Wearable devices can take many forms, but in order to be used safely next to the skin, voltages need to be relatively low. Such has been the problem with alternating-current electroluminescent (ACEL) displays, which can exhibit a nice green glow, but need an alternating electric field with voltages in the 100 to 1000V range for ‘practical brightness.’
Scientists, however, have developed an ACEL display method that not only works at 10 to 35V, but is also highly deformable. These stretchable ACEL devices still use an alternating electric field to stimulate phosphors for light emission, but implement high-permittivity dielectric materials, polar elastomers, and ceramic nanofilters in the design in order to reach sufficient brightness at these voltages.
As a demonstration of this technology, the researchers have created a four-digit seven-segment stopwatch display that can safely be applied to the skin, using a a print and etch process to generate the circuit. An Arduino Mega is implemented for control, along with EL Escudo Dos sequencers from SparkFun, and a commercial electroluminescent inverter supplies power. The results is a display that looks like it came off of a car dashboard from the 1990s, or perhaps an AV receiver, that can safely be worn on one’s hand as a temporary tattoo.