OSCILLATION SUPPRESSION COMPONENT INVESTIGATION: CAPACITANCE AS A FUNCTION OF TEMPERATURE AND VOLTAGE MICHAEL GURR ME304 FALL 2012

CERAMIC CAPACITORS Most widely used type of capacitor Two terminal, non-polar, passive device Fixed capacitor with ceramic material serving as a dielectric Composition of ceramic material determines dielectric properties Have rated voltage and temperature ranges (i.e. tolerances)

CAPACITANCE The ability of a body to store electric charge With linear thermal expansion defined by Factors in surface mount ceramic capacitance calculation include: Dissipation factor Dielectric withstanding voltage Insulation/Heat resistance Project will focus on the effects of temperature and sustained voltage on capacitance

RADAR Object detection system that uses radio waves Transmits pulses of radio waves or microwaves that bounce off any object in their path Object returns a tiny part of the wave's energy to a dish or antenna Frequency of the wave received by the antenna is the same as the one transmitted, with the phase shifted by reflection

FILTERING Band pass filters used to single out the frequency sent out by the radar Low pass filter followed by a high pass filter creates a band pass filter Filters are used to localize the frequencies accepted by the antennae Small changes in frequency occur between atmospheric and material boundaries

METHODS Custom PCB with pinout for Au headers Voltage measurements Temperature measurements Capacitor mounting Temperatures Tested: 40°C, 75°C, 100°C, 125°C, 150°C, 200°C, 240°C Voltages Tested: 10V, 25V, 50V, 75V, 150V

OVERDRIVEN CAPACITORS

RESULTS: VOLTAGE DEPENDENCE

RESULTS: TEMPERATURE DEPENDENCE

ANALYSIS AND CONCLUSIONS Thicker dielectric has a higher voltage rating – Major tradeoff X7R has a very high dielectric withstanding voltage, which measures the momentary over-voltage the capacitor is capable of withstanding with no damage Above the rated voltage of 100V, the capacitance hits a plateau and does not drop off as quickly X7R at 240°C has expanded 14.9% from its room temperature size (leading to the decreased capacitance Voltage rating is okay (max voltage is 28V in system), but temperature failure is not good – look into Tantalum capacitors for lower ESR (less of a temperature dependence)