Hi-Z Technology, Inc.

Technical Papers from 2006

Thermoelectric Quantum Well Energy Harvesting Device

Dr. Saeid Ghamaty , Norbert B. Elsner , Velimir Jovanovic

Abstract
Hi-Z Technology, Inc., has recently fabricated a Quantum Well (QW) device with two couples of N- and P-type Si/SiGe deposited on both sides of a Kapton™ substrate. This nanotechnology device is being fabricated for the U.S. Navy milliwatt energy harvesting applications. Only two out of twenty-six couples of the complete energy-harvesting device were contacted due to limited tooling and fixtures in the high vacuum chamber. An improved sputtering process was successfully developed to deposit the Mo metal contacts that exhibit a negligible contact resistance with both the N and P material. Initial measurements of power output from this Mo contacted device, from Tc = 26 to Th = 66 C, appear promising as they are close to the expected results of output power of 5 mWatts at 3 Volts for the complete device. The output voltage form this device was 225 mVolt, and total power was 0.371 mWatt at a temperature difference of ~40 C. The power and output voltage of this device at the design dT = 40 C are very close (<10%) to the calculated values of the N and P materials. Extrapolating the two couple data to a full size device yields a total power of ~4.8 mWatt @ ~2.93 Volt for a complete 26 couple energy harvesting device enough power to operate a wireless sensor.

Full-text article available for download. (PDF)

Design, Fabrication and Testing of a Novel Energy-Harvesting Thermoelectric Power Supply for Wireless Sensors

Velimir Jovanovic, Saeid Ghamaty and John C. Bass
Abstract
A prototype energy-harvesting thermoelectric generator (TEG) was designed and fabricated and it is being tested to provide power for wireless sensors used in the health monitoring (monitoring of temperatures, vibrations, strains, etc) of Navy shipboard machinery. TEGs are rugged, reliable, solid-state devices that convert heat directly into electricity without any moving parts. The TEGs designed in this project utilize the heat transfer between shipboard waste heat sources and ambient air to generate electricity. To satisfy the required small design volume of less than one cubic inch, Hi-Z Technology, Inc. (Hi-Z) is using its innovative Quantum Well (QW) thermoelectric technology that provides a factor of four increase in the conversion efficiency, and a large reduction in the design volume over the currently used bulk bismuth- telluride thermoelectics. QWs are nanostructured multi-layer thin films. These wireless sensors can be used to detect cracks, corrosion, impact damage, and temperature and vibration excursions as part of the Condition Based Maintenance (CBM) of the Navy ship machinery. The CBM of ship machinery can be significantly improved by automating the process with the use of self-powered wireless sensors. These power-harvesting TEGs can be used to replace batteries as electrical power sources and to eliminate tethered wires and cables, thus significantly reducing the installation and maintenance costs. The very first QW TEG module anywhere was just successfully tested (it produced electricity from heat). It remains to package this module with thermal insulation in the housing and heat sink, and to test this entire TEG device in a simulated thermal environment of a Navy gas turbine. Following this test, it is planned to attach this device to the surface of a gas turbine on a Navy ship and to test it in its actual environment, in conjunction with a wireless sensor. This power supply for wireless sensors can also be used in health monitoring of equipment in the nuclear and conventional power plants, process plants, and the monitoring of temperatures, vibrations and pressures of steam lines, etc. Hi-Z has chosen this small power supply as the first practical application of its emerging QW TEG technology. However, this technology can also be used on a much larger scale in, for example, recovering the waste heat from the exhaust of the truck and automobile engines, where the generated electricity can be used to eliminate the alternator and thus reduce the load on the engine, improve overall efficiency and reduce fuel consumption.

Full-text article available for download. (PDF)

Predicted Performance of Quantum Well Thermoelectrics for Waste Heat Recovery Power Generation

Daniel J. Krommenhoek, Saeid Ghamaty, John C. Bass and Norbert B. Elsner

Abstract
Hi-Z has measured the thermoelectric properties of N-type Si/SiGe and P-type B4C/B9C on a Si substrate from room temperature to 260°C and fabricated a couple demonstrating 14% efficiency at a temperature difference of 200°C. Based on this data, concept design features for quantum well modules and waste heat recovery electrical generators are reviewed. Predictions using measured thermoelectric properties and prior thermoelectric generator design work show how quantum well thermoelectric modules compare to current commercial Hi-Z Bi2Te3 alloy thermoelectric modules. Quantum well thermoelectric data is presented showing negligible change of power factor in initial life tests. Also, latest data is presented for quantum well thermoelectric films fabricated in a new large-scale sputtering machine.

Predictions of power output for a module with quantum well films shows that greater than 50 Watts of electricity will be generated at greater than 15% efficiency in a square module 2.5 inches on a side. This is over three times the output and efficiency of the current commercial Hi-Z Bi2Te3 alloys. It is shown how performance (power, efficiency, voltage, etc.) depends on the quantum well film material and substrate material. A low thermal conductivity substrate reduces parasitic heat losses and increases efficiency; and also provides a design method to adjust for the operational environment.

For generating several kilowatts of electricity from a waste heat stream, concept designs are presented for the thermoelectric generators with quantum well materials. Hi-Z builds on experience in designing and testing one kilowatt and 300 Watt generators for vehicle waste heat recovery. As an example, over 3 kilowatts at >15% efficiency are predicted with an exhaust stream at 500°C and a quantum well generator that has an outside diameter less than12 inches and length less than two feet. They key challenge to achieve this is to increase the sputtering volume of quantum well films at affordable costs.

Full-text article available for download. (PDF)