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Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications

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

Deadline for manuscript submissions: closed (15 November 2024) | Viewed by 16772

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Special Issue Editors

Prof. Dr. Stefano Pisa

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Guest Editor

Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, 00184 Rome, Italy
Interests: interaction between electromagnetic fields and biological systems; therapeutic and diagnostic applications of electromagnetic fields; radar-based techniques for remote monitoring of subject position and cardio-respiratory activity; algorithms for radar image reconstruction; permittivity measurements and models of construction and biological materials

Dr. Giulia Sacco

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Guest Editor

UMR CNRS6164-IETR, Campus de Beaulieu, 263 Avenue du Général Leclerc, 35042 Rennes CEDEX, France
Interests: interactions between EM fields and human body; biomedical radars; mmWaves; dosimetry; wearable antennas
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Special Issue Information

Dear Colleagues,

Nowadays radars are increasingly used in short-range scenarios. Emerging applications involve distance measurement (e.g., in driver-assistance systems, level measurements in tanks, engineered white canes for visually impaired people) and displacement detection (e.g., for remote monitoring of cardio-respiratory activity, building vibrations, and development of human–computer interfaces). Radars are also used to obtain images of scenarios through walls (TWRI) and under rubble, or to track multiple people and detect fall events of elderly subjects in an indoor environment. Finally, radar imaging techniques for breast cancer and haemorrhagic brain stroke diagnosis have seen significant progress. For all these applications, various radar topologies have been proposed, including continuous-wave (CW) Doppler radars, frequency-modulated continuous-wave (FMCW) radars, ultra-wideband (UWB) pulsed radars, and UWB-modulated (M-UWB) pulse radars. In addition to conventional architectures, subharmonic, harmonic, and intermodulation radars have also been investigated. For short range applications, specific models and signal processing algorithms have been developed, in some cases with the support of machine learning techniques. Within the context of this continuously evolving scenario, this Special Issue aims to collect original contributions in the field of radar applications and techniques, but also on innovative architectures both in terms of electronics and antennas.

Prof. Dr. Stefano Pisa
Dr. Giulia Sacco
Guest Editors

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Keywords

distance and displacement measurements
environmental monitoring
doppler and FMCW radars
ultra-wideband radar
harmonic and intermodulation radar
radar signal processing
radar image reconstructions
machine learning-based radars

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Published Papers (10 papers)

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Research

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21 pages, 2300 KiB

Open AccessArticle

Incorporating Radar Frequency-Domain Deramping into Variational Shape-Based Scene Reconstruction: A Feasibility Study Using Active Contours

by Alper Yildirim, Samuel Bignardi, Christopher F. Barnes and Anthony Joseph Yezzi

Sensors 2025, 25(8), 2451; https://doi.org/10.3390/s25082451 - 13 Apr 2025

Viewed by 152

Abstract

Multi-view stereo techniques with traditional cameras have wide applications in robotics and computer vision for scene reconstruction. Their dependence on the visible spectrum, however, poses several limitations that radar sensing could overcome in obstructing conditions such as fog and smoke. We propose a new radar-based multi-view stereo method for scene reconstruction, which combines the power of multi-view stereo techniques with the advantages of radar sensing by extending upon our previous work in this direction, where we demonstrated a time-domain inversion approach by leveraging a set of independent radar echoes acquired at sparse locations to reconstruct the scene’s geometry. Here, we show how radar stretch processing can be incorporated into a similar geometric framework to leverage frequency-domain information. Our method fundamentally differs from classical radar imaging by utilizing an explicit geometric shape representation, allowing the imposition of shape priors and the ability to model visibility and occlusions, and a forward model based on the electric field strength density over the antenna range embedded within the deramped echo. An iterative scheme is then used to evolve an initial shape toward an optimal configuration to best explain the data. We conclude by showing the initial proof of concept for the success of this method through a set of simulated 2D experiments of increasing complexity. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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20 pages, 4379 KiB

Open AccessArticle

Feasibility of Early Assessment for Psychological Distress: HRV-Based Evaluation Using IR-UWB Radar

by Yuna Lee, Kounseok Lee, Sarfaraz Ahmed and Sung Ho Cho

Sensors 2024, 24(19), 6210; https://doi.org/10.3390/s24196210 - 25 Sep 2024

Viewed by 1415

Abstract

Mental distress-induced imbalances in autonomic nervous system activities adversely affect the electrical stability of the cardiac system, with heart rate variability (HRV) identified as a related indicator. Traditional HRV measurements use electrocardiography (ECG), but impulse radio ultra-wideband (IR-UWB) radar has shown potential in HRV measurement, although it is rarely applied to psychological studies. This study aimed to assess early high levels of mental distress using HRV indices obtained using radar through modified signal processing tailored to reduce phase noise and improve positional accuracy. We conducted 120 evaluations on 15 office workers from a software startup, with each 5 min evaluation using both radar and ECG. Visual analog scale (VAS) scores were collected to assess mental distress, with evaluations scoring 7.5 or higher classified as high-mental distress group, while the remainder formed the control group. Evaluations indicating high levels of mental distress showed significantly lower HRV compared to the control group, with radar-derived indices correlating strongly with ECG results. The radar-based analysis demonstrated a significant ability to differentiate high mental distress, supported by receiver operating characteristic (ROC) analysis. These findings suggest that IR-UWB radar could be a supportive tool for distinguishing high levels of mental stress, offering clinicians complementary diagnostic insights. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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15 pages, 2848 KiB

Open AccessArticle

Improving the Accuracy of mmWave Radar for Ethical Patient Monitoring in Mental Health Settings

by Colm Dowling, Hadi Larijani, Mike Mannion, Matt Marais and Simon Black

Sensors 2024, 24(18), 6074; https://doi.org/10.3390/s24186074 - 19 Sep 2024

Cited by 1 | Viewed by 2009

Abstract

Monitoring patient safety in high-risk mental health environments is a challenge for clinical staff. There has been a recent increase in the adoption of contactless sensing solutions for remote patient monitoring. mmWave radar is a technology that has high potential in this field due it its low cost and protection of privacy; however, it is prone to multipath reflections and other sources of environmental noise. This paper discusses some of the challenges in mmWave remote sensing applications for patient safety in mental health wards. In line with these challenges, we propose a novel low-data solution to mitigate the impact of multipath reflections and other sources of noise in mmWave sensing. Our solution uses an unscented Kalman filter for target tracking over time and analyses features of movement to determine whether targets are human or not. We chose a commercial off-the-shelf radar and compared the accuracy and reliability of sensor measurements before and after applying our solution. Our results show a marked decrease in false positives and false negatives during human target tracking, as well as an improvement in spatial location detection in a two-dimensional space. These improvements demonstrate how a simple low-data solution can improve existing mmWave sensors, making them more suitable for patient safety solutions in high-risk environments. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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23 pages, 11804 KiB

Open AccessArticle

Therapeutic Exercise Recognition Using a Single UWB Radar with AI-Driven Feature Fusion and ML Techniques in a Real Environment

by Shahzad Hussain, Hafeez Ur Rehman Siddiqui, Adil Ali Saleem, Muhammad Amjad Raza, Josep Alemany Iturriaga, Alvaro Velarde-Sotres and Isabel De la Torre Díez

Sensors 2024, 24(17), 5533; https://doi.org/10.3390/s24175533 - 27 Aug 2024

Viewed by 1216

Abstract

Physiotherapy plays a crucial role in the rehabilitation of damaged or defective organs due to injuries or illnesses, often requiring long-term supervision by a physiotherapist in clinical settings or at home. AI-based support systems have been developed to enhance the precision and effectiveness of physiotherapy, particularly during the COVID-19 pandemic. These systems, which include game-based or tele-rehabilitation monitoring using camera-based optical systems like Vicon and Microsoft Kinect, face challenges such as privacy concerns, occlusion, and sensitivity to environmental light. Non-optical sensor alternatives, such as Inertial Movement Units (IMUs), Wi-Fi, ultrasound sensors, and ultrawide band (UWB) radar, have emerged to address these issues. Although IMUs are portable and cost-effective, they suffer from disadvantages like drift over time, limited range, and susceptibility to magnetic interference. In this study, a single UWB radar was utilized to recognize five therapeutic exercises related to the upper limb, performed by 34 male volunteers in a real environment. A novel feature fusion approach was developed to extract distinguishing features for these exercises. Various machine learning methods were applied, with the EnsembleRRGraBoost ensemble method achieving the highest recognition accuracy of 99.45%. The performance of the EnsembleRRGraBoost model was further validated using five-fold cross-validation, maintaining its high accuracy. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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13 pages, 9958 KiB

Open AccessArticle

Extraction and Validation of Biomechanical Gait Parameters with Contactless FMCW Radar

by Linyu Wang, Zhongfei Ni and Binke Huang

Sensors 2024, 24(13), 4184; https://doi.org/10.3390/s24134184 - 27 Jun 2024

Cited by 1 | Viewed by 1188

Abstract

A 77 GHz frequency-modulated continuous wave (FMCW) radar was utilized to extract biomechanical parameters for gait analysis in indoor scenarios. By preprocessing the collected raw radar data and eliminating environmental noise, a range–velocity–time (RVT) data cube encompassing the subjects’ information was derived. The strongest signals from the torso in the velocity and range dimensions and the enveloped signal from the toe in the velocity dimension were individually separated for the gait parameters extraction. Then, six gait parameters, including step time, stride time, step length, stride length, torso velocity, and toe velocity, were measured. In addition, the Qualisys system was concurrently utilized to measure the gait parameters of the subjects as the ground truth. The reliability of the parameters extracted by the radar was validated through the application of the Wilcoxon test, the intraclass correlation coefficient (ICC) value, and Bland–Altman plots. The average errors of the gait parameters in the time, range, and velocity dimensions were less than 0.004 s, 0.002 m, and 0.045 m/s, respectively. This non-contact radar modality promises to be employable for gait monitoring and analysis of the elderly at home. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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16 pages, 13553 KiB

Open AccessArticle

Evaluation of Lateral Radar Positioning for Vital Sign Monitoring: An Empirical Study

by Lars Hornig, Benedek Szmola, Wiebke Pätzold, Jan Paul Vox and Karen Insa Wolf

Sensors 2024, 24(11), 3548; https://doi.org/10.3390/s24113548 - 31 May 2024

Cited by 1 | Viewed by 1334

Abstract

Vital sign monitoring is dominated by precise but costly contact-based sensors. Contactless devices such as radars provide a promising alternative. In this article, the effects of lateral radar positions on breathing and heartbeat extraction are evaluated based on a sleep study. A lateral radar position is a radar placement from which multiple human body zones are mapped onto different radar range sections. These body zones can be used to extract breathing and heartbeat motions independently from one another via these different range sections. Radars were positioned above the bed as a conventional approach and on a bedside table as well as at the foot end of the bed as lateral positions. These positions were evaluated based on six nights of sleep collected from healthy volunteers with polysomnography (PSG) as a reference system. For breathing extraction, comparable results were observed for all three radar positions. For heartbeat extraction, a higher level of agreement between the radar foot end position and the PSG was found. An example of the distinction between thoracic and abdominal breathing using a lateral radar position is shown. Lateral radar positions could lead to a more detailed analysis of movements along the body, with the potential for diagnostic applications. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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15 pages, 11687 KiB

Open AccessArticle

Subcranial Encephalic Temnograph-Shaped Helmet for Brain Stroke Monitoring

by Antonio Cuccaro, Angela Dell’Aversano, Bruno Basile, Maria Antonia Maisto and Raffaele Solimene

Sensors 2024, 24(9), 2887; https://doi.org/10.3390/s24092887 - 30 Apr 2024

Cited by 4 | Viewed by 1738

Abstract

In this contribution, a wearable microwave imaging system for real-time monitoring of brain stroke in the post-acute stage is described and validated. The system exploits multistatic/multifrequency (only 50 frequency samples) data collected via a low-cost and low-complexity architecture. Data are collected by an array of only 16 antennas moved by pneumatic system. Phantoms, built from ABS material and filled with appropriate Triton X-100-based mixtures to mimic the different head human tissues, are employed for the experiments. The microwave system exploits the differential scattering measures and the Incoherent MUSIC algorithm to provide a 3D image of the region under investigation. The shown results, although preliminary, confirm the potential of the proposed microwave system in providing reliable results, including for targets whose evolution is as small as 16 mL in volume. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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16 pages, 11312 KiB

Open AccessArticle

Fully Integrated 24-GHz 1TX-2RX Transceiver for Compact FMCW Radar Applications

by Goo-Han Ko, Seung-Jin Moon, Seong-Hoon Kim, Jeong-Geun Kim and Donghyun Baek

Sensors 2024, 24(5), 1460; https://doi.org/10.3390/s24051460 - 23 Feb 2024

Cited by 2 | Viewed by 2535

Abstract

A fully integrated 24-GHz radar transceiver with one transmitter (TX) and two receivers (RXs) for compact frequency modulated continuous wave (FMCW) radar applications is here presented. The FMCW synthesizer was realized using a fractional-N phase-locked loop (PLL) and programmable chirp generator, which are completely integrated in the proposed transceiver. The measured output phase noise of the synthesizer is −80 dBc/Hz at 100 kHz offset. The TX consists of a three-bit bridged t-type attenuator for gain control, a two-stage drive amplifier (DA) and a one-stage power amplifier (PA). The TX chain provides an output power of 13 dBm while achieving <0.5 dB output power variation within the range of 24 to 24.25 GHz. The RX with a direct conversion I-Q structure is composed of a two-stage low noise amplifier (LNA), I-Q generator, mixer, transimpedance amplifier (TIA), a two-stage biquad band pass filter (BPF), and a differential-to-single (DTS) amplifier. The TIA and the BPF employ a DC offset cancellation (DCOC) circuit to suppress the strong reflection signal and TX-RX leakage. The RX chain exhibits an overall gain of 100 dB. The proposed radar transceiver is fabricated using a 65 nm CMOS technology. The transceiver consumes 220 mW from a 1 V supply voltage and has 4.84 mm² die size including all pads. The prototype FMCW radar is realized with the proposed transceiver and Yagi antenna to verify the radar functionality, such as the distance and angle of targets. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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15 pages, 7798 KiB

Open AccessArticle

An Intermodulation Radar for Non-Linear Target and Transceiver Detection

by Stefano Pisa, Alessandro Trifiletti, Pasquale Tommasino, Pietro Monsurrò, Piero Tognolatti, Giorgio Leuzzi, Alessandro Di Carlofelice and Emidio Di Giampaolo

Sensors 2024, 24(5), 1433; https://doi.org/10.3390/s24051433 - 23 Feb 2024

Viewed by 1587

Abstract

The design and the characterization of a non-linear target to test an intermodulation radar was performed using the AWR design environment Version 22 by Cadence software. Two experimental setups for intermodulation measurements were realized in order to characterize connectorized or antenna-equipped devices. Both setups were modeled using the VSS software available inside AWR Version 22. The comparison between measurements and simulations on the designed target showed a very good agreement. Intermodulation measurements were performed on connectorized devices present inside electronic systems and on various transceiver available on the market. This experimental study evidenced that the non-linearities of devices such as amplifiers and mixers are visible at their access ports even when the device is switched off. Moreover, this study highlights the ability of an intermodulation radar to remotely detect the presence of a particular transceiver, even when the latter is switched off, thanks to the specific frequency response of its intermodulation products. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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Review

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29 pages, 454 KiB

Open AccessReview

Overview of Vivaldi Antenna Selection for Through-Wall Radar Applications

by Mariana Amador, André Rouco, Daniel Albuquerque and Pedro Pinho

Sensors 2024, 24(20), 6536; https://doi.org/10.3390/s24206536 - 10 Oct 2024

Viewed by 2946

Abstract

This paper analyzes broadband antennas, with a special focus on Vivaldi antennas, for their suitability for through-wall radar applications. It assesses various antenna designs, emphasizing high gain, wide impedance bandwidth, and effective wall penetration capabilities. Vivaldi antennas are superior due to their broad bandwidth, high gain, and directional radiation patterns. This study further explores structural optimizations, feeding techniques, and performance enhancement strategies to refine Vivaldi antenna designs for through-wall radar systems. Through a comparative analysis and technical evaluation, this paper highlights Vivaldi antennas’ potential for improving through-wall radar systems’ imaging and sensing capabilities. This presents a pathway for future ultra-wideband advancements. Full article

(This article belongs to the Special Issue Short-Range Radar-Based Techniques for Remote Monitoring and Medical Related Applications)

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