Piezoresistive monitoring

The three main categories of respiratory rate monitoring are impedance pneumography, inductive plethysmography, and piezoresistive monitoring. 

Piezoresistive monitoring assesses the thoracic circumference and measures the resistance of a sensor made of conductive material when it is stretched (Merrit, 2008 Al-Khalidi et al., 2011). 

In addition to mechanical reinforcement, the presence of nanocarbons in these hierarchical composites can also be used for piezoresistive structural health monitoring or damage evaluation by thermal imaging. Other functions of the nanocarbon, for example in structural supercapacitors, are likely to emerge in the near future. 

Figure 10.1 Respiratory-monitoring shirt with integrated piezoresistive sensors. Data are acquired and wirelessly transmitted using a Shimmer device.

Kim, S., Rahman, T., Senesac, L. R., Davison, B. H., and Thundat, T. 2009. Piezoresistive cantilever array sensor for consolidated bioprocess monitoring. Scanning 31,204-210. 

A low-cost, low-power-consuming micromachined flow and pressure sensing device has also been reported. This sensor can be used for monitoring pressure and flow rate in clean fluids without particles and without the tendency to coat the channel. The pressure is measured with capacitive or piezoresistive pressure sensors and the flow rate is computed from the pressure drop over a well-defined, hydraulic resistance. Although this device is yet to be used for process analysis in industrial stream, it will gain more use in this area in the future. 

A prototype garment shown in Fig. 28.21 was developed to monitor breathing [40]. The two piezoresistive sensors were produced with a coating of conductive silicone (ELASTOSEL LR3162) on the surface of the garment. By this a device is able to mimic an otherwise denoted material property, piezoresistivity. The sensors were placed on the chest and abdominal positions, respectively. The sensors were coated... 

SFM cantilevers and tips are often made of silicon or silicon nitride SFM tips possess radii of curvature at the apex between few and several tens to hundreds of nanometers (Fig. 1). A piezoelectric transducer is used in order to position the sample accurately. Depending on the scanner type (piezo tube length and design) the maximum scan sizes vary between ca 1 /rm and several himdred micrometers, with an accuracy of positioning in the best cases of O.Ol nm. The cantilever deflection is typically monitored by an optical beam deflection technique (Fig. la). Other possibilities to measure the deflection include STM, piezoresistive, capacitance, or interferrometric detection schemes (22). In the optical beam deflection setup, laser light is reflected off the end of the cantilever and is collected by a position-sensitive photodiode. For instance, a 4-quadrant photodiode can simultaneously measure deflections in vertical (surface normal) and horizontal (lateral) direction (Fig. la). 

Thin films are integral parts of many micro-electro-mechanical systems designed to serve as sensors or actuators. For example, a piezoelectric or piezoresistive thin film deposited on a silicon membrane can be used to detect electronically a deflection of the membrane in response to a pressure applied on its surface or by an acceleration of its supports. Devices based on thin film technology are used as microphones in hearing aids, monitors of blood pressure during exercise, electronically positioned thin film mirrors on flexible supports in optical display systems, and probes for detecting the degree of ripeness of fruits. 

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