Embedded metallized optical fibers for high temperature applications

Abstract

Embedding fiber optics in metal components could enable new capabilities such as active monitoring of spatially distributed strain. Ultrasonic additive manufacturing is a suitable technique for embedding fiber optics because it allows fibers to be embedded in metals without melting and without the use of epoxy. However, for harsh environments that could have high temperatures or high radiation doses, traditional polymer-coated fibers cannot survive for extended periods of time. This work demonstrates successful embedding of commercially available copper-, nickel-, and aluminum-coated fibers into aluminum without any observable damage to the fiber. Copper-coated fibers embedded in copper show adequate light transmission, although residual strain could not be resolved. With further processing improvements, fibers embedded in copper or other hightemperature materials could enable even higher temperature operation. Optical transmission and spatially distributed strain were measured in the fibers embedded in aluminum. Measurements were taken after embedding and during heating to temperatures greater than 500 °C. Within the embedded region, both the copper-and aluminum-coated fibers showed strain that matched the expected strain in the surrounding aluminum matrix during heating. This suggests a strong interfacial bond strength that exceeds the maximum estimated fiber strain of 1.2% (871 MPa tensile stress). This demonstration of embedded fibers that can survive high temperatures and remain bonded to the metal matrix is the first step toward embedded fiber optic sensors for harsh environment applications.

Demonstrate embedding of sensors in a relevant microreactor component

“…All the sensors generally show no significant reductions in the reflected signal amplitude before, within, and after the embedded region. This is a significant improvement from previous efforts to embed fiber-optic sensors that showed more significant signal attenuation [2]. It is expected that the improvement in signal attenuation is due to the use of a low-bendloss optical fiber, which reduces microbending losses that can be introduced during the embedding process.…”

“…This loose coupling is required to prevent strain effects from influencing the temperature measurements. On the other hand, spatially distributed strain can be measured by directly embedding metal coated fibers in the component and compensating for temperature effects using loosely-coupled fiber-optic temperature sensors or TCs, similar to previous efforts [2,3]. Fiber-optic sensors have been demonstrated at temperatures up to 1,000°C [16,17,21] and in high radiation environments [22][23][24][25][26][27][28][29][30].…”

“…Similar work is being performed to embed sensors in ceramic structures under the Transformational Challenge Reactor (TCR) Program [1]. The present work leverages additive manufacturing technologies that were initially developed using Laboratory Directed Research and Development (LDRD) funding from Oak Ridge National Laboratory (ORNL) [2][3][4][5]. The work described herein is a step towards extending ultrasonic additive manufacturing (UAM) technology to embed sensors within more complex metal components relevant to microreactors.…”

Demonstration of Embedded Sensors in Ceramic Structures

“…Sapphire fiber-based sensors could extend the operational temperature range to 1,500°C or higher [16][17][18][19], although these sensors have a relatively low technology readiness level. Fiber-optic sensors are also being considered for spatially distributed strain measurements based on success performing similar measurements after embedding the sensors in metals [20][21][22].…”

Information integrated glass module fabricated by integrated additive and subtractive manufacturing

“…Compared with the conventional sensor packaging method, which is realized by attaching or mounting sensors on structures after being fabricated, additive manufacturing approach in sensor development has been initiated recently by directly embedding sensors into functional parts or smart structures to realize in situ measurement of parameters of interests. Optical fiber sensors have been demonstrated to be embedded in 3D printed ceramic and metal composites and shown the potential for high temperature sensing applications [11,14,15]. However, considering different material properties, especially the large difference of thermal expansion coefficient (CTE) between embedded structure and optical fiber, extra protective coating layers on fiber or external protectors may be necessary to avoid embedded fiber damage [11,14,15].…”