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What Is a Microphone?

A microphone is a device that converts sound into an electrical signal.

It is also commonly referred to as a microphone for short. By converting sound vibrations into electrical signals, microphones are mainly used for communication, recording, and voice amplification.

Whether digital or analog, microphones are generally referred to as audio input devices. While a microphone is an audio input device, a device that converts electrical signals into audio and outputs them is called a speaker.

Uses of Microphones

Microphones are used as audio input devices and are used in various forms for different purposes, such as broadcasting, music recording, and noise level meter measurements. They are also built into many electronic devices such as smartphones, PCs, IC recorders, and cameras for voice input and voice recognition.

They are also useful as loudspeakers for delivering voices to a large audience at concerts, live performances, lectures, and events. They are widely used in familiar places such as karaoke, sports events, and school events.

Principle of Microphones

Microphones convert acoustic vibrations into electrical signals, and there are various methods of this conversion. Specifically, there are dynamic types, condenser types, etc.

1. Dynamic Type

The dynamic type has a simple structure, with a coil attached to a diaphragm that converts sound into an electrical signal. The diaphragm called a diaphragm, voice coil, and magnet are used, and the magnetic flux is changed by the sound vibration and converted into an electrical signal.

The dynamic type is robust, easy to handle, and produces powerful sound, so it is often used for performances, live music, lectures, etc.

2. Capacitor Type

The capacitor type has a complex structure. The diaphragm serves as the electrode for the capacitor, which converts sound into an electrical signal. The diaphragm, which is charged with electricity, and the back plate, which is called the back plate, are combined to form an electrical capacitor. The distance between the diaphragm and the back plate changes the electric field in the capacitor due to changes in vibration. This change is used as the electrical input. It is characterized by higher sensitivity than the dynamic type.

Condenser microphones are more complex in construction, require internal electronic circuits, and are more expensive than dynamic microphones.

Types of Microphones 

1. Moving Coil Type

Moving coil-type microphones convert sound = air vibrations into electrical signals when a coil attached to a diaphragm, which is a diaphragm, moves in a magnetic field. This structure is similar to the magnetic pickup microphones used for guitars and basses, where the vibration of the strings generates an electrical signal.

2. Ribbon Type

A ribbon-type microphone uses a thin metal foil ribbon hanging between slits sandwiched by magnetic poles as a vibrating system, and the sound vibration generates an electrical signal at both ends of the ribbon. The lightweight structure of the vibrating system allows the microphone to pick up sound in a wide range of frequencies from high to low, and the frequency response is less peculiar and more natural sounding.

3. Carbon Microphone

Carbon microphones are microphones that utilize the change in contact resistance of carbon powder to obtain audio signals. It is constructed by placing carbon powder between two plate-shaped electrodes.

When a direct current is applied between the electrodes with one fixed electrode and the other movable electrode, the movable electrode vibrates due to voice, and the contact resistance between the electrode and the carbon powder changes to obtain a voice signal. Carbon microphones are robust and have very high sensitivity, but since they use the change in contact resistance of the carbon powder, they have the weakness of easily distorting the sound.

4. Piezoelectric Microphone

Piezoelectric microphones use piezoelectric elements to obtain sound signals by vibrating electrodes caused by voice. The sensitivity is high, but the output power is low.

They are mainly used in situations where bandwidth is limited. Wireless communication and concrete microphones are typical examples.

5. Laser Microphone

A laser microphone is a type of microphone that uses a laser beam to detect and demodulate light fluctuations caused by voice vibration using a light-receiving element. It is intended for use in environments and situations where conventional microphones are difficult to use, and several forms exist, including those based on the Doppler effect and interferometry.

Microphones called ion microphones or plasma microphones, which generate plasma without a diaphragm and apply sound waves to it to extract modulated sound waves, are also being studied.

What Is a Lithium Ion Battery?

A lithium-ion battery is a rechargeable battery that charges and discharges as lithium ions move between the positive and negative electrodes.

They are used in electric vehicles, industrial storage batteries, smartphones, and laptop computers. Compared to lead-acid batteries, the voltage is higher, and the ratio of active materials that can store energy in the battery is smaller, which has the advantage of making the battery smaller in size compared to batteries with the same amount of energy.

Batteries are products that deteriorate as they are repeatedly charged and discharged and eventually reach the end of their useful life. Lithium-ion batteries are no exception, but they have been confirmed to have a longer life than other batteries in an endurance test called a cycle test.

Applications of Lithium-Ion Batteries

Typical applications for lithium-ion batteries include IT, automotive, and energy.

Lithium-ion batteries have a high energy density, making it possible to produce small, thin, and high-capacity batteries. Applications such as cell phones and notebook PCs require smaller and lighter batteries, and lithium-ion batteries are widely used to meet these demands, with lithium-ion batteries being used in almost all products.

They are also used as a medium and large-sized batteries for electric vehicles (EVs) and energy storage systems, taking advantage of their high electric capacity.

Structure of a Lithium Ion Battery

A lithium-ion battery is similar to a typical storage battery, consisting of a cathode, an anode, and an electrolyte in which they are immersed.

The cathode and anode are separated by a membrane called a separator that allows lithium ions to pass through but not electrons, and the gap between them is filled with electrolytes. The lithium ions in the electrolyte move from the positive electrode to the negative electrode during charging, generating a potential difference (voltage) between the negative and positive electrodes, which can be connected to the desired circuit to generate a current (discharge).

In charging, lithium ions are transferred from the positive electrode active material to the negative electrode active material by applying an external voltage. After charging, lithium ions can move again in the direction of discharge, so the battery can be used repeatedly for charging and discharging.

Other Information on Lithium Ion Batteries

1. Electrode Materials

Cathode-active materials are mainly lithium-based oxides, such as lithium cobalt oxide (LCO). The type of cathode active material greatly affects the performance of lithium-ion batteries.

Carbon-based materials such as artificial graphite, natural graphite, and hard carbon are the main active materials for the negative electrode. Less commonly used materials include silicon (Si) and tin (Sn) alloys and lithium oxides such as titanium (Ti) and niobium (Nb).

2. Reaction Equation of Discharge in Lithium-Ion Battery

The reaction equation for discharge in a lithium-ion battery varies depending on the type of metal oxide and other factors, but an example is shown below. When charging, the reaction occurs in the opposite direction of when discharging, i.e., from the right side to the left side.

• Reaction on the cathode side: Li(1-x)MO2 + xLi^(+) + xe^(-) → LiMO2
  *M is a metallic element
• Reaction on the anode side: LixC → C + xLi^(+) + xe^(-)
• Reaction of the whole system: Li(1-x)MO2 + LixC → LiMO2 + C

3. Safety of Lithium-Ion Batteries

Abnormal Heat Generation in Lithium-Ion Batteries
The electrolyte used in lithium-ion batteries is a carbonate-based organic solvent that is highly flammable. Therefore, if a lithium-ion battery malfunctions and the temperature rises excessively, it may cause a fire or explosion.

Most abnormal heat generation is caused by a short circuit (short circuit) between electrodes. Short circuits between electrodes can be caused by various factors, such as strong external shocks and lithium metal precipitation (lithium dendrites) in the electrodes. Accidents involving the ignition of lithium-ion batteries can occur not only by mishandling but also during normal use.

How to Prevent Lithium-Ion Battery Ignition Accidents

The majority of lithium-ion battery-related ignition accidents are caused by misuse. Therefore, it is necessary to understand the proper handling of lithium-ion batteries in order to prevent ignition accidents. Specific precautions are as follows.

• Always use the charger specified by the manufacturer when charging.
• If you notice anything unusual during charging, stop using the battery immediately and consult the manufacturer or seller.
• If the lithium-ion battery swells or smells strange, stop using it and replace it with a new one. It is also essential not to disassemble or replace the lithium-ion battery forcibly, as it is difficult to replace it in some products and is not recommended.

It is also essential to select products with guaranteed safety. Products that have passed the safety standards set by the government are marked with the PSE mark, which indicates safety.

What Is a Rotary Coded Switch?

A rotary coded switch is an electric switch that can be switched by operating a lever or a button.

The main body has an operating shaft and a number of terminals to switch contact points.

Depending on the manufacturer, they are called by various names, such as rotary coded switches, rotary cord switches, and DIP cord switches.

The shape of the actuator of a rotary coded switch varies from flat to shaft-shaped. Some are small and require a screwdriver for switching operations.

Uses of Rotary Coded Switches

Rotary coded switches are often used to adjust the volume of audio equipment, but they are also used in a variety of other applications.

They are also used to set electrical values for microwave ovens, knobs on electric fans and other electronic devices, switch settings for pilots operating aircraft, switch settings for medical equipment, switch settings for construction and agricultural equipment, and stepwise control settings for AC/DC drives, among many other applications.

They are used in a variety of locations as switches that allow settings to be changed on human-operated inputs.

Principle of Rotary Coded Switches

A rotary coded switch has a step mechanism, COM contacts, contacts, etc., on the bottom of the rotary actuator and a number of terminals (contacts) around the bottom of the rotary coded switch.

As the actuator of the rotary coded switch rotates, the step mechanism moves the contacts at a predetermined angle, causing each contact to conduct with the COM contact.

Rotary coded switches are classified into two types, shorting type and non-shorting type, depending on the state of electrical connection between the contacts as they move during switching. The shorting type moves to the next switching point by shorting the two points when moving between the two contacts. Unlike the shorting type, the non-shorting type moves to the next switching point by opening once when moving between the two contacts.

When designing a circuit, care should be taken when selecting components since the design may vary depending on whether the two points are shorted or open.

What Is a Tube Fuse?

Tube fuses are safety devices used to protect electrical circuits by interrupting current flow when it exceeds safe levels. They contain a fusible metal wire within a glass or ceramic tube that melts (blows) under excessive current, thereby breaking the circuit.

Applications of Tube Fuses

Widely used in consumer electronics, automotive circuits, industrial machinery, and more, tube fuses safeguard against electrical faults. They are particularly valuable in systems where frequent current fluctuations occur, offering protection without the need for constant replacement.

Principle of Tube Fuses

The operation of tube fuses is based on the melting of a fuse element made from materials like lead, tin, or silver, whose composition determines the fuse’s melting point. This feature allows tube fuses to cater to a broad spectrum of rated currents, from low-power applications to those requiring currents of 30A or more.

Types of Tube Fuses

• Normal Fusing Type: Standard fuse for household electronics.
• Fast-Acting Fusing Type: Designed for quick response, suitable for semiconductor protection.
• Time Lag Fusing Type: Delays blowing for applications like motors, accommodating initial power surges.
• Glass Tube Fuse: Offers a visual indication of fuse status through a transparent glass body.
• Ceramic Tube Fuse: Provides higher breaking capacity and additional safety features like arc suppression.

How to Choose a Tube Fuse

Selection involves ensuring the fuse’s rated current exceeds the normal operational current of the circuit but responds appropriately under fault conditions. Factors such as material type, fusing speed, and application-specific requirements guide the choice of the appropriate tube fuse.

What Is a Surveillance Camera?

Surveillance cameras serve as electronic eyes, providing continuous monitoring in locations where constant human supervision is impractical. These cameras capture video footage for security and monitoring purposes, often utilizing digital storage to record events over time.

Applications of Surveillance Cameras

Surveillance cameras are essential across various settings, from retail stores and museums to power plants and control rooms in process factories. Their primary function is to enhance security, monitor operations, and ensure safety in both public and private spaces.

Principle of Surveillance Cameras

Modern surveillance systems comprise three main components: the camera itself, transmission wiring for signal relay, and a recording device for data storage. Transitioning from analog film to digital data storage has significantly improved efficiency, allowing for broader application and easier management of recorded footage.

How to Choose a Surveillance Camera

• Monitoring Range and Viewing Angle: Select based on the surveillance area, opting for wide-angle or zoom-capable cameras as needed.
• Resolution: Choose a resolution that meets your detail requirements, from 720p HD to 4K Ultra HD, depending on the need for clarity.
• Day/Night Capability: For 24/7 monitoring, ensure the camera performs well under varying lighting conditions, considering IR cameras for low-light environments.
• Security Features: Advanced features like motion detection and facial recognition enhance monitoring effectiveness and crime prevention.
• Reliability and Durability: Durability is critical for long-term operation, so look for cameras with environmental resistance and a solid warranty.
• Compatibility and Extensibility: Ensure the camera integrates well with existing systems and offers the flexibility to expand your surveillance network.

What Is a Pipe Fitting?

A pipe fitting is a component used to connect different types of pipes.

It is one of the main methods of connecting pipes, but it also serves not only to extend pipes but also to change the direction of routes, branch or join pipes, enlarge or reduce the diameter of pipes, and seal the ends of pipes. Some pipe fittings are removable after connection, while others are not. In terms of ease of maintenance, it is recommended that removable pipe fittings be used for part of the piping.

It is very convenient to use both types of fittings, because while fixing the entire pipe increases its strength, doing so makes it impossible to replace only the faulty part. There are also various shapes, materials, and connection methods. It is necessary to select the appropriate pipe fitting according to the application of the fitting and the type and material of the piping.

Uses of Pipe Fittings

A pipe fitting is a component that connects pipes that transport gases and liquids. Therefore, a pipe fitting is used in facilities that use piping.

Specifically, they are used in water supply facilities, hot water supply facilities, drainage pipes, ventilation pipes, gas piping, fire prevention piping, cold and hot water circulation systems for air conditioning, agricultural water piping, chemical plant piping, and hydraulic piping. In addition to fluid piping, pipe fittings are also used for cable protection in the electric power and telecommunications fields, and are expected to improve construction work efficiency in the future as the use of utility poles is promoted.

Principle of Pipe Fittings

A pipe fitting is generally connected in two ways: flanged and screwed.

1. Flange Method

In the flange method, pipes are connected using a flange, which is a ring of two planes fixed to each other with a fitting in between. Since the fittings are secured to each other via the flanges and tightened with bolts, this method is characterized by high durability. 

2. Screw-in Method

The screw-in method connects pipes by making a cut at the end of the pipe, creating a spiral groove in the groove, and cutting a spiral groove that matches the end of the pipe to be connected. This method is simpler than the flange method and is used for relatively small pipes.

Types of Pipe Fittings

A pipe fitting has a wide variety of shapes and connection methods due to its extremely wide range of applications. In many cases, products from different manufacturers can be connected to each other, but it is important to check for compatibility before use.

The main types of Pipe Fitting are as follows:

• Socket
  Sockets are used to connect straight pipes of the same diameter with the same external threads.
• Nipple
  Connects straight pipes of the same diameter with the same internal thread.
• Coupling
  Directly connects straight pipes of the same diameter without threading.
• Elbow
  Used to bend the direction of piping. Bending angles include 45°, 90°, and 180°.
• Bend
  Used to bend the direction of piping. Compared to elbows, bends have a larger radius of curvature.
• Reducer
  Used to connect straight pipes of different diameters.
• Cheese
  Pipe Fitting with a T-shape to branch a pipe into a T-shape.
• Cross
  Pipe Fitting in the shape of a cross, which branches a pipe in four directions.
• Cap
  A cap is connected to a pipe by placing it over the pipe or by connecting it to the outer thread of the pipe to seal the end of the pipe.
• Plug
  A plug is connected to a pipe by fitting it into the pipe or connecting it to the inner thread of the pipe and sealing the end of the pipe.

Other Information on Pipe Fittings

1. How to Connect Pipe Fittings

Pipe fitting connection methods include threaded, welded, and flanged.

Threaded type
The pipe fitting is threaded, and the piping person threads it out for use. Since this connection method is removable, it is easy to repair and maintain.

Welded Type
The pipe fitting is inserted into the pipe and welded by insertion welding, or butt-welded by butt-welding the ends of the pipe and fitting against each other. This type of welding is stronger and more reliable than the screwed-in type.

Flange Type
Pipe flanges are connected with a bottle and nut.

Shafting Type
The pipe fitting is inserted into the pipe and welded by insertion is connected by wedging the sleeve of the pipe fitting into the pipe. When using a pipe fitting, the appropriate pipe fitting should be selected based on the shape, connection method, material, and size (pipe diameter) as described above. 

2. Threaded Sealing Material

When using a screw-in pipe fitting, a sealing material is required. Sealant prevents leakage from the joint. There are two types of sealing materials: liquid type and tape type.

In the case of screws, even when fastened, a gap exists between the outer and inner threads. The role of the sealant is to fill the gap at the screw.

What Is a Rare Earth Magnet?

Rare earth magnets are permanent magnets composed mainly of rare earth elements.

There are several rare earth magnets, including neodymium magnets, samarium cobalt magnets, praseodymium magnets, and samarium magnets. Rare earth magnets are characterized by their far superior magnetic properties compared to ferrite magnets.

Applications of Rare Earth Magnets

Rare earth magnets are used in many fields due to their small size and large magnetic force. Specifically, they are used in small magnetic sensors, small relays, small speakers, motor magnets, rotor parts, and rotor magnets in watches. In particular, the miniaturization of motors and other power sources has led to the miniaturization of products that use motors (e.g., robot arms). The use of rare earth magnets is expected to further advance in fields where product miniaturization and higher performance are required.

Characteristics of Rare Earth Magnets

Rare earth magnets are characterized by their magnetic strength. Compared to ferrite magnets and alnico magnets, rare earth magnets have far superior magnetic properties. Their magnetic force is more than six times stronger than that of ferrite magnets. The characteristics of rare earth magnets vary depending on the type of rare earth element they contain. Individual characteristics are described below:

• Neodymium Magnet

Neodymium magnets have the strongest magnetic force among rare earth magnets. The main raw materials are neodymium and iron. Since neodymium raw materials are relatively abundant, the cost is comparatively low among rare earth magnets. It is a rust-prone material and is thus usually plated or coated.

• Samarium Cobalt Magnet

Compared to neodymium magnets, the change (decrease) in magnetic force due to temperature is about 1/4 of that of neodymium magnets. It is suitable for maintaining stability at various temperatures, including high temperatures. Since it is a rust-resistant material, no plating or coating is required in normal use. It is a brittle material and care must be taken in its use and handling.

• Praseodymium Magnets

Praseodymium magnets are anisotropic rare earth magnets. It is characterized by high mechanical strength, with tensile strength more than three times that of neodymium magnets. There is no cracking or chipping. Machining is also relatively easy, and drilling and threading are possible.

What Is a Silver Oxide Battery?

Figure 1: Image of a Silver Oxide Battery

Silver oxide batteries, also known as SR batteries or silver-zinc batteries, utilize silver oxide and zinc as electrodes to deliver high energy density. This makes them ideal for compact, high-capacity applications like button batteries.

Applications of Silver Oxide Batteries

These batteries maintain a stable operating voltage, offering reliable power for precision instruments and medical devices, such as watches, hearing aids, cameras, and electronic thermometers. Their consistent performance is crucial for devices requiring accurate voltage, like quartz clocks and medical equipment.

Principle of Silver Oxide Batteries

Their operation is based on the chemical reactions between the silver(I) oxide positive electrode and zinc negative electrode, using potassium hydroxide or sodium hydroxide as the electrolyte. These reactions enable the generation of electricity with high efficiency and minimal environmental impact, as modern batteries are designed to be mercury-free.

Types of Silver Oxide Batteries

Varieties include small button cells and high-voltage stacked cells, differentiated by electrolyte type (potassium hydroxide as W type, sodium hydroxide as SW type) to suit specific applications. Advances in design have also focused on environmental safety and leakage prevention.

Other Information About Silver Oxide Batteries

1. Advantages

They offer high mechanical strength, low self-discharge rates, and excellent voltage stability, supporting a broad operating temperature range. Their energy density significantly surpasses that of lead-acid and alkaline button batteries.

2. Disadvantages

The primary drawbacks are their higher cost due to silver content, limited recharge cycles, and longer charging times compared to other battery types.

What Is a Lubricant?

A lubricant is a substance designed to reduce friction between moving parts, facilitate smooth movement, prevent wear, and dissipate heat generated from friction. It also serves as an anti-corrosion agent by forming a protective oil film on surfaces.

Lubricants range from liquids (lubricating oils) and semi-solids (grease) to solids (graphite, molybdenum disulfide, polytetrafluoroethylene [PTFE]), each suited to specific applications.

Applications of Lubricants

Lubricants play a critical role wherever parts move, from machinery to household items.

1. Liquid Lubricants

These are used in machinery like sewing machines, bicycles, and power tools for their ability to penetrate narrow gaps, facilitating smooth operation. They also serve as cutting oils in machining processes.

2. Semi-Solid Lubricants

Semi-solid forms, such as grease, are applied to components like shutters and gears during assembly for their non-permeable properties.

3. Solid Lubricants

Solid lubricants create durable films and are ideal for high-temperature environments or where maintenance is challenging.

Principle of Lubrication

Lubrication methods can be categorized into fluid lubrication, offering ideal conditions with minimal wear, and boundary lubrication, where direct contact between parts can lead to durability issues.

1. Fluid Lubrication

This method involves a thick oil film preventing direct contact between parts, significantly reducing friction and wear through the “wedge effect.”

2. Boundary Lubrication

Occurs when parts directly contact each other without a sufficient oil film, potentially causing galling or seizing, especially with similar metals.

Types of Lubricants

Lubricants are classified based on their state: liquid, semi-solid, and solid.

1. Liquid Lubricants

Includes cutting oils for metal processing and anti-corrosion/penetrating lubricants for loosening rusted components. Spindle oil, used for the smooth operation of machinery, and silicone-based oils for material slippage improvement are also common.

2. Semi-Solid Lubricants

Greases and compounds that contain thickeners to reduce wear and friction while providing rust prevention and lubrication.

3. Solid Lubricants

Materials like PTFE, molybdenum disulfide, and graphite offer low surface friction, high melting points, and resistance to seizing, suited for extreme conditions.

What Is a Pyroelectric Infrared Sensor?

Pyroelectric infrared sensors apply a physical phenomenon called the pyroelectric effect to infrared detection.

It is a sensor that detects heat generated from the human body or an object as infrared rays and captures the heat source.

The pyroelectric effect is a phenomenon in which polarization occurs inside a solid when heat is applied to ferroelectric material. Silicate minerals and tartaric acid are used as materials.

Pyroelectric infrared sensors have been adopted in many countries and are used as sensors in security alarms and motion detectors.

Applications of Pyroelectric Infrared Sensor

Pyroelectric infrared sensors are devices that detect infrared radiation emitted by heated objects, allowing them to identify the heat source, such as a person or object.

Compact, high-performance pyroelectric infrared sensors are widely used in a variety of situations where sensors are required.

There are many examples of the use of these sensors, mainly as intruder alarms for crime prevention and as motion-sensitive illuminators.

In recent years, pyroelectric infrared sensors have also been used in general households to detect people in air conditioning and heating equipment, televisions, and IoT devices.

Principle of Pyroelectric Infrared Sensor

The pyroelectric effect is a phenomenon in which an electric charge is generated by the polarization of molecules on the surface of a dielectric crystal when it is heated.

As the temperature rises, the polarization inside the dielectric responds immediately, and the constituent molecules respond as the polarization relaxes.

However, surface charges cannot respond as immediately as molecular polarization. Charges appear on the surface of the dielectric only as the polarization relaxes.

When a high-impedance load is connected to the electrodes on both sides of the dielectric, a current flows between the electrodes (called pyroelectric current). This pyroelectric current is used to detect the charge generated on the surface.

Since the pyroelectric current is generated when a temperature change occurs, it functions as a sensor when external thermal energy is applied.

Infrared light emitted from an external heat source is focused onto the sensor by an optical lens called a Fresnel lens. Optical filters are also used to avoid the effects of sunlight and illumination.

The output from the sensor is transmitted through an amplifier to increase the signal strength, which is then detected as a waveform.