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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

Materials

Measurement Setup and Performance

 





How does ultrasound measure temperature?

Ultrasonic thermometry is based on the thermal dependence of the speed of sound in materials.  Sound recorded through a material inherently contains information about the temperatures within that material.  Our technology is able to see and extract that information as a material changes temperature.

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. 

  1. Lynnworth, L. C. in Ultrasonic Measurements for Process Control, Chapter 5 pp.369-422, Academic Press Inc. San Diego, CA, 1989.
  2. E. H. Carnevale, S. Wolnik, G. Larson and C. Carey,Physics of Fluids 2(7), 1459-1467 (July 1967).
  3. E. H. Carnevale et a l . ,Final Report, NASw-549 (Dec. 1964).
  4. H. A. Tasman, M. Campana, D Pel, J. Richter,Ultrasonic Thin Wire Thermometry for Nuclear Applications, Temperature—Its Measurement & Control in Science and Industry, AIP, pp 1191-1196 (1982)

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.  Thermocouples measure temperature as heat moves into the thermal mass of the sensor, which ideally is positioned at the surface or a location within a material, thus the temperature being measured can only respond as fast as the thermal mass of the thermocouple.  Ultrasonic thermometry responds at the speed of sound through an object.  In order to gain thermal information on the interior of a component, a thermocouple must be drilled into the component, compromising integrity.  Ultrasonic thermometry is non-intrusive and can even be non-contact which maintains the integrity of the component and thermal transport and any flow conditions.  Thermocouples cannot easily reach high temperatures, while ultrasonic thermometry has been demonstrated at over 2000°C without issue.

The output of a thermocouple is only a measure of the temperature that goes into the thermocouple.  The output of Ultrasonic thermometry, on the other hand, is a measure of the temperature that goes through the material under test.  Thermocouples can measure temperature absolutely within their operating range.  Ultrasonic Thermometry measures changes in temperature and is not as limited by operating range.


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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?

Direct measurement using material features as well as inversion techniques can be used to extract desired thermal information.  See the following links for more information:

Localization Methods in Ultrasonic Thermometry

Thermal Measurement of Harsh Environments using Indirect Acoustic Pyrometry

Ultrasonic Measurements of Bore Temperature on Large Caliber Guns



Materials

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.


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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:

Localization Methods in Ultrasonic Thermometry

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.



Measurement Setup and Performance

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.  The instrumentation currently for sale through IMS, Inc. has demonstrated sustained measurement at 5000hz.  Faster response instrumentation is under development.

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


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What is the difference between ultrasonic heat flux measurement and thermopiles or other heat flux instruments?

Ultrasonic Thermometry is exclusively the only heat flux measurement technology that passively measures heat flux without disrupting flow or thermal transport as other methodologies require.  Heat flux extraction requires no extra sensor attachment allowing for non-intrusive measurement.

What is the highest temperature that can be measured?

Measurements can be made up to the melting point of the material under test. To date, IMS Inc. has demonstrated measurements in excess of 2000°C.

2000°C measurements

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. 

What if there is strong vibration, shock or acceleration in the material?

We have demonstrated measurement on Navy guns that undergo severe shock during firing.  Generally, the frequency and method of measurement isolate acoustic shock and vibration effects.  Elastic behavior is material dependent and more elastic materials can have an influence on the measurement as the propagation path of the ultrasound changes due to shape changes in the material.  In some cases, these effects can be compensated for.  In other cases, the magnitude of these effects is very small relative to the change due to temperature.  Overall, vibration, shock and acceleration have application specific effects, but do not preclude ultrasonic measurement and will not destroy or disrupt ultrasonic sensors.

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.

How much does it cost?

The revolutionary capabilities of ultrasonic thermometry are truly unique and offer incredible measurement advantages in terms of response, range, accuracy and accessibility.  It is ideally suited for high temperature applications such as arc-jet materials testing, directed energy testing, hypersonic vehicle surface testing, combustion chamber measurement, regenerative cooling channel monitoring or turbine inlet temperature measurement to name a few.  Ultrasonic instrumentation is significantly more complex and advanced than thermocouple measurement, which induces an increase in cost.  For a more specific quote or for more information, contact us.  We are currently developing increasingly cost-effective multi-channel instrumentation units.


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