With the advancement of communication technologies, high-performance and tunable microstrip bandpass filters in the W-band (75-110 GHz) are increasingly vital for millimeter-wave systems. However, their development faces key challenges, including complex multi-parameter dependencies that hinder performance understanding, the lack of systematic analysis on graphene integration strategies, and uncertainties in achieving optimal tunability. This study employs machine learning tools to investigate how structural and coupling parameters influence core filter characteristics such as bandwidth, insertion loss, and out-of-band rejection. Based on the data-driven insights, several graphene-based integration schemes are evaluated to realize voltage-controlled amplitude modulation. Among them, a resonator-coupled configuration achieves a modulation depth of 15.10 dB at 2.5 eV, while an extended variant reaches 10.75 dB at just 0.6 eV. These results demonstrate a quantifiable trade-off between modulation depth and driving power, providing a practical reference for designing energy-efficient, reconfigurable mmWave front-end components.

Background Neonatal mortality remains a major public health challenge in low- and middle-income countries, where access to continuous physiological monitoring is often limited. Monitoring devices such as pulse oximeters and thermometers are essential for early detection of neonatal complications, yet gaps in device availability, functionality, and trained workforce capacity remain common. Few studies have simultaneously examined neonatal outcomes, monitoring device functionality, and staffing capacity within the same healthcare facilities. Methods A mixed-methods study was conducted across six public health facilities in Jimma Zone, Ethiopia. Retrospective neonatal admission records collected between June 2024 and June 2025 were reviewed to assess neonatal outcomes and causes of admission. Facility assessments were performed to evaluate the availability and functionality of monitoring devices. Focus group discussions with healthcare providers explored challenges related to monitoring practices, device functionality, and maintenance systems. Results Facility assessments revealed substantial gaps in monitoring infrastructure. Across the six facilities, 15 pulse oximeters were identified, of which only 6 were functional, while 9 were non-functional. Eleven thermometers were reported, with 7 functional and 4 non-functional. Only one functional neonatal patient monitoring system was identified. Qualitative findings highlighted recurring challenges related to equipment malfunction, lack of preventive maintenance, limited biomedical engineering support, and insufficient staff training. Conclusions Strengthening neonatal monitoring systems requires not only increasing device availability but also improving equipment maintenance systems, biomedical engineering support, and workforce training in resource-constrained healthcare settings.

Following the recognition of intra-abdominal pressure (IAP) as a vital sign in critically ill patients, substantial research has focused on improving IAP monitoring techniques and devices. The Abdominal Compartment Society’s guidelines state that any novel IAP measurement method must be validated against a reference method. Literature shows that insufflators are commonly used during laparoscopic surgeries as a reference, although their use poses challenges and requires several precautions. This research aims to investigate the agreement between IAP measurements via the bladder and insufflators during laparoscopic surgeries and to address whether insufflators can be used as a reference method to examine new IAP measurement techniques via the bladder. A prospective observational study was conducted in patients undergoing laparoscopic surgery. A total of 202 paired IAP measurements were performed in 18 patients. Patients were stratified into two study groups according to the baseline IAP (IAP0 < 12 mmHg or IAP0 ≥ 12 mmHg). The agreement between IAP measurement via the TraumaGuard bladder catheter (IAPTG) and IAP obtained via Stryker or Conmed insufflator (IAPinsuf) was assessed using correlation, concordance, Bland–Altman, and error-grid analyses. The average IAP0 was 7.5 ± 1.9 mmHg and 15.4 ± 2.6 mmHg in patients without and with IAH. We found a two-way mixed-effects absolute agreement intraclass correlation coefficient of 0.7 for patients without baseline IAH and –0.3 for the patients with baseline IAH, indicating moderate agreement between bladder and insufflation pressures only in patients without baseline IAH. Nevertheless, Pearson’s correlation coefficient revealed a high linear relationship between the measured variables in both groups. Bland and Altman’s analysis showed a bias of 2.8 ± 2.7 mmHg, with ± 5.3 mmHg as the limits of agreement for patients without IAH. In contrast, patients with IAH had a bias of 10.6 ± 5.3 and limits of agreement of ± 10.4 mmHg. The findings support not using insufflation pressure as a gold standard reference for future validation studies due to its inherent limitations.

Photoplethysmography (PPG) is a widely used optical technique for measuring physiological parameters such as oxygen saturation (SpO _2 ) and pulse rate. It forms the basis of pulse oximeters and wearable health devices. However, PPG signal acquisition is susceptible to various factors that affect accuracy and reliability. We are developing a novel PPG-based system that enhances measurement robustness to address these limitations. While this technology has significant valorization potential, a critical gap exists in understanding how regulatory requirements influence early-stage research and the pathway to market. This work evaluates how medical device regulations impact the road to market of a research prototype in early development, like our PPG-based technology. Unlike traditional approaches, this study integrates regulatory, quality, and clinical affairs (CARAQA) considerations into the early medical device development research phase. By doing so, it explores how compliance with European MDR and U.S. FDA regulations can guide academic and early-stage innovations toward successful clinical translation and commercialization.

Although graphene's THz absorption rate increases with number of graphene layers, the absorbance is limited and unsatisfactory as a practicable absorber. Patterned graphene or graphene-based surface plasmon resonance has been proved to enhance THz absorption, but the performance is prone to be affected by graphene defects and local multilayer stacks. In this paper, we proposed to use a double circular metal ring (DCMR) array to enhance both the graphene's THz absorption with an ultrawide bandwidth and the tolerance of graphene's physical impurities. A DCMR array is patterned on the top surface of graphene layer with dielectric substrates, which excites a broadband spoof surface plasmons polaritons (SPPs) in the THz frequency range. The broadband spoof SPPs locally confine and strengthen THz wave interaction with graphene, and further enhance graphene's THz absorption, which is confirmed by numerically simulated dispersion relations. A four-layer graphene composite structure is fabricated to validate the scenario, which consists of graphene, a SiO2-capped doped-silicon substrate covered by graphene, and the DCMR array on the top surface of graphene. Time domain spectroscopy test shows that the THz absorption enhancement of the graphene composite with DCMR array covers the frequency range from 0.3 to 1.1 THz with 110% bandwidth. The THz absorption of the proposed graphene composite increases to more than 70% over a wide bandwidth of 77% at 0.65 THz compared with the graphene composite without DCMR array.

The development of polarization converters is crucial for various applications, such as communication and sensing technologies. However, traditional polarization converters often encounter challenges in optimizing performance due to the complexity of multiparameter structures. In this study, we propose a novel multiparameter linear-to-circular polarization (LCP) converter design that addresses the difficulties of comprehensive optimization, where balancing multiple structural parameters is key to maximizing device performance. To solve this issue, we employ a machine learning (ML)-guided approach that effectively navigates the complexities of parameter interactions and optimizes the design. By utilizing the XGBoost model, we analyze a dataset of over 1.3 million parameter combinations and successfully predict high-performing designs. The results highlight that key parameters, such as the graphene Fermi level, square frame size, and VO2 conductivity, play a dominant role in determining the performance of the LCP converter. This approach not only provides new insights into the design of LCP converters but also offers a practical solution to the complex challenge of multiparameter optimization in device engineering.

This study explores optimization strategies for the attenuation performance and modulation depth of Graphene-based Microstrip Line Attenuators (GMSLAs). Existing GMSLAs mainly rely on rectangular attenuation units, such as single-layer graphene sheets and graphene composite sandwich structures, which have limitations in meeting diverse performance requirements. To address this, this study systematically investigates which configuration within the same class of structures yields the most optimal and reliable attenuation performance. Using finite element simulations, this study systematically examines the attenuation performance and modulation characteristics of graphene ring-shaped attenuation units with five distinct geometric configurations (circle, regular triangle, square, regular pentagon, and regular hexagon) in the 40-70 GHz V-band. The results indicate that among individual units, the hexagonal unit exhibits the highest average reflection transmission loss and modulation depth. The triangular unit demonstrates a relatively stable and high average reflection transmission loss as well as the most stable modulation depth, whereas the square unit possesses the most stable average reflection transmission loss. Furthermore, by adjusting the rotation angle of the hexagonal units, significant polarization-dependent attenuation was observed. When combining multiple hexagonal units, their performance exceeded the simple sum of individual unit performances, showing superlinear growth. This study overcomes the limitations of traditional graphene attenuation unit designs by introducing a range of geometric configurations, offering new insights into the development of highly efficient, tunable attenuators with superior performance in high-frequency bands.

Proper synchronization between transmitter and receiver ports in time-domain measurements is of great importance. This study presents a novel synchronization method that can be applied to data acquired from dual single-shot samplers in real time, diverging from the conventional approach that utilizes a single-shot sampler with an external trigger to synchronize the input signal. Following synchronization algorithm, its effectiveness is validated through experimental testing using a time-dependent, narrow-band transient radar signal. The experiments on a 5-cm thick polyvinylchloride (PVC) sample demonstrated the reliability of the proposed method. The transient radar signal utilized in the experiments had a carrier frequency of approximately 10 GHz, while data acquisition was carried out with an independent external trigger using only a 2 MHz sinusoidal signal. Applying the synchronization technique to the measurement results yielded a complex relative dielectric permittivity of (2.55 ± 0.02) - (0.23 ± 0.01)j. Using this value to calculate the speed of light in the PVC sample, the thickness was determined to be 5.29 ± 0.13 cm. Further refinement of the effective angle enhanced measurement accuracy, ultimately yielding a thickness of 4.83 ± 0.11 cm and reducing the relative error from 5.8 to 3.4%.

VO_2, a prototypical phase-change material, exhibits a reversible insulator-to-metal transition near 68 °C, accompanied by several orders of magnitude change in electrical conductivity while preserving structural integrity. Graphene, renowned for its tunable electronic properties and superior optical response, has emerged as a promising alternative to conventional periodic metal structures in metamaterials, or as an interfacial layer in composite devices. In this study, we integrate graphene and VO_2 into a multilayer heterostructured metamaterial absorber and incorporate machine learning techniques to optimize its geometric parameters, to achieve switchable high-performance absorption behavior. The designed absorber consists of a patterned metallic top layer, a graphene sheet, a VO_2-based functional layer, two dielectric layers, and a metallic aluminum ground plane. Leveraging the thermally induced phase transition of VO_2, the device enables dynamic switching of different absorption modes without changing its geometric shape and parameters. Specifically, in the metallic state of VO_2 (>68 °C), the absorber demonstrates broadband absorption performance with an average absorption exceeding 90

Photoplethysmography is a widely used optical technique to extract physiological information non-invasively. Despite its large use and adoption, multiple factors influence the signal shape and quality, including the instrumentation used. This work analyzes the variability of the DC component of the PPG signal at three source–detector distances (6 mm, 9 mm, and 12 mm) using green, red, and infrared light and four photodiodes per distance. The coefficient of variation (CV) is proposed as a new signal quality index (SQI) to evaluate signal variabilities. This study first characterizes the PPG system, which is then used to acquire PPG signals in the chest of 14 healthy participants. Results show a great DC variability at 6 mm, homogenizing at 9 and 12 mm. This suggests that PPG systems are also sensitive to the near- and far-field effects commonly reported and studied in optics, which can impact the accuracy of physiological parameters dependent on the DC component, such as oxygen saturation (SpO2).

Almost one in four critically ill patients suffer from intra-abdominal hypertension (IAH). Currently, the gold standard for measuring intra-abdominal pressure (IAP) is via the bladder. Measurement of IAP is important to identify IAH early and thus implement appropriate management in order to avoid complications. It may be possible to use anthropometric parameters to predict IAP and thus identify IAH non-invasively. This retrospective observational study investigated how the most relevant body parameters evolve in relation to IAP, and whether IAP can be predicted based on anthropometric parameters. The IAP and 28 body parameters of 96 critically ill patients were recorded. Following statistical analyses such as Pearson’s and mutual information correlation, the collected data were used to train a simulation model to examine reliable relationships between IAP, predict IAP values, and detect IAH. Three metrics were shown to sufficiently predict intra-bladder pressure (IBP) with a Pearson’s correlation of 0.75 (R2 = 0.56). These parameters are the difference between the convex and horizontal xiphoid-to-pubis distance, sagittal abdominal diameter, and abdominal compliance. Subsequently, we found 1 metric that is able to predict the presence of IAH with Pearson correlation of 0.89 (R2 = 0.79). This metric is the difference between the convex and horizontal xiphoid to pubis distance. Three measured body parameters showed a correlation of more than 50% with IBP and they are sufficient for a reliable prediction of IBP, however, IAH can be most reliably predicted based on the difference between the convex and horizontal xiphoid-pubis distance and sagittal abdominal diameter. Future studies with larger patient populations and diverse body shapes are warranted to confirm these findings.

Photoplethysmography (PPG) is a non-invasive optical technique used to extract physiological information by means of light interaction with the skin. PPG is widely used in pulse oximeters, and the evolution of wearable technologies is further enlarging its applications. A great variety of influencing factors impact the PPG waveform, making the correct feature extraction difficult and, therefore, limiting the accuracy of many PPG applications. The device hardware and software are among these influencing factors. This study evaluates the impact on the PPG signal quality of the LED viewing angle (luminous aperture) and the protective glass material, thickness, and anti-reflective coating, both important building blocks of a PPG sensor. Results suggest that the larger the viewing angle, the smaller the detected signal amplitude. The protective glass properties on the contrary does not seem to impact the detected signal amplitudes.

Textile-reinforced cementitious sandwich are lightweight, slender, non-corrosive, and cost-effective composites that have been recently proposed for structural applications. However, its composite nature depicts a complex fracture behavior, and manufacturing defects, such as a deficient interlaminar bond, can produce premature debonding. Lateral debonding can reduce up to 70% of the maximum load. Early detection of damage is key to reduce the cost and increase the impact of repair. Nondestructive testing (NDT) techniques have widely shown their ability to characterize and detect damage in cementitious composite materials. Microwave and millimeter wave (MMW) are electromagnetic (EM) NDTs that, besides not being attenuated by the insulating core, provide non-contact and real-time measurements. However, EM-based NDTs, besides Ground Penetrating Radar (GPR), have not been sufficiently explored for damage monitoring of cementitious media. Additionally, the complex fracture behavior of the composite makes the EM wave response difficult to interpret. In this manuscript, reference and artificially debonded TRC sandwich beams are tested in three-point bending and monitored with MMW spectrometry. Digital image correlation (DIC) is employed to monitor surface strain and interpret the EM wave response of the material. Results showed the sensitivity and characterization power of MMW spectrometry to different damage mechanisms such as matrix cracking, interfacial debonding, and changes in the angle of incidence, among others.

Chronic diseases are the most prevalent and non-communicable health crisis globally. Most chronic disease patients require continuous physiological monitoring, using wearable technology for timely treatment, precise illness detection, and preventive healthcare. Nonetheless, efficient power management is required for such resource-constrained wearable devices. This work aims to analyze low-power techniques (LPTs) in wearable medical devices using a data-driven approach and identify novel approaches promising higher power savings. Through an intensive literature analysis, we identify the most relevant LPTs for minimizing power consumption in wearable devices for physiological monitoring while recognizing the barriers to adopting these techniques. As a result, a novel taxonomy based on the common characteristics of the LPTs is proposed, along with strategies for the combination of LPTs. Through our analysis, we propose possible enhancements in using LPTs and suggest mechanisms for the medical device industry to facilitate their adoption. Overall, our proposed strategies guide the use of LPTs on wearable medical devices toward continuous physiological monitoring.

Photoplethysmography (PPG) is a non-invasive method used for cardiovascular monitoring, with multi-wavelength PPG (MW-PPG) enhancing its efficacy by using multiple wavelengths for improved assessment. This study explores how contact force (CF) variations impact MW-PPG signals. Data from 11 healthy subjects are analyzed to investigate the still understudied specific effects of CF on PPG signals. The obtained dataset includes simultaneous recording of five PPG wavelengths (470, 525, 590, 631, and 940 nm), CF, skin temperature, and the tonometric measurement derived from CF. The evolution of raw signals and the PPG DC and AC components are analyzed in relation to the increasing and decreasing faces of the CF. Findings reveal individual variability in signal responses related to skin and vasculature properties and demonstrate hysteresis and wavelength-dependent responses to CF changes. Notably, all wavelengths except 631 nm showed that the DC component of PPG signals correlates with CF trends, suggesting the potential use of this component as an indirect CF indicator. However, further validation is needed for practical application. The study underscores the importance of biomechanical properties at the measurement site and inter-individual variability and proposes the arterial pressure wave as a key factor in PPG signal formation.

Photoplethysmography (PPG) is widely used to assess cardiovascular health. Yet, its effectiveness is often hindered by external factors like contact force (CF), which significantly affects the accuracy and reliability of measurements. This study investigates how variations in the CF at the index fingertips influence six signal quality indices (SQIs)—including the perfusion index, skewness, kurtosis, entropy, zero-crossing rate, and relative power—using data from 11 healthy participants. Our analysis of normalized CF values reveals that lower CF ranges (0.2 to 0.4) may be optimal for extracting information about perfusion and blood flow. However, they may not be the best range to capture all the physiological details within the PPG pulse. In contrast, higher CF ranges (0.4 to 0.6) enable capturing more complex signals that could be physiologically representative. The findings underscore the necessity of considering viscoelastic tissue properties and individual biomechanical differences, advocating for both the normalization of CF for improved cross-subject comparison and personalized CF calibration to adapt PPG devices to diverse populations. These strategies ensure measurement reliability and consistency, thereby advancing the accuracy of cardiac and vascular assessments. Our study offers guidelines for adjusting the CF levels to balance signal detail and perfusion quality, customized to meet specific analytical requirements, with direct implications for both clinical and research environments.

Graphene has great application potential in the field of electromagnetic modulation field because of its excellent physical and electronic properties. Studies have demonstrated that the properties of graphene films with different layers are also different due to the difference in energy band structure. Nowadays, the modulation mechanism of monolayer graphene (MLG) and bilayer graphene (BLG) has been gradually discovered, but for graphene with more than three layers, the mechanism of whether it is tunable remains to be explored, especially on the proving from an experimental perspective. In this study, the CVD-prepared highly homogeneous few-layer graphene (FLG) film was combined with SiO2 nanolayers and P-doped Si substrate to form an MIS-like capacitor structure, a unique electromagnetic behavior of mutant amplitude modulation exhibited by FLG film was found, which was different from that of mono- and bi-layers of graphene. The results show that the structure exhibits obvious modulation behavior in the ultra-wideband frequency of 500-750 GHz and the bias of 0.9 V, up to 3.1 dB. This study makes a new supplement to a gap in the EM modulation system of graphene series material.

This paper presents a comprehensive study focusing on the detection and characterization of droplets with volumes in the nanoliter range. Leveraging the precise control of minute liquid volumes, we introduced a novel spectroscopic on-chip microsensor equipped with integrated microfluidic channels for droplet generation, characterization, and sensing simultaneously. The microsensor, designed with interdigitated ring-shaped electrodes (IRSE) and seamlessly integrated with microfluidic channels, offers enhanced capacitance and impedance signal amplitudes, reproducibility, and reliability in droplet analysis. We were able to make analyses of droplet length in the range of 1.0–6.0 mm, velocity of 0.66–2.51 mm/s, and volume of 1.07 nL–113.46 nL. Experimental results demonstrated that the microsensor’s performance is great in terms of droplet size, velocity, and length, with a significant signal amplitude of capacitance and impedance and real-time detection capabilities, thereby highlighting its potential for facilitating microcapsule reactions and enabling on-site real-time detection for chemical and biosensor analyses on-chip. This droplet-based microfluidics platform has great potential to be directly employed to promote advances in biomedical research, pharmaceuticals, drug discovery, food engineering, flow chemistry, and cosmetics.

Background: Intra-abdominal pressure (IAP) is a critical parameter in the care of critically ill patients, as elevated IAP can lead to reduced cardiac output and organ perfusion, potentially resulting in multiple organ dysfunction and failure. The current gold standard for measuring IAP is an indirect technique via the bladder. According to the Abdominal Compartment Society’s Guidelines, new measurement methods/devices for IAP must be validated against the gold standard. Objectives: This study introduces Ventra, an abdominal phantom designed to simulate different IAP levels, abdominal compliance, respiration-related IAP variations, and bladder dynamics. Ventra aims to facilitate the development and validation of new IAP measurement devices while reducing reliance on animal and cadaveric studies. Additionally, it offers potential applications in training and education for biomedical engineering students. This study provides a thorough explanation on the phantom’s design and fabrication, which provides a low-cost solution for advancing IAP measurement research and education. The design concept, technical aspects, and a series of validation experiments determining whether Ventra is a suitable tool for future research are presented in this study. Methods: Ventra’s performance was evaluated through a series of validation tests using a pressure gauge and two intra-gastric (Spiegelberg and CiMON) and two intra-bladder (Accuryn and TraumaGuard) pressure measurement devices. The mean and standard deviation of IAP recordings by each device were investigated. Bland–Altman analysis was used to evaluate bias, precision, limits of agreement, and percentage error for each system. Concordance analysis was performed to assess the ability of Ventra in tracking IAP changes. Results: The phantom demonstrated excellent agreement with reference pressure measurements, showing an average bias of 0.11 ± 0.49 mmHg. A concordance coefficient of 100% was observed for the phantom as well. Ventra accurately simulated different abdominal compliances, with higher IAP values resulting in lower compliance. Abdominal volume changes showed a bias of 0.08 ± 0.07 L/min, and bladder fill volume measurements showed an average difference of 0.90 ± 4.33 mL for volumes ranging from 50 to 500 mL. Conclusion: The validation results were in agreement with the research guidelines of the world abdominal society. Ventra is a reliable tool that will facilitate the development and validation of new IAP measurement devices. It is an effective educational tool for biomedical engineering students as well.

Cementitious materials are susceptible to damage not only from mechanical loading, but also from environmental (physical, chemical, and biological) factors. For Textile-Reinforced Cementitious (TRC) composites, durability poses a significant challenge, and a reliable method to assess long-term performance is still lacking. Among various durability attacks, freeze-thaw can induce internal cracking within the cementitious matrix, and weaken the textile-matrix bond. Such cracks result from hydraulic, osmotic, and crystallization pressure arising from the thermal cycles, leading to a reduction in the stiffness in the TRC composites. Early detection of freeze-thaw deterioration can significantly reduce the cost of repair, which is only possible through periodic, full-field monitoring of the composite. Full-field monitoring provides a comprehensive view of the damage distribution, offering valuable insights into the causes and progression of damage. The crack location, size, and pattern give more information than that offered by single-point measurement. While visual inspections are commonly employed for crack assessment, they are often time-consuming. Technological advances now enable crack pattern classification based on high-quality surface images; however, these methods only provide information limited to the surface. Elastic wave-based non-destructive testing (NDT) methods are highly sensitive to the material's mechanical properties, and therefore are widely used for damage monitoring. On the other hand, electromagnetic wave-based NDTs offer the advantage of fast, non-contact measurements. Micro- and millimeter wave frequencies offer a balance of high resolution and wave penetration, although they have not yet been sufficiently explored for detecting damage in cementitious composites. In this study, TRC specimens were subjected to up to 150 freeze-thaw cycles and monitored using a combination of active elastic and electromagnetic wave-based NDT mapping methods. For this purpose, transmission measurements were conducted at multiple points, with ultrasonic pulse velocity (UPV) employed as a benchmark and, for the first time, millimeter wave (MMW) spectrometry applied. This multi-modal mapping approach enabled the tracking of damage progression, and the identification of degraded zones.