Alic Chen

Dispenser-printed planar thick-film thermoelectric energy generators

This work presents advancements in dispenser-printed thick film thermoelectric materials for the fabrication of planar and printable thermoelectric energy generators. The thermoelectric properties of the printed thermoelectric materials were measured as a function of temperature. The maximum dimensionless figures of merit (ZTs) at 302 K for the n-type Bi2Te3-epoxy composite and the p-type Sb2Te3-epoxy composite are 0.18 and 0.19, respectively. A 50-couple prototype with 5 mm × 640 µm × 90 µm printed element dimensions was fabricated on a polyimide substrate with evaporated metal contacts. The prototype device produced a power output of 10.5 µW at 61.3 µA and 171.6 mV for a temperature difference of 20 K resulting in a device areal power density of 75 µW cm−2.

Evaluation of upper extremity reachable workspace using Kinect camera

BACKGROUND In clinical evaluation of upper extremity, there is a lack of assessment methods that are quantitative, reliable, and informative of the overall functional capability of an individual. OBJECTIVE We present new methodology for the assessment of upper extremity impairments based on the concept of 3-dimensional reachable workspace using Microsoft Kinect. METHODS We quantify the reachable workspace by the relative surface area representing the portion of the unit hemi-sphere that is covered by the hand movement. We examine accuracy of joint positions, joint angles, and reachable workspace computation between the Kinect and motion capture system. RESULTS The results of our analysis in 10 healthy subjects showed that the accuracy of the joint positions was within 66.3 mm for our experimental protocol. We found that the dynamic angle measurements had relatively large deviations (between 9° to 28°). The acquired reachable workspace envelope showed high agreement between the two systems with high repeatability between trials (correlation coefficients between 0.86 and 0.93). CONCLUSIONS The findings indicate that the proposed Kinect-based 3D reachable workspace analysis provides sufficiently accurate and reliable results as compared to motion capture system. The proposed method could be promising for clinical evaluation of upper extremity in neurological or musculoskeletal conditions.

Dispenser printed composite thermoelectric thick films for thermoelectric generator applications

This paper describes novel processes for preparing thermoelectric composite materials compatible with thick film dispenser printing fabrication processes. Optimization of process parameters to improve thermoelectric properties is introduced. We explore the use of n-type Bi2Te3 and p-type Sb2Te3 materials to achieve properties suitable for use in low cost high aspect ratio microscale thermoelectric generators. Printable thermoelectric inks consisted of dispersed semiconductor powders in an epoxy resin system. Thick films were printed on glass substrates and cured at temperatures ranging from 150 to 350 °C. The best achievable power factors for n-type Bi2Te3-epoxy and p-type Sb2Te3-epoxy composite films were 1.5×10−4 W/m K2 and 8.4×10−4 W/m K2, respectively. Figure of merit (ZT) values for n-type Bi2Te3-epoxy and p-type Sb2Te3-epoxy composites were 0.16 and 0.41, respectively, which are much higher than previously reported ZT values for composite thermoelectric materials.

Enhanced Performance of Dispenser Printed MA n-type Bi2Te3 Composite Thermoelectric Generators

This work presents performance advancements of dispenser printed composite thermoelectric materials and devices. Dispenser printed thick films allow for low-cost and scalable manufacturing of microscale energy harvesting devices. A maximum ZT value of 0.31 has been achieved for mechanically alloyed (MA) n-type Bi₂Te₃-epoxy composite films with 1 wt % Se cured at 350 °C. The enhancement of ZT is a result of increase in the electrical conductivity through the addition of Se, which ultimately lowers the sintering temperature (350 °C). A 62 single-leg thermoelectric generator (TEG) prototype with 5 mm ×700 μm × 120 μm printed element dimensions was fabricated on a custom designed polyimide substrate with thick metal contacts. The prototype device produced a power output of 25 μW at 0.23 mA current and 109 mV voltage for a temperature difference of 20 °C, which is sufficient for low power generation for autonomous microsystem applications.

High-Performance Dispenser Printed MA p-Type Bi0.5Sb1.5Te3 Flexible Thermoelectric Generators for Powering Wireless Sensor Networks

This work presents a novel method to synthesize p-type composite thermoelectric materials to print scalable thermoelectric generator (TEG) devices in a cost-effective way. A maximum ZT of 0.2 was achieved for mechanically alloyed (MA) p-type Bi0.5Sb1.5Te3 (8 wt % extra Te additive)-epoxy composite films cured at 250 °C. A 50% increase in Seebeck coefficient as a result of adding 8 wt % extra Te in stoichiometric Bi0.5Sb1.5Te3 contributed to the increase in ZT. To demonstrate cost-effective and scalable manufacturing, we fabricated a sixty element thermoelectric generator prototype with 5.0 mm × 600 μm × 120 μm printed dimensions on a custom designed polyimide substrate with thick metal contacts. The prototype TEG device produced a power output of 20.5 μW at 0.15 mA and 130 mV for a temperature difference of 20 K resulting in a device areal power density of 152 μW/cm(2). This power is sufficient for low power applications such as wireless sensor network (WSN) devices.

Integration of dispenser-printed ultra-low-voltage thermoelectric and energy storage devices

This paper reports on an integrated energy harvesting prototype that consists of dispenser-printed thermoelectric energy harvesting and electrochemical energy storage devices. Parallel-connected thermoelectric devices with low internal resistances were designed, fabricated and characterized. The use of a commercially available dc-to-dc converter was explored to step-up a 27.1 mV input voltage from a printed thermoelectric device to a regulated 2.34 V output at a maximum of 34% conversion efficiency. The regulated power succeeds in charging dispenser-printed, zinc-based micro-batteries with charging efficiencies of up to 67%. The prototype presented in this work demonstrates the feasibility of deploying a printable, cost-effective and perpetual power solution for practical wireless sensor network applications.

Thick film thermoelectric energy harvesting systems for biomedical applications

The potential for the microfabrication of thermoelectric generators has been shown for powering autonomous wireless sensors in and around the human body. Existing bulk fabrication methods (extrusion and dicing) as well as traditional microfabrication methods (sputtering and etching) cannot create structures with the correct size factors and aspect ratios for optimal power generation. As a result, this paper describes a new promising printing method, specifically developed to additively create microscale generators. Early results show that the method is both cost effective and scalable for the mass production of thermoelectric generators to power medical devices.

Dispenser printed circular thermoelectric devices using Bi and Bi0.5Sb1.5Te3

This work presents polymer based composite materials used in slurries form to print low cost and scalable micro-scale Thermoelectric Generator (TEG) devices. Bi-epoxy composite is chosen as n-type material and mechanical alloy p-type Bi0.5Sb1.5Te3 with 8 wt. % extra Te-epoxy composite is used as p-type material. Maximum power factor of 0.00008 W/m-K2 is achieved for Bi-epoxy and Bi0.5Sb1.5Te3 with 8 wt. % extra Te-epoxy composite dispenser printed thick films. A 10 couple dispenser printed circular TEG prototype produced 130 μW power at ΔT of 70 K resulting in a device areal power density of 1230 μW/cm2.

Technologies for an Autonomous Wireless Home Healthcare System

We present a design study highlighting our recent technological developments that will enable the implementation of autonomous wireless sensor networks for home healthcare monitoring systems. We outline the power requirements for a commercially available implantable glucose sensor which transmits measurements to an external wireless sensor node embedded in the home. A network of these sensor nodes will relay the data to a base station, such as a computer with internet connection, which will record and report this data to the user. We explore the feasibility of powering these sensors using energy scavenging from both body temperature gradients and vibrations in the home, and discuss our developments in energy storage and low power consuming hardware.

Dispenser Printed Microscale Thermoelectric Generators for Powering Wireless Sensor Networks

Wireless sensor networks (WSN) are a promising technology for ubiquitous, active monitoring in residential, industrial and medical applications. These nodes combine a radio transceiver, microcontroller and sensors into a low power package. A current bottleneck for widespread adoption of WSN’s is the power supplies. While the power demands can be somewhat alleviated through novel electronics, any primary battery will have a finite lifetime. Energy harvesting, from ambient vibration, light, and heat sources, offers an opportunity to significantly extend the lifetime of the nodes and possibly provide perpetual power. Thermal energy is an ideal source for WSNs due to the availability of low-grade ambient waste heat sources. Thermoelectric devices convert temperature gradients into DC electric power in compact form factors. Efficient device designs require hundreds of high-aspect ratio semi-conductor microelements fabricated electrically in series and thermally in parallel. This design requirement presents problems for standard microfabrication techniques due to thickness limitations of standard semiconductor processes. We present a new method of contact dispenser printing, specifically developed to additively create microscale generators. Initial materials performance results show promising results and are further detailed in this work.Copyright