How do IoT sensors sense the real world around them?

In recent decades, computing technology has witnessed remarkable advancements, an era that engineers find nothing short of fascinating, given the vast computing power at their disposal. Among the most prevalent computing devices are personal computers, laptops, and handheld gadgets like smartphones and smartwatches. The integration of computing technology in our daily lives has become essential as we struggle to scratch the surface of the immense potential of these intelligent machines.

However, the advent of the Internet of Things (IoT) has taken computing technology to new heights, reshaping the concept of "smart" to unprecedented levels. The excitement is just beginning to unravel as we brace ourselves for an impending surge of technological innovation.

What is IoT?

IoT stands for "Internet of Things," which refers to a network of physical objects, devices, vehicles, and other items embedded with sensors, software, and connectivity, allowing them to collect and exchange data over the internet. IoT sensors are the devices that allow this data to be collected.

IoT sensors make things responsive to real world

IoT sensors can be used for various applications, from monitoring the temperature and humidity levels in a room to tracking the location and status of vehicles and equipment. Some common types of IoT sensors include:

Temperature sensors measure the temperature of an environment.

Humidity sensors measure the humidity level in an environment.

Proximity sensors detect the presence of objects or people in a certain area.

Accelerometers measure changes in acceleration, such as a vehicle's movement or a device's shaking.

GPS sensors determine the location of a device or vehicle.

Light sensors detect the level of light in an environment.

Motion sensors detect movement in a certain area.

Pressure sensors measure pressure changes, such as the air pressure in a tire or the water pressure in a pipe.

These are just a few examples of the many types of IoT sensors available. The data collected from these sensors can be used to improve efficiency, optimize performance, and enhance safety in various industries and applications.

In an IoT system, a sensor is a gateway between the physical and digital worlds. Consequently, the sensor must translate any physical phenomenon it perceives into a format that a computing device can interpret. Fortunately, electrical energy serves as the common link between the two worlds. As a result, we arrive at a technical definition of a sensor in an IoT system: a device that detects the desired physical quantity and converts it into an electrical signal transmitted directly to a central cloud-based server or via an on-site microcontroller.

The importance of micro-electromechanical systems

Micro-electromechanical systems (MEMS) is a highly advanced microsystems technology encompassing tiny components constructed using semiconductor materials, such as silicon, with dimensions in the micrometer range.

In the world of sensors, MEMS technology has become the gold standard for detecting mechanical energy. One of the most well-known and widely used examples is the accelerometer. This can largely be attributed to the explosive growth and increasing dependence on computing technology.

Because MEMS technology uses semiconductors as its manufacturing material, one of its primary advantages is its ability to be embedded into an integrated circuit (IC). An IC consists of other computing components constructed from semiconductor materials that work in conjunction with the sensor data received.

Moreover, the small size and integration of MEMS-based sensors into an IC results in significant cost savings. One can obtain a MEMS-based accelerometer for less than $4. Additionally, MEMS-based sensors exhibit high sensitivity and can detect even the slightest changes, a previously unimaginable feat with traditional sensors.

Overall, MEMS technology has revolutionized the sensor industry, enabling highly accurate, low-cost, and miniaturized sensors that have proven indispensable in various applications, ranging from smartphones and wearables to smart homes and factories.

Sensing mechanisms

In MEMS technology, the sensing mechanism employed by a sensor is determined by the physical quantity it detects. While some sensors use resistive-based sensing, others use capacitive-based sensing to convert physical changes into electrical signals.

Both sensing mechanisms rely on the basic principle that a change in the physical quantity being measured causes a corresponding change in the electrical resistance or capacitance of the sensor material. This means that a larger physical change results in a larger change in the resistance or capacitance of the material and vice versa.

The main difference between resistive and capacitive-based sensing lies in the working mechanism. In resistive-based sensing, a resistor detects physical changes, while capacitive-based sensing utilizes a capacitor for this purpose.

Resistive-Based Sensing

Resistive-based sensing has been a reliable means of detecting and measuring physical quantities for over a century. The principle of such sensing involves the relationship between the electrical resistance of a material and the physical quantity it is meant to detect. Physical changes, like pressure, result in changes in the material's electrical resistance, indicating the amount of change in the physical quantity.

Several physical principles, including the Photoconductive Effect, the Thermoresistive Effect of Semiconductors, and the Piezoresistive Effect, govern the changes in electrical resistance in response to a physical quantity.

However, the sensing mechanism differs when detecting non-mechanical quantities like light and temperature. For instance, light sensors require a light-sensitive material, such as a photoresistor. These materials exhibit a decrease in electrical resistance as the light's intensity increases, thereby enabling light detection.

Temperature sensing, on the other hand, requires materials that are receptive to changes in the ambient temperature, such as a thermistor. In this case, the material's electrical resistance decreases with increasing temperature.

Chemical sensors are another type of sensor that detects a particular chemical. They usually contain a sensing layer made up of a material that changes resistance when it reacts with the chemical. Gas sensors like the MQ series are popular chemical sensors in IoT systems. These sensors detect the presence of various types of gases like carbon monoxide and methane.

Ohm's Law

Ohm's Law, named after its discoverer Georg Simon Ohm, is a fundamental principle in electronics. It states that the voltage (V) applied across a conductor is directly proportional to the current (I) flowing through it, given a constant resistance (R). This relationship is expressed mathematically as V = IR.

The remarkable thing about Ohm's Law is that it allows us to measure changes in resistance with great precision. This is particularly useful in the context of IoT sensors, where even tiny variations in resistance can be converted into electrical signals and analyzed by a computer.

Resistance-based IoT sensors rely on the principle that changes in a physical quantity, like temperature, pressure, or light, can alter the resistance of a sensing element made of a suitable material like a thermistor or photoresistor. By measuring the resulting changes in voltage or current across the sensing element, we can accurately measure the physical quantity being sensed.

Thus, Ohm's Law plays a crucial role in the functioning of many IoT sensors, enabling them to convert physical changes into meaningful electrical signals that a computer can interpret and act upon.

Capacitive-Based Sensing

The capacitive-based sensing mechanism in IoT sensors relies on changes in physical geometry, including the material's area, distance, and capacitance. Capacitive touch sensors, commonly found in smartphones and other devices, are pressure sensors that detect physical touch by measuring changes in capacitance. When pressure is applied to the screen, the area and distance change, causing a change in capacitance that triggers an electrical signal.

Unlike resistive-based sensing systems, capacitive-based systems rely on their unique relationship between changes in capacitance and voltage/current. This relationship allows even small changes in capacitance to be quickly and accurately detected, making capacitive-based sensing systems highly effective for many applications in IoT devices.

Capacitive vs. resistive sensing

Resistive-based sensing has been the go-to method for measuring physical quantities for over a century. Still, it does have its limitations when it comes to detecting non-mechanical quantities such as light and temperature. This is where capacitive-based sensing systems can shine. These systems rely on changes in physical geometry, such as the area and distance between components. As a result, the sensing procedure remains relatively uniform regardless of the measured quantity.

Although capacitive-based sensing is still a relatively new technology, it has shown great promise in detecting mechanical systems using MEMS technology. However, the need for specialized materials in resistive-based sensing can provide a unique advantage in detecting specific quantities that may not be easily measurable with a capacitive-based system. Overall, both sensing mechanisms have their strengths and shortcomings, and the choice of which one to use depends on the specific application and the quantity being measured.