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Oscillator

Gist

An oscillator is an electronic circuit that converts DC (Direct Current) into a periodic, repeating AC (Alternating Current) signal—such as a sine, square, or triangle wave—without needing an external input signal. These devices are essential for generating, timing, and controlling frequencies in systems like radio, clocks, computers, and sensors.

Oscillators are fundamental in electronics, generating precise frequencies for applications like clocks in computers, carrier waves in radios & Wi-Fi, and timing signals in microcontrollers, enabling everything from timekeeping (watches) to data synchronization (Bluetooth) and medical devices (ultrasound), acting as versatile signal generators for diverse needs. 

Summary

An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found in many electronic devices, such as radio receivers, television sets, radio and television broadcast transmitters, computers, computer peripherals, cellphones, radar, and many other devices.

Oscillators are often characterized by the frequency of their output signal:

* A low-frequency oscillator (LFO) is an oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.
* An audio oscillator produces frequencies in the audio range, 20 Hz to 20 kHz.
* A radio frequency (RF) oscillator produces signals above the audio range, more generally in the range of 100 kHz to 100 GHz.

There are two general types of electronic oscillators: the linear or harmonic oscillator, and the nonlinear or relaxation oscillator. The two types are fundamentally different in how oscillation is produced, as well as in the characteristic type of output signal that is generated.

The most-common linear oscillator in use is the crystal oscillator, in which the output frequency is controlled by a piezo-electric resonator consisting of a vibrating quartz crystal. Crystal oscillators are ubiquitous in modern electronics, being the source for the clock signal in computers and digital watches, as well as a source for the signals generated in radio transmitters and receivers. As a crystal oscillator's “native” output waveform is sinusoidal, a signal-conditioning circuit may be used to convert the output to other waveform types, such as the square wave typically utilized in computer clock circuits.

Details

Oscillators are essential components in the world of electronics, playing a crucial role in generating periodic signals. From the simplest applications to complex systems, oscillators provide the timing signals needed for synchronization and control. This article explains what oscillators are and how they work, explores the various types and their performance characteristics, highlights their applications across industries, and reviews recent advancements in this essential technology.

What is an Oscillator?

An oscillator is an electronic circuit that produces a continuous, periodic signal - typically in the form of a sine wave, square wave, or triangle wave - without requiring an input signal. These signals are defined by their frequency and amplitude, which can be precisely controlled to suit specific applications. In essence, an oscillator converts energy from a DC power supply into an AC signal.

Oscillators are found in a wide array of devices, including clocks, radios, and computers. They are considered the heartbeat of electronic systems, serving as timing references that enable circuits to synchronize and function properly.

What is an Oscillator in a CPU?

A CPU oscillator is responsible for generating clock signals that regulate the timing and speed of the processor. These clock signals synchronize various CPU components, allowing for the coordinated execution of instructions.

Typically, a crystal oscillator is used, which relies on the mechanical resonance of a vibrating quartz crystal to produce a stable frequency. This precise timing is critical to a CPU’s performance and efficiency, as it directly affects the instruction execution rate.

How Do Oscillators Work?

Oscillators generate a continuous, periodic signal - such as a sine wave or square wave - without requiring an input signal of the same frequency. They achieve this through the combined principles of feedback and resonance.

Basic Components

• Amplifier: Boosts the signal.

• Feedback Network: Determines the frequency of oscillation.

• Energy Source: Supplies power to sustain the oscillation.

The system continuously feeds part of its output back to the input, allowing the signal to regenerate itself. The frequency of oscillation depends on the configuration of components such as resistors, capacitors, and inductors within the feedback loop.

Purpose of an Oscillator

The primary purpose of an oscillator is to generate consistent clock signals that control the timing and synchronization of electronic systems, especially CPUs. These signals are essential for ensuring the coordinated execution of instructions, which in turn impacts overall system performance.

Types of Oscillators:

What is an oscillator? And what are the types of oscillators?

Oscillators, essential components in electronic circuits, can be categorized based on the type of waveform they produce and their method of operation. These components are generally divided into two main categories.

Relaxation vs Linear Oscillators

Relaxation Oscillators: Produce non-sinusoidal waveforms such as sawtooth or square waves.

Linear Oscillators: Generate sinusoidal waveforms.

Specific Types

Crystal Oscillators: Crystal oscillators are linear oscillators, and use quartz crystals to generate precise frequencies. Known for their stability and accuracy, they are ideal for communication devices and clocks.

RC Oscillators: RC oscillators can be both relaxation oscillators and linear oscillators. These oscillators utilize resistors and capacitors to generate sine or square waves. Often used in audio applications due to their simplicity and cost-effectiveness.

LC Oscillators: LC oscillators are considered linear oscillators and use inductors (L) and capacitors (C) to produce oscillations. Typically employed in radio frequency (RF) applications due to their high-frequency capability.

Phase-Locked Loop (PLL) Oscillators: PLL oscillators are primarily considered linear oscillators and are used for frequency synthesis and modulation. Essential in telecommunications for signal processing and frequency control.

Emerging Oscillator Technologies

Recent advancements in oscillator technology focus on performance improvement, miniaturization, and integration with other electronic components.

MEMS Oscillators: Microelectromechanical systems offer smaller form factors, highly stable reference frequencies, and low power consumption - ideal for portable devices.

Programmable Oscillators: Allow for customized frequency outputs, reducing component count and streamlining the design process.

Devices That Use Oscillators

Many electronic devices rely on oscillators for essential functions like timing, signal generation, and frequency control. Their ability to produce consistent waveforms makes them indispensable in both consumer electronics and industrial systems.

Examples:

Quartz Watches: Use crystal oscillators to generate highly accurate timekeeping signals, ensuring the watch maintains precise seconds, minutes, and hours.

Radios: Rely on oscillators to generate carrier frequencies and to tune into specific broadcast channels for both AM and FM signals.

Computers: Employ oscillators in their system clocks to synchronize processor operations, manage data transfer, and maintain stable performance.

Cellphones: Utilize oscillators for network synchronization, frequency hopping in wireless communication, and internal clocking for processors and sensors.

Radar Systems: Depend on high-frequency oscillators to generate the radio waves that detect and measure the speed, range, and position of objects.

Metal Detectors: Use oscillators to produce electromagnetic fields that interact with metallic objects, enabling detection through changes in oscillation frequency or amplitude.

Performance Characteristics of Oscillators

Oscillators are evaluated based on several performance metrics that directly influence their suitability for specific applications. The three most critical are frequency stability, phase noise, and waveform shape.

Frequency Stability

Frequency stability describes an oscillator’s ability to maintain its output frequency under varying conditions over time.

• Short-Term Stability: Covers rapid variations over seconds or minutes, often caused by noise or small environmental changes.
• Long-Term Stability: Considers changes over hours, days, or years, typically influenced by component aging and gradual environmental shifts.
• Environmental Factors: Temperature fluctuations, supply voltage changes, and mechanical vibrations can affect stability.
• Crystal Oscillators: These oscillators excel in this area because the resonant frequency of a quartz crystal is highly resistant to such disturbances, making them ideal for precision timing applications like GPS, telecommunications, and laboratory measurement systems.

Phase Noise

Phase noise measures short-term, rapid fluctuations in the oscillator's phase, which manifest as small, random deviations from the ideal frequency.

• It is usually represented as a power density (dBc/Hz) at a given frequency offset from the carrier signal.
• Low Phase Noise: Essential in high-performance systems, such as satellite communications, radar, and high-speed data links, where timing jitter can degrade system performance or cause data errors.
• High Phase Noise: Can lead to signal distortion, reduced sensitivity in receivers, and degraded performance in frequency synthesizers.

Waveform Shape

The oscillator’s output waveform determines how well it interfaces with downstream circuitry.

• Sine Waves: Preferred in RF applications because they have minimal harmonic content, reducing the need for filtering.
• Square Waves: Common in digital clocking applications, as their fast transitions make it easy for digital circuits to detect logic states.
• Sawtooth or Triangular Waveforms: May be required in specialized systems, such as sweep generators in analog oscilloscopes.
• Poor Waveform Shape: Can cause signal integrity issues, increased electromagnetic interference (EMI), or inaccurate timing in digital circuits.

Are Oscillators Active Components?

Oscillators are classified as active components. They amplify electrical signals and generate power, distinguishing them from passive components like resistors and capacitors. While oscillators incorporate passive elements in their circuits, their role in signal generation qualifies them as active devices.

Industries That Use Oscillators

Oscillators' ability to generate stable, precise signals makes them indispensable for timing, synchronization, and frequency control across a wide range of sectors. The specific oscillator type used often depends on the application's demands - whether it’s ultra-high precision, rugged durability, or low power consumption.

Telecommunications: Oscillators generate carrier signals for data transmission. Their stability and accuracy ensure signal integrity over long distances. Crystal and PLL oscillators are widely used here.

Consumer Electronics: Devices like smartphones and TVs rely on oscillators to generate clock signals for microcontrollers. Their precision directly impacts device performance.

Automotive: Used in engine control units, infotainment systems, and sensor applications (e.g., ABS), oscillators regulate timing for ignition and fuel injection.

Medical Devices: Essential in pacemakers and diagnostic tools, where reliability and precision are critical. Crystal oscillators are often chosen for their long-term stability.

Additional Information

An oscillator is an electronic device that produces repetitive oscillating signals in the form of a sine wave, a square wave, or a triangle wave. Basically, this circuit converts DC (Direct Current) into an AC (Alternating Current) signal at a specific frequency.

An oscillator is essential in various electronic devices. It is used in Bluetooth modules for frequency generation and maintaining a stable connection. In relays, oscillators help with debouncing and pulse generation.

In sensors, they are used for generating carrier signals and stabilizing readings. Integrated circuits (ICs) use oscillators for clock generation and data synchronization. In connectors, oscillators assist with signal integrity and timing matching.

Microcontrollers rely on oscillators for peripheral operation and system clock management. Additionally, oscillators are used in LCD and LED displays for backlight control and data driving.

A basic oscillator circuit typically includes components like an amplifier stage, a feedback network, frequency-determining components, and a power supply.

1. Amplifier

An amplifier in an oscillator can be a transistor, an operational amplifier, or any active device that boosts small signals to maintain continuous oscillations. For that amplifier must provide a gain greater than or equal to one to sustain oscillations.

2. Feedback Network

In this network, it feeds a portion of the output back to the input with the correct phase. This network includes components like capacitive, inductive, or resistive networks like LC circuits or RC circuits.

3. Frequency Determining Components

This component sets the frequency at which the oscillator operates, which includes RC networks, LC networks, and crystal resonators.

4. Power Supply

It provides the necessary voltage and current for operation.

Types of Oscillators

Based on the design, frequency range, and application, oscillators are classified into various types. They are as follows:

1. LC Oscillator

An LC oscillator uses an inductor and a capacitor to determine the frequency of oscillation. It is a high-frequency operation oscillator that gives a smooth sine wave output, and its frequency depends on the values of L and C.

LC oscillator consists of different types like Hartley Oscillator (uses a tapped inductor), Colpitts Oscillator (uses a capacitive voltage divider), and Clapp Oscillator ( it is a variation of the Colpitts with an additional capacitor for better frequency stability.

It is mostly used in radio transmitters, RF communication circuits, and signal generators.

2. RC Oscillator

RC oscillator uses resistors and capacitors to produce oscillations. It produces stable low-frequency sine waves and is ideal for audio frequency generation, which is cost cost-effective design.

This includes the Wien bridge oscillator (for audio applications) and the Phase shift oscillator (produces sine waves using multiple RC stages). RC oscillators are used in audio signal generation, function generation, and low-frequency timing circuits.

3. Crystal Oscillator

To create a very stable frequency oscillation, a crystal oscillator uses the mechanical resonance of a quartz crystal. It generates a pure sine wave output with extremely high frequency stability. They have very low frequency drift due to temperature changes.

These are of the types Pierce oscillator and AT-cut crystal oscillator (widely used in microcontrollers). It is used in microcontrollers and microprocessors, Bluetooth and Wi-Fi modules, digital watches and clocks, and GPS systems.

Working Principle of Oscillator

The working principle of an oscillator is based on the concept of positive feedback and energy conversion from a direct current (DC) source into an alternating current (AC) signal at a specific, stable frequency.

The working of the oscillator is explained in step below:

1. Initial

Due to thermal activity, every electronic circuit has inherent noise, and this tiny noise signal acts as the seed for oscillation.

2. Amplification

At the amplification stage, the amplifier boosts this initial noise signal, and amplification must be sufficient to compensate for any losses in the feedback network.

3. Positive Feedback Loop

A portion of the output is fed back to the input in phase, which reinforces the input signal rather than cancelling it.

4. Frequency Selection

The frequency-determining network (RC, LC, or crystal) controls the frequency of oscillation.

5. Steady State Oscillation

As the feedback sustains the oscillations, the amplitude stabilizes. Non-linear effects or amplitude limiting mechanisms prevent the output from growing indefinitely, ensuring stable oscillations.

Applications of Oscillators

1. Communication Systems

* Oscillators generate high-frequency carrier signals for AM, FM, and digital modulation.
* Used to produce a range of frequencies from a single oscillator source.
* LC and crystal oscillators are used for tuning and frequency control.

Example: Radio Transmitters, Mobile phones, Wi-Fi modules, Bluetooth devices

2. Microcontrollers and Microprocessors

* Oscillators provide the clock signals needed for the timing and operation of microcontrollers and microprocessors.
* Crystal oscillators generate precise timing signals that ensure all processes operate in harmony and within correct timing constraints.

Example: Arduino boards, PIC microcontrollers, Embedded systems.

3. Sensors

* Oscillators are used in sensor circuits for data acquisition and signal processing.

Example: Proximity sensors, Ultrasonic sensors, and Environmental monitoring systems.

4. Display Technologies

Oscillators help maintain the refresh rate of digital displays. Used in the PWM (Pulse Width Modulation) circuits for adjusting display brightness.

Example: LED displays, LCD displays, OLED panels, Digital signage.

Frequently Asked Questions:

1. Is an Oscillator AC or DC?

An oscillator converts DC power into an AC signal by generating a continuous, oscillating waveform without an external input.

2. Is the Oscillator Negative or Positive?

An oscillator uses positive feedback to sustain continuous oscillations.

3. Which Oscillator is Better?

The crystal oscillator is considered better for applications requiring high-frequency stability and accuracy.

4. How Does an Oscillator Differ from an Amplifier?

An oscillator generates its own periodic signal without an external input, while an amplifier boosts the strength of an existing input signal.

5. What is the Difference Between RC and LC Oscillators?

An RC oscillator uses resistors and capacitors for low-frequency generation, while an LC oscillator uses inductors and capacitors for high-frequency generation.

6. What Causes an Oscillator to Fail?

An oscillator can fail due to component aging, temperature variations, power supply issues, or physical damage to the resonator elements, like crystals or inductors.

7. Can an Oscillator be Used as a Signal Generator?

Yes, an oscillator can be used as a signal generator to produce continuous waveforms like sine, square, or triangular signals.

Anion

Gist

An anion is an atom or molecule that carries a net negative electrical charge because it has gained one or more electrons, resulting in more electrons than protons. Formed typically by non-metals, anions are attracted to the positive electrode (anode) during electrolysis and readily combine with positive ions (cations) to form ionic compounds, like chloride or sulfate.

Anions are negatively-charged ions (meaning they have more electrons than protons due to having gained one or more electrons). Cations are also called positive ions, and anions are also called negative ions.

Summary

Anions are atoms or groups of atoms that have a negative electric charge. An anion has more electrons in its atomic orbitals than it has protons in its atomic nucleus. The opposite of an anion is a cation, which has a positive charge.

The name "anion" comes from the words anode and ion. In an electrochemical cell, anions are attracted to the positively charged anode.

Anions can be monatomic, made of only one atom, or polyatomic, made of multiple atoms. Anions can exist on their own only as gases: to make a solid, ionic liquid, or solution the total electrical charge must be zero, meaning a mix of anions and cations.

Properties

In many crystals the anions are bigger; the little cations fit into the spaces between them.

All anions are Brønsted bases: they can make a chemical bond with a proton, H+, to form a conjugate acid.

Examples

Oxide is the most common anion on Earth. It is made from an oxygen atom with two extra electrons. The formula for oxide is written O2−. The oxide ion reacts with water, so it cannot be dissolved to make a solution.

Chloride is a monatomic anion made from an atom of chlorine with an extra electron. The chemical formula is written Cl−. Chloride is the most common anion in seawater.

Sulfate is the second most common anion in seawater after chloride. It is made of a sulfur atom, four oxygen atoms, and two extra electrons. Sulfate is a special type of anion called an oxyanion, which are made of a central element (like sulfur) surrounded by oxygen atoms.

Hydroxide is a polyatomic anion made of one oxygen atom, one hydrogen atom, and one extra electron. It has the formula OH−. Hydroxide is the conjugate base of water, so it is the strongest base that can be mixed with water. Other strong bases, including the oxide anion, react with water to make hydroxide.  

Details

Anions are negatively charged ions formed when an atom or group of atoms gains one or more valence electrons. The term "anion" comes from "anode ions," reflecting their movement toward the positive terminal in an electrolytic solution. Anions, along with positively charged cations, form ionic bonds that are fundamental to many chemical compounds, such as table salt (sodium chloride). Common examples of anions include fluoride, chloride, and sulfate, each named based on their elemental origin or structural characteristics, following specific nomenclature rules established by the International Union of Pure and Applied Chemistry (IUPAC).

The formation of anions is closely tied to the electronic structure of atoms, which consists of a dense nucleus surrounded by electron shells containing orbitals that dictate the arrangement and behavior of electrons. Elements tend to achieve stability by completing their outer electron shell, often following the octet rule, which promotes the formation of anions in various chemical reactions. Understanding anions is essential for grasping broader concepts related to atomic structure, chemical bonding, and the periodic table's organization.

The basic structure of anions is defined, and the development of the modern theory of atomic structure is elaborated. Electronic structure is fundamental to all chemical behaviors and is responsible for the relationships seen in the periodic table.

The Nature of Anions

An anion is any atom or group of atoms that bears a net negative charge due to the presence of one or more extra valence electrons. The term is a contraction of "anode ions," which is a reference to the fact that when a direct electric current is applied to an electrolytic solution, negatively charged ions are attracted to the anode, or positive terminal, of the source of the current. By the same token, cations, from "cathode ions," have a net positive charge and are attracted to the cathode, or negative terminal, of the current source. Anions and cations often combine to form compounds held together with ionic bonds; one common example is sodium chloride (NaCl), better known as table salt, which is created when the sodium cation, Na+, bonds to the chloride anion, Cl−.

The formation of any ion is the result of an atom or molecule gaining or losing one or more valence electrons. This is most apparent in monatomic (single-atom) ions, in which the electrical charge is equal to the oxidation state. For example, the halogens—fluorine, chlorine, bromine, iodine, and astatine—are all highly electronegative, meaning that they readily accept an extra valence electron so that their outer electron shell is completely full and therefore stable. The resulting anions are called fluoride, chloride, bromide, iodide, and astatinide, respectively, and they have an electrical charge of 1− because they gained one electron and thus one unit of negative charge. Similarly, the chalcogens oxygen (O) and sulfur (S) readily accept two extra electrons to form the oxide ion, O2−, and the sulfide ion, S2−.

Compound ions in which a central atom is bonded to a number of oxygen atoms are extremely common. These oxoanions tend to form very stable compounds and are the basic materials of many minerals.

The Electronics of Anion Formation

According to the modern theory of atomic structure, each atom contains a very small, extremely dense nucleus that holds at least 99.98 percent of the atom’s mass and all of its positive electrical charge. The nucleus is surrounded by a diffuse and comparatively very large cloud of electrons containing all of the atom’s negative electrical charge. These electrons are allowed to possess only very specific energies. This restricts their movement around the nucleus to specific regions called "electron shells." Within each shell are well-defined regions called "orbitals." The strict geometric arrangement of the orbitals regulates the formation of chemical bonds between atoms.

Each shell and orbital is subject to a number of restrictions that dictate how many electrons it can hold. There are four different types of electron orbitals, designated s, p, d, and f, each of which can contain a specific number of electrons: s orbitals can hold a maximum of two electrons; p orbitals, a maximum of six; d orbitals, a maximum of ten; and f orbitals, a maximum of fourteen. One or more of these orbitals make up an electron shell. The various electron shells are indicated by an integer value known as the "principal quantum number," starting with 1 for the innermost shell, typically referred to as the "n = 1 shell." The standard notation to describe an electron orbital is the principal quantum number, followed by the type of orbital, followed by a superscript number indicating how many electrons it holds. For example, helium has only one s orbital, which is completely full, so its electron configuration is represented as 1s2. The first p orbital appears in the n = 2 shell, the first d orbital in the n = 3 shell, and the first f orbital in the n = 4 shell. Due to variances in energy levels, electrons usually fill atomic orbitals in the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s . . . rather than in strict numerical order.

The outermost electron shell is the valence shell, and in all elements, except the noble gases (helium, neon, argon, krypton, xenon, and radon), the valence shell is incompletely occupied. Because of this, the noble gases are often called "inert gases," reflecting the fact that they are far less chemically reactive than elements whose valence shells are not filled. All noble gases except for helium have eight electrons in their valence shell, as a shell with eight electrons approximates a stable closed-shell configuration of s2p6. This is the basis of the octet rule, which states that atoms of lower atomic numbers tend to achieve the greatest stability when they have eight electrons in their valence shells. The closer an element is to having eight valence electrons, the more likely it is to undergo ionization or a chemical reaction in order to achieve a stable configuration, either by gaining enough electrons to complete the octet or by losing all valence electrons so that the next-highest completed shell becomes the outermost shell. Elements with similar electron distributions in their valence shells typically exhibit similar chemical behaviors, which is the basis on which the periodictable of the elements is arranged.

Naming the Anions

The rules for naming various chemical species are established and standardized by the International Union of Pure and Applied Chemistry (IUPAC). Monatomic anions and polyatomic anions composed of a single element are named by adding the suffix -ide to the name of the element, either instead of or in addition to the existing suffix. Thus a sulfur anion becomes sulfide, a xenon anion becomes xenonide, a potassium anion becomes potasside, and so on. In some cases, the suffix is added to the element’s Latin name instead of its common name; for example, an anion of silver, which has the Latin name argentum, is called argentide.

Oxoanions are generally named for the central atom of the anion and the number of oxygen atoms that surround it, with the charge number given in parentheses at the end. An oxoanion consisting of a sulfur atom surrounded by three oxygen atoms has the formal name trioxidosulfate, while one with a sulfur atom and four oxygen atoms is called tetraoxidosulfate. The common (nonsystematic) names of these two oxoanions are sulfite and sulfate, respectively, following the convention that the oxoanion with fewer oxygen atoms takes the suffix -ite and the one with more oxygen atoms takes the suffix -ate. If one element is capable of forming more than two different oxoanions, as is the case with chlorine, the prefixes hypo- and per- are used as well, so that the common name of ClO− is hypochlorite, ClO2− is chlorite, ClO3− is chlorate, and ClO4− is perchlorate.

Principal Terms

cation: any chemical species bearing a net positive electrical charge, which causes it to be drawn toward the negative pole, or cathode, of an electrochemical cell.
ionic bond: a type of chemical bond formed by mutual attraction between two ions of opposite charges.
ionization: the process by which an atom or molecule loses or gains one or more electrons to acquire a net positive or negative electrical charge.
oxoanion: an ion consisting of one or more central atoms bonded to a number of oxygen atoms and bearing a net negative electrical charge.
valence electron: an electron that occupies the outermost or valence shell of an atom and participates in chemical processes such as bond formation and ionization.

Additional Information

An anion is an atom that has a negative charge. So, given that anion definition, the answer to the question "Is an anion negative?" is yes. Anions are a type of atom, the smallest particle of an element that still retains the element's properties. Atoms are made of three types of subatomic particles: neutrons, protons, and electrons. Neutrons are neutrally charged subatomic particles and, along with protons, they make up the nucleus. Protons have a positive charge. Electrons are very small subatomic particles that orbit the nucleus in levels called shells. Electrons have a negative charge.

Anions are created when an atom gains one or more electrons. The number of electrons gained by an atom is determined by how many are needed to fill their outer shell. For example, fluorine has seven electrons in its outer shell, but a full outer shell contains eight electrons. Thus, fluorine tends to gain one electron to fill its outer shell and generally has a charge of -1. Oxygen, on the other hand, has an outer shell of six electrons. This means it requires two electrons to complete its outer shell and tends to carry a charge of -2.

Uses for Anions

Fluoride ion is widely used in water supplies to help prevent tooth decay. Chloride is an important component in ion balance in blood. Iodide ion is needed by the thyroid gland to make the hormone thyroxine.

Summary

* Anions are formed by the addition of one or more electrons to the outer shell of an atom.
* Group 17 elements add one electron to the outer shell, group 16 elements add two electrons, and group 15 elements add three electrons.
* Anions are named by dropping the ending of the element's name and adding -ide.

Come Quotes - III

1. Put two ships in the open sea, without wind or tide, and, at last, they will come together. Throw two planets into space, and they will fall one on the other. Place two enemies in the midst of a crowd, and they will inevitably meet; it is a fatality, a question of time; that is all. - Jules Verne

2. On two occasions I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question. - Charles Babbage

3. I've always believed that if you put in the work, the results will come. - Michael Jordan

4. From the deepest desires often come the deadliest hate. - Socrates

5. The most important thing about Spaceship Earth - an instruction book didn't come with it. - R. Buckminster Fuller

6. Hope smiles from the threshold of the year to come, whispering, 'It will be happier.' - Alfred Lord Tennyson

7. Tears come from the heart and not from the brain. - Leonardo da Vinci

8. What goes up must come down. - Isaac Newton.

Acoustics

Gist

Acoustics: The branch of physics that is concerned with the study of sound is known as acoustics. We can define acoustics as, The science that deals with the study of sound and its production, transmission, and effects.

"Acoustic" relates to sound or hearing, describing things like instruments not needing electronic amplification (acoustic guitar), materials controlling sound (acoustic panels), or the scientific study of sound waves (acoustics) in physics, architecture, and medicine. It signifies natural sound production or properties that affect sound quality, from the science of hearing to the design of concert halls or musical styles.

Summary

Acoustics is a branch of continuum mechanics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Hearing is one of the most crucial means of survival in the animal world and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as a key element of mating rituals or for marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay's "Wheel of Acoustics" is a well-accepted overview of the various fields in acoustics.

Details

Acoustics is the science concerned with the production, control, transmission, reception, and effects of sound. The term is derived from the Greek akoustos, meaning “heard.”

Beginning with its origins in the study of mechanical vibrations and the radiation of these vibrations through mechanical waves, acoustics has had important applications in almost every area of life. It has been fundamental to many developments in the arts—some of which, especially in the area of musical scales and instruments, took place after long experimentation by artists and were only much later explained as theory by scientists. For example, much of what is now known about architectural acoustics was actually learned by trial and error over centuries of experience and was only recently formalized into a science.

Other applications of acoustic technology are in the study of geologic, atmospheric, and underwater phenomena. Psychoacoustics, the study of the physical effects of sound on biological systems, has been of interest since Pythagoras first heard the sounds of vibrating strings and of hammers hitting anvils in the 6th century bc, but the application of modern ultrasonic technology has only recently provided some of the most exciting developments in medicine. Even today, research continues into many aspects of the fundamental physical processes involved in waves and sound and into possible applications of these processes in modern life.

Sound waves follow physical principles that can be applied to the study of all waves; these principles are discussed thoroughly in the article mechanics of solids. The article here explains in detail the physiological process of hearing—that is, receiving certain wave vibrations and interpreting them as sound.

Early experimentation

The origin of the science of acoustics is generally attributed to the Greek philosopher Pythagoras (6th century bc), whose experiments on the properties of vibrating strings that produce pleasing musical intervals were of such merit that they led to a tuning system that bears his name. Aristotle (4th century bc) correctly suggested that a sound wave propagates in air through motion of the air—a hypothesis based more on philosophy than on experimental physics; however, he also incorrectly suggested that high frequencies propagate faster than low frequencies—an error that persisted for many centuries. Vitruvius, a Roman architectural engineer of the 1st century bc, determined the correct mechanism for the transmission of sound waves, and he contributed substantially to the acoustic design of theatres. In the 6th century ad, the Roman philosopher Boethius documented several ideas relating science to music, including a suggestion that the human perception of pitch is related to the physical property of frequency.

The modern study of waves and acoustics is said to have originated with Galileo Galilei (1564–1642), who elevated to the level of science the study of vibrations and the correlation between pitch and frequency of the sound source. His interest in sound was inspired in part by his father, who was a mathematician, musician, and composer of some repute. Following Galileo’s foundation work, progress in acoustics came relatively rapidly. The French mathematician Marin Mersenne studied the vibration of stretched strings; the results of these studies were summarized in the three Mersenne’s laws. Mersenne’s Harmonicorum Libri (1636) provided the basis for modern musical acoustics. Later in the century Robert Hooke, an English physicist, first produced a sound wave of known frequency, using a rotating cog wheel as a measuring device. Further developed in the 19th century by the French physicist Félix Savart, and now commonly called Savart’s disk, this device is often used today for demonstrations during physics lectures. In the late 17th and early 18th centuries, detailed studies of the relationship between frequency and pitch and of waves in stretched strings were carried out by the French physicist Joseph Sauveur, who provided a legacy of acoustic terms used to this day and first suggested the name acoustics for the study of sound.

One of the most interesting controversies in the history of acoustics involves the famous and often misinterpreted “bell-in-vacuum” experiment, which has become a staple of contemporary physics lecture demonstrations. In this experiment the air is pumped out of a jar in which a ringing bell is located; as air is pumped out, the sound of the bell diminishes until it becomes inaudible. As late as the 17th century many philosophers and scientists believed that sound propagated via invisible particles originating at the source of the sound and moving through space to affect the ear of the observer. The concept of sound as a wave directly challenged this view, but it was not established experimentally until the first bell-in-vacuum experiment was performed by Athanasius Kircher, a German scholar, who described it in his book Musurgia Universalis (1650). Even after pumping the air out of the jar, Kircher could still hear the bell, so he concluded incorrectly that air was not required to transmit sound. In fact, Kircher’s jar was not entirely free of air, probably because of inadequacy in his vacuum pump. By 1660 the Anglo-Irish scientist Robert Boyle had improved vacuum technology to the point where he could observe sound intensity decreasing virtually to zero as air was pumped out. Boyle then came to the correct conclusion that a medium such as air is required for transmission of sound waves. Although this conclusion is correct, as an explanation for the results of the bell-in-vacuum experiment it is misleading. Even with the mechanical pumps of today, the amount of air remaining in a vacuum jar is more than sufficient to transmit a sound wave. The real reason for a decrease in sound level upon pumping air out of the jar is that the bell is unable to transmit the sound vibrations efficiently to the less dense air remaining, and that air is likewise unable to transmit the sound efficiently to the glass jar. Thus, the real problem is one of an impedance mismatch between the air and the denser solid materials—and not the lack of a medium such as air, as is generally presented in textbooks. Nevertheless, despite the confusion regarding this experiment, it did aid in establishing sound as a wave rather than as particles.

Measuring the speed of sound

Once it was recognized that sound is in fact a wave, measurement of the speed of sound became a serious goal. In the 17th century, the French scientist and philosopher Pierre Gassendi made the earliest known attempt at measuring the speed of sound in air. Assuming correctly that the speed of light is effectively infinite compared with the speed of sound, Gassendi measured the time difference between spotting the flash of a gun and hearing its report over a long distance on a still day. Although the value he obtained was too high—about 478.4 metres per second (1,569.6 feet per second)—he correctly concluded that the speed of sound is independent of frequency. In the 1650s, Italian physicists Giovanni Alfonso Borelli and Vincenzo Viviani obtained the much better value of 350 metres per second using the same technique. Their compatriot G.L. Bianconi demonstrated in 1740 that the speed of sound in air increases with temperature. The earliest precise experimental value for the speed of sound, obtained at the Academy of Sciences in Paris in 1738, was 332 metres per second—incredibly close to the presently accepted value, considering the rudimentary nature of the measuring tools of the day. A more recent value for the speed of sound, 331.45 metres per second (1,087.4 feet per second), was obtained in 1942; it was amended in 1986 to 331.29 metres per second at 0° C (1,086.9 feet per second at 32° F).

The speed of sound in water was first measured by Daniel Colladon, a Swiss physicist, in 1826. Strangely enough, his primary interest was not in measuring the speed of sound in water but in calculating water’s compressibility—a theoretical relationship between the speed of sound in a material and the material’s compressibility having been established previously. Colladon came up with a speed of 1,435 metres per second at 8° C; the presently accepted value interpolated at that temperature is about 1,439 metres per second.

Two approaches were employed to determine the velocity of sound in solids. In 1808 Jean-Baptiste Biot, a French physicist, conducted direct measurements of the speed of sound in 1,000 metres of iron pipe by comparing it with the speed of sound in air. A better measurement had earlier been carried out by a German, Ernst Florenz Friedrich Chladni, using analysis of the nodal pattern in standing-wave vibrations in long rods.

Modern advances

Simultaneous with these early studies in acoustics, theoreticians were developing the mathematical theory of waves required for the development of modern physics, including acoustics. In the early 18th century, the English mathematician Brook Taylor developed a mathematical theory of vibrating strings that agreed with previous experimental observations, but he was not able to deal with vibrating systems in general without the proper mathematical base. This was provided by Isaac Newton of England and Gottfried Wilhelm Leibniz of Germany, who, in pursuing other interests, independently developed the theory of calculus, which in turn allowed the derivation of the general wave equation by the French mathematician and scientist Jean Le Rond d’Alembert in the 1740s. The Swiss mathematicians Daniel Bernoulli and Leonhard Euler, as well as the Italian-French mathematician Joseph-Louis Lagrange, further applied the new equations of calculus to waves in strings and in the air. In the 19th century, Siméon-Denis Poisson of France extended these developments to stretched membranes, and the German mathematician Rudolf Friedrich Alfred Clebsch completed Poisson’s earlier studies. A German experimental physicist, August Kundt, developed a number of important techniques for investigating properties of sound waves.

One of the most important developments in the 19th century involved the theory of vibrating plates. In addition to his work on the speed of sound in metals, Chladni had earlier introduced a technique of observing standing-wave patterns on vibrating plates by sprinkling sand onto the plates—a demonstration commonly used today. Perhaps the most significant step in the theoretical explanation of these vibrations was provided in 1816 by the French mathematician Sophie Germain, whose explanation was of such elegance and sophistication that errors in her treatment of the problem were not recognized until some 35 years later, by the German physicist Gustav Robert Kirchhoff.

The analysis of a complex periodic wave into its spectral components was theoretically established early in the 19th century by Jean-Baptiste-Joseph Fourier of France and is now commonly referred to as the Fourier theorem. The German physicist Georg Simon Ohm first suggested that the ear is sensitive to these spectral components; his idea that the ear is sensitive to the amplitudes but not the phases of the harmonics of a complex tone is known as Ohm’s law of hearing (distinguishing it from the more famous Ohm’s law of electrical resistance).

Hermann von Helmholtz made substantial contributions to understanding the mechanisms of hearing and to the psychophysics of sound and music. His book On the Sensations of Tone As a Physiological Basis for the Theory of Music (1863) is one of the classics of acoustics. In addition, he constructed a set of resonators, covering much of the audio spectrum, which were used in the spectral analysis of musical tones. The Prussian physicist Karl Rudolph Koenig, an extremely clever and creative experimenter, designed many of the instruments used for research in hearing and music, including a frequency standard and the manometric flame. The flame-tube device, used to render standing sound waves “visible,” is still one of the most fascinating of physics classroom demonstrations. The English physical scientist John William Strutt, 3rd Baron Rayleigh, carried out an enormous variety of acoustic research; much of it was included in his two-volume treatise, The Theory of Sound, publication of which in 1877–78 is now thought to mark the beginning of modern acoustics. Much of Rayleigh’s work is still directly quoted in contemporary physics textbooks.

The study of ultrasonics was initiated by the American scientist John LeConte, who in the 1850s developed a technique for observing the existence of ultrasonic waves with a gas flame. This technique was later used by the British physicist John Tyndall for the detailed study of the properties of sound waves. The piezoelectric effect, a primary means of producing and sensing ultrasonic waves, was discovered by the French physical chemist Pierre Curie and his brother Jacques in 1880. Applications of ultrasonics, however, were not possible until the development in the early 20th century of the electronic oscillator and amplifier, which were used to drive the piezoelectric element.

Among 20th-century innovators were the American physicist Wallace Sabine, considered to be the originator of modern architectural acoustics, and the Hungarian-born American physicist Georg von Békésy, who carried out experimentation on the ear and hearing and validated the commonly accepted place theory of hearing first suggested by Helmholtz. Békésy’s book Experiments in Hearing, published in 1960, is the magnum opus of the modern theory of the ear.

Amplifying, recording, and reproducing

The earliest known attempt to amplify a sound wave was made by Athanasius Kircher, of “bell-in-vacuum” fame; Kircher designed a parabolic horn that could be used either as a hearing aid or as a voice amplifier. The amplification of body sounds became an important goal, and the first stethoscope was invented by a French physician, René Laënnec, in the early 19th century.

Attempts to record and reproduce sound waves originated with the invention in 1857 of a mechanical sound-recording device called the phonautograph by Édouard-Léon Scott de Martinville. The first device that could actually record and play back sounds was developed by the American inventor Thomas Alva Edison in 1877. Edison’s phonograph employed grooves of varying depth in a cylindrical sheet of foil, but a spiral groove on a flat rotating disk was introduced a decade later by the German-born American inventor Emil Berliner in an invention he called the gramophone. Much significant progress in recording and reproduction techniques was made during the first half of the 20th century, with the development of high-quality electromechanical transducers and linear electronic circuits. The most important improvement on the standard phonograph record in the second half of the century was the compact disc, which employed digital techniques developed in mid-century that substantially reduced noise and increased the fidelity and durability of the recording.

Architectural acoustics:

Reverberation time

Although architectural acoustics has been an integral part of the design of structures for at least 2,000 years, the subject was only placed on a firm scientific basis at the beginning of the 20th century by Wallace Sabine. Sabine pointed out that the most important quantity in determining the acoustic suitability of a room for a particular use is its reverberation time, and he provided a scientific basis by which the reverberation time can be determined or predicted.

When a source creates a sound wave in a room or auditorium, observers hear not only the sound wave propagating directly from the source but also the myriad reflections from the walls, floor, and ceiling. These latter form the reflected wave, or reverberant sound. After the source ceases, the reverberant sound can be heard for some time as it grows softer. The time required, after the sound source ceases, for the absolute intensity to drop by a factor of {10}^{6} - or, equivalently, the time for the intensity level to drop by 60 decibels—is defined as the reverberation time (RT, sometimes referred to as RT60). Sabine recognized that the reverberation time of an auditorium is related to the volume of the auditorium and to the ability of the walls, ceiling, floor, and contents of the room to absorb sound. Using these assumptions, he set forth the empirical relationship through which the reverberation time could be determined: RT = 0.05V/A, where RT is the reverberation time in seconds, V is the volume of the room in cubic feet, and A is the total sound absorption of the room, measured by the unit sabin. The sabin is the absorption equivalent to one square foot of perfectly absorbing surface—for example, a one-square-foot hole in a wall or five square feet of surface that absorbs 20 percent of the sound striking it.

Both the design and the analysis of room acoustics begin with this equation. Using the equation and the absorption coefficients of the materials from which the walls are to be constructed, an approximation can be obtained for the way in which the room will function acoustically. Absorbers and reflectors, or some combination of the two, can then be used to modify the reverberation time and its frequency dependence, thereby achieving the most desirable characteristics for specific uses.

While there is no exact value of reverberation time that can be called ideal, there is a range of values deemed to be appropriate for each application. These vary with the size of the room, but the averages can be calculated and indicated by lines on a graph. The need for clarity in understanding speech dictates that rooms used for talking must have a reasonably short reverberation time. On the other hand, the full sound desirable in the performance of music of the Romantic era, such as Wagner operas or Mahler symphonies, requires a long reverberation time. Obtaining a clarity suitable for the light, rapid passages of Bach or Mozart requires an intermediate value of reverberation time. For playing back recordings on an audio system, the reverberation time should be short, so as not to create confusion with the reverberation time of the music in the hall where it was recorded.

Acoustic criteria

Many of the acoustic characteristics of rooms and auditoriums can be directly attributed to specific physically measurable properties. Because the music critic or performing artist uses a different vocabulary to describe these characteristics than does the physicist, it is helpful to survey some of the more important features of acoustics and correlate the two sets of descriptions.

“Liveness” refers directly to reverberation time. A live room has a long reverberation time and a dead room a short reverberation time. “Intimacy” refers to the feeling that listeners have of being physically close to the performing group. A room is generally judged intimate when the first reverberant sound reaches the listener within about 20 milliseconds of the direct sound. This condition is met easily in a small room, but it can also be achieved in large halls by the use of orchestral shells that partially enclose the performers. Another example is a canopy placed above a speaker in a large room such as a cathedral: this leads to both a strong and a quick first reverberation and thus to a sense of intimacy with the person speaking.

The amplitude of the reverberant sound relative to the direct sound is referred to as fullness. Clarity, the opposite of fullness, is achieved by reducing the amplitude of the reverberant sound. Fullness generally implies a long reverberation time, while clarity implies a shorter reverberation time. A fuller sound is generally required of Romantic music or performances by larger groups, while more clarity would be desirable in the performance of rapid passages from Bach or Mozart or in speech.

“Warmth” and “brilliance” refer to the reverberation time at low frequencies relative to that at higher frequencies. Above about 500 hertz, the reverberation time should be the same for all frequencies. But at low frequencies an increase in the reverberation time creates a warm sound, while, if the reverberation time increased less at low frequencies, the room would be characterized as more brilliant.

“Texture” refers to the time interval between the arrival of the direct sound and the arrival of the first few reverberations. To obtain good texture, it is necessary that the first five reflections arrive at the observer within about 60 milliseconds of the direct sound. An important corollary to this requirement is that the intensity of the reverberations should decrease monotonically; there should be no unusually large late reflections.

“Blend” refers to the mixing of sounds from all the performers and their uniform distribution to the listeners. To achieve proper blend it is often necessary to place a collection of reflectors on the stage that distribute the sound randomly to all points in the audience.

Although the above features of auditorium acoustics apply to listeners, the idea of ensemble applies primarily to performers. In order to perform coherently, members of the ensemble must be able to hear one another. Reverberant sound cannot be heard by the members of an orchestra, for example, if the stage is too wide, has too high a ceiling, or has too much sound absorption on its sides.

Acoustic problems

Certain acoustic problems often result from improper design or from construction limitations. If large echoes are to be avoided, focusing of the sound wave must be avoided. Smooth, curved reflecting surfaces such as domes and curved walls act as focusing elements, creating large echoes and leading to bad texture. Improper blend results if sound from one part of the ensemble is focused to one section of the audience. In addition, parallel walls in an auditorium reflect sound back and forth, creating a rapid, repetitive pulsing of sound known as flutter echo and even leading to destructive interference of the sound wave. Resonances at certain frequencies should also be avoided by use of oblique walls.

Acoustic shadows, regions in which some frequency regions of sound are attenuated, can be caused by diffraction effects as the sound wave passes around large pillars and corners or underneath a low balcony. Large reflectors called clouds, suspended over the performers, can be of such a size as to reflect certain frequency regions while allowing others to pass, thus affecting the mixture of the sound.

External noise can be a serious problem for halls in urban areas or near airports or highways. One technique often used for avoiding external noise is to construct the auditorium as a smaller room within a larger room. Noise from air blowers or other mechanical vibrations can be reduced using techniques involving impedance and by isolating air handlers.

Good acoustic design must take account of all these possible problems while emphasizing the desired acoustic features. One of the problems in a large auditorium involves simply delivering an adequate amount of sound to the rear of the hall. The intensity of a spherical sound wave decreases in intensity at a rate of six decibels for each factor of two increase in distance from the source, as shown above. If the auditorium is flat, a hemispherical wave will result. Absorption of the diffracted wave by the floor or audience near the bottom of the hemisphere will result in even greater absorption, so that the resulting intensity level will fall off at twice the theoretical rate, at about 12 decibels for each factor of two in distance. Because of this absorption, the floors of an auditorium are generally sloped upward toward the rear.

Additional Information

Acoustics is defined as the science that deals with the production, control, transmission, reception, and effects of sound (as defined by Merriam-Webster). Many people mistakenly think that acoustics is strictly musical or architectural in nature. While acoustics does include the study of musical instruments and architectural spaces, it also covers a vast range of topics, including: noise control, SONAR for submarine navigation, ultrasounds for medical imaging, thermoacoustic refrigeration, seismology, bioacoustics, and electroacoustic communication. Below is the so called "Lindsay's Wheel of Acoustics", created by R. Bruce Lindsey in J. Acoust. Soc. Am. V. 36, p. 2242 (1964). This wheel describes the scope of acoustics starting from the four broad fields of Earth Sciences, Engineering, Life Sciences, and the Arts. The outer circle lists the various disciplines one may study to prepare for a career in acoustics. The inner circle lists the fields within acoustics that the various disciplines naturally lead to.

Curiously enough, Lindsey (himself a physicist) didn't list physics specifically in the outer circle. This is likely because a background in physics provides one with the foundational knowledge necessary to study nearly any of the fields of acoustics research. In fact, the Acoustical Society of America (ASA) (founded in 1929) was one of the five original societies that helped in the formation of the American Institute of Physics in 1931. The ASA is composed of 13 main areas of study called Technical Committees (TCs):

* Acoustical Oceanography (AO)
* Animal Bioacoustics (AB)
* Architectural Acoustics (AA)
* Biomedical Ultrasound/Bioresponse to Vibration (BB)
* Engineering Acoustics (EA)
* Musical Acoustics (MU)
* Noise (NS)
* Physical Acoustics (PA)
* Psychological and Physiological Acoustics (PP)
* Signal Processing in Acoustics (SP)
* Speech Communication (SC)
* Structural Acoustics and Vibration (SA)
* Underwater Acoustics (UW).

Come Quotes - II

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3. Hope smiles from the threshold of the year to come, whispering, 'It will be happier.' - Alfred Lord Tennyson

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6. I will prepare and some day my chance will come. - Abraham Lincoln

7. I've always believed that if you put in the work, the results will come. - Michael Jordan

8. Death does not concern us, because as long as we exist, death is not here. And when it does come, we no longer exist. - Epicurus.