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www rutronik com Committed to Excellence Powered by 1 2021 5 Knowhow Development trends with ceramic capacitors Hi were the new guys! There are many demands placed on ceramic capacitors smaller construction large temperature ranges higher efficiency stricter tolerances optimized functions and higher frequencies not to mention the desire for applicationspecific versions The manufacturers do a lot to satisfy all these requests By Jürgen Geier Technical Support and Pascal Kundelius Product Sales Manager Ceramic Capacitors both at Rutronik In order to continue optimizing their ceramic capacitors manufacturers develop new materials and mixtures as well as new approaches to the construction engineering and interior structure i e the forms of the electrode surfaces They also deliberately make use of certain properties such as the widely negatively viewed effect of DC bias This effect occurs in ferromagnetic ceramic materials such as barium titanate which is currently the material most commonly used for MLCCs multilayer ceramic capacitors Alongside the more widely known designs such as highfrequency HiQ RF microwave lowinductance and lowloss capacitors a range of specific and novel ceramic capacitors has recently started appearing on the market that are still broadly unknowngiven the current deluge of new developments this is hardly a surprise We introduce some of the most important features here Variable capacity thanks to DC bias Variable capacitors do just as the name suggeststhey offer variable capacitance Using their DC bias reduces the effective capacities when a DC current is applied to their control electrodes so they could also be referred to as VACsvoltage adjustable capacitors These electrically trimmable capacitors are available with capacitance ratings of 33 pF to 200 pF for control voltages of up to 3 or 5 V DC allowing them to be adjusted to up to 50% of their base capacitance Compared to regular trimmer capacitors this provides them with unimagined opportunitiesespecially given that they can not only be set to fixed values but also used to form control loops They are available in construction sizes of 0 6 mm × 0 6 mm and 1 3 mm × 0 9 mm for working voltages of 10 Vpp and 30 Vpp Applications for which these are especially ideal include NFC antenna circuits 13 56 MHz band such as those used in smartphones and check cards because the variable capacitors here enable frequency adjustments to be performed by simply applying the appropriate voltage in conjunction with the NFC ICs They also compensate for variance in the antennas Lvalue making f0 adjustment easier and also facilitate debugging during certification testing and simplify deviation adjustments during installation in the housing Figure Murata Figure Murata Figure 2 Substitute circuit diagram for variable capacitors Figure 1 Variable capacitors offer adjustable capacitance by using DC bias