The integration of haptics within Augmented Reality may help to deliver an enriched experience, while facilitating the performance of specific actions (e.g. repositioning or resizin ) that are still dependent on the user's skills. This paper gathers the description of a flexible architecture designed to deploy haptically-enabled AR applications. The haptic feedback may be generated through a variety of devices (e.g., wearable, graspable, or mid-air ones), and the architecture facilitates handling the specificity of each. For this reason, it is discussed how to generate a haptic representation of a 3D digital object depending on the application and the target device. Additionally, it is included an analysis of practical, relevant issues that arise when setting up a system to work with specific devices like Head-Mounted Displays (e.g., HoloLens) and mid-air haptic devices (e.g., Ultrahaptics UHK), such as the alignment between the real world and the virtual one. The architecture applicability is demonstrated through the implementation of two applications: Form Inspector and Simon Game, built for HoloLens and iOS mobile phones for visualization and for UHK for mid-air haptics delivery. These applications have been used by nine users to explore the efficiency, meaningfulness, and usefulness of mid-air haptics for form perception, object resizing, and push interaction tasks. Results show that, although mobile interaction is preferred when this option is available, haptics turn out to be more meaningful in identifying shapes when compared to what users initially expect and in contributing to the execution of resizing tasks. Moreover, this preliminary user study reveals that users may be expecting a tailored interface metaphor, not necessarily inspired in natural interaction.

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