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Redetermination of Boltzmann Constant





Division of Thermophysics and Process Measurements has carried out research program on Redetermination of the Boltzmann Constant by the Fixed-Path-Length Acoustic Cylindrical Resonators since December, 2006.

The project aims to redetermine Boltzmann constant by the fixed-path-length cylindrical resonators. The study is a part of the redefinitions of the fundamental SI units on the fundamental natural constants.

Boltzmann constant kB, the constant re-defining the Kelvin scale, is one urgently needed to be re-determined. The acoustic resonant procedure is widely recognized as the most accurate method for the determination of kB up-to-date. We have applied a considerably independent method, the fixed-path-length acoustic cylindrical resonators, in the project in order to commit to the recommendation of the Consultative Committee of Thermometry (CCT) that kB shall be re-determined by different methods.


Implementing the study of the project obtains the following accomplishments:

- Applying the fixed-path-length cylindrical acoustic resonator in the redetermination of kB. This approach is considerably independent among the studies by the acoustic resonant method.

- Characterizing considerably the imperfections perturbing the acoustic resonances with the fixed-path-length cavities

- Proposing and applying piezoelectric transducers for driving and receiving the acoustic signals. This design increases the signal-to-noise ratio, maintains the fullness of the wall of cylindrical resonators, lowers the transducer perturbation to resonances and protects the gas inside the cavities from connection with the environmental gas

- Determining kB to the uncertainty of around 3 parts of million by a single cylindrical resonator

- Proposing the novel two-cylinder method to eliminate the perturbations with some types of shell motions that are hard to be well characterized

- Determining kB to the uncertainty of around 2 parts of million by the two-cylinder method