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1. Chemical Haptics: Rendering Haptic Sensations via Topical Stimulants

   https://doi.org/10.1145/3472749.3474747  

   Lu, Jasmine ; Liu, Ziwei ; Brooks, Jas ; Lopes, Pedro ( January 2021 , ACM Symposium on User Interface Software and Technology)

   We propose a new class of haptic devices that provide haptic sensations by delivering liquid-stimulants to the user's skin; we call this chemical haptics. Upon absorbing these stimulants, which contain safe and small doses of key active ingredients, receptors in the user's skin are chemically triggered, rendering distinct haptic sensations. We identified five chemicals that can render lasting haptic sensations: tingling (sanshool), numbing (lidocaine), stinging (cinnamaldehyde), warming (capsaicin), and cooling (menthol). To enable the application of our novel approach in a variety of settings (such as VR), we engineered a self-contained wearable that can be worn anywhere on the user's skin (e.g., face, arms, legs). Implemented as a soft silicone patch, our device uses micropumps to push the liquid stimulants through channels that are open to the user's skin, enabling topical stimulants to be absorbed by the skin as they pass through. Our approach presents two unique benefits. First, it enables sensations, such as numbing, not possible with existing haptic devices. Second, our approach offers a new pathway, via the skin's chemical receptors, for achieving multiple haptic sensations using a single actuator, which would otherwise require combining multiple actuators (e.g., Peltier, vibration motors, electro-tactile stimulation). We evaluated our approach by means of two studies. In our first study, we characterized the temporal profiles of sensations elicited by each chemical. Using these insights, we designed five interactive VR experiences utilizing chemical haptics, and in our second user study, participants rated these VR experiences with chemical haptics as more immersive than without. Finally, as the first work exploring the use of chemical haptics on the skin, we offer recommendations to designers for how they may employ our approach for their interactive experiences. 

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2. Psychophysical Studies of Interleaving Narrowband Tactile Stimuli to Achieve Broadband Perceptual Effects

   https://doi.org/10.3389/frvir.2022.894575  

   Martinez, Juan S. ; Tan, Hong Z. ; Cholewiak, Roger W. ( May 2022 , Frontiers in Virtual Reality)

   Despite the ubiquitous presence of tactile actuators (tactors) in mobile devices, there is a continuing need for more advanced tactors that can cover the entire frequency range of human tactile perception. Broadband tactors can increase information transmission and enrich sensory experience. The engineering challenges are multifold in that the ideal tactors should exhibit an effective bandwidth of at least 300 Hz, small form factor, robustness, power efficiency and low cost. For wearable applications, there are the additional challenges of ease of mounting and maintaining adequate skin contact during body movements. We propose an approach to interleave narrowband tactile stimuli to achieve broadband effects, taking advantage of the limited spatial resolution of the skin on the torso and limbs. Three psychophysical experiments were conducted to assess the validity of this approach. Participants performed pairwise discriminations of two broadband stimuli delivered using one or two tactors. The broadband stimuli consisted of one mid-frequency and one high-frequency component delivered through one tactor by mixing the two components, or through two tactors (one component per tactor). The first two experiments revealed extraneous cues such as localization and mutual masking of mid- and high-frequency components that were subsequently eliminated in the third experiment. Results from 12 participants confirmed that performance on pairwise comparisons was below the discrimination threshold, confirming that broadband haptic effects can be achieved through narrowband tactors placed within the skin’s two-point limen. 

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3. Haptic and Audio Interaction Design

   https://doi.org/10.1007/978-3-031-15019-7_5  

   Jones, Lynette A. ; Ho, Hsin-Ni ( August 2022 , Haptic and Audio Interaction Design)

   Saitis, C. ; Farkhatdinov, I ; Papetti, S. (Ed.)

   There are fundamental differences between the tactile and thermal sensory systems that must be accommodated when designing multisensory cutaneous displays for use in virtual or teleoperated robotic environments. In this review we highlight the marked temporal and spatial differences between the senses of cold and warmth as revealed in psychophysical experiments. Cold and warmth are distinct senses with marked differences in the time taken to respond to stimulation and in their temporal filtering processes. Such variations must be taken into account when time-varying profiles of thermal stimulation are delivered to the skin concurrent with tactile stimulation since the resulting sensations will not be perceived on the same time scale. Although it is often reported that the thermal senses are markedly inferior to the sense of touch with respect to their spatial acuity, it is also clear that there is considerable variability across the body in the accuracy with which thermal stimuli can be localized. The distal to proximal gradient in thermal acuity suggests that locations other than the palmar surface of the hand are better suited for displaying thermal cues, in contrast to the situation for tactile inputs. As was noted for temporal processes, there are differences between localizing warmth and cold stimuli, with localization being superior for cold. These properties provide benchmarks that can be used in designing thermal and multisensory displays. 

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4. Inkjet Printing of PEDOT:PSS Inks for Robotic Skin Sensors

   https://doi.org/10.1115/msec2022-80989  

   Olowo, Olalekan O. ; Zhang, Ruoshi ; Sherehiy, Andriy ; Goulet, Brian ; Curry, Alexander ; Wei, Danming ; Yang, Zhong ; Alqatamin, Moath ; Popa, Dan O. ( June 2022 , ASME 2022 17th International Manufacturing Science and Engineering Conference)

   Enhancing physical human-robot interaction requires the improvement in the tactile perception of physical touch. Robot skin sensors exhibiting piezoresistive behavior can be used in conjunction with collaborative robots. In past work, fabrication of these tactile arrays was done using cleanroom techniques such as spin coating, photolithography, sputtering, wet and dry etching onto flexible polymers. In this paper, we present an addictive, non-cleanroom improved process of depositing PEDOT: PSS, which is the organic polymer responsible for the piezoresistive phenomenon of the robot skin sensor arrays. This publication details the patterning of the robot skin sensor structures and the adaptation of the inkjet printing technology to the fabrication process. This increases the possibility of scaling the production output while reducing the cleanroom fabrication cost and time from an approximately five-hour PEDOT: PSS deposition process to five minutes. Furthermore, the testing of these skin sensor arrays is carried out on a testing station equipped with a force plunger and an integrated circuit designed to provide perception feedback on various force load profiles controlled in an automated process. The results show uniform deposition of the PEDOT: PSS, consistent resistance measurement, and appropriate tactile response across an array of 16 sensors.

    

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5. Force-Aware Interface via Electromyography for Natural VR/AR Interaction

   https://doi.org/10.1145/3550454.3555461  

   Zhang, Yunxiang ; Liang, Benjamin ; Chen, Boyuan ; Torrens, Paul M. ; Atashzar, S. Farokh ; Lin, Dahua ; Sun, Qi ( December 2022 , ACM Transactions on Graphics)

   While tremendous advances in visual and auditory realism have been made for virtual and augmented reality (VR/AR), introducing a plausible sense of physicality into the virtual world remains challenging. Closing the gap between real-world physicality and immersive virtual experience requires a closed interaction loop: applying user-exerted physical forces to the virtual environment and generating haptic sensations back to the users. However, existing VR/AR solutions either completely ignore the force inputs from the users or rely on obtrusive sensing devices that compromise user experience. By identifying users' muscle activation patterns while engaging in VR/AR, we design a learning-based neural interface for natural and intuitive force inputs. Specifically, we show that lightweight electromyography sensors, resting non-invasively on users' forearm skin, inform and establish a robust understanding of their complex hand activities. Fuelled by a neural-network-based model, our interface can decode finger-wise forces in real-time with 3.3% mean error, and generalize to new users with little calibration. Through an interactive psychophysical study, we show that human perception of virtual objects' physical properties, such as stiffness, can be significantly enhanced by our interface. We further demonstrate that our interface enables ubiquitous control via finger tapping. Ultimately, we envision our findings to push forward research towards more realistic physicality in future VR/AR. 

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