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Sensing for the Perfectly Firm Tomato
Published in Denise Wilson, Sensing the Perfect Tomato, 2019
Force vs. contact area measurements are likely to use one or more of three primary sensing technologies: piezoresistive, piezoelectric, and capacitive. Piezoresistive sensors are one of the simplest means to transform mechanical forces into signals useful for estimating firmness (Doll and Pruitt 2013). These sensors respond to applied stress, pressure, force, or touch with a change in electrical resistance. When a material such as silicon, germanium, or diamond (or a structure such as a carbon nanotube or carbon nanowire) mechanically bends or deforms in response to an applied force (Barlian et al. 2009), resistance changes either isotropically (i.e., the same in all directions) or anisotropically. Wheatstone bridge measurement circuits can be used to eliminate the large baselines in these piezoresistors and provide an output that is nonzero only when the sensor is perturbed (i.e., measuring an input of interest). Piezoresistors are small and well suited to being implemented in high-resolution arrays for accurate contact area information in small spaces. Furthermore, because many piezoresitive materials can be used in standard integrated circuit fabrication processes, piezoresistive sensors can also be easily integrated with readout and processing circuitry, thus reducing overall cost and size. For their size and ease of fabrication, these sensors are also quite robust, except for inherent hysteresis, which may limit their use as force sensors. Hysteresis will produce inconsistency in measurements between squeezing the target fruit compared to releasing pressure or force on that same fruit.
Theoretical Electromagnetic Survey
Published in Laurent A. Francis, Krzysztof Iniewski, Novel Advances in Microsystems Technologies and Their Applications, 2017
Among the various transduction principles, the piezoresistive microphones have the advantage of using a simple manufacturing process and are easily integrated into semiconductor devices [6]. The piezoresistive property of a material is defined as the change of resistivity due to deformation or mechanical stress. The semiconductor piezoresistivity has been demonstrated for many materials such as germanium and polycrystalline or amorphous silicon. A piezoresistive microphone consists of a thin membrane that is usually equipped by four piezoresistive also called piezoresistive gauges in a Wheatstone bridge configuration (see Figure 10.1). The first MEMS piezoresistive sensor [7] had a 1 μm thick silicon membrane, highly boron doped, with an area of 1 mm2. The piezoresistive microphones have many advantages such as robustness, ease of micromachining and the lack of a need for integrated electronics, thanks to a low output impedance [8]. However, piezoresistive microphones have some drawbacks, such as high noise floor, high power consumption and mainly thermal degradation of piezoresistive material due to heating by Joule effect and by constraint [9]. Unfortunately, this leads to a strong temperature dependence of the piezoresistive sensor.
Nanocarbon-Based Sensor for Wearable Health Monitoring
Published in Suresh Kaushik, Vijay Soni, Efstathia Skotti, Nanosensors for Futuristic Smart and Intelligent Healthcare Systems, 2022
Md. Milon Hossain, Abbas Ahmed, Maliha Marzana
Piezoresistivity is the most used mechanism to fabricate wearable health monitoring sensors due to its simplicity, cost-effectiveness, large ranges of pressure, suitability, and high pixel density (Zang et al. 2015). Moreover, the working principle of these sensors is straightforward (Homayounfar and Andrew 2020). The piezoresistive sensor converts the electric resistance of a system into an electrical signal when a mechanical stimulus is applied (Figure 2a) (Wan et al. 2017). It can measure the strains and stresses to monitor the health signal, to build a relationship between the human and computer, and may function as electronic skin (Yang et al. 2017).
Influence of measurement parameters on hydrogen absorption properties of hydrogen storage alloys
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Manoj S. Choudhari, Josy James, Man Mohan, Vinod Kumar Sharma, E. Anil Kumar, Prem Kumar Chaurasiya
The block diagram of the experimental setup used for reaction kinetics measurement is presented in Figure 1. The experimental setup comprises the calibrated stainless steel (SS) cylinders for hydrogen storage and supply, and kept in a water bath, bellow sealed valves to control hydrogen flow, and SS-316 tubing. The SS tubing is best suited for hydrogen supply (Javaheri 2023). Pressure was measured at several sites using piezoresistive pressure transducers with a 0–200 bar operational range. During absorption and desorption, a thermostatic bath was employed to keep the reactor at an isothermal condition. Temperatures are measured using “K”-type thermocouples (±0.1°C accuracy), while for the measurement of vacuum level, a digital Pirani gauge (±0.5% accuracy) was used. To study the reaction kinetics of 10–20 g of MH (Figure 2), a completely sealed SS reactor was designed and fabricated. A PTFE washer was used to seal the reactor. A “K”-type thermocouple was attached to continually record the material temperature. For the uniform supply of hydrogen to the reactor, a tube was fitted in the top with a filter assembly to inhibit the MH powder during desorption and evacuation. A data acquisition system is employed to note the temperature and pressure readings at various locations of the system.
Nanomaterial-based wearable pressure sensors: A minireview
Published in Instrumentation Science & Technology, 2020
For piezoresistive pressure sensors, expanding the linear detection range and increasing sensitivity remains a challenge. Song et al.[64] designed a flexible pressure sensor based on a hollow structure. The hollow structure was constructed by depositing two-dimensional transition metal carbide flakes on the frame of the nickel foam, next filling with polydimethylsiloxane, and then etching the nickel foam substrate. The piezoresistive sensor based on the hollow structure offers long-term reliability, satisfactory structural stability, and high sensitivity. In addition, when the sensor is attached to a person’s eyelid, it can detect subtle muscle movements. The sensor can also distinguish signals with different wrist bending speeds. These results demonstrate that the sensor has great application potential for human activity and subtle activity detection.
Stretchable and sensitive sensor based on carbon nanotubes/polymer composite with serpentine shapes via molding technique
Published in Journal of Biomaterials Science, Polymer Edition, 2019
Xiang Fu, Ahmed M. Al-Jumaily, Maximiano Ramos, Ata Meshkinzar, Xiyong Huang
Stretchable strain sensors have attracted considerable attention owing to diverse future applications, like wearable electronics [1,2], soft robotics [3,4], smart textiles [5,6] and various biomedical applications [7–9]. Among several types of transducers available for such applications, piezoresistive type sensors are the most popular due to the simple structure and high sensitivity [10–13]. In recent years, composites composed of electrically conductive nanomaterials and elastomers, which exhibit pronounced piezoresistivity, have always been fabricated and employed as the core material of novel stretchable piezoresistive strain sensors [14–16]. There are common conductive fillers, like carbon nanotubes (CNTs) [17], carbon fibres [18], graphene [6], silver nanowire [19] and so on [20,21]. Among them, CNTs are extensively embedded into various polymers due to their superior mechanical and electrical properties [22,23].