There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

Starting from human ?sense of touch,? this paper reviews the state of tactile sensing in robotics. The physiology, coding, and transferring tactile data and perceptual importance of the ?sense of touch? in humans are discussed. Following this, a number of design hints derived for robotic tactile sensing are presented. Various technologies and transduction methods used to improve the touch sense capability of robots are presented. Tactile sensing, focused to fingertips and hands until past decade or so, has now been extended to whole body, even though many issues remain open. Trend and methods to develop tactile sensing arrays for various body sites are presented. Finally, various system issues that keep tactile sensing away from widespread utility are discussed.

Tactile Sensing—From Humans to Humanoids

http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

Atmospheric-pressure, non-equilibrium plasmas are susceptible to instabilities and, in particular, to arcing (glow-to-arc transition). Spatially confining the plasma to dimensions of 1 mm or less is a promising approach to the generation and maintenance of stable, glow discharges at atmospheric-pressure. Often referred to as microdischarges or microplasmas, these weakly-ionized discharges represent a new and fascinating realm of plasma science, where issues such as the possible breakdown of 'pd scaling' and the role of boundary-dominated phenomena come to the fore. Microplasmas are generated under conditions that promote the efficient production of transient molecular species such as the rare gas excimers, which generally are formed by three-body collisions. Pulsed excitation on a sub-microsecond time scale results in microplasmas with significant shifts in both the temperatures and energy distribution functions associated with the ions and electrons. This allows for the selective production of chemically reactive species and opens the door to a wide range of new applications of microplasmas. The implementation of semiconductor and microelectronics and MEMs microfabrication techniques has resulted in the realization of microplasma arrays as large as 250,000 devices. Fabricated in silicon or ceramics with characteristic device dimensions as small as 10 µm and at packing densities up to 104 cm−2, these arrays offer optical and electrical characteristics well suited for applications in medical diagnostics, displays and environmental sensing. Several microplasma device structures, including their fundamental properties and selected applications, will be discussed.

Microplasmas and applications

We present the development of a polyimide-based two-dimensional tactile sensing array realized using a novel inverted fabrication technique. Thermal silicon oxide or Pyrex® substrates are treated such that their surfaces are OH group terminated, allowing good adhesion between such substrates and a spun-on polyimide film during processing through what are suspected to be hydrogen bonds that can be selectively broken when release is desired. The release of the continuous polyimide film is rapidly accomplished by breaking these bonds. This process results in robust, low-cost and continuous polymer-film devices. The developed sensor skin contains an array of membrane-based tactile sensors (taxels). Micromachined thin-film metal strain gauges are positioned on the edges of polyimide membranes. The change in resistance from each strain gauge resulting from normal forces applied to tactile bumps on the top of the membranes is used to image force distribution. Response of an individual taxel is characterized. The effective gauge factor of the taxels is found to be approximately 1.3. Sensor array output is experimentally obtained. The demonstrated devices are robust enough for direct contact with humans, everyday objects and contaminants without undue care.

https://iopscience.iop.org/article/10.1088/0960-1317/13/3/302/pdf

Development of polyimide flexible tactile sensor skin

Underwater flow sensing is important for many robotics and military applications, including underwater robots and vessels. We report the development of micromachined, distributed flow sensors based on a biological inspiration, the fish lateral line sensors. Design and fabrication processes for realizing individual lateral line sensor nodes are discussed in this paper, along with preliminary characterization results.

https://iopscience.iop.org/article/10.1088/0960-1317/12/5/322/pdf

Design and fabrication of artificial lateral line flow sensors

We present the design, fabrication process, and characterization of a multimodal tactile sensor made of polymer materials and metal thin film sensors The multimodal sensor can detect the hardness, thermal conductivity, temperature, and surface contour of a contact object for comprehensive evaluation of contact objects and events Polymer materials reduce the cost and the fabrication complexity for the sensor skin, while increasing mechanical flexibility and robustness Experimental tests show the skin is able to differentiate between objects using measured properties

Polymer micromachined multimodal tactile sensors

Nearly all underwater vehicles and surface ships today use sonar and vision for imaging and navigation. However, sonar and vision systems face various limitations, e.g., sonar blind zones, dark or murky environments, etc. Evolved over millions of years, fish use the lateral line, a distributed linear array of flow sensing organs, for underwater hydrodynamic imaging and information extraction. We demonstrate here a proof-of-concept artificial lateral line system. It enables a distant touch hydrodynamic imaging capability to critically augment sonar and vision systems. We show that the artificial lateral line can successfully perform dipole source localization and hydrodynamic wake detection. The development of the artificial lateral line is aimed at fundamentally enhancing human ability to detect, navigate, and survive in the underwater environment.

https://www.pnas.org/content/pnas/103/50/18891.full.pdf

Distant touch hydrodynamic imaging with an artificial lateral line

We discuss two types of micromachined flow sensors realized by using novel microfabrication processes—a hot-wire an- emometer ~based on thermal transfer! and a biologically inspired flow sensor ~based on momentum transfer!. Both sensors are enabled by a new, efficient three-dimensional assembly technique called the plastic deformation magnetic assembly method. The sensors can be packaged in high-density, two-dimensional arrays efficiently, with each sensor node capable of performing two-component or three- component flow sensing. We first discuss the development of new hot-wire anemometers ~HWA!. The HWA uses a thermal element ~hot wire! that is made of Pt/Ni/Pt film with a measured temperature coefficient of resistance of 2,700 ppm/°C. The thermal element is elevated out of plane by using support beams made of polyimide, a polymer material. Both steady-state and transient characteristics of the sensor have been experimentally obtained. The second type of flow sensor is based on momentum transfer principles and inspired by fish lateral line sensors. Each sensor consists of a vertical cilium attached to a horizontal cantilever. Fluid flow imparts moment on the vertical cilium, and causes the horizontal cantilever to bend. The fabrication process and preliminary measurement data are presented.

Jack Chen

Papers

Development of polyimide flexible tactile sensor skin

Design and fabrication of artificial lateral line flow sensors

Polymer micromachined multimodal tactile sensors

Distant touch hydrodynamic imaging with an artificial lateral line

Two-Dimensional Micromachined Flow Sensor Array for Fluid Mechanics Studies