Investigation of far field electromagnetic emission behavior of electronic heatsinks

Technological developments have increased the use of semiconductor switching elements (FET, JFET, MOSFET, BJT, etc.) have integrated circuit structure with respect to high power requirement. This development has made the circuit structure of electronic devices more complex, and the speed of electronic switching elements has increased in line with the resulting high frequency requirements. These elements produce unwanted harmonic components due to their high switching speeds, and by their nature, they generate more heat during operation. In order to achieve proper working performance, this high heat must be removed from the environment. The main element used for this process is metallic heat sinks, and there is a linear relationship between cooling performance and surface area of coolant. However, it is a known fact that the varying surface area will behave as an antenna which has different radiation pattern. The meaning of this is that the actual signals produced by the switching elements and their unintentional harmonics are going to be emitted through these heat sinks to the external environment. The problem should therefore be considered as an electromagnetic compatibility problem, since the heat sinks exhibit an antenna behavior. The main subject of this thesis is to observe the effect of the physical dimension and geometry of heat sink and location of induction of signals on the metal. When the heat sinks are considered as antennas, it has been observed that the simulation and measurement results closely follow each other, and that the radiation pattern differs depending on the position of the connection/injection point (relative to the edges and corners) of the heat sink to the switching element and the frequency of the signal produced. Minimum beam width has been measured as 30o (4 GHz) whose center angle is ϕ=285o and maximum beam width has been measured as 120o (4 GHz) whose center angle is ϕ=90o. When the heat sinks were evaluated as an antenna, two different resonance frequency values (via S parameters measurement) were obtained depending on the base area (patch antenna behavior) and fin heights (monopoly antenna behavior), and it was observed that these values change according to the feed point. At some feeding points (to be favorable in terms of electromagnetic compatibility) no radiation was observed. Parametric analyzes of geometry of heat sink have been performed. When the number of fins (the structure formed to increase the surface area), which is one of these parameters, was changed, the effect on electromagnetic radiation was found to be very low and the value remained below 2.5 dB. Based on the patch antenna behavior, resonances occurring at certain frequencies were shifted proportionally towards to the low frequency region. This is because of increasing base length and width.