Surface vibration tactile feedback is capable of conveying various semantic information to humans via the handheld electronic devices, like smartphone, touch panel,and game controller. However, covering the whole device contacting surface with dense actuator arrangement can affect its normal use, how to produce desired vibration patterns at any contact point with only several sparse actuators deployed on the handled device surface remains a significant challenge. In this work, we develop a tactile feedback board with only five actuators in the size of a smartphone, and achieve the precise vibration pattern production that can focus at any desired position all over the board. Specifically, we investigate the vibration characteristics of single passive coil actuator, and construct its vibration pattern model at any position on the feedback board surface. Optimal phase and amplitude modulation, found with the simulated annealing algorithm, is employed with five actuators in a sparse array. And all actuators' vibration patterns are superimposed linearly to synthetically generate different onboard vibration energy distribution for tactile sensing. Experiments demonstrated that for point-wise vibration pattern production on our tactile board achieved an average level of about 0.9 in the Structural Similarity Index Measure (SSIM) evaluation, when compared to the ideal single-point-focused target vibration pattern. The sparse actuator array can be easily embedded into usual handheld electronic devices, which shows a good significant implication for enriching their haptic interaction functionalities.

翻译：表面振动触觉反馈能够通过手持电子设备（如智能手机、触摸面板和游戏控制器）向人类传递各种语义信息。然而，用密集的致动器阵列覆盖整个设备接触表面会干扰其正常使用，如何在仅部署几个稀疏致动器的情况下，在手持设备表面的任意接触点产生期望的振动模式，仍然是一个重大挑战。在这项工作中，我们开发了一个尺寸与智能手机相当的触觉反馈板，仅使用五个致动器，便实现了可在整个板上任意指定位置聚焦的精确振动模式生成。具体而言，我们研究了单个无源线圈致动器的振动特性，并构建了其在反馈板表面任意位置的振动模式模型。通过模拟退火算法优化得到的相位和幅度调制方案，被应用于五个致动器构成的稀疏阵列中。所有致动器的振动模式通过线性叠加，合成生成板上不同的振动能量分布，以用于触觉感知。实验表明，在我们的触觉板上进行点状振动模式生成时，与理想的单点聚焦目标振动模式相比，其结构相似性指数（SSIM）评估的平均水平约为0.9。该稀疏致动器阵列可轻松嵌入常见手持电子设备中，对丰富其触觉交互功能具有重要的实际意义。