A Method for Distribution Control of Aerial Ultrasound Radiation Pressure for Remote Vibrotactile Display Keisuke HASEGAWA and Hiroyuki SHINODA 1 1 Department of Information Physics and Computing, Graduate School of Information Science and Technology, the University of Tokyo, Tokyo, Japan (Tel : +81-3-5841-7433; E-mail: keisuke@alab.t.u-tokyo.ac.jp) (Tel : +81-3-5841-6926; E-mail: shino@alab.t.u-tokyo.ac.jp) Abstract: We propose a calculation method for phase and amplitude of ultrasound transducers in arrays, which are supposed to generate proper spatial distribution of radiation pressure on users ’ skin corresponding to vibrotactile sensation conveyed to users. The phased array technique has been applied for ultrasound transducer array and converged energy in a focus of magnified amplitude in the air has been successfully generated as well as vibrotactile stimulation in a point. In this paper we expand that phasing scheme for a single focus to arbitrary three-dimensional distribution amplitude with transducers located in three-dimensional disposition. We verify the validity of our method with numerical experiments. Keywords: Tactile Display, Airborne Ultrasound, Amplitude Control, Inverse-problem 1. INTRODUCTION It has been of a great interest of many researchers to reveal and establish a new application of human haptic information. A number of framework and devices have been investigated and proposed for display of tactile stimuli. They are often related to some specific sort of tactile stimuli which are related to certain virtual objects so that the user can tactually feel the existence of them. They can be categorized into mechanical and electrical methods. Most of current tactile displays are classified in former, on which mechanical actuator like wires, motors, vibrators are mounted. They basically are supposed to be attached on a part of human bodies and give tactile sensation on a region in contact with the devices. The same goes for the latter, which gives tactile stimuli via electrodes on the surface of the skins or connected to nerves transmitting sense signals. Our approach has been different in terms of that we give vibrotactile sensation remotely. We have proposed a framework to generate a focal spot of airborne ultrasound, which enables us to feel localized tactile sensation in the air without wearing any devices on our bodies. Our newest prototype can generate a focus of static pressure of 7.4gf in force and switch the focal amplitude quantized into 320 levels with the sampling rate of 2 kHz (Figure 1). We fabricated multiple ultrasound transducer units which operate simultaneously in harmony. As a result, we realized enlarged aperture of an ultrasound phased array and generated a focus without blur in further region from the device than we did in the past research with a single transducer unit. With the framework we have developed several interfaces including the visual and tactile display which allows us to tactually feel virtual visible objects [1][2] The concept of composing a larger aperture with multiple units can be expanded to three-dimensional aperture structures. Multiple units with different directions of their surface normal vectors can form more spatially complicated energy distribution in comparison with a single planar transducer array. With a proper spatial distribution of ultrasound pressure, it is possible to enable users to feel aerial tangible objects with their three-dimensional volumes such as a floating ball. In order to create a given planer output amplitude distribution in a far field, it has been well known that the proper phases and amplitudes at arbitrary points on a lens as a function of two-dimensional coordinates are given as the spatial Fourier inverse transformation of the resultant image. However this solution is feasible only in generating a two-dimensional image which is parallel to the aperture [3]. When the resulting image should be three-dimensional, other solution will be necessary. Figure 1: Our newest system of the 9-unit AUTD. The total area of the 3 by 3 units is 57×45cm 2 . Vibrotactile sensation is produced on the user ’ s palm by focused ultrasound emitted from the transducer array mounted above the user. SICE Annual Conference 2013 September 14-17, 2013, Nagoya University, Nagoya, Japan 223 PR0001/13/0000-0223 ¥400 © 2013