Sheaths are formed around the surfaces of airless bodies, which both collect and emit electrons. Depending on the ratio of the emitted to collected electron fluxes Γ, the sheath potential structure can be quite different. We present the first experimental measurements of all the three types of the sheath potentials: classical, space‐charge‐limited (SCL), and inverse. A solid surface immersed in plasmas emits secondary electrons. The potential structure changes from a monotonic classical to a nonmonotonic SCL sheath as Γ increases. At the critical electron emission with zero electric field at the surface, the sheath potential is determined by the plasma electron temperature, and Γ approaches but remains smaller than 1, in agreement with the theoretical expectation. The nonmonotonic SCL sheath persists steadily for Γ > 1. When the emitted electron density becomes larger than the plasma electron density, a monotonic inverse sheath forms with a positive surface potential relative to the ambient.

Langmuir probes on spacecraft have been used for characterizing the ambient plasma parameters in space. When their boom is short compared to the Debye length, the probes remain immersed in the spacecraft sheath, causing the current-voltage (I-V) characteristics to deviate from that of a probe far away from the spacecraft. We present identification of when a Langmuir probe is in a sheath, based on the secondary electron (SE) emission from the probe itself. The I-V characteristics of a spherical probe are investigated in a plasma sheath above a conducting plate. Plasmas with cold and hot electrons (1 eV and 10 eV), as well as monoenergetic electrons (50-100 eV), are created. The derivative (dI/dV) of the probe I-V curves shows that in addition to a "knee" at a potential more positive than the plasma potential, an additional knee appears at a sheath potential at the probe location. This additional knee is created due to the SE emission from the probe and is identified as an indication of the probe being immersed in the sheath. Our experimental results reproduced the aspects of the Cassini Langmuir probe I-V characteristics, suggesting that at times, the probe may have been immersed in the sheath of the spacecraft in Saturn's magnetosphere, and SE emission from the probe itself may have significantly altered its I-V characteristics.

The lack of haptic feedback during Minimally Invasive Surgery (MIS) can be potentially dangerous, and has been a factor in preventing a wider application of MIS. A Wired Palpation Device (WPD), which is designed to provide the surgeon with soft tissue viscoelasticity information during MIS, can be an appealing solution to this challenge. As a novel device, the validation of its functionality is critical before being put into actual usage. In this paper, a procedure assessing the effectiveness of the WPD in characterizing soft tissue material properties was introduced. Strain creep indentation tests were performed using the WPD method on four different synthetic tissue samples, followed by standard stress relaxation indentation tests on the same samples. The results showed that the WPD was reliable in characterizing the long-term material response when compared to the traditional method (an average of 5.21% difference), but may still need improvement in its capability of capturing short-term transient soft tissue response.