An LC Wireless Microfluidic Sensor Based on Low Temperature Co-Fired Ceramic (LTCC) Technology

A Systematic Review of Advanced Sensor Technologies for Non-Destructive Testing and Structural Health Monitoring

This paper reviews recent advances in sensor technologies for non-destructive testing (NDT) and structural health monitoring (SHM) of civil structures. The article is motivated by the rapid developments in sensor technologies and data analytics leading to ever-advancing systems for assessing and monitoring structures. Conventional and advanced sensor technologies are systematically reviewed and evaluated in the context of providing input parameters for NDT and SHM systems and for their suitability to determine the health state of structures. The presented sensing technologies and monitoring systems are selected based on their capabilities, reliability, maturity, affordability, popularity, ease of use, resilience, and innovation. A significant focus is placed on evaluating the selected technologies and associated data analytics, highlighting limitations, advantages, and disadvantages. The paper presents sensing techniques such as fiber optics, laser vibrometry, acoustic emission, ultrasonics, thermography, drones, microelectromechanical systems (MEMS), magnetostrictive sensors, and next-generation technologies.

Flow-based green ceramics microdevice with smartphone image colorimetric detection for free chlorine determination in drinking water

The residual free chlorine concentration is an important parameter to evaluate the potability of water and the efficiency of disinfection in the water treatment system. As a restricted range of residual free chlorine concentration at all points of the distribution network is needed to ensure efficiency and to avoid deleterious effects, fast and in situ quantification of this specie is important. This work deals with the development and validation of two procedures based on DPD (N,N-diethyl-p-phenylenediamine) and OT (ortho-tolidine, 3,3-dimethylbenzidine) for the determination of residual free chlorine in water by exploiting a flow-based microdevice built with Low Temperature Co-Fired Ceramic (LTCC) technology. The analytical signal was monitored by a smartphone camera through RGB values obtained by a free application (Color Grab®). Under optimized conditions, linear ranges within 0.6-2.5 mg/L and 0.1-2.3 mg/L were obtained for DPD and OT methods, with limits of detection and quantification of 0.023 and 0.077 mg/L (DPD) and 0.026 and 0.089 mg/L (OT). Precision expressed as RSD (2.0 mg/L free chlorine, n = 10), was 1.3 % and 0.7 %, respectively. Both procedures were successfully applied to the analysis of samples from a water treatment plant. The flow-based microdevice coupled to digital-image colorimetry is an innovative, sustainable, and cost-effective analytical tool for in-field chemical analysis.

Planar Elliptical Inductor Design for Wireless Implantable Medical Devices

Wireless implantable medical devices (WIMDs) have seen unprecedented progress in the past three decades. WIMDs help clinicians in better-understanding diseases and enhance medical treatment by allowing for remote data collection and delivering tailored patient care. The wireless connectivity range between the external reader and the implanted device is considered one of the key design parameters in WIMD technology. One of the common modes of communication in battery-free WIMDs is inductive coupling, where the power and data between the reader and the implanted device are transmitted via magnetically coupled inductors. The design and shape of these inductors depend on the requirements of the application. Several studies have reported models of standard planar inductors such as circular, square, hexagonal, and octagonal in medical applications. However, for applications, constrained by narrow implantable locations, elliptical planar inductors may perform better than standard-shaped planar inductors. The aim of this study is to develop a numerical model for elliptical inductors. This model allows for the calculation of the inductance of the elliptical planar inductor and its parasitic components, which are key design parameters for the development of WIMDs powered by inductive coupling. An area transformation technique is used to transform and derive elliptical inductor formulas from standard circular inductor formulas. The proposed model is validated for various combinations of the number of turns, trace width, trace separation, and different inner and outer diameters of the elliptical planar inductor. For a thorough experimental validation of the proposed numerical model, more than 75 elliptical planar inductors were fabricated, measured, and compared with the numerical output of the proposed model. The mean error between the measured inductor parameters and numerical estimates using the proposed model is <5%, with a standard deviation of <3.18%. The proposed model provides an accurate analytical method for estimating and optimizing elliptical planar inductor parameters using a combination of current sheet expression and area transformation techniques. An elliptical planar inductor integrated with a sensing element can be used as a wireless implant to monitor the physiological signal from narrow implantation sites.

In-Vitro Demonstration of Ultra-Reliable, Wireless and Batteryless Implanted Intracranial Sensors Operated on Loci of Exceptional Points

Vital signal monitoring, such as pulse, respiration rate, intra-organ and intra-vascular pressure, can provide important information for determination of clinic diagnosis, treatments, and surgical protocols. Nowadays, micromachined bioimplants, equipped with antennas for converting bio-signals to modulated radio transmissions, may allow remote continuous monitoring of patients' vital signs. Yet, current passive biotelemetry techniques usually suffer from poor signal reproducibility and robustness in light of inevitable misalignment between transmitting and receiving antennas. Here, we seek to address this long-existing challenge and to robustly acquire information from a passive wireless intracranial pressure (or brain pressure) sensor by introducing a novel, high-performance biotelemetry system. In spite of variable inductive links, this biotelemetry system may have absolute accuracy by leveraging the uniqueness of loci of exceptional points (EPs) in non-Hermitian radio-frequency (RF) electronic systems with parity-time (PT) symmetry. Our in-vitro experimental demonstration shows that the proposed intracranial (ICP) monitoring system can provide a sub-mmHg resolution in the ICP range of 0-20 mmHg and ultra-robust wireless data acquisition against the misalignment-induced weakening of inductive link. Our results could provide a practical pathway toward reliable, real-time wireless monitoring of ICP, and other vital signals generated by bio-implants and wearables.

Wireless Microfluidic Sensor for Metal Ion Detection in Water

In the present work, a wireless microfluidic sensor based on low-temperature cofired ceramic (LTCC) technology for real-time detection of metal ions in water is proposed. The wireless sensor is composed of a planar spiral inductor and parallel plate capacitor (LC) resonant antenna, which integrates with the microchannel in the LTCC substrate between the capacitor plates. Aqueous solutions of Pb(NO₃)₂, Cd(NO₃)₂, Mg(NO₃)₂, Ca(NO₃)₂, NaNO₃, and KNO₃ with concentrations of 0-100 mM were tested with the sensors. The metal ion and its concentration in water can be tested by the amplitude of the reflection coefficient (S ₁₁) and the resonance frequency (f _r) of the wireless microfluidic sensor. The metal ion species can be distinguished from the wireless response behavior of the sensor. The detection limit of the sensor for the selected metal ionic solutions could reach as low as 5 μM. The normalized sensitivity of the sensor is 0.47%, which is higher than that of the reported liquid microfluidic sensors based on microwave resonators. The wireless microfluidic sensor of this study is promising for rapid and convenient detection of heavy metal ion pollutants in the industrial wastewater.

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.

Microfluidic Modules Integrated with Microwave Components-Overview of Applications from the Perspective of Different Manufacturing Technologies

The constant increase in the number of microfluidic-microwave devices can be explained by various advantages, such as relatively easy integration of various microwave circuits in the device, which contains microfluidic components. To achieve the aforementioned solutions, four trends of manufacturing appear—manufacturing based on epoxy-glass laminates, polymer materials (mostly common in use are polydimethylsiloxane (PDMS) and polymethyl 2-methylpropenoate (PMMA)), glass/silicon substrates, and Low-Temperature Cofired Ceramics (LTCCs). Additionally, the domains of applications the microwave-microfluidic devices can be divided into three main fields—dielectric heating, microwave-based detection in microfluidic devices, and the reactors for microwave-enhanced chemistry. Such an approach allows heating or delivering the microwave power to the liquid in the microchannels, as well as the detection of its dielectric parameters. This article consists of a literature review of exemplary solutions that are based on the above-mentioned technologies with the possibilities, comparison, and exemplary applications based on each aforementioned technology.

A Flow-Through Microfluidic Relative Permittivity Sensor

In this paper, we present the design, simulation, fabrication and characterization of a microfluidic relative permittivity sensor in which the fluid flows through an interdigitated electrode structure. Sensor fabrication is based on an silicon on insulator (SOI) wafer where the fluidic inlet and outlet are etched through the handle layer and the interdigitated electrodes are made in the device layer. An impedance analyzer was used to measure the impedance between the interdigitated electrodes for various non-conducting fluids with a relative permittivity ranging from 1 to 41. The sensor shows good linearity over this range of relative permittivity and can be integrated with other microfluidic sensors in a multiparameter chip.

LTCC Flow Sensor with RFID Interface

The idea of battery-less flow sensors and their implementation in wireless measurement systems is presented in this research article. The authors take advantage of their latest achievements in the Low Temperature Co-fired Ceramic (LTCC) technology, RadioFrequency Identification (RFID) technique, and increasing availability of low power electronics in order to get rid of the need to use electrochemical cells in a power supply unit of the elaborated device. To reach this assumption, special care has to be put on the energy balance in such an autonomous sensor node. First of all, the new concept of an electromagnetic LTCC turbine transducer with a signal conditioner which only draws a current of around 15 µA, is proposed for measuring a flow rate of fluids. Next, the autonomy of the device is showed; measured data are gathered in a microcontroller memory and sent to a control unit via an RFID interface which enables both information exchange and power transfer. The energy harvested from the electromagnetic field is used to conduct a data transmission, but also its excess can be accumulated, so the proposed sensor operates as a semi-passive transponder. The total autonomy of the device is achieved by implementing a second harvester that continually gathers energy from the environmental electromagnetic field of common active radio systems (e.g., Global System for Mobile Communications (GSM), wireless network Wi-Fi).

A Flexible Wireless Dielectric Sensor for Noninvasive Fluid Monitoring

A flexible wireless dielectric sensor is presented here for noninvasively monitoring the permittivity and conductivity of fluids, based on resistor–inductor–capacitor (RLC) resonant circuit and capacitively coupled contactless conductivity detection (C⁴D) technique. The RLC sensor consists of one single-turn inductor and one interdigital capacitor. The resonant frequency of the device is sensitive to the surrounding environment, thanks to the electric field leaked out between the interdigital capacitor electrodes. Through the high-frequency structure simulator (HFSS) simulation, and experiments on ethanol/water solutions and NaCl solutions, it was confirmed that a fluid’s permittivity and conductivity could be detected by the return loss curve (S₁₁). With great repeatability and stability, the proposed sensor has potential for broad applications, especially in wearable low-cost smart devices.

Microfluidics-Based Four Fundamental Electronic Circuit Elements Resistor, Inductor, Capacitor and Memristor

The microfluidics domain has been progressing rapidly recently, particularly considering its useful applications in the field of biomedicine. This paper presents a novel, microfluidics-based design for four fundamental circuit elements in electronics, namely resistor, inductor, capacitor, and memristor. These widely used passive components were fabricated using a precise and cost-effective xurography technique, which enables the construction of multi-layered structures on foil, with gold used as a conductive material. To complete their assembly, an appropriate fluid was injected into the microfluidic channel of each component: the resistor, inductor, capacitor, and memristor were charged with transformer oil, ferrofluid, NaCl solution, and TiO2 solution, respectively. The electrical performance of these components was determined using an Impedance Analyzer and Keithley 2410 High-Voltage Source Meter instrument and the observed characteristics are promising for a wide range of applications in the field of microfluidic electronics.

Bismuth trioxide-tailored sintering temperature, microstructure and NTCR characteristics of Mn1.1Co1.5Fe0.4O4 ceramics

Mn1.1Co1.5Fe0.4O4 ceramics with tailored sintering temperature, microstructure, and NTCR characteristics were prepared using Bi2O3 sintering additive by a solid-state reaction route. Densification and morphological characterization indicate that bismuth trioxide can play a critical role in the sintering process. The results reveal that the sintering temperature can be decreased significantly from 1200 °C to 1050 °C by using the appropriate content of Bi2O3 additive. The resistivity decreases first and then increases with increasing Bi2O3 content. The obtained B 25/50 value and ρ 25 ranges were 3647-3697 K, and 800-1075 Ω cm, respectively. Oxygen sorption theory can be used to illustrate the optimal thermal stability (ΔR/R 0 = 0.10%). Complex impedance analysis further elucidates that grain boundaries make a dominant contribution to the total resistance. The mechanisms of grain boundary conduction and relaxation behavior are systematically analyzed. These findings open up a window for the further advancement of NTC ceramics at lower sintering temperature.

Differential Microfluidic Sensors Based on Dumbbell-Shaped Defect Ground Structures in Microstrip Technology: Analysis, Optimization, and Applications

A microstrip defect ground structure (DGS) based on a pair of dumbbell-shaped slots is used for sensing. The device is a differential sensor consisting of a pair of mirrored lines loaded with a dumbbell-shaped DGS, and the output variable is the cross-mode transmission coefficient. Such a variable is very sensitive to asymmetries in the line pair, e.g., caused by an asymmetric dielectric load in the dumbbell-shaped DGSs. Therefore, the sensor is of special interest for the dielectric characterization of solids and liquids, or for the measurement of variables related to complex permittivity changes. It is shown in this work that by adding fluidic channels on top of the dumbbell-shaped DGSs, the device is useful for liquid characterization, particularly for the measurement of solute concentration in very diluted solutions. A sensitivity analysis useful for sensor design is carried out in this paper.