A sensor can be broadly defined as a device that receives a stimulus and emits a signal.1 For example, a fire alarm is an acoustic sensor that emits a loud noise to alert bystanders that there is a fire nearby. This changed the state of silence to a state of a loud noise. A chemical sensor based on changes of acidity, like a litmus paper, uses the chemical changes in the paper to emit an optical signal; changing the color from red to blue as the acidity decreases or maintaining the original color of the litmus paper if the substance is of neutral acidity (like pure water). And an electrical sensor works by changing the electric current of a circuit (by a specific amount) when in the presence of a particular substance. This can further be imagined by a circuit connected to a multimeter that is set to measure current from a source while adding different resistances and observing the change in current (Figure 1).
Most of today’s research depends considerably on electric sensors. Generally, “there are two types of electric sensors; direct and complex. A direct sensor converts a stimulus into an electrical signal or modifies an electrical signal by using an appropriate physical effect. On the other hand, a complex sensor also needs one or more transducers of energy (to change from one form of energy to another) before a direct sensor can measure the electrical output.”1 By understanding how sensors can be organized, it’s possible to enhance their measurements and maximize their use within the system; thus, allowing us dive deeper and farther into the unknown.
Figure 1: Diagram of an electrical circuit that depicts a change in current when a substance is added to a substrate.
The hands, nose, mouth, ears and eyes are the sensors which our bodies use to understand our surroundings. And with the aid of modern sensors, we can enhance our ability to detect changes that would otherwise elude us, such as slight variations in hardness of metals or miniscule alterations in atomic structures that can greatly impact experimental procedures and lead to discoveries that pave the future. But it is important to note that this field has its obstacles to overcome, such as increasing the precision, maintaining functionality in extreme conditions and reducing single-use materials. Therefore, material researchers have the responsibility to not only meet the demands of society’s needs, but also be conscious of the repercussions their developments can have on the environment in the short- and long-term future.
Reference:
Fraden, J. Chapter 1 - 2. In Handbook of modern sensors physics, designs, and applications; Springer New York: New York, NY, 2010; pp. 1–25.