V.T.Grinchenko, V.N.Oliynik Dynamic properties of a visco-elastic layer at harmonic loading by a round piston |
Acoustic bulletin, Vol. 8 ¹ 1-2, (2005) |
| The paper deals with solution of a linear problem on harmonic vibrations of viscoelastic layer loaded with a smooth plane round piston under the conditions of full adhesion and smooth contact. Such a statement is used to model the contact interaction between the surface biotissue and the vibrator or sensor. An efficient algorithm is developed for determining physico-mechanical fields and impedance of the surface contacting with the piston. It is proved that the system demonstrates resonant behavior in the considered frequency range, and the resonant frequency decreases with the increase of relative piston radius. The active and reactive parts of the impedance are of the same order for small pistons. The piston radius being increased, the share of the active impedance component decreases. It is shown that the reactive impedance components have close values at smooth contact and full adhesion. At the same time, at full adhesion the active component of the layer impedance increases with frequency much faster. For relatively small vibrators and sensors the surface impedance of compliant layer lies significantly below the value given by rod approximation for the cylinder. For the devices with the contact zone radius exceeding the layer height, the impedance increases in comparison with the rod approximation. Such behavior allows the adequate description within the unified approach of the results obtained by different research groups under various geometric parameters of the system "human body surface - contact sensor (vibrator)". A sharp increase of normal and tangential stresses at the piston edge is the evidence of the tendency to its separation when vibrating on the surface of the investigated object. Originating from this fact, when developing the techniques of signal recording from compliant surfaces, the top-priority attention should be given to reliable fixture of the edges of contact sensors. |
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KEY WORDS: harmonic vibrations of viscoelastic layer, round piston,biotissue, impedance, normal and tangential stresses |
| TEXT LANGUAGE: Ukrainian |