Haptogram: Ultrasonic Point-Cloud Tactile Stimulation

Studies of the stimulating effect of ultrasound as a tactile display have recently become more intensive in the haptic domain. In this paper, we present the design, development, and evaluation of Haptogram; a system designed to provide point-cloud tactile display via acoustic radiation pressure. A tiled 2-D array of ultrasound transducers is used to produce a focal point that is animated to produce arbitrary 2-D and 3-D tactile shapes. The switching speed is very high, so that humans feel the distributed points simultaneously. The Haptogram system comprises a software component and a hardware component. The software component enables users to author and/or select a tactile object, create a point-cloud representation, and generate a sequence of focal points to drive the hardware. The hardware component comprises a tiled 2-D array of ultrasound transducers, each driven by an FPGA. A quantitative analysis is conducted to measure the Haptogram ability to display various tactile shapes, including a single point, 2-D shapes (a straight line and a circle) and a 3-D object (a hemisphere). Results show that all displayed tactile objects are perceivable by the human skin (an average of 2.65 kPa for 200 focal points). A usability study is also conducted to evaluate the ability of humans to recognize 2-D shapes. Results show that the recognition rate was well above the chance level (average of 59.44% and standard deviation of 12.75%) while the recognition time averaged 13.87 s (standard deviation of 3.92 s).