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Tantalum Capacitors are electrolytic capacitors that is use a material called tantalum for the electrodes. Large values of capacitance similar to aluminum electrolytic capacitors can be obtained. Also, tantalum capacitors are superior to aluminum electrolytic capacitors in temperature and frequency characteristics. When tantalum powder is baked in order to solidify it, a crack forms inside. An electric charge can be stored on this crack.

These capacitors have polarity as well. Usually, the "+" symbol is used to show the positive component lead. Do not make a mistake with the polarity on these types.

Tantalum capacitors are a little bit more expensive than aluminum electrolytic capacitors. Capacitance can change with temperature as well as frequency, and these types are very stable. Therefore, tantalum capacitors are used for circuits which demand high stability in the capacitance values. Also, it is said to be common sense to use tantalum capacitors for analog signal systems, because the current-spike noise that occurs with aluminum electrolytic capacitors does not appear. Aluminum electrolytic capacitors are fine if you don't use them for circuits which need the high stability characteristics of tantalum capacitors.

When using a capacitor, you must pay attention to the maximum voltage which can be used. This is the "breakdown voltage." The breakdown voltage depends on the kind of capacitor being used. You must be especially careful with electrolytic capacitors because the breakdown voltage is comparatively low. The breakdown voltage of electrolytic capacitors is displayed as Working Voltage.

The breakdown voltage is the voltage that when exceeded will cause the dielectric (insulator) inside the capacitor to break down and conduct. When this happens, the failure can be catastrophic.

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---All kinds of Capacitors

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor.

Many variable capacitors have very short spindles which are not suitable for the standard knobs used for variable resistors and rotary switches. It would be wise to check that a suitable knob is available before ordering a variable capacitor.

Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period.

Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.

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---All kinds of Capacitors

Trimmer capacitors (trimmers) are miniature variable capacitors. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built.

A small screwdriver or similar tool is required to adjust trimmers. The process of adjusting them requires patience because the presence of your hand and the tool will slightly change the capacitance of the circuit in the region of the trimmer!

Trimmer capacitors are only available with very small capacitances, normally less than 100pF. It is impossible to reduce their capacitance to zero, so they are usually specified by their minimum and maximum values, for example 2-10pF.

Trimmers are the capacitor equivalent of presets which are miniature variable resistors.

Storage—there is never enough of it. I still remember when I thought my 700MB hard drive was huge... until I tried to copy an entire CD onto it for faster access. After that, I spent a period stuck choosing music to stick on my three GB hard drive. Two weeks ago, I ditched six months' worth of simulation data because my 320GB hard drive was full. One TB of new drive later, and I'm wondering how soon it will be before I start feeling the squeeze again. Maybe never, if some of the latest research coming out of Korea and Germany bears fruit.

One of the cool things about hard drive technology is how it has actually kept pace with computer needs. The basic mechanism for hard drive storage, however, does have some fundamental limitations, which manufacturers will have to deal with fairly soon. Bits are currently stored in the orientation of tiny magnets, called ferromagnetic domains, on a hard drive platter. The smaller the domain, the easier it is for that orientation to be scrambled by temperature or stray electromagnetic fields. At a certain size, thermal photons (e.g., heat energy from the surrounding case or the underlying disk) have enough energy to flip a domain's orientation. Manufacturers will have to keep their domain sizes significantly bigger than that threshold size to ensure data integrity, which puts a ceiling on storage density, one we're rapidly approaching.

An alternative is to use ferroelectric domains. Unlike ferromagnetic domains, ferroelectric domains have a natural electric field with an orientation that can be used to represent data. Until recently, these haven't looked that attractive because they have pretty much the same limitations that ferromagnetic domains have, but they lack the cool read-out tricks. Ferroelectric materials, however, do have one big advantage over ferromagnetic materials: they can be used to make really good capacitors. This is exactly what the latest research, published in Nature Nanotechnology, is about.