The ultrasound tortuosity meter (or ultrasound refractometer) is designed to obtain reliable measurements of tortuosity and characteristic lengths of a wide range of porous materials typically used in noise control.  The system uses both ultrasound reflection and transmission methods with 1 or 2 gases (2 gases is optional).

Reflection and Transmission TOR


Measured Properties


Two Gases Transmission and Reflection TOR


Two Gases TOR Specifications


The Two Gases option includes measurement in air and helium.

  • The combination of the measurements makes it possible to compute the viscous characteristic length as well as the thermal characteristic length;

  • Advanced measurement, signal processing and post-processing for better accuracy;

  • Method based on several scientific research [1, 2, 3, 4, 5, 6 and 7].



Mecanum’s ultrasound tortuosity meter is used by the world’s leading material suppliers to both the automotive and aircraft industry for:

  • Quality control in the manufacturing process of materials;

  • Research, development, and innovation;

  • Feeding acoustical prediction software dealing with sound absorbing materials.



The system includes two air-coupled ultrasound transducers, one high voltage pulser/receiver system, specimen holders, USB-DAQ and the TOR-X software.  The TOR-X software assists the experimenter during the measurement and calculates the statistics on the measurement of tortuosity and equivalent length. Two ultrasound methods are included: reflection and transmission. The system works with disc shaped samples. To obtain viscous and thermal characteristic lengths, a two-gases method is available as an option.


Main Advantages of the Product


Measurement method from the scientific literature


User-friendly interface


Advanced calculation algorithms following the established literature


Automatic calculation of the global statistics

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More Information


[1] J.-F. Allard, B. Castagnède, M. Henry, W. Lauriks, “Evaluation of tortuosity in acoustic porous materials saturated by air,” Rev Sci. Instrum. 65, 754–755 (1994).

[2] A. Moussatov, C. Ayrault, B. Castagnède, “Porous material characterization – ultrasonic method for estimation of tortuosity and charateristic length using a barometric chamber,” Ultrasonics 39, 195–202 (2001).

[3] P. Bonfiglio and F. Pompoli, “Frequency dependent tortuosity measurement by means of ultrasonic tests,” conference paper, ICSV14, 9-12 July, Cairns, Australia (2007).

[4] J.-F. Allard and N. Atalla, Propagation of sound in porous media: modeling sound absorbing materials (2nd Edition, Wiley, 2009).

[5] Foam-X Software (Characterization of the non-acoustical properties of porous material from impedance tube measurements).

[6] N. Kino, “Ultrasonic measurements of the two characteristic lengths in fibrous materials,” Applied Acoustics 68, 1427-1438, 2007.

[7] Ph. Leclaire, L. Kelders, W Lauriks, M. Melon, N. Brown, and B. Castagnède, “Determination of the viscous and thermal characteristic lengths of plastic foams by ultrasonic measurements in helium and air,” Journal of Applied Physics 80, 2009 (1996); doi: 10.1063/1.363817.