Inductively Coupled Passive Resonance Sensors: Readout Methods and Applications

Measurement systems are used to acquire information from the surrounding world. The requirements of the measurement system depend on the application, and the acquired information is used in different ways. For example, measurements are taken as part of the control systems of industrial processes. Alternatively, the information obtained from the measurements can be used to provide answers to scientific questions. Each measurement has a case-specific importance for the user and a certain cost in terms of time and money. Therefore, the same measurement approach is not optimal in every case. The design process of the measurement systems always includes a compromise between performance, viability, and cost. These factors are, in turn, strongly dependent on the implementation of the measurement system in each separate case. Inductively coupled passive resonance sensors provide a measurement method that has two notable benefits: the simple structure of the sensors and the possibility to take short-range wireless measurements. However, the limitations of the available readout devices have often impeded the use and development of these sensors in many demanding applications. In addition, uncertainty in the measurement results due to inductive coupling hinders the use of this method.This work concerns the development and implementation of a measurement system based on inductively coupled passive resonance sensors. A custom-made readout device to improve the feasibility of the readout in applications where continuous field measurements are performed was both specified and produced. The readout device was implemented using a simplified version of the method used in conventional impedance analyzers. In addition, signal processing methods were developed which can extract resonance characteristics from the measured data. A special algorithm was developed to compensate for the effects of the changes in the inductive coupling when the measurement distance varies. The operation of the developed readout methods was studied using simulations, and several realistic measurement configurations were tested. Competing readout methods published in the literature were also simulated. The accuracy of all the studied methods depended on the configuration of the measurement system. The inductive coupling coefficient also had a significant influence on the accuracy of the tested methods.The newly-developed readout methods and the inductively coupled passive resonance sensor were then utilized in a medical application to monitor the pressure between the skin and compression garments. These garments are used, for example, to improve the healing of burns and reduce swelling in the legs. Effective medical treatment of such conditions requires that the appropriate pressure is applied. With this system, the pressure reading under the compression garment can be obtained by using simple disposable sensors that can be read wirelessly through a thin fabric. Using our inductive coupling compensation method, the sensor enabled the monitoring of the pressure with the required level of precision.Inductively coupled resonance sensors can also be used to monitor the properties of the materials around the sensor. This monitoring is possible because the permittivity of the environment near to the sensor affects the sensor’s resonance characteristics. This method was tested in two applications. In the first application, the manufacturing process of ceramic slurry was monitored by a sensor that was installed inside the container where the slurry was mixed. The resonance characteristics of the sensor were measured as the manufacturing process was incrementally carried out. The results indicated that the method could be used to control the composition of the slurry. In the second application, the inductively coupled sensors were tested in monitoring the degradation processes of two different polymers during hydrolysis. In this application, the sensors were encapsulated into the tested polymers. The polymer samples were kept inside containers filled with buffer solution and the resonance characteristics of the encapsulated sensors were then measured wirelessly from outside. The results showed a clear difference in degradation profiles between the tested polymers. The method may provide a novel way to continuously monitor the degradation processes of certain materials.In summary, the developed readout methods improved the applicability of inductive coupled passive resonance sensors in the tested applications and created novel ways to acquire information. This new technology provides a good starting point for the development of a new generation of inductively coupled passive resonance sensors

Inductively Coupled Passive Resonance Sensors: Readout Methods and Applications

Measurement systems are used to acquire information from the surrounding world. The requirements of the measurement system depend on the application, and the acquired information is used in different ways. For example, measurements are taken as part of the control systems of industrial processes. Alternatively, the information obtained from the measurements can be used to provide answers to scientific questions. Each measurement has a case-specific importance for the user and a certain cost in terms of time and money. Therefore, the same measurement approach is not optimal in every case. The design process of the measurement systems always includes a compromise between performance, viability, and cost. These factors are, in turn, strongly dependent on the implementation of the measurement system in each separate case. Inductively coupled passive resonance sensors provide a measurement method that has two notable benefits: the simple structure of the sensors and the possibility to take short-range wireless measurements. However, the limitations of the available readout devices have often impeded the use and development of these sensors in many demanding applications. In addition, uncertainty in the measurement results due to inductive coupling hinders the use of this method.This work concerns the development and implementation of a measurement system based on inductively coupled passive resonance sensors. A custom-made readout device to improve the feasibility of the readout in applications where continuous field measurements are performed was both specified and produced. The readout device was implemented using a simplified version of the method used in conventional impedance analyzers. In addition, signal processing methods were developed which can extract resonance characteristics from the measured data. A special algorithm was developed to compensate for the effects of the changes in the inductive coupling when the measurement distance varies. The operation of the developed readout methods was studied using simulations, and several realistic measurement configurations were tested. Competing readout methods published in the literature were also simulated. The accuracy of all the studied methods depended on the configuration of the measurement system. The inductive coupling coefficient also had a significant influence on the accuracy of the tested methods.The newly-developed readout methods and the inductively coupled passive resonance sensor were then utilized in a medical application to monitor the pressure between the skin and compression garments. These garments are used, for example, to improve the healing of burns and reduce swelling in the legs. Effective medical treatment of such conditions requires that the appropriate pressure is applied. With this system, the pressure reading under the compression garment can be obtained by using simple disposable sensors that can be read wirelessly through a thin fabric. Using our inductive coupling compensation method, the sensor enabled the monitoring of the pressure with the required level of precision.Inductively coupled resonance sensors can also be used to monitor the properties of the materials around the sensor. This monitoring is possible because the permittivity of the environment near to the sensor affects the sensor’s resonance characteristics. This method was tested in two applications. In the first application, the manufacturing process of ceramic slurry was monitored by a sensor that was installed inside the container where the slurry was mixed. The resonance characteristics of the sensor were measured as the manufacturing process was incrementally carried out. The results indicated that the method could be used to control the composition of the slurry. In the second application, the inductively coupled sensors were tested in monitoring the degradation processes of two different polymers during hydrolysis. In this application, the sensors were encapsulated into the tested polymers. The polymer samples were kept inside containers filled with buffer solution and the resonance characteristics of the encapsulated sensors were then measured wirelessly from outside. The results showed a clear difference in degradation profiles between the tested polymers. The method may provide a novel way to continuously monitor the degradation processes of certain materials.In summary, the developed readout methods improved the applicability of inductive coupled passive resonance sensors in the tested applications and created novel ways to acquire information. This new technology provides a good starting point for the development of a new generation of inductively coupled passive resonance sensors

Testing and comparing of film-type sensor materials in measurement of plantar pressure distribution

Simple in-shoe sensors based on film-type sensor materials were developed in this study. Three sensor materials were tested: polyvinylidenefluoride (PVDF), cellulose nanofibrils (CNF) and ElectroMechanical Film (EMFi). Plantar pressure distributions of a subject were measured with the developed in-shoe sensors; each consisting of three sensor channels (lateral and medial metatarsal heads and heel). In addition, piezoelectric sensor sensitivities and crosstalk between the sensor channels were determined. Differences between the tested film-type materials and measured plantar pressure distribution signals were studied.acceptedVersionPeer reviewe

Wireless interrogation techniques for sensors utilizing inductively coupled resonance circuits

AbstractThe methods needed to interrogate passive resonance sensors are studied. A portable impedance measurement unit and the methods to extract a coupling coefficient compensated resonance frequency are presented. The interrogation methods are demonstrated with ECG and pressure measurements. The results show that the quality of the ECG signal measured with a flexible textile coil is sufficient to extract the heart rate. In the case of a pressure sensor, the errors caused by the changes in the inductive coupling were satisfactorily removed by the introduced method

An Inductively Coupled Biodegradable Capacitive Pressure Sensor

A biodegradable inductively coupled pressure sensor is presented. Three sensors were fabricated using melt processed biodegradable polymers and electron-beam evaporated magnesium. All the sensors showed similar pressure responses from 0 to 0.2 bar. In addition, the responses of the sensors to temperature changes and static pressure are reported. Due to the limited quality factor of the resonance sensors, single measurements were noisy. For this reason, averaging of multiple measurements was needed to achieve consistent results

Simulation of the Readout Methods for Inductively Coupled High-Frequency Resonance Sensors

The readout methods for inductively coupled resonance sensors were simulated using a lumped element model. The purpose of the study was to analyze the readout methods at high frequencies where the self-resonance of the reader coil is likely to interfere with the measurements. Furthermore, the changes in the reading distance cause measurement errors. This phenomenon was studied using simulation. In addition, an algorithm that compensates these errors was tested. The simulation results were in agreement with the test measurements. In addition, the tested error compensation improved the resonance frequency estimates calculated using the simulated and measured data.publishedVersionPeer reviewe

Biodegradable passive resonance sensor : Fabrication and initial testing

Biodegradable resonance circuits were studied. The circuits have a novel two-layer resonator structure without galvanic through hole vias. A patterned magnesium layers were evaporated on biodegradable PLA sheets by using a 3D printed mask. The circuits were assembled by heat sealing two magnesium patterned sheets together to encapsulate the circuit structure. An inductive link is used to wirelessly detect the resonance frequency of the circuit. The circuits were tested when immersed in de-ionised water and saline. According to the tests, the designed resonator structure can be measured in aqueous environment. The resonance of the tested circuit was observable at least for 51 hours. The concept still needs more development to extend degradation time and to increase the stability during immersion.publishedVersionPeer reviewe