Visually impaired individuals often rely on assistive technologies such as white canes for independent navigation. Many electronic enhancements to the traditional white cane have been proposed. However, only a few of these proof-of-concept technologies have been tested with authentic users, as most studies rely on blindfolded non-visually impaired participants or no testing with participants at all. Experiments involving blind users are usually not contrasted with the traditional white cane. This study set out to compare an ultrasound-based electronic cane with a traditional white cane. Moreover, we also compared the performance of a group of visually impaired participants (N = 10) with a group of blindfolded participants without visual impairments (N = 31). The results show that walking speed with the electronic cane is significantly slower compared to the traditional white cane. Moreover, the results show that the performance of the participants without visual impairments is significantly slower than for the visually impaired participants. No significant differences in obstacle detection rates were observed across participant groups and device types for obstacles on the ground, while 79% of the hanging obstacles were detected by the electronic cane. The results of this study thus suggest that electronic canes present only one advantage over the traditional cane, namely in its ability to detect hanging obstacles, at least without prolonged practice. Next, blindfolded participants are insufficient substitutes for blind participants who are expert cane users. The implication of this study is that research into digital white cane enhancements should include blind participants. These participants should be followed over time in longitudinal experiments to document if practice will lead to improvements that surpass the performance achieved with traditional canes.

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Microwave expansion of a plasma is certainly a promising process by which to obtain a large-diameter plasma profile; however, it generates instability regions and local inhomogeneities. The purpose of this work is to study the wave-propagation conditions and plasma-expansion profile in a pure argon discharge and in argon-methane mixture. Spatially resolved plasma parameters are measured using an array of electrostatic probes (simple and double) moving along the discharge axis. This device gives radial and axial measurements which are correlated to the spatially resolved Ar(420 nm) emission line intensity. We show that, as expected, the wave-propagation conditions are satisfied within the luminous part of the discharge. In this region the electron energy distribution function (EEDF) can be roughly approximated by using a Maxwell distribution function of low temperature (about 1000 K). The absorbed microwave power is mainly transferred to electrons as potential energy. Instabilities appear at the edge of this luminous region, where the wave-propagation conditions are not satisfied. In this region the EEDF is strongly disturbed and cannot be approximated using a Maxwell distribution function. The microwave incident power is mainly reflected, so the potential energy of electrons decreases strongly. Nevertheless, the kinetic energy of electrons increases because of stochastic electron heating due to strong inhomogeneities in the charged particle density producing local electrical fields. When methane is mixed with argon, the energy necessary to maintain an electron free in the plasma increases with increasing frequency of inelastic collisions. Consequently, the plasma expansion length decreases with increasing percentage of methane added to argon.