Journal
SENSORS
Volume 19, Issue 21, Pages -Publisher
MDPI
DOI: 10.3390/s19214755
Keywords
piezoelectric; high-temperature ultrasonic testing; radiation resistance; field-deployable sensor; guided-wave send-receive; spray-on transducers; piezocomposites
Funding
- US Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office [DE-AC07-051D14517]
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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 degrees C. Some industrial applications require much higher temperatures, i.e., 1000-1200 degrees C and possible nuclear radiation up to 10(20) n/cm(2) 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 degrees 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 x 10(13) ncm(-2); fast flux 2 (>1.0 MeV) = 4.05 x 10(13) ncm(-2); gamma dose rate: 1 x 10(9) r/h; temperature: 400-500 degrees 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 degrees 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 degrees 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.
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