Thermoelectric phenomenon describes the relationship between the flow of heat and electricity. Two main categories encompassed in thermoelectric theory are the Seebeck and Peltier effects. The Seebeck effect is the generation of a voltage in a device that consists of two different materials in the presence of a temperature gradient, while the Peltier effect is the generation of a temperature gradient across a device of two different materials in the presence of an electrical current. This project focuses on the first of these two phenomena, where the Seebeck effect is used in a novel heat flux sensor that is transverse in nature. Transverse thermoelectric devices are characterized by their anisotropy, meaning that a temperature gradient generated across a device will be perpendicular to the flow of electricity through the device. This orthogonal arrangement allows for the manipulation of material properties, device arrangement, and construction methods for device optimization. This project characterizes the heat flux sensing capabilities of an artificially anisotropic transverse thermoelectric device via experimental and theoretical methods. The device tested is constructed out of bismuth telluride and titanium grade 5. Bismuth telluride is a standard thermoelectric material, while the titanium is used because of its high melting point and good electrical conductivity. The device is constructed by alternating rectangular pieces of these two materials. These pieces are bonded together at a given angle to simulate anisotropy. Several devices are constructed in a range of angles from 59 to 88°. These devices are each tested in a vacuum chamber where a heater heats one side of the device. This heat flux into the device creates a temperature gradient across the device and the device generates a voltage perpendicular to this temperature gradient. Steady state data are collected for both the temperature difference between the two sides of the device and the voltage generated by the device. This procedure is repeated on each device for a range of heat fluxes from 0 to 2.6 W/cm². This range generates voltage signals up to 14341 µV for an angle of 59°. Data collected are then used to generate a linear trend line that describes the devices response to a given heat flux. These experimental results are compared to theoretical predictions using thermoelectric theory. The results indicate that the device does exhibit transverse thermoelectric characteristics and the experimental data follow the predicted trends. This thesis documents the process of constructing, testing, and analyzing this device. / Master of Science

While thermoelectric technology has developed steadily over the last 50 years, transverse thermoelectrics have generally been ignored in the industrial and commercial uses of thermoelectric devices to date. This project focuses on investigating transverse thermoelectric effects for localized cooling and heat flux sensing. Thermoelectric cooling devices are useful when their advantages (small size, solid state, active temperature control) outweigh their relatively poor efficiency. Transverse heat flux sensors, which generate an electric field in a direction orthogonal to the heat flow, have the advantage that the signal depends on the length of the device rather than the thickness. Thus, they can be made very thin for fast response times while maintaining a large signal. A prototype transverse device was built out of bulk samples of bismuth and bismuth telluride, which are common thermoelectric materials. The device was constructed of alternating layers of the constituent materials to simulate the effects of an intrinsically anisotropic material. The device was tested for its cooling and heat flux sensing capabilities, and the results of this testing were compared to predicted values. Although the device failed to demonstrate cooling, its heat flux sensing capabilities were promising. The device was tilted to several angles of inclination between 44° and 84° from horizontal, and the output voltage was recorded for several values of heat flux. The signal strength varied between 190.2 and 2321.6 ìV/(W/cm2), at inclination angles of 84° and 44°, respectively. The results followed the trend of the predicted values well, but the magnitude of the output voltage was significantly lower than expected. An uncertainty analysis was performed, and it was determined that the most likely source of error was the uncertainty in the amount of heat flux that went through the device during testing. This thesis outlines the process of building and testing the device, and the analysis of the results. Recommendations for future work are also given. / Master of Science