I'm not sure if I'm missing the point completely, but I don't understand why this is any way surprising, in fact I would be very surprised if a capacitor didn't behave this way. Is this really unique to ceramic caps???
Given a bias voltage (i.e. a constant voltage difference between the two pins/"plates" of the capacitor) I would think that the capacitor already holds a certain charge*. The total amount of charge it is able to hold depends on the (total) voltage differential (in a non-linear relationship).
*This can easily be demonstrated: as soon as the bias voltage is removed, the cap will discharge.
Aren't some of the letter codes in the table for tolerance reversed?
I have a bag of Y5V capacitors and it says that they are -20% +80% and not +20% -80%.
And googling it gives various results:
This is similar to the one Dave used: http://m.eet.com/media/1174806/table1.jpg
and this one seems to be right: http://2.bp.blogspot.com/_c8EartLqdVs/TMmr-6Wn0WI/AAAAAAAAAkc/8A00KvYYR0g/s1600/Tolerance+code.bmp
My pet peeve: ferrite beads. I ask you: what's the point of a 10A ferrite bead when it saturates at 100mA? Nothing, that's what! Even if you dig through their database programs (Kemet, TDK, etc. all have their things), you rarely find bias data for ferrite beads. If you need DC filtering, don't look at ferrite beads, look at the "inductor" listing -- they make multilayer ferrite chip inductors, outwardly identical to ferrite beads, that are just as cheap and plentiful, but actually perform correctly.
A bit offtopic
Dave, when you said at around 5:30 "Come with me" i almost said out loud "Dave, you watched too much Cosmos"
A bit offtopic
Dave, when you said at around 5:30 "Come with me" i almost said out loud "Dave, you watched too much Cosmos"
Well he did name his kid after Carl Sagan.
Here is the physical process, as explained by muRata.
The mechanism of DC bias characteristic:
In the high dielectric constant capacitor type of monolithic ceramic capacitors, at present mainly BaTiO3 (barium titanate) is used as a principal component of high dielectric.
BaTiO3 has a perovskite shaped crystal structure and above the Curie temperature it becomes a cubic shape with Ba2+ ions to the vertices, O2- ion to face center and Ti4+ ion in a body centered position.
At the Curie temperature (approx 125°C) or more, it has a cubic crystal structure, and below the Curie temperature and within an ambient temperature range, one axis (axis C) stretches and other the axes shrink and turn to a tetragonal crystal structure.
In this case, polarization occurs as a result of the unit shift of axially elongated Ti4+ ion crystal. This polarization occurs without applying an external electric field or pressure, and is known as "spontaneous polarization." As explained above, a characteristic that has a spontaneous polarization and a property of changing orientation of spontaneous polarization by an external electric field to reverse is called "Ferro electricity."
The reversal of the spontaneous polarization per unit volume is equivalent to relative permittivity. Relative permittivity is observed as a capacitance.
Without a DC voltage, spontaneous polarization can happen freely. However, when a DC voltage is externally applied, spontaneous polarization is tied to the direction of the electric field in the dielectric, and independent reversal of spontaneous polarization is inhibited. As a result, the capacitance becomes lower than before applying the bias.
This is a mechanism of decrease in the capacitance after applying DC voltage.
http://www.murata.com/products/capacitor/design/faq/mlcc/property/05_more.html
Dear God, please don't let the 'golden ear' crowd hear about this. They're sure to claim it's audible.