The Function of Ferrites in Electronics

Engineers often use ferrite components in electronic circuits. These ferrite components are nonconductive, ceramic compound materials made with numerous combinations of iron oxides. Electronic components typically use them because of their high electrical resistivity and low eddy current losses. Ferrites can have various properties depending on their condition of synthesis, sintering temperature, composition, and grain size.

Manufacturers classify ferrites based on their crystal structure and magnetic properties. In general, they are of two types—soft and hard. Soft ferrites, made from magnesium, manganese, nickel, cobalt, and zinc, have low coercivity, such that their magnetism changes easily, and they act as conductors of magnetic fields. On the other hand, hard ferrites make very good permanent magnets, owing to their high coercivity.

It is also possible to classify ferrites based on their crystal structure. Typically, there are four groups— spinel, garnet, ortho, and hexagonal. Manufacturers distinguish them based on the molar ratio of ferric oxide to other oxide compounds present in the ferrite ceramic.

Crystallizing spinel ferrite results in a cubic structure with oxygen anions in a closely packed arrangement. Here, a unit cell comprises 32 oxygen ions. The anions form an FCC or face-centered cubic array.

Ferrites typically exhibit a permanent type of magnetism that physicists refer to as ferrimagnetism. This is a phenomenon that aligns the magnetic moments of atoms in both antiparallel and parallel directions. This alignment partially cancels the magnetic field, making the overall magnetic field of a ferrite material weaker than that of ferromagnetic materials.

Various types of ferrites are available. In electronic circuits, engineers typically use them as beads. For a ferrite bead, the resistivity is the strongest in a thin frequency band. This feature makes ferrite beads very useful as frequency-dependant resistors. Above the frequency band, the impedance of the bead begins to appear capacitative.

Other types of ferrites structures are also available for use in electronics. For instance, there are flat ferrites, typically rectangular or disc-shaped. Engineers use them in applications where they need a flat shape, such as power inductors, planar transformers, filters, and power inductors. Flat ferrites are very useful for suppressing radio frequency interference and electromagnetic emissions.

Ferrite rings and sleeves are also available. These are cylindrical-shaped components, suitable for placing around a wire or cable. It acts like a filter that can block high-frequency noise, allowing only low-frequency signals to pass through the wire or cable. Manufacturers choose the inner diameter of the ferrite to closely match the outer diameter of the cable, as this maximizes the benefits of interference suppression. Ferrite rings and sleeves are very useful in applications like data communications, consumer electronics, and power supplies to improve signal integrity and reduce interference effects on circuit performance.

Multi-hole ferrite beads are cylindrical cores with typically 6 through-holes running along the axis of the cylinder. When a trace or wire in a circuit is wound through its holes, the multi-hole ferrite bead behaves as a low-pass filter. It blocks unwanted high-frequency interference signals and allows only low-frequency signals to pass through the wire.

3D Printed RF Components

Most RF system designers view air simply as a medium for electromagnetic energy propagation from the source to the receiver. This is usually the case, allowing them to focus the bulk of their design effort on interconnections and integrated circuits that define the physical system.

However, that is only a simplistic view, as other properties of air are also important. For instance, air can keep electronics cool with convection, and it has dielectric properties that some RF components find critical.

Heinrich Hertz first demonstrated wireless signals in 1888. He energized a spark gap of 1 millimeter using high voltage, creating a wideband pulse. A dipole antenna transmitted this pulse. The antenna had two collinear metal rods with capacitive metal plates. At standard atmospheric conditions, air has a dielectric strength of about 30-70 volts/mil or 3-7 kV/mm. Discharged through air across the gap, the high voltage spark caused brief standing waves of oscillating current in the antenna, which then radiated this energy as a brief pulse of radio waves.

With the growth and maturing of wireless, RF tuners often had variable capacitors. These consisted of multiple parallel plates with air gaps that decided the capacitance value of the tuning assembly. By rotating a shaft, it was possible to adjust the position of the moving plates with reference to the static ones, thereby changing the capacitance between them from near zero to several hundred picofarads.

Vacuum has the ideal unit dielectric constant, while air is very close, with a value of 1.00058986. In comparison, the dielectric constant of PTFE is 2.0, and for FR4 it is about 4.4.

Another important property of vacuum, is its dielectric loss, dissipation factor, or loss tangent is zero, and so it is for air as well. Moreover, air characteristics are stable well into the terahertz frequency range, but it is not so for other dielectrics.

However, both vacuum and air have a common weakness. Neither has any structural strength. Therefore, they require a supporting form to hold them. Engineers find this a challenge as there must be an adequate amount of air within the structural medium of the dielectric.

The solution to this problem lies in using AM or additive manufacturing, also known as 3D printing, along with foam, and a family of photopolymer materials. Roger’s Corp typically supplies specialty RF materials, such as the Radix family of 3D printable, high-resolution materials. Radix is a photo-curable, highly viscous resin. It is a high filler concentration that offers good mechanical and electrical properties even at high frequencies.

3DFortify, of Boston, makes a particular type of Flux Core 3D printer. This is the only printer in the market that can effectively print using the Radix resin. The two companies are now partnered to produce 3D-printed RF components.

The printer layers the material with a thickness of less than 100 µm and cures it with a UV digital light processing projector in one flash for every layer. They provide both metalized and non-metalized versions. With the 3D-printing approach, the manufacturer can vary the structural strength of the material as necessary. They can give thick and strong structures at places subject to physical pressure or connections. 

DAWSense Turns Any Surface into an Input Device

Although we are used to traditional interfaces like touchscreens and keyboards, interfacing with computers has traversed a long distance over the years. Now, it is possible to turn any surface into an input device. DAWSense can do this by utilizing machine learning and taking advantage of surface acoustic wave technology. With different situations requiring varying methods of input, researchers are now exploring newer methods of human-computer interfacing. One of them is to embed the interface within everyday objects, thereby enhancing user experiences.

Human-machine interfaces may take many forms. For instance, the industry often uses microphones or cameras to control devices using methods like speech or gesture recognition. Although such systems may be of immense help in certain applications, they may not be practical for others. In a camera-based system, it is easy to obscure the arrangement by introducing objects in front of the camera. Similarly, microphone-based systems involving speech recognition may not function properly in noisy environments.

As an alternative, researchers were experimenting with transforming any arbitrary surface to act as an input device. For instance, for controlling a smart home, they have experimented with the arm of a couch acting as a TV remote, or an interactive wall. They have tried many methods for building such functionality so far, with accelerometers standing out as one of the most promising solutions, as they can sense touch gestures on various surfaces without any modifications on them.

However, the sampling bandwidth of accelerometers incorporated into a surface to act as a touch-sensing device is not enough to capture more than a few relatively coarse gestures. Now, a collaboration between researchers at the Meta Reality Labs and the University of Michigan has demonstrated another method that offers the necessary bandwidth for creating user interfaces that are more advanced.

The new method relies on SAWs or surface acoustic waves rather than mechanical vibrations for sensing touch inputs. The team has also fashioned a VPU or voice pick-up unit for detecting subtle touch gestures. They have designed the VPU to conduct the surface waves into a hermetically sealed chamber that contains the actual sensor. This practically removes any interference from background noise. As the team has fabricated each VPU using the MEMS process, the sensor has the necessary high bandwidth that is typically associated with a MEMS microphone.

Although the MEMS sensor was a high-performance one, the researchers still needed a method for converting the SAWs into swipes, taps, and other gestures. A hard-coded logic would fail to convert them satisfactorily, so the team had to design a machine-learning model with an algorithm to learn from the data.

VPUs typically collect a huge amount of data, and processing this data on an edge computing device in real-time would be a challenge. The researchers dealt with this problem by calculating Mel-Frequency Cepstral Coefficients, which helped in understanding the most informative features of the data. With this analysis, the researchers could reduce the number of features they needed to consider from 24,000 to just 128. They then fed the features into a Random Forest classifier for determining the exact representation of the surface waves.

FireBeetle Drives Artificial Internet of Things

The next generation of the FireBeetle 2 development board is now available. Targeting the IoT, especially the Artificial Intelligence of Things, it has an onboard camera. According to DFRobot, the creator, the FireBeetle boasts Bluetooth and Wi-Fi connectivity, and an Espressif ESP32-S3 module.

Built around the ESP32-S3-WROOM-1-N16R8 module, the main controller of the FireBeetle provides high performance. It operates with 16MB of flash RAM, along with 8MB of pseudo-static RAM or PSRAM that allows it to store more data. The ESP32-S3 chip provides acceleration for computing neural networks and processing signals for high workloads. This makes the FireBeetle ideal for many applications like image recognition, speech recognition, and many more.

DFRobot has designed the heart of the FireBeetle, the ESP32-S3, for edge AI and low-power tinyML work. With two CPU cores, the Tensilica Xtensa LX7, both operating at 240 MHz, the ESP32-S3 also offers vector processing extensions. The design specifically targets accelerated machine learning, including workloads of artificial intelligence. In addition to the 8MB PSRAM and the 16MB Flash memory, the board also has 384kB of flash and 512kB of on-chip SRAM.

The FireBeetle development board, along with its BLE or Bluetooth 5 Low Energy and Wi-Fi connectivity, also includes an onboard camera interface driven by a dedicated power supply circuit. The camera has a 2-megapixel sensor with a 68-degree FOV or Field of Vision. There is a GDI connector, which is useful for adding a TFT display.

DFRobot offers two variants of the FireBeetle development board. One of them is the standard version, namely the FireBeetle 2 ESP32-S3, containing a PCB antenna for wireless connectivity. The second variation is the FireBeetle 2 ESP32-S3-U, and it offers a connector for rigging up an external antenna. It is possible to program both boards from Arduino IDE, ESP-IDF, and MicroPython.

It is possible to order both development boards from the DFRobot website store, The second variant is the costlier of the two, and both come with volume discounts. Although both variants come with the board and camera, the pin headers are bundled loosely but not soldered. DFRobot has published a simple project for the FireBeetle—a camera-based monitor to oversee the growth of plants.

It is possible to use the FireBeetle development board to build a DIY plant growth recorder. It allows monitoring the entire growth process of the plant, starting from seeding right up to maturity, while tracking the environmental conditions throughout. This makes it possible to identify any changes easily that could affect the health and growth of the plant, along with any fluctuations in temperature, light levels, and humidity. This information helps to organize and optimize the growing conditions of the plant, thereby ensuring that the plants get everything they need for proper growth.

The project has a screen for displaying the various parameters it is monitoring. The camera periodically captures images of the plant as it grows, storing them in the board’s memory. The board transmits real-time images and environmental data over Wi-Fi or Bluetooth for regular viewing.

Preserving IoT Battery Life

At MIT, researchers have built a wake-up receiver for IoT devices. The receiver uses terahertz waves to communicate, making the chip more than ten times smaller than contemporary devices. The receiver also includes authentication that helps protect it from certain types of attacks. The low power consumption of the chip means it can help preserve battery life in robots or tiny sensors.

The current trend is towards developing ever-smaller devices for IoT or the Internet of Things. For instance, sensors can be smaller than a fingertip, capable of making any object trackable. Most of these tiny sensors, however, have even tinier batteries that are nearly impossible to replace. Therefore, engineers need to incorporate a wake-up device in these sensors. It keeps the device in a low-power sleep mode when not operating, thereby preserving battery life. The new device from MIT is capable of protecting the device from certain attacks that could drain its battery rather quickly.

The present generation of wake-up receivers is typical of the centimeter scale. This is because their antennas need to be proportional to the length of the radio waves they use for communicating. On the other hand, the MIT team utilized the terahertz wave for the receiver. As these waves are about one-tenth the length of regular radio waves, they could design the chip to be barely greater than a square millimeter.

It is possible to incorporate the wake-up receiver into microbots for monitoring environmental changes in locations that are either hazardous or too small for other robots to reach. As the device operates on terahertz frequencies, it is possible to use them in emerging applications like radio networks that operate as field-deployable swarms for collecting localized data.

Using terahertz frequencies, the researchers could make antennas the size of a few hundred micrometers on either side. The implication of such small-size antennas is that it is possible to integrate them on the chip, thereby creating a totally integrated solution. Ultimately, the researchers could build a wake-up receiver tiny enough to attach to tiny radios or sensors.

On the electromagnetic spectrum, terahertz waves exist between infrared light and microwaves. At very high frequencies, they travel much quicker than radio waves can. Terahertz waves, also known as pencil beams, travel in a rather direct path as compared to other signals, making them more secure.

However, terahertz receivers often multiply their signal by another signal so that they can alter their frequency. This process is termed frequency mixing or modulation, and it consumes a huge amount of power. The researchers at MIT used a pair of tiny transistors as antennas for detecting terahertz waves. This method of detecting consumes very little power, as it does not involve frequency mixing.

Even when they placed both antennas on the chip, the MIT wake-up chip was only 1.54 square millimeters and used only 3 microwatts to operate. The presence of two antennas maximizes its performance and makes it more sensitive to receiving signals. Once it detects the terahertz signal, it converts the analog signal into digital data for processing. The received signal contains a token, which, if it matches the wake-up receiver’s token, will activate the device.

In-Circuit Monitors for Electronic Devices

During a chip’s lifetime, there can be a wide variety of issues cropping up. Engineers are using sensors that can address them. As the semiconductor ecosystem touches a wide application space, sensors, and in-circuit monitors are playing an increasing role in managing the silicon lifecycle, thereby improving its resiliency and reliability.

Engineers are expecting a drastic improvement in the reliability of electronic devices with the addition of these sensors and in-circuit monitors. These expectations are due to a combination of sensor placements in true system-level design, in- and on-chip monitors, and an improvement in data analysis.

In the future, with engineers placing more monitors and sensors at strategic locations for collecting data, the combination, and analysis of this data is likely to increase tremendously. In addition, this will lead to a much more detailed understanding of what goes wrong in real time in the life of a semiconductor. Important to note, this is likely to open the door to recovery schemes for keeping devices functioning until they are due for replacement or repair.

All of the above depends on the complexity of the product. Although some regulatory standards for miniaturization are under study, the complexity of the product drives the use of sensors and in-circuit monitors. With consumers wanting greater capabilities in their hands, the requirement is going to increase substantially.

Although users were not interested earlier in concepts like resilience, predictability, and observability, things are changing fast. Chip architects are paying more attention to how systems and devices behave over time, including issues such as silent data corruption. Where earlier, it was hard to articulate the business reasons for such inclusion, chip architects are realizing there are missing pieces. While it is still a tussle between the why and how much, the realization is dawning that it is impossible to have all the computing resources or complex monitors-on-chip that can tackle all scenarios. Especially when such additions need real estate and power to function.

Designers are beginning to realize that advanced design techniques, in conjunction with manufacturing complexities and the latest process nodes, are leading to new challenges. These challenges appear as variable power consumption and affect the useful life of the semiconductor. The power consumption pattern and performance characteristics of a chip change as it travels along the silicon value chain. The variation starts with the pre-silicon design, moving on to new-product bring-up, to system integration, and finally, to its in-field usage.

Monitoring the way a chip degrades over time, can throw light on many types of semiconductor failures, especially with BTI or bias temperature instability. Using in-circuit monitors, it is now possible to measure areas that show performance and power degradation, on-die temperature variations, and workload stress, and monitor die-to-die interconnects for heterogeneous designs. Mission-critical systems define specifications such as safety and reliability as the key differentiating parameters. Moreover, with device functionality degrading over time, it is necessary to evolve tests that include lifetime operation as well.

The industry is now widely adopting an approach that includes more and more sensors and in-circuit monitors for electronic devices to monitor the most prominent slack paths. 

Wireless Chips for Internet of Things

TI® or Texas Instruments® has announced a new family of companion integrated circuits for SimpleLink®. According to TI®, these offer BLE or Bluetooth 5.3 Low Energy and Wi-Fi 6. The specialty of these chips is they provide connectivity in any type of environment, even when the temperature is over 220 °F (104.44 °C).

Industrial designs such as electric vehicle charging systems operating in the outdoors and sometimes hard-to-access environments is a challenging and expensive options for designers. Under such circumstances, the new SimpleLink® family of Wi-Fi devices from TI® is significantly simpler to install, and more affordable to implement, than ever before.

The SimpleLink® family consists of two chips, differentiated by their functionality. These are the CC3300 and the CC3301. While the lower-cost CC3300 offers Wi-Fi 6 connectivity alone, the other chip, the CC3301 adds the BLE or Bluetooth 5.3 Low Energy support. Both the ICs require pairing with a host microcontroller. This is a departure from TI®’s earlier SimpleLink® designs that combine a microcontroller and the radio. Significantly, there is no vendor tie-in, as both chips can work seamlessly with many types of controllers and processors from TI® and brands other than TI® that support real-time or Linux operating systems.

TI® is offering the devices in a QFN or quad flat no-lead package. Later in the year, TI® plans on introducing pin-compatible CC3xx variants that will add dual-band Wi-Fi connectivity, like 2.4 GHz and 5 GHz. At present, TI®® is also offering the BP-CC3301, an evaluation board.

With a SimpleLink® CC3301, it is easy to add BLE and Wi-Fi 6 connectivity to devices. It offers affordable, secure, and reliable connectivity in embedded applications. All it needs is a MCU host running RTOS, or a processor host running Linux. The BP-CC3301 is a test and development board from TI that the user can easily connect to any TI® Launchpad development kit or to a processor board, thereby enabling rapid software development. 

The user can use the kit in three configurations. One, for MCU and RTOS evaluation they can use the BP-CC3301 and LaunchPad with the MCU like the LP-AM243 running TCP/IP. Two, for processor and Linux evaluation, they can use the BP-CC3301 along with the BP-CC33-BBB-ADAPT and the BEAGLE-BONE-BLACK. Third, for RF testing using PC Tools, they can use the BP-CC3301 and the LP-XDS110. Additionally, the user can also wire the BP-CC3301 to any other RTOS or Linux host board that is also running the TCP/IP stack.

The BP-CC3301 has many useful features. It offers a companion IC providing Wi-Fi 6 and BLE in a QFN package. It has a BoosterPack plug-in module header or a 2×20 pin stackable connector to connect to plug-in modules of BoosterPack or other TIR LaunchPad development kits. The development kit comes with an on-the-board chip antenna with an option for testing based on SMA/U.FL. The kit also provides an SWD type interface for RF testing and standalone operation.

TI® has designed the development kit to accept power from a connected LaunchPad® kit. However, some LaunchPad® kits cannot supply the peak current requirement when the Wi-Fi 6 is operating. In such cases, the user can provide additional power from the USB connector.

Clamp-On Energy Meters

Traditional energy meters are mostly inline, meaning, the meter is in series with the circuit whose energy consumption it is monitoring. However, there is another type of energy meter that clamps onto the pipeline it must monitor, rather than break into the pipeline. This is an ultrasonic alternative and is specifically useful for energy management and billing applications that commercial, domestic, district, or shared cooling and heating systems use. Obviously, the clamp-on energy meter offers several advantages over its traditional in-line counterpart, the most significant of them being easier installation, cost savings, and maintenance benefits.

For the efficient operation of new or existing buildings, it is necessary to identify the waste, optimize the use, and accurately monitor for billing the use of energy and water. Optimizing the consumption of water and energy is essential and crucial for any type of building, whether it is a housing or accommodation, school, hospital, condo, office block, or shopping center, in the private or public sector. Mostly, energy monitoring applications associate automatic meter readings with a third-party cloud provider, thereby allowing for ease of use and seamless integration. These new type of meters are also suitable or retrofitting older and traditional energy meters in existing buildings that mostly have limited drawings and old pipework.

Managing fluid consumption requires finding out what is flowing where. The clamp-on energy meters accomplish this very easily, as there is no need to drain down the system, shut it down, or cut into the existing pipework. Therefore, using clamp-on energy meters saves a lot of time and money when retrofitting existing buildings.

There are several benefits to using clamp-on energy meters. It is possible to clamp them on a wide range of pipes, and they provide cross-correlation flow measurement systems for accuracy. These meters come with an optional RS485 serial interface and a Modbus RTU slave. They feature a 1-MHz transducer that is powerful enough to measure through poor or old thick wall pipes and larger pipes.

These new energy meters are a clamp-on and non-invasive alternative to traditional in-line meter installation. They are simple to install, simply connect power, enter the inside diameter of the pipe, adjust the sensors, and finally, clamp it on the pipe. No special tools or skills are necessary. The installation provides dry servicing, minimum downtime, and maximum availability.

The non-invasive energy meters require little or no maintenance since they have no moving parts or sensors to wear out or require calibration. Therefore, they have a longer service life with very few repair requirements. Being generally less expensive for installing and maintaining than invasive meters, the non-invasive meters do not require cutting into pipes or installing additional sensors. As it is not necessary to cut into the pipe, the risk of leaks is very much reduced. This is especially important in applications where the fluid in the pipe is expensive or hazardous. Overall, non-invasive clamp-on energy meters are a cost-effective and effective solution for measuring the energy flow in a surprisingly wide range of applications.

These meters are very useful in various types of buildings, including residential buildings, schools, hospitals, and offices.

How is a Wire Harness Made?

Many sectors, including industrial and consumer electronics, continue to use wire harnesses, and their use is increasing continuously. Therefore, there is an urgent need to understand the process of manufacturing this vital component. Wire harnesses link different electrical or electronic modules to allow the complete system to work seamlessly.

Wire harness assemblies are a bunch of wires processed with a protective sheath. They may end in different types of terminations. Harnessing is important as it organizes the wires for easy implementation. Wire harnesses must not be confused with cable assemblies, which bind multiple covered wires with a protective covering, enabling them to work in harsh environments.

The use of wire harness assemblies results in several advantages. The organized wires optimize space while helping to improve assembly times. The harness helps in customizing the appliance to its bespoke needs. The protective covering on the wires improves equipment safety while improving the life of the wires. A variety of appliances use wire harnesses extensively. These include heavy equipment, panel displays, flight simulators, control panels, vehicles, and more.

The wire harness manufacturing process begins with design. Each product requires a custom-designed harness. It is imperative to choose each component of the wire harness carefully to achieve full functionality and life.

The primary requirement is the length of each wire in the harness. As the wire may require routing through the equipment, the length of individual wires in the bunch may differ. The length of the wires may also depend on their diameter, as thicker wires require more space to bend.

Each wire must also be considered for the maximum current it will carry. In a wire harness, some wires may carry power while some may carry low-frequency signals. They will require wires of different gauges.

Once the designer determines the length and gauge of each wire, they must concentrate on the wire terminations, which are necessary to connect each wire to its starting and ending points. This depends on the end termination of the two devices the wire will be joining. The terminations may use lugs, crimps, connectors, or something similar.

Once the wires are bunched together to form the harness, it will be difficult to identify them individually. Therefore, the designer will require some means of identifying individual wires in the bunch. Ferrules are a low-cost choice for this purpose. They are available in different diameters and individually marked with numbers and alphabets. By using the same combination of ferrules with numbers and alphabets on both ends of a wire, it becomes easy to identify the wire, even after bunching it with several others. However, this identification is only necessary if the operator will connect each wire individually. They are not necessary if the termination ends in a connector.

Next, wire harnesses may require a jig to form them into the final shape necessary for implementation in the system. Once the operator arranges or dresses the wire harness in the jig, they may require a means to bunch all the wires together. This may take different forms, like a plastic wire or sheath covering the full length of the wire harness.

What is Diode Biasing?

PCB assemblies often contain numerous components. The engineer designing the board selects these components individually, based on their function in the circuit. For a successful project, it is essential to understand the basic operation of these components individually, and in relation to one another. One such component is the diode.

A diode is a semiconductor device with a PN junction. It supports current flow in only the forward direction—from the anode to the cathode—and not in the reverse. However, to allow current flow in the forward direction, a diode must be given a particular voltage to overcome the bias in its PN junction. Diode biasing is the application of a DC voltage across the diode’s terminals for overcoming the PN junction bias.

It is possible to bias a diode in two ways—forward and reverse. When forward biased, the diode allows current flow from its anode to its cathode, provided the biasing voltage is greater than the PN junction bias. However, when reverse-biased, the biasing voltage cannot overcome the PN junction bias, and the diode blocks any current flow. Reverse biasing a diode is a convenient way for using it to convert alternating current to direct current. Proper use of forward and reverse biasing also allows other functions, such as electronic signal control.

Diodes are mostly germanium or silicon-based. A diode consists of a layer of P-type semiconductor material and another layer of an N-type semiconductor material joined together. The P-type material forms the anode terminal and the N-type material forms the cathode terminal of the diode.

When fabricating a diode, the manufacturer dopes the two layers differently. They dope one of the layers with boron or aluminum to make it P-type, which gives it a slightly positive charge. The P-type semiconductor, therefore, has a deficit of electrons or an abundance of holes. They dope the other layer with phosphorus or arsenic to give it a slightly negative charge and make it N-type. Therefore, the N-type semiconductor has an abundance of electrons.

At the junction of the P-type and N-type layers, electrons and holes combine to form a sort of neutral zone. Therefore, when a current must flow, a voltage bias is necessary to push the electrons and holes through this neutral zone. The neutral zone is less than a millimeter in thickness.

A forward bias pushes holes from the P-type layer, across the neutral zone, into the N-type layer. The forward bias reduces the width of the neutral zone to allow the current to flow. The forward bias necessary depends on the material of the diode. It is 0.7 VDC for silicon diodes and about 0.3 VDC for germanium diodes.

On the other hand, a reverse bias adds more electrons to the N-type layer and holes to the P-type layer. This increases the width of the neutral zone, making it impossible for current to flow across it.

Therefore, forward biasing allows current flow through the diode from the anode to the cathode, and reverse biasing prevents current flow. Even with forward biasing, there is no current flow until the voltage is able to overcome the PN junction bias.