A Humidifier Is Quite Interesting / How Does a Piezoelement Work?

There are different types of humidifiers, Dyson ones that cost all your money, they look fancy like a brand new car, and Chinese ones that try to attract you with a cute appearance. Obviously, they are much cheaper and obviously less effective. However, I'm not gonna measure abilities of these Chinese humidifiers and compare it to Dyson ones. In this video, I would like to talk about how it works and how this stream of water is created, about the physics of the process. So, let's disassemble it to look at what is inside. There are several main parts. Water tank, wick, electronics that control the humidifier, and the most important part of it, which creates all the magic, is the piezo element. All these together works in the following way. Water from the tank through the wick flows into piezo element, which spreads water into the air, converting it to the fog. To understand its working principle deeper, let's just split the cat into two most crucial parts, which are the control board and piezo element itself, and we'll try to figure out how they work. So, let's start with the element itself. Piezo element is created from a special material, which can convert electrical energy into mechanical. For example, when voltage is applied to it, it deforms. It changes its dimensions. Even if it's really hard to notice, because deformation is really slight, it is enough to make a lot of cool stuff with its help. For example, it is used in actuators, in hard disk drives. Or, as in this case, it is a part of the humidifier. Also worth mentioning that piezo element can work in the opposite way. It can generate electricity when it's deformed. For example, some lighters use piezo element in order to get a spark. So, piezo electric effect is just a unique ability of some materials that allows to convert one form of energy into another. But the question here is the same. How with its help it is possible to create a fog? Let's look at it deeper. In humidifiers, such piezo element usually has a form of a flat disk that has two contacts to apply voltage to it. So, when voltage is applied to it, it deforms, as I already said. And it can do it really fast. Really, really fast. The frequency can go up to 5 MHz, which is 5 million times per second. So, when piezo element vibrates and there is water on its surface, it creates ripples causing droplets to break away and rise into the air, which creates fog. For example, on those pictures you can see step-by-step process of water droplets creation. It starts with a wave, then connected droplet, and finally a droplet in the air. And, as you can see, the process is periodic. That means that droplets are created in a close distance to each other with some periodicity, which, as you may have guessed, depends on an oscillation frequency. Lower frequency leads to bigger droplets, but the number of them is also lower. And higher frequency leads to smaller droplets, but more of them. Now, let's have a look at the electronics part. As you may have guessed, responsible for the control is this board, which has the following schematic. The control circuit is based on a 555 timer. The timer generates pulses at the gate of the transistor with a specific frequency, forcing piezo element to vibrate. But there is another one more thing that we need to know about piezo element before we start controlling it. Piezo element in reality has something more inside of it. It's not just two plates of metal. From an electronics point of view, piezo element has following structure with capacitors, inductor and resistor inside of it. All these components somehow are present inside. And because piezo has such a structure, its control is a little bit complicated because of the resonances. So, basically, resonance is a phenomenon of increased amplitude that occurs when the natural oscillations in the system match the external force. Don't be scared, it's really easy. Because the simplest example from the real world is a swing. For example, if somebody pushes you at a specific moment, the swing amplitude is gonna increase. And even if you stop applying force, you will continue swinging due to accumulated energy. However, because of different resistances of air, shaft, you will eventually stop. And that exact thing happens in here, in piezo element. If we push energy in a specific moment, the swing amplitude is gonna increase. But in case of piezo element, it's voltages and currents that increases. So, if you take those components in piezo element, their natural oscillating frequency can be calculated using the next formula. And because they are connected in series, the resonance is called series resonance. And if it comes to these components, because capacitor is connected in parallel, resonance will be parallel. And actually it is very important, because it is two different types of resonances with very different properties. These components are connected in series, and the current that flows through them is the same, but the voltage is not. Wait a minute, it's all gonna make sense when I show you the simulation. In this example, AC voltage source has 15 V amplitude. The parameters of the circuit doesn't matter for now. And just with a slate of hand and no cheating, you can see how 15 V at the source converts into almost 100 V at the passive components, capacitor and inductor. But how it is possible? As I said, it's a swing. By applying force in phase with the oscillations, 100 000 times per second, we were able to achieve such high values. Also, if you pay attention, you can see that voltage at the capacitor and inductor are in opposite phases. That means that they just exchange energy with each other. Energy goes from one element to another. So, that is how series resonance works. In series resonance, the voltage at the components are much higher than the input. And if you want to calculate it, it can be done using the Q factor, which basically shows how many times the voltage at the components is higher than the input voltage. In example, I gave you Q factor equals approximately 7. So, if we multiply 15 by Q, which is 7, it gives us approximately 100 V at the output. The second resonance that occurs in the other element is parallel resonance. I don't want to explain it from the beginning, but it is the same. But instead of voltage, it is the current resonance. Current in these two branches is Q times higher than the input one. And voltage is the same, because elements are connected in parallel. So, now you know the difference between series and parallel resonance. But so far it is not clear which resonance do we need to use in the humidifier. Parallel or series? Because it can have both. Both of them are exist. And if you have paid attention to this picture, you might have seen the mechanical part inscription. That means that the series resonance is more important in such case. Because the maximum power is transferred to the piezo. So, the external source should be working with that frequency. So, when you know how the piezo element works inside and its resonance frequency, it is time to apply an external force that has the same frequency. In the CAT humidifier it is 555 timer, which turns on and off MOSFET transistor. This inductor limits the maximum current that flows through transistor when it turns on, and additionally increases the voltage that is applied to piezo element when the transistor turns off, like in a simple boost converter. Also, as you can see, it is not obligatory to have bipolar source in order to have resonance. It is possible to push energy into the circuit during only half wave. Like with a swing. You don't have to have two people standing on both sides. Only one is enough in order to have fun. And if you want to read something more about the topic, I'm gonna put all the information from this video in the description, so you can read more about it if you want. That was Chinese humidifier. Press like and subscribe and see you in the next video. Bye!