The contact between the fingertip and an object is formed by a collection of micro-scale junctions, which collectively constitute the real contact area. This real area of contact is only a fraction of the apparent area of contact and is directly linked to the frictional strength of the contact (i.e., the lateral force at which the finger starts sliding). As a consequence, a measure of this area of real contact can help probe into the mechanism behind the friction of skin on glass. In this article, we present two methods to measure the variations of contact area; one that improves upon a tried-and-true fingertip imaging technique to provide ground truth, and the other that relies on the absorption and reflection of acoustic energy. To achieve precise measurements, the ultrasonic method exploits a recently developed model of the interaction that incorporates the non-linearity of squeeze film levitation. The two methods are in good agreement (ρ = 0.94) over a large range of normal forces and vibration amplitudes. Since the real area of contact fundamentally underlies fingertip friction, the methods described in the article have importance for studying human grasping, understanding friction perception, and controlling surface-haptic devices.

中文翻译：

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如何测量皮肤与玻璃的实际接触面积


指尖与物体之间的接触是由微尺度结点的集合形成的，这些结点共同构成了真实的接触区域。该实际接触面积仅是表观接触面积的一小部分，并且与接触的摩擦强度（即手指开始滑动时的侧向力）直接相关。因此，测量实际接触面积可以帮助探究皮肤与玻璃摩擦背后的机制。在本文中，我们提出了两种测量接触面积变化的方法；一种改进了久经考验的指尖成像技术来提供地面真相，另一种则依赖于声能的吸收和反射。为了实现精确测量，超声波方法利用了最近开发的相互作用模型，该模型结合了挤压膜悬浮的非线性。这两种方法在大范围的法向力和振动幅度上具有很好的一致性（ρ = 0.94）。由于实际接触区域从根本上是指尖摩擦的基础，因此本文中描述的方法对于研究人类抓握、理解摩擦感知和控制表面触觉设备具有重要意义。