Online Master of Science in Electrical Engineering

Intro to Microwaves: Theory and Devices

Microwaves are generally defined as electromagnetic waves with a frequency between 300 MHz to 300 GHz. Typically, the wavelengths of these electromagnetic waves are defined as well, with the range being from 1m to 1mm.

Microwaves obey the laws of optics, such as Snell’s law and the law of reflection, and thus can be transferred, assimilated, or reflected, which is extremely important when considering how microwaves operate.

 

Modern Usage

Microwaves are ubiquitous in modern technology, with one of its most popular industries being television. As one may realize upon noting that television programs are available across the globe, the wide frequency/wave length of microwaves allows for the transcontinental transference of television content. Using a variety of intricate networks (i.e. transmitter and receiver) local stations receive television signals and instantly transfigure the signal to a more appropriate, lower signal so personal television sets can broadcast the desired content.

Microwaves are also popular amongst national and local security channels. For example, missile guidance infrastructures utilize microwaves in order to control the parameters and speed of their missiles.

 

The Microwave Oven

Yet, despite its popularity in a variety of other industries, one of the most common uses of microwaves is the ever popular microwave oven.

Individuals generally think of microwave ovens as similar to traditional ovens, except that microwave ovens can heat at a faster rate. But in truly understanding microwaves, it is essential to note that their heating process is actually quite different from that of traditional ovens[1]. With traditional ovens, heat derives from sources external to the object; whereas, materials in microwave ovens generate heat internally.

The internal heating process gives microwaves a quicker, more flexible range of heating. For example, foods or materials of various shapes, sizes, and dimensions can all be cooked at a fast rate due to the heat coming from within, while external heat would have to operate parallel to a material’s size and contour.

The nature of microwave energy also allows for selective heating, which is particularly beneficial for experiments. For example, due to selective heating, experimenters can aim directly at a material’s magnetic constituent, which thus translates to precise demagnetization.

 

Loss Mechanisms

There are a multitude of mechanisms through which microwave energy can combine or be lost within a system, with the four most popular being

  • Dielectric
  • Conduction
  • Hysteresis
  • Resonance

Understanding which loss mechanism occurred in which sample can be extremely difficult; yet, there still are a distinguishable difference between these mechanisms when it comes to elements such as microstructure, frequency, or temperature.

 

Devices

Circuits

Circuits, which can be considered as a series of electronic components, are one of the most important elements of microwave infrastructures. In general terms, circuits are made to configure electromagnetic occurrences to send different signals to the appropriate location.

The origins of microwave circuits derived slightly after World War II when clunky, massive pipes were used. Engineers soon found these metallic pipes to be too heavy and expensive, so they created the lighter planar circuits, which remain particularly popular to this day.

Yet with novel techniques and technological advancements, engineers are seeking to further diminish the cost, size, and density of microwave circuits. For example, engineers have designed a system in which multiple layers of circuits are stacked on top of each other for maximum efficiency.

Antennae

Microwave antennas are components of a microwave system that send and receive data between various sites. So, in continuing the television example mentioned above, television antennas allow the personal television to receive data from local, national, or international broadcasters, and vice versa.

In order to properly receive signals, antennas should be place at a location where it will not be blocked. Thus, microwave antennas of high importance are typically place on top of large hills, towers, or mountains so they can have supreme access to long distance signals.

Resonators

When in reference to microwaves, resonators are typically called radio frequency cavities (or microwave cavities). A radio frequency cavity traps electromagnetic phenomena within the microwave vector of the wave spectrum. Thus, without radio frequency cavities, it would be extremely difficult to send or receive microwave signals on a consistent basis.

Furthermore, to provide a clear example of radio frequency cavities’ role in a microwave system, it is best to think of them as extremely selective filters that allows particular frequencies to pass while denying those that are deemed unwanted or unnecessary.

As aforementioned, microwaves are responsible for a large majority of our technological advancements, particularly those within the television and security industries. Yet, as technology continues to increase power and decreasing size, it will be extremely interesting to see how strong and miniscule fully functioning microwave systems will be in the future.

 

Sources:

http://www.liv.ac.uk/~mimi/Chapter3.pdf

http://www.madmadscientist.com/html/Theory.htm

http://www.microwaves101.com/encyclopedias/basic-concepts

http://ethw.org/Microwave_Circuits

 

[1] Note: This is in most general terms, for in relation to magnetic particles, conventional and microwave heating has been found to be quite similar.

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