INTRODUCTION TO NANOSENSORS

In this post we will learn about fundamental principles that allows us to sense the world around us. Whit use of our senses we can see how to move our hands, or to pick objects. We can smell food, fire, perfume. We can taste the food. We can hear car, bus or train coming.

We can feel heat and cold. In general these are five senses that we possess:

1)      sight,

2)      hearing,

3)      touch,

4)      smell and

5)      taste.

Senses

We use many different products such as cars, phones and computers. These products have senses that we call sensors and some of the sensors that we know are:

1)      Temperature sensor,

2)      Pressure sensors and

3)      Light sensor etc.

But what if we had products that could discern what we want to do? Let’s say phone that knows you are in a meeting and can independently silence itself. A computer that knows exactly what you want to do and helps you to do just that. To perform any of these applications, these products need a range of sensors and very clever designs. More and more of these types of products are being developed.

For example a self-driving car need sensors in order to see and position it’s self on the road, to stop when pedestrians are on the road, to park itself in parking spot and more. Google developed self-driving car (See Google driverless car).

Figure 1 – A Lexus RX450h retrofitted by Google for its driverless car fleet

Here is a short video which demonstrates Google driverless car.

Game consoles that sense your movement and interpret your movement in games.

Figure 2 – XBOX ONE

Here is short video which demonstrates features of XBOX One.

General definition of a sense is: “A system that consists of a group of sensory cell types that responds to a specific physical or chemical phenomena, and that corresponds to a particular group of regions within the brain where the signals are received and interpreted.”

We can divide senses into two main groups:    

1)      Senses that respond to chemical signals and

2)      Senses that respond to physical phenomena

Human Vision

Visual perception is the ability to interpret surrounding environment by processing information that is contained in the visible light. So in order for one to see, a light source is needed. Without source of light for example the sun everything would be black. Light consists of little particles which are emitted from the source called photons and they are scattered in all directions which eventually reach our eye.

The human eye is an organ that reacts to light and has several purposes. As a sense organ or one of five human sensors allows vision. The tissues that they pass through must be transparent to allow clear vision. First the photons pass through the cornea which is located at the front of the eye to the crystalline lens behind the pupil, then through vitreous body in the eye center. The photons than reach retina (the eye photographic plate) and complete their journey at the retinal pigment epithelium where they initiate nerve pulses. These pulses are directed towards the optic nerve, and then, the optic pathways, before arriving at the occipital brain where the image is formed. This process is what enables us to taken the world around us.

Figure 3 – Human eye

Following video demonstrates the vision process.

Hearing  

When we hear a sound coming from speakers it’s just vibrations that are transmitted through air into our ears. The speaker is a membrane which vibrates and generates acoustic pressure on air. The air then transmits the wave and it reaches our ear. The ear consists of three parts:

1)      The outer ear,

2)      The middle ear and

3)      The inner ear.

These components all work together to pass sound through the ear and to the brain. First, the pinna acts like a funnel to collect the sound waves. These sounds waves pass through the ear canal and reach the eardrum and cause it to vibrate. The higher the pitch or the frequency of the sound, the faster the eardrum will vibrate. These vibrations then pass on to the middle ear. The middle ear contains three tiny bones called the ossicles. These are joined together and connected to the eardrum. They amplify the sound waves and pass them on to the middle ear. The vibrations from the ossicles pass through a small window and into a part in the middle ear called the cochlea. Sound waves pass through the fluid of the cochlea and move the tiny hairs inside, initiating an electrical signal that varies depending on sound pitch and volume. The signal travels through the auditory nerve to the brain, where it is interpreted.  

Figure 4 – Human ear

Next video demonstrates the process and function of human ear.

Smell

The smell detecting nasal cavity is located beneath the eyes and contains a sticky nucleus fluid; this nucleus membrane is only six hundredths of a millimeter thick. Olfactory nerve cells are another part of the smelling system. These cells are tasked with the transportation of messages from smell molecules to the olfactory bulbs. Each small cell is comprised of three main parts - the cell body in centered between tiny hairs called cilia on one end and nerve extensions called axons on the other. These axons, numbering between 10 to 100, work together to transport the cell signal to the olfactory bulb inside the brain. They form a bundle that reaches the olfactory bulbs and as a group, pass through a porous, paper thin bone called the cribriform plate. This bone has pores in it through which the olfactory neurons pass. The bone design allows connections between neurons and makes smelling possible.

Figure 5 – Anatomy of smell

The olfactory bulb is another important part of the smell system. It lies on the front side of the brain above the nasal cavity. There are two olfactory lobes in the brain just as the nose has two nasal cavities. Each of these lobes is approximately as large as a pea. The olfactory lobes work like a news room – all the signals coming in from the olfactory receptors gather in the center. Millions of pieces of information are reorganized here. Later they are sent to the relevant parts of the brain.

Here is short video which describes the anatomy of smell.