Past research aimed at increasing the sensitivity of capacitive pressure sensors has mostly focused on developing dielectric layers with surface/porous structures or higher dielectric constants. However, such strategies have only been effective in improving sensitivities at low pressure ranges (e.g., up to 3 kPa). To overcome this well‐known obstacle, herein, a flexible hybrid‐response pressure sensor (HRPS) composed of an electrically conductive porous nanocomposite (PNC) laminated with an ultrathin dielectric layer is devised. Using a nickel foam template, the PNC is fabricated with carbon nanotubes (CNTs)‐doped Ecoflex to be 86% porous and electrically conductive. The PNC exhibits hybrid piezoresistive and piezocapacitive responses, resulting in significantly enhanced sensitivities (i.e., more than 400%) over wide pressure ranges, from 3.13 kPa−1 within 0–1 kPa to 0.43 kPa−1 within 30–50 kPa. The effect of the hybrid responses is differentiated from the effect of porosity or high dielectric constants by comparing the HRPS with its purely piezocapacitive counterparts. Fundamental understanding of the HRPS and the prediction of optimal CNT doping are achieved through simplified analytical models. The HRPS is able to measure pressures from as subtle as the temporal arterial pulse to as large as footsteps.
In this paper, we devise methods for the multiobjective control of humanoid robots, a.k.a. prioritized wholebody controllers, that achieve efficiency and robustness in the algorithmic computations. We use a form of whole-body controllers that is very general via incorporating centroidal momentum dynamics, operational task priorities, contact reaction forces, and internal force constraints. First, we achieve efficiency by solving a quadratic program that only involves the floating base dynamics and the reaction forces. Second, we achieve computational robustness by relaxing task accelerations such that they comply with friction cone constraints. Finally, we incorporate methods for smooth contact transitions to enhance the control of dynamic locomotion behaviors. The proposed methods are demonstrated both in simulation and in real experiments using a passive-ankle bipedal robot.
Time-dependent dielectric breakdown (TDDB) and high-field stress-induced leakage behavior of ultrathin oxide (40-110 b) under static and dynamic electrical stress conditions were investigated. Both thermally grown oxides and oxynitrides prepared by oxidation in N,O were used for comparison. For thicker dielectrics, it was found that the charge-to-breakdown (e,,) values are much larger when the dielectrics were stressed under bipolar waveform than those under unipolar. However, for thinner oxides ( < 60 A), TDDB behavior is significantly worse under bipolar stressing. The anomalous behavior can be explained by the weak spot region of a fixed thickness at the polycrystalline silicon / oxide interface.
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