Reference Sensor Research Articles

A public dataset of dogs vital signs recorded with ultra wideband radar and reference sensors

Recently, radar sensors have been extensively used for vital sign monitoring in dogs, owing to their noncontact and noninvasive nature. However, a public dataset on dog vital signs has yet to be proposed since capturing data from dogs requires special training and approval. This work presents the first ever ultra wideband radar-based dog vital sign (UWB-DVS) dataset, which was captured in two independent scenarios. In the first scenario, clinical reference sensors are attached to the fainted dogs, and data from UWB radar and reference sensors are captured synchronously. In the second scenario, the dogs can move freely, and video recordings are provided as a reference for movement detection and breathing extraction. For technical validation, a high correlation, above 0.9, is found between the radar and clinical reference sensors for both the heart rate and breathing rate measurements in scenario 1. In scenario 2, the vital signs and movement of the dogs are shown in the form of dashboards, demonstrating the long-term monitoring capability of the radar sensor.

Measuring Turbulent Water Vapor Fluxes Using a Tunable Diode Laser-Based Open-Path Gas Analyzer

The reliable observation and accurate estimates of land–atmosphere water vapor (H2O) flux is essential for ecosystem management and the development of Earth system models. Currently, the most direct measurement method for H2O flux is eddy covariance (EC), which depends on the development of fast-response H2O sensors. In this study, we presented a cost-efficient open-path H2O analyzer (model: HT1800) based on the tunable diode laser absorption spectroscopy (TDLAS) technique, and investigated its applicability for measuring atmospheric turbulent flux of H2O using the EC method. We prepared two HT1800 analyzers with lasers that operate at wavelengths of 1392 nm and 1877 nm, respectively. The field performance of the two analyzers was evaluated through inter-comparative experiments with LI-7500RS and IRGASON, two of the most commonly used H2O analyzers in the EC community. Water vapor densities measured by the three types of analyzers had high overall agreement with the reference sensor; however, they all experienced drift. The mean density drifts of HT1800, LI-7500 and IRGASON were 3.7–5.2%, 4.0% and 3.8%, respectively. Even so, the half-hourly H2O fluxes measured by HT1800 were highly consistent with those by LI-7500RS and IRGASON (with a difference of less than 2%), suggesting that HT1800 can obtain H2O fluxes with high confidence. The HT1800 was also proved to be suitable for EC application in terms of data availability, flux detection limit and response to the high-frequency turbulent variation. Furthermore, we investigated how the spectroscopic effect influences the measurements of H2O density and flux. Despite the fact that the 1392 nm laser was much more susceptible to the spectroscopic effect, the fluxes after correcting for this bias showed excellent agreement with the IRGASON fluxes. Considering the cost advantage in laser and photodetector, the HT1800 analyzer using a 1392 nm infrared laser is a promising and economical solution for EC measurement studies of water vapor.

Cross-Calibration of HY-1D/COCTS Thermal Emissive Bands in the South China Sea

Haiyang-1D (HY-1D) is the second operational satellite in China’s Haiyang-1 series of satellites, carrying the Chinese Ocean Color and Temperature Scanner (COCTS) to provide ocean color and temperature observations. The radiometric calibration is a prerequisite to guarantee the quality of the satellite observations and the derived products, and the radiometric calibration of the thermal emissive bands of HY-1D/COCTS can effectively improve the accuracy of sea surface temperature (SST) derived from the thermal infrared data. In this paper, a study on the regional cross-calibration of the COCTS thermal emissive bands is conducted for high-accuracy SST observations in the South China Sea. The Visible Infrared Imaging Radiometer Suite (VIIRS) on board the NOAA-20 satellite launched by the National Oceanic and Atmospheric Administration (NOAA) is selected as the calibration reference sensor, and a double-difference cross-calibration method is used for HY-1D/COCTS thermal infrared brightness temperature (BT) evaluation. The results show that the bias of the 11 µm and 12 µm thermal emissive bands of COCTS and VIIRS in the South China Sea are 0.101 K and 0.892 K, respectively, and the differences in BTs between the two sensors show temperature dependence. The cross-calibration coefficients are obtained and used to correct the BT of the COCTS thermal emissive bands. The bias of the BT of the 11 µm and 12 µm bands of COCTS are about 0.01 K after cross-calibration. To further validate the results, COCTS post-calibration data were examined using the NOAA-20 Cross-track Infrared Sounder (CrIS) data as a third-party source. The BT is calculated with the spectral response functions of the COCTS thermal emissive bands using the convolution calculation of the CrIS hyperspectral region observations. The comparison shows a small bias between the post-calibration COCTS thermal emissive band observations and CrIS, which is consistent with the comparison between VIIRS and CrIS. The accuracy of the post-calibration COCTS thermal emissive band BT data in the South China Sea has been significantly improved.

Multiple reference active noise control – The attainable suppression

Active noise control is a well-known technology for the attenuation of disturbing sound or vibration. Feedforward control is efficiently employed, especially if stochastic disturbances are to be suppressed. If the unwanted noise is generated by multiples sources, multiple reference sensors are also used. The behavior of multiple reference feedforward systems has been investigated in the last decades, with special emphasis on the speed of convergence. It has been proven that reference preprocessing can significantly speed up such systems. However, less attention has been paid to the attainable suppression. This paper provides the analysis of multiple reference systems with respect to the steady state, and an upper bound for suppression is also expressed. Besides, the single reference case, and the influence of preprocessing is discussed. The theoretical results are supported by simulation and experimental examples.

Monitoring of Composite Structures for Re-Usable Space Applications Using FBGs: The Influence of Low Earth Orbit Conditions.

Fiber Bragg grating sensors (FBGs) are promising for structural health monitoring (SHM) of composite structures in space owing to their lightweight nature, resilience to harsh environments, and immunity to electromagnetic interference. In this paper, we investigated the influence of low Earth orbit (LEO) conditions on the integrity of composite structures with embedded optical fiber sensors, specifically FBGs. The LEO conditions were simulated by subjecting carbon fiber-reinforced polymer (CFRP) coupons to 10 cycles of thermal conditioning in a vacuum (TVac). Coupons with embedded optical fibers (OFs) or capillaries were compared with reference coupons without embedded OFs or capillaries. Embedded capillaries were necessary to create in situ temperature sensors. Tensile and compression tests were performed on these coupons, and the interlaminar shear strength was determined to assess the influence of TVac conditioning on the integrity of the composite. Additionally, a visual inspection of the cross-sections was conducted. The impact on the proper functioning of the embedded FBGs was tested by comparing the reflection spectra before and after TVac conditioning and by performing tensile tests in which the strain measured using the embedded FBGs was compared with the output of reference strain sensors applied after TVac conditioning. The measured strain of the embedded FBGs showed excellent agreement with the reference sensors, and the reflection spectra did not exhibit any significant degradation. The results of the mechanical testing and visual inspection revealed no degradation of the structural integrity when comparing TVac-conditioned coupons with non-TVac-conditioned coupons of the same type. Consequently, it was concluded that TVac conditioning does not influence the functionality of the embedded FBGs or the structural integrity of the composite itself. Although in this paper FBG sensors were tested, the results can be extrapolated to other sensing techniques based on optical fibers.

An experimental study of the sensorized strain wave gear RT1-T and its capabilities for torque control in robotic joints.

The idea of sensorizing a strain wave gear to measure the transmitted torque has been reported since the 1980s. The strain in the elastic flex spline is typically measured by strain gages attached to it. The resulting voltages relate to the transmitted torque in the gear. However, periodic inaccuracies in the measured torque signal (sensing ripple), resulting from positioning inaccuracies of strain gages on the flex spline, prevented this technology from being used outside a lab environment. Regardless of these difficulties, measuring the torque directly in the strain wave gear would bring many advantages, especially in robotic applications, where design space is highly limited. Traditionally, robotic joints are equipped with link-sided torque sensors, which reduce the available design volume, lower the joint stiffness, and require complex cable routing. This paper presents an experimental study of a novel sensorized strain wave gear named RT1-T, which was developed by Schaeffler Technologies. The study was implemented on a joint testbed, including a high-resolution reference torque sensor at the link side. In addition to the measurement accuracy and linearity, a torque ripple analysis is performed. The joint torque control capabilities are determined along dynamic trajectories and compared to the performance achieved with a link-sided reference sensor. The sensor employed in the testbed has a static torque error of 0.42 Nm and an average closed-loop torque control error of 0.65 Nm above the reference sensor.

Low-noise ice galloping monitoring of OPGW lines based on reference sensors

Low-noise ice galloping monitoring of OPGW lines based on reference sensors

Case study: Reference optimization for active control of air conditioning noise at defrost mode in vehicles

Air conditioning noise at defrost mode in vehicles is annoying, especially when the fan speed is high. A case study of active control of air conditioning noise at defrost mode around the driver’s ears in an electric vehicle is reported in this paper. For the feedforward control system under investigation, coherence analysis is conducted first to optimize the location and number of the reference sensors. The simulation results show that the reference microphones should be placed around the main defrost vent toward the front windshield and the other air vents as well to achieve effective noise reduction. Based on the Wiener filtering simulations, about 10.9 dBA noise reduction can be obtained with 20 reference microphones. In the real time experiments with 12 reference microphones at optimized positions on the console, about 6.5 dBA noise reduction was obtained around the driver’s ears with little noise amplification at other seats.

Electronic Measurement System for IoT Sensors Studying

The paper substantiates the choice of methodology and develops an electronic measuring system that provides opportunities to study the sensors of Internet of Things systems. Based on the analysis of existing methods of building similar systems, we chose an approach and offered a method of ensuring the given level of temperature and humidity in the climate chamber. In particular, the determination of the level of relative humidity for its further regulation is carried out using a reference sensor of relative humidity and temperature. The parameters of the sensor studied by the students are determined based on the measurement of the frequency of the generator built using the NE555 chip. The necessary humidity level in the climatic chamber is maintained by mixing wet and dry air, which flows are regulated by valves of different diameters. The developed electronic measuring system was manufactured, and its experimental testing was carried out. The experimental results of the dependence of the humidity in the climate chamber, measured using the reference sensor DHT22, on the ratio of the areas of the holes in the valves indicate its nonlinearity. At the same time, the dependence of the frequency of generated oscillations and the capacity of the analog capacitive humidity sensor on the relative humidity in the climate chamber is practically linear. According to the results of the experiments we obtained an empirical formula, taken into account when programming the device and intended for further measurements of relative humidity. The main characteristics of the developed electronic measuring system are the relative humidity adjustment range (40–80 %), the temperature change range (20–80 °C), and the time to set the specified humidity level after replacing the valves (6–7 minutes). The electronic measuring system can be used for educational purposes, as well as for solving practical tasks related to the control and regulation of temperature and relative humidity of air in a closed space.

Magnetostrictive strain monitoring in Non-Oriented Si-Fe steels using a SAW resonator sensor

The aim of this study is to introduce a new technique for characterizing the magnetostrictive behavior of non-oriented ferromagnetic steel sheets using miniaturized wireless surface acoustic wave sensors (SAW). Unlike conventional optical and electromechanical techniques, this type of sensor offers advantages such as on-board capability, high-temperature resistance (up to 400 °C), and the ability to be connected remotely. The final objective is to monitor magnetic stresses in electrical machines, aligning with the requirements of Industry 4.0 and predictive maintenance. The focus of the present study is the measurement of magnetostriction in ferromagnetic steel sheets, employing a wireless surface acoustic wave resonator operating within the 433 MHz ISM band, under various mechanical fixation configurations. To ensure the accuracy and reliability of SAW measurements, a commercial strain gauge is employed as a reference sensor. Measurements are conducted at different excitation frequencies to explore the phenomenon comprehensively.

An efficient offline scheme to compute an FIR controller for active reduction of acoustic reflections in an anechoic chamber

This paper presents an offline iterative scheme to efficiently obtain a fixed controller for larger-scale active noise control systems. The approach reduces the computational complexity of the scheme by applying preconditioning and prewhitening via the frequency domain, followed by conversion of the filters to the time domain using the inverse Fourier transform. Although the filters are not necessarily causal, causality is ensured by utilizing delay and truncation techniques. The use of these filters in the iterative scheme leads to improved convergence, lowering computational effort while also being memory efficient. Regularization is applied to maintain convergence while allowing for larger step sizes between iterations. The controller minimizes the reflected sound field, which is measured by the performance sensors. The signals of the performance sensors are computed with the Kirchhoff–Helmholtz integral. The results show that this allows for global control of the reflected sound field within the microphone area. A simulation is shown of a noise control setup with 12 primary sources, 12 secondary sources, 12 reference sensors, 12 error sensors and 37 performance sensors. Although the delay of the filters in the direct path is reflected in the filter coefficients, this delay can be truncated to obtain filter coefficients without any delay. Despite the truncation resulting in an average loss in performance of 1.6 dB, the control system without any delays is able to reduce the average reflected sound at the performance sensors by 13.8 dB, when the reference signal is known.

Development of low cost pyranometer IoT based solar irradiance measurement station

This paper presents the design of self-sustainable IoT pyranometer station using low cost BPW34 photodiode. The sustainable power of the station is achieved by a 20W solar panel charges a 7.2Ah lead acid battery through a charge controller. This station uses low cost BPW34 sensors which are connected to a 16-bit ADC module to convert the analog voltage into digital data. This module is connected to an ESP32 microcontroller that connects to Wi-Fi and sends sensor readings to ThingSpeak IoT platform to allow monitoring. This study collected over 36000 data points throughout February 2023 with an average daily data loss of 2.47%. Polynomial regression method was used to determine a best fit curve equation between the BPW34 sensor and the reference sensor. The result shows that the proposed BPW34 sensor achieve the highest error of ±80W/m2 with approximate 3% of daily data. The summary, a second order polynomial equation is found best fit for the proposed low cost BPW34 sensor.

An Efficient Narrowband FxLMS Algorithm for A 3-Axis Active Mount

The Active Mount (AM) controls the vibrations caused by the movement of a mechanical system resting on top of it. Vibration caused by mechanical systems often consists of several dominant frequency components. Therefore, we need an adaptive algorithm controlling tonal vibration components effectively. The FxLMS algorithm widely used for active vibration control raises several issues as the tone number and control channel increase. This paper proposes an efficient narrowband FxLMS algorithm for controlling multiple tonal vibrations occurring in a 3-axis AM. To this end, the secondary path's magnitude and phase responses are modeled tone-by-tone, independently using two-tap filters. Narrowband control filters are constructed for each tone using a narrowband signal model. In addition, a reference sensor is mounted on top of AM, from which tonal references are estimated using adaptive notch filters (ANFs). The proposed algorithm was simulated using transfer functions obtained in a 3-axis AM. Results show that the proposed algorithm effectively controls multiple tonal components by minimizing total errors measured along the 3-axis.

Multi-channel active noise reduction system realizes the local area sound field control of the subway driver's cabin

Aerodynamic noise, air conditioning fan noise, and wheel-rail noise during subway operation have an adverse effect on drivers' physical and emotional well-being and can jeopardize the safe operation of vehicles. On the basis of the original passive acoustic treatment, multi-channel active control technology is used to manage the local sound field in order to further enhance the acoustic comfort of subway drivers' working environment. The multi-channel active noise reduction system installed on the driver's seat is described in this paper. In order to properly prevent the issues of ear pain and obstruction brought on by prolonged use of noise-canceling headphones, the system integrates reference sensors, error sensors, speakers, and a power amplifier within the headrest. The noise in the carriage is picked up using a multi-channel reference signal, and a low delay and anti-interference algorithm is investigated in accordance with the wide frequency band's characteristics and the abrupt change in sound pressure level when the vehicle is running. The test results demonstrate the system's ability to stabilize under situations of abrupt changes in driving noise and in-car broadcast, as well as to successfully minimize noise in the head area of subway drivers.

Cross-Radiometric Calibration and NDVI Application Comparison of FY-4A/AGRI Based on Aqua-MODIS

To enhance the accuracy and stability of FY-4A/AGRI detection data, the MODIS, with highly accurate onboard calibration, is selected as the reference sensor for cross-radiation calibration calculations. The following are the data selection conditions: full considered time, observation geometries, field angles, cloud cover, etc. FY-4A/AGRI and Aqua-MODIS image data are selected as matching sample region locations, where the time difference between the observations for the same ground object is less than 15 min, the satellite zenith angle is less than 30°, and the field angle difference is less than 0.01. The 245 collected reflectance spectral curves are convolved with the spectral response functions of the two sensors, and the spectral band adjustment factors of the corresponding bands are calculated for spectral correction purposes. The cross-calibration coefficients for the red and near-infrared bands are calculated by linearly fitting the simulated top of the atmosphere reflectance values and digital number values from the AGRI sensor in a homogeneous area. In this paper, 16 cross-calibration calculations are performed on FY-4A/AGRI image data from August 2018 to September 2020, and the results are compared with the original calibration coefficients to test the feasibility of the proposed method. Additionally, 31 cross-calibration calculations are performed on image data from October 2020 to December 2022 to study the resulting AGRI sensor quality and performance changes. The NDVI of the FY-4A/AGRI image data was calculated before and after the cross-radiometric calibration using the maximum synthesis method. Additionally, the NDVI of the MODIS image data was compared and analyzed from three aspects: time, space, and the change trend. The results show that the spectral band adjustment factor calculated using the reflectance spectral curves of the ground objects in this paper can effectively correct for the spectral differences between the two sensors. Sixteen cross-calibration coefficients are less than 5.2% different from the original calibration coefficients, which fully proves the feasibility of the method used in this paper. All of the cross-calibration results show that the AGRI sensors have a certain degree of attenuation in the red and near-infrared bands, and the annual attenuation rates are approximately 1.37% and 2.55%, respectively. Cross-radiometric calibration has further improved the quality of the NDVI in FY-4A/AGRI imagery, enhancing the precision of its data application.

Low-cost carbon dioxide concentration sensors for assessing air quality in the built environment: an on-site evaluation of their measurement performance

Carbon dioxide (CO2) concentration is commonly used to determine indoor air quality. However, wearable environmental monitoring devices have not considered CO2 content, because they have mainly focused on the outdoor environment. Our goal is to develop a new wearable monitoring system for indoor research purposes that also incorporates a CO2 concentration sensor. We evaluated the performance of two low-cost CO2 sensors, the Senseair K30 and the Sensirion SCD30, by comparing them with a professional reference sensor in two different environments: a Test Cell and the LabZEB of ITC-CNR. A first result shows that both low-cost sensors have acceptable performance, with the K30 showing a trend closer to that of the professional reference sensor and better overall performance. For this reason, we conducted a third test in which we encapsulated the selected K30 low-cost sensor in a 3D-printed, wearable housing that supports the sensor and control unit to see if the 3D-printed part could affect measurement performance. The result shows no interference in measurement performance. This suggests that low-cost sensors can be used in a wearable system to assess indoor air quality for environmental and human-centered research in the built environment.

Assessment of magnetic field on body axis and orbit axis of RazakSAT in Near Equatorial Orbit using IGRF model

Magnetometer is reference sensor of satellite that function to measure the vector of magnetic field during satellite enter the orbit. The magnetic field measurement vector will be employed in the Attitude Determination System (ADS) to calculate the satellite’s orientation with respect to the Earth. However, any misalignments or disturbances on the ADS can affect the orientation of the satellite in terms of the orbital position. Therefore, in this paper assessment of magnetic field on body axis and orbit axis of RazakSAT by using The International Geomagnetic Reference Field (IGRF) model. RazakSAT as references to verify the IGRF model by using residual analysis that percentage error less than 5% requirement from Astronautic Technology Sdn Bhd (ATSB). The result show, Y-axis and Z-axis from orbit frame meet the requirement of ATSB is less than 5%.

Dual quaternion-based dynamics and control for gravity recovery missions

A novel dual quaternion modeling and control approach is introduced as a better alternative to traditional modeling methods for formation flying spacecraft utilized for gravity recovery missions. The new formulation for the equations of motion for the relative dynamics of formation flying spacecraft and an interior test mass results in two coupled six degree-of-freedom models that show superior performance over traditional linearized and uncoupled methodologies. Utilizing data products from the Gravity Recovery and Climate Experiment Follow-On mission, a comparison of modeling methods is presented which demonstrates the advantage of the proposed dual quaternion-based modeling approach. Also, a dual quaternion-based Lyapunov controller is formulated and proven to control a test mass within specified gravitational reference sensor development requirements. Additional fidelity is added to the simulation by modeling the voltage-to-force and-torque equations of electrodes located within an electrode housing with appropriate white noise added to the commanded voltages. Equations are also derived and presented for modeling the coupling between the spacecraft and the test mass, and for modeling the density of the atmosphere so that the simulations of the spacecraft and test mass include both gravitational and nongravitational effects. This research ultimately lays the ground work and shows the need for, dual quaternions on future gravity recovery missions.

Fabrication, characterization, and repair of nanocarbon-loaded aircraft paint-based sensors for real-world SHM: studies at the laboratory scale

There has been considerable interest in piezoresistive nanocarbon-loaded polymer films for structural health monitoring, including damage detection and strain monitoring. While good performance has been demonstrated, issues related to practical implementation have received less attention. Here we present sensors made from exfoliated graphite nanoplatelets (xGnP) incorporated into a commercial paint that is applied to Sikorsky aircraft. A formulation and a fabrication method are developed that deliver high piezoresistive strain sensitivity alongside mechanical integrity. At approximately 7 wt% xGnP, the gauge factor in tension is in the range of 30–55, and the effectiveness of the sensors for damage monitoring is demonstrated by the detection of perforations. To obtain a paintable solution, key considerations in choosing the solvent employed for introducing the nanocarbon are compatibility and the ability to keep the nanocarbon suspended, which is achieved using ethyl acetate. The ability to form sensors in situ on aircraft structures requires an uncomplicated method of making robust electrical connections, which is demonstrated here using embedded copper mesh. The strong, often nonlinear, environmental sensitivity of polymer-nanocarbon materials must also be considered in applications; here, increasing temperature and humidity both raise sensor resistance. This work shows that a second, unstrained reference sensor would work well for automatic compensation. Lastly, a method for effecting a repair that employs standard processes and maintains the high gauge factor is demonstrated. With these advances, the paint-xGnP sensors are ready for in-the-field testing on aircraft.

Robust improved multiband-structured subband adaptive filter for active noise control with impulsive interference

The feedforward filtered-x least mean square algorithm is extensively implemented for active control of broadband noise. However, the control performance is substantially deteriorated due to colored noise and the presence of uncorrelated disturbances near the reference and error sensors. To tackle these issues, in this paper, a robust improved multiband-structured subband adaptive filter based on logarithmic and total least squares method is proposed for active control. Unlike the conventional method of total least squares, the proposed algorithm adopts logarithmic and Rayleigh quotient functions. The closed loop implementation of the improved multiband-structured subband adaptive filter is adopted to meet the delayless requirement. The proposed algorithm is well-suited for environments where the reference signal is highly correlated and the residual noise is contaminated by impulsive noise. Furthermore, an affine combination of the proposed algorithm is developed to meet the complementary requirements of faster convergence and improved noise reduction. Eventually, the stability and computational complexity are studied. Simulation results using measured acoustic paths in an anechoic chamber and a normal room illustrate the effectiveness of the proposed algorithm for controlling broadband noise with impulsive interference. In addition, the tracking control performance is evaluated in a time-varying acoustic environment.