Amplifiers: RFs Overlooked Components And More Interesting Than You Think
By John Oncea, Editor
Whenever people need to magnify an RF signal, the amplifier plays a pivotal role. They are used in commercial and defense avionics, space and deep space, electronic warfare, naval applications, mobile internet, satellite communication, and wireless communications.
Ask me what I think of when I think about amplifiers and I’ll tell you these go to 11. If you watched the clip I linked to you might have noticed the amp Spinal Tap lead guitarist Nigel Tufnel was showing off was a Marshall, perhaps the most well-known amplifier in the music industry.
Jim Marshall, a British engineer, musician, and owner of Marshall Amplification died nearly 13 years ago. But he’ll be forever remembered for building the amplifiers that bear his name, amps he began making in the early 1960s in a small shop in West London.
“Marshall amps became a key part of the rock ‘n’ roll sound,” reported NPR at the time of Jim Marshall’s death. “(Jimi) Hendrix grinded his guitar into one before setting it on fire at the Monterey Pop Festival in 1967. Lemmy Kilmister, the bassist and singer for the heavy metal band Motorhead, plays in front of a giant wall of them and name-drops the amps in the song “Dr. Rock.” Pete Townsend, known for destroying his instruments, made them a trademark part of his assault.”
Marshall amps – from the Bluesbreaker and the Plexi of the ‘60s to the JMP and Silver Jubilee of the ‘70s and ‘80s to the DSL and JVM lines of the ‘90s – continue to “offer all the crunch that players always have found so appealing,” writes Guitar.com.
But music isn’t the only industry making use of amplifiers. They are used in everything from consumer electronics (like TVs, radios, and home audio systems), automotive manufacturing (car audio systems), telecommunications and broadcasting, medical devices, and industrial applications where signal amplification is needed. Any industry utilizing electronic devices that require increased signal strength will utilize amplifiers.
Amplifiers In Space
Amplifiers are designed to increase the strength of an electrical signal, acting as a building block within a larger electronic system, taking a weak electrical signal and amplifying its voltage, current, or power to produce a stronger output signal. This makes them a key component in many devices like radios, TVs, and audio equipment, and even helpful in weather prediction and research.
Well-known uses of amplifiers include driving specialized antennas in electronic warfare (EW) applications, signal amplification in deep space communication, and use in medical imaging technologies like magnetic resonance imaging (MRI) where precise RF pulses are required.
When applied to deep-space communication, signal amplification enables the transmission and reception of data across vast distances in the Solar System. High-power amplifiers, such as klystrons, are employed to boost outgoing signals from Earth to spacecraft.
These devices can transform around 100 kilowatts of electrical power into 20 kilowatts of radio frequency power, amplifying the signal approximately 100,000 times. This significant amplification is necessary to ensure that commands and data reach distant probes across millions of kilometers of space.
On the receiving end, low-noise amplifiers (LNAs) are essential for capturing faint signals from distant spacecraft. According to NASA, these amplifiers, which may be cryogenically cooled masers or solid-state high-electron-mobility transistors (HEMTs), amplify incoming radio frequencies while introducing minimal noise.
For instance, NASA's Deep Space Network uses masers cooled with liquid helium to keep RF noise to a minimum, allowing the detection of signals that may be billions of times weaker than those used in everyday electronics.
Recent research has explored novel amplification methods to improve deep-space communication. One promising approach, according to Phys.org, involves phase-sensitive optical amplifiers (PSAs), which have demonstrated the ability to achieve error-free transmission with just one photon per information bit at rates of 10.5 Gb/s. This technology could significantly enhance the sensitivity of receivers used in free-space and deep-space communication links.
By leveraging these advanced amplification techniques, space agencies can maintain reliable communication with interplanetary missions, enabling the transmission of critical commands and the reception of valuable scientific data from the far reaches of our Solar System.
Amplifiers And Defense
As a part of EW systems, high-power amplifiers (HPAs) and low-noise amplifiers (LNAs) are essential components that significantly improve signal transmission, reception, and processing, notes Military + Aerospace Electronics.
HPAs are used in electronic attack (EA) systems to boost signal strength for jamming enemy communications and radar systems. These amplifiers enable EW systems to project powerful electromagnetic signals over long distances, effectively disrupting or deceiving enemy electronic equipment. Advanced gallium nitride (GaN)-based power amplifiers are particularly valuable in EW applications due to their high output power and efficiency.
LNAs are critical in electronic support (ES) systems, where they amplify weak signals intercepted from enemy emitters without introducing significant noise. This enables better signal detection and analysis, enhancing intelligence-gathering capabilities, writes ERZIA. For instance, Ka-band LNA achieves a remarkably low noise figure of 1.3 dB, making it ideal for military satellite communications and airborne systems.
The development of wideband amplifiers has further improved EW systems by enabling them to operate across broader frequency ranges. This capability is crucial for detecting and countering threats that may use various parts of the electromagnetic spectrum.
However, thermal management remains a significant challenge in EW amplifier design. Research programs like DARPA's THREADS aim to overcome thermal limitations in GaN-based power amplifiers, which can hinder performance and reliability in high-power EW applications.
Amplifiers And Medicine
Finally, MRI systems in which amplifiers serve two primary functions: signal excitation and signal reception.
For signal excitation, RF power amplifiers are used to generate high-power RF pulses that excite the hydrogen atoms in the body, writes the National Center for Biotechnology Information. These amplifiers, known as transmit (Tx) coils, broadcast RF power to rotate the net magnetization away from its alignment with the main magnetic field. This process creates a transverse precessing magnetization, which is essential for producing the MRI signal.
In signal reception, RF amplifiers, or receive (Rx) coils, detect, and amplify the weak signals emitted by the excited hydrogen atoms1. These amplifiers are designed to have very low noise characteristics to ensure high sensitivity and signal-to-noise ratio (SNR) in the resulting images.
Modern MRI systems often use phased-array technologies, which incorporate multiple receiver elements to improve image quality and enable parallel imaging techniques. These advanced RF coil designs allow for faster image acquisition and higher spatial resolution.
RF amplifiers for MRI applications must meet specific requirements, according to TOMCO Technologies. These include high linearity to maintain signal fidelity, fast pulse rise and fall times for precise timing control, low interpulse noise to minimize image artifacts, and the ability to handle complex pulse sequences.
The performance of RF amplifiers directly impacts the spatial and temporal resolution, sensitivity, and uniformity of MRI scans. As MRI technology continues to advance, RF amplifier designs are evolving to meet the demands of higher field strengths and more sophisticated imaging techniques.
Bonus: 7 Somewhat Surprising Uses Of Amplifiers
RF amplifiers have several unexpected applications beyond the traditional uses already covered. This includes:
- Plasma Generation: In semiconductor manufacturing and materials processing, RF amplifiers power plasma generators for etching and deposition processes.
- Particle Accelerators: High-power RF amplifiers drive particle accelerators in scientific research facilities, enabling experiments in particle physics.
- Microwave Cooking: Industrial microwave ovens use RF amplifiers to generate high-power microwave energy for food processing and sterilization, according to Elite RF.
- Electromagnetic Compatibility Testing: RF amplifiers are employed in EMC testing facilities to generate controlled electromagnetic fields for evaluating electronic device performance.
- Wireless Power Transfer: Emerging technologies use RF amplifiers to transmit power wirelessly over short distances for charging electronic devices.
- Non-Destructive Testing: In industrial quality control, RF amplifiers power equipment used for non-invasive inspection of materials and structures.
- Pest Control: Some agricultural applications use RF amplifiers to generate electromagnetic fields that repel or control pests in crops, according to Arrow.
These diverse applications highlight the versatility of RF amplifiers beyond traditional communication systems, demonstrating their importance in various scientific, industrial, and technological fields.