Microwave Radio Frequencies and Components

Microwave radio frequencies are electromagnetic waves with wavelength with the sizes ranging between 1mm – 1m. The frequency utilized are in the 0.3 GH and 300 GHz range. Microwave ovens are basically accelerated radio wave machines that contain a concentrated radio frequency inside a chamber. Microwave frequencies have adverse effects on humans. This is why the government employs the “Active Denial System” Energy Weapon for crowd control. More importantly, microwave frequencies cause heat in water.


Radio Frequencies

In the table below you will see how microwave frequencies are used and what their frequencies are.

Band name Abbr band Frequency
and
Wavelength
Example uses
Extremely low frequency ELF 1 3–30 Hz
100,000 km – 10,000 km
Communication with submarines
Super low frequency SLF 2 30–300 Hz
10,000 km – 1000 km
Communication with submarines
Ultra low frequency ULF 3 300–3000 Hz
1000 km – 100 km
Communication within underground mines
Very low frequency VLF 4 3–30 kHz
100 km – 10 km
Submarine communication, avalanche beacons, wireless heart rate monitors, and geophysics
Low frequency LF 5 30–300 kHz
10 km – 1 km
Navigation, Time signals, AM Radio
Medium frequency MF 6 300–3000 kHz
1 km – 100 m
AM Radio
High frequency HF 7 3–30 MHz
100 m – 10 m
Shortwave Radio and aviation communications
Very high frequency VHF 8 30–300 MHz
10 m – 1 m
FM Radio, TV broadcasts, and aircraft communications
Ultra high frequency UHF 9 300–3000 MHz
1 m – 100 mm
TV broadcasts, microwave ovens, mobile phones, wireless LAN, Bluetooth, GPS, and Two-Way Radios
Super high frequency SHF 10 3–30 GHz
100 mm – 10 mm
Radars, Mobile Phones, and Commercial Wireless LAN
Extremely high frequency EHF 11 30–300 GHz
10 mm – 1 mm
High-speed satellite microwave transmission
Source from Wikipedia Radio Frequency

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Electromagnetic Spectrum: Microwaves

The video below explains how microwaves fit in the electromagnetic spectrum. This video is from “the Science Channel” and it gives an excellent overview of how microwaves are used. Microwaves are used in an incredible rate and are everywhere.

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Waveguide Polarization- How microwaves travel

Polarization is an important part of Microwave frequency transmissions. The Microwave transmission will have a linear or circular form. Each pattern is produced by a specifically constructed wave guide.

The radiowave is an electromagnetic waveform composed of both electric and magnetic fields. In free space, the fields are mutually perpendicular and are also perpendicular to the direction of propagation.

The term polarization commonly refers to the electric field component of the radiowave. In terrestrial microwave antennas, the polarization of the radio waves will be either horizontal or vertical. That is, the electric field will be either horizontal or vertically orientated.
Back To Basics In Microwave Systems: Polarization Derren Oliver on May 22, 2014

Below is a graphical representation created by Bruce R. Elbert in his presentation on “Communications Payload Design and Satellite System Architecture: Bent Pipe and Digital Processor-based Course Sampler.

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We will use the Microwave Oven as an example of the concept

How a Microwave Oven works?

This is a drawing of how a microwave oven works.

This is a drawing of how a microwave oven works.

In order to understand how microwaves work in general, it is necessary to understand how radio frequencies cause heating. The parts of a microwave that create the radio frequencies are the transformer, cavity magnetron, micro controller, and wave guide.Click here for a great explanation of Radio Frequency Heating. Microwave ovens work by passing non ionizing microwave radiation through the food, at a frequency approximately 2.5 GHz. Microwave ovens produce waves similar to that of a typical wireless phone.

Microwave radio frequencies pass through water, fat, and other substances causing a process called dielectric heating. Water molecules have a positive charge at one end and a negative charge at the other called electric dipoles. As microwaves pass through water molecules, the molecules rotate as they try to align themselves with the alternating electric field. This molecular movement creates heat. Microwave heating is most effective on liquid water.

This is an image of molecular friction due to RF heating from the<a href="http://www.colorado.edu/physics/2000/microwaves/water_rotates4.html" target="_blank">Colorado EDU</a>

This is an image of molecular friction due to RF heating from the Colorado EDU

The image to the left is an illustration from the Colorado EDU. This illustration shows how molecules rotate and cause friction between each other when microwave radio frequencies passed through. But what about lower wattage’s. Lower wattage’s can cause things to cook as well, the only difference is that it takes longer. That is why Microwave ovens have different power settings. Factors like, concentration of the waves, power wattage, and frequency levels are what determine how fast something will cook or melt.

One may ask themselves, “Do microwave ovens have any hazards?” In fact microwave ovens can leak microwave frequencies outside of the oven. Some say that the newer microwaves today have no health risks due to better constructed units. (See the Canadian Center for Health and Safety) Exposure to higher wattage can affect a humans health.

Whether the microwave oven itself is hazardous is not a focus of this topic. What we need to know is do microwave transmissions in our atmosphere cause Climate change, adverse weather patters, or warming on a global scale.

 


Microwave Oven Components

A microwave oven consists of:

  • a high voltage transformer, which passes energy to the magnetron
  • a cavity magnetron,
  • a magnetron control circuit (usually with a microcontroller),
  • a waveguide, and
  • a cooking chamber

 

Microwave oven waveguide

Microwave oven waveguide

Magnetron with section removed (magnet is not shown) picture taken by HCRS

Magnetron with section removed (magnet is not shown) picture taken by HCRS

Understanding how a microwave works can be achieved by studying the parts and how they work. First we will take a close look at the specifications a waveguide. The waveguide is an essential function of the microwave oven.

A Waveguide (Graphic to the left) is any linear structure that guides electromagnetic waves for the purpose of transmitting power or signals. Generally constructed of a hollow metal pipe. Placing a waveguide into a vacuum causes radio waves to scatter.

A Cavity magnetron (Graphic to the right) is a microwave antenna placed in a vacuum tube and oscillated in an electromagnetic field in order to produce high GHz microwaves. Magnetrons are in microwave ovens and radar systems.

This is a picture of a micro controller.

This is a picture of a micro controller.

This is how a transformer works.

This is how a transformer works.

A Microcontroller (Graphic to the left) is a microprocessor that is integrated on a circuit board. Like in cell phones and satellite dishes. Here is a SIS chip on a graphics card. This is what an integrated processor looks like. The microcontroller controls the waveguide and the entire unit so the microwaves are emitted at a constant rate.

A Transformer (Graphic to the right) is two or more coupled winding and a magnetic flux core that transfers electrical energy through a circuit by magnetic coupling without using motion between parts. These are used for supplying power to the magnetron.

A Cooking Chamber (Graphic to the left) is a microwave safe container the prevents microwaves from escaping. The door has a microwave proof mesh with holes that are just small enough that microwaves can’t pass through but light waves can. The cooking chamber itself is a Faraday cage enclosure which prevents the microwaves from escaping into the environment.

The oven door is usually a glass panel for easy viewing, but has a layer of conductive mesh to maintain the shielding. Because the size of the perforations in the mesh is much less than the wavelength of 12 cm, most of the microwave radiation cannot pass through the door, while visible light (with a much shorter wavelength) can.

Video by EngineerGuy on how a microwave works

“Bill details how a microwave oven heats food. He describes how the microwave vacuum tube, called a magnetron, generates radio frequencies that cause the water in food to rotate back and forth. He shows the standing wave inside the oven, and notes how you can measure the wavelength with melted cheese. He concludes by describing how a magnetron generates radio waves. You can learn more about the microwave oven from the EngineerGuy team’s new book Eight Amazing Engineering Stories