We report a method to locally assess the complex shear modulus of a viscoelastic medium. The proposed approach is based on the application of a magnetic force to a millimeter-sized steel sphere embedded in the medium and the subsequent monitoring of its dynamical response. A coil is used to create a magnetic field inducing the displacement of the sphere located inside a gelatin phantom. Then, a phased-array system using 3 MHz ultrasound probe operating in pulse-echo mode is used to track the displacement of the sphere. Experiments were conducted on several samples and repeated as a function of phantom temperature. The dynamic response of the sphere measured experimentally is in good agreement with Kelvin-Voigt theory. Since the magnetic force is not affected by weak diamagnetic media, our proposal results in an accurate estimation of the force acting on the inclusion. Consequently, the estimated viscoelastic parameters show excellent robustness and the elastic modulus agrees with the measurements using a quasi-static indentation method, obtaining errors below 10% in the whole temperature range. The use of the macroscopic inclusion limits the direct application of this method in a biomedical context, but it provides a robust estimation of the elastic modulus that can be used for material characterization in industrial applications.

中文翻译：

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在嵌入式软磁球上结合超声和磁力感应振动的粘弹性介质的表征。

我们报告了一种局部评估粘弹性介质复杂剪切模量的方法。所提出的方法基于对嵌入介质中的毫米大小的钢球施加磁力，并随后对其动态响应进行监测。线圈用于产生磁场，诱导位于明胶模型内的球体发生位移。然后，使用在脉冲回波模式下运行的 3 MHz 超声探头的相控阵系统用于跟踪球体的位移。对几个样品进行了实验，并作为幻影温度的函数进行了重复。实验测量的球体动态响应与 Kelvin-Voigt 理论非常吻合。由于磁力不受弱抗磁介质的影响，我们的建议可以准确估计作用在夹杂物上的力。因此，估计的粘弹性参数显示出优异的稳健性，弹性模量与使用准静态压痕方法的测量结果一致，在整个温度范围内获得低于 10% 的误差。宏观内含物的使用限制了该方法在生物医学环境中的直接应用，但它提供了弹性模量的稳健估计，可用于工业应用中的材料表征。