This paper describes a tactile display which provides unrestricted tactile feedback in air without any mechanical contact. It controls ultrasound and produces a stress field in a 3D space. The principle is based on a nonlinear phenomenon of ultrasound: Acoustic radiation pressure. The fabricated prototype consists of 324 airborne ultrasound transducers, and the phase and intensity of each transducer are controlled individually to generate a focal point. The DC output force at the focal point is 16 mN and the diameter of the focal point is 20 mm. The prototype produces vibrations up to 1 kHz. An interaction system including the prototype is also introduced, which enables users to see and touch virtual objects.

The essence of levitation technology is the countervailing of gravity. It is known that an ultrasound standing wave is capable of suspending small particles at its sound pressure nodes. The acoustic axis of the ultrasound beam in conventional studies was parallel to the gravitational force, and the levitated objects were manipulated along the fixed axis (i.e. one-dimensionally) by controlling the phases or frequencies of bolted Langevin-type transducers. In the present study, we considered extended acoustic manipulation whereby millimetre-sized particles were levitated and moved three-dimensionally by localised ultrasonic standing waves, which were generated by ultrasonic phased arrays. Our manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its centre is also utilised. The other is the manipulation principle by which a localised standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays. We experimentally confirmed that expanded-polystyrene particles of 0.6 mm, 1 mm, and 2 mm in diameter could be manipulated by our proposed method.

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Body ownership can be modulated through illusory visual-tactile integration or visual-motor synchronicity/contingency. Recently, it has been reported that illusory ownership of an invisible body can be induced by illusory visual-tactile integration from a first-person view. We aimed to test whether a similar illusory ownership of the invisible body could be induced by the active method of visual-motor synchronicity and if the illusory invisible body could be experienced in front of and facing away from the observer. Participants observed left and right white gloves and socks in front of them, at a distance of 2 m, in a virtual room through a head-mounted display. The white gloves and socks were synchronized with the observers’ actions. In the experiments, we tested the effect of synchronization, and compared this to a whole-body avatar, measuring self-localization drift. We observed that visual hands and feet were sufficient to induce illusory body ownership, and this effect was as strong as using a whole-body avatar.

A three-dimensional acoustic manipulation in air is presented. Two arrays of ultrasonic transducers are arranged opposite each other, generating a localized standing wave at an arbitrary position through the phased-array focusing technique. Small particles are suspended in the nodes of the standing wave and also manipulated according to the position of the standing wave. This paper gives the following principles of the proposed method: the theory of acoustic levitation, the ultrasonic phased array, and the estimation of the radial and axial forces. It was experimentally confirmed that particles of 0.6 mm diameter are trapped in the nodes. The length of the localized standing wave, the suspension endurance, and the size of the work space were investigated. It was also demonstrated that a mass of particles can be scooped up when the localized standing wave moves through the mass.

Figure 1: Application images of Pixie Dust, levitated and manipulated objects in graphic metaphors. (a) Floating screen with projection. (b-c) Whale (hung by string) with particles and projected spout. (d) Physical vector graphics (showing "heart"). (e) Physical raster graphics. AbstractWe propose a novel graphics system based on the expansion of 3D acoustic-manipulation technology. In conventional research on acoustic levitation, small objects are trapped in the acoustic beams of standing waves. We expand this method by changing the distribution of the acoustic-potential field (APF). Using this technique, we can generate the graphics using levitated small objects. Our approach makes available many expressions, such as the expression by materials and non-digital appearance. These kinds of expressions are used in many applications, and we aim to combine them with digital controllability. In the current system, multiple particles are levitated together at 4.25-mm intervals. The spatial resolution of the position is 0.5 mm. Particles move at up to 72 cm/s. The allowable density of the material can be up to 7 g/cm 3 . For this study, we use three options of APF: 2D grid, high-speed movement, and combination with motion capture. These are used to realize floating screen or mid-air raster graphics, mid-air vector graphics, and interaction with levitated objects. This paper reports the details of the acoustic-potential field generator on the design, control, performance evaluation, and exploration of the application space. To discuss the various noncontact manipulation technologies in a unified manner, we introduce a concept called "computational potential field" (CPF).

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The strain dependence of the free-exciton resonance energies in AlN epilayers is presented and the values are analyzed using an appropriate Hamiltonian assuming equibiaxial stress for the wurtzite crystal structure in order to obtain valence band parameters. Based on the results, we study the strain dependence of the valence band ordering, optical transition probability, and free-exciton binding energy. As a result of these calculations, the following strain-free values are obtained for the energy gap, averaged dielectric constants, and ordinary and extraordinary dielectric constants: Eg=6.095 eV at T=11 K, ϵ=7.87, ϵ⊥=7.33, and ϵ∥=8.45, respectively. A brief discussion of the valence band ordering in bulk AlxGa1−xN is also presented.