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Ultrasonic Thermometry Portal Ultrasonic Thermometry is a revolutionary technology designed to look through objects to estimate temperature and heat flux at surfaces, through a material and between regions of a material. Ultrasonic Thermometry is a non-intrusive, fast response, and temperature independent method of measurement. Click the Frequently Asked Questions below for more information. Frequently Asked Questions
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How does ultrasound measure
temperature?
Ultrasonic thermometry is based
on the thermal dependence of the speed of sound in materials.
What are the benefits of using
ultrasonic thermometry? Remotely located sensors can acquire temperature and thermal conditions without disrupting flow, altering thermal transport or compromising component integrity. All of this while allowing the sensor to be isolated from harsh or chemically reactive environments. Ultrasonic Thermometry is fast response, limited only by the speed of sound through an object rather than the thermal mass of the sensor. Thermal measurement is not dependent on temperature, so accuracy is uniform throughout measurement. Is Ultrasonic Thermometry new? The
use of ultrasound to measure temperature is not new. Techniques
suitable for measurements in solids, liquids, and gases have been
available for more than 50 years1.
Ultrasonic-based measurement techniques with sub-millisecond
temporal response capable of measuring temperatures as high as 9000K
in shock tubes2 and greater than 20,000K in plasmas3
have been demonstrated.
Thin wire sensors have been used in nuclear and industrial
applications where conditions preclude the use of thermocouples,
resistance devices or optical pyrometers.
The capability for continuous monitoring of temperatures in
excess of 2000°C
for nuclear reactors has been reported4.
In the past, ultrasonic instrumentation has been size and
cost prohibitive.
What is the difference between
ultrasonic temperature measurements and a thermocouple measurement? Unlike thermocouples which measure temperature at a
single point, ultrasound measures the integral of the temperature.
If ultrasound is a measurement of
average temperature over the propagation path, how can it be used to
make local temperature and heat flux measurements?
Localization
Methods in Ultrasonic Thermometry
Thermal Measurement of Harsh Environments using Indirect Acoustic
Pyrometry
Ultrasonic Measurements of
Bore Temperature on Large Caliber Guns
What kinds of materials can be measured? Ultrasound propagates through solids, liquids and gas. To date, IMS, Inc. has demonstrated ultrasonic thermometry on many different kinds of solids, like metals, ceramics and plastics, as well as liquids including JP8 in regenerative cooling channels. Carbon composites can be used depending on material properties and configuration. Carbon-carbon is difficult to propagate through but other carbon composites are less porous and attenuating, depending on configuration. Materials of differing density, grain structure, or multiple interfaces can all be used with Ultrasonic Thermometry, but not in all cases. If you have any questions about a particular material or a configuration, please contact us to see if ultrasonic thermometry is right for you. Does ultrasound work on inhomogeneous or anisotropic materials, laminates, ceramics, or composites? Yes, but not in all conditions. Some materials attenuate at the frequencies used for ultrasonic thermometry. Typically highly porous or void-filled materials will attenuate high frequency sound propagation. In some materials this attenuation makes it difficult or impossible to measure, while in many it just requires higher amplification of the ultrasonic instrumentation. Contact us to take a look at any component that may be difficult to measure and we can let you know how viable it may be. In addition, because Ultrasonic Thermometry works so well in homogenous solids, Ultrasonic Thermometry can be used on material probes to measure surface conditions or atmospheric conditions on or near any component regardless of internal composition. Ultrasonic Thermometry can be configured in many ways for your thermal sensing needs. Does ultrasound require knowing the emissivity of a material? No, emissivity is a unique requirement to optical thermal measurement such as pyrometers and IR imaging. Because the emissivity of a material can change with temperature or due to chemical processes at high temperatures, pyrometers and IR imaging may not work well or at all in certain situations. Because of this, Ultrasonic Thermometry is better suited for extreme high temperature thermal monitoring in many situations. What material information is needed for Ultrasonic Thermometry? The ultrasonic velocity expansion coefficient is the only material property needed to make temperature measurements. This parameter is measured in a lab under isothermal conditions, or can be inferred using a material's coefficient of thermal expansion and bulk modulus change with temperature. IMS Inc. has a growing database of material parameters.While material shape and configuration can change the way ultrasound propagates through a material, the propagation path and material shape does not need to be known for thermal measurement. Is the measurement affected by ablation or erosion? Yes, the transit time change will be due to a non-temperature related effect; however, interestingly enough, most materials that are ablative have a coarse grain structure which allows for localization techniques that enable measurements of both ablation and temperature distribution. See the following link for more information on localization techniques:
Can ultrasound measure thermal barrier coatings, or into material covered by a TBC? To date, we have demonstrated localization of temperature within a ~30mil TBC, however ultrasonic thermometry may not work for all coatings. In most cases ultrasound can propagate through a thermal barrier coating or a thermal protection coating to measure the temperature of the material contained inside.
How fast can ultrasound measure
temperature?
The response time of ultrasonic thermometry is limited
only by the velocity of sound and not the thermal mass of a sensor
(as in thermocouples or thermopiles), and has a virtually unlimited
high temperature response.
Response Time Application
Note
What is heat flux and how does
ultrasound measure it?
Heat flux is the flow of energy per unit of area per unit
of time. Since
ultrasound is a measure of the total input energy over the area of
the sound wave during its propagation time it is ideally suited to
make direct, high accuracy measurement of heat flux.
Heat Flux Determination from Ultrasonic Pulse Measurements
What is the highest
temperature that can be measured?
Measurements can be made up
to the melting point of the material under test.
What is the accuracy of Ultrasonic Thermometry? Unlike Thermocouple technology, the accuracy of Ultrasonic Thermometry is constant over the entire temperature range. The accuracy of Ultrasonic thermometry is dependent on our ability to determine transit time changes. Our proprietary processing algorithm is capable of measuring changes in transit time less than 100 picoseconds. For a steel sample and a standard transducer this allows for temperature measurement precision of less than 1°C. This varies by material type and propagation length so contact us and we can provide more accuracy information based on your application.
What is the effect of balloting,
high-rate bending and shear stresses during armature passage?
Ultrasound is actually used commonly to measure bending
and stresses in non-temperature varying situations.
However the effects cannot be separated, therefore at short
times when one could assume constant temperature ultrasound could be
used to measure geometric alterations and stresses.
When one assumes all the mechanical action is quiescent,
temperature measurements can
be made.
How does it handle very high temperature
gradients?
Gradients within a material is where ultrasound shines.
Since the ultrasonic wave is sampling a material's temperature at every
instant in time, the resultant data is an integral of the total
temperature gradient. This is how using ultrasound is advantageous to measuring heat flux.
Instead of being a series of temperature measurements such as
that of a thermopile, it is truly measuring the total energy input
into the sample itself.
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