ABSTRACT
In spatiotemporal modulation (STM) and lateral modulation (LM) used in conventional mid-air ultrasound tactile stimulation, single or multiple focuses are moved by switching the ultrasound transducer phases. A problem with the phase switching method is the limitation of the focus motion speed due to rapid phase switching that causes sound pressure fluctuations. This paper proposes an LM method using multiple-frequency ultrasound to shift the ultrasound focal point without switching the phase. This method can demonstrate a continuous and stable moving stimulus with high-frequency components, without producing unnecessary audible noise. Using the proposed broadband LM covering up to 400 Hz, we found that a high-frequency 400 Hz LM applied at a finger pad can display a stimulation area with the diameters comparable to or less than the half wavelength of 40 kHz ultrasound, where the perceptual size was evaluated as 4. 2 mm for the long axis diameter and 3. 4 mm for the short axis diameter.
ABSTRACT
In midair haptics, ultrasound phased arrays are mainly used due to their high spatiotemporal controllability. The constraint on the presentation distance of phased arrays to form a focus can be mitigated by utilizing concave reflectors. This paper numerically examines the convergence of a surface approximated by multiple planes serving as a reflector, substituted for an ideal concave surface. A mirrored phased array produced by the planar segments forms a focus and concurrently creates interference among imaginary sources. A single-point convergence condition is derived that constrains the accuracy of the approximated reflector and the phased array size. As long as it satisfies the convergence condition, the approximated reflector can form a single focal point. Numerical simulations were conducted to confirm the validity of the convergence equation and the 5% tolerance of the segment size for the reflector deformation. An experimental campaign was also conducted and confirmed that the polyhedral reflector was able to form a single small focus by controlling the phase shift of the sound source.
ABSTRACT
Ultrasound focusing with curved reflectors has various advantages in mid-air tactile presentation. First, tactile sensations can be presented from various directions without placing a large number of transducers. It also avoids conflicts in the arrangement of transducer arrays with optical sensors and visual displays. Furthermore, the blurring of the focus can be suppressed. We propose a method for focusing reflected ultrasound by solving the boundary integral equation for the sound field on a reflector divided into elements. This method does not require a prior measurement of the response to each transducer at the tactile presentation point, as in the previous method. It enables real-time focusing on arbitrary locations by formulating the relationship between the transducer input and the reflected sound field. This method also enhances the focus intensity by incorporating the tactile presentation's target object into the boundary element model. Numerical simulations and measurements showed that the proposed method could focus ultrasound reflected from a hemispherical dome. A numerical analysis was also performed to determine the region where focus generation with sufficient intensity was possible.
Subject(s)
Touch Perception , Humans , Ultrasonography , TransducersABSTRACT
Automated blood cell counters can distinguish cells based on their size and the presence or absence of a nucleus. However, most vertebrates have nucleated blood cells that cannot be counted automatically. We established an alternative automatic method for counting peripheral blood cells by staining cells with the fluorescent dye acridine orange (AO) and analysing cell populations using flow cytometry (FCM). As promising new animal models, we chose Xenopus laevis and three inbred strains of X. tropicalis. We compared the haematological phenotypes, including blood cell types, cell sizes, cellular structure, and erythrocyte lifespans/turnover rate among X. laevis and the three inbred strains of X. tropicalis. Each cell type from X. laevis was sorted according to six parameters: forward- and side-scattered light emission, AO red and green fluorescence intensity, and cellular red and green fluorescence. Remarkably, the erythrocyte count was the highest in the Golden line, suggesting that genetic factors were associated with the blood cells. Furthermore, immature erythrocytes in anaemic X. laevis could be separated from normal blood cells based on red fluorescence intensity. These results show that FCM with AO staining allows for an accurate analysis of peripheral blood cells from various species.
