@article{garcia_kim_vinod_sahoo_wax_kim_fang_narayanaswamy_wu_jiang_2024, title={Carbon nanofibers/liquid metal composites for high temperature laser ultrasound}, volume={138}, ISSN={["1874-9968"]}, url={https://doi.org/10.1016/j.ultras.2024.107245}, DOI={10.1016/j.ultras.2024.107245}, abstractNote={As the demand for clean energy becomes greater worldwide, there will also be an increasing demand for next generation nuclear power plants that incorporate advanced sensors and monitoring equipment. A major challenge posed by nuclear power plants is that, during normal operation, the reactor compartment is subjected to high operating temperatures and radiation flux. Diagnostic sensors monitoring such structures are also subject to temperatures reaching hundreds of degrees Celsius, which puts them at risk for heat degradation. In this work, the ability of carbon nanofibers to work in conjunction with a liquid metal as a photoacoustic transmitter was demonstrated at high temperatures. Fields metal, a Bi-In-Sn eutectic, and gallium are compared as acoustic mediums. Fields metal was shown experimentally to have superior performance over gallium and other reference cases. Under stimulation from a low fluence 6 ns pulse laser at 6 mJ/cm2 with 532 nm green light, the Fields metal transducer transmitted a 200 kHz longitudinal wave with amplitude >5.5 times that generated by a gallium transducer at 300 °C. Each high temperature test was conducted from a hot to cold progression, beginning as high as 300 °C, and then cooling down to 100 °C. Each test shows increasing signal amplitude of the liquid metal transducers as temperature decreases. Carbon nanofibers show a strong improvement over previously used candle-soot nanoparticles in both their ability to produce strong acoustic signals and absorb higher laser fluences up to 12 mJ/cm2.}, journal={ULTRASONICS}, author={Garcia, Nicholas and Kim, Howuk and Vinod, Kaushik and Sahoo, Abinash and Wax, Michael and Kim, Taeyang and Fang, Tiegang and Narayanaswamy, Venkat and Wu, Huaiyu and Jiang, Xiaoning}, year={2024}, month={Mar} }
 @article{garcia_kim_vinod_kim_fang_jiang_2023, title={A Bi-In-Sn eutectic multi-layer high temperature ultrasound transmitter with candle-soot nanoparticles for improved photoacoustic efficiency}, volume={12487}, ISBN={["978-1-5106-6081-6"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2658480}, abstractNote={There is a growing need for non-invasive structural health monitoring in extreme environments. For nuclear power plants, pressure and temperature sensing under hazardous environment plays an important role for coolant system safety and stability management. Current sensing methods are intrusive, and suffer from degradation in the plant environment, limited life cycle, and complicated repair and replacement procedures. In this paper, we present an advanced Bi-In-Sn liquid metal (LM) transducer with the addition of candle-soot nanoparticles (CSNP) for improved photoacoustic efficiency and a metallic stencil for control of the liquid metal layer thickness. The sensitivity of the liquid metal candle-soot nanoparticle (LM-CSNP) ultrasound transmitter was characterized under 2 mJ/cm2 at 65 °C, and 6 mJ/cm2 at 100 °C —300 °C. Compared with existing LM transmitter, the newly presented transmitter showed a sensitivity 6.6 times stronger than previously reported LM only transmitter.}, journal={NONDESTRUCTIVE CHARACTERIZATION AND MONITORING OF ADVANCED MATERIALS, AEROSPACE, CIVIL INFRASTRUCTURE, AND TRANSPORTATION XVII}, author={Garcia, Nicholas and Kim, Ho-Wuk and Vinod, Kaushik and Kim, Taeyang and Fang, Tiegang and Jiang, Xiaoning}, year={2023} }
 @article{kim_balagopal_kerrigan_garcia_chow_bourham_fang_jiang_2023, title={Noninvasive liquid level sensing with laser generated ultrasonic waves}, volume={130}, ISSN={0041-624X}, url={http://dx.doi.org/10.1016/j.ultras.2023.106926}, DOI={10.1016/j.ultras.2023.106926}, abstractNote={This article proposes a noninvasive liquid level sensing technique using laser-generated ultrasound waves for nuclear power plant applications. Liquid level sensors play an important role of managing the coolant system safely and stably in the plant structure. Current sensing techniques are mostly intrusive, performing inside the fluidic structure, which is disadvantageous in terms of the regular maintenance of the plant system. Furthermore, typical intrusive sensors do not perform stably under varying environmental conditions such as temperature and radiation. In this study, sensing units are attached to the outer surface of a liquid vessel to capture guided ultrasound waves in a nonintrusive manner. The signal intensity of the guided wave dissipates when the signal interacts with the internal liquid media. The sensing mechanism is mathematically expressed as an index value to correlate the liquid level with the sensor signal. For the acoustic wave generation, laser-generated ultrasound was adopted instead of using typical contact type transducers. Following the simulation validation of the proposed concept, the performance of the developed sensor was confirmed through experimental results under elevated liquid temperature conditions. The nonlinear multivariable regression exhibited the best-fit to the datasets measured under the variable liquid level and temperature conditions.}, journal={Ultrasonics}, publisher={Elsevier BV}, author={Kim, Howuk and Balagopal, Bharat and Kerrigan, Sean and Garcia, Nicholas and Chow, Mo-Yuen and Bourham, Mohamed and Fang, Tiegang and Jiang, Xiaoning}, year={2023}, month={Apr}, pages={106926} }
 @article{kim_kim_garcia_fang_jiang_2021, title={Liquid metallic laser ultrasound transducer for high-temperature applications}, volume={118}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0046052}, DOI={10.1063/5.0046052}, abstractNote={This study aims to investigate a laser ultrasound (LUS) transducer for high-temperature (>100 °C) applications. For decades, many researchers have investigated efficient LUS transducers, yet studies on laser ultrasound transducers capable of performing at the high-temperature condition are rarely found in the literature. Most current LUS transducers still utilize a polymer-based composite material, that is, not stable at varying temperature conditions. This study introduces a liquid metallic (LM) LUS transducer that utilizes field's metal, which has a high thermal expansion (∼3 × 10−4 K−1). We hypothesized that such a high thermal expansion of the liquid metal can effectively produce laser-generated ultrasound waves, substituting for conventional polymer-based transducers. A numerical simulation predicted that the LM LUS transducer would produce higher LUS intensity (∼22 dB) than that without the LUS transducer. Experiment results confirmed that the LM transducer effectively intensifies the ultrasound wave signals, obtaining a signal-to-noise gain over 30 dB. Moreover, the transducer was found capable of transmitting detectable wave packets in relatively high-temperature conditions (∼400 °C), while conventional candle soot nanoparticle-polydimethylsiloxane could not perform stably at these elevated temperatures. The investigations introduced in this article are scientifically significant since we demonstrated the engineering feasibility of liquid metallic materials for LUS transducers.}, number={18}, journal={APPLIED PHYSICS LETTERS}, author={Kim, Howuk and Kim, Kyunghoon and Garcia, Nicholas and Fang, Tiegang and Jiang, Xiaoning}, year={2021}, month={May} }