Sensors, mechanical deformation

Many of the variations developed to make pressure sensors and accelerometers for a wide variety of appHcations have been reviewed (5). These sensors can be made in very large batches using photoHthographic techniques that keep unit manufacturing costs low and ensure part-to-part uniformity. A pressure differential across these thin diaphragms causes mechanical deformation that can be monitored in several ways piezoresistors implanted on the diaphragm are one way changes in electrical capacitance are another. 

To demonstrate that the sensor does not respond with and to electrical signal changes in pressure, recordings can be made in an electrolyte-filled sealed chamber, within which pressure was rapidly altered. As can be seen in Figure 17, alterations in pressure have no measurable effect on the amperometric current generated by the sensor, which was immersed in the confined electrolyte solution. In order to estimate potential piezoelectric electrical interference due to mechanical deformation of the sensor tip, a micromanipulator can be used to deform the sensor tip at a physiologically relevant frequency (1-3 Hz). This usually generates small electrical noises, six to ten times smaller... 

Changes in the impedance of an IPMC may be used to create a self-sensing actuating device [Park et al. (2008)]. An advantage of such a device is that the deformation estimation is an intrinsic property of the actuator, i.e. there is no need to equip separate senors as it can function as a coexisting sensor. The capacitance and the resistance of an IPMC are caused by structural featmes of the Pt electrode particles, such as the space between each particle and the density of the particles. The internal electrical characteristics of the IPMC, especially the resistance and capacitance of the electrodes, are changed with the mechanical deformation of the IPMC. When an IPMC is bent, one electrode surface becomes concave (+), and the other convex (-). 

When a comparison is made between the two plots, it is revealed that the upper sensor curves appear to be noisier and more hysterical as compared to the lower sensor curves. This signifies an important difference in energy absorption/release mechanism and mechanical deformation phenomena (compression and traction) at the top and bottom faces of the composite specimen during cyclic loading. 

A sensor that is especially interesting and instructive is made from a quartz crystal microbalance, or QCM. This device is based on the piezoelectric characteristics of quartz. When quartz is mechanically deformed, an electrical potential difference develops across its surface. Furthermore, when a voltage is impressed across the faces of a quartz crystal, the crystal deforms., A crystal connected in an appropriate electrical circuit oscillates at a frequency that is characteristic of the mass and shape of the crystal and that is amazingly constant as long as the mass of the crystal is constant. This property of some crystalline materials is called the piezoelectric effect and forms the basis for the QCM. Moreover, the characteristic constant frequency of the quartz crystal is the basis for modern high-precision clocks, time bases, counters, timers, and frequency meters, which in turn have led to many highly accurate and precise analyTical instrumental svsiems. 

Bruns et al. pioneered self-reporting materials based on the mechanical perturbation of proteins within polymeric matrices/ " The protein cage thermosome (THS), a chaperonin from the archaea Thermoplasma acid-ophilum, is composed of sixteen protein subunits that form two hemispheres with the ability to enclose macromolecular guests (Figure 11.13)/ THS is approx. 16 nm in diameter. The hemispheres of chaperonins are connected through a mechanically weak plane, so that the two halves of these protein cages can be separated from each other by mechanical forces, as demonstrated in AFM experiments.THS was turned into a sensor for mechanical deformation by covalently linking two proteins, enhanced cyan fluorescent protein (eCFP) and enhanced yellow fluorescent protein (eYFP), into the... 

Coupling mesophase transitions and director reorientations to mechanical deformation lends itself to some novel applications. Mechano-optical sensors/switches may be fabricated. At low strains, chiral elastomeric mesophases exhibit unique electromechanical phenomena that originate from the change in electric polarization caused by a mechanical deformation. The opposite interaction - a change in... 

A piezoelectric sensor is a device that can convert mechanical stress into an electrical charge, and vice versa. An electric polarization occurs in a fixed direction when the piezoelectric crystal is deformed. The polarization causes an electrical potential difference over the crystal. Natural piezoelectric materials are quartz and tourmaline, and synthetic polymers such as polyvinyUdene fluoride (PVDF) exhibit piezoelectricity several times greater than quartz. Because the effect is reversible, which means that the electrical stimuli can lead to mechanical deformations, the piezoelectric effect is also useful to create some actuators in smart clothing. 

The term "ChG-based fiber optic sensor" covers a broad range of devices that work in many different ways. Beside chemical and biochemical species sensing, this technology has proven very efficient in the probing of physical parameters such as temperature, pressure, and mechanical deformation. 

Generally, the computational effort increases when going from the macroscale over the mesoscale up to the microscale. If real sensor or actuator apphcations are of interest, in most cases mesoscopic or macroscopic modeling is predestined. In order to understand the physicochemical mechanisms underlying the conversion, i.e., the mechanical deformation, the theoretical and experimental facts behind the swelling process have to be investigated. 

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