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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Intelligent Sensors".

Deadline for manuscript submissions: 20 May 2024 | Viewed by 14234

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Special Issue Editor

Prof. Dr. Jong-Ryul Yang

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Guest Editor

Department of Electrical and Electronics Engineering, Konkuk University, 120, Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
Interests: RF/millimeter-wave transceiver front-end IC design for radar systems; terahertz-wave integrated circuits and systems; MMIC design; miniaturized radar sensors; CW/FSK/FMCW radar sensors; remote vital sign detection; HRV analysis using radar sensors
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Special Issue Information

Dear Colleagues,

Sensor technology in smart environments (Sensors for Smart Environments), which means intelligent detection and information acquisition in various environments, is a core, cutting-edge technology that is leading the 4th industrial revolution—for example, autonomous driving, artificial intelligence robots, IoT sensors, and so on. Additionally, it is regarded as one of the most important techniques for safe daily life with the emergence of the corona pandemic. Sensors for smart environments include a sensing technology that detects the characteristics of an object or person with remote or contact devices, a wireless data transmitting/receiving technology that transmits the information obtained from environments, and energy harvesting/wireless power transmission technologies for continuous monitoring in various environments. This Special Issue covers a wide range of technology categories across all fields of electronics, such as sensing techniques and devices, including temperature, pressure, gas, velocity, distance, displacement, motions, and vital signs, sensor implementation using integrated circuits and miniaturized modules, and up-to-date algorithms and modeling for signal conditioning and data acquisition and processing. Al-assisted sensing, control, and analysis techniques for various environments are also included in this Special Issue.

Prof. Dr. Jong-Ryul Yang
Guest Editor

Manuscript Submission Information

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Keywords

innovative sensing technologies and applications for smart environments
novel sensors for detecting the information of objects or human beings in various environments
circuits and systems related to sensors, sensing components and devices for smart environments
signal processing and analysis of sensors in various environments
energy harvesting and wireless power transmission for smart sensors in various environments
Al-assisted sensor technologies, including machine/deep learning and big data analysis
radar sensing and sensor fusion technologies for smart environments
RF/millimeter-wave/terahertz systems for electromagnetic-based sensors
diagnosis analysis with continuous monitoring obtained using sensors in the smart environments

Published Papers (7 papers)

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Research

17 pages, 4086 KiB

Open AccessArticle

Using Surrogate Parameters to Enhance Monitoring of Community Wastewater Management System Performance for Sustainable Operations

by Zhining Shi, Christopher W. K. Chow, Jing Gao, Ke Xing, Jixue Liu and Jiuyong Li

Sensors 2024, 24(6), 1857; https://0-doi-org.brum.beds.ac.uk/10.3390/s24061857 - 14 Mar 2024

Viewed by 371

Abstract

Community wastewater management systems (CWMS) are small-scale wastewater treatment systems typically in regional and rural areas with less sophisticated treatment processes and often managed by local governments or communities. Research and industrial applications have demonstrated that online UV-Vis sensors have great potential for improving wastewater monitoring and treatment processes. Existing studies on the development of surrogate parameters with models from spectral data for wastewater were largely limited to lab-based. In contrast, industrial applications of these sensors have primarily targeted large wastewater treatment plants (WWTPs), leaving a gap in research for small-scale WWTPs. This paper demonstrates the suitability of using a field-based online UV-Vis sensor combined with advanced data analytics for CWMSs as an early warning for process upset to support sustainable operations. An industry case study is provided to demonstrate the development of surrogate monitoring parameters for total suspended solids (TSSs) and chemical oxygen demand (COD) using the UV-Vis spectral data from an online UV-Vis sensor. Absorbances at a wavelength of 625 nm (UV₆₂₅) and absorbances at a wavelength of 265 nm (UV₂₆₅) were identified as surrogate parameters to measure TSSs and COD, respectively. This study contributes to the improvement of WWTP performance with a continuous monitoring system by developing a process monitoring framework and optimization strategy. Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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17 pages, 3965 KiB

Open AccessArticle

Deep Learning for Counting People from UWB Channel Impulse Response Signals

by Gun Lee, Subin An, Byung-Jun Jang and Soochahn Lee

Sensors 2023, 23(16), 7093; https://0-doi-org.brum.beds.ac.uk/10.3390/s23167093 - 10 Aug 2023

Viewed by 992

Abstract

The use of higher frequency bands compared to other wireless communication protocols enhances the capability of accurately determining locations from ultra-wideband (UWB) signals. It can also be used to estimate the number of people in a room based on the waveform of the channel impulse response (CIR) from UWB transceivers. In this paper, we apply deep neural networks to UWB CIR signals for the purpose of estimating the number of people in a room. We especially focus on empirically investigating the various network architectures for classification from single UWB CIR data, as well as from various ensemble configurations. We present our processes for acquiring and preprocessing CIR data, our designs of the different network architectures and ensembles that were applied, and the comparative experimental evaluations. We demonstrate that deep neural networks can accurately classify the number of people within a Line of Sight (LoS), thereby achieving an 99% performance and efficiency with respect to both memory size and FLOPs (Floating Point Operations Per Second). Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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17 pages, 10485 KiB

Open AccessArticle

Reconstruction of Range-Doppler Map Corrupted by FMCW Radar Asynchronization

by Kyung-Min Lee, In-Seong Lee, Hee-Sub Shin, Jae-Woo Ok, Jae-Hyuk Youn, Eung-Noh You, Jong-Ryul Yang and Kyung-Tae Kim

Sensors 2023, 23(12), 5605; https://0-doi-org.brum.beds.ac.uk/10.3390/s23125605 - 15 Jun 2023

Cited by 1 | Viewed by 1571

Abstract

Frequency-modulated continuous wave (FMCW) radar system synchronization using external clock signals can cause repeated Range-Doppler (R-D) map corruption when clock signal asynchronization problems occur between the transmitter and receiver. In this paper, we propose a signal processing method for the reconstruction of the corrupted R-D map owing to the FMCW radar’s asynchronization. After calculating the image entropy for each R-D map, the corrupted ones are extracted and reconstructed using the normal R-D maps acquired before and after the individual maps. To verify the effectiveness of the proposed method, three target detection experiments were conducted: a human target detection in an indoor environment and a wide place and a moving bike-rider target detection in an outdoor environment. The corrupted R-D map sequence of observed targets in each case was reconstructed properly and showed the validity by comparing the map-by-map range and speed changes in the detected target with the ground-truth information of the target. Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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27 pages, 4032 KiB

Open AccessArticle

A Low-Cost Multi-Purpose IoT Sensor for Biologging and Soundscape Activities

by Dinarte Vasconcelos and Nuno Jardim Nunes

Sensors 2022, 22(19), 7100; https://0-doi-org.brum.beds.ac.uk/10.3390/s22197100 - 20 Sep 2022

Cited by 5 | Viewed by 2406

Abstract

The rapid expansion in miniaturization, usability, energy efficiency, and affordability of Internet of Things (IoT) sensors, integrated with innovations in smart capability, is greatly increasing opportunities in ground-level monitoring of ecosystems at a specific scale using sensor grids. Surrounding sound is a powerful data source for investigating urban and non-urban ecosystem health, and researchers commonly use robust but expensive passive sensors as monitoring equipment to capture it. This paper comprehensively describes the hardware behind our low-cost, small multipurpose prototype, capable of monitoring different environments (e.g., remote locations) with onboard processing power. The device consists of a printed circuit board, microprocessor, local memory, environmental sensor, microphones, optical sensors and LoRa (Long Range) communication systems. The device was successfully used in different use cases, from monitoring mosquitoes enhanced with optical sensors to ocean activities using a hydrophone. Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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22 pages, 4025 KiB

Open AccessArticle

Machine Learning-Based Boosted Regression Ensemble Combined with Hyperparameter Tuning for Optimal Adaptive Learning

by Joseph Isabona, Agbotiname Lucky Imoize and Yongsung Kim

Sensors 2022, 22(10), 3776; https://0-doi-org.brum.beds.ac.uk/10.3390/s22103776 - 16 May 2022

Cited by 36 | Viewed by 2940

Abstract

Over the past couple of decades, many telecommunication industries have passed through the different facets of the digital revolution by integrating artificial intelligence (AI) techniques into the way they run and define their processes. Relevant data acquisition, analysis, harnessing, and mining are now fully considered vital drivers for business growth in these industries. Machine learning, a subset of artificial intelligence (AI), can assist, particularly in learning patterns in big data chunks, intelligent extrapolative extraction of data and automatic decision-making in predictive learning. Firstly, in this paper, a detailed performance benchmarking of adaptive learning capacities of different key machine-learning-based regression models is provided for extrapolative analysis of throughput data acquired at the different user communication distances to the gNodeB transmitter in 5G new radio networks. Secondly, a random forest (RF)-based machine learning model combined with a least-squares boosting algorithm and Bayesian hyperparameter tuning method for further extrapolative analysis of the acquired throughput data is proposed. The proposed model is herein referred to as the RF-LS-BPT method. While the least-squares boosting algorithm is engaged to turn the possible RF weak learners to form stronger ones, resulting in a single strong prediction model, the Bayesian hyperparameter tuning automatically determines the best RF hyperparameter values, thereby enabling the proposed RF-LS-BPT model to obtain desired optimal prediction performance. The application of the proposed RF-LS-BPT method showed superior prediction accuracy over the ordinary random forest model and six other machine-learning-based regression models on the acquired throughput data. The coefficient of determination (Rsq) and mean absolute error (MAE) values obtained for the throughput prediction at different user locations using the proposed RF-LS-BPT method range from 0.9800 to 0.9999 and 0.42 to 4.24, respectively. The standard RF models attained 0.9644 to 0.9944 Rsq and 5.47 to 12.56 MAE values. The improved throughput prediction accuracy of the proposed RF-LS-BPT method demonstrates the significance of hyperparameter tuning/optimization in developing precise and reliable machine-learning-based regression models. The projected model would find valuable applications in throughput estimation and modeling in 5G and beyond 5G wireless communication systems. Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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13 pages, 6515 KiB

Open AccessArticle

Space Target Classification Improvement by Generating Micro-Doppler Signatures Considering Incident Angle

by Jae-In Lee, Nammon Kim, Sawon Min, Jeongwoo Kim, Dae-Kyo Jeong and Dong-Wook Seo

Sensors 2022, 22(4), 1653; https://0-doi-org.brum.beds.ac.uk/10.3390/s22041653 - 20 Feb 2022

Cited by 6 | Viewed by 1742

Abstract

Classifying space targets from debris is critical for radar resource management as well as rapid response during the mid-course phase of space target flight. Due to advances in deep learning techniques, various approaches have been studied to classify space targets by using micro-Doppler signatures. Previous studies have only used micro-Doppler signatures such as spectrogram and cadence velocity diagram (CVD), but in this paper, we propose a method to generate micro-Doppler signatures taking into account the relative incident angle that a radar can obtain during the target tracking process. The AlexNet and ResNet-18 networks, which are representative convolutional neural network architectures, are transfer-learned using two types of datasets constructed using the proposed and conventional signatures to classify six classes of space targets and a debris–cone, rounded cone, cone with empennages, cylinder, curved plate, and square plate. Among the proposed signatures, the spectrogram had lower classification accuracy than the conventional spectrogram, but the classification accuracy increased from 88.97% to 92.11% for CVD. Furthermore, when recalculated not with six classes but simply with only two classes of precessing space targets and tumbling debris, the proposed spectrogram and CVD show the classification accuracy of over 99.82% for both AlexNet and ResNet-18. Specially, for two classes, CVD provided results with higher accuracy than the spectrogram. Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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17 pages, 7325 KiB

Open AccessArticle

by In-Seong Lee, Jae-Hyun Park and Jong-Ryul Yang

Sensors 2021, 21(19), 6376; https://0-doi-org.brum.beds.ac.uk/10.3390/s21196376 - 24 Sep 2021

Cited by 5 | Viewed by 2926

Abstract

A detrending technique is proposed for continuous-wave (CW) radar to remove the effects of direct current (DC) offset, including DC drift, which is a very slow noise that appears near DC. DC drift is mainly caused by unwanted vibrations (generated by the radar itself, target objects, or surroundings) or characteristic changes in components in the radar owing to internal heating. It reduces the accuracy of the circle fitting method required for I/Q imbalance calibration and DC offset removal. The proposed technique effectively removes DC drift from the time-domain waveform of the baseband signals obtained for a certain time using polynomial fitting. The accuracy improvement in the circle fitting by the proposed technique using a 5.8 GHz CW radar decreases the error in the displacement measurement and increases the signal-to-noise ratio (SNR) in vital signal detection. The measurement results using a 5.8 GHz radar show that the proposed technique using a fifth-order polynomial fitting decreased the displacement error from 1.34 mm to 0.62 mm on average when the target was at a distance of 1 m. For a subject at a distance of 0.8 m, the measured SNR improved by 7.2 dB for respiration and 6.6 dB for heartbeat. Full article

(This article belongs to the Special Issue Sensors for Smart Environments)

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