Spatiotemporal Pinpoint Cooling Sensation Produced by Ultrasound-Driven Mist Vaporization on Skin

Abstract

In this study, we achieved a noncontact tactile display that presents a pinpoint and instantaneous cooling sensation on the skin surface with no devices directly in contact with the user's body. We employed ultrasound phased arrays to generate a focused ultrasound, which locally and instantaneously expedites the vaporization of room-temperature water mist floating near the surface of the user's skin, offering a sudden pinpoint cooling sensation. In this paper, we describe the physical configuration of the proposed method and show the measurement results, demonstrating how the user's skin surface was cooled.During the experiments, we discovered that a part of the skin exposed to a focused ultrasound within the floating mist was selectively cooled with negligible delay.Our prototype system offers a cooling spot of approximately 15 mm in diameter, which causes a temperature decrease of 4.6 K in 1 s and 3.3 K in the first 0.5 s on a hand situated 500 mm away from the device. Additionally, the ultrasound-driven cooling spot can be controlled on the skin surface, which is felt as a cool moving spot. Such a position-free cooling system with a high spatiotemporal resolution will open the door to unprecedented practical tactile applications.

Intensity-Adjustable Non-Contact Cold Sensation Presentation Based on the Vortex Effect

“…Although contact thermal displays reproduce touch sensations, creating various artificial environments, such as a coast with a breeze or a snow field with a strong wind, requires non-contact cold presentations. To generate these, Nakajima et al [5]- [7] developed a cooling method with evaporation as the main factor of temperature change. By using focused ultrasound, they transported a mist to the skin to cool it.…”

“…The change in skin temperature is related to the output volume flow rate, K, of cold air and the distance, d, between the skin and the cold air outlet. By using (7), the skin temperature change can be estimated to elicit target temperature changes by adjusting the volume flow rate of the cold air.…”

“…For non-contact cooling, Nakajima et al [5]- [7] proposed an effective method that uses ultrasound to transport mist to the skin. The focused ultrasound would accelerate the evaporation of mist on the skin to create a cooling spot, achieving a maximum temperature change of 4.6 • C in 1 s. The dominant factor enabling this method to affect temperature change is evaporation.…”

High-Speed Non-Contact Thermal Display Using Infrared Rays and Shutter Mechanism

“…Han et al combined infrared lamp, mist, water drop and air conditioning [7]. Other non-contact-type methods are air transportations [20,22,31], humidity adjustment [9], vaporization [21],visuo-thermal interaction [18,19,27], and olfactory [2]. These non-contact-type methods do not require contacts to the devices that can result in reductions in the senses of immersion and presence.…”

A novel method to selectively elicit cold sensations without touch

“…These approaches have some advantages, but importantly have limitations for studying interactions between mechanical and cooling signals in the context of sensory binding and object perception. A recent study presented a new method to cool the skin with a non-contact tactile display driven by ultrasound waves (Nakajima et al, 2021). While this method allows precise spatial and temporal control of the cooling stimulation, it does not selectively elicit cold sensations because ultrasounds generate vibrotactile sensations.…”