PIEZO TECHNOLOGY
An ingenious phenomenon …
… is based on the piezo element: the release of voltage through pressure. The crystalline elements are predestined for use in keyboards. Their sensitivity is so extreme, that the switching cycle can even be produced through 4 mm thick panels, which can be made from many different materials.
We have perfected piezo technology. In the past, ceramic elements have been incorporated in the technical parts of a keyboard, but we have developed a technology to apply piezo-electric lacquer on the surface. This unique method, developed and patented by Algra, guarantees the same precise switching characteristics as conventional piezo elements.
Piezoelectricity
In 1880, the French physicists Pierre and Jacques Curie discovered that mechanical pressure on the surface of certain crystals (e.g. PZT, lead-zirconate-titanate) generates electrical charges. They called this phenomenon the piezo effect. “Piezo” is derived from Greek and means both “pressure” or “press”.
An electrical charge can be measured on two surfaces while the pressure changes (bending, stretching, pressing) which is proportional to the force expended. The stretching is extremely minimal – ultimately a crystal cannot be pressed together like a sponge.
The illustrations provide a greatly simplified presentation of the functions of the piezo effect. The first image shows a rendering of a six-sided crystal structure cell. All charges are mutually equalized so that the cell has a neutral electrical effect from the outside in.
The pressure on this structural cell (image in centre) causes a shift of the centres of gravity of the positive and negative charges against each other. The resulting difference in the charge is evaluated as voltage or a charge (right image).
Known applications
Lighter
Here a small hammer is pre-stressed which then strikes the piezo-electrical crystal. A spark can be generated by the resuluting voltage which ignites the gas.
Alarm clocks
Most electronic alarm clocks use the piezo effect. Acoustic pressure is formed through the creation of alternating voltaged which even wakes up the deepest of sleepers.
Pick-ups for musical instruments
Piezo-electrical pick-ups are attached, for example, on the bridge of a guitar under the strings. They pick up vibrations created by the strings. These vibrations are converted into electrical signals. A solution which has had a sustained influence on rock and pop music.
Alarm systems
Sensors, e.g. on the panes of a display window, pick up the impact sounds and convert them to electrical signals. Sounds and vibrations which are caused by instruments used for a break-in result in the alarm being triggered just as the break-in attempt begins.
Buzzers
Conversely, the electrical vibration can be transferred to a crystal using the inverse piezo effect. The air is made to vibrate and thereby becomes audible.
Piezo-electrical switches
Piezo-electrical switches only need a stroke from 1 to 10µm in order to generate a usable turn-own voltage or charge. It is rather the application of force as a motion which creates an output signal in the switch element. The switch processes are triggered even through several millimetres of thick plates.
Because the required movement is negligibly small for the activation of a piezo-electrical switch element, the designers can use practically any material for every overlaying; polyester, polycarbonate, anodized aluminium, steel or other metals, plexiglass and glass, wood or even stone. The keyboard can even be bent depending on the materials. This makes environmental and aesthetic compromises no longer necessary in the man-machine interface.
It also means that every window in the overlays (e.g. for LC displays) should be made thick enough to guarantee the most reliable protection even in the roughest environments. When overlay materials are selected, requirements such as moisture, chemicals or even resistance to rays can be taken into account. These keyboards can resist any type of vandalism.
