NASA Marshall Space Flight Center developed designs for two micro-electromechanical systems (MEMS) motion and position sensors: a single-axis accelerometer and a gyroscope. The designs leverage a highly aligned multi-wall carbon nanotube (MWCNT) tape with a P(VDF-TrFE) matrix that is mechanically robust and has excellent piezoelectric properties as the sensing and actuating element.
The use of CNT tape in a gyroscope is made possible by recent improvements to CNT processing that yield longer CNTs that are more highly aligned. The use of CNTs makes the accelerometer and gyroscopes stronger and more robust, without increasing their size or weight. The chief advantage, compared to silicone (Si) and quartz sensors, is easier manufacturing that requires no machining.
NASA's accelerometer was designed to address the shortcomings of conventional piezoelectric-based accelerometers that are made from ceramic materials such as barium titanate (BaTiO3) or lead titanate (PZT). These materials are inherently brittle, have a tendency to be noisy, have difficulty sensing low frequencies, are subject to static charge buildup that affects polarization, and are relatively large and expensive. The unique feature of the NASA innovation is the use of carbon nanotube/P(VDF-TrFE) tape as the actuating and sensing element.
The new accelerometer acts as a spring-mass system. There is a moving mass between fixed walls and attached to two CNT tapes on both sides. The mass is displaced along a single axis when an applied force acts on the mass. This sensor uses one tape as an actuator to damp motion of the moving mass, while the other tape is used for sensing the mass displacement.
The single-axis accelerometer can be used alone or as the basis for a two-axis gyroscope. The CNT tape is used as the vibrating element in the gyroscope. The NASA gyroscope design covers three configurations: CNT tape wrapped around the conductive rotor of the gyroscope, the same CNT tape layered with piezo material to form a rotor shape, and piezo-sprayed CNT tape used as a rotor.