Ethem Erkan Aktakka

A Piezoelectric Parametric Frequency Increased Generator for Harvesting Low-Frequency Vibrations

This paper presents the design, fabrication, and testing of a piezoelectric parametric frequency increased generator for harvesting low-frequency non-periodic vibrations. The generator incorporates a bulk piezoelectric ceramic machined using ultrafast laser ablation. The electromechanical transducer is designed as a clamped-clamped spiral beam in order to decrease the stiffness within a limited footprint. An internal mechanism up-converts the ambient vibration frequency to a higher internal operation frequency in order to achieve better electromechanical coupling and efficiency. To gain maximum power output, the optimum width and thickness values of a spiral up-conversion unit are computed via multi-physics finite-element analysis simulations. The fabricated device generated a peak power of 100 μW and an average power of 3.25 μW from an input acceleration of 9.8 m/s2 at 10 Hz. The device operates over a frequency range of 24 Hz. The internal volume of the generator is 1.2 cm3.

Microsystems for energy harvesting

This paper reviews the state of the art in miniature microsystems for harvesting energy from external environmental vibration, and describes two specific microsystems developed at the University of Michigan. One of these microsystems allows broadband harvesting of mechanical energy from extremely low frequency (1–5 Hz) random vibrations abundant in civil infrastructure, such as bridges. These parametric frequency increased generators have a combined operating range covering two orders of magnitude in acceleration (0.54–19.6 m/s2) and a frequency range spanning up to 60Hz, making them some of the most versatile harvesters in existence. The second of these systems is an integrated microsystem for harvesting energy from periodic vibrations at moderate frequencies (50–400 Hz) typically present in devices such as motors or transportation systems. This harvester utilizes a thinned-PZT structure to produce 2.74 µW at 0.1 g (167 Hz) and 205 µW at 1.5 g (154 Hz) at resonance. Challenges in the design of electronic circuitry (integrated or hybrid) for regulating the scavenged energy are briefly discussed.

Thinned-PZT on SOI process and design optimization for piezoelectric inertial energy harvesting

This paper presents the design, fabrication, and testing of a thinned-PZT/Si unimorph for vibration energy harvesting. It produces a record power output and has state-of-the-art efficiency. The harvester utilizes thinning of bulk-PZT pieces bonded to an SOI wafer, and takes advantage of the similar thermal expansion between PZT and Si to minimize beam bending due to residual stress. Monolithic integration of a tungsten proof mass lowers the resonance frequency and increases the power output. The harvester dimensions, including the PZT/Si thickness ratio and the proof-mass/total-beam length ratio, are optimized via parametric multi-physics FEA. Additionally, a fabrication process for hermetic packaging of the harvester is introduced. It uses vertical Si vias for electrical feed-throughs. An unpackaged harvester with a tungsten proof mass produces 2.74 µW at 0.1 g (167 Hz), and 205 µW at 1.5 g (154 Hz) at resonance (here, g = 9.8 m/s2). The active device volume is 27 mm3 (7 × 7 × 0.55 mm3). We report the highest power output, Normalized Power Density (N.P.D.), and Figure of Merit (N.P.D. × Bandwidth) amongst reported microfabricated vibration energy harvesters.

A Micro Inertial Energy Harvesting Platform With Self-Supplied Power Management Circuit for Autonomous Wireless Sensor Nodes

A 0.25 cm3 autonomous energy harvesting micro-platform is realized to efficiently scavenge, rectify and store ambient vibration energy with batteryless cold start-up and zero sleep-mode power consumption. The fabricated compact system integrates a high-performance vacuum-packaged piezoelectric MEMS energy harvester with a power management IC and surface-mount components including an ultra-capacitor. The power management circuit incorporates a rectification stage with ~30 mV voltage drop, a bias-Ωip stage with a novel control system for increased harvesting efficiency, a trickle charger for permanent storage of harvested energy, and a low power supply-independent bias circuitry. The overall system weighs less than 0.6 grams, does not require a precharged battery, and has power consumption of 0.5 μW in active-mode and 10 pW in sleep-mode operation. While excited with 1 g vibration, the platform is tested to charge an initially depleted 70 mF ultra-capacitor to 1.85 V in 50 minutes (at 155 Hz vibration), and a 20 mF ultra-capacitor to 1.35 V in 7.5 min (at 419 Hz). The end-to-end rectification efficiency from the harvester to the ultra-capacitor is measured as 58-86%. The system can harvest from a minimum vibration level of 0.1 g.

A piezoelectric frequency-increased power generator for scavenging low-frequency ambient vibration

This paper presents the design, fabrication, and testing of a piezoelectric inertial micro power generator for scavenging low-frequency non-periodic vibrations. A mechanism up-converts the ambient vibration frequency to a higher internal operation frequency, in order to achieve better electromechanical coupling and efficiency: enhancing the generators performance at very low frequencies (≪30Hz). The generator incorporates a bulk piezoelectric ceramic machined using ultrafast laser ablation. The fabricated device generated a peak power of 100µW and an average power of 3.25µW from an input acceleration of 9.8m/s2 at 10Hz. The device operates over a frequency range of 24Hz. The internal volume of the generator is 1.2cm3.

A self-supplied inertial piezoelectric energy harvester with power-management IC

Harvesting energy from ambient vibrations is a promising technology for fully autonomous wireless sensor nodes, which can give birth to new applications in biomedical, industrial, and environmental monitoring. There have been independent solutions in increasing the harvesting efficiency either on the mechanical harvester [1] or on its power management circuitry [2,3]. Recently, a piezoelectric MEMS harvester using AlN was demonstrated to generate enough energy to autonomously power a wireless temperature sensor with a full-bridge rectifier built with off-the-shelf components [1]. Meanwhile, AC-DC converters for piezoelectric harvesters have been designed to enable efficient power extraction [2], or efficient rectification of low-voltage outputs [3], and have been tested with commercial meso-scale piezoelectric beams. However, to realize an efficient stand-alone energy generator platform, it is necessary to integrate these efforts into a single low-volume system. This paper presents a self-supplied energy generator, which includes a MEMS harvester hybridly integrated with its power management circuitry for autonomous charging of an energy reservoir (Fig. 6.9.1). The proposed packaging of the generator is <0.3cm3. Initial testing results are obtained with an unpackaged MEMS harvester.

Energy scavenging from insect flight

This paper reports the design, fabrication and testing of an energy scavenger that generates power from the wing motion of a Green June Beetle (Cotinis nitida) during its tethered flight. The generator utilizes non-resonant piezoelectric bimorphs operated in the d31 bending mode to convert mechanical vibrations of a beetle into electrical output. The available deflection, force, and power output from oscillatory movements at different locations on a beetle are measured with a meso-scale piezoelectric beam. This way, the optimum location to scavenge energy is determined, and up to ∼115 μW total power is generated from body movements. Two initial generator prototypes were fabricated, mounted on a beetle, and harvested 11.5 and 7.5 μW in device volumes of 11.0 and 5.6 mm 3 , respectively, from 85 to 100 Hz wing strokes during the beetle’s tethered flight. A spiral generator was designed to maximize the power output by employing a compliant structure in a limited area. The necessary technology needed to fabricate this prototype was developed, including a process to machine high-aspect ratio devices from bulk piezoelectric substrates with minimum damage to the material using a femto-second laser. The fabricated lightweight spiral generators produced 18.5‐22.5 μ Wo n a bench-top test setup mimicking beetles’ wing strokes. Placing two generators (one on each wing) can result in more than 45 μW of power per insect. A direct connection between the generator and the flight muscles of the insect is expected to increase the final power output by one order of magnitude. (Some figures in this article are in colour only in the electronic version)

Wafer level fabrication of high performance MEMS using bonded and thinned bulk piezoelectric substrates

We report a batch-mode fabrication technology for integration of bulk piezoelectric materials into MEMS devices, and test results of high-performance out-of-plane piezoelectric actuators fabricated with this technology. Low-temperature (200°C), reliable AuIn and Parylene bonding of PZT wafers/dies on Si wafers is achieved, and lapping is used to obtain ≪10µm PZT films. Conservation of the piezoelectric properties is confirmed with a hysteresis measurement. Additionally, square and circular shaped PZT diaphragms with 4mm×4mm, 2mm×2mm, and 1mm×1mm sizes operating in the d31-mode are fabricated with a 2-mask fabrication process. Greater than 12µm peak-to-peak deflection is obtained by actuation of a 1mm2 diaphragm at resonance (110.9kHz) with a power consumption of ≪7mW.

Wafer-Level Integration of High-Quality Bulk Piezoelectric Ceramics on Silicon

In this paper, we present a new post-CMOS-compatible piezoelectric thin/thick film technology that allows wafer-level integration of bulk piezoelectric ceramics such as lead zirconium titanate (PZT) and lead magnesium niobate-lead titanate (PMN-PT) on silicon substrates with precisely determined final film thickness of 5-100 μm while preserving the original material quality. We bond commercially available bulk piezoelectric substrates to silicon using reliable and low-temperature (200°C) gold-indium (Au-In) diffusion bonding or parylene bonding. An enhanced fixed-abrasive lapping/polishing process thins the piezoelectric layer to the desired thickness with high precision and wafer-level uniformity (±0.5 μm). The fabricated films have bond interface shear strength of 1.5-4.5 MPa and average surface roughness of 43 nm, with bulk ferroelectric/piezoelectric properties preserved, such as remnant polarization (37.7 μC/cm2), coercive field (1.95 kV/mm), and effective longitudinal piezoelectric strain coefficients (140-840 pm/V). In addition, extensions of this process show the feasibility of fabricating bimorph layers via successive bonding/thinning, and of forming suspended structures on silicon via surface micromachining. The flexible process can easily be adapted for batch-mode silicon integration of a variety of other electroceramics.

A Microactuation and Sensing Platform With Active Lockdown for In Situ Calibration of Scale Factor Drifts in Dual-Axis Gyroscopes

This paper presents the design and experimental results of a microvibratory actuation and sensing platform to provide on-chip physical stimulus for in situ calibration of long-term scale factor drifts in multiaxis microelectromechanical systems (MEMS) inertial sensors. The platform consists of a three degrees-of-freedom micromotion stage that can provide piezoelectric actuation for X/Y-tilting reference stimuli, compensation of undesired off-axis motion, integrated sensing of applied periodic stimulus, and electrostatic position lock-down for shock protection. A dual-axis MEMS gyroscope is mounted on top of the microplatform, and its electrical interconnects are provided through microfabricated highly flexible parylene cables with virtually zero-loading. The piezoelectric stage is measured to provide up to 280°/s angular ac excitation to a 25-mg inertial sensor payload at an expense of <;100 μW, while providing an analog sensing signal (11 mV/°/s) to determine the applied rate with a precision of 1.2 °/s. The estimated scale factor has <; 0.8% deviation from rate-table characterized values on the same-model gyroscope samples. With further improvements in control precision and angular velocity estimation, the introduced platform is expected enable on-chip self-calibration of long-term scale-factor drifts to <; 100 ppm.