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Telemetric Technique for Wireless Strain Measurement From an Inkjet-Printed Resistive Sensor

Strain monitoring allows obtaining critical information regarding the conditions of several systems. It would help, for example, to avoid possible structural damages. However, not all the existing devices are suitable to accomplish this task for a great number of applications, because of the characteristics of measurement environment, which prevent the use of batteries or wired connections. The use of telemetric devices may overcome these limitations, since they rely on the magnetic coupling between two inductors for wireless sensor supply and data transmission. The work treated in this paper presents a technique that permits us to calculate the output of a resistive strain gauge from a measurement of system impedance phase performed at a specific frequency, when distance between the inductors is fixed. We validated the method using a real device working with a low-cost sensor fabricated through inkjet-printing technology on a flexible substrate. We applied successive deformations, until 1% of sensor length at rest position. Calculated strain presents a percentage deviation from measured values going from 0.7% to 7%, whereas the highest uncertainty is 0.02% of sensor length at rest. Experimental results put in evidence, on one hand, the potential of inkjet printing to fabricate valid sensing elements and, on the other hand, that the proposed approach is successful in strain estimation.

Study on a telemetrie system that works with an inkjet-printed resistive strain gauge

Measuring strain is a task frequently required in many applications and, often, measurement devices have to adopt technologies that respect specific requirements, especially concerning power supply and transmission of information. In particular, the exploitation of wired solutions or batteries has several problems or it should be avoided in harsh environments. A valid answer to these issues is provided by telemetric systems, which consist of a reading unit that communicates with a passive sensor through the magnetic field established between two inductors connected to these components. The present work describes a study carried out on a telemetric system that has some elements of novelty with respect to the major part of those found in the literature. In fact, it operates with a resistive strain gauge realized through the innovative technology of inkjet printing on a flexible substrate. This permits to introduce advantages relating to design variability and low production cost of the components. Experimental tests were conducted in order to characterize the strain gauge and analyze overall system frequency behavior. Preliminary achieved results are satisfying, highlighting the possibility to measure telemetrically the strain from an inkjet-printed resistive sensor.

Novel telemetric technique for passive resistive sensors based on impedance phase angle measurement at constant frequency

Telemetric systems are a valid alternative to measurement devices exploiting batteries or cabled connections, which may be not suitable in some cases, such as in harsh or hermetic measurement environments. They permit either to supply a passive sensor or to carry out monitoring tasks without contact. In this paper, we propose a novel measurement technique for telemetric systems working with a resistive sensing element. Such technique is based on a reading of system impedance phase angle always at sensing inductors resonant frequency, while relative distance between system inductors is kept fixed. Analytical expressions have been derived to calculate sensor resistive output from phase angle value. They have been obtained from a proper circuit model of the telemetric device. The proposed method has been applied to the wireless measurement of temperature inside an oven. Experimental tests have been carried out, by putting a resistive sensor inside the oven and increasing its internal temperature from about 28 °C to about 134 °C. Preliminary results show that calculated temperature values present an average deviation from reference equal to 1.7 °C. Furthermore, uncertainty related to such values is 1.2 °C. Therefore, they prove the feasibility of implementing the proposed technique in all the applications that require the use of telemetric devices with passive resistive sensors.

Flexible monitoring system for automated detection of bacterial growth in a commercial specimen processing platform

Diagnosing the presence of bacteria in a biological sample is a task to accomplish as early as possible, since bacterial infections still represent a serious threat to human health. In the market, there are commercial systems carrying out pre-analytical tests on biological specimens. An example is provided by the WASPLab, by COPAN Italia S.p.A., which monitors bacterial growth on Petri dishes that contain the samples, by taking and processing images of one dish at a time in a completely automated way. In this paper, we propose a newly monitoring sensor system for all the Petri dishes at the same time for the detection of bacterial growth with the aim of integrating it directly in the WASPLab. It could permit to obtain quantitative information about bacterial activity in real time directly inside the incubator, offering a more rapid and complete diagnosis response and avoiding the movement of the samples. In addition, the user can set measurement parameters according to his/her needs. This allows the system reaching a great level of flexibility. We tested our solution in two ways. First, we analyzed the behavior of the proposed solution comparing the output signals with the data obtained using an impedance analyzer (HP4194A) as reference. We obtained an average deviation equal to 0.768 Ω in magnitude and 0.059 ° in phase angle. Second, we carried out a 24-hour test to monitor the activity of Staphylococcus Aureus AT C 6538 in a climate chamber. We found that our system succeeded in observing bacterial growth, with an early detection time of 4 hours. Research is undergoing to integrate the proposed system in the WASPLab.

Study on Impedance Behavior of a Telemetric System Operating with an Inkjet-Printed Resistive Strain Gauge

Devices that measure the strain applied to a body can find several applications in many fields, especially if they are able to satisfy precise specifications about power supply and transmission of information. Telemetric systems offer a viable solution, since they rely on the inductive coupling between the coils connected to a passive sensor and a readout unit. Therefore, they require neither batteries nor wired connections. The present work illustrates a preliminary analysis on a telemetric device made of Printed Circuit Board (PCB) planar inductors and a resistive strain gauge fabricated through inkjet printing on a flexible substrate. We carried out experimental tests to evaluate system frequency behaviour. Firstly, we measured its impedance phase at readout inductor terminals while varying sensor resistance, with the inductors put at a fixed relative distance. Then, we repeated the same operation when that distance changed, with strain gauge at rest position. Obtained results report a total variation of phase most sensitive point of about 0.12° for a strain equal to 1% of sensor length at rest, suggesting that measuring strain with such a structure is feasible. On the other hand, they highlight that distance variation has a strong influence on that result; thus, it has to be taken into account during measurement process.

Modular Acquiring System for Lower Limb Rehabilitation Machines

The present paper refers to a research work aiming at implementing a modular acquiring system to be exploited in machines designed for lower limb muscles active rehabilitation. Mechatronic devices, as explained in H.S. Lo and S.Q. Xie, Med. Eng. & Phys 34:261–268 2012 and X. Cheng et al., Proc. Eng 15:688–692, 2011, have given a relevant contribution to this field during last years, offering intensive treatments allowing individuals to restore as much as possible their motion capabilities, damaged by an injury, a disease or a lesion. But many machines do not have the possibility to obtain information about patient’s biomechanical parameters during an active rehabilitation exercise. Starting from this concept, sensors, whether introduced into such devices, make accurate measurements and provide real-time data, which could be useful performance indicators, helping the physician to evaluate subject’s condition and therapy efficiency. This work is articulated as follows: after having described the system, performed experimental analysis will be illustrated, and obtained results will be provided.