Artificial Nerves Sensors

Materials that allow an intelligent or smart structure to adapt to its environment are known as actuators. These materials have the ability to change the shape, stiffness, position, natural frequency, damping, friction, fluid flow rate, and other mechanical characteristics of adaptronic structures in response to changes in temperature, electric field, or magnetic field. The most common actuator materials are shape memory alloys, piezoelectric materials, mag-netostrictive materials, electrorheological fluids, and magnetorheological fluids [2]. Actuators with these materials will be described in detail in Sects. 6.2 to 6.6 therefore you will find only a brief overview below. 

Shape memory alloys (SMA) undergo solid-to-solid martensitic phase transformations, which allow them to exhibit large, recoverable strains [3]. Nickel-titanium, also known as nitinol (Ni for nickel, Ti for titanium, and nol for Naval Ordnance Lab), are high-performance shape memory alloy actuator materials exhibiting strains of up to 8% by heating the SMA above its phase transformation temperature - a temperature which can be altered by changing the composition of the alloy. 

Piezoelectric materials can enact deformation and mechanical forces in response to an applied voltage. Rather than undergoing a phase transformation, piezoelectric materials change shape when their electrical dipoles spontaneously align in electric fields, causing deformation of the crystal structure. 

In contrast with linear piezoelectricity, the electrostrictive response is quadratic in electric field. Hence, the direction of the electrostriction does not switch as the polarity of the electric field is switched. 

Piezoelectric materials have found widespread use as sensors in adaptronic structures [4] (see Sect. 7.3). Piezoelectric ceramics and polymers pro- 

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For Amputee Patients (Figure 34.14) BPBs, working as biopotential sensors, would be inserted in the stump to pick up motor nerve signals, which can be used to control movement of the artificial limb flexible components . 

Artificial skin for permanent wear is a different matter. Here the idea is to provide a covering for prosthetic limbs, which would feel and function like natural skin. A possible approach to this ambitious goal starts from a durable, flexible polymer (of which many are available) containing carbon nanotubes. This material will conduct heat so could restore the sensation of hot and cold. Because nerves can now be led from other parts of the body, it is proposed to incorporate arrays of pressure sensors into the skin, and thus provide a sense of touch. 

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