250 DPI at 1000 Hz acquisition rate S0 lamb wave digitizing pen

This paper presents an active stylus (X, Y) flat digitizing tablet (AST). The tablet features an acquisition rate of 1000 pts/s with 0.1 mm resolution. The cordless stylus incorporates a 1-mA low-power pulse generator. Precision is limited by diffraction to about ±0.3 mm on a 57 × 57 mm region of a 71 × 71 × 1 mm digitizing plate. Selective generation and detection of the S₀ Lamb mode with a precessing tip is the key feature of this tablet. We first highlight the ultrasonic propagation inside the stylus tip and stability of Lamb wave generation when the stylus is inclined, rotated, and slid. Then, modeling of the limitations imposed by diffraction of a 1-MHz burst S₀ plane Lamb wave packet is carried out. The model takes into account high-order zero crossing detection as well as reflections and shear horizontal (SH) conversions of the S₀ Lamb mode at free edges of a glass plate. Reflection and transmission through an isotropic PZT bar are also calculated. Finally, localization precision by time difference of arrival (TDOA) is calculated and experimentally verified near the borders of the plate, taking into account the angular sensitivity of the precessing tip.