Chip-scale optical airflow sensor

Airflow sensors are an essential component in a wide range of industrial, biomedical, and environmental applications. The development of compact devices with a fast response and wide measurement range capable of in situ airflow monitoring is highly desirable. Herein, we report a miniaturized optical airflow sensor based on a GaN chip with a flexible PDMS membrane. The compact GaN chip is responsible for light emission and photodetection. The PDMS membrane fabricated using a droplet-based molding process can effectively transform the airflow stimuli into optical reflectance changes that can be monitored by an on-chip photodetector. Without the use of external components for light coupling, the proposed sensor adopting the novel integration scheme is capable of detecting airflow rates of up to 53.5 ms−1 and exhibits a fast response time of 12 ms, holding great promise for diverse practical applications. The potential use in monitoring human breathing is also demonstrated.

Polymeric piezoresistive airflow sensor to monitor respiratory patterns

Monitoring human respiratory patterns is of great importance as it gives essential information for various medical conditions, e.g. sleep apnoea syndrome and chronic obstructive pulmonary disease and asthma, etc. Herein, we have developed a polymeric airflow sensor based on nanocomposites of vertically grown graphene nanosheets (VGNs) with polydimethylsiloxane (PDMS) and explored their applications in monitoring human respiration. The sensing performance of the VGNs/PDMS nanocomposite was characterized by exposing to a range of airflow rates (20–130 l min −1 ), and a linear performance with high sensitivity and low response time (mostly below 1 s) was observed. To evaluate the experimental results, finite-element simulation models were developed in the COMSOL Multiphysics package. The piezoresistive properties of VGNs/PDMS thin film and fluid–solid interaction were thoroughly studied. Laser Doppler vibrometry measures of sensor tip displacement closely approximated simulated deflection results and validated the dynamic response of the sensor. By comparing the proposed sensor and some other airflow sensors in the literature, it is concluded that the VGNs/PDMS airflow sensor has excellent features in terms of sensor height, detection range and sensitivity. The potential application of the VGNs/PDMS airflow sensor in detecting the respiration pattern of human exercises like walking, jogging and running has been demonstrated.

Barium titanate piezoelectric-film-based beam-array airflow sensor for wearable breath-monitoring application

This study presents a barium titanate (BaTiO3) film-based piezoelectric airflow sensor. This sensor integrated a piezoelectric beam array with a poly(dimethylsiloxane) orifice membrane as the core sensing component. The compact size of the micromachined device fit the requirements for a wearable device. The hydrothermally grown barium titanate film exhibited an orthorhombic crystal structure with good piezoelectric properties. We propose an algorithm to determine the airflow sensor performance using data from the measured piezoelectric signal and the displacement of the piezoelectric beam. This algorithm correlates the discharge coefficient of the core sensing component, Reynold’s number, airflow velocity, pressure difference across the component, displacement of the piezoelectric beam, strain of the barium titanate film, and generated charge from the sensor, which is rarely reported in the literature. The Young’s modulus and piezoelectric constant of the barium titanate film could also be derived as 100 GPa and 8 pC/N, respectively. Utilizing this algorithm and the generated piezoelectric signal of the sensor, important breath parameters of a young male subject at rest were monitored.

IoT-Based Personal Protective Equipment Monitoring System to Prevent the Risk of Dehydration in Health Workers for COVID-19 Pandemic

The extraordinary case of Covid-19 has made health workers the front line in handling it. To prevent the risk of contracting, health workers must use Personal Protective Equipment (PPE) as protection. PPE that must be worn for at least 5 hours a day and is waterproof makes users experience much sweating. If not prevented, health workers can be exposed to dehydration and even death. Based on the explanation above, PPE has been designed that can cool IoT-based health workers. Also, all activities can be monitored remotely via the WEB, accessible via a smartphone or computer. In addition to WEB, data can be displayed via the LCD. The DHT22 sensor and the airflow sensor will detect the hazmat's temperature, humidity, and airflow. Furthermore, the tool is also equipped with UVC rays that can clean the air from microorganisms. Activity data will be stored in cloud storage, which is helpful as an evaluation material and reference for health workers' health progress. From the tests' results, the tool will function when the temperature and humidity follow the setpoint.

Seabird Biologging System with Compact Waterproof Airflow Sensor

This paper presents a seabird biologging system with a compact waterproof airflow sensor. Although biologging methods have attracted attention in the evaluation of seabird flight performance, a direct measurement method of airflow velocity has not yet been established. When an airflow sensor is added to a biologging system, a more accurate assessment of the flight performance can be obtained. We developed a compact Pitot tube-type airflow sensor that is specialized for seabird biologging systems. Here, we integrated micro electro mechanical system (MEMS) sensor chips and a sensing circuit into the Pitot tube housing. Then, we conducted a wind tunnel experiment using a stuffed seabird and the fabricated sensor. The results confirmed that the sensor responds to the wind speed even when attached to the dorsal surface of the seabird. Based on the above, we believe that the proposed sensor can be applied to practical seabird biologging systems.

A Direct-Writing Approach for Fabrication of CNT/Paper-Based Piezoresistive Pressure Sensors for Airflow Sensing

Airflow sensor is a crucial component for monitoring environmental airflow conditions in many engineering fields, especially in the field of aerospace engineering. However, conventional airflow sensors have been suffering from issues such as complexity and bulk in structures, high cost in fabrication and maintenance, and low stability and durability. In this work, we developed a facile direct-writing method for fabricating a low-cost piezoresistive element aiming at high-performance airflow sensing, in which a commercial pen was utilized to drop solutions of single-walled carbon nanotubes onto tissue paper to form a piezoresistive sensing element. The encapsulated piezoresistive element was tested for electromechanical properties under two loading modes: one loading mode is the so-called pressure mode in which the piezoresistive element is pressed by a normal pressure, and another mode is the so-called bending mode in which the piezoresistive element is bended as a cantilever beam. Unlike many other developed airflow sensors among which the sensing elements are normally employed as cantilever beams for facing winds, we designed a fin structure to be incorporated with the piezoresistive element for airflow sensing; the main function of the fin is to face winds instead of the piezoresistive element, and subsequently transfer and enlarge the airflow pressure to the piezoresistive element for the normal pressure loading mode. With this design, the piezoresistive element can also be protected by avoiding experiencing large strains and direct contact with external airflows so that the stability and durability of the sensor can be maintained. Moreover, we experimentally found that the performance parameters of the airflow sensor could be effectively tuned by varying the size of the fin structure. When the fin sizes of the airflow sensors were 20 mm, 30 mm, and 40 mm, the detection limits and sensitivities of the fabricated airflow sensors were measured as 8.2 m/s, 6.2 m/s, 3.2 m/s, 0.0121 (m/s)−2, 0.01657 (m/s)−2, and 0.02264 (m/s)−2, respectively. Therefore, the design of the fin structure could pave an easy way for adjusting the sensor performance without changing the sensor itself toward different application scenarios.