Near-field Sensor Research Articles

Near-field metasurface sensor for an early-stage breast cancer detection

In this paper, a novel and highly sensitive metasurface sensor for microwave breast tumor detection is proposed. The proposed sensor array comprises 8 × 8 small-size sensor elements that are capable of reacting to changes in both electric and magnetic fields. This allows the sensor to detect even minor variations in the surrounding medium, resulting in improved sensitivity. Additionally, designing a sensor array improves sensitivity by covering all areas of the breast tissues with multiple small sensor elements. Numerical studies have been conducted to assess the sensor sensitivity using realistic healthy and non-healthy breast models with diagnosed tumors placed at different locations within healthy breast models in the CST simulation environment at varying stand-off distances. An experiment was conducted to validate the sensor’s concept. It involved testing a metasurface sensor with phantoms resembling both healthy female breast tissues and those with a 10 mm tumor. The results from simulations and experiments demonstrate that the metasurface sensor is capable of detecting breast tumors at different distances. For safety compliance, specific absorption rate (SAR) values were obtained through both simulation and experimentation. The simulated SAR values were calculated to be 0.357 W/kg and 0.216 W/kg at 1 g and 10 g, respectively, using 17 dBm for safety. The measured SAR values were 0.101 W/kg and 0.1 W/kg at 1 g and 10 g, respectively.

Spatiotemporal Information, Near-Field Perception, and Service for Tourists by Distributed Camera and BeiDou Positioning System in Mountainous Scenic Areas

The collaborative use of camera near-field sensors for monitoring the number and status of tourists is a crucial aspect of smart scenic spot management. This paper proposes a near-field perception technical system that achieves dynamic and accurate detection of tourist targets in mountainous scenic areas, addressing the challenges of real-time passive perception and safety management of tourists. The technical framework involves the following steps: Firstly, real-time video stream signals are collected from multiple cameras to create a distributed perception network. Then, the YOLOX network model is enhanced with the CBAM module and ASFF method to improve the dynamic recognition of preliminary tourist targets in complex scenes. Additionally, the BYTE target dynamic tracking algorithm is employed to address the issue of target occlusion in mountainous scenic areas, thereby enhancing the accuracy of model detection. Finally, the video target monocular spatial positioning algorithm is utilized to determine the actual geographic location of tourists based on the image coordinates. The algorithm was deployed in the Tianmeng Scenic Area of Yimeng Mountain in Shandong Province, and the results demonstrate that this technical system effectively assists in accurately perceiving and spatially positioning tourists in mountainous scenic spots. The system demonstrates an overall accuracy in tourist perception of over 90%, with spatial positioning errors less than 1.0 m and a root mean square error (RMSE) of less than 1.14. This provides auxiliary technical support and effective data support for passive real-time dynamic precise perception and safety management of regional tourist targets in mountainous scenic areas with no/weak satellite navigation signals.

Noncontact Rotational Speed Measurement with Near-Field Microwave of Open-Ended Waveguide

Rotational speed measurement is important for many applications. Here, a noncontact rotational speed test method based on the detection of the periodically perturbed near-field microwave of an open-ended waveguide is proposed. Both simulations and experiments were conducted to verify the near-field microwave rotational speed sensor. The constructed rotation speed sensing system was composed of a standard open-ended WR-42 waveguide (in our measurements, a waveguide-to-coaxial adapter was used to represent an open-ended waveguide) working at ~18 GHz, a radio frequency (RF) circulator, a signal generator, a, RF detector and an oscilloscope. A rotating fan to be measured was placed close to the waveguide’s mouth and, thus, the waveguide’s reflection coefficient was periodically modulated by the rotating fan blades. Then, the RF detector converted this varying reflection coefficient into a direct current (DC) voltage, namely, a periodical waveform. Finally, the rotational speed of the fan could be extracted from this waveform. Measurements using both the proposed near-field microwave method and conventional optical transmission/reflection methods were conducted for verification. The effect of the rotating fan’s location relative to the waveguide’s mouth was also studied. The results show the following: 1. The proposed method works well with a rotational speed of up to ~5000 RPM (rounds per minute), and an accuracy of 1.7% can be achieved. 2. Metallic or non-metallic fan blades are all suitable for this method. Compared with the existing radar method, the proposed method may be advantageous for rotation detection in a constrained space.

Highly sensitive near-field leakage-enhanced optical fiber SPR sensor based on gold nanoarrays modulation

A novel near-field leakage-enhanced optical fiber surface plasmon resonance (NLF-SPR) sensor based on the synergistic sensitization of cuboid gold nanoarrays and WSe2 film is proposed for the first time to our knowledge. The sensor is composed of a side-polished multimode fiber, a continuous gold film, a continuous tungsten selenide (WSe2) film, and well-arranged cuboid gold nanoarrays. The sensor leverages the high carrier mobility characteristic of the WSe2 film, the near-field leakage enhancement arising from the nanoarrays structure, and the localized electric field enhancement property introduced by nanotips to enhance the refractive index sensitivity. In order to optimize the spectral characteristic, the modulation of electric field distribution and spectral characteristic by the structural parameters of gold nanoarrays is investigated through three-dimensional (3D) finite element simulation. Results show that in the refractive index range of 1.3332–1.3432 refractive index unit (RIU), the average sensitivity of the NLF-SPR sensor can reach up to 10108 nm/RIU, and the highest sensitivity can reach up to 14692.46 nm/RIU. The average sensitivity and the highest sensitivity are 1.87 times and 2.56 times higher, respectively, than those of the side-polished fiber SPR sensor with a monolayer gold film. Furthermore, the experimental results demonstrate that the near-field leakage enhancement introduced by gold nanoarrays improves the performance of the fiber SPR sensor, resulting in a 49.3 % increment in sensitivity. The experimental results are in agreement with the trend of the simulation results. Even better performance improvements have been achieved compared to existing methods and a more flexible approach to performance tuning is provided. With the maturity and development of various nanoarray processing techniques such as focused ion beam, electron beam lithography, and nanoimprint lithography, the proposed NLF-SPR sensor has the potential to be fabricated on a large scale and is expected to be widely employed in biomedical, clinical applications, and other fields.

Review of Microwave Near-Field Sensing and Imaging Devices in Medical Applications.

Microwaves can safely and non-destructively illuminate and penetrate dielectric materials, making them an attractive solution for various medical tasks, including detection, diagnosis, classification, and monitoring. Their inherent electromagnetic properties, portability, cost-effectiveness, and the growth in computing capabilities have encouraged the development of numerous microwave sensing and imaging systems in the medical field, with the potential to complement or even replace current gold-standard methods. This review aims to provide a comprehensive update on the latest advances in medical applications of microwaves, particularly focusing on the near-field ones working within the 1-15 GHz frequency range. It specifically examines significant strides in the development of clinical devices for brain stroke diagnosis and classification, breast cancer screening, and continuous blood glucose monitoring. The technical implementation and algorithmic aspects of prototypes and devices are discussed in detail, including the transceiver systems, radiating elements (such as antennas and sensors), and the imaging algorithms. Additionally, it provides an overview of other promising cutting-edge microwave medical applications, such as knee injuries and colon polyps detection, torso scanning and image-based monitoring of thermal therapy intervention. Finally, the review discusses the challenges of achieving clinical engagement with microwave-based technologies and explores future perspectives.

A CMOS-integrated terahertz near-field sensor based on an ultra-strongly coupled meta-atom

Recently, plasmonic-based sensors operating in the terahertz frequency range have emerged as perspective tools for rapid and efficient label-free biosensing applications. In this work, we present a fully electronic approach allowing us to achieve state-of-the-art sensitivity by utilizing a near-field-coupled electronic sensor. We demonstrate that the proposed concept enables the efficient implementation and probing of a so-called ultra-strongly coupled sub-wavelength meta-atom as well as a single resonant circuit, allowing to limit the volume of material under test down to a few picoliter range. The sensor has been monolithically integrated into a cost-efficient silicon-based CMOS technology. Our findings are supported by both numerical and analytical models and validated through experiments. They lay the groundwork for near-future developments, outlining the perspectives for a terahertz microfluidic lab-on-chip dielectric spectroscopy sensor.

High-Resolved Near-Field Sensing by Means of Dielectric Grating With a Box-Like Resonance Shape

High-Resolved Near-Field Sensing by Means of Dielectric Grating With a Box-Like Resonance Shape

Design of Long-Life Wireless Near-Field Hydrogen Gas Sensor.

A compact wireless near-field hydrogen gas sensor is proposed, which detects leaking hydrogen near its source to achieve fast responses and high reliability. A semiconductor-type sensing element is implemented in the sensor, which can provide a significant response in 100 ms when stimulated by pure hydrogen. The overall response time is shortened by orders of magnitude compared to conventional sensors according to simulation results, which will be within 200 ms, compared with over 25 s for spatial concentration sensors under the worst conditions. Over 1 year maintenance intervals are enabled by wireless design based on the Bluetooth low energy protocol. The average energy consumption during a single alarm process is 153 μJ/s. The whole sensor is integrated on a 20 × 26 mm circuit board for compact use.

High Energy Physics Applications on Fiber Optic Sensors in Relative Humidity

Our multidisciplinary research group has been conducting studies in recent years on the use of fiber grating-based sensors for relative humidity measurement in the Compact Muon Solenoid (CMS) instrument at CERN in Geneva. In order to monitor low relative humidity (RH) values even in cold temperatures, our multidisciplinary research group has been working to develop near-field fibre optic sensors based on tin dioxide particle layers, in light of the extensive research conducted in the past few years to evaluate the radiation hardness capability of fibre optic technology in high-energy physics settings. Compared to other sensor types, optical fiber sensors provide several advantages. These benefits mostly stem from the characteristics of optical fibers, which include their tiny size, inexpensive, electromagnetic passivity, resistance to high pressure, and resistance to high temperatures. Sensing is the process of measuring variables like temperatures, stress, or angular velocity by examining the characteristics of light. To evaluate the sensors' performance under the circumstances needed for CERN experiments, untried tests in the [0-65] %RH range at various temperatures were conducted. There were other campaigns of progressive irradiation using γ-ionizing radiations. The results obtained show that the suggested technologies have great potential for usage in High Energy Physics (HEP) activities as a reliable and acceptable replacement for commercial hygrometers in the future.

Realistic sensor simulations for the digital twin

Digital twins use actual sensor data to replicate the current state of a plant in a virtual model. They can be used to evaluate the current state, predict future behavior, and thus allow to refine control or optimize operation, enable predictive maintenance as well as detection of anomalies and failures.The model of a digital twin includes models of the components, behaviors and dynamics of a system. With the ability to simulate real scenarios, such models can therefore also be used before a plant is actually implemented, e.g., to predict the actual performance, identify potential issues for the implementation and to develop optimal operation strategy and algorithms. Furthermore, interfaces may be defined, implemented, and tested with such models allowing fast and easy commissioning of the physical implementation.Accurate digital twins therefore also need to include realistic sensor models, considering adverse effects that impact their output signals. The proposed work presents approaches for accurate sensor simulations allowing researchers and industries to assess sensor performance, optimize algorithms, and evaluate system-level integration. We address Frequency Modulated Continuous Wave (FMCW) radar sensors and time-of-flight cameras as examples for far-field sensors and capacitive sensors as an example for near-field sensors. The approaches can be transferred to other sensors, e.g., ultrasound sensors, LiDAR sensors and inductive or magnetic sensors so that a wide range of industrial sensors can be covered.The proposed simulations are benchmarked with different tests, including real-world experiments and compared with the corresponding real sensors.

Simulation and experimental study of active noise barrier based on multiple-channel and decentralized system design

Active noise barrier (ANB) was helpful to enhance the noise reduction performance of noise barrier especially in low-frequency range. But it was quite difficult to realize an ideal effect in the far-field as most of the exiting work of ANB took the realization of soft boundary at the edge of noise barriers as the target. An active control strategy based on the decentralized system design was proposed in this paper. The virtual sensor technology was used in order to obtain the far-field noise signal with the help of near-field sensor, while multiple-channel design of both centralized system and decentralized system was studied. An experimental ANB system was then built in semi-anechoic chamber. The performance of the above control strategies was calculated with the actual measured parameters, and the advantages and disadvantages of different systems were compared and studied. The effectiveness of the new strategy was verified through the noise reduction tests of active noise control. The ANB established in this paper which was based on decentralized system design, could be extended to large scale usage directly in the future.

NFC-Enabled Dual-Channel Flexible Printed Sensor Tag.

Wireless sensor tags in flexible formats have numerous applications; some are commercially available for specific target applications. However, most of these wireless sensor tags have been used for single-sensing applications. In this study, we designed a printed circuit board (PCB) module (13 mm × 13 mm) for near-field communication-enabled sensor tags with both electrical resistance and capacitance read-out channels that enables dual-channel sensing. As part of the wireless sensor tag, a square antenna pattern was printed directly on a flexible poly(ethylene terephthalate) (PET) substrate and integrated into the PCB module to demonstrate a dual-channel temperature and ethylene gas sensor. The temperature and ethylene sensors were printed using a positive temperature coefficient ink and a tin oxide (SnO2) nanoparticle ink, respectively. With dual sensing capabilities, this type of sensor tag can be used in smart packaging for the quality monitoring of fresh produce (e.g., bananas) by tracking temperature and ethylene concentration in the storage/transport environment.

Systolic Time Interval Extraction in Hypertensive and Hypotensive Pig Models Using Wearable Near-Field Radio-Frequency Sensors.

Screening and monitoring for cardiovascular diseases (CVDs) can be enabled by analyzing systolic time intervals (STIs). As CVDs have a strong causal correlation with hypertension, it is important to validate STI sensor accuracy in hypertensive hearts to ensure consistent performance in this prevalent cardiac disease state. This work presents STI extraction using a non-invasive near-field radio-frequency (RF) sensor during normotension, hypertension, and hypotension in a pig model. Waveform features of semilunar and atrioventricular valve dynamics during systole were extracted to derive isovolumic contraction time (ICT) and left ventricular ejection time (LVET), benchmarked by a phonocardiogram and aortic catheterization. Study-wide mean relative ICT and LVET errors were -4.4ms and -3.6ms, respectively, demonstrating high accuracy during both normal and abnormal systemic pressures.Clinical relevance- This work demonstrates accurate STI extraction with relative error less than 5 ms from a non-invasive near-field RF sensor during normotensive, hypotensive, and hypertensive systemic pressures, validating the sensor's accuracy as a screening tool during this disease state.

Real-Time Estimation of Jet-Surface Interaction Noise

Motivated by the growing concerns for the noise emissions generated by the interaction between the engine jet and the airframe surfaces consequent to the progressive increase of the engine by-pass ratio in commercial aircraft architectures, we study the estimation of the far-field noise radiated by a jet in an installed configuration based on sensor readings in the near field of the jet. We carry out an experimental investigation of the jet-surface interaction phenomena in a simplified set-up where a flat plate is installed parallel to the nozzle axis of a subsonic jet. Real-time estimation is performed using empirical linear transfer functions identified between near-field sensors and far-field observers. The transfer function and the accuracy of the noise estimation performed are characterised as a function of jet flow conditions, type and streamwise position of near-field sensors and radial distance between the jet and the edge. This analysis can guide the positioning of near-field sensors for the implementation of closed-loop control strategies for the jet-surface interaction noise.

Jugular Venous Pulse Waveform Extraction From a Wearable Radio Frequency Sensor.

Many prevalent heart diseases can be indicated by the features of the jugular venous pulse (JVP), an efficacious indicator of right heart health. However, JVP dynamics are not widely utilized in clinical settings as its observation and sensing remain cumbersome. Non-invasive measures of cardiac behavior, including the JVP, are of growing interest to enable continuous and at-home monitoring of cardiac disorders. In this work, we propose a wearable near-field radio-frequency (RF) sensor affixed with a neck collar on the clavicle over the internal jugular vein to enable non-invasive JVP sensing. We employed a complex vector injection signal processing method to extract repeatable JVP waveform features in multiple postures. With a 21-subject human study, we demonstrated morphologically consistent JVP sensing with consistent a-, c-, and v-wave feature timings, benchmarked by synchronous electrocardiogram and phonocardiogram. Further, inter-postural experiments demonstrated the capability of the proposed system to quantify morphological changes to the JVP which are present in many cardiac disorders. The results of this work suggest the proposed near-field RF sensor is capable of non-invasive JVP monitoring, potentially enabling improved sensing in both clinical and ambulatory environments.

A Bulk Acoustic Wave Strain Sensor for Near-Field Passive Wireless Sensing.

Near-field passive wireless sensors can realize non-contact strain measurement, so these sensors have extensive applications in structural health monitoring. However, these sensors suffer from low stability and short wireless sensing distance. This paper presents a bulk acoustic wave (BAW) passive wireless strain sensor, which consists of two coils and a BAW sensor. The force-sensitive element is a quartz wafer with a high quality factor, which is embedded into the sensor housing, so the sensor can convert the strain of the measured surface into the shift of resonant frequency. A double-mass-spring-damper model is developed to analyze the interaction between the quartz and the sensor housing. A lumped parameter model is established to investigate the influence of the contact force on the sensor signal. Experiments show that a prototype BAW passive wireless sensor has a sensitivity of 4 Hz/με when the wireless sensing distance is 10 cm. The resonant frequency of the sensor is almost independent of the coupling coefficient, which indicates that the sensor can reduce the measurement error caused by misalignment or relative movement between coils. Thanks to the high stability and modest sensing distance, this sensor may be compatible with a UAV-based monitoring platform for the strain monitoring of large buildings.

Near-field sensor array with 65-GHz CMOS oscillators can rapidly and comprehensively evaluate drug susceptibility of Mycobacterium

Multidrug-resistant tuberculosis (MDR-TB) is a major clinical problem. Because Mycobacterium, the causative agent of tuberculosis, are slow-growing bacteria, it takes 6–8 weeks to complete drug susceptibility testing, and this delay contributes to the development of MDR-TB. Real-time drug resistance monitoring technology would be effective for suppressing the development of MDR-TB. In the electromagnetic frequency from GHz to THz regions, the spectrum of the dielectric response of biological samples has a high dielectric constant owing to the relaxation of the orientation of the overwhelmingly contained water molecule network. By measuring the change in dielectric constant in this frequency band in a micro-liquid culture of Mycobacterium, the growth ability can be detected from the quantitative fluctuation of bulk water. The 65-GHz near-field sensor array enables a real-time assessment of the drug susceptibility and growth ability of Mycobacterium bovis (BCG). We propose the application of this technology as a potential new method for MDR-TB testing.

Finite-Element Method Simulations of the Tunable Magnetic Anapole State in an All-Graphene Metasurface: Implications for Near-Field Sensing, Nanoscale Optical Trapping, and Cloaking

In this article, we have proposed an all-graphene metasurface where the magnetic anapole state can be dynamically tuned. The structure is composed of two layers of graphene separated by a dielectric spacer on an oxide substrate, forming a gap surface plasmons resonator structure in the long-wavelength infrared region. The top graphene layer is patterned into interconnected disks, while the interconnection is for electrical tuning purposes only. By multipolar analysis using the finite-element method (FEM) simulation, we have shown that at the particular dimension, the dominant electric dipole scattering can be minimized. This happens at the resonant point where along with the electric dipole suppression, the magnetic and magnetic toroidal dipoles destructively interfere, which gives rise to a magnetic anapole state. This resonant point can be tuned in two ways, either passively, which is the lithographical variation of structure parameters, or actively, by harnessing the chemical potential of the graphene. We have shown here both mechanisms whereby actively tuning we can shift the magnetic anapole to the far-infrared region. Through the interplay of multipole analysis, we have shown that by varying the angle of incidence, we can control the radiating channels, which can be termed an anapole switch. For the active tuning cases, by voltage mapping of the chemical potential, we have shown the effect of chemical potential on the components of the multipolar families. Our device concept and such implementations hold promise for the application in near-field sensing, nanoscale optical trapping, cloaking, etc.

Radio-Frequency Near-Field Sensor Design for Minuscule Internal Motion

We present the improved design of a radio-frequency (RF) near-field sensor for minuscule internal motion inside structures and small animals. The design tradeoffs of the antenna placement and transceiver configuration are explored experimentally by a structural setup of the fluid stirrer. The sensor performance is benchmarked in various antenna configurations and quadrature baseband sampling settings. An optimized antenna pair holder design is then applied to a continuous touchless recording for the respiration and heartbeat of nestling and adult tree swallows noninvasively. Furthermore, we also built a low-power portable all-in-one RF sensor printed circuit board (PCB) using the system parameters from previous experiments. A 40-min experiment on a conscious and free-to-move 13-day-old nestling tree swallow for respiration monitoring was successfully conducted.

Two-dimensional space–time terahertz memory in bulk SrTiO3

Polarizable materials with ultrafast responses are of great interest for the development of new sensors and memories under the influence of an electromagnetic field. Recent research efforts have demonstrated the role of optical excitation and intense terahertz (THz) pulses in inducing an ultrafast polar order and revealing a hidden phase transition in S r T i O 3 (STO), respectively. Here we show that the surfaces of STO crystals at room temperature act as ultrafast sensors that enable sub-picosecond switching through the Kerr effect and recording of polar THz intensity with spatial resolution below the diffraction limit through THz-field-induced dipole alignment followed by multi-picosecond relaxation time recovery. The contrast sensitivity and spatial resolution achieved by the STO sensor are significantly superior to those of present-day near-field THz sensors based on the linear Pockels effect, and more importantly, its ability to remain polarized for several picoseconds opens the door to a new strategy for building an ultrafast space–time THz memory.