Differential inductive sensing system for truly contactless measuring of liquids’ electromagnetic properties in tubing

Certain applications require a contactless measurement to eliminate the risk of sensorinduced sample contamination. Examples can be found in chemical process control, biotechnology or medical technology. For instance, in critically ill patients requiring renal replacement therapy, continuous in‐line monitoring of blood conductivity as a measure for sodium should be considered. A differential inductive sensing system based on a differential transformer using a specific flow chamber has already proven suitable for this application. However, since the blood in renal replacement therapy is carried in plastic tubing, a direct measurement through the tubing offers a contactless method. Therefore, in this work we present a differential transformer for measuring directly through electrically non‐conductive tubing by winding the tube around the ferrite core of the transformer. Here, the dependence of the winding type and the number of turns of the tubing on the sensitivity has been analyzed by using a mathematical model, simulations and experimental validation. A maximum sensitivity of 364.9 mV/mol/L is measured for radial winding around the core. A longitudinal winding turns out to be less effective with 92.8 mV/mol/L. However, the findings prove the ability to use the differential transformer as a truly contactless sensing system. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Development of Non-Destructive Testing by Eddy Currents for Highly Demanding Engineering Applications

Defect detection with Non-Destructive Testing (NDT) is essential in accidents prevention, requiring R&TD to generate new scientific and procedural knowledge for new products with high safety requirements. A current challenge lies in the detection of surface and sub-surface micro defects with NDT by Eddy Currents (EC). The main objective of this work was the development of applied research, technological innovation and experimental validation of EC customized systems for three highly demanding inspection scenarios: micro defects in tubular geometries; brazed joints for the automotive industry; and high-speed moving composite materials. This objective implied starting from the scientific fundamentals of NDT by EC to design and simulate EC probes and the prototypes developed were tested in industrial environment, reaching a TRL ≈ 5. Another objective, of a more scientific and disruptive nature, was to test a new technique for the creation of EC in the materials to be inspect, named Magnetic Permeability Pattern Substrate (MPPS). This technique consists on the development of substrates/films with patterns of different magnetic permeabilities rather than the use of excitation bobbin coils or filaments of complex geometry. The experimental results demonstrated that the prototypes developed for the three industrial applications studied outperformed the state of the art, allowing the detection of target defects with a very good signal-to-noise ratio: in tubular geometries defects with depth of 0.5 mm and thickness of 0.2 mm in any scanning position; in the laser brazed weld beads pores with 0.13 mm diameter and internal artificial defects 1 mm from the weld surface; in composite materials defects under 1 mm at speeds up to 4 m/s and 3 mm lift-off. The numerical simulations assisted the probe design, allowing to describe and characterize electrical and magnetic phenomena. The new MPPS concept for the introduction of EC was validated numerically and experimentally

Eddy current angular position sensor for automotive

Programa doutoral em Líderes para Indústrias TecnológicasOs sensores angulares usados em aplicações automóveis, requerem uma boa resolução, fiabilidade, baixa manutenção, baixo custo de produção e capacidade de trabalhar sob condições adversas. Devido a estes requisitos, os sensores mais utilizados são os magnéticos, indutivos e magneto-indutivos. Outro fator crítico é a dimensão do sensor, quanto mais reduzido e compacto, maior é o número de aplicações em que pode ser aplicado. No caso dos sensores magneto-indutivos e indutivos, uma forma de reduzir o seu tamanho é através do uso de a bobines planares impressas em placas de circuito impresso (PCB). Estas, para além de mais compactas, conseguem também reduzir os custos de produção, otimizar a repetibilidade e assemblagem, e permitir que o seu desenho seja facilmente adaptado às suas aplicações. No desenvolvimento de sensores indutivos, obter a indutância das bobinas, que funcionam como elemento transdutor, é essencial e desafiador no caso de bobinas planas. Atualmente, há duas abordagens no estado da arte: fórmulas de aproximação (para geometrias regulares), e simulações de modelos de elementos finitos (FEM). As simulações são demoradas e recorrem a ferramentas de software dispendiosas e que exigem muitos recursos computacionais. Esta tese tem como objetivo desenvolver uma ferramenta de cálculo analítico para obter a indutância de bobinas planas genéricas, reduzindo o tempo de desenvolvimento. A ferramenta possibilita ainda o cálculo da interferência que um alvo planar condutivo tem na indutância da bobine, tornando assim possível obter a resposta de um sensor indutivo baseado em eddy currents durante a sua fase de desenvolvimento. Esta tese, além de detalhar o desenvolvimento da ferramenta mencionada, também descreve todos os processos de validação implementados, através de simulações FEM e testes experimentais. A metodologia proposta foi aplicada com sucesso no desenvolvimento de um sensor de posição angular automotivo baseado em eddy currrents. Foi possível comprovar que a precisão da ferramenta desenvolvida está de acordo com as metodologias usualmente utilizadas, com a vantagem de ser mais rápida e económica.Angular sensors used in automotive applications require good precision, reliability, low maintenance, low production costs and the ability to work in harsh conditions. Due to these requirements, magnetic, inductive and magneto-inductive sensors are preferred and are used in current generations of automotive angular position sensors. The size of the sensors is another relevant factor in the development of new solutions. The smaller and more compact, the larger the number of applications in which they can be applied. In the case of magneto-inductive and inductive sensors, one way to reduce their size is to use planar coils printed on printed circuit boards (PCBs). These, in addition to occupy a smaller volume when compared to solenoids, also reduce production costs and optimize repeatability and simplify assembly. When developing inductive sensors, knowing the required inductance value of its coils is essential and this task can be challenging in the case of planar coils. Currently, two approaches are used to calculate the inductances of planar coils. When the coils have regular geometry approximation formulas are used, configuring some parameters. When they have irregular geometry or a more accurate result is desired, simulations using finite element methods (FEM) are chosen. These simulations have the disadvantage of being time-consuming, requiring expensive software applications and a huge computing resources. In view of the budget and the reduction of development time, this thesis provides an analytical calculation tool for the inductance of generic multi-layer planar coils. In this way, it is possible to develop dedicated applications in reduced time. The tool also allows to calculate the interference that a planar conductive target, of arbitrary geometry, can have on the coil inductance. Thus, it is possible to obtain the response of an inductive sensor based on eddy currents during its development phase. This thesis, in addition to detailing the development of the aforementioned tool, also describes all the validation processes implemented using FEM simulations and experimental tests. The proposed methodology was successfully applied in the development of an automotive angular position sensor based on eddy currents. It was possible to prove that the precision of the developed analytical tool is in concordance with the methodologies usually used, with the advantage of being faster and open source.Fundação para a Ciência e a Tecnologia (FCT) - bolsa de doutoramento PD/BD/128142/201

How geometry affects sensitivity of a differential transformer for contactless characterization of liquids

The electrical and dielectric properties of liquids can be used for sensing. Specific appli-cations, e.g., the continuous in-line monitoring of blood conductivity as a measure of the sodium concentration during dialysis treatment, require contactless measuring methods to avoid any contam-ination of the medium. The differential transformer is one promising approach for such applications, since its principle is based on a contactless, magnetically induced conductivity measurement. The objective of this work is to investigate the impact of the geometric parameters of the sample or medium under test on the sensitivity and the noise of the differential transformer to derive design rules for an optimized setup. By fundamental investigations, an equation for the field penetration depth of a differential transformer is derived. Furthermore, it is found that increasing height and radius of the medium is accompanied by an enhancement in sensitivity and precision. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Contactless Energy Transfer Techniques for Industrial Applications. Power and Data Transfer to Moving Parts

Contactless energy transfer (CET) systems are gaining increasing interest in the automatic machinery industries. For this reason, circuit equivalent networks of CET systems considered in the literature are introduced with emphasis on their industrial applicability. The main operating principles and the required compensating networks, along with different topologies of power supplies optimised for wireless powering, are discussed. The analysis of the wireless transfer, at the maximum efficiency, of high power levels shows that, in the kHz range, highly coupled inductive links are needed and soft-switching power sources required. The employment of CET units in controlled systems requires combining a link for data communication with the wireless power channel. At low frequencies, capacitive and inductive couplings are integrated in a unique platform to implement the wireless data and power links, respectively. Differently, at UHF, an increased data channel transfer efficiency is made possible by exploiting auto-resonant structures, such as split-ring resonators instead of capacitances, one at each far-end side of the link. The design procedure of a power CET system, including the dc/ac converter, a rotary transformer and its windings, is discussed and the results presented. A different version of a WPT system, which involves multiple transmitting coils and a sliding receiver, is also presented. A low frequency RFID capacitive data link is then combined with the rotary CET unit to provide the temperature feedback of a controlled system, wherein the rectifying part of a passive tag is exploited to simultaneously power and read a temperature probe. Subsequently, a split-ring based near-field UHF data link is designed to ensure an improved temperature detection in terms of accuracy and resolution. The sensor readout is performed at the transmitter side by measuring the reflected power by the load rectifier

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