Integrated nanophotonic waveguide-based devices for IR and Raman gas spectroscopy

On-chip devices for absorption spectroscopy and Raman spectroscopy have been developing rapidly in the last few years, triggered by the growing availability of compact and affordable tunable lasers, detectors, and on-chip spectrometers. Material processing that is compatible with mass production has been proven to be capable of long low-loss waveguides of sophisticated designs, which are indispensable for high-light–analyte interactions. Sensitivity and selectivity have been further improved by the development of sorbent cladding. In this review, we discuss the latest advances and challenges in the field of waveguide-enhanced Raman spectroscopy (WERS) and waveguide infrared absorption spectroscopy (WIRAS). The development of integrated light sources and detectors toward miniaturization will be presented, together with the recent advances on waveguides and cladding to improve sensitivity. The latest reports on gas-sensing applications and main configurations for WERS and WIRAS will be described, and the most relevant figures of merit and limitations of different sensor realizations summarized

Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems

Review of recent microwave planar resonator-based sensors: Techniques of complex permittivity extraction, applications, open challenges and future research directions

Recent developments in the field of microwave planar sensors have led to a renewed interest in industrial, chemical, biological and medical applications that are capable of performing real-time and non-invasive measurement of material properties. Among the plausible advantages of microwave planar sensors is that they have a compact size, a low cost and the ease of fabrication and integration compared to prevailing sensors. However, some of their main drawbacks can be considered that restrict their usage and limit the range of applications such as their sensitivity and selectivity. The development of high-sensitivity microwave planar sensors is required for highly accurate complex permittivity measurements to monitor the small variations among different material samples. Therefore, the purpose of this paper is to review recent research on the development of microwave planar sensors and further challenges of their sensitivity and selectivity. Furthermore, the techniques of the complex permittivity extraction (real and imaginary parts) are discussed based on the different approaches of mathematical models. The outcomes of this review may facilitate improvements of and an alternative solution for the enhancement of microwave planar sensors’ normalized sensitivity for material characterization, especially in biochemical and beverage industry applications

A Recent Approach towards Fluidic Microstrip Devices and Gas Sensors: A Review

This paper aims to review some of the available tunable devices with emphasis on the techniques employed, fabrications, merits, and demerits of each technique. In the era of fluidic microstrip communication devices, versatility and stability have become key features of microfluidic devices. These fluidic devices allow advanced fabrication techniques such as 3D printing, spraying, or injecting the conductive fluid on the flexible/rigid substrate. Fluidic techniques are used either in the form of loading components, switching, or as the radiating/conducting path of a microwave component such as liquid metals. The major benefits and drawbacks of each technology are also emphasized. In this review, there is a brief discussion of the most widely used microfluidic materials, their novel fabrication/patterning methods

Double-layered metamaterial-based resonator operating at millimetre wave for detection of dengue virus

The interest in microwave technology for biological applications using metamaterial as sensing element is increasing due to strong electric field compared to traditional microwave sensors. The operation at millimetre-wave frequencies further enhances the field intensity leading to increased sensitivity, which can be used in the detection of the dengue virus and it can be vital in controlling the disease. The millimetre-wave metamaterial-based resonators are presented in this thesis to characterise blood’s dielectric properties in the case of the dengue virus. The correlation coefficient, t-test, and cross-correlation were applied on S11 phase responses. During measurements, tap water was used instead of blood, and methylated alcohol was added to the water to lower its permittivity, mimicking the dielectric response of infected blood. First, a single-layered design with an engraved space to hold blood samples is presented as a proof of concept for blood-sensing and the application of statistical models. This sensor showed a resonance shift of 0.22 GHz due to an 8 unit decrease in blood’s permittivity. In contrast, three (3) designs of two-layered sensors are proposed with replaceable sensing layers suitable for repeated measurements. Double-layered Sensor 1 showed resonance at 36.28 GHz for normal blood. The perturbation observed was 0.88 GHz when the blood’s permittivity was reduced by 8 units. Sensor 2 showed a resonance shift from 27.22 GHz to 29.82 GHz with the 8 unit change in blood’s permittivity. Sensor 3 showed a lesser resonance shift, which is 0.44 GHz. However, the double-layered Sensor 3 has the edge over other designs in terms of its performance in all statistical methods. In double-layered sensors, the replaceable sensing layer provides quick and accurate results. As a result, the sensors presented here can detect the dengue virus using a simple finger-prick blood extraction method

Substrate-integrated waveguide (SIW) microwave sensor theory and model in characterising dielectric material : A review

Microwave sensors offer appealing features such as susceptibility, quick response, and non-invasiveness, making them valuable tools for highly accurate measurements of material characterisation. A wide range of techniques, including cavity waveguide, planar transmission line, cavity waveguide perturbation, open-ended coaxial probe, and free-space transmission, have been employed to characterise materials that are essential for their cost-effectiveness, ease of manufacturing, high sensitivity, good quality factor (Q-factor), and compact size, allowing them to be applied to different material types. Among the microwave sensor types, the substrate-integrated waveguide (SIW) has emerged as a promising technology in order to characterise materials in an efficient manner. This paper presents a review of the current state and potential opportunities of SIW microwave sensors in the characterisation of dielectric materials. It provides insights into various design principles, techniques, and applications of SIW microwave sensors across different sectors, highlighting their advantages and limitations compared to conventional waveguide-based sensors. Furthermore, the paper summarises several fabrication methods that can be implemented for SIW microwave sensors to enable the production of efficient and reliable sensors. Additionally, the future directions provided in this paper aim to contribute to the ongoing development and optimisation of SIW-based microwave sensors for accurate and efficient dielectric material characterisation. Overall, this review article serves as a beneficial resource for new researchers seeking to understand the role of SIW microwave sensors in material characterisation. It outlines the current status, opportunities, and potential advancements of SIW sensors, shedding light on their significance and potential impact in the field of material characterisatio

Compact microwave microfluidic sensors and applicator

There is a need in the industrial, chemical, biological, and medical applications for sensors capable for providing on line real-time non-destructive and non‐chemical measurements methods of liquid properties. There are huge advantages that microwave-based microfluidic sensing techniques offer over conventional methods due to the strong interaction of microwave electromagnetic fields with the molecules of polar liquids, so their properties can be revealed. Furthermore, in recent years there has been growing interest in utilizing microwaves in microfluidic heating owing to the efficient, selective, and volumetric properties of the resultant heating, which is also easily controlled. The research work presented here encapsulates: (1) The design and realization of novel microwave microfluidic microstrip sensors which can be used to characterize accurately liquid permittivities. This resonator is both compact and planar, making it suitable for a lab-on-a-chip approach. Moreover, the sensor has been developed to measure properties of multi-phase liquids where the sensor is a variant of the split ring resonator realized in a microstrip implementation. (2) A microwave microstrip sensor incorporating a split ring resonator for microsphere detection and dielectric characterization within a microfluidic channel. (3) A new dual mode microwave microfluidic microstrip sensor which has the ability to measure the liquid permittivity with temperature variations. Two quarter ring resonators were designed and fabricated. The first resonator is a microfluidic sensor whose resonant frequency and quality factor depend on the liquid sample. The second is used as a reference to adjust for any changes in temperature. (4) A microwave microfluidic applicator with electronically-controlled heating, which has been proposed, designed, and realized. The concept is based on feeding the resonator with two synchronized inputs that have a variable phase shift between them