Four piezoelectric transducers with aluminum nitride (AlN), zinc oxide (ZnO), and bismuth titanate (BiTi) as the active elements and two magnetostrictive transducers were fabricated with Remendur and Galfenol as the active elements. The irradiation was for 18 months with an integrated neutron fluence of approximately 8.68x1020 n/cm2 for E >1 MeV, temperatures in excess of 420 °C, and a gamma fluence of 7.23x1021 gamma/cm2. The sensor performance is explained in the context of the pulse-echo signals. The feasibility of ultrasonic transducers in a nuclear reactor has been established. This opens the door to leave-in-place sensors for in-reactor conditions and materials.

In field applications currently used for health monitoring and nondestructive testing, ultrasonic transducers primarily employ PZT5-H as the piezoelectric element for ultrasound transmission and detection. This material has a Curie–Weiss temperature that limits its use to about 210 °C. Some industrial applications require much higher temperatures, i.e., 1000–1200 °C and possible nuclear radiation up to 10²⁰ n/cm² when performance is required in a reactor environment. The goal of this paper is the survey and review of piezoelectric elements for use in harsh environments for the ultimate purpose for structural health monitoring (SHM), non-destructive evaluation (NDE) and material characterization (NDMC). The survey comprises the following categories: 1. High-temperature applications with single crystals, thick-film ceramics, and composite ceramics, 2. Radiation-tolerant materials, and 3. Spray-on transducers for harsh-environment applications. In each category the known characteristics are listed, and examples are given of performance in harsh environments. Highlighting some examples, the performance of single-crystal lithium niobate wafers is demonstrated up to 1100 °C. The wafers with the C-direction normal to the wafer plane were mounted on steel cylinders with high-temperature Sauereisen and silver paste wire mountings and tested in air. In another example, the practical use in harsh radiation environments aluminum nitride (AlN) was found to be a good candidate operating well in two different nuclear reactors. The radiation hardness of AlN was evident from the unaltered piezoelectric coefficient after a fast and thermal neutron exposure in a nuclear reactor core (thermal flux = 2.12 × 10¹³ ncm⁻²; fast flux 2 (>1.0 MeV) = 4.05 × 10¹³ ncm⁻²; gamma dose rate: 1 × 10⁹ r/h; temperature: 400–500 °C). Additionally, some of the high-temperature transducers are shown to be capable of mounting without requiring coupling material. Pulse-echo signal amplitudes (peak-to-peak) for the first two reflections as a function of the temperature for lithium niobate thick-film, spray-on transducers were observed to temperatures of about 900 °C. Guided-wave send-and-receive operation in the 2–4 MHz range was demonstrated on 2–3 mm thick Aluminum (6061) structures for possible field deployable applications where standard ultrasonic coupling media do not survive because of the harsh environment. This approach would benefit steam generators and steam pipes where temperatures are above 210 °C. In summary, there are several promising approaches to ultrasonic transducers for harsh environments and this paper presents a survey based on literature searches and in-house laboratory observations.

A mechanical scanning acoustic reflection microscope was applied to living cells (e.g., osteoblasts) to observe their undisguised shapes and to evaluate their adhesive conditions at a substrate interface. A conditioned medium was collected from a bone-metastatic breast cancer cell line, MDA-MB-231, and cultured with an immature osteoblast cell line, MC3T3-E1. To characterize the cellular adhesion, MC3T3-E1 osteoblasts were cultured with or without MDA-MB-231 conditioned medium for 2 days, then assayed with the scanning acoustic reflection microscope. At 600 MHz the scanning acoustic reflection microscope clearly indicated that MC3T3-E1 cells cultured with MDA-MB-231 conditioned medium had both an abnormal shape and poor adhesion at the substrate interface. The results arc compared with those obtained with laser scanning con- focal microscopy and are supported by a simple multilayer model.

This paper presents results on high-frequency ultrasonic imaging of bonds between different materials with application to friction stir welding (FSW). The unique feature of this paper is the use of high numerical aperture lenses that allow the excitation of leaky surface acoustic waves. These interact with weak bonds to produce wave interference of incident and reflected waves at weak bond interfaces. The interference provides a vivid contrast marking the weak interface bond as an easily recognisable feature. Presented are a description of the high-frequency lenses, simulation of the contrast phenomenon and the application to friction stir welds. The welds were between cast A356 and wrought 6061 Al alloys obtained under four different processing conditions. The selected sections of these were imaged at high frequencies in the GHz range by bringing the acoustic lenses towards the specimen's surface far enough so that the peripheral lens rays were incident at large enough angles to exceed the first and second critical angles and to excite leaky surface acoustic waves. The interference of these waves allowed the imaging of the bond details with a resolution of about 1.5–3 μm. The features and flaws observed in the images were correlated with those reported on in the literature as well as those obtained from scanning electron microscopy and tensile property evaluation. The quality of weld bonds inferred from the images was correlated to the tensile fracture experiments, which showed that improperly bonded specimens showed a relatively larger number of flaws. The results suggest that high-frequency acoustic microscopy is indeed a useful method for the diagnostic evaluation of FSW, especially since acoustic microscopes are now available as portable instruments commercially.

Several Department of Energy Office of Nuclear Energy (DOE-NE) programs, such as the Fuel Cycle Research and Development (FCRD), Advanced Reactor Concepts (ARC), Light Water Reactor Sustainability, and Next Generation Nuclear Power Plants (NGNP), are investigating new fuels, materials, and inspection paradigms for advanced and existing reactors. A key objective of such programs is to understand the performance of these fuels and materials during irradiation. In DOE-NE’s FCRD program, ultrasonic based technology was identified as a key approach that should be pursued to obtain the high-fidelity, high-accuracy data required to characterize the behavior and performance of new candidate fuels and structural materials during irradiation testing. The radiation, high temperatures, and pressure can limit the available tools and characterization methods. In this work piezoelectric transducers capable of making these measurements are developed. Specifically, three piezoelectric sensors (Bismuth Titanate, Aluminum Nitride, and Zinc Oxide) are tested in the Massachusetts Institute of Technology Research reactor to a fast neutron fluence of 8.65×10²⁰ n_f/cm². It is demonstrated that Bismuth Titanate is capable of transduction up to 5 × 10²⁰ n_f/cm², Zinc Oxide is capable of transduction up to at least 6.27 × 10²⁰ n_f/cm², and Aluminum Nitride is capable of transduction up to at least 8.65 × 10²⁰ n_f/cm².