Deep dive into the space of Electronics — Part 2

Adhish Velingkar
12 min readFeb 13, 2022

Being an inquisitive ENTC engineer, I am also fond of baking some amazing savoury food. After working and studying throughout the weekdays, I always try to spend every weekend with my mom learning about her baking mastery.

Well, I would like to call myself an amateur in this field since it’s been only 2.5 years that I have been baking dishes as a part of my hobby.

Are you eggcited to bake?

But I would like to say that this short stint of baking has taught me a lot of things that I can relate to in my day to day life such as:

  1. Organisation & Planning — Baked dishes are the one that needs to be perfect in every aspect of their ingredient. Balance is everything.
  2. Patience — I believe this is an underrated virtue. Those who have either flipped a dosa or a roti before its time would know what am I saying here.
  3. Substitutions — As eating the same kind of food every day can make anyone bored is just like switching from C to C++ to Python or whatever technology you may name because life is too short to struggle through unnecessary things.
  4. Practice — Everyone is aware of the quote “Practice makes Perfect” but I think, practising is all about making ‘progress’ in one’s life and not necessarily being perfect.
  5. Seek Help — Supporting my above point, experience teaches you a lot and one should not be afraid to ask for relevant guidance. Thus, I believe one should always improve against themself, not others.

I hope you must have figured out the topic till now since I have mentioned briefly what baking means to me!!

So let's start off with the topic right away and explore the electronics world in our daily life!

Microwave Convection Oven

While studying microwave engineering and electromagnetic field theory during my senior undergraduate years, it never excited me whenever I used to come across the terms like waveguides, Helmholtz — Maxwell equations, isolators, resonators, etc.

Not being able to create a perfect image in my mind of what I used to study often made me hate this subject a lot. It was until a few weeks before my exams, fortunately (to my benefit) the microwave oven in my house stopped functioning due to some technical faults in it.

Seeing this as an opportunity and being experienced in tearing down household appliances I thought of exploring each component present in it to the core.

Internal Circuit of my old Microwave oven

Since these ovens work at a very high-level voltage and high power, hence while dismantling them one should take care. Owing to this, I already had knowledge related to EMI-EMC (Electromagnetic Interference-Compatibility) during my junior year which demonstrated the safety use cases and tips while testing any high power devices be it in the automotive, military or healthcare sector which made half of the work easy for me while dismantling.

Having knowledge of EMI-EMC is not necessary, but I would highly recommend you to go through it once which will give you a clear idea of how such powerful devices work and cause no harm to humans.

To study in-depth you can refer to the below Wikipedia page.

Structural View of Microwave Oven

The main components of Microwave Oven and their uses are as follows:

  1. Transformer (commonly referred to as MOT):
High Voltage Transformer (240V AC I/P — India)

A typical home microwave transformer (MOT) has two secondary windings. The low-voltage winding provides 3.1 to 3.2 volts, while the high voltage winding provides between 1800–2800 volts (average ~2200 volts). The high voltage AC output from the transformer is changed to DC and doubled using a voltage doubling circuit (diode and HV capacitor) to power the magnetron.

Thus, the more windings you have on the secondary, the higher the voltage and lower the amps and vice versa.

If you are planning to make use of the transformer, well here is how you can reuse it

2. High Voltage Capacitor-Diode (Voltage Doubler Circuit):

The capacitor is in series between the secondary of the transformer and the magnetron which is used to provide power to the magnetron with the help of a diode.

The microwave’s diode converts alternating current (AC) to direct current (DC), which doubles the voltage and powers the magnetron that heats the food. Without the diode, the magnetron would not receive enough voltage to do its job. The diode is part of a voltage doubler.

Schematic of Voltage Doubler Principle

In the schematic, the top coil of the secondary is the heater power supply. It is used to heat up a filament inside the magnetron to emit electrons. These are thermal electrons without much energy.

The voltage doubler is used to provide negative bias to the filament to ‘kick’ the electrons out of the filament.

EM Wave Orientation

With the help of an external axial magnetic field, the now energetic electrons can then go spiralling around a couple of microwave cavities, utilizing cyclotron resonance to exchange their kinetic energies into the microwave.

In a nutshell, it is acting like a cyclotron(used for accelerating charged particles into high energies) but in reverse.

One can refer to the below data for more insights in the case of discharging the capacitor and diode.

3. Magnetron — Heart of the Microwave:

Cavity Magnetron structure

Microwaves are part of the electromagnetic spectrum. The term microwave refers to electromagnetic energy having a frequency higher than 1 gigahertz (billions of cycles per second), corresponding to wavelength shorter than 30 centimetres (wavelength that is shorter than radiowaves).

Magnetron Connection Diagram

The high-voltage transformer passes electricity to the magnetron. The Cavity Magnetron consists of a magnetic field. The Cavity Magnetron transforms the energy into microwave radiation. The microwave radiation created in the magnetron moves through a waveguide device which is located above the oven’s cavity where the food is placed.

The microwave radiation then passes through a revolving stirrer blade and bathes the food, causing it to heat up. The walls of the oven cavity are made of metal to reflect the radiation inward toward the food

Off-topic: Don’t even think of messing with this Magnetron, it is as harmful as ‘Magneto’ from the X-Men series! If you haven’t watched it or read the X-Men comic yet then I don’t know what were you doing in your childhood!!

Erik Lehnsherr — Magneto !!!!

4. High Capacity Thermostat:

Thermostat

The thermostat is used for switching the microwave off when it begins to overheat. It closes with heat to run the vent fan and ensure the temperature is at a safer level.

5. Front Panel

PCB Design — Keypad Control

The front panel board generally consists of the control mechanism which is used to select the timer mode, grill mode, convection mode, etc. It consists of a touchpad with a combination of pushbuttons for start-stop-resume.

Most modern ovens have clocks, digital timers and rotating turntable plates to turn food while it’s cooking. Microwaves can also have removable racks and sensors that are designed to prevent over-cooking.

I would like to cover this part of the information in my upcoming articles based on microcontroller units (MCU) and embedded systems in which I will give a detailed description of the algorithmic logic used.

6. Exhaust Fan

Fan for cooling purposes

Microwave exhaust fans work by drawing in the warmer air from inside a microwave and exhausting it outside. It also reduces the magnetron’s operating temperature and ensures its efficacy and longevity.

Modern Microwave ovens have internal sensors that help to determine when enough time has passed, at which point the unit will turn on its fan automatically.

PHYSICS behind the heating of the food!

Interaction of H2O molecules — Microwaves (EF +MF)

Microwave ovens work on the principle of conversion of electromagnetic energy into thermal energy. Electromagnetic (EM) energy refers to the radiation (waves) comprising an electrical field and magnetic field oscillating perpendicular to each other.

When a polar molecule, i.e., a molecule containing opposite charges, falls in the path of these EM radiations, it oscillates to align with them.

Heating of Food

The molecules have a lot of room to move around inside the cooking chamber. The molecules will eventually run into each other. When they run into each other, friction is created. The friction then causes heat, which causes the food to cook. As these molecules change direction rapidly (millions of times per second), they gain energy, which increases the temperature of the material. This process is called dielectric heating.

The microwave energy diminishes according to the inverse square law, and therefore, the cavity chamber, where we place food, is designed in such a way that it carries out the maximum efficiency of the heating effect of microwaves.

The water molecules present inside our food products go under a similar phenomenon when they come in contact with microwave radiations, heating the food from inside out.

In most of the ovens, the microwave used is of 2.24GHz frequency. These dimensions allow microwaves to penetrate deep inside the food and cook it from inside, while the temperature of the air present around the food remains constant as air is nonpolar.

Stirrer Plate

Food cooks in a microwave depend mostly on what it’s made from. Microwaves excite the liquids in foods more strongly, so something like a choco lava cake (with a higher liquid content in the center) will indeed cook from the inside out because the inside has the highest water content.

Also, one may have often noticed that frozen food and dry food (such as rice) don’t cook as efficiently because these objects lack moisture and do not respond quickly or uniformly to microwave radiation. To ensure that food cooks more evenly, many microwave ovens feature a rotating plate to turn the food around during cooking.

Another important factor is the size and shape of what you’re cooking. Microwaves can’t penetrate more than a centimetre or two (perhaps an inch) into food. Like swimmers diving into the water, they’re losing energy from the moment they enter the water, and after that first centimetre or so they don’t have enough energy left to penetrate any deeper.

Hence, this is how our food gets cooked, baked and heats up in a square box filled with such an amazing combination of electrical-electronic components.

Advantages:

  1. A microwave oven cooks many foods in about 1/4th of the time necessary on a gas burner. There is no wastage of energy.
  2. It saves time in heating frozen foods. Dangerous organisms have less time to thrive on food that is cooked in the microwave because the food is brought to a high temperature quickly and can be served right away.
  3. Flavour and texture do not change when reheated in a microwave oven and also preserve the natural colour of vegetables and fruits.
  4. Loss of nutrients is minimized. Other conventional cooking methods, however, may destroy some polar as well as non-polar ingredients during the process. (Vitamin C are better retained by microwave cooking compared to pressure cooking and saucepan cooking)
  5. The user interface and micro-controller facilitate precise control over the cooking temperature.
  6. Microwave ovens only use electricity, not gas, charcoal or oil, which reduces their carbon footprint and eliminates pollution beyond that which is created in the production of electricity.

Disadvantages:

  1. It is important to take care of what kind of utensils are being used in a microwave. A dish that is not microwave-safe will set off a chemical reaction between the food and the container.
  2. It is not possible to make chapatti or tandoori roti in it. It cannot cook soft or hard-boiled eggs. Deep frying necessary for puris, jalebis, and vadas cannot be done in it. (Sad stuff for real!)
  3. Microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn. (while repairing) especially to the eyes and the testes because there is relatively less blood flow in them.
  4. Since it has limited capacity, therefore it won't be able to benefit anyone having a huge number of members in a family.

Miscellaneous:

Currently, in my kitchen, there are two types of oven namely Godrej Eon’s Microwave Convection Oven for heating, cooking-maggie-oats-brownie, etc.(Prior to this, I had Electrolux brand which lasted for 10 long years — whose internal circuit I had attached above for reference) & another one is the USHA electronics OTG (Oven Toaster Griller) — a conventional oven basically which is used for baking, grilling and roasting purposes.

Convection vs OTG

I have never opened a conventional oven before because it was replaced by the time when I was mature enough to tear it down !!! In future, maybe!

OTG and Convection oven has their own pros and cons and that’s why bakers try to use them according to their convenience. As you can see in the above comparison table given.

Coming from a middle-class Indian people, we don't intend to have two microwaves at home as the family tradition prefers to use a steamer or a pressure cooker for baking or heating purposes thus trying to save money which is actually good but not the best way in terms of getting the expected result.

But I would say if you are really interested in baking stuff, want to eat less oily stuff (which my Mom makes me eat a lotttt) and if you like spending on technology then buying two ovens makes a lot of sense. Otherwise, you can have a simple convection microwave oven that can cook the basic food in your daily routine.

I hope I tried to cover every possible aspect of the microwave oven in the field of electronics along with its day to day usage. Thus, I would like to end this article by sharing some of the snaps I have taken after baking a few of my best dishes during my weekends.

Son bakes Savoury- Tortillas -Pasta-Puffs!!!

I guess now after learning about the tech stuff involved in the oven which I discussed today, I hope you would be also thriving to make some amazing dishes like above….Until then see you next weekend!

Thank you !!!

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Adhish Velingkar

A novice blogger who talks about Power-Analog Electronics, EV's, Low Voltage devices, Embedded interface, Hardware-Simulation, Renewables, Electrical Designs