Issue No. 2, August

Abstract

We study the influence of ripple waves on graphene sheets and graphene nanoribbons. Such waves are originating from the electromechanical effects, among other possible mechanisms. By considering variations in the in-plane and out-of-plane displacement vector, we show that the spontaneous generation of ripple waves has no preferred orientation. Intrinsic properties of ripple waves induce a large pseudopotential that in its turn is to induce large pseudomagentic fields that can be implemented into the band engineering of graphene structures.

Abstract

In this paper we presented the synthesis of TEOS with photoresist in order to use it like a hybrid material for 3D printer on the micrometer scale by means of the two-photon polymerization process, in which two photon are absorbed simultaneously by the material using an ultrafast laser causing its polymerization. We analyzed the mix of TEOS and photoresist with UV-VIS and FTIR spectrometers, checking that complies with two important conditions: has an optical transmission at 780 nm and absorbs at 390 nm. Finally we fabricated micro-structures with a new hybrid material; TEOS does not absorb the laser in this system and does not interfere with the formation of a threedimensional structure. After formation the 3D microstructure, samples were heated to form the SiO. These samples of microstructures were observed under digital microscope and SEM.

Abstract

The bursting wireless communication market, including 5G, advanced satellite communication systems and COTM (Communication On The Move) terminals, require ever more sophisticated functions, from multi-band and multi-function operations to electronically steerable and reconfigurable antennas, pushing technological developments towards the use of tunable microwave components and circuits. Reconfigurability allows indeed for reduced complexity and cost of the apparatuses. In this context, RF MEMS (Micro-Electro-Mechanical-Systems) technology has emerged as a very attractive solution to realize both tunable devices (e.g. variable capacitors, inductors and micro-relays), as well as complex circuits (e.g. tunable filters, reconfigurable matching networks and reconfigurable beam forming networks for phased array antennas). High linearity, low loss and high miniaturization are the typical advantages of RF MEMS over conventional technologies. Micromechanical components fabricated via IC-compatible MEMS technologies and capable of low-loss filtering, switching and frequency generation allow for miniaturized wireless front-ends via higher levels of integration. In addition, the inherent high linearity of the MEMS switches enables carrier aggregations without introducing intermodulation distortions. This paper will review the recent advances in the development of the RF MEMS to RF tunable circuits and systems.

Abstract

Manufacture of piezoelectric energy harvesters typically assumes bulk piezoelectric material for the transducer until the reduction in size of the device prevents this. However when designing piezoelectric harvesters, the complete system must be taken into account including the transducer, power circuit, and battery, as these will impose restrictions on what can be achieved. Therefore a comparison between MEMS and meso-scale piezoelectric energy harvesting systems using a fully parametrised model is required. The comparison was restricted to a piezoelectric beam with a mass at the end connected to a single supply pre-biasing circuit to provide the optimal damping force and rectification. A buck converter was used to transfer extracted energy to a 1.5V battery. The results indicate that for devices with a volume side length less than 16.25 mm, no device using meso-scale properties can be made to resonant at 100 Hz or less due to the length and stiffness of the beam. Whereas above this limit, the voltage required to damp devices with MEMS scale properties causes a breakdown in the dielectric. We present a comparison of the theoretical limits of MEMS and meso-scale piezoelectric harvesters to provide design insight for future devices to maximise power generation.

Abstract

We present a novel structure to supply gases to microchambers in microfluidic chips. An exemplary application is the continuous feeding of oxygen and CO2 for on-chip cell cultivation of mammalian cells. In our device, the surrounding air diffuses into the culture medium inside the chip through a porous wall of agarose hydrogel resulting in an easy and robust design.
One common method is the usage of gas permeable PDMS chips. However, liquid medium in which the cells grow is absorbed by PDMS causing unknown concentrations and memory effects.
Another possibility is a complex setup where medium with already dissolved gas is pumped constantly through the chip.
We designed and realized a silicon and borosilicate glass chip containing a gas permeable wall of agarose preventing leakage of medium. In order to precisely position the walls in the chip, we made use of surficial phaseguides (50nm high).
The blue-bottle-experiment makes the effective dissipation of oxygen visible when the colorless leucomethylen-blue reacts to methylene-blue. Successful results were achieved when applying 0.5 g/l methylene blue, 10 g/l glucose and a pH of 12.6 set by a buffer solution. As a result a continuous color gradient through the chip was obtained, which reflects the oxygen gradient and confirms the oxygen diffusion.

Abstract

Obesity and dysphagia are of potential and direct serious harm to the human body health. A commonly used method is controlling food intake to avoid obesity or determining if dysphagia exists by monitoring the swallow. This paper proposes a swallow detecting principle based on nanometer materials sensor, and implements a wearable detecting system with advantage of improved DTW algorithm. The system efficiently detects and faithfully identifies swallowing. In addition, it reduces the demand for hardware computing power. The system meets the features of a wearable system, such as soft and comfortable, lightweight, portable, and noninvasive.

Abstract

Fungi growth on bananas during transportation not only results in loss of food but it also incurs considerable transport losses. To investigate the influence of spores on the development of fungi growth on the bananas we present a sensor sticker. The sticker can be put on the banana surface for the detection of spore concentration. The designed sensor comprises of a thin layer of culture medium (PDA agarose) coated on a capacitive sensor fabricated on a polyimide foil (5 μm). As spores germinate, the capacitance of the culture medium changes which is measured by the interdigital capacitive element that contains 2 electrodes (with 428 fingers) that have a length of 3 mm, a width and a gap of 7 μm. In addition to the culture medium one of the major requirements for the fungi to grow is air. As air cannot diffuse through the sticker, air cavities are integrated in the culture medium layer to provide the necessary amount of air for fungi growth. This method was successfully applied to determine different concentrations of Fusarium Oxysporum, a major fungi species responsible for banana contamination. Measured capacitance change after a fixed time interval depends on the initial concentration of spores. The measurement takes typically 6 hours.

Abstract

Silicon-based MEMS technology has furthered the introduction of sensors and actuators in many applications. Particularly in inertial sensing, where no contact with a medium to be sensed is required, highly reliable and cost-effective solutions have been developed. For application in fluidic environments, special demands regarding the interaction can occur. Also, silicon-based technology is not cost-effective in low-volume applications.
In our recent work, we thus consider hybrid technologies and concentrate on physical sensor principles, which often provide more robustness in process control and condition monitoring than dedicated chemical sensors featuring chemical reactions with the environment by means of specific chemical interfaces. The latter are frequently prone to reliability issues, e.g. due to poisoning, drift, etc. Examples for physical parameters are thermal and electrical conductivity, permittivity, viscosity, speed of sound, and density. In this contribution, sensing concepts addressing these target parameters are reviewed.