Winner of an HP Workstation

Small-Area Thin-Film Heat Flux Sensor

Mahmoud Assaad
The Goodyear Tire & Rubber Co.
Akron, OH
Small-Area Thin-Film Heat Flux Sensor

This sensor is being used in tires of all types and sizes, and has also been applied to engineering products such as hoses, belts, and conveyor belts. The product can be used in components for process control, modeling validation, determination of cooling requirements, and general calorimetry in rocketry, aerospace, and automotive environments. The sensor allows transient, bidirectional heat flux measurements on curved and flexing surfaces over areas that are smaller than those allowed by other sensors. This makes it perfect for measuring the convective heat transfer coefficient on various parts of a rolling tire.

Since temperature is one of the primary damage indicators of a tire under service conditions, accurate prediction of the temperature in a tire is vital. The sensor provides the engineers, designers, and material scientists with a means of verifying that the temperature will not reach a level where rubber reversion can occur. This state can only be predicted with accurate heat transfer analysis of the tire. With this information, tire designers and material scientists will be better able to design a tire structure that will not have critical zones of high temperature anywhere within the tire cross-section.

This new sensor design consists of a Wheatstone resistor bridge fabricated onto a 1/4-mm (0.010") thick polyester film, with half the bridge on each side of the film. The temperature sensitive element is sputter-deposited platinum, patterned and applied using a photolithography technique, with line width and line spacing approximately 60 microns. With no heat flux applied to the sensor, all of the resistor bridge elements are at the same ambient temperature, and have the same initial resistance. With the application of heat flux, the resistance of the two elements of the bridge on the hot side of the polyester film changes due to platinum’s temperature coefficient of resistance.

The resistor elements of the bridge on the cold side of the polyester film also change resistance, but by a lesser amount. The change of the resistances unbalances the bridge, and a precise measure of the heat flux can be determined from the output based on the fractional change of the resistances and the excitation voltage. With the application of “negative” heat flux (that is, a reversed heat flow), the output of the bridge will change sign. Thus, the sensor determines the direction of heat flux as well as its magnitude.

For more information, contact the inventor at This email address is being protected from spambots. You need JavaScript enabled to view it..

Honorable Mentions

Automated 3-Axis Instant Printed Circuit Board Prototyping Machine

Ryan Anderson
Sandia National Laboratories
Albuquerque, NM
Automated 3-Axis Instant Printed Circuit Board Prototyping Machine

Today, printed circuit board (PCB) production involves cutting the board, printing the masking pattern, etching, rinsing, applying flux, drilling holes, and soldering components onto the board. This new method for creating a PCB involves cutting the board, drawing traces, drilling holes, and soldering the components. This machine has three axes of motion, each controlled by a small stepper motor. The three axes move a plate located on the front of the machine. Attached to this plate is a magnetic tool changer that allows the user to change between a silver-loaded pen and a drill. When the user is ready to create a PCB, a blank piece of C10 board is secured in the slot on the steel base of the machine, the silver loaded pen is attached to the tool changer, and the CNC is used to run the automated tool path.

LumenFlow 360-Degree View Imaging System

Harold Brunt
LumenFlow Corp.
Middleville, MI

LumenFlow 360-Degree View Imaging System
This imaging system is a photonic device capable of illuminating the interior surface of any near-cylindrical object and then focusing the reflected light on the detector of a CCD camera (or any device configured to accept an image from a camera lens). The configurable system has the ability to resolve features as small as 20 microns along the interior of a cylindrical object within a range of diameters. Vertical walls, under-cut diameters, deep bores, or gaps beneath inserted components can be viewed and inspected. The system is inserted within the cylindrical surface, the image is captured, and areas of interest are identified and then analyzed. The device can be used in machine vision applications where automating bore inspection is not currently taking place.

NASA Tech Briefs Magazine

This article first appeared in the April, 2009 issue of NASA Tech Briefs Magazine.

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