Ant-sized piezoelectric robots

Tiny perambulating 3D-printed robots move by harnessing vibrations from piezoelectric actuators or ultrasound sources. Swarms of what their developers at Georgia Institute of Technology call their "micro-bristle-bots" could be used en masse as environmental sensors or in a distant future be used to carry out injury repair in the human body.

The robots consist of a piezoelectric actuator (made from lead zirconate titanate) glued on to a polymer body that is 3D-printed using two-photon polymerization lithography (TPP). The team is currently working on scale-up to allow them to print thousands of their bristle-bots at a time. [Kim, DG et al, J Micromech Microeng; DOI: 10.1088/1361-6439/ab309b]

The actuator is powered by an external battery and generates the vibrations that make the bristle-bots move. However, vibrations in the surface on which they stand would also cause them to move. A robot can be designed to respond to a different vibration frequency depending on the length and diameter of its legs and the robot's overall design and geometry. Bigger vibrations make the robots move faster. Conversely, vibrations in the robots themselves would generate a current in the lead zirconate titanate piezoelectric component and so could be used to power sensors.

"As the micro-bristle-bots move up and down, the vertical motion is translated into a directional movement by optimizing the design of the legs, which look like bristles," explains team member Azadeh Ansari. "The legs of the micro-robot are designed with specific angles that allow them to bend and move in one direction in resonant response to the vibration."

Ansari and her team are working to add steering capability to the robots by joining two slightly different micro-bristle-bots together. Because each of the joined micro-bots would respond to different vibration frequencies, the combination could be steered by varying the frequencies and amplitudes. While other research teams have developed similar micro-robots, those used magnetic fields to move them. Ansari points out that a magnetic field could only be used to move a swarm simultaneously. Her team's bristle-bots can be controlled individually or in groups using different vibrational frequencies and amplitudes.

Ansari adds that the team is taking inspiration from nature in developing their bristle-bots. "We can look at the collective behavior of ants, for example, and apply what we learn from them to our little robots," she explains. "These micro-bristle-bots walk nicely in a laboratory environment, but there is a lot more we will have to do before they can go out into the outside world."