Chapter 1: Sensor

In the context of detecting a physical phenomena, a sensor is a device that generates an output signal for the purpose of its detection.

A device, module, machine, or subsystem that detects events or changes in its surroundings and transmits the information to other electronic devices, most commonly a computer processor, is referred to as a sensor. This description gives the sensor the broadest possible meaning.

There are countless applications for sensors, the majority of which are never brought to the attention of the average person. Some examples of sensors that are utilized in daily products include touch-sensitive elevator buttons (tactile sensor) and lamps that dim or brighten when the base is touched. As a result of developments in micromachinery and platforms for microcontrollers that are simple to operate, the applications of sensors have moved beyond the traditional disciplines of temperature, pressure, and flow measurement. One example of this is the development of MARG meters.

Potentiometers and force-sensing resistors are two examples of analog sensors that are still extensively seen in usage today. Manufacturing and machinery, aircraft and aerospace, automobiles, medical, robotics, and a great deal of other parts of our day-to-day lives are all examples of application areas for these materials. There are a broad variety of additional sensors that may measure the chemical and physical properties of materials. Some examples of these sensors include optical sensors, which measure the refractive index, vibrational sensors, which measure the viscosity of fluids, and electro-chemical sensors, which monitor the pH of fluids.

The sensitivity of a sensor is equal to the degree to which its output shifts in response to changes in the quantity that it measures as input. As an illustration, if the mercury in a thermometer travels by one centimeter whenever the temperature shifts by one degree Celsius, then the thermometer's sensitivity is one centimeter per degree Celsius (it is essentially the slope dy/dx assuming a linear characteristic). Some sensors can also have an effect on the data that they collect; for example, if a thermometer that is set to room temperature is placed inside of a cup of hot liquid, the thermometer will cool the liquid while the liquid will heat the thermometer. The majority of the time, sensors are intended to have a minimal impact on the thing that is being monitored; reducing the size of the sensor typically improves this and may also bring about additional benefits.

As technology advances, it becomes possible to make an increasing number of sensors on a minuscule scale as microsensors by utilizing MEMS technology. A microsensor, in comparison to macroscopic methods, is capable of achieving a substantially faster measurement time and a higher level of sensitivity in the majority of situations. Disposable sensors, which are low-cost and easy-to-use devices for short-term monitoring or single-shot measurements, have recently gained considerable relevance. This is mostly due to the growing demand for information that is both quick and economical in today's environment. With the help of this category of sensors, vital analytical information can be received by anyone, at any time, in any location, and without the need for recalibration or the concern of contamination.

Rules that a good sensor must adhere to are as follows:

The majority of sensors have a transfer function that is linear. After that, the sensitivity is evaluated by determining the ratio between the output signal and the property that was measured. For instance, if a sensor is able to sense temperature and simultaneously produce a voltage output, then the sensitivity remains the same regardless of the units [V/K]. The slope of the transfer function is what we refer to as the sensitivity. Therefore, in order to convert the electrical output of the sensor (for example, V) to the units that are being measured (for example, K), it is necessary to divide the electrical output by the slope (or multiply it by its reciprocal function). In addition, an offset is typically added or subtracted into the equation. As an illustration, if the output is 0 V and the input is -40 C, then the extra value of -40 must be added to the output.

Using an analog-to-digital converter, an analog sensor signal must be transformed into a digital signal before it can be processed or utilized in digital equipment. This is necessary in order to utilize the signal.

Due to the fact that sensors are unable to recreate an ideal transfer function, their accuracy can be limited by a number of different sorts of deviations, including the following:

Random errors and systematic errors are two categories that can be used to describe all of these discrepancies. When it comes to compensating for systematic mistakes, there are instances when a calibration technique of some kind can become necessary. Signal processing techniques, such as filtering, can be utilized to reduce noise, which is a type of random mistake. However, this is typically accomplished at the price of the sensor's dynamic behavior.

The resolution of the sensor, also known as the measurement resolution, refers to the smallest change that may be noticed in the amount that is being precisely measured. In most cases, the numerical resolution of the digital output is what is considered to be the resolution of a sensor that has a digital transmission. On the other hand, the resolution and the precision with which the measurement is made are not the same thing. The resolution is related to the precision. It is possible that the accuracy of a sensor is far smaller than its resolution.

The term "chemical sensor" refers to an analytical equipment that is self-contained and has the capability to offer information regarding the chemical composition of its surroundings, which can be either a liquid or a gas environment. This information is presented in the form of a detectable physical signal that is connected with the concentration of a particular chemical species, which is referred to as an analyte. There are two primary processes that are involved in the operation of a chemical sensor. These processes are known as recognition and transduction. During the recognition process, analyte molecules engage in selective interactions with receptor molecules or sites that are incorporated into the structure of the recognition element of the sensor. As a consequence of this, a characteristic physical parameter undergoes a change, and this change is communicated through the utilization of an integrated transducer that is responsible for producing the output signal.

The term "biosensor" refers to a chemical sensor that is grounded in the recognition material of biological origin. Furthermore, because synthetic biomimetic materials are going to replace recognition biomaterials to some extent, it is unnecessary to make a clear distinction between a biosensor and a conventional chemical sensor. Aptamers and molecularly imprinted polymers are two examples of biomimetic materials that are typically utilized in the manufacture of sensors.

In the fields of biomedicine and biotechnology, the term "biosensor" refers to sensors that are able to detect analytes by utilizing a biological component. Examples of such components include cells, proteins, nucleic acid, and biomimetic polymers.

On the other hand, a sensor or nanosensor is used to refer to a non-biological sensor, even an organic one (carbon chemistry), when it is used to detect biological biomarkers. Both in-vitro and in-vivo applications employ this phrase in their respective contexts.

The encapsulation of the biological component in biosensors presents a slightly different challenge than that of conventional sensors. This can be accomplished through the utilization of a semipermeable barrier, such as a dialysis membrane or a hydrogel, or through the utilization of a three-dimensional polymer matrix, which either physically constrains the sensing macromolecule or chemically constrains the macromolecule by binding it to the scaffold.

These sensors are known as neuromorphic sensors, and they are able to physically imitate the structures and functions of biological brain units. This is demonstrated by the event camera, for instance.

MOSFET sensors, also known as MOS sensors, were later developed after the MOSFET was invented at Bell Labs between the years 1955 and 1960. Since then, MOSFET sensors have been widely utilized for the purpose of measuring various physical, chemical, biological, and environmental characteristics.

MOSFET sensors have been designed for the purpose of monitoring a variety of factors, including those that are physical, chemical, biological, and environmental. The earliest MOSFET sensors include the open-gate field-effect transistor (OGFET), which was first introduced by Johannessen in 1970; the ion-sensitive field-effect transistor (ISFET), which was invented by Piet Bergveld in 1970; the adsorption field-effect transistor (ADFET), which was patented by P.F. Cox in 1974; and a hydrogen-sensitive MOSFET, which was demonstrated by I. Lundstrom, M.S. Shivaraman, C.S. Svenson, and L. Lundkvist in 1975. An ion-sensitive membrane, electrolyte solution, and reference electrode are used in place of the metal gate in an ISFET, which is a variation of the MOSFET. The ISFET is a unique type of MOSFET that has a gate that is located at a specific distance. An extensive range of biological applications make extensive use of the ISFET. These applications include the detection of DNA hybridization, the detection of biomarkers from blood, the detection of antibodies, the measurement of glucose, the sensing of pH, and genetic...