What Are Transducers

Transducers are electric or electronic devices that transform energy from one manifestation into another. Most people, when they think of transducers, think specifically of devices that perform this transformation to gather or transfer information. In reality, however, anything that converts energy can be considered a transducer.

Found Throughout Everyday Life

Common transducers that detect or transmit information include microphones, Geiger meters, pressure sensors, thermometers and antennae. A microphone, for example, converts sound waves that strike its diaphragm into an analogous electrical signal that can be transmitted over wires. A pressure sensor turns the physical force being exerted on the sensing apparatus into an analog reading that can be easily represented. Many people think of a transducer as being some sort of technical device, but they can be found in many places throughout everyday life.

Most transducers have an inverse that allows for the energy to be returned to its original form. Audio cassettes, for example, are created by using a transducer to turn the electrical signal from the microphone pick-up — which went through a transducer to convert the sound waves into an electrical signal — into magnetic fluctuations on the tape head. These magnetic fluctuations are then read and converted by another transducer — in this case, the stereo system — to be turned back into an electrical signal. This signal is then fed by wire to speakers that act as yet another transducer to turn the electrical signal back into audio waves. 

Other transducers turn one type of energy into another form, not to measure something in the external environment or to communicate information, but rather to make use of that energy in a more productive manner. A light bulb, for example, converts electrical energy into visible light. Electric motors are another common form of electromechanical transducer, converting electrical energy into kinetic energy to perform a mechanical task. The inverse of an electric motor — a generator — also is a transducer, turning kinetic energy into electrical energy that can then be used by other devices.

Efficiency

As in all energy conversions, some energy is lost when transducers operate. The efficiency of a transducer is found by comparing the total energy put into it to the total energy coming out of the system. Some transducers are very efficient, and others are extraordinarily inefficient. 

A radio antenna is one example of an efficient transducer. The antenna acts as a transducer to turn radio frequency power into an electromagnetic field. When the antenna is operating well, this process can be more than 80 percent efficient. Most electrical motors, by contrast, are less than 50 percent efficient. A common light bulb, because of the amount of energy that is lost as heat, is less than 10 percent efficient.

What is a DVD-ROM

A Digital Versatile Disc — Read Only Memory, or DVD-ROM, is a media storage disk that closely resembles a CD or compact disk. The major difference is that the DVD-ROM is formatted to hold far more data. A CD commonly has a capacity of 650 megabytes, while the smallest capacity DVD can store about seven times more data, or 4.38 gigabytes (GB). 

There are various kinds of DVDs, but the DVD-ROM refers to a read-only disc, or a disc that cannot be written over. If you purchase a DVD movie from the local video store, you have a good example of a DVD-ROM. Blank DVDs with designations like "DVD-R" and "DVD+R" are formatted, recordable DVDs. The —R and +R refer to competing format standards, but both will record movies, audio or other data.

A DVD-ROM encodes data in the form of a spiraling trail of pits and lands separated by mere nanometers. The trail starts at the center of the DVD-ROM and winds around countless times until it reaches the outer edge. In the case of a double layer disk, the trail continues on a second layer of material. If the disc is also double-sided, the trail of pits and lands extends to side two. 

A laser beam in the DVD player tracks the beam as the disc spins, while a special device reads the intensity of the reflection as it bounces off the pits and lands. The reflective variance gets translated to bits of data which form bytes. Hence, DVDs, including the DVD-ROM, can vary in capacity as follows:

1. Single-sided single-layer disc — 4.38 GB
2. Single-sided double-layer disc — 7.95 GB
3. Double-sided single-layer disc — 8.75 GB
4. Double-sided double-layer disc — 15.9 GB

The DVD-ROM has replaced the videocassette, being far more efficient and superior in all respects. For one, a DVD-ROM stores data in digital form, while the videocassette uses less precise analog technology. A DVD-ROM, under normal conditions, remains error free and consistent, regardless of the amount of times it is viewed, while a video cassette stretches with wear and eventually needs replacement. The DVD-ROM can also hold more information in a higher format, and one can skip to specific scenes without the need for fast-forwarding or rewinding. Finally, the DVD-ROM is much more compact and easier to store, and DVD players can double as CD players.

If purchasing a DVD player, be sure to get one that can play all DVD-ROM formats, including double-sided, double-layered discs. For home theater systems look for models equipped with a 192 kilohertz (kHz), 24-bit digital/analog converter (DAC) for true Dolby theater quality. By comparison, standard DVD players use 96 kHz, 24-bit DACs. This is still a big improvement over CDs, however, which use 44.1 kHz, 16-bit sampling to produce audio. For this reason, people are moving towards DVDs to store music. An audio DVD can hold just over an hour of multi-channel music at 192 kHz, the highest bit rate; about two hours at 96 kHz; and close to seven hours at the standard CD sampling rate of 44.1 kHz. 

While cassettes, videocassettes and laser diskc have become legacy technologies, the DVD-ROM appears to be here to stay. Recordable DVDs are available wherever music and movies are sold, including department stores, office supply chains and discount marts.

What Is CDMA

CDMA stands for Code Division Multiple Access. It is a technique used for digital communication, and wireless technology in particular, that involves multiplexing. Whereas conventional communication systems use constant frequencies, CDMA uses multiple access, or multiplexing. Accomplished through the specific type known as spread spectrum in this case, multiplexing uses varied frequencies to transmit audio signals. This, coupled with code division, which requires a certain code to send and receive the frequency, further protects CDMA communications from interference.

Radio systems, one of the earliest forms of telecommunication, required users to communicate on distinct frequencies. Frequency Division Multiple Access (FDMA), one form of early wireless communication, only allowed users to operate on a single frequency. When tuning in to a radio to get sound, for instance, the listener must select one frequency or another, and must tune the frequency to filter out noise in the spectrum. Another form of early radio communication was Time Division Multiple Access (TDMA). In this case, users could not share a frequency, and each user had to coordinate his or her turn on that frequency in order to communicate.

Both FDMA and TDMA posed restrictions for early users, particularly the military. As early as World War II, militaries recognized the high value in using wireless technology to communicate across vast distances. Military communication units did not always have the time to wait their turn to transmit sound, or to find the right frequency. 

Some telecommunication systems allowed military communication units to transmit sound into the same spectrum their adversaries used. Military signals needed a unique identification through a distinct code to avoid interference from enemy communication. The receiver of that message on the other end could then retrieve the message based on its unique code in the spectrum. 

Just as the radio moved from military use to commercial use, so too was the case with the wireless technology. CDMA became the early choice for personal communication because it could allow multiple users to communicate within the spectrum, avoiding interference or blocking among users. In 1999, CDMA became the standard technology for the telecommunications industry for its growing wireless systems. Since there are large numbers of users in the system communicating at the same time, code division ensures that each user’s signal remains separate in the spectrum.