Feature Review Papers in Physical Sensors

Dear Colleagues,

This Special Issue aims to publish high-quality review papers in the field of physical sensors. Contributions may focus on all types of physical sensors, based on the magnetic, semiconducting, dielectric, conducting and superconducting properties of various materials, and thus may refer to magnetic, electric, optic, acoustic and other types of physical sensors, used in the industry, biomedicine, defense, transportation, etc.

Manuscripts should include the current state of the art and perspectives in the field, illustating the advances offered by the authors. All types of reviews will be considered as long as they meet the journal’s standards. We encourage researchers from various fields to contribute reviews highlighting the latest developments in their field or to invite relevant experts and colleagues to do so.

Prof. Dr. Evangelos Hristoforou
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• sensors based on magnetic properties
• sensors based on semiconducting properties
• sensors based on dielectric properties
• sensors based on conducting properties
• sensors based on superconducting properties
• magnetic sensors
• optic sensors
• acoustic sensors
• electric sensors
• industrial applications
• defense applications
• transportation applications
• biomedical applications
• multidisciplinary

Title: Magnetostrictive Delay Lines: Arrangements, Properties, Materials & Sensing Applications
Authors: Eleni Mangiorou, Spyros Angelopoulos, Aphrodite Ktena, Evangelos Hristoforou
Affiliation: Laboratory of Electronic Sensors, National TU of Athens, Zografou Campus, Athens, Greece 15780
Abstract: The paper illustrates a review on magnetostrictive delay lines (MDL), reffering to materials, topological arrangements, materials used and of course different families of sensors. At first, almost all topological arrangements based on MDLs are illustrated, followed by the most important engineering properties that should be examined for sensing applications. Then, the possible materials and their methodological characterization is illustrated. Then, the position-displacement-tactile, stress-force-pressure and field sensors based on MDLs are presented, with some distinct applications. Finally, an analytical model of the MDL operation is also provided.

Title: Implantable passive sensors for biomedical applications
Authors: Emmanouel Hourdakis1 and Panagiotis Kassanos2
Affiliation: 1 School of Electrical and Computer Engineering (ECE), National Technical University of Athens (NTUA), Greece 2 The Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK, SW7 2AZ*
Abstract: In recent years, implantable sensors are being extensively researched since they allow localized sensing at an area of interest (e.g. within the vicinity of a surgical site or other implant) unintrusive and potentially continuous sensing, enabling greater specificity, early warning capabilities, and thus timely clinical intervention. Wireless communication schemes such as RF, inductive coupling or ultrasounds are being used to allow the wireless remote interrogation of the implanted sensor and, if needed, bidirectional communication between the implanted device and an external device. Two categories of implantable sensors are available, namely active and passive. Active sensors offer greater capabilities, such as on-node signal and data processing, multiplexing and multimodal sensing, when several sensors and sensors operating with different modalities are used in implanted sensor arrays, while also allowing lower detection limits and the possibility to encode patient sensitive information. However, they require an energy source to operate. Battery implantation, and maintenance, remains a very important constraint in many implantable applications even though energy can be provided wirelessly through the external device, in some cases. On the other hand, passive sensors offer the possibility for detection without the need for a local energy source or active electronics. They also offer significant advantages in the areas of sensor node and system complexity, cost and size. These offset their inherent lower detection limit capabilities, in many applications. In this review, implantable passive sensor technologies will be discussed along with their communication schemes. Materials, detection strategies and applications of passive sensors will be described. Advantages over active sensor technologies will be highlighted, as well as critical aspects related to packaging (hermeticity) and biocompatibility.

Title: Mobile device with IoT capabilities for the detection of R32 and R134a refrigerants using IR sensors
Authors: Nikolaos Argirusis; Achilleas Achilleos; John Konstantaras; Zafeiria Dimou; Pavlos Pandis; Petros Karvelis; Christos Argirusis; Georgia Sourkouni
Affiliation: mat4nrg GmbH, 38678 Clausthal-Zellerfeld, Germany
Abstract: Fluorinated greenhouse gases (FGGs) are classified as worldwide pollutants and have a high global warming potential compared to other greenhouse gases. Detecting the existence and concentration of new and older refrigerant gases is crucial for assessing system functionality and determining whether they can be recycled or need to be disposed of. Additional justifications for the necessity of quantitative measurements of these gases include the manufacturing of air conditioning components, leak detection is conducted to ensure they are free of leaks. Fast Fourier transform spectroscopy enables the detection and measurement of substances while being delicate, unwieldy, costly, and typically requiring a skilled technician to operate them in the field. Thus, a portable, user-friendly, and cost-effective detection device would be beneficial. This article provides an in-depth analysis of the categorization of refrigerant gases in Internet of Things (IoT) gas detection devices. We demonstrate the functionality in effectively differentiating between important refrigerant gases like R32 and R134a, with low delay, through practical tests. This study utilizes data collected from the refrigerants R32 and R134a. Hence, comprehensive IR spectra of the specific refrigerants are required. The IR spectra were collected using a custom-made 3D-printed tubular reactor equipped with two BaF2 windows, suitable for use in the beamline of a Bruker IR-Spectrometer. Calibration was performed by exposing the IR-sensor to controlled gas environments with varying amounts of refrigerant gases using accurately produced gas mixtures. Following the measurement, data was immediately sent to an Internet of Things (IoT) platform and shared with business-to-business (B2B) clients.

Title: Open magnetic circuit measurement methods for the non-destructive evaluation of steel strip mechanical properties
Authors: Anastassios Skarlatos
Affiliation: Commissariat à l’Énergie Atomique et aux Énergies Alternatives (CEA), Laboratory for Integration of Systems and Technology (LIST), Université Paris-Saclay, F-91120 Palaiseau, France
Abstract: Magnetic characterisation measurements usually involve a closed magnetic circuit with a ribbon-type specimen. This experimental arrangement assures the maximisation of the magnetic flux that crosses the material and its collimation in a single direction. Two characteristic examples of such setups are the Epstein frame and the single or double yoke circuit also known as single sheet tester. These setups however require a special preparation of the specimen in the sense that a ribbon sample must be detached from the piece under study, which makes them quasi-destructive and hence impractical for in-situ characterisation. This is the reason why a number of different devices has been developed for the nondestructive characterisation of ferromagnetic materials. These methods find the application in the industry for the control of finished or semi-finished products in form of planar sheets. Common feature of these methods is that they involve open-circuit measurements, in the sense that the applied magnetic flux is closed in the air in form of stray field. A second feature of these methods, closely related with the first, is that they provide only indirect information hysteresis curve via a number of well-chosen identifiers due to the incapability of the setup to provide a complete hysteresis curve measurements. In this review article, an overview of the different available methods will be presented and a detailed discussion of the involved identifiers and their pertinence for characterisation of specific magnetic and mechanical features will be provided. Some well-known industrial realisations of these setups such as the IMPOC, HACOM, PropertyMon and the 3MA will be also given. The article will conclude with a brief discussion of model-based inversion methods for recovering the full hysteresis curve from such partial information, a subject of ongoing research.

Title: Wearable, Non-invasive Electrical Stimulator: A Review of Design and Medical Applications
Authors: Wei Ju, Aidan McConnell-Trevillion, David Vaca-Benavides, Kianoush Nazarpour, and Srinjoy Mitra
Affiliation: School of Engineering, Institute of Integrated Micro and Nano Systems, The University of Edinburgh, Edinburgh EH9 3FF, UK
Abstract: This review paper discusses the current advancements in wearable non-invasive electrical stimulators, emphasizing the burgeoning field of medical electronics driven by on-demand and advanced technologies. Previous literature has predominantly explored the design and technological features of these devices. This review shifts the focus towards the medical applications of existing systems and the critical components, particularly the drive circuit. Additionally, it addresses essential considerations for safety and protective features in the design of medical devices, aiming to provide a comprehensive understanding of the integration of advanced circuitry in therapeutic applications.

Title: Implantable passive sensors for biomedical applications
Authors: Emmanouel Hourdakis
Affiliation: School of Electrical and Computer Engineering, National Technical University of Athens, Athens, Greece
Abstract: In recent years, implantable sensors are being extensively researched since they allow localized sensing at an area of interest (e.g. within the vicinity of a surgical site or other implant). They allow unintrusive and potentially continuous sensing, enabling greater specificity, early warning capabilities, and thus timely clinical intervention. Wireless remote interrogation of the implanted sensor is typically achieved using RF, inductive coupling or ultrasounds through an external device. Two categories of implantable sensors are available, namely active and passive. Active sensors offer greater capabilities, such as on-node signal and data processing, multiplexing and multimodal sensing, when several sensors and sensors operating with different modalities are used in implanted sensor arrays, while also allowing lower detection limits and the possibility to encode patient sensitive information, as well as bidirectional communication. However, they require an energy source to operate. Battery implantation, and maintenance, remains a very important constraint in many implantable applications even though energy can be provided wirelessly through the external device, in some cases. On the other hand, passive sensors offer the possibility of detection without the need for a local energy source or active electronics. They also offer significant advantages in the areas of sensor node and system complexity, cost and size. In this review, implantable passive sensor technologies will be discussed along with their communication and readout schemes. Materials, detection strategies and clinical applications of passive sensors will be described. Advantages over active sensor technologies will be highlighted, as well as critical aspects related to packaging and biocompatibility.

Title: FPGA-based Lock-in Amplifier System with Signal Enhancement: A Comprehensive Review on the Design for Advanced Measurement Applications
Authors: Jose Alejandro Galaviz-Aguilar; Cesar Vargas-Rosales; Francisco Falcone; Carlos Aguilar-Avelar
Affiliation: Facultad de Ingeniería Mexicali, Universidad Autónoma de Baja California, Blvd. Benito Juárez S/N, Mexicali, C.P. 21280, Baja California, Mexico
Abstract: Lock-in amplifiers (LIAs) are widely used in precision measuring instruments, especially where there exists a weak signal that leads to difficult extraction due to noise. The advantages of signal processing algorithms and hardware synthesizing have provided techniques for accurate signal extraction from extremely noisy environments, highly used in sensor applications for health care, industry, and services. For instance, electrical impedance measurement of the human body, organs, tissues, and cells, known as bioelectrical impedance, is commonly used in biomedical and healthcare applications, because it is non-invasive and relatively inexpensive. Also, due to its portability and miniaturization capabilities, it has great potential for the development of new point-of-care and portable testing devices. In this document, we highlight existing techniques for high-frequency resolution and precise phase-detection in LIAs reference signals from field-programmable gate array (FPGA) designs. A comprehensive review is presented under key requirements and techniques for single and dual-phase digital LIA architectures, where relevant insights are provided to address the LIAs digital-precision in measurement system configurations. Finally, a summary on the applications of impedance measurement is provided, highlighting the wide range of fields that can benefit from the design of high-performance measurement systems. In addition, we address signal enhancement capabilities by proposing a novel technique for improving the spurious-free dynamic range (SFDR), further advancing the precision and effectiveness of these systems in complex measurement environments.