Developing a self-sustained leadless pacemaker requires the development of an ultralow-frequency energy harvesting system that can fit within the required dimensions. This paper reports on the design and development of two types of PiezoMEMS energy harvesters that fit within the capsule dimensions and have a low resonant frequency between 20 to 30 Hz, which is required for the application. A bullet-shaped mass was designed to maximize the displacement and enhance power density of the devices. In addition, two types of devices were fabricated and compared (i) a silicon-based cantilever and (ii) a parylene-C-based cantilever with a thin aluminum nitride layer. The silicon device demonstrated higher peak power of 29.8 μW compared with the 6.4 μW for the parylene device. However, due to the low duty cycle of the heart rate and the damping factors of the two materials the average power was significantly higher for the parylene device (2.71 μW) compared with the silicon device (1.22 μW) per cantilever. The results demonstrate that a polymer-based energy harvester can increase the average power due to low damping for an impulse-based vibration application.
Biomimetic micro-robots try to mimic the motion of a living system in the form of a synthetically developed microfabricated device. Dynamic motion of living systems have evolved through the years, but trying to mimic these motions is challenging. Micro-robotics are particular challenging as the fabrication of devices and controlling the motion in 3 dimensions is difficult. However, micro-scale robotics have potential to be used in a wide range of applications. MEMS based robots that can move and function in a liquid environment is of particular interest. This paper describes the development of a piezoMEMS based device that mimics the movement of a jellyfish. The paper focuses on the development of a finite element model that investigates a method of controlling the individual piezoelectric beams in order to create a jet propulsion motion, consisting of a quick excitation pulse followed by a slow recovery pulse in order to maximize thrust and velocity. By controlling the individual beams or legs of the jellyfish robot the authors can control the robot to move precisely in 3 dimensions.
MEMS based vibrational energy harvesting devices have been a highly researched topic over the past decade. The application targeted in this paper focuses on a leadless pacemaker that will be implanted in the right ventricle of the heart. A leadless pacemaker requires the same functionality as a normal pacemaker, but with significantly reduced volume. The reduced volume limits the space for a battery; therefore an energy harvesting device is required. This paper compares varying the dimensions of a linear MEMS based piezoelectric energy harvester that can harvest energy from the mechanical vibrations of the heart due to shock induced vibration. Typical MEMS linear energy harvesting devices operate at high frequency (<50 Hz) with low acceleration (< 1g). The force generated from the heart acts as a series of impulses as opposed to traditional sinusoidal vibration force with high acceleration (1-4 g). Therefore the design of a MEMS harvester that is based on shock-induced vibration is necessary. PiezoMEMS energy harvesting devices consisting of a silicon substrate and mass with aluminium nitride piezoelectric material were developed and characterized using acceleration forces that mimic the heartbeat. Peak powers of up to 25μW were obtained at 1 g acceleration with a powder density of approximately 1.5 mW cm<sup>-3</sup>.
Piezoelectric materials are widely used in various applications including sensors, actuators, and energy harvesting
devices. Energy harvesting devices can be used to power autonomous wireless sensors that are placed in remote or
difficult to reach areas, where replacing a battery is not practical or feasible. In this paper the authors present work on the
fabrication and design of a CMOS compatible Aluminium Nitride (AlN) piezoelectric based MEMS cantilever structure
for harvesting vibrational energy. In order for AlN to be piezoelectric it needs to be highly structured in the c-axis (002)
crystal orientation. The deposition of highly structured AlN and its polarity is dependent on the underlying films and
their crystal orientation. XRD rocking curve results from this paper show a highly oriented (002) AlN film with a
FWHM value of 2.1°. The MEMS cantilever structures were fabricated using standard MEMS fabrication techniques
using SOI wafers. By optimising the AlN material deposition process and the stress values in the cantilever structures the
authors were able obtain a power density of 2.55 mW/ cm<sup>3</sup>/g<sup>2</sup> for a single MEMS structure with 500 nm thick AlN. The
cantilever structure had a resonant frequency of approximately 150 Hz. In this paper the authors also investigated
methods to increase the bandwidth of the cantilever structures, by building an array of devices with slightly varying