Photostrictive microactuators

The continuing thrust toward greater miniaturization and integration of microrobotics and microelectronics has resulted in significant work toward the development of piezoelectric actuators. One of the bottlenecks of the piezo-actuator is its necessity of the electric lead wire, which is too heavy for a miniaturized self-propelling robot less than 1 cm3. The important reason is a drastic reduction of the propelling friction force due to the increase in specific area; that is, surface area/volume or weight ratio. “What if you, an expert on actuators, could produce a remote-controlled actuator that would bypass the electrical lead?" To many people, “remote control” equals control by radio waves, light waves, or sound. Light-controlled actuators require that light energy be transduced twice: first from light energy to electrical energy, and second from electrical energy to mechanical energy. These are “photovoltaic” and “piezoelectric” effects. A solar cell is a wellknown photovoltaic device, but it does not generate sufficient voltage to drive a piezoelectric device; in other words, this combination fails due to the electric impedance mismatch. The key to success is to adopt a high-impedance photovoltaic effect (so-called anomalous or bulk photovoltaic effect in piezoelectrics), which is totally different from the p-n junction-based solar cell.