Plural ultrasonic waveguide measurements of spatially distributed properties

Description (excerpt)

CROSS REFERENCE TO RELATED APPLICATION This application claims priority to and the benefit of U.S. provisional application 63/634,136, filed Apr. 15, 2024, the contents of which are incorporated herein by reference. RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured, licensed and used by and for the Government of the United States for all governmental purposes without the payment of any royalty. FIELD OF THE INVENTION The present invention relates to ultrasonic waveguides configured to determine intensive properties and more particularly to such waveguides which provide differential echogenic responses usable to determine temperature distributions. BACKGROUND OF THE INVENTION Extreme environments include harsh conditions of temperature, pressure, oxidation, shock and/or electromagnetic effects. Such harsh conditions exist, for example, within the combustion chambers of rocket engines, during energy conversion, during material processing and in aerospace applications. Extreme environments have been characterized by using inserted sensors which are treated to withstand harsh conditions, but are typically limited to model based, inferential measurements or limited to noninvasive measurements. For example, tolerant insertion sensors in the prior art were designed to withstand exposure to extreme environments. Such sensors utilize protective sheathing, active mitigation measures (e.g., cooling) or resiliently appropriate materials. But protective sheaths are subject to breach and active cooling adds complexity. One particular attempt in the art uses pointwise and distributed temperature measurements with glass fiberoptic transducers—such as fiberoptic Bragg grating (FBG), optical resonator cavity, and fluorescence. But these transducers degrade as the temperature approaches 1,000° C., at which temperature silica fiber loses mechanical strength and becomes brittle. By replacing the glass with sapphire, the range of measurable temperatures has been extended somewhat, but commercial manufacturing of single-crystal sapphire fibers with high-temperature cladding has remained elusive. Yet, some environments are so harsh that even the most robust insertion sensors do not survive prolonged exposure. When insertion sensor measurements are infeasible, the interdependence between process variables becomes necessary in order even estimate properties based on the available data. Estimation of inaccessible states or properties using the available secondary measurements is variably known in the art as soft sensing, virtual metrology, inferential measurements, causal interference or state estimation. A model is needed to perform the inference, whether empirical or based on first principles, and must be validated by the direct measurements of the properties to be estimated and still be adaptable to changing process conditions and disturbances which may require further validation at the expense of time and cost. But the inherent dependence of soft sensing on a model is inherently less reliable than direct measurements. Other attempts in the art include noninvasive measurement modalities that rely upon electromagnetic fields. Such fields have spectral ranges including RF, optical, X-ray gamma-ray and acoustic/ultrasonic responses in fluids or solids. Yet other signals such as electrical capacitance, electrical resistance and magnetic resonance have been used to gauge the states and properties of interest. In a forgiving environment, a noninvasive quantification, such as nondestructive evaluation (NDE) could be an alternative to traditional insertion sensors. But (NDE) techniques are typically used on-demand, as-needed or at pre-determined infrequent inspections. NDE is unsuitable for or requires modifications in order to provide for repeated online measurements with an adequate sampling rate to monitor processes and to provide feedback on environmental conditions to control process and systems operations. Optical techniques are among the noninvasive sensing modalities capable of temperature measurements of extreme environments. But optical techniques are limited to line of sight, which may be impossible to establish. And even if possible, laborious effort is often required to maintain an optically transparent line-of-sight in many applications. Acoustic pyrometry is a noninvasive thermometry method built on the dependence of the speed of sound (SOS) on the gas temperature. Acoustic pyrometry has been applied to energy conversion and other industrial applications. The attenuation of acoustic signals in gasses limits the frequency of acoustic excitations that can be used for pyrometry, which may cause interference from acoustic emissions by turbulent flows, combustion instabilities, and other pressure oscillations in the acoustic range. Furthermore, when the temperat