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plibe
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Hi guys,
I've got an exam in a few days and my lecturer is unresponsive, so wondering if you can help me. The question I am solving is the following:
Calculate the impedance at the surface of a layer of spruce wood of thickness d equal to 2mm, and of density rho equal to 0.47 Mg/m3 at 1000Hz. Assume the porosity of wood is 0.4 and the bulk modulus of the wood is 1.5GPa.
(Hint: first calculate the wave number by using k=w*sqrt(rho/K), secondly calculate the characteristic impedace using Zc= sqrt(K*rho), then calculate the surface impedance using Z(M)=-j*(Zc/porosity)*cot(kd))
Am I supposed to convert the K=1.5GPa to Pa? My lecture notes say to use GPa in the Zc formula, but I don't know if it's right.
If I use 1.5GPa=1500000000Pa, then I get Zc= 839642.7812 and Z(M) comes to -298418017.3j
If my impedance values are correct, what units are they in? And how could Z(M) be a negative value?
Thanks in advance for any help! X
I've got an exam in a few days and my lecturer is unresponsive, so wondering if you can help me. The question I am solving is the following:
Calculate the impedance at the surface of a layer of spruce wood of thickness d equal to 2mm, and of density rho equal to 0.47 Mg/m3 at 1000Hz. Assume the porosity of wood is 0.4 and the bulk modulus of the wood is 1.5GPa.
(Hint: first calculate the wave number by using k=w*sqrt(rho/K), secondly calculate the characteristic impedace using Zc= sqrt(K*rho), then calculate the surface impedance using Z(M)=-j*(Zc/porosity)*cot(kd))
Am I supposed to convert the K=1.5GPa to Pa? My lecture notes say to use GPa in the Zc formula, but I don't know if it's right.
If I use 1.5GPa=1500000000Pa, then I get Zc= 839642.7812 and Z(M) comes to -298418017.3j
If my impedance values are correct, what units are they in? And how could Z(M) be a negative value?
Thanks in advance for any help! X