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

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

By virtue of their wide applications in personal electronic devices and industrial monitoring, pressure sensors are attractive candidates for promoting the advancement of science and technology in modern society. Flexible pressure sensors based on organic materials, which combine unique advantages of flexibility and low-cost, have emerged as a highly active field due to their promising applications in artificial intelligence systems and wearable health care devices. In this review, we focus on the fundamentals of flexible pressure sensors, and subsequently on several critical concepts for the exploration of functional materials and optimization of sensing devices toward practical applications. Perspectives on self-powered, transparent and implantable pressure sensing devices are also examined to highlight the development directions in this exciting research field.

Advances of flexible pressure sensors toward artificial intelligence and health care applications

13. 벼잎선충의 약제처리 방법별 방제 효과

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, present ab initio calculations of β-cristobalite BiO(2) which exhibits three Dirac points at the Fermi level. We find that β-cristobalite BiO(2) is metastable, so it can be physically realized as a 3D analog to graphene.

Dirac Semimetal in Three Dimensions

Flexible electronics, which can be distributed on any surface we need, are highly demanded in the development of Internet of Things (IoT), robot technology and electronic skins. Temperature is a fundamental physical parameter, and it is an important indicator in many applications. Therefore, a flexible temperature sensor is required. Here, we report a simple method to fabricate three lightweight, low-cost and flexible temperature sensors, whose sensitive materials are reduced graphene oxide (r-GO), single-walled carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). By comparing linearity, sensitive and repeatability, we found that the r-GO temperature sensor had the most balanced performance. Furthermore, the r-GO temperature sensor showed good mechanical properties and it could be bent in different angles with negligible resistance change. In addition, the performance of the r-GO temperature sensor remained stable under different kinds of pressure and was unaffected by surrounding environments, like humidity or other gases, because of the insulating layer on its sensitive layer. The easy-fabricated process and economy, together with the remarkable performance of the r-GO temperature sensor, suggest that it is suitable for use as a robot skin or used in the environment of IoT.

https://www.mdpi.com/1424-8220/18/5/1400/pdf

A Flexible Temperature Sensor Based on Reduced Graphene Oxide for Robot Skin Used in Internet of Things.

Fluid–surface interactions can become dominant in microfluidics, which is a central technology in a number of miniaturized systems for chemical, biological and medical applications. In this paper, two kinds of hydrophobic valves in microfluidic applications were presented. One is based on special geometrical designs and chemical modification for silicon dioxide and glass microchannels. Silicon dioxide and Pyrex glass surfaces, which are hydrophilic originally, are modified with octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) to be hydrophobic, with the contact angles up to ∼102 and 103°, respectively, for water. The formation of OTS SAMs takes

Passive valves based on hydrophobic microfluidics

We propose a flexible wireless pressure sensor, which uses a graphene/polydimethylsiloxane (GR/PDMS) sponge as the dielectric layer. The sponge is sandwiched between two surfaces of a folded flexible printed circuit with patterned Cu as the antenna and electrode. By adjusting graphene and NH4HCO3 concentrations, a composite with 20% concentration of NH4HCO3 and 2% concentration of graphene as the dielectric layer is obtained, which exhibits high sensitivity (2.2 MHz/kPa), wide operating range (0–500 kPa), rapid response time (~7 ms), low detection limit (5 Pa), and good stability, recoverability, and repeatability. In addition, the sensor is sensitive to finger bending and facial muscle movements for smile and frown, that are transmitted using wireless electromagnetic coupling; therefore, it has potential for a wide range of applications such as intelligent robots, bionic-electronic skin and wearable electronic devices.

Wireless wide-range pressure sensor based on graphene/PDMS sponge for tactile monitoring

This paper presents a wireless capacitive pressure sensor based on LTCC (low temperature co-fired ceramic) technology, where the design, fabrication, and measurement of the sensor is demonstrated and discussed. Differ from traditional LTCC process flow, a unique process of screen-printing sacrifice layer has been introduced to avoid deformation of the capacitive embedded cavity during lamination or sintering, which leads to a better performance of the sensor. A greater sensitivity of the sensor, comparing with its predecessors, is showed during measurement. Finally ways for future optimization are proposed.

Wireless LTCC-based capacitive pressure sensor for harsh environment

High-performance flexible pressure sensors have attracted more attention because of their high-sensitivity, strong-flexibility, implantable and wearable characteristics. Here, we propose a flexible high-performance pressure sensor using a micro-patterned graphene/polydimethylsiloxane (Gr/PDMS) composite as the dielectric layer, which is sandwiched by folding the PDMS substrate with the cavity and the wrinkled continuous Au pattern as the antenna and electrode. By investigating graphene with different concentration, the composite with a thickness of 200 μm and a concentration of 2% as the dielectric layer exhibits the highest sensitivity. The sensors are tested under cyclic pressure, exhibiting outstanding stability and durability, low detection limit, and rapid response time, and they can be utilized to detect subtle pressure. In addition, the sensors can be sensitive to hand bending and facial muscle movements, and thus they have the potential to be used for highly sensitive wireless detection in the wide range of wearable electronic devices, bionic-electronic skins and intelligent robot.

Jijun Xiong

Papers

A Flexible Temperature Sensor Based on Reduced Graphene Oxide for Robot Skin Used in Internet of Things.

Passive valves based on hydrophobic microfluidics

Wireless wide-range pressure sensor based on graphene/PDMS sponge for tactile monitoring

Wireless LTCC-based capacitive pressure sensor for harsh environment

Wireless flexible pressure sensor based on micro-patterned Graphene/PDMS composite