Tactile vision substitution devices are assistive technologies for the blind that redirect visual information to the tactile sense. They typically include a tactile display that conveys visual... Show moreTactile vision substitution devices are assistive technologies for the blind that redirect visual information to the tactile sense. They typically include a tactile display that conveys visual information to the skin. Two important parameters that determine the maximum information bandwidth of tactile displays are the spatial acuity of the skin, and the ability of the user to discriminate between stimulus intensities. These two parameters were investigated by determining the two-point discrimination (TPD) threshold and the just-noticeable intensity difference (JND) using coin motors on the lower back. Coin motors are eccentric rotating-mass motors that are affordable, energy-efficient, and easy to implement. The lower back was chosen because it is a discreet place to wear assistive technology. It is generally available for use, as it is usually not critically involved in activities of daily living. Rehabilitation with sensory substitution devices often requires training by professional occupational therapists, because the user needs to extract visual information from sparse information presented through an alternative channel such as the skin. In this study they determined whether short, automated training sessions of 5 min each could improve the TPD threshold and JND. It was found that 10 min of computer-assisted training improved the vibrotactile TPD threshold on the lower back by 36%, and that 18 min of training improved the just-noticeable intensity difference (JND) by 44%. It was concluded that short, automated training sessions could provide a fast and inexpensive means to improve people's basic spatial acuity and intensity discrimination skills with coin motors. Show less
Nuclear magnetic resonance force microscopy (MRFM) is a technique which combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). The final goal is to develop this technique... Show moreNuclear magnetic resonance force microscopy (MRFM) is a technique which combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). The final goal is to develop this technique to such a level that the atomic structure of a virus or protein can be revealed by this microscope. This thesis shows nuclear magnetic resonance force measurements on copper in which the interaction of the magnetic moments of the nuclei of copper with a magnetic cantilever has delivered a detectable signal at a temperature of 50 millikelvin. Furthermore, we show measurements, which support a new theory where at low magnetic field and low temperature, non contact friction between the magnetic cantilever and paramagnetic electron spins is described. These measurements were enabled by technical improvements such as vibration reduction in a cryogen free dilution refrigerator. As a benchmark for the low vibration, we show atomic resolution scanning tunneling microscopy at 15 millikelvin temperature on graphite. We also show a method to create small magnets for MRFM from a thin magnet film. With these small magnets the field gradient and therefore the sensitivity may be significantly enhanced. Show less
Imaging subsurface structures with nanometer resolution has been a long-standing desire in science and industry. To obtain subsurface information one usually applies ultrasound, like e.g. in... Show moreImaging subsurface structures with nanometer resolution has been a long-standing desire in science and industry. To obtain subsurface information one usually applies ultrasound, like e.g. in echocardiography. Implementing ultrasound in an Atomic Force Microscope, a setup that is capable of imaging surfaces with atomic resolution, gives access to additional information. In particular, it is possible to image subsurface structures with nanometer resolution. However, it is not known why the subsurface structures become visible when applying ultrasound during the imaging with an Atomic Force Microscope. Based on a special excitation scheme, which makes use of two ultrasound excitations (one through the sample and one through the cantilever), Heterodyne Force Microscopy seems to be the most promising candidate for imaging deeply buried objects or structures with nanometer resolution. This thesis focuses on the poorly understood elements in Heterodyne Force Microscopy. We studied the ultrasound propagation in the sample, the dynamics of an ultrasonically excited cantilever near a sample that is also vibrating at a slightly diff erent frequency, and the generation of the heterodyne signal. The insight we gained in these matters allowed us to determine the contrast mechanism in a very well-de fined model sample, which contains gold nanoparticles buried in a soft polymer matrix. We show that the contrast in this system is determined by “friction at shaking nanoparticles”. Show less
