Manufacturing Bits: June 15

Next-gen RF signal processors
Sandia National Laboratories has taken steps to realize the development of acoustic wave amplifiers, a technology that could one day pave the way towards long-awaited tiny RF signal processors.

Researchers have developed piezoelectric acoustic devices using surface acoustic wave (SAW) technology and demonstrated the ability to manufacture these devices. Still in R&D, Sandia’s device involves a 276-megahertz amplifier, which measures a mere 0.0008 square inch (0.5 square millimeter). The amplifier and other components could enable the development of a small, all-acoustic RF signal processor.

Source: Sandia National Labs. Scientists Matt Eichenfield, left, and Lisa Hackett led the team at Sandia National Laboratories that created the world’s smallest and best acoustic amplifier. (Photo by Bret Latter)

The technology could one day be used in futuristic wireless devices. Nonetheless, today’s smartphones incorporate digital chips and RF components. The digital part consists of a modem. The RF components include a RF front-end module.

The front-end module consists of several components in the same unit, including power amplifiers, low-noise amplifiers (LNAs), filters, and RF switches. Power amps provide the power for a signal to reach a destination. LNAs amplify a small signal, while filters block out the noise. Switch chips route signals from one component to another.

These RF devices work in systems, but they are also complex and bulky. They are also based on different processes and materials. Plus, the new phones require more RF content. As carriers move from 4G to 5G wireless networks, the phones require more RF components in order to keep up with a growing number of frequency bands.

So, to reduce the complexity, there is a pressing need to develop smaller or more integrated RF components. That’s where RF signal processors based on SAW technology fit in–they could integrate several of today’s RF components on a single device.

This technology isn’t new. In the 1970s, the industry tried to develop piezoelectric acoustic devices using SAW technology. In SAW technology, “acoustic waves at the interface between a solid and vacuum are pinned to the interface,” according to Sandia.

The technology enabled powerful amplifiers for RF applications. But these devices were prone to noise and had lackluster efficiency, according to Sandia. So, the work was abandoned in favor of today’s RF semiconductor amplifiers.

Sandia, however, has found a new way to enable acoustic wave amplifiers. This in turn could enable the long-awaited miniaturized RF signal processor. In the lab, researchers demonstrated three of the main components for RF signal processors–passive delay line filters, amplifiers, and circulators.

Sandia’s acoustic wave amplifiers exhibit a high gain per unit length and DC power dissipation. Researchers also demonstrated the world’s first acoustoelectric circulator with an isolation of 46dB with a pulsed DC bias.

The RF signal processor is developed using an acoustoelectric materials platform. It consists of a 50nm indium-gallium-arsenide (InGaAs) epitaxial semiconductor film on a lithium niobate piezoelectric substrate.

Sandia’s new acoustic amplifier is 10 times more effective compared the versions built in the 1970s. It can boost the signal strength by a factor of 100 in an 0.008-inch (0.2 millimeter) area with only 36 volts of electricity and 20 milliwatts of power, according to Sandia.

“Acoustic wave devices are inherently compact because the wavelengths of sound at these frequencies are so small — smaller than the diameter of human hair,” said Lisa Hackett, a scientist at Sandia.

Sandia scientist Matt Eichenfield added: “We are the first to show that it’s practical to make the functions that are normally being done in the electronic domain in the acoustic domain.”

Acoustic pulp fibers
Researchers from Aalto University and Lumir, a Finnish acoustics company, discovered that wood-based pulp fibers can make eco-friendly acoustic materials, improving sound absorption in buildings.

The acoustics insulation market is a growing industry, which is expected to reach $15 million by 2022. Acoustics play an important role in construction, as good workplace acoustics improve worker efficiency and productivity.

Jose Cucharero, a PhD candidate at Aalto, is looking for a way for acoustic insulation to be more eco-friendly and sustainable, while also improving quality.

Wood-based pulp is made from natural cellulose fibers, and does better than synthetic fibers in indoors acoustics insulation. “Synthetic fibers, such as fiberglass and rockwool, are uniform in quality. Cellulose fibers have a complex structure with natural irregularities, which can be an asset for absorbing sound indoors,” writes Aalto University. “The production of cellulose fibers is considerably more energy-efficient, and the fibers also absorb significant amounts of carbon dioxide from the atmosphere. Using the fiber in construction materials is an effective way to store carbon: buildings last for decades, unlike single-use packaging and paper where cellulose is typically used.”

Due to the unique nature of cellulose fibers, this eco-friendly acoustic insulation would help companies around the world achieve their carbon neutral goals. Acoustic sprays made from cellulose fibers can also improve the insulation in buildings without changing their visual appearance.