With an advanced acoustic material characterization, determine up to 10 parameters which are needed for accurate simulation of poroelastic materials: Porosity, Airflow Resistivity, Tortuosity, Viscous & Thermal Characteristic Lengths, Static Thermal Permeability, Frame Bulk Density, Young’s Modulus, Damping Loss Factor and Poisson Ratio.
Choose Your Method: JCAL, Biot and Complex Characterization Models
Specific test benches were developed by Mecanum to directly measure some of these parameters during an acoustic material characterization.
JCAL Characterization
For a JCAL characterization, up to 7 parameters are needed. Three (3) measurements and one (1) simulation are performed to determine Porosity, Bulk Density, Airflow Resistivity, Tortuosity, Viscous and Thermal Characteristic Lengths, and Static Thermal Permeability.
Porosity and Bulk Density Meter
Measure both the porosity and the frame bulk density using the isothermal pressure-mas method.
Airflow Resistance Meter
Follows ISO 9053-1 and ASTM C522 to measure the quasistatic airflow resistivity.
Tortuosity Meter
Measures tortuosity in transmission for low resistivity materials or in reflection for high resistive materials.
FOAM-X
Retrieves viscous and thermal characteristic lengths, and static thermal permeability from impedance tube measurements. Uses inverse or indirect methods.
Biot Characterization
For a Biot characterization, up to 10 parameters are needed. Four (4) measurements and one (1) simulation are performed to determine Porosity, Bulk Density, Airflow Resistivity, Tortuosity, Viscous and Thermal Characteristic Lengths, Static Thermal Permeability, Complex Young’s Modulus, Damping Loss Factor and Poisson Ratio.
Porosity and Bulk Density Meter
Measure both the porosity and the frame bulk density using the isothermal pressure-mas method.
Airflow Resistance Meter
Follows ISO 9053-1 and ASTM C522 to measure the quasistatic airflow resistivity.
Tortuosity Meter
Measures tortuosity in transmission for low resistivity materials or in reflection for high resistive materials.
Quasi-static Mechanical Analyzer
Follows ISO 18437-5 to measure complex Young’s Modulus, Damping Loss Factor and Poisson Ratio.
FOAM-X
Retrieves viscous and thermal characteristic lengths, and static thermal permeability from impedance tube measurements. Uses inverse or indirect methods.
Complex Simulation
All these parameters can also be derived through inverse or indirect characterization using our software, FOAM-X.
Inverse characterization employs a genetic algorithm to identify parameters that best replicate the measured absorption curve from impedance tube data. The two characteristic lengths Λ, Λ’ are determined by this method, as well as the static thermal permeability. The use of both direct and inverse characterization ensures the quality and reliability of data.
Many complex sound treatments used in the automotive or aircraft industrie are composed by a succession of different layers, combining resistive screens, porous or fibrous materials, heavy layers, compressed felt, etc.
Characterizing these materials implies to separate each layer and characterize it individually. Once the properties of each layer are determined, we can simulate the complex sound treatment with our software NOVA. In some cases, layers cannot be separate and an inverse characterization is performed on the complete material giving properties of the equivalent material
What are JCAL and Biot Advanced Material Models?
Modern acoustic simulation software as Nastran, Comsol, VA-One, CATIA, NOVA etc. integrate the a JCAL model or a Biot model to accurately simulate the behavior of acoustic materials. Let’s discover both models!
Johnson-Champoux-Allard-Lafarge (JCAL) Model
The Johnson-Champoux-Allard-Lafarge (JCAL) model is a powerful approach for modeling the acoustic behavior of porous materials by treating them as equivalent fluids and neglects the elastic behavior of the frame. This model will use what we name the equivalent fluid parameters of the material to describe its acoustic behavior.
These parameters are:
Porosity (φ)
Represents the fraction of the material volume that is occupied by air (or fluid).
Airflow Resistivity (σ)
Measures the resistance to airflow through the material.
Tortuosity (α∞)
Refers to the complexity of the path sound waves take through the material compared to free air.
Characteristic Lengths (Λ Λ’)
Viscous and Thermal characteristic lengths. Relate to the pores size and structure.
Frame Bulk Density (ρ)
Required to account for the inertia effect of the frame.
Thermal Permeability (ko’)
Describes thermal exchanges between the frame and the saturating fluid.
Two different approximations are used to represent the interaction with the frame of the material:
✓ Rigid Frame Approximation: Stipulate that the frame do not move under the acoustic excitation (usually in low frequency or for solid foams).
✓ Limp Frame Approximation: Considers that the frame moves with the acoustic waves.
Extending to Biot Model
When frame deformation affects acoustic performance – especially in elastic materials – the Biot Model provides a complete poroelastic model that includes interactions between the fluid and solid phases.
For this comprehensive characterization, the following parameters are required:
Porosity (φ)
Represents the fraction of the material volume that is occupied by air (or fluid).
Airflow Resistivity (σ)
Measures the resistance to airflow through the material.
Tortuosity (α∞)
Refers to the complexity of the path sound waves take through the material compared to free air.
Characteristic Lengths (Λ Λ’)
Viscous and Thermal characteristic lengths. Relate to the pores size and structure.
Frame Bulk Density (ρ)
Required to account for the inertia effect of the frame.
Thermal Permeability (ko’)
Describes thermal exchanges between the frame and the saturating fluid.
Young’s Modulus (E)
Relates to the frame rigidity.
Loss Factor (η)
Relates to the frame damping.
Poisson Ratio (ν)
Relates lateral and longitudinal strain relations.
How to Choose Between a JCA Model and a Biot Model?
Together, these parameters allow for precise modeling and prediction of sound behavior in porous materials, covering a broad range of frequencies and conditions. The choice of model — whether JCA or Biot — depends on the specific characteristics of the material and the frequency range of interest.
Why Rely on Modern Acoustic Material Characterization?
The growing demands of predictive engineering and acoustic simulations have shifted the focus from traditional absorption and transmission measurements to more comprehensive methods.
For porous and fibrous materials, new advanced models are developed. They consider the acoustic material at a macroscopic scale as a combination of a fluid phase coupled to a solid phase. These models use macroscopic parameters to accurately and precisely simulate their acoustic behavior over a large frequency range and in many different applications.
Why Choose Mecanum for your Acoustic Material Characterization?
With over 25 years of specialized experience, Mecanum has established itself as an industry leader, partnering with major companies in automotive, construction, and aerospace sectors. Here’s why clients consistently rely on us:
Innovation and R&D
Mecanum leads in developing new measurement techniques, regularly updating software, and offering custom solutions. FOAM-X and NOVA software integration allows for systematic multilayer material characterization, ensuring accuracy and reliability.
Quality Assurance
Compliance with ISO and ASTM standards for airflow resistance, impedance measurements, and mechanical properties underpins all processes. Mecanum’s regular equipment calibration, round-robin testing, and reference comparisons ensure consistent, reproducible results, backed by comprehensive reporting and material handling guidance.