Phononic and photonic band gap structures: modelling and applications

AbstractPhotonic crystals (PhCs) are artificial materials with a permittivity which is a periodic function of the position, with a period comparable to the wavelength of light. The most interesting characteristic of such materials is the presence of photonic band gaps (PBGs). PhCs have very interesting properties of light confinement and localization together with the strong reduction of the device size, orders of magnitude less than the conventional photonic devices, allowing a potential very high scale of integration. These structures possess unique characteristics enabling to operate as optical waveguides, high Q resonators, selective filters, lens or superprism. The ability to mould and guide light leads naturally to novel applications in several fields.Band gap formation in periodic structures also pertains to elastic wave propagation. Composite materials with elastic coefficients which are periodic functions of the position are named phononic crystals. They have properties similar to those of photonic crystals and corresponding applications too. By properly choosing the parameters one may obtain phononic crystals (PhnCs) with specific frequency gaps. An elastic wave, whose frequency lies within an absolute gap of a phononic crystal, will be completely reflected by it. This property allows realizing non-absorbing mirrors of elastic waves and vibration-free cavities which might be useful in high-precision mechanical systems operating in a given frequency range. Moreover, one can use elastic waves to study phenomena such as those associated with disorder, in more or less the same manner as with electromagnetic waves.The authors present in this paper an introductory survey of the basic concepts of these new technologies with particular emphasis on their main applications, together with a description of some modelling approaches

Modeling of Slot Waveguide Sensors Based on Polymeric Materials

Slot waveguides are very promising for optical sensing applications because of their peculiar spatial mode profile. In this paper we have carried out a detailed analysis of mode confinement properties in slot waveguides realized in very low refractive index materials. We show that the sensitivity of a slot waveguide is not directly related to the refractive index contrast of high and low materials forming the waveguide. Thus, a careful design of the structures allows the realization of high sensitivity devices even in very low refractive index materials (e.g., polymers) to be achieved. Advantages of low index dielectrics in terms of cost, functionalization and ease of fabrication are discussed while keeping both CMOS compatibility and integrable design schemes. Finally, applications of low index slot waveguides as substitute of bulky fiber capillary sensors or in ring resonator architectures are addressed. Theoretical results of this work are relevant to well established polymer technologies

Efficient Chemical Sensing by Coupled Slot SOI Waveguides

A guided-wave chemical sensor for the detection of environmental pollutants or biochemical substances has been designed. The sensor is based on an asymmetric directional coupler employing slot optical waveguides. The use of a nanometer guiding structure where optical mode is confined in a low-index region permits a very compact sensor (device area about 1200 μm2) to be realized, having the minimum detectable refractive index change as low as 10-5. Silicon-on-Insulator technology has been assumed in sensor design and a very accurate modelling procedure based on Finite Element Method and Coupled Mode Theory has been pointed out. Sensor design and optimization have allowed a very good trade-off between device length and sensitivity. Expected device sensitivity to glucose concentration change in an aqueous solution is of the order of 0.1 g/L

Modeling and Design of a New Flexible Graphene-on-Silicon Schottky Junction Solar Cell

A new graphene-based flexible solar cell with a power conversion efficiency >10% has been designed. The environmental stability and the low complexity of the fabrication process are the two main advantages of the proposed device with respect to other flexible solar cells. The designed solar cell is a graphene/silicon Schottky junction whose performance has been enhanced by a graphene oxide layer deposited on the graphene sheet. The effect of the graphene oxide is to dope the graphene and to act as anti-reflection coating. A silicon dioxide ultrathin layer interposed between the n-Si and the graphene increases the open-circuit voltage of the cell. The solar cell optimization has been achieved through a mathematical model, which has been validated by using experimental data reported in literature. The new flexible photovoltaic device can be integrated in a wide range of microsystems powered by solar energy

Multiplexed Liquid Biopsy and Tumor Imaging Using Surface-Enhanced Raman Scattering

The recent improvements in diagnosis enabled by advances in liquid biopsy and oncological imaging significantly better cancer care. Both these complementary approaches, which are used for early tumor detection, characterization, and monitoring, can benefit from applying techniques based on surface-enhanced Raman scattering (SERS). With a detection sensitivity at the single-molecule level, SERS spectroscopy is widely used in cell and molecular biology, and its capability for the in vitro detection of several types of cancer biomarkers is well established. In the last few years, several intriguing SERS applications have emerged, including in vivo imaging for tumor targeting and the monitoring of drug release. In this paper, selected recent developments and trends in SERS applications in the field of liquid biopsy and tumor imaging are critically reviewed, with a special emphasis on results that demonstrate the clinical utility of SERS

Modeling and Design of a New Flexible Graphene-on-Silicon Schottky Junction Solar Cell

A new graphene-based flexible solar cell with a power conversion efficiency >10% has been designed. The environmental stability and the low complexity of the fabrication process are the two main advantages of the proposed device with respect to other flexible solar cells. The designed solar cell is a graphene/silicon Schottky junction whose performance has been enhanced by a graphene oxide layer deposited on the graphene sheet. The effect of the graphene oxide is to dope the graphene and to act as anti-reflection coating. A silicon dioxide ultrathin layer interposed between the n-Si and the graphene increases the open-circuit voltage of the cell. The solar cell optimization has been achieved through a mathematical model, which has been validated by using experimental data reported in literature. The new flexible photovoltaic device can be integrated in a wide range of microsystems powered by solar energy

Low-Cost Wireless Wearable System for Posture Monitoring

Posture monitoring aiming at preventing many of the pathologies affecting the spine is becoming more and more essential in many contexts, including telemedicine. The market pushes towards the development of new technical solutions that are comfortable for the user and that are increasingly becoming lower in terms of cost. Some systems at the state of the art level are effective and sometimes quite comfortable, but they have a degree of complexity that is not compatible with some market segments. Here, we report on the development, at a prototype level, a simple, low-cost, and potentially very comfortable microcontroller-based system capable of signaling incorrect postures with great sensitivity. The prototype, which has been tested also using video analysis, has shown its capacity to be easily integrated into a garment. Experimental activity has proven the prototype’s functionality. The wearable embedded system is able to detect flections in the back region monitored by the flex sensor with an accuracy of <3°. The achievement represents a further demonstration of the potential of wearable electronics in the context of cyber-physical systems for healthcare

Design of a New Ultracompact Resonant Plasmonic Multi-Analyte Label-Free Biosensing Platform

In this paper, we report on the design of a bio-multisensing platform for the selective label-free detection of protein biomarkers, carried out through a 3D numerical algorithm. The platform includes a number of biosensors, each of them is based on a plasmonic nanocavity, consisting of a periodic metal structure to be deposited on a silicon oxide substrate. Light is strongly confined in a region with extremely small size (=1.57 μm2), to enhance the light-matter interaction. A surface sensitivity Ss = 1.8 nm/nm has been calculated together with a detection limit of 128 pg/mm2. Such performance, together with the extremely small footprint, allow the integration of several devices on a single chip to realize extremely compact lab-on-chip microsystems. In addition, each sensing element of the platform has a good chemical stability that is guaranteed by the selection of gold for its fabrication

The role of autoimmune diseases in the prognosis of lymphoma

The connection between autoimmune disease (AID) and lymphoproliferative disorders is a complex bidirectional relationship that has long been a focus of attention by researchers and physicians. Although advances in pathobiology knowledge have ascertained an AID role in the development of lymphoproliferative diseases developing, results about AID influence on the prognosis of lymphoma are discordant. In this review, we collect the most relevant literature debating a direct or indirect link between immune-mediated diseases and lymphoma prognosis. We also consider the molecular, genetic, and microenvironmental factors involved in the pathobiology of these diseases in order to gain a deeper understanding of the nature of this link

The Role of Autoimmune Diseases in the Prognosis of Lymphoma

The connection between autoimmune disease (AID) and lymphoproliferative disorders is a complex bidirectional relationship that has long been a focus of attention by researchers and physicians. Although advances in pathobiology knowledge have ascertained an AID role in the development of lymphoproliferative diseases developing, results about AID influence on the prognosis of lymphoma are discordant. In this review, we collect the most relevant literature debating a direct or indirect link between immune-mediated diseases and lymphoma prognosis. We also consider the molecular, genetic, and microenvironmental factors involved in the pathobiology of these diseases in order to gain a deeper understanding of the nature of this link