Saturday, 29 June 2013

86. Smart Structures: Blurring the Distinction between the Living and the Nonliving

Robots, discussed in Parts 84 and 85, are a subset of 'smart structures'. Smart bridges, smart surfaces, smart wings of aircraft, and smart cars are some other examples of smart structures.

In all probability there is no clear distinction between life and nonlife. This will become more and more apparent as we humans make progress in the field of smart structures (Wadhawan (2007): Smart Structures: Blurring the Distinction Between the Living and the Nonliving).

Smart or 'adaptronic' structures are defined as structures with an ability to respond adaptively in a pre-designed useful and efficient manner to changing environmental conditions, including any changes in their own condition. The response is adaptive in the sense that two or more stimuli or inputs may be received and yet there is a single response function as per design. The structure is designed to ensure that it gives optimal performance under a variety of environmental conditions.

Any smart structure, biological or artificial, typically has a host structure or ‘body’, which has an interface with a source of energy. The body houses or supports one or more sensors (e.g. ‘nerves’) and one or more actuators (e.g. ‘muscles’). The sensors and the actuators interface with a control centre or ‘brain’. Since both sensors and actuators interface with the control centre, they interface with each other also, albeit indirectly. In a good smart structure there is extensive and continuous feedback and communication of information among the various subunits.

The basic action plan of a smart structure is essentially as follows: The input of data by the sensors is analysed by the control centre. If the course of action is clear, the control centre signals the actuators to take the action. If the course of action is not clear, the control centre directs the sensors to collect additional data. This goes on cyclically, till the course of action is clear, and then the action is taken. The action taken depends on the overall purpose or objective.

To consider the example of a human (obviously a smart structure), if a person puts his / her hand on a hot surface, the tactile sensors send a signal to the brain, which then immediately directs the muscles to take the hand away from the hot surface. The purpose of the smart structure here is to survive and propagate.

Since the smartest structures around us are those designed by Nature through aeons of trial and error and evolution, it makes sense for us to emulate Nature when we want to design artificial smart structures. In fact, an alternative definition of a smart structure can be given as follows:

Smart structures are those which possess characteristics close to, and, if possible, exceeding, those found in biological structures.


Sensing involves measurement followed by information-processing. The sensor may be a system by itself, or it may be a subsystem in a larger system (e.g. a complete smart system). In artificial smart structures, optical fibres constitute the most versatile sensors. A variety of ferroic materials also serve as sensor materials. Some notable examples are piezoelectric materials like quartz and PZT, and relaxor ferroelectrics like PMN-PT.

The concept of 'integrated sensors' has been gaining ground for quite some time. Typically, there is a microsensor integrated with signal-processing circuits on a single package. This package not only transduces the sensor inputs into electrical signals, but may also have other signal-processing and decision-making capabilities. There are several advantages of integrated sensors: better signal-to-noise ratio; improved characteristics; and signal conditioning and formatting.


An actuator creates controllable mechanical motion from other forms of energy. Materials used for sensor and actuators in smart structures fall into three categories: ferroic materials; nanostructured materials; and soft materials.

Microactuators are the current rage. At present it is usually necessary that they be compatible with the materials and processing technologies used in silicon microelectronics. The two main types of microactuators are ‘mechanisms’ and ‘deformable microstructures’. The former provide displacement through rigid-body motion. The latter do this by mechanical deformation or straining.

Control systems

The use of computers is necessary for developing sophisticated control systems for smart structures (e.g. robots) which can learn and take decisions. There are various approaches to computational intelligence and evolutionary robotics. The evolution of distributed intelligence should be emphasized in this context; I shall discuss this in the next post.

Microelectromechanical systems (MEMS)

MEMS are the current rage, as they involve a high degree of miniaturization and integration of sensors, actuators, and control systems comprising the smart structure or system. Miniaturization and integration have many advantages: lower cost; higher reliability; higher speed; and capability for a higher degree of complexity and sophistication. Some authors equate smart structures with MEMS.

Modern applications of MEMS include those in biomedical engineering, wireless communications, and data storage. Some of the more integrated and complex applications are in microfluidics, aerospace, and biomedical devices.

Silicon tops the list of materials used for MEMS because of its favourable mechanical and electrical properties, and also because of the already entrenched IC-chip technology. More recently, there have been advances in the technology of using multifunctional polymers for fabricating 3-dimensional MEMS (Varadan, Jiang and Varadan 2001). Organic-materials-based MEMS are also conceivable now, after the invention of the organic thin-film transistor. In the overall smart systems involving MEMS, there is also use for ceramics, metals, and alloys, as also a number of ferroic or multiferroic materials.

I shall discuss robots of the future in a separate post. Suffice it to say here that, as Kurzweil predicts, we are approaching a 'technological singularity', beyond which robots will overtake us in all abilities, and technological progress will be so rapid as to outstrip our present ability to comprehend it. We shall transform ourselves and augment our minds and bodies with genetic alterations, MEMS, NEMS (nanoelectromechanical systems), and true machine intelligence. That would mark a complete blurring of the distinction between the 'living' and the 'nonliving'.

Watch this movie for a glimpse of what the future may be like:

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