Today you have to choose: Blackberry-style keypad or the touch screen of iPhone and others. Keypads provide handy tactile feedback and are durable, but the keys are small and cut down the screen size. The dynamic keypads of touch-sensitive screens let you easily summon or dismiss letters, numbers or symbols, but the lack of well-defined keys make accuracy challenging, and typing on a flat surface is less pleasing for some users. Add-on keypads can be snapped onto touch-screen phones, of course, but add bulk.

What if raised keys could appear and then vanish whenever you wanted? The Tactile Layer panel from Tactus Technology promises to offer just that in a deformable surface, which was demonstrated earlier this month in a prototype Google Android tablet made by Touch Revolution at the Society for Information Display's Display Week 2012 show in Boston. Tactus said it expects commercial applications on mobile phones, tablets, navigation devices and other gadgets next year. The transparent panel would match the weight and thickness of current touch screens, according to the company.

The prototype panel might be constructed in a number of configurations, depending on need, according to the U.S. Patent and Trademark Office patent awarded to Tactus in May. In general, the panel would consist of a firm lower sheet of glass or plastic and a thin, elastic covering of polymers or silicon-based elastomers. Between the two layers are cavities filled with any transparent substance that could expand or contract: a liquid (water, glycerin or ethylene glycol), a gas (air, nitrogen or argon) or any other flexible material, according to the patent. The number of cavities depends on whether the panel will assume the features of a conventional QWERTY keyboard, a calculator or some other arrangement.

The elastic covering rests flat atop the base layer until the gadget runs a program that requires raised buttons. A displacement device located within the panel then pushes expanding fluid through the open tops of the cavities, which presses against the elastic layer creating a bulge. If a liquid is used, the displacement device might be a pump; for gas, it might be a heating element. Either way, the result is fluid-filled bumps on the surface. Sensors beneath the cavities detect fluid pressure changes or a fluctuation in an electrical field when a user applies force by depressing the temporary buttons. When the keyboard is not in use, the fluid contracts and the surface becomes flat again.

The company has not provided a more specific time frame or named the first consumer device (or devices) that will use the panel. Whenever the technology appears, it is expected to offer an adaptive interface that will benefit users as mobile devices become smaller and more powerful.