Low-cost Transducer Research Articles

An innovative geotechnical and structural monitoring system based on the use of NSHT

The development of innovative early warning systems (EWS), structural health monitoring (SHM) and structural health monitoring and reinforcement (SHMR) systems is essential to prevent the occurrence of potentially dangerous events on engineering works, buildings and in the natural environment. Their effectiveness can be improved by using new generation sensors able to realize widespread, low-cost monitoring at increasing spatial and temporal resolution. The main aim of the research is, therefore, to develop a versatile strain transducer capable of monitoring elements of different nature such as slopes, buildings and linear infrastructures performing distributed real-time measurements. The paper introduces a new smart hybrid transducer (NSHT), a strain transducer belonging to the distributed optical fiber sensors family, appositely designed to overcome the drawbacks of traditional solutions. An experimental laboratory setup was arranged to test its reliability and a comparison between measurements retrieved by the NSHT and traditional devices were done. The results showed that the NSHT is able to perform strain monitoring with spatial resolution as high as 5 cm and accuracy comparable to that of the traditional devices. Finally, an integrated structural and geotechnical monitoring system architecture based on its use is proposed for the Petacciato site, where a deep-seated landslide affects the historical town and some infrastructures. To realize a single communication line in such a complex monitoring system, where multiple elements have to be monitored, a specific tool was also designed and tested, that allows the exact spatial identification of the various elements under observation. Although on-site validation is needed, these early results are encouraging and demonstrate that the NSHT is a low-cost transducer with great potential and that, looking forward, it can be used to increase the effectiveness of the existing EW, SHM and SHMR Systems. The development of systems involving NSHT also follows the new approach to innovation policy contributing to different points of the 2030 Agenda

Application of Low-Cost Transducers for Indirect In-Cylinder Pressure Measurements

Application of Low-Cost Transducers for Indirect In-Cylinder Pressure Measurements

Real-Time 3-D Imaging Using an Air-Coupled Ultrasonic Phased-Array.

We present an air-coupled ultrasonic imaging system based on a 40-kHz 8×8 phased-array for 3-D real-time localization of multiple objects in the far-field. By attaching a waveguide to the array, the effective interelement spacing is reduced to half wavelength. This enables grating lobe-free transmit and receive beamforming with a uniform rectangular array of efficient low-cost transducers. The system further includes custom transceiver electronics, an field programmable gate array (FPGA) system-on-chip and a PC for GPU accelerated frequency domain signal processing, consisting of matched filtering, conventional beamforming, and envelope extraction using Nvidia Compute Unified Device Architecture (CUDA) and OpenGL for visualization. The uniform rectangular layout allows utilizing multiple transmit and receive methods, known from medical imaging applications. Thus, the system is dynamically adaptable to maximize the frame rate or detection range. One implemented method demonstrates the real-time capability by transmitting a hemispherical pulse (HP) with a single transducer to irradiate the surroundings simultaneously, whereas all transducers are used for echo reception. The imaging properties, such as axial and lateral resolution, field of view and range of view, are characterized in an anechoic chamber. The object localization is validated for a horizontal and vertical field of view of ±80° and a range of view of 0.5-3 m with 29 frames/s. Using the same system, a comparison between the HP method and the dynamic transmit beamforming method, which transmits multiple sequential beamformed pulses for long-range localization, is provided.

Venting in the Comparative Study of Flexural Ultrasonic Transducers to Improve Resilience at Elevated Environmental Pressure Levels

The classical form of a flexural ultrasonic transducer is a piezoelectric ceramic disc bonded to a circular metallic membrane. This ceramic induces vibration modes of the membrane for the generation and detection of ultrasound. The transducer has been popular for proximity sensing and metrology, particularly for industrial applications at ambient pressures around 1 bar. The classical flexural ultrasonic transducer is not designed for operation at elevated pressures, such as those associated with natural gas transportation or petrochemical processes. It is reliant on a rear seal which forms an internal air cavity, making the transducer susceptible to deformation through pressure imbalance. The application potential of the classical transducer is therefore severely limited. In this study, a venting strategy which balances the pressure between the internal transducer structure and the external environment is studied through experimental methods including electrical impedance analysis and pitch-catch ultrasound measurement. The vented transducer is compared with a commercial equivalent in air towards 90 bar. Venting is shown to be viable for a new generation of low cost and robust industrial ultrasonic transducers, suitable for operation at high environmental pressure levels.

Liquid Level Sensing Using Commodity WiFi in a Smart Home Environment

The popularity of Internet-of-Things (IoT) has provided us with unprecedented opportunities to enable a variety of emerging services in a smart home environment. Among those services, sensing the liquid level in a container is critical to building many smart home and mobile healthcare applications that improve the quality of life. This paper presents LiquidSense, a liquid level sensing system that is low-cost, high accuracy, widely applicable to different daily liquids and containers, and can be easily integrated with existing smart home networks. LiquidSense uses existing home WiFi network and a low-cost transducer that attached to the container to sense the resonance of the container for liquid level detection. In particular, our system mounts a low-cost transducer on the surface of the container and emits a well-designed chirp signal to make the container resonant, which introduces subtle changes to the home WiFi signals. By analyzing the subtle phase changes of the WiFi signals, LiquidSense extracts the resonance frequency as a feature for liquid level detection. Our system constructs prediction models for both continuous and discrete predictions using curve fitting and SVM respectively. We evaluate LiquidSense in home environments with containers of three different materials and six types of liquids. Results show that LiquidSense achieves an overall accuracy of 97% for continuous prediction and an overall F-score of 0.968 for discrete predication. Results also show that our system has a large coverage in a home environment and works well under non-line-of-sight (NLOS) scenarios.

A Magnetic Transducer for the Detection of the Fetal Engagement Level in Part-Task Trainers

Assessing the level of descent of the fetal head in the birth canal during a pelvic examination is a critical skill required by gynecologists and midwifes to avoid injuries for the mother and the newborn. A way to train this ability in a riskless environment is through medical simulation; however, the majority of tools do neither provide visual feedback of the location of the fetus inside the birth canal, nor give the possibility to quantitatively assess this skill. This work aimed at creating a low-cost transducer based on magnetic fields that discriminates between nine levels of descent of the fetal head, namely engagement levels, usable with part-tasks pelvic trainers. Starting with neodymium magnets, we designed a magnetic transducer so that each level was identified by a unique combination of magnetic fields. Three Hall effect sensors detect polarity and intensity of the field generated by 27 permanent magnets, organized in a $9\times 3$ matrix, and each level, corresponding to one row of the matrix, is uniquely encoded by the sensors. The system was theoretically analyzed in simulation, then tested using a customized prototype and finally integrated into an existing birth simulator. The transducer is wireless and avoids any obstruction in the birth canal, as it does not require any power supply to generate magnetic fields and the sensors are connected to the hardware in the fetal manikin. Also, its dimension and ease to install make it usable with many pelvic models, which can be turned into sensorized simulators providing visual feedback and quantitative evaluations.

A portable medical diagnostic device utilizing free-standing responsive polymer film-based biosensors and low-cost transducer for point-of-care applications

The development of medical diagnostic devices for point-of-care applications (PoC) is a key demand towards the establishment of decentralized health-care systems. The cost of miniaturized transducers, the need for elaborated modification of the sensing surface and the complexity of the assay workflow impede the widespread use of current biosensing technologies to PoC applications. Herein, we describe a portable medical diagnostic device (we call it “BioPoC”), which employs free-standing enzyme-modified responsive polymer membrane-based biosensors and a newly devised low-cost transduction principle. The device includes a single vertical channel with an integrated sample dosing well. Its operation is based on the measurement of the time required the originally infinite electric resistance between two, separated by the enzyme-modified responsive polymer membrane, conductive strips to reach a finite value (typically <20 MOhm) as a result of the target-triggered degradation of the polymer membrane and the ensuing vertical flow of the sample, which thus establishes an electrical communication between the conductive strips. The time (R∞→R20MOhm) is proportional to the concentration of the target. By proper combination of different responsive polymers and enzyme(s), BioPoC device can enable the drop-volume, one-step biosensing of a variety of biomarkers. Data demonstrate an outstanding selectivity against the components of the matrix, while the detection range can be tuned over the normal range of the analyte of interest. As part of the proof-of-concept, BioPoC device was employed for the determination of urea in undiluted human urine and the near-patient detection of Helicobacter pylori in gastric antrum bioptic samples.

An Industrial Digitalization Platform for Condition Monitoring and Predictive Maintenance of Pumping Equipment.

This paper is concerned with the implementation and field-testing of an edge device for real-time condition monitoring and fault detection for large-scale rotating equipment in the UK water industry. The edge device implements a local digital twin, processing information from low-cost transducers mounted on the equipment in real-time. Condition monitoring is achieved with sliding-mode observers employed as soft sensors to estimate critical internal pump parameters to help detect equipment wear before damage occurs. The paper describes the implementation of the edge system on a prototype microcontroller-based embedded platform, which supports the Modbus protocol; IP/GSM communication gateways provide remote connectivity to the network core, allowing further detailed analytics for predictive maintenance to take place. The paper first describes validation testing of the edge device using Hardware-In-The-Loop techniques, followed by trials on large-scale pumping equipment in the field. The paper concludes that the proposed system potentially delivers a flexible and low-cost industrial digitalization platform for condition monitoring and predictive maintenance applications in the water industry.

Practical Adaptation of a Low-Cost Voltage Transducer with an Open Feedback Loop for Precise Measurement of Distorted Voltages.

This paper presents the project proposal of a low-cost transducer with a Hall-effect sensor placed in a ferromagnetic core’s air gap, which enables the measurement of the distorted voltage instantaneous values without the feedback loop used for measurements in electrical machines. The presented transducer allows for electrical separation between the measured voltage and the voltage at the output. Moreover, the influences of frequency, additional resistance, and the reactance of the winding circuit on the voltage phase shift caused by winding inductance with ferrite core and amplitude are discussed. The result of simulating leakage inductance of measuring winding with ferrite core with an air gap is calculated using finite element analysis. Experimental investigations of the voltage phase shift angle and output voltage amplitude drop for the voltage transducers with an open feedback loop are carried out, taking into account the linear core magnetization characteristic.

Design and development of a novel level transmitter utilizing lithium niobate (LiNbO3) Mach-Zehnder modulator for hazardous regions

In the proposed work, a very low-cost transducer and a novel photonic based transmission technique have developed for liquid level measurement. Two copper parallel plates are used to measure the liquid level in the sensing tube. For transmission of the measured quantity to the remote location, electrical (1–5 V DC), as well as optical technique, has been used. A lithium niobate (LiNbO3) based Mach Zehnder interferometer has been used for the optical transmission. In the proposed method 40GHz, Photline made MXAN-LN-40 light intensity Mach-Zehnder modulator was used. The optical output was analyzed with the help of optical spectrum analyzer (MS9710B) as well as optical meter. Optical transmission was not affected by EMI interference and very advantageous in the inflammable regions. With the help of the proposed method, the sensitivity of 7.02 pF/cm. from the sensor and −0.236 dBm/cm. from the modulator were achieved. The output of the sensor, signal conditioning, and optically transmitted data has been analyzed experimentally.

Ultrasound Transducers for Biomedical Imaging and Therapy

Ultrasound Transducers for Biomedical Imaging and Therapy

Detection of nitrous oxide by resonant photoacoustic spectroscopy based on mid infrared quantum cascade laser

Atmospheric greenhouse gases have great influence on the climate forcing, which is important to human being and also for natural systems. Nitrous oxide (N2O), such as carbon dioxide and methane, is an important greenhouse gas. It plays an important role in the atmospheric environment. Therefore, sensitive measurement of N2O concentration is of significance for studying the atmospheric environment. In this paper, a photoacoustic spectroscopy (PAS) system based on 7.6 m mid infrared quantum cascade laser combined with resonant PAS technique is established for the sensitive detection of N2O concentration. The PAS has been regarded as a highly sensitive and selective technique to measure trace gases. Compared with laser absorption spectroscopy, the PAS offers several intrinsic attractive features including ultra-compact size and no cross-response of light scattering. In addition, the signal of PAS is recorded with low-cost wavelength-independent acoustic transducer. The performance of the developed system is optimized and improved based on the traditional photoacoustic spectroscopic detection. Dual beam enhancement method is used to increase the effective optical power which effectively improves the detection sensitivity of the system. The N2O absorption line at 1307.66 cm-1 is chosen as the target line, and an operation pressure of 50 kPa is selected for reducing cross-talking from H2O absorption line. By detecting the photoacoustic signals of a certain concentration of N2O at different modulation frequencies and modulation amplitudes, the optimal modulation frequency and modulation amplitude of the system are determined to be 800 Hz and 90 mV, respectively. Different concentrations of N2O gas are detected under the optimized parameters, and calibration curve of the system, that is, the curve of photoacoustic signal versus concentration of N2O is obtained, which shows good linearity. The experimental results show that the minimum detection limit of the system is 150 ppb at a pressure of 50 kPa with an integration time of 30 ms. The system noise can be further reduced by increasing the averaging time. A minimum detection limit of 37 ppb is achieved by averaging signals 100 times, and the signal of N2O in the atmosphere is obtained.

Magnetic Field Sensing Based on Bi-Tapered Optical Fibers Using Spectral Phase Analysis.

A compact, magnetic field sensor system based on a short, bi-tapered optical fiber (BTOF) span lying on a magnetic tape was designed, fabricated, and characterized. We monitored the transmission spectrum from a broadband light source, which displayed a strong interference signal. After data collection, we applied a phase analysis of the interference optical spectrum. We here report the results on two fabricated, BTOFs with different interference spectrum characteristics; we analyzed the signal based on the interference between a high-order modal component and the core fiber mode. The sensor exhibited a linear response for magnetic field increments, and we achieved a phase sensitivity of around 0.28 rad/mT. The sensing setup presented remote sensing operation and low-cost transducer magnetic material.

Template-based Quality Assessment of the Doppler Ultrasound Signal for Fetal Monitoring.

One dimensional Doppler Ultrasound (DUS) is a low cost method for fetal auscultation. However, accuracy of any metrics derived from the DUS signals depends on their quality, which relies heavily on operator skills. In low resource settings, where skill levels are sparse, it is important for the device to provide real time signal quality feedback to allow the re-recording of data. Retrospectively, signal quality assessment can help remove low quality recordings when processing large amounts of data. To this end, we proposed a novel template-based method, to assess DUS signal quality. Data used in this study were collected from 17 pregnant women using a low-cost transducer connected to a smart phone. Recordings were split into 1990 segments of 3.75 s duration, and hand labeled for quality by three independent annotators. The proposed template-based method uses Empirical Mode Decomposition (EMD) to allow detection of the fetal heart beats and segmentation into short, time-aligned temporal windows. Templates were derived for each 15 s window of the recordings. The DUS signal quality index (SQI) was calculated by correlating the segments in each window with the corresponding running template using four different pre-processing steps: (i) no additional preprocessing, (ii) linear resampling of each beat, (iii) dynamic time warping (DTW) of each beat and (iv) weighted DTW of each beat. The template-based SQIs were combined with additional features based on sample entropy and power spectral density. To assess the performance of the method, the dataset was split into training and test subsets. The training set was used to obtain the best combination of features for predicting the DUS quality using cross validation, and the test set was used to estimate the classification accuracy using bootstrap resampling. A median out of sample classification accuracy on the test set of 85.8% was found using three features; template-based SQI, sample entropy and the relative power in the 160 to 660 Hz range. The results suggest that the new automated method can reliably assess the DUS quality, thereby helping users to consistently record DUS signals with acceptable quality for fetal monitoring.

Design optimization of embedded ultrasonic transducers for concrete structures assessment

In the last decades, the field of structural health monitoring and damage detection has been intensively explored. Active vibration techniques allow to excite structures at high frequency vibrations which are sensitive to small damage. Piezoelectric PZT transducers are perfect candidates for such testing due to their small size, low cost and large bandwidth. Current ultrasonic systems are based on external piezoelectric transducers which need to be placed on two faces of the concrete specimen. The limited accessibility of in-service structures makes such an arrangement often impractical. An alternative is to embed permanently low-cost transducers inside the structure. Such types of transducers have been applied successfully for the in-situ estimation of the P-wave velocity in fresh concrete, and for crack monitoring. Up to now, the design of such transducers was essentially based on trial and error, or in a few cases, on the limitation of the acoustic impedance mismatch between the PZT and concrete. In the present study, we explore the working principles of embedded piezoelectric transducers which are found to be significantly different from external transducers. One of the major challenges concerning embedded transducers is to produce very low cost transducers. We show that a practical way to achieve this imperative is to consider the radial mode of actuation of bulk PZT elements. This is done by developing a simple finite element model of a piezoelectric transducer embedded in an infinite medium. The model is coupled with a multi-objective genetic algorithm which is used to design specific ultrasonic embedded transducers both for hard and fresh concrete monitoring. The results show the efficiency of the approach and a few designs are proposed which are optimal for hard concrete, fresh concrete, or both, in a given frequency band of interest.

A Low-Cost Label-Free AFB1 Impedimetric Immunosensor Based on Functionalized CD-Trodes

This work describes the investigation of a label-free immunosensor for the detection of aflatoxin B1 (AFB1). CD-trodes (electrodes obtained from recordable compact disks) were used as low-cost and disposable transducers after modification with a self-assembled monolayer (SAM) of lipoic acid. The anti-aflatoxin B1 antibody was immobilized via EDC/NHS activation, followed by blocking with bovine serum albumin and immunoassays with AFB1. The optimization of analytical parameters and the detection were carried out using electrochemical impedance measurements. Using chemometric tools, the best conditions for the immunosensor development were defined as: anti-AFB1 antibody at 1:2000 dilution and surface blocking with 0.5% bovine serum albumin, both incubated for 1 h, and antibody–antigen immunoreaction for 30 min. The impedimetric immunosensor showed a linear range from 5 × 10−9 to 1 × 10−7 mol·L−1 (1.56–31.2 ng·mL−1), limit of detection and limit of quantification, respectively, 3.6 × 10−10 and 1.1 × 10−9mol·L−1 (0.11 and 0.34 ng·mL−1). The proposed immunosensor was applied to analyze peanut samples.

Grain loss sensor for pneumatic separation systems of grain-cleaning machines

One of the reasons of poor effectiveness of machines for postharvest grain handling is the difficulty of optimal modes setting under constantly changing input actions. Using of hardware check and technological process control instead of manual adjustment will reduce the costs and improve the quality of postharvest grain handling. A grain loss sensor for device of parameter checkout of technological process of pneumatic systems of grain-cleaning machines is developed. Its operation is based on the analysis of parameters of sound pressure signal, that arises when grains blowing together with impurities are hitting against a wall of settling chamber. The sensor design is developed on the basis of Soho T-1 low-cost piezometric transducer. The sensor is located on the outer side of a wall against which grains are hitting, and lies outside the air stream carrying the impurities and dust. Therefore, the reliability of the sensor increases, and the air stream structure in pneumatic separation system remains steady. The parameters of sound signal arising when grains are hitting against a wall of settling chamber are determined. The researches were conducted with the grains of wheat, rye, oats and barley; the grain moisture content was varied within the range from 12.6 to 35%. The dependencies between the parameters of sound signal arising when grains are hitting against a wall of settling chamber and the grain loss level have been obtained. The operational capability of the sensor was tested on an experimental model of pneumatic separator installed on postharvest grain handling line. The sensor can be adapted for operation in other pneumatic systems of grain-cleaning machines.

Design and Characterization of a Low-Cost Self-Oscillating Fluxgate Transducer for Precision Measurement of High-Current

Precision measurement of dc high current is usually realized by second harmonic fluxgate current transducers, but the complicated modulation and demodulation circuits with high cost have been limiting their applications. This paper presents a low-cost transducer that can substitute the traditional ones for precision measurement of high current. The new transducer, based on the principle of zero-flux, is the combination of an improved self-oscillating fluxgate sensor with a magnetic integrator in a common feedback loop. The transfer function of the zero-flux control strategy of the transducer is established to verify the validity of the qualitative analysis on operating principle. Origins and major influence factors of the modulation ripple, respectively, caused by the useful signal extraction circuit and the transformer effect are studied, and related suppression methods are proposed, which can be considered as one of the major technical modifications for performance improvement. As verification, a prototype is realized, and several key specifications, including the linearity, small-signal bandwidth, modulation ripple, ratio stability under full load, power-on repeatability, magnetic error, and temperature coefficient, are characterized. Measurement results show that the new transducer with the maximum output ripple 0.3 $\mu \text{A}$ can measure dc current up to ±600 A with a relative accuracy 1.3 ppm in the full scale, and it also can measure ac current and has a −3 dB bandwidth greater than 100 kHz.

Invertase-labeling gold-dendrimer for in situ amplified detection mercury(II) with glucometer readout and thymine-Hg(2+)-thymine coordination chemistry.

A simple, low-cost transducer with glucometer readout was designed for sensitive detection of mercury(II) (Hg(2+)), coupling with thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry and invertase-functionalized gold-dendrimer nanospheres for the signal amplification. Initially, nanogold-encapsulated poly(amidoamine) dendrimers (Au DENs) were synthesized by in-situ reduction of gold(III). Thereafter, the as-prepared Au DENs were utilized for the labeling of invertase and T-rich signal DNA probe. In the presence of target Hg(2+), the functionalized Au DENs were conjugated to capture DNA probe-modified electrode via T-Hg(2+)-T coordination chemistry. Accompanying the Au DENs, the labeled invertase could hydrolyze sucrose into glucose, which could be quantitatively monitored by an external personal glucometer (PGM). The PGM signal increased with the increasing target Hg(2+) in the sample. Under the optimal conditions, our designed sensing platform exhibited good PGM responses toward target Hg(2+), and allowed the detection of Hg(2+) at a concentration as low as 4.2 pM. This sensing system also displayed remarkable specificity relative to target Hg(2+) against other competing ions, and could be applied for reliable monitoring of spiked Hg(2+) into the environmental water samples with satisfactory results. With the advantages of cost-effectiveness, simplicity, portability, and convenience, our strategy provides a tremendous potential to be a promising candidate for point-of-use monitoring of non-glucose targets by the public.

Low-Cost Transducer Based On Surface Scattering Using Side-Polished D-Shaped Optical Fibers

This work presents a new low-cost and environmentally friendly optical transducer based on surface scattering in a side-polished fiber mounted on a glass groove. The surface roughness caused by polishing is used to estimate the change in refractive index on top of the fiber. Changing the surrounding index affects the scattering properties and, consequently, the leakage of the guided mode. This effect is experimentally investigated through the change in the attenuation coefficient when the surrounding refractive index is changed by dropping different weight ratios of glucose solutions onto the polished side. The measured change of the attenuation coefficient is consistent with the finite-element calculations. The effect of different polished depths was theoretically investigated to optimize the working conditions.