In the last decade, we have witnessed a drastic change in the form factor of audio and vision technologies, from heavy and grounded machines to lightweight devices that naturally fit our bodies. However, only recently, haptic systems have started to be designed with wearability in mind. The wearability of haptic systems enables novel forms of communication, cooperation, and integration between humans and machines. Wearable haptic interfaces are capable of communicating with the human wearers during their interaction with the environment they share, in a natural and yet private way. This paper presents a taxonomy and review of wearable haptic systems for the fingertip and the hand, focusing on those systems directly addressing wearability challenges. The paper also discusses the main technological and design challenges for the development of wearable haptic interfaces, and it reports on the future perspectives of the field. Finally, the paper includes two tables summarizing the characteristics and features of the most representative wearable haptic systems for the fingertip and the hand.

/pdf/wearable-haptic-systems-for-the-fingertip-and-the-hand-17lqq0lw0j.pdf

Wearable Haptic Systems for the Fingertip and the Hand: Taxonomy, Review, and Perspectives

Recent trends in three-dimensional (3D) display technologies are very interesting in that both old-fashioned and up-to-date technologies are being actively investigated together. The release of the first commercially successful 3D display product raised new research topics in stereoscopic display. Autostereoscopic display renders a ray field of a 3D image, whereas holography replicates a wave field of it. Many investigations have been conducted on the next candidates for commercial products to resolve existing limitations. Up-to-date see-through 3D display is a concept close to the ultimate goal of presenting seamless virtual images. Although it is still far from practical use, many efforts have been made to resolve issues such as occlusion problems.

http://faculty.cas.usf.edu/mkkim/papers.pdf/2011%20AO%20JHong.pdf

Three-dimensional display technologies of recent interest: principles, status, and issues [Invited]

In 1965 Ivan E. Sutherland envisioned the Ultimate Display, a room in which a computer can directly control the existence of matter.
This type of display would merge the digital and the physical world, dramatically changing how people interact with computers.
This thesis explores flat displays, deformable displays, flexible materials, static, and mobile projection displays in dynamic environments. 
%Dynamic environments are inherent to human behavior, but pose big problems to Human-Computer Interaction since computing devices rely on many assumptions of the interaction.
Two aspects of the dynamic environment are considered. One is mobile human nature -- a person moving through or inside an environment. The other is the change or movement of the environment itself.

The initial study consisted of a mixed reality application, based on recent motor learning research. It tested if a performer's attentional focus on markers external to the body improves the accuracy and duration of acquiring a motor skill, as compared with the performer focusing on their own body accompanied by verbal instructions. This experiment showed the need for displays that resemble physical reality. 


Deformable displays and Organic User Interfaces (OUIs) leverage shape, material, and the inherent properties of matter in order to create natural, intuitive forms of interaction. We suggested designing OUIs employing depth sensors as 3D input, deformable displays as 3D output, and identifying attributes that couple matter to human perception and motor skills. 

Flexible materials were explored by developing a soft gripper able to hold everyday objects of various shapes and sizes. It did not use complex hardware or control algorithms, but rather combined sheets of flexible plastic materials and a single servo motor.
The gripper showed how a simple design with a minimal control mechanism can solve a complex problem in a dynamic environment.
It serves as an example application for merging the digital and the physical through flexible materials, embodied computation, and actuation.

The next two experiments merge digital information with the physical dynamic environment by using mobile and static projectors.
The mobile projector experiment consisted of GPS navigation using a bike-mounted projector, displaying a map on the pavement in front of the bike. We found out that if compared with a bike-mounted smartphone, the mobile projector yields a lower cognitive load for the map navigation task. 
A dynamic space emerges from the navigation task requirements, and the projected display becomes a part of the physical environment. 

In the final experiment, a person interacts with a changing, growing environment, on which digital information is projected from above using a static projector. The interactive space consists of cardboard building blocks, the arrangement of which are limited by the area of projection. The user adds cardboard blocks to the cluster based upon feedback projected from above.
Concepts from artificial intelligence and architecture were applied for understanding the interaction between the environment, the user, the morphology, and the material of the physical building system.

https://publications.lib.chalmers.se/records/fulltext/198101/198101.pdf

The Ultimate Display

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO3 ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO3 nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.

High-Performance Piezoelectric Nanogenerators with Imprinted P(VDF-TrFE)/BaTiO3 Nanocomposite Micropillars for Self-Powered Flexible Sensors.

Ferroelectric polymers are the most promising electroactive materials with outstanding properties that can be integrated into a variety of flexible electronic devices. Their multifunctional capabilities, ability to bend and stretch, ease of processing, chemical stability, and the high biocompatibility of polyvinylidene fluoride (PVDF)-based polymers make them attractive for applications in flexible memories, energy transducers, and electronic skins. Here, recent advance in the research of PVDF-based flexible electronic devices is reviewed, including nonvolatile memories, energy-harvesting devices, and multifunctional portable sensors.

PVDF-Based Ferroelectric Polymers in Modern Flexible Electronics

Virtual and physical worlds are merging. Currently users of head-mounted displays cannot have unobtrusive tactile feedback while touching virtual objects. We present a mid-air tactile feedback system for head-mounted displays. Our prototype uses the focus of a modulated ultrasonic phased array for unobtrusive mid-air tactile feedback generation. The array and the hand position sensor are mounted on the front surface of a head-mounted virtual reality display. The presented system can enhance 3D user interfaces and virtual reality in a new way. To evaluate the tactile feedback together with visuals on an Oculus Rift VR headset, we had 13 participants do a simple virtual keypad tapping task with and without tactile feedback. The results indicate that while the measured speed and accuracy differed only a little, the subjects were nearly unanimous in that they preferred to use the tactile feedback. The "raw" NASA TLX questionnaires conducted after use revealed that the participants felt slightly less mental, physical and temporal demand with the tactile feedback. The participants' self-assessment of their performance was also higher with the tactile feedback.

Head-mounted display with mid-air tactile feedback

The ongoing revolution of touch-based user interfaces sets new requirements for touch panel technologies, including the need to operate in a wide range of environments. Such touch panels need to endure moisture and sunlight. Moreover, they often need to be curved or flexible. Thus, there is a need for new technologies suitable, for example, for home appliances used in the kitchen or the bathroom, automotive applications, and e-paper. In this work, the development of transparent and flexible touch panels for moist environments is reported. A piezoelectric polymer, poly(vinylidene difluoride) (PVDF), is used as a functional substrate material. Transparent electrodes are fabricated on both sides of a PVDF film using a graphene-based ink and spray coating. The excellent performance of the touch panels is demonstrated in moist and underwater conditions. Also, the transparent device shows very small pyroelectric response to radiative heating in comparison to a non-transparent device. Solution processable electrode materials in combination with functional substrates allow the low-cost and high-throughput manufacturing of touch panels using printing technologies.

Printable, Transparent, and Flexible Touch Panels Working in Sunlight and Moist Environments

Combustion of activated aluminum

The FogScreen is an immaterial projection screen that consists of air and a little humidity, and enables high-quality projected images in thin air. Objects and images appear to float in mid-air, and touching or walking through them enhances the impression, as the screen feels just like air. One nice feature is the possibility to project different images on each side without having them interfere with each other.

The interactive FogScreen

Accurate displacement measurement using quadrature Doppler radar requires amplitudes and phase imbalance compensation. Previously, this imbalance calibration has required cumbersome hardware modifications and thus can only be performed in a laboratory setting. Recently, a data-based method that does not require hardware modifications has been proposed. This simplifies the calibration process and allows the calibration to be performed on-site periodically. The method is called ellipse fitting. In this paper, the different factors affecting imbalance estimation accuracy, namely, arc length, initial phase angle, and noise level were thoroughly investigated. The Levenberg–Marquardt (LM) algorithm is proposed for the first time to increase the estimation accuracy as compared to the previously suggested algebraic fitting. Comprehensive simulations and experimental data show that the algebraic fitting method results in biased estimates. The proposed LM method has also been demonstrated to be more robust to noise, varying arc lengths, and different initial angles. The LM method reaches sufficient imbalance estimation accuracy with an arc length of 40% and a noise level of 1.5%.

Karri Palovuori

Papers

Head-mounted display with mid-air tactile feedback

Printable, Transparent, and Flexible Touch Panels Working in Sunlight and Moist Environments

Combustion of activated aluminum

The interactive FogScreen

Quadrature Imbalance Compensation With Ellipse-Fitting Methods for Microwave Radar Physiological Sensing