by electronic circuits are so great that *no passive heatsink of a reasonable size will be able to do the cooling job*. This is because passive sinks dissipate heat mainly through natural convection, but natural convection is no longer sufficient to extract the heat generated by the operation of these power components. Thus, the use of active cooling systems, with or without refrigeration or phase change is necessary [20, 21] for the safe operation of power electronics.

Active cooling systems are heat exchangers where the flow of the heat transfer medium (air or liquid) is forced by a fan or a pump. Several technologies exist. They can be sorted into two categories:

