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Finding and identifying the minimal number of sensor nodes for a sensor network is one of the most basic problems for the implementation of distributed state estimators. Despite a plethora of research studied sensor networks, most of them ignored this problem or assumed the considered sensor network comes with an ideal number of sensor nodes. We revisit this problem in the current paper. To this end, the minimal number of sensor nodes problem is first formalized and a novel observability condition, namely, minimal nodes uniform observability (MNUO), is then proposed. Next, this MNUO is applied to study the stability issues of the distributed Kalman filtering algorithm. In what follows, under the condition of MNUO, conditions to ensure its stability are given and the results about the relation of the filtering performance before and after selecting the minimal number of sensor nodes are obtained. Finally, optimization solutions and an example are given to find the minimal number of sensor nodes for a sensor network.

In vitroinvestigations of host-pathogen interactions of viruses are reliant on suitable cell and tissue culture models. Results are only as good as the model they have been generated in. However, choosing cell models forin vitrowork often depends on what is available in labs or what has previously been used. Despite the vast increase in coronavirus research activity over the past few years, researchers are still heavily reliant on: non-human cells, for example Vero E6, highly heterogeneous or not fully differentiated cells, such as Calu-3, or naturally unsusceptible cells requiring overexpression of receptors and other accessory factors, such as ACE2 and TMPRSS2. Complex cell models, such as primary cell-derived air-liquid interface epithelial models are highly representative of human tissues but are expensive and time-consuming to develop and maintain. They have limited suitability for large-scale and high-throughput analysis.Using tissue-specific expression pattern as a selection criteria, we identified human kidney cells as an ideal target for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and broader coronavirus infection. We show the use of the highly characterized human kidney cell line Caki-1 for infection with three human coronaviruses:BetacoronavirusesSARS-CoV-2 and Middle Eastern respiratory syndrome coronavirus (MERS-CoV) andAlphacoronavirushuman coronavirus 229E (hCoV-229E). Caki-1 cells show equal or superior susceptibility to all three coronaviruses when compared to other commonly used cell lines for the cultivation of the respective virus. Antibody staining against SARS-CoV-2 N protein shows comparable replication rates. Using a panel of 21 antibodies in infected Caki-1 cells using immunocytochemistry shows the location of viral proteins during replication. In addition, Caki-1 cells were found to be susceptible to two other human respiratory viruses, influenza A virus and respiratory syncytial virus, making them an ideal model for cross-comparison of not only a broad range of coronaviruses but respiratory viruses in general.Author SummaryInvestigating how viruses interact with their host relies models used for laboratory research. The closer a model matches the host, the more conclusive results are. Complex cell systems based on primary epithelial or stem cells are the gold standard ofin vitroresearch. However, they are expensive, time consuming, and laborious to establish. Therefore, cell lines remain the backbone of virus research.Despite vastly increased research into human coronaviruses following the COVID-19 pandemic, researchers continue to rely on suboptimal cell line models, for example ells of non-human origin like the VeroE6 African Green Monkey cell line. Using known expression patterns of the entry factors of the COVID-19 causative agent severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) we identified the Caki-1 cell line as a target for SARS-CoV-2. This cell line could be shown to be infectable with a wide range of coronaviruses including common cold virus hCoV-229E, epidemic virus MERS-CoV, and SARS-CoV-2 as well as other important respiratory viruses influenza A virus and respiratory syncytial virus. We could show that SARS-CoV-2 proteins can be stained for and localized in Caki-1 cells and the cells are competent of forming a cellular immune response. Together, this makes Caki-1 cells a unique tool for cross-virus comparison in one cell line.

An inward-looking wearable antenna can be used for radio communications with internal transceivers in vivo. The radio transmissions are recorded using an array of electric field sensors on the skin. This paper reports the effect of living tissue on a small cavity-backed slot antenna pressed onto soft tissue of the human torso at 2.09 GHz. In-vivo measurements were made on the skin surface at 13 torso locations using eight participants (age range, 22-68 years old), with body mass index ranging between 20.3 and 31.6 kg/m2 . Ultrasound imaging was used to determine the skin and fat thickness at every measurement location. The variation in the antenna input impedance measurements demonstrated that the human tissues (fat and muscle) affect the antenna impedance but the mismatch creates field strength measurement errors of less than 2 dB. Fat thickness in the range of 3-30 mm can slightly degrade the performance of these wearable antennas. These effects can be partly mitigated by selective location and antenna retuning to improve transceiver communications. Bioelectromagnetics. 2021. © 2021 Bioelectromagnetics Society.

Athlete movement data are integral for optimizing athlete-performance and can lead to reduced fatigue and in turn can mitigate injury risk. There is a substantial amount of scientific literature, which investigates the ability of computer-vision and inertial sensor technologies to classify sport-specific movements. The coupling of automatic sport action labeling and athlete-monitoring data can significantly enhance athlete work-load monitoring. Two recent systematic reviews of the literature, pertinent to sport-specific movement classification, revealed that the majority of journal articles use athlete-dependent classification model training and evaluation methods. These methods can significantly enhance model classification performance, particularly with movements which have high interathlete technique variation. This is because it enables models to learn features distinctive to all athletes during training. This letter details the training and evaluation of supervised machine learning models to automatically classify running surface (athletics track, hard sand, and soft sand) using features extracted from an upper-back inertial measurement unit sensor. Possible classification performance enhancement is demonstrated by comparing athlete independent and athlete dependent supervised machine learning methods. Using athlete dependent methods significantly increased the classification performance in terms of weighted average precision, recall, F1-score, and accuracy ( p ) .

Radio signal strength indicator (RSSI)-based localization methods for wireless capsule endoscopy (WCE) application require a patient to wear on-body sensors detecting the RF signals from the capsule. The main advantage of WCE is to allow the patient to live normally and to move freely during the natural transit time, which could take up to 73 hours. Changes in posture can be accompanied by the movement of soft tissues in the abdominal region. This will affect the propagation path length between on-body receiving sensors and the ingested wireless capsule, and consequently the received signal strength (RSS). This article explores potential variations in RSSI measurements created by postural change. Retroreflective markers placed in direct contact with the skin of a participant were used to represent appropriate locations of the on-body slot antennas, which could be used for WCE localization. Optical motion capture technology was used to determine an estimate of the location of the markers and corresponding skin position for different postures. The relative displacement of the markers from their initial location (the standing posture) was a maximum of 24 mm for the lying posture (supine position) for the participant with a BMI of 29 kg/m2. The maximum variation of the surface electric field of 13.77 dB was calculated using the attenuation path loss (PL) model for the human abdominal region propagation environment at 2.45 GHz. If not anticipated, posture-induced variations in RSSI can produce misleading interpretations and will require adjustments of WCE localization algorithms.

Machine learning is a powerful tool for data classification and has been used to classify movement data recorded by wearable inertial sensors in general living and sports. Inertial sensors can provide valuable biofeedback in combat sports such as boxing, however, the use of such technology has not had a global uptake. If simple inertial sensor configurations can be used to automatically classify strike type, then cumbersome tasks such as video labelling can be bypassed and the foundation for automated workload monitoring of combat sport athletes is set. This investigation evaluates the classification performance of six different supervised machine learning models (tuned and untuned) when using two simple inertial sensor configurations (configuration 1&mdash, inertial sensor worn on both wrists, configuration 2&mdash, inertial sensor worn on both wrists and third thoracic vertebrae [T3]). When trained on one athlete, strike prediction accuracy was good using both configurations (sensor configuration 1 mean overall accuracy: 0.90 &plusmn, 0.12, sensor configuration 2 mean overall accuracy: 0.87 &plusmn, 0.09). There was no significant statistical difference in prediction accuracy between both configurations and tuned and untuned models (p &gt, 0.05). Moreover, there was no significant statistical difference in computational training time for tuned and untuned models (p &gt, 0.05). For sensor configuration 1, a support vector machine (SVM) model with a Gaussian rbf kernel performed the best (accuracy = 0.96), for sensor configuration 2, a multi-layered perceptron neural network (MLP-NN) model performed the best (accuracy = 0.98). Wearable inertial sensors can be used to accurately classify strike-type in boxing pad work, this means that cumbersome tasks such as video and notational analysis can be bypassed. Additionally, automated workload and performance monitoring of athletes throughout training camp is possible. Future investigations will evaluate the performance of this algorithm on a greater sample size and test the influence of impact window-size on prediction accuracy. Additionally, supervised machine learning models should be trained on data collected during sparring to see if high accuracy holds in a competition setting. This can help move closer towards automatic scoring in boxing.

We report a sensitive, yet low-cost biosensor based on laser induced graphene for femtomolar microRNA (miRNA) detection. Combined with the miRNA extraction and magnetic isolation process, the target miRNAs were purified for further detection using laser induced graphene sensor. The laser induced graphene was prepared by direct laser writing on commercial polyimide (PI) and patterned via a computer-aided design system as an electrode for electrochemical biosensing. We found that the laser reduction of PI resulted in nitrogen-doped porous graphene, not only improving its conductivity but also its sensitivity to nucleic acids. Preeclampsia specific miRNA hsa-miR-486-5p was magnetically purified and directly adsorbed on the surface of graphene electrode via graphene-miRNA affinity interaction. Surface attached miRNAs were then electrochemically quantified using [Fe(CN)6]3-/4- redox system. Our assay demonstrates detection of miRNA has-miR-486-5p up to concentrations as low as 10 fM with excellent reproducibility. Owing to its facile fabrication, low cost and high performance, the laser induced N-doped graphene biosensor presented here shows great potential for applications in detecting miRNA in biomedical applications.

A small slot antenna has desirable characteristics for radio communications and location of an internal transceiver in-vivo medical applications. The effect of coupling between two identical antennas on the human torso was measured between 2.1 GHz antennas on the skin surface. The effect of an external field was measured as a function of the angle in the horizontal plane to quantify noise isolation. The perimeter separation loss was approximately 0.25 dB/mm. The external radio source induces currents in the soft conducting tissue resulting in a sinc radiation pattern for the antenna/body combination with a front-to-back ratio of approximately 12 dB. As the UHF band is commonly used in many non-medical applications, there is concern that external radio sources can result in a reduced signal to noise ratio and perturbed field strength measurements on the skin.

Objective : The precise location of an ingested radio transmitter/sensor is of importance in gastroenterology studies. Given the complex geometry of the gut and the very large variations in human size and electromagnetic characteristics, inverse modeling from surface-based measurements is very complex, and a unique location solution is not possible. This paper proposes a simple method based on far-field approximation of the attenuated field from the ingested transmitter. Methods : The validation experiments for an ellipsoid cylinder using averaged electromagnetic properties of the human gastrointestinal tract (conductivity 0.87 S/m, relative permittivity 62) and a Hertzian dipole radiator inside the body with a frequency of 433 MHz were conducted assuming a receiver dynamic range of less than 100 dB. Results : The surface field intensity distribution patterns and the amplitude ranges were established for different positions and orientation of the dipole in every segment of the tract. The reliability of the method was verified by comparison with finite-difference time-domain modeling. Conclusion : The method provides an analytical solution to estimate the surface field intensity depending on the dipole location and orientation with a negligible computational cost. Significance : This efficient algorithm can be incorporated into an inversion algorithm for localization of wireless endoscopy sensors to allow precise targeted treatment.

Running surfaces influence energy consumption and gait parameters including swing time and stance time. This paper compares running gait cycle time, swing time and stance time, recorded on an athletics track, soft sand, and hard sand. The training and evaluation of supervised machine learning models for running surface prediction were developed using an ankle-worn inertial sensor. Models were trained using statistical features extracted from six participants using gyroscope-based stride cycles. Six different model types were trained and the performance of each model was evaluated using precision, recall, F1-score, Matthews correlation coefficient, area under the precision–recall curve and accuracy. There was a significant statistical difference in swing time and stance time across the surfaces for all participants (p

Floating wireless sensor networks present unique communications challenges. Monopole and loop antennas have been used in seawater; however, a hemispherical antenna has the advantage of an increased efficiency and propagation range compared to other designs. This paper reports the design, construction, testing, and simulation of a hemispherical antenna and its propagation across the sea surface. Antenna modeling shows a return loss of −15 dB and a radiation efficiency of 57% in a partially submerged condition. The modeled and measured bandwidths were 47% and 36%, respectively. The radiation pattern corresponds to that of a vertical monopole antenna, when the hemisphere is floating on the water surface. Propagation range measurements in a calm coastal bay showed two separate attenuation trends of 2 dB/m and 4 dB/m, before and after the reference distance (40 m), respectively. The link range was greater than 135 m using a transmit power of 10 dBm and a receiver sensitivity of −100 dBm. Results show that the floating hemispherical antenna can be successfully deployed and used in wireless sensor network applications for coastal areas.

Organic matter in Archean hydrothermal cherts may provide an important archive for molecular traces of the earliest life on Earth. The geobiological interpretation of this archive, however, requires a sound understanding of organic matter preservation and alteration in hydrothermal systems. Here we report on organic matter (including molecular biosignatures) enclosed in hydrothermally influenced cherts of the Pleistocene Lake Magadi (Kenya; High Magadi Beds and Green Beds). The Magadi cherts contain low organic carbon (n-alkanes, hopanes, and polycyclic aromatic hydrocarbons (PAHs) indicate that a fraction of the bitumen has been thermally altered to early or peak oil window maturity. This more mature fraction likely originated from defunctionalization of dissolved organic matter and/or hydrothermal petroleum formation at places of higher thermal flux. Like the bitumens, the kerogens also show variations in thermal maturities, which can partly be explained by admixture of thermally pre-altered macromolecules. However, findings of archaea-derived isoprenoid moieties (C20 and C25 chains) in kerogen pyrolysates indicate rapid sequestration of some archaeal lipids into kerogen while hydrothermal alteration was active. We posit that such early sequestration may enhance the resistance of molecular biosignatures against in situ hydrothermal and post-depositional alteration. Furthermore, the co-occurrence of organic matter with different thermal maturities in the Lake Magadi cherts suggests that similar findings in Archean hydrothermal deposits could partly reflect original environmental conditions and not exclusively post-depositional overprint or contamination. Our results support the view that kerogen in Archean hydrothermal cherts may contain important information on early life. Our study also highlights the suitability of Lake Magadi as an analog system for hydrothermal chert environments on the Archean Earth.

Humans move continuously as part of normal living, even when asleep. The health of your heart, lungs, and digestive system-and even your mental health-are greatly improved through exercise. In modern times, technical aids have significantly reduced opportunities for physical activity; e.g., jobs are more sedentary, household chores require less physical effort, and commuting usually involves sitting in a vehicle. The result is increased obesity and ill health in the population, with the extreme case of type 2 diabetes becoming far too common in youth and younger adults. Individuals, governments, and corporations (particularly in the fitness industries) attempt to counter this through various exercise schemes, and, given the human motivation to win, sports are thought to play a leading role.

Graphene has excellent mechanical and conducting properties. Scattering parameter measurements were made in W‐band (75‐110 GHz) on 25 mm × 25 mm monolayer graphene film printed on polyethylene terephthalate (PET) substrate. From near field measurements using WR10 horn antennas the surface conductivity was de‐embedded after calibrating the s11 data against the reflection of a copper plate of same cross‐sectional dimensions as the DUT and calibrating the s21 data against horn‐to‐horn measurements. A monolayer graphene strip (20 mm × 2 mm) printed on PET substrate (25 mm × 25 mm) showed higher reflection when it was aligned with the E field of the incident radiation (as compared to H field alignment). The surface conductivity of graphene was de‐embedded from s11 measurements using standard transmission line theory and from s21 measurements using cascade matrix theory. The measured real part of the surface conductivity of graphene ranges between 0.7 and 1.8 mS/sq.

The fundamental properties of carbon nanotube (CN) loop antennas have been determined using numerical modeling in both transmitting and receiving modes. The variation of the antenna impedance, reflection coefficient, radiation efficiency, Q- factor, and extinction cross section with varying loop radii was determined numerically using method-of-moment simulations incorporating the quantum mechanical conductivity of carbon nanotubes. Contrary to metallic loop antennas (well known for their inductive input impedance), the carbon nanotube loops with a large circumference show capacitive reactance over the entire frequency range. Therefore, one cannot make CN loop to act as an inductive radiator or even a simple inductor (when $\boldsymbol {ka} \to 0$ ) if the circumference is beyond ∼56 μm. However, the carbon nanotube loops with circumference smaller than ∼56 μm exhibit properties similar to ordinary loop antennas by going through antiresonance and then resonance regions. Despite the dispersive conductivity model, carbon nanotube loop antennas possess normalized dispersion relation, which is linearly related to the frequency.

Frequency-selective surfaces (FSSs) are commonly employed at microwave frequencies in electromagnetic filtering applications. This paper reports the use of cascaded dual miniaturized elements for radio secure environments where miniaturized elements have been used creating a reduced unit cell (μm. The linearly polarized transmission response was investigated numerically by exploring the scattering parameters and the surface currents at resonance. Miniaturized elements in both single and cascaded FSS structures, have been explored to create both broadband and multiband responses across the L and S frequency bands. The theoretical and experimental results were in good agreement for the fabricated dual element dual layer translated band-stop FSS, displaying a resonant frequency reduction of 70% compared to a square loop with the same dimensions, along with significantly broad operation bandwidths of 118% and 104% for simulated and measured, respectively. These improvements were due to the selection of the individual elements in the array, their geometric arrangement, and the introduction of additional layers with lateral offsets.

Researchers have heralded the power of inertial sensors as a reliable swimmer-centric monitoring technology, however, regular uptake of this technology has not become common practice. Twenty-six elite swimmers participated in this study. An IMU (100Hz/500Hz) sensor was secured in the participant's third lumbar vertebrae. Features were extracted from swimming data using two techniques: a novel intrastroke cycle segmentation technique and conventional sliding window technique. Six supervised machine learning models were assessed on stroke prediction performance. Models trained using both feature extraction methods demonstrated high performance (≥ 0.99 weighted average precision, recall, F1-score, area under ROC curve and accuracy), low computational training times (3 seconds - bar XGB and when hyperparameters were tuned) and low computational prediction times (1 second). Significant differences were observed in weighted average stroke prediction F1-score (

The accurate location of an internal radio transmitter is important for long-term patient monitoring. An inverse solution for the surface field attenuation-based algorithm provides a simple position estimation but is degraded by noise and movement artefacts. Using the minimum cost function between the predicted and experimentally received signal strength indicators (RSSI) for four skin-surface receivers, the localization accuracy within 10 mm was achieved even with movement and external Gaussian noise. The relationship between RMSE value of each coordinate component in 3D under various noise levels provides a location accuracy estimate.

Sand sports include running, volleyball, soccer, beach flags, ironman, and fitness training. An increased amount of soft tissue injuries have been widely reported. A novel technique of determining the surface stiffness of beach sand in-situ used a simple drop-test penetrometer. The relationship between drop height and the depth of penetration squared was linear (Pearson’s correlation coefficient r2 > 0.92). The stiffness ratio between the soft dry sand and ocean-saturated wet sand compacted by eight hours of coastal water exposure was approximately seven, which was similar to previously reported stiffness measurements in a sand box. However, the absolute stiffness values were much smaller. While this technique was manually operated, an automatic system is postulated for future studies.

Variability in the running surface can cause an athlete to alter their gait. Most literature report running on grass, a treadmill or athletics running tracks using inertial sensors. This study compares the signals obtained by 9 degrees of freedom (DOF) inertial-magnetic sensors incorporating an accelerometer (±16 g), gyroscope (±2000°/s) and magnetometer (±8 gauss). The sensors were placed on the participant’s shank, knee, lower spine and upper spine, and the participants were asked to run on three different surfaces (running track, hard sand and soft sand). The calculated player loads for a 400 m run on each surface type was very similar. The mean and standard deviation values were 577 ± 130, 581 ± 128, 568 ± 124 for soft sand, hard sand and the running track, respectively. This did not correlate with the participant’s self-assessment RPE (Rate of perceived exertion), which demonstrated running on soft sand to be significantly more challenging, yielding a mean and standard deviation of 5.3 ± 2.5 (Hard to Very Hard). Soft sand running had a decreased swing time duration but increased variability (0.44 ± 0.02 s—Swing Time, 6.5 ± 1.1%—CV), hard sand running had the longest swing and intermediate variability duration (0.46 ± 0.02 s—Swing Time, 3.30 ± 2.58 %—CV) and running track running had the medium swing time but lowest variability (0.45 ± 0.02 s, 2.7 ± 0.9%—CV). Gait dominance was not consistent across the surfaces for each participant and remained below a ratio of 0.4. These results provide an insight into how athletes modify their gait mechanics to accommodate different running surfaces.

Laser reduction of graphene oxide is a promising technology for manufacturing advanced devices such as supercapacitors, sensors and transistors, owing to its distinctive advantages in selective and localized GO reduction, direct micro-nanoscale patterning, and no requirement for chemicals. However, the fundamental mechanism underlying the laser induced reduction is still not well understood. In this paper, we demonstrate that by adjusting the power and scanning speed of a 780 nm femtosecond laser, not only can one distinguish, but also effectively tune, two coexisting sub-processes during the laser reduction, namely the direct conversion from sp3 to sp2 carbon and removal of oxygen functional groups. Different oxygen containing groups demonstrate varied degrees of reduction when the power of the laser was varied. Our study provides solid and direct evidence for the coexistence of two sub-processes in the laser induced reduction of graphene oxide, which is essential for both mechanistic understanding and practical adoption of this technique in real word applications.

Student engagement continues to be a major challenge, particularly in electromagnetics courses. This is independent of whether courses are compulsory or elective. This paper presents an approach to assessing students that provides them with an opportunity for experiential learning, following Kolb’s learning cycle. Final year students are required to develop and complete two experimental projects over the 12-week trimester. At the outset of each project, pairs of students choose a three-line project outline; projects are unique to each two-person group with an obscure but practical industrial outcome designed to complement the lecture material. To succeed, students must continue to discuss their project strategies, measurements and final applications with the teaching team throughout the trimester. Students have rated the course experience very highly, and in some cases, their projects have enhanced their post-graduation employment opportunities in the field directly related to one of their projects.

A tuned small slot antenna has been used for radio communications with internal transceivers/transmitters for invivo medical applications. The 2.45 GHz properties (permittivity and conductivity) shows that porcine skin tissue can be used as a substitute for human skin tissue in medical applications. In this study, a measure of the E-field distribution on the skin surface of human and porcine tissue is presented. Ex vivo measurements on boneless layered pork belly-fat (45mm thick 300mm x 150 mm sample of skin, fat and muscle) were compared with numerical modelling for a subdermal PIFA tuned antenna. The surface electric field distribution is quite well matched to an analytical formula over a 70dB dynamic range. The conductivity $(\sigma = 4 \mathrm{S}/\mathrm{m}, \varepsilon_{\mathrm{r}} = 10)$ and relative permittivity adjusted to fit the measurement profile aligned with previously reported values. These results support the strategy that field strength measurements can be used to locate an injects radio transmitter.

A new method to measure the surface conductivity $\sigma_{s}$ of thin conductors has been recently proposed, that requires placement of a narrow strip inside a rectangular waveguide. Infinite series appear in the calculations required to extract $\sigma_{s}$ from the measured scattering parameters. In this paper, we explore the convergence of the different series that are associated with two choices of basis functions (uniform & cosh). We also show the impact of the series truncation on the final computed values of the complex surface conductivity of 10- $j$ 10mS=Sq at 10GHz.

This paper reports the effect of seawater conductivity on gain, efficiency and resonant frequency of a hemispherical helical antenna. The size of the copper ground plane for the hemispherical antenna can be reduced using conductive seawater as part of the ground plane for the antenna. Seawater increases the gain from 6 dBi to 8 dBi but with a decreased efficiency. The simulated radiation efficiency of the antenna on water surface is 61%. Specific Absorption Rate (SAR) results show absorption of 2.19 W/kg. This paper also reports the design of a low cost floating buoy. The buoy provides a waterproof setup for the circuitry and antenna. The buoy can be effectively used for shallow water coastal monitoring.

A thin, flexible, insulated wire submerged in seawater forms a coaxial cable which has attenuation at ultra-high frequency (UHF) dependent on the operating frequency, the diameter of the insulating material and the diameter of the inner conductor. An extension of the insulated wire above the surface through a spherical float forms a monopole antenna. Attenuation through the wire depends on the conductivity and temperature of seawater. This paper reports the effect of electromagnetic (EM) wave propagation at 433 MHz through insulated wires with different radii of the insulating material and inner conductor. The attenuation was calculated and measured in the range of 32-47 dB/m. The propagation from the monopole antenna to a fixed shore based receiver was measured to be approximately equal to 1 dB/m. The propagation measurements were compared with a shielded coaxial cable. Results show that the propagation range depends on the ratio of the insulation radius to conductor radius for insulated wire, however, a shielded coaxial cable showed no significant attenuation. The technique has applications in coastal wireless sensor networks where the water depth changes continually due to tide and wave motion.

Sacrum located IMU sensors were used to monitor three-axis acceleration and three-axis rotation from elite swimmers in competition conditions. The intrastroke velocity was determined for each swimmer using their preferred swim stroke (freestyle, backstroke, and breaststroke) using three different calculation techniquesdual-axis acceleration, dual-axis acceleration eliminating the static gravity constant, and altitude and heading reference system. The mean intrastroke velocity variation (averaged over one 50-m lap) in freestyle swimming was less than 0.6 in all cases. This resulted in a timing under-estimate of less than 0.60ms for freestyle, 4.0ms for breaststroke, and a timing overestimate of less than 6.2ms for backstroke. The difference was less than 5 over the complete stroke (one way ANOVA p > 0.05), indicating no significant difference in the velocity profiles. These simple, robust analysis techniques can be used to quantify variations in every stroke as the swimmer fatigues, providing significant information to coaching staff and athletes.

Frequency-selective surfaces (FSSs) on thin substrates using screen printing technology are popular due to their flexible nature, low profile, easy installation, and low-cost mass production. This paper proposes the deployment of screen printed FSS on window panes in office buildings and investigates the shielding effect on the radio wave propagation through such structures. The shielding surface is an array of modified meandered squares with a unit cell size $0.083\lambda _{o}$ , on a flexible transparent substrate (polyethylene terephthalate) of relative permittivity 3.4. This sheet was then bonded on the window glass. With this FSS, desirable shielding is achieved in the frequency range from 1.5 to 2.5 GHz, with a potential application of shielding for the Universal Mobile Telecommunications System 2 GHz frequency band, while allowing all other bands to pass with little attenuation. Investigations involved the transmission response through the unprinted and printed substrate with and without standard window size float glass. With the optimized FSS design, good agreement was achieved between the theoretical and experimental results, validating the manufactured prototype. Measurements indicate that the FSS window has approximately 38 dB better rejection in 1.5–2.5 GHz band than that of the unshielded window. However, the notch frequency depends on the permittivity and thickness of the glass, and the angle of incidence on the surface. The FSS design can be tuned to shield various frequency bands by rescaling the various physical parameters of the element.

Frequency selective surfaces (FSSs) have applications across multiple disciplines due to their unique electromagnetic properties. This paper investigates the use of both rounded square loops, and simple loop type dual elements arranged in unique patterns, to control the transmission and reflection bandwidth and resonant frequencies over KU and K frequency bands supported by equivalent circuit models. The FSSs were fabricated using laser engraving to create conductive loop type elements on a thin, flexible and optically transparent Mylar substrate (relative permittivity of 2.7 and thickness of 65 μm). The frequency response of the surfaces are controlled through the element self-inductance and capacitive coupling with neighbouring elements. This work shows that different arrangements result in the formation of multiple distinct resonances. The theoretical and experimental results were in good agreement where rounded squares and dual element arrays were employed to create broadband and multiband band-stop FSSs. A polarization sensitive surface exhibited stop-bands at 12 and 16 GHz in transverse electric polarization and a stop-band at 14.4 GHz in transverse magnetic polarization. This technique can be applied to any periodic array through careful selection of the individual elements in the array, as well as their arrangement.

Temperature controlled food transport is essential for human safety and to minimise food waste. The thermal properties of food are important for determining the heat transfer during the transient stages of transportation (door opening during loading and unloading processes). For example, the temperature of most dairy products must be confined to a very narrow range (3–7 °C). If a predefined critical temperature is exceeded, the food is defined as spoiled and unfit for human consumption. An improved empirical model for the thermal conductivity and specific heat capacity of a wide range of food products was derived based on the food composition (moisture, fat, protein, carbohydrate and ash). The models that developed using linear regression analysis were compared with the published measured parameters in addition to previously published theoretical and empirical models. It was found that the maximum variation in the predicated thermal properties leads to less than 0.3 °C temperature change. The correlation coefficient for these models was 0.96. The t-Stat test (P-value >0.99) demonstrated that the model results are an improvement on previous works. The transient heat transfer based on the food composition and the temperature boundary conditions was found for a Camembert cheese (short cylindrical shape) using a multiple dimension finite difference method code. The result was verified using the heat transfer today (HTT) educational software which is based on finite volume method. The core temperature rises from the initial temperature (2.7 °C) to the maximum safe temperature in ambient air (20.24 °C) was predicted to within about 35.4 ± 0.5 min. The simulation results agree very well (+0.2 °C) with the measured temperature data. This improved model impacts on temperature estimation during loading and unloading the trucks and provides a clear direction for temperature control in all refrigerated transport applications.

Presents information on the MATLAB-Based Interactive tool for teaching electromagnetics. This was created for a second-year university-level electromagnetics course using a MATLAB-based graphical user interface (GUI). It aims to improve learning outcomes, reduce staff workload, and engage online students through blended learning. The tool allows for the random generation of inputs for a large number of problems, provides automatic feedback when the answers are incorrect, and generates a report when the answers are correct. Examples of electrostatics, magnetostatics, dynamic fields, and transmission lines problem sets are presented.

Low-cost tethered buoys are important for seawater observation, coastal area monitoring, and pollution sensing. Underwater sensor networks operating at 433 MHz (ISM band) suffer high attenuation due to seawater conductivity. Significant propagation distance cannot be achieved through seawater or along the seabed. This paper reports a novel technique for communication between sensors operating in shallow water. A sensor tethered to the bottom was connected to a floating monopole antenna via an insulated wire transmission line. Experiments and calculations show that the attenuation along the transmission line was 38 dB/m. Surface propagation for buoy-to-base station was approximately 1 dB/m with a communication range of 30 m using a 10-dBm transmitter circuit with receiver sensitivity of ${-}$ 110 dBm. For buoy to buoy the surface propagation was measured as 3.5 dB/m with a communication range of 4 m. Experiments were carried out in calm water conditions. The results demonstrate that significant sensor network coverage of coastal regions is possible.

The interaction of body-worn antennas with the human body causes a significant decrease in antenna efficiency and a shift in resonant frequency. A resonant slot in a small conductive box placed on the body has been shown to reduce these effects. The specific absorption rate is less than international health standards for most wearable antennas due to small transmitter power. This paper reports the linear relationship between power absorbed by biological tissues at different locations on the body and radiation efficiency based on numerical modeling (r = 0.99). While the -10 dB bandwidth of the antenna remained constant and equal to 12.5%, the maximum frequency shift occurred when the antenna was close to the elbow (6.61%) and on the thigh (5.86%). The smallest change was found on the torso (4.21%). Participants with body-mass index (BMI) between 17 and 29 kg/m2 took part in experimental measurements, where the maximum frequency shift was 2.51%. Measurements showed better agreement with simulations on the upper arm. These experimental results demonstrate that the BMI for each individual had little effect on the performance of the antenna. Bioelectromagnetics. 39:25-34, 2018. © 2017 Wiley Periodicals, Inc.

Electromagnetic interference between a direct ray and a lateral wave was postulated theoretically but has been only observed near to the ground surface in a forest canopy. This communication reports surface measurements of the electric field profile from a 433 MHz transmitter buried up to 600 mm in sand (relative permittivity 2.13, conductivity 10−4 S/m). A strong interference pattern with nulls greater than −20 dB were observed extending laterally to more than 5 m. This interference was evident when both the transmitter and receiver lay on the surface and when separated by an above ground conducting shield. Forward modeling using the impedance method and the finite integral technique adequately predict the interference pattern. These observations impact open-pit mining, surface and buried wireless sensor networks, and under-road communications systems.

Automating measures of performance can allow for heightened understanding of how an athlete is performing, not only during a session but over time. Physical and mental performance degrades in high-intensity skilled sports like boxing as the athlete fatigues. Although the use of low cost, ubiquitous inertial sensors have been reported effective for performance classification in boxing, no assessment of a boxer's efficacy has been reported under fatigue conditions. This letter evaluates the use of inertial sensors for automatic classification of fatigue by assessing the punch consistency in terms of pitch angle, punch force through acceleration, and hand speed, using the inverse time between punches. To achieve this, bespoke software was created in MATLAB, aided by the use of an attitude and heading reference system orientation filter. Six right-handed male elite boxers from the Pacific Nations, in preparation for the 2018 Gold Coast Commonwealth Games, Australia, consented to participate in the study. A noticeable decrease in performance for both hand speed (inverse time between punches) and force production (acceleration) was observed over time during intensive training, resulting in a Pearson's correlation coefficient of r 0.97 for the acceleration component and r 0.89 for the timing component. Inertial-magnetic sensors, with bespoke software, were experimentally found to be an effective tool for the automatic classification of boxing fatigue performance metrics. This study was conducted under ethical approval (ENG1413HREC).

A novel fabrication process using a laser machining is proposed, allowing for the creation of arbitrary conductor geometries on an ultrathin dielectric substrate. During the engraving process, a thin aluminum layer is removed from a Mylar substrate, leaving a periodic conductive array. This process provides several advantages over existing techniques and may open additional applications due to the ability to economically create ultra-thin, conformal, optically transparent, light weight surfaces. The proposed technique is modelled and validated through experimental measurements of fabricated simple band-stop square and circle loop frequency selective surfaces (FSSs). Good agreement is observed between the simulated and measured results with resonances 9.9 GHz and 10 GHz for the square loop and 14.2 GHz and 14.4 GHz for the circle loop.

Laser reduced graphene has been increasingly attracting broad attention owing to its unique properties and potential applications in energy conversion and storage, flexible electronics, optoelectronics, and nanocomposites. In this study, graphene sheets decorated with Au nanoparticles are fabricated in situ using milliwatt femtosecond laser reduction. The findings reveal an enhancement in both the reduction of graphene oxide sheets and the nucleation and growth of the Au nanoparticles during the in situ laser treatment. Three stages of reactions are considered, namely, (i) the spontaneous redox reaction between HAuCl4 and graphene oxide, (ii) the laser‐induced decomposition of HAuCl4 and reduction of graphene oxide, and (iii) the localized surface plasmon resonance enhanced photoreduction in the presence of Au particles. Moreover, the Au nanoparticles form densely and evenly distributed square‐lattice‐like microcrack networks that ensure a linear resistance change over the tested strain range. This microcrack network architecture enables the development of flexible graphene/Au strain sensors with gauge factors up to 52.5, and linear behaviour up to 25.4% strain. This strain sensor is demonstrated to effectively monitor human motions. The findings leverage the resistive properties of graphene/metal nanoparticle composites with fundamental mechanisms, laying a critical step toward highly functional, low‐cost, flexible, and wearable graphene‐based electronics.

The paper describes the first field measurements using recently developed TranSIM instrumentation. The method is based on registering horizontal components of electric and magnetic field of distant lightning strokes (sferics). In fact it is an expansion of classical MT method in the VLF frequency range of 3 to 30 kHz thus providing information about conductivity distribution at the depths of approximately 50 to 300 meters. Measurements are conducted atop basalt body in the vicinity of Ipswich (Queensland) over 16 sites on 2 parallel profiles. From 20 to 50 sferics were registered at every site. Data was processed using short time Fourier transform obtaining spectrograms of electric and magnetic field. Apparent resistivity was calculated and frequency pseudo sections are presented. The apparent resistivity sections were matched with geological scheme of the site. Highly resistive zones correlate with high thickness of a basalt layer and conductive zones show where the underlying basalt sandstone is closest to the surface.