Human Motion Detection Research Articles

A flexible piezoresistive three-dimensional strain sensor based on laser-induced graphene/nanosilver/MWCNTs for precise human all-range motion detection

Flexible piezoresistive strain sensors are crucial for monitoring human motion, but achieving the right balance between sensitivity and operating range has always been challenging. Additionally, the complexity of muscle movements across different body parts means that relying on sensors with limited dimensional sensing is insufficient. This paper presents a flexible piezoresistive three-dimensional strain sensor (FPTDSS) designed to address these challenges. The FPTDSS features a wide operating range capable of detecting various human movements and boasts a high sensitivity, with a maximum gauge factor of 20 479. It can capture strain information along both the X- and Y-axes, as well as small vibrations along the Z-axis, through its intrinsic stretching and vibration properties. The sensor's effectiveness comes from the synergy between laser-induced graphene, silver nanoparticles (a zero-dimensional nanomaterial), and multi-walled carbon nanotubes (a one-dimensional nanomaterial). The synergistic effect of nanomaterials with different dimensions enables the FPTDSS to perform three-dimensional strain sensing, allowing for accurate detection of a broad range of complex human motions without requiring intricate circuit designs or preparation processes. This approach moves beyond limited strain information to provide a comprehensive view of three-dimensional strain, making the sensor versatile for detecting everything from subtle pulse vibrations to significant joint movements.

Hierarchical elastic and conductive multiwall carbon nanotube carboxymethylcellulose silica hybrid aerogel for strain sensors

Abstract Flexible and wearable piezoelectric pressure sensors have attracted extensive interest for their potential applications in human health monitoring. However, it remains a challenge to fabricate exceedingly elastic, conductive and steady strain-sensitive aerogels. Herein, an elastic and conductive carboxymethylcellulose sodium/methyltrimethoxysilane/multiwall carbon nanotube (CMC/MTMS/MWCNT) aerogel with interconnected porous microstructure was fabricated by a solution mixing and freeze-drying technique. Owing to covalent, ionic and hydrogen-bonding interactions between flexible CMC chains, MTMS and MWCNTs, the as-prepared CMC/MTMS/MWCNT hydrophobic aerogel with 50 wt% MWCNT loading exhibits good elasticity (1500 steady compression cycles at 30% strain), a broad pressure detection range (0–150 kPa) and reasonable compression sensitivity with gauge factor of 1.02 under 20%–30% strain. Additionally, the CMC/MTMS/MWCNT aerogel was used as a strain sensor and successfully demonstrated human motion detection—not only large-scale actions (finger bending) but also small-scale muscle movements (swallowing). With these results, our CMC/MTMS-50 aerogel is a promising candidate for utilization in flexible and wearable strain sensors.

A flexible wearable sensor based on the multiple interaction and synergistic effect of the hydrogel components with anti-freezing, low swelling for human motion detection and underwater communication.

To meet the increasing demand for wearable sensor in special environment such as low temperature or underwater, a multifunctional ionic conducting hydrogel (Gel/PSAA-Al3+ hydrogel) with anti-freezing and low swelling for human motion detection and underwater communication was prepared using gelatin (Gel), [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA), acrylamide (AAm), acrylic acid (AAc), and AlCl3. Due to reversible hydrogen bonding, electrostatic interactions and metal coordination crosslinking between the polymer networks, the resulting Gel/PSAA-Al3+ hydrogels present low swelling property in water and exhibit large tensile properties (~1050 %), high tensile strength (~250 kPa) and excellent fatigue resistance. In addition, the hydration capacity of SBMA and AlCl3 endows the Gel/PSAA-Al3+ hydrogel fantastic anti-freezing (-31.58 °C) and water retention properties. Moreover, the electrostatic interaction between SBMA and AlCl3 due to the ion hopping mechanism endows the hydrogel with excellent ionic conductivity (6.38 mS/cm). The Gel/PSAA-Al3+ hydrogel sensors present good biocompatibility and provide a wide operating range (0 %-1050 %), fast response time (229 ms) and recovery time (248 ms), high sensitivity (GF = 1.61) and excellent stability for detecting large and small body movements. The Gel/PSAA-Al3+ hydrogel shows potential applications as a wearable sensor for communication at low temperature or underwater.

Synthesis of shape-tunable PbZrTiO3 nanocrystals with lattice variations for piezoelectric energy harvesting and human motion detection

PbZr0.7Ti0.3O3 cubes with tunable sizes and cuboids have been hydrothermally synthesized. PbZrTiO3 cubes with three different Zr:Ti atomic percentages were also prepared. Analysis of synchrotron X-ray diffraction (XRD) patterns reveal...

Flexible, rapid self-healing and ultra-sensitive hydrogel sensor with dynamic multi-interactions for human motion detection

Hydrogels are extensively utilized as strain sensors in the domain of wearable devices. However, balancing mechanical properties, adhesion, and self-healing capabilities in hydrogel sensors has consistently been a research challenge. In this study, a novel P(AA-AMPS)/PEI hydrogel was synthesized through a straightforward one-step radical polymerization with acrylic acid (AA) and 2-Acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as monomers, polyethyleneimine (PEI) and AlCl3 as physical crosslinkers to effectively solve the above challenge. The P(AA-AMPS)/PEI hydrogel demonstrated good mechanical properties with a tensile strength of 42.54 kPa, a high self-adhesion strength to pigskin up to 37.48 kPa, and rapid self-healing efficiency of 100 % after 1 h. The P(AA-AMPS)/PEI hydrogel sensor exhibited good stability, precision, and dependability in real-time monitoring of both subtle and large human movements due to the ultra-high sensitivity (GF values were 5.92, 13.82, and 20.89 within the strain ranges of 0–300 %, 300–600 %, and 600–850 %). It must be noted that the sensing performance of the healed P(AA-AMPS)/PEI hydrogel remained unchanged. The developed hydrogel sensor exhibited promising applications in wearable devices, electronic skin, and human–machine interaction.

Piezoresistive Sensor Based on Porous Sponge with Superhydrophobic and Flame Retardant Properties for Motion Monitoring and Fire Alarm.

Polyurethane sponge is frequently selected as a substrate material for constructing flexible compressible sensors due to its excellent resilience and compressibility. However, being highly hydrophilic and flammable, it not only narrows the range of use of the sensor but also poses a great potential threat to human safety. In this paper, a conductive flexible piezoresistive sensor (CHAP-PU) with superhydrophobicity and high flame retardancy was prepared by a simple dip-coating method using A-CNTs/HGM/ADP coatings deposited on the surface of a sponge skeleton and modified with polydimethylsiloxane. With great sensitivity and durability (>3000 cycles) as well as fast response/recovery time (152 ms/178 ms), the sensor is capable of monitoring human movement as a wearable device. The modified material surface has a hydrophobicity angle of 153°, which provides significant self-cleaning and weather resistance. Furthermore, the CHAP-PU sensor is able to respond stably to underwater movements. Importantly, when the sponge was directly exposed to an open flame, no flame spreading or dripping of molten material was detected, indicating excellent flame retardancy. Meanwhile, CHAP-PU was also equipped as a smart fire alarm system, and the results showed that an alarm signal was triggered within 2 s under flame erosion. Therefore, the flame-retardant superhydrophobic CHAP-PU sponge-based sensor shows great potential for human motion detection and fire alarm applications.

A miniaturized toroidal piezoelectric device for monitoring human movement and powering wearable electronics

Abstract Wearable micro-energy devices offer the exciting potential to serve as self-powered monitors for human motion and as power sources for wearable electronics. However, challenges persist, particularly in low-frequency energy conversion and multi-dimensional motion monitoring. In this paper, we report a highly stable and durable miniaturized toroidal piezoelectric device (MTPD) to detect and recognize human movement with exceptional sensitivity, while also storing the generated electrical energy in capacitors to power wearable electronics. The system features a PVDF film that oscillates between ring brackets in a contactless manner, enabling it to capture multi-directional body motion and convert it into electrical signals. By incorporating multiple magnets, the system enhances the deformation of the piezoelectric thin film, thereby improving the output voltage. Furthermore, the integration of multi-channel signal fusion within a compact space refines the accuracy of motion recognition algorithms. We have validated the MTPD’s capability to identify arm and leg movements, highlighting its potential for use in human motion detection. Additionally, we demonstrated the system viability to serve as a power source by efficient charging a capacitor within a short period.

Silkworm‐Shaped MoS2 Growing on Graphene Foam for Highly Sensitive and Flexible Strain Sensor with Full‐Scale Human Motion Detection Ability

AbstractHigh‐performance piezoresistive strain sensors (PSS) are important components of wearable electronics for human health management and are considered a key technology for future applications in fields such as artificial intelligence and human medical monitoring. Recently, many PSS have been developed based on a variety of electrosensitive materials. Among them, 3D graphene foams (GrF) have attracted significant attention owing to their excellent thermal conductivity, tensile properties, and light weight. Herein, a novel GrF‐based composite is developed by growing 2D molybdenum disulfide (MoS2) nanosheets directly. Many lathy nanosheets stand vertically on the GrF, similar to silkworms creeping on the leaf, making the composite more sensitive to mechanical deformation stimuli. The obtained MoS2@GrF composite is processed into PSS with a wide sensing range (0%–80%), high gauge factor values (16 below 1% and 39 over 40%), detection limit of 0.1% strain with 106/123 ms response/recovery time, and good cyclic stability (≥3000 cycles). Moreover, the as‐fabricated strain sensors exhibit excellent Joule heating performance, which can be adjusted by strain. As such, the PSS allows for full‐range body motion monitoring and thermal management, which has great potential for next‐generation smart wearable electronics.

Flexible Strain Sensor Based on a Dual Crosslinked Network of PAMgA/GL/PANI Antifreeze Conductive Hydrogel

AbstractConductive hydrogels possess excellent flexibility, conductivity, and sensing properties, making them important carrier materials for flexible strain sensors. They show promising application prospects in fields such as human motion detection and artificial intelligence. This paper introduces polyaniline (PANI) and glycerol (GL) into the magnesium acrylate (AMgA) monomer and prepares the polymagnesium acrylate/glycerol/polyaniline (PAMgA/GL/PANI) hydrogel by free radical polymerization method. When the addition of PANI is 9 wt.%, the PAMgA/GL/PANI hydrogel exhibits good mechanical properties, with a tensile strength of 0.385 MPa, an elongation at break of up to 505%, a compressive strength of 1.04 MPa, and its room temperature conductivity is 1.437 S m−1. Even after freezing at −20 °C, its conductivity can still reach 1.254 S m−1. When the tensile deformation of this conductive hydrogel reaches 500%, the gauge factor (GF) reaches 10.33. In addition, the PAMgA/GL/PANI hydrogel also has good self‐healing, adhesion, and moisture retention. These excellent characteristics make it suitable as a flexible strain sensor that can not only accurately monitor human joint movements and subtle physiological signals but also serve as an encrypted information transmission medium.

High strength, high sensitivity, hydrophobic and conductive vegetable oil-based composites for human motion detection

The vulnerability of infants and young children due to their fragile bodies and inability to effectively express physical discomfort has raised widespread of concern in the society. As it continues to be difficult to develop sensors with superior mechanical qualities and response sensitivity for use in health monitoring and recognition. Here, a polymer known as, Polyurethane Thermoplastic Elastomer, enhanced by crosslinking which is prepared from Isophorone Diisocyanate (IPDI), soybean oil polyol ED, and polycaprolactone triol (PCT-L) also referred to as PTIED, was prepared based on previously prepared soybean oil polyol ED and polycaprolactone triol (PCT-L) as soft segments, with IPDI as hard segments. This was followed by the preparation of the PTIED-CNT sensor by using PTIED as a matrix and hydroxyl carbon nanotubes (CNT) as a conductive filler. The mechanical properties of the obtained PTIED-CNT sensor have been enhanced, with a tensile strength of approximately 5 MPa. The sensitivity GF of the PTIED-CNT7 % can reach up to 805.67 and remains stable after 4500 seconds of continuous operation at 10 % strain. Moreover, the device can support high stability in a simulated sweat environment and exhibit antibacterial and hydrophobic, which could be used to check for small movements, such as those of the face and throat, and could also recognize sound. Therefore, its potential applications in respiratory monitoring of infants as well as other health monitoring applications are expected.

Human presence and motion detection through electrostatic sensing

Human presence and motion detection through electrostatic sensing

A highly stretchable, self-healing, self-adhesive polyacrylic acid/chitosan multifunctional composite hydrogel for flexible strain sensors

Conductive hydrogels have emerged as excellent candidates for the design and construction of flexible wearable sensors and have attracted great attention in the field of wearable sensors. However, there are still serious challenges to integrating high stretchability, self-healing, self-adhesion, excellent sensing properties, and good biocompatibility into hydrogel wearable devices through easy and green strategies. In this paper, multifunctional conductive hydrogels (PCGB) with good biocompatibility, high tensile (1694 % strain), self-adhesive, and self-healing properties were fabricated by incorporating boric acid (BA) and glucose (Glu) simultaneously into polyacrylic acid (PAA) and chitosan (CS) polymer networks using a simple one-pot polymerization method. Furthermore, the hydrogel strain sensor constructed from the PCGB assembly had great sensing property including high sensitivity (GF = 5.7), durability and stability (5000 cycles). The hydrogel strain sensor was applied to the detection of human motion, which exhibited accurate detection behavior for both large-scale motions and small activities. A strategy to design and fabricate multifunctional conductive hydrogels integrating high stretchability, self-healing, self-adhesion and good biocompatibility was provided, and the multifunctional conductive hydrogels broadened the application of hydrogel-based wearable sensor.

Vision-based approach for human motion detection and smart appliance control

This study focuses on the use of computer vision technology and motion detection sensors to create an intelligent system that recognizes human presence in monitored spaces. The system uses a relay module for automation and control of household appliances while sensing motion detection, operated by an ESP32 microcontroller. This innovative solution addresses two major issues in home automation: reliable human presence recognition and seamless appliance control. The research merges a camera-based vision system with motion sensors, comparing motion and vision-based identification. The ESP32 microcontroller improves motion detection precision and context awareness by integrating motion sensors and computer vision technologies. The integration of a camera module allows real-time analysis and recognition of human presence, reducing false alarms. The relay module also enables automated control of home appliances, synchronizing and feedbacking operations with sensed human presence. The dynamic adaptation of the system improves user convenience and energy efficiency.

TPU-Supported Ti3C2Tx/TiO2/Ru electrospun mat towards flexible and multi-functional sensors for human motion and NH3 detection

Nowadays, the demand for smart wearable devices has been increasing significantly. Integrating multiple functions into a single sensor has become a continuous challenge for researchers. To address these issues, a novel two-dimensional material, MXene (Ti3C2Tx), is now being utilized to fabricate flexible multifunctional sensors. TPU (thermoplastic polyurethane) fiber mats are prepared through electrospinning. Using TPU fiber mats as the substrate, MXene/TiO2/Ru composites are synthesized through a simple and effective method and loaded onto the fiber mats. Experimental tests have revealed that the TPU/MXene/TiO2/Ru flexible sensor exhibits characteristics such as a large stretching range, good durability, high sensitivity, and excellent breathability. The response of the TPU/MXene/TiO2/Ru flexible sensor can reach up to 80.4 k when it is stretched to 120 % of its original length at a stretching speed of 0.5 mm/s. Moreover, this sensor can be used to detect movements in human wrists, arms, faces, legs, fingers, and even vocal cord vibrations, responding to voice recognition through specific word combinations. Furthermore, this sensor exhibits a maximum response of 15.06 % to 100 ppm NH3 at room temperature, accompanied by high selectivity and stability, indicating its excellent multifunctionality in the fields of human health and environmental protection.

Human motion recognition based on feature fusion and residual networks

Addressing the issue of low recognition accuracy in human motion detection when relying on a single feature, a novel approach integrating Frequency Modulated Continuous Wave (FMCW) radar technology with a Residual Network (ResNet) architecture has been proposed. This method commences by capturing the echo signals of six distinct human motions using an FMCW radar. These signals undergo preprocessing, followed by the application of a two-dimensional Fourier transform to derive the Range-time Map (RTM) and Doppler-time Map (DTM) representations of the human motions. To enhance the extraction and precise identification of human motion features, the conventional single-channel input structure of convolutional neural networks has been refined. Specifically, the ResNet18 residuals have been upgraded by incorporating Inception V1 modules. Furthermore, the Convolutional Block Attention Module (CBAM) has been integrated to engineer a dual-channel fusion residual network capable of recognizing and classifying human motions effectively. Empirical results demonstrate that the recognition accuracy of human motion detection has been enhanced by 1–4% when employing this dual-feature fusion structure, as compared to single-feature domain recognition. This improvement attests to the robust recognition capabilities of the proposed model.

Flexible pressure sensor based on CNTs/CB/PDMS sponge with porous and microdome structures for sitting posture discrimination

The application fields of flexible pressure sensors are constantly expanding benefiting from their characteristics of being lightweight, flexible, easy to install, etc. Various structures have been developed for the purpose of improving the sensing performances of these sensors. However, the traditional structure designs typically enhance only a single aspect of performance. In this study, a flexible pressure sensor based on carbon nanotubes (CNTs)/carbon black (CB)/polydimethylsiloxane (PDMS) conductive sponge (CCPS) with both porous and microdome dual microstructures is prepared through the double template and swelling ultrasound methods. The introduction of two microstructures leads to the synergistic effect of dual sensing mechanisms, and the dual sensing mechanisms have been discussed according to the changes in microstructure morphology and finite element analysis results. Thanks to the synergistic effect of dual sensing mechanisms, CCPS exhibits comprehensive pressure sensing performances including a wide pressure sensing range of more than 350 kPa, high sensitivity under low pressure (7.10 kPa−1 over 0–25 kPa, 2.96 kPa−1 over 25–135 kPa, 1.09 kPa−1 over 135 kPa), and satisfactory long-term using performance of over 2000 cycles. CCPS is finally demonstrated for applications such as human motion detection, Morse code, and sitting position discrimination, indicating its broad application possibilities.

Highly breathable and stretchable strain sensors based on porous films for human motion and gas detection

With the rapid development of flexible wearable sensors in the fields of medical detection and environmental monitoring, it is urgent to develop multifunctional sensors with high sensitivity, fast response, wide sensing range, excellent comfort and multi-stimulus response. In this paper, a porous thermoplastic polyurethane (TPU) film with high stretchability and breathability was prepared by facial liquid phase separation, and a flexible wearable sensor was developed through vapor deposition of polypyrrole (PPy) within the porous TPU film matrix. The fabricated sensor can detect pressure, strain and gas, has a wide pressure detection range (up to 98 kPa), fast response speed (100 ms), sensitivity of up to 0.33 kPa−1 and working stability. Furthermore, it has an extremely high tensile strength of 790 % and can operate in the 0–400 % stretch range with a maximum sensitivity of 238.2. Importantly, the flexible porous TPU/PPy multifunctional sensor has excellent breathability and the capability to monitor NH3 gas, and the gas detection limit can reach 10 ppm. This work provides a new route for achieving high-performance and wearing comfortable strain sensors with broad application prospects in human activity detection and NH3 gas monitoring devices.

Self-healing and transparent ionic conductive PVA/pullulan/borax hydrogels with multi-sensing capabilities for wearable sensors

Conductive hydrogels as wearable sensors have been used for numerous applications in human motion detection, personal healthcare monitoring and other diverse scenarios. However, it remains a challenge to integrate self-healing ability, multiple sensing capabilities, and transparency in one single unit. In this work, multifunctional polyvinyl alcohol (PVA)/Pullulan/Borax conductive hydrogels were fabricated by introducing borate ester bonds and hydrogen bonds. The described hydrogels showed fast self-healing properties, which could autonomously completely recover within 15 s. The hydrogels possessed high optical transparency (92.9%) in the visible light range and had multi-sensing capabilities, such as strain, temperature and humidity sensing. The assembled hydrogel sensor displayed a high strain sensitivity of 2.74 within the strain range of 300%, and it could be used to monitor human motions such as finger and wrist bending. In addition, the hydrogel sensor could sense temperature variations with a temperature coefficient of resistance of −0.914 °C−1 over 28–46 °C. Besides, the hydrogel sensor demonstrated the humidity sensing ability and can recognize human inhale and exhale. The overall sensing performance of the PVA/Pullulan/Borax hydrogel was satisfactory and repeatable. This conductive hydrogel shows great potential in wearable electronics and personal healthcare and inspires a new generation of multifunctional hydrogel sensors.

Skin‐Like Soft Thermoelectric Composites with a “J‐Shaped” Stress–Strain Behavior for Self‐Powered Strain Sensing

AbstractPolymer thermoelectric (TE) materials present a promising alternative to actuating low‐power wearable electronics without an additional power source, among which poly(3,4‐ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS) is a promising candidate. However, it is too hard and brittle to integrate into wearables seamlessly and comfortably. Herein, PEDOT:PSS‐based TE composites with simultaneous softness and stretchability are fabricated by a water‐borne polyurethane (WPU) and PEDOT:PSS mixture containing the judiciously chosen ionic liquid (IL) and subsequent drop casting. The obtained composites show a stable TE voltage, high stretchability (>500%), ultra‐flexibility, and excellent sensitivity (gauge factor = 1251). More importantly, it exhibited “J‐shaped” stress–strain curves resembling human skins after a loading/releasing treatment. The skin‐like nonlinear elastic behavior combines enough softness in the “toe” region, high stretchability, and a strong strain hardening at the late deformation stage, enabling its seamless and comfortable integration with the human body. Given the desired mechanical performance and strain‐sensing capability, the composite is designed to serve as a self‐powered sensor with high sensitivity and accuracy, suggesting a high potential in human motion detection. This work demonstrates the versatility of the developed skin‐like PEDOT:PSS‐based composites in wearable electronics.

Carbon Quantum Dot/Multiwalled Carbon Nanotube-Based Self-Powered Strain Sensors for Remote Human Motion Detection

Carbon Quantum Dot/Multiwalled Carbon Nanotube-Based Self-Powered Strain Sensors for Remote Human Motion Detection