Alex Yuandong Gu

Flow-driven triboelectric generator for directly powering a wireless sensor node.

A triboelectric generator (TEG) for scavenging flow-driven mechanical -energy to directly power a wireless sensor node is demonstrated for the first time. The output performances of TEGs with different dimensions are systematically investigated, indicating that a largest output power of about 3.7 mW for one TEG can be achieved under an external load of 3 MΩ.

Elasto-Aerodynamics-Driven Triboelectric Nanogenerator for Scavenging Air-Flow Energy

Efficient scavenging the kinetic energy from air-flow represents a promising approach for obtaining clean, sustainable electricity. Here, we report an elasto-aerodynamics-driven triboelectric nanogenerator (TENG) based on contact electrification. The reported TENG consists of a Kapton film with two Cu electrodes at each side, fixed on two ends in an acrylic fluid channel. The relationship between the TENG output power density and its fluid channel dimensions is systematically studied. TENG with a fluid channel size of 125 × 10 × 1.6 mm(3) delivers the maximum output power density of about 9 kW/m(3) under a loading resistance of 2.3 MΩ. Aero-elastic flutter effect explains the air-flow induced vibration of Kapton film well. The output power scales nearly linearly with parallel wiring of multiple TENGs. Connecting 10 TENGs in parallel gives an output power of 25 mW, which allows direct powering of a globe light. The TENG is also utilized to scavenge human breath induced air-flow energy to sustainably power a human body temperature sensor.

Methods for improving electromechanical coupling coefficient in two dimensional electric field excited AlN Lamb wave resonators

An AlN piezoelectric Lamb-wave resonator, which is excited by two dimensional electric field, is reported in this paper. Rhombus-shape electrodes are arranged on AlN thin film in a checkered formation. When out-of-phase alternating currents are applied to adjacent checkers, two dimensional acoustic Lamb waves are excited in the piezoelectric layer along orthogonal directions, achieving high electromechanical coupling coefficient, which is comparable to film bulk acoustic resonators. The electromechanical coupling coefficient of the 285.3 MHz resonator presented in this paper is 5.33%, which is the highest among AlN based Lamb-wave resonators reported in literature. Moreover, the spurious signal within a wide frequency range is significantly suppressed to be 90% lower than that of the resonance mode. By varying the electrode dimension and inter-electrode distance, resonators having different resonant frequencies can be fabricated on a single wafer, making single-chip broadband filters, duplexers, and multi...

A monolithic 9 degree of freedom (DOF) capacitive inertial MEMS platform

A monolithic 9 degree of freedom capacitive inertial MEMS platform is presented in this paper. This platform for the first time integrates 3 axis gyroscopes, accelerometers, and Lorentz Force magnetometers together on the same chip without using any magnetic materials. This reduces the assembly cost, and fully eliminates the need of magnetic material processing and axis misalignment calibration. The fabricated sensors, vacuum packaged (vacuum ~100mTorr) at wafer level with epi-polysilicon through silicon interposer (TSI) wafer using eutectic bonding, performed within 10% of the simulation results.

Flutter Phenomenon in Flow Driven Energy Harvester–A Unified Theoretical Model for “Stiff” and “Flexible” Materials

Here, we report a stable and predictable aero-elastic motion in the flow-driven energy harvester, which is different from flapping and vortex-induced-vibration (VIV). A unified theoretical frame work that describes the flutter phenomenon observed in both “stiff” and “flexible” materials for flow driven energy harvester was presented in this work. We prove flutter in both types of materials is the results of the coupled effects of torsional and bending modes. Compared to “stiff” materials, which has a flow velocity-independent flutter frequency, flexible material presents a flutter frequency that almost linearly scales with the flow velocity. Specific to “flexible” materials, pre-stress modulates the frequency range in which flutter occurs. It is experimentally observed that a double-clamped “flexible” piezoelectric P(VDF-TrFE) thin belt, when driven into the flutter state, yields a 1,000 times increase in the output voltage compared to that of the non-fluttered state. At a fixed flow velocity, increase in pre-stress level of the P(VDF-TrFE) thin belt up-shifts the flutter frequency. In addition, this work allows the rational design of flexible piezoelectric devices, including flow-driven energy harvester, triboelectric energy harvester, and self-powered wireless flow speed sensor.

Integration of RF MEMS resonators and phononic crystals for high frequency applications with frequency-selective heat management and efficient power handling

We report a radio frequency micro electromechanical system (RFMEMS) device integrated with phononic crystals (PnC) that provide a Lamb-wave resonator with frequency-selective heat management, power handling capability, and more efficient electromechanical coupling at ultra high frequency (UHF) and low microwave bands. The integrated device is fabricated in a silicon-on-insulator (SOI) aluminum nitride (AlN) platform and boosts thermal performance by 40%, power handling by 3 dB, and coupling coefficient by three times. Design approach is scalable to higher frequencies.

0.2 λ0 Thick Adaptive Retroreflector Made of Spin-Locked Metasurface

The metasurface concept is employed to planarize retroflectors by stacking two metasurfaces with separation that is two orders larger than the wavelength. Here, a retroreflective metasurface using subwavelength-thick reconfigurable C-shaped resonators (RCRs) is reported, which reduces the overall thickness from the previous record of 590 λ0 down to only 0.2 λ0 . The geometry of RCRs could be in situ controlled to realize equal amplitude and phase modulation onto transverse magnetic (TM)-polarized and transverse electric (TE)-polarized incidences. With the phase gradient being engineered, an in-plane momentum could be imparted to the incident wave, guaranteeing the spin state of the retro-reflected wave identical to that of the incident light. Such spin-locked metasurface is natively adaptive toward different incident angles to realize retroreflection by mechanically altering the geometry of RCRs. As a proof of concept, an ultrathin retroreflective metasurface is validated at 15 GHz, under various illumination angles at 10°, 12°, 15°, and 20°. Such adaptive spin-locked metasurface could find promising applications in spin-based optical devices, communication systems, remote sensing, RCS enhancement, and so on.

A microfabricated neural probe with porous si-parylene hybrid structure to enable a reliable brain-machine interface

To establish a reliable brain-machine interface (BMI), we report for the first time, a multifunctional porous silicon (PSi)-parylene neural probe using a CMOS compatible fabrication process. The biodegradable PSi shank serves as a mechanical stiffener for insertion process, then dissolves to leave only the polymeric structure to reduce stiffness mismatch between implant and cortical tissue, thus attenuates tissue responses. Moreover, its porous structure can serve as drug reservoir. The healing of the insertion trauma can be enhanced by continuously releasing pre-loaded drugs with the PSi degradation. Hence, the neural probe enables a more reliable BMI.

Aln-on-SOI platform-based MEMS hydrophone with ultra-low operation frequency and ultra-high noise resolution

This paper reports a piezoelectric aluminum nitride (AlN) based MEMS hydrophone with ultra-low operation frequency and ultra-high noise resolution. The hydrophone was fabricated on a cavity SOI substrate using a 7-mask AlN-on-SOI process platform. The fabricated hydrophone achieved a non-linearity of 0.11%, a sensitivity of -182.5dB±0.3dB (ref. to 1Vrms/μPa) and a noise floor of -125dBV/√Hz, i.e. a noise resolution 57.5dB referenced to 1 μPa/√Hz within the ultra-low operation frequency of 10Hz~100Hz, the highest noise resolution of MEMS hydrophones and better than traditional bulky hydrophones[1].