Hi,

I have a setup, where I measure and simulate ultrasonics on multi-layer polymeric structures. The materials can have high attenuation coefficients, e.g y = 1.18, alpha_coeff = 4 dB/(MHz^y*cm) or even higher. Furthermore the exponent is not always the same for all materials. For my larger samples (d=20.5 mm) I expected an amplitude reduction of the initial 5 MHz impulse based on the acoustical paramters of the main material:

alpha = 4*5^1.18 = 26.7 dB/cm

Resulting amplitude reduction ca. 110 dB (alpha*2*d)

For verification, I first compared measurement results with a simple A-Scan model, where a plane wave and just reflection/transmission and attenuation coefficients of the different layers are taken into account (cf. H. Azhari, Basics of biomedical ultrasound for engineers). I could get a good agreement for the amplitude reduction, i.e. the amplitude of a reflection at an inner interface is in the range of 5e-6 compared to the reflection on the surface of the sample (amplitude normalized to 1). But this simplified model of course does not contain a frequency dependent attenuation. Thus, the shape of the measured and simulated signal differed greatly.

After that I performed 1D and 3D k-wave simulations with the same sample setup and acoustical parameters. CFL was varied down to 0.1. In all cases I could achieve a frequency dependent attenuation and the signal shape showed an improved resemblance to the measured signal. But the amplitude of the k-wave simulated signal is in the range of 2e-2, which is four orders of magnitude larger than the measurement/simplified model results.

Therefore three questions:

1.) In many comments it was written, that the k-wave toolbox may not function properly at high attenuation values. Could this already be the explanation for the amplitude difference?

2.) The alpha_power exponent can only be put as a scalar for the whole domain. Since the materials in the domain have different exponents, I chose the exponent of the material of the thickest layer in the domain. All other attenuation coefficients are therefore slightly off (e.g. y1 = 1.18, y2 = 1.01). Is there any experience how large the effect of different exponents is?

3.) Will a variation of the alpha_power exponent across the simulation domain be possible in the future?

Kind regards

Henning