A 50-year-old hypothesis has Resulted in the world’s smallest and best Acoustic Amplifier

Eniola Elizabeth Fase

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Sandia National Lab’s acoustoelectric device reveals new road to miniaturising wireless tech

Sandia National Laboratories scientists have created the world’s smallest and most powerful acoustic amplifier. And they accomplished it with an idea that had been largely forgotten for nearly 50 years. The device seems to be more than 10 times more effective than previous iterations, according to research published in Nature Communications on May 13. For smaller wireless technology, the design and future research areas hold promise.

Modern cell phones are packed with radios to send and receive phone calls, text messages, and high-speed data. The more radios in a device, the more it can do. While most radio components, including amplifiers, are electronic, they can potentially be made smaller and better as acoustic devices. This means they would use sound waves instead of electrons to process radio signals.

According to Sandia scientist Lisa Hackett,  “Acoustic wave devices are inherently compact because the wavelengths of sound at these frequencies are so small — smaller than the diameter of human hair,” he said. However, many of these components have previously been unable to use sound waves.

World's smallest, best acoustic amplifier emerges from 50-year-old hypothesis
An acousto-electric chip, top, produced at Sandia National Laboratories includes a radio-frequency amplifier, circulator and filter. An image taken by scanning electron microscopy shows details of the amplifier. Credit: Photo by Bret Latter. Microscopy image courtesy of Matt Eichenfield

Sandia’s acoustic 276-MHz amplifier, which measures just 0.0008 square inches (0.5 square millimeters), illustrates the huge, largely enormous potential of acoustics in reducing radios. The gadget would be even smaller to amplify 2 gigahertz frequencies, which transmit much of modern mobile phone traffic, with a footprint that would fit easily inside a grain of sodium chloride and is more than 10 times smaller than existing state-of-the-art innovations.

The team also invented the first acoustic circulator, which separates emitted and received signals in radio transmissions. According to Sandia scientist Matt Eichenfield, the tiny pieces provide an essentially undiscovered road toward making all systems that send and receive information with radio waves smaller and more complex. Eichenfield explained that they are the first to demonstrate that the functions that are ordinarily performed in the electronic domain can be performed in the acoustic domain.

Resurrecting a decades-old design:

Scientists attempted to develop acoustic radio-frequency amplifiers centuries back, but the last major academic papers on the subject were released in the 1970s.

Their gadgets performed too badly to be usable without modern nanofabrication technology. With the earlier devices, boosting a signal by a factor of 100 required 0.4 inch (1 centimeter) of space and 2,000 volts of electricity. They also produced a lot of heat and consumed more than 500 milliwatts of electricity.

In a few areas, the new and better amplifier is more than ten times as effective as the 1970s ones. With only 36 volts of electricity and 20 milliwatts of power, it can raise the signal intensity by a factor of 100 in 0.008 inches (0.2 millimeters).

Previous research into using layers of semiconductor materials to improve acoustic devices that are incapable of amplification or circulation on their own came to a halt. The new material had to be very thin and of excellent quality for their notion to work, but scientists only had procedures to create one or the other.

Sandia found technology to do both decades later in order to improve solar cells by layering a series of thin semiconducting materials on top. The Sandia scientist in charge of the project happened to work in the same office as Eichenfield. Sandia used semiconductor materials with 83 layers of atoms — 1,000 times thinner than a human hair — to create its amplifier.

Growing crystals on top of other crystals, connecting them to yet more crystals, and finally chemically eliminating 99.99 percent of the materials to form a completely smooth contact surface were all involved in welding an ultrathin semiconducting layer onto a dissimilar acoustic device. Heterogeneous integration, a research field of growing interest at Sandia’s Microsystems Engineering, Science and Applications complex throughout the semiconductor industry, refers to nanofabrication technologies like this.

Sandia built circulators, amplifiers, and filters on the same acousto-electric chip, which is unusual because they are all different technologies. Manufacturing gets easier and more efficient as more technologies may be built on the same chip. According to the team’s research, the other radio signal processing elements might be manufactured as extensions of the devices that have previously been shown.

The Center for Integrated Nanotechnologies, a user facility run jointly by Sandia and Los Alamos National Laboratories and Sandia’s Laboratory Directed Research and Development program provided funding for the project How long before these tiny radio components end up inside your phone? Probably not for a while, according to Eichenfield. He believes that converting mass-produced, commercial devices like mobile phones to all-acousto-electric technology will necessitate a huge redesign of the production infrastructure. However, the method offers greater immediate potential for small-scale manufacturing of specific gadgets.

Sandia is now looking into adapting its technology to enhance all-optical signal processing as well. They’re also curious if the innovation can be used to isolate and control single quanta of sound, known as phonons, which might be valuable for regulating and performing measurements in quantum computers.

Reference:

  • Lisa Hackett et al, Towards single-chip radiofrequency signal processing via acoustoelectric electron–phonon interactions, Nature Communications (2021). DOI: 10.1038/s41467-021-22935-1
  • https://www.google.com/amp/s/phys.org/news/2021-06-world-smallest-acoustic-amplifier-emerges.amp
  • https://www.sciencedaily.com/releases/2021/06/210602091153.htm
  • https://compoundsemiconductor.net/article/113300/Smallest_acoustic_amplifier_emerges_from_50-year-old_hypothesis

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