Kee S. Moon

A Vibration-Based PMN-PT Energy Harvester

We report design, modeling, analysis, and experimental study of a vibration-based piezoelectric energy harvester. The energy harvester is made of a composite cantilever of a single crystal relaxor ferroelectric material, (1- x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), and a polydimethylsiloxane (PDMS) base layer. A PDMS proof mass is constructed at the tip of the composite cantilever beam and is used as a means to tune the system natural frequency. The use of the PMN-PT piezoelectric material and an interdigited electrodes (IDEs) design improves the energy conversion efficiency. A dynamic systems modeling approach is employed to analyze the responses and the performance of the harvester design. We have demonstrated that a prototype of the harvester with a size of 7.4 mm times 2 mm times 110 mum outputs a voltage of 10 V (0.3 mW power) under a vibration excitation with a peak-to-peak amplitude of 1 mm at a frequency around 1.3 kHz. Based on the experimental results, the power density prediction of the proposed harvester design shows a superior performance than that of the other reported piezoelectric harvesters.

A PMMA coated PMN?PT single crystal resonator for sensing chemical agents

A highly sensitive lead magnesium niobate–lead titanate (PMN–PT) single crystal resonator coated with a thin film of polymethylmethacrylate (PMMA) useful for detecting chemical agents such as acetone, methanol, and isopropyl alcohol is presented. Swelling of the cured PMMA polymer layer in the presence of acetone, methanol, and isopropyl alcohol vapors is sensed as a mass change transduced to an electrical signal by the PMN–PT thickness shear mode sensor. Frequency change in the PMN–PT sensor is demonstrated to vary according to the concentration of the chemical vapor present within the sensing chamber. For acetone, the results indicate a frequency change more than 6000 times greater than that which would be expected from a quartz crystal microbalance coated with PMMA. This study is the first of its kind to demonstrate vapor loading of adsorbed chemical agents onto a polymer coated PMN–PT resonator.

A Wireless 32-Channel Implantable Bidirectional Brain Machine Interface.

All neural information systems (NIS) rely on sensing neural activity to supply commands and control signals for computers, machines and a variety of prosthetic devices. Invasive systems achieve a high signal-to-noise ratio (SNR) by eliminating the volume conduction problems caused by tissue and bone. An implantable brain machine interface (BMI) using intracortical electrodes provides excellent detection of a broad range of frequency oscillatory activities through the placement of a sensor in direct contact with cortex. This paper introduces a compact-sized implantable wireless 32-channel bidirectional brain machine interface (BBMI) to be used with freely-moving primates. The system is designed to monitor brain sensorimotor rhythms and present current stimuli with a configurable duration, frequency and amplitude in real time to the brain based on the brain activity report. The battery is charged via a novel ultrasonic wireless power delivery module developed for efficient delivery of power into a deeply-implanted system. The system was successfully tested through bench tests and in vivo tests on a behaving primate to record the local field potential (LFP) oscillation and stimulate the target area at the same time.

Resonant ultrasonic wireless power transmission for bio-implants

In this paper, we present the ultrasonic wireless power transmission system as part of a brain-machine interface (BMI) system in development to supply the required electric power. Making a small-size implantable BMI, it is essential to design a low power unit with a rechargeable battery. The ultrasonic power transmission system has two piezoelectric transducers, facing each other between skin tissues converting electrical energy to mechanical vibrational energy or vice versa. Ultrasound is free from the electromagnetic coupling effect and medical frequency band limitations which making it a promising candidate for implantable purposes. In this paper, we present the design of piezoelectric composite transducer, the rectifier circuit, and rechargeable battery that all packaged in biocompatible titanium can. An initial prototype device was built for demonstration purpose. The early experimental results demonstrate the prototype device can reach 50% of energy transmission efficiency in a water medium at 20mm distance and 18% in animal skin tissue at 18mm distance, respectively.

PMN-PT single crystal resonators for sensing acetone vapors

This paper compares frequency measurements in lead magnesium niobate-lead titanate (PMN-PT) resonators with conventional quartz crystal microbalance (QCM) resonators when exposed to acetone vapors under identical test conditions. A pumpless mechanism for driving acetone vapors by convection force was developed in our experimental setup. The frequency shift recorded in response to acetone vapor exposure for the PMN-PT resonator was more than 10,000 times larger than for the QCM resonator. Our experimental results reinforce the notion that PMN-PT resonators could be a superior replacement for QCM resonators in a variety of biosensor applications. The experimental setup heated water to produce acetone vapors, a volatile organic chemical, which were delivered to a sensing chamber to interact with the sensing unit. Chemical vapors were driven toward the sensing unit and circulated through the system via a pumpless mechanism by the principle of convection. Both types of resonators displayed a change in frequency as acetone vapors were applied, but PMN-PT showed a more significant change by several orders of magnitude.

Reactive Current-Activated Tip-Based Sintering of Ni–Al Intermetallics

Current-activated tip-based sintering (CATS) is a new process that imposes local current-activated sintering conditions to consolidate selected areas of a powder compact/bed through the controlled application of a contacting tip electrode. The process has the ability of achieving very high sintering rates and obtaining complex-sintered geometries through the controlled precision motion of the electrically conductive tip. In this study, the high current densities afforded by CATS are utilized to locally activate a macroscopic combustion synthesis type reaction in compacts of reactive mixtures of nickel and aluminum to rapidly form nickel aluminides. The effect of current intensity on the ignition time, microstructure, homogeneity, and properties of the combustion synthesized products is discussed in this article. It was found that ultra-rapid formation of aluminum-rich intermetallics precedes and contributes to the major ignition event. Moreover, time to ignition was found to decrease with an increase in current intensity, also leading to less homogenous microstructures.

MEMS acoustic sensor using PMN-PT single-crystal diaphragm

The MEMS (micro-electro-mechanical systems) microphone enables the manufacturing of small mechanical components on the surface of a silicon wafer. The MEMS microphones are less susceptible to vibration because of the smaller diaphragm mass and an excellent candidate for chip-scale packaging. The PMN-PT materials itself exhibit extremely high piezoelectric coefficients and other desirable properties for an acoustic sensor. In this paper, we present a piezoelectric MEMS microphone based on PMN-PT single crystal diaphragm. The fabrication process including dry etching conditions and scale-factored prototype is presented. In particular, this paper introduces the design of a PMN-PT single crystal diaphragm with interdigitated electrode.

Wireless Photoplethysmograph Knuckle Sensor System for Measuring Finger Motions

In this paper, we present the on-going study to explore the use of photoplethysmograph (PPG), and inertial measurement unit (IMU) sensors to sense the movement of the fingers and the orientation of the hand. This paper focuses on an optical sensor system that can detect the movement of the fingers by utilizing the photoplethysmograph (PPG). The optical sensor consists of the light emitting and detecting components, which are two LEDs and a photodiode in our system. The photodiode senses the intensity of the light emitted from each LED after the light passes through the tissue. As a finger moves, the light diffused through the skin of the knuckle, therefore, finger position can be differentiated. In this paper, we discuss the sensitivity and the response time of the knuckle sensor system with respect to the finger motions.

Development of a PMN-PT/PDMS Vibrational Energy Harvester

Improving the energy conversion efficiency is one critical factor for practical usage of vibrational energy harvesting devices. In this paper, we design and prototype a vibration-based energy harvester with a high output energy density. The proposed harvester is based on a composite cantilever beam-mass design. The cantilever beam is made of a high piezoelectric constant, lead magnesium niobate-lead titanate (PMN-PT) material. A polydimethylsiloxane (PDMS) coating is applied to the cantilevers to decrease stress concentration of the thin PMN-PT and therefore increase the strength of the cantilever. A PDMS proof mass is also added to decrease the natural frequency of the cantilever system and to increase displacement and the voltage output. It is found that a 7.4 mm PMN-PT cantilever with a PDMS coating and proof mass produces a sustained 0.7 mW of RMS power (16.8 V, 58 μA) at an acceleration of 55 m/s2.

Design of a PMN-PT-based monolithic nanomanipulator

In this paper, a cantilever-based manipulator using (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single-crystal relaxor ferroelectric material is presented. We report the design of a novel piezoelectric multi-degree-of-freedom motion cantilever. The structure has interdigitated electrode (IDE) on the top and bottom surfaces of the cantilever and possesses both longitudinal and flexural actuation capabilities. PMN-PT materials are ideal for actuator applications since they exhibit a very high piezoelectric strain. We separately pattern interdigitated electrode (IDE) on the top and bottom surfaces of a single crystal cantilever beam. Furthermore, we propose a novel L-shaped cantilever manipulator that can provide up to four-degrees of freedom motion. The small and planar structure has potential applications in optical beam steering systems and nano-manipulators inside a scanning electron microscope.