Power/Performance Bits: Oct. 5

Modeling resistive-switching memory
Researchers from Singapore University of Technology and Design (SUTD) and Chang Gung University developed a new toolkit for modeling current in resistive-switching memory devices.

The team said that traditional physical-based models need to consider complex behaviors to model current in resistive memory, and there’s a risk of permanent device damage due to incorrect current being applied to the resistive memory device during initial testing. Instead, they say their method has excellent accuracy without the need for complex physical-based equations.

“The most exciting potential applications for resistive memory include edge computing, autonomous driving, visual processing and other applications. Using new tools, like machine learning, to develop a better understanding of how the natural world works can lead to dramatic technological breakthroughs. Our results could allow computer designers to reduce risk of permanent device damage, bringing these applications closer to reality,” said Desmond Loke, assistant professor at SUTD.

The technique uses machine learning to consider the relationship between device parameter values such as low-resistance state, high-resistance state, set voltage, and reset voltage. “We formulated a machine learning model and inferred model parameters by fitting the model to experimental datasets to allow for accurate and reliable predictions and forecasts of the minimum current needed to program a device. Our easy-to-use representation of current can outperform traditional representations improving prediction accuracy by around ten times, a significant step towards practical applications on near-term resistive memory,” Loke added.

“By developing these new techniques that are tuned to resistive memory limitations, we may enable potential breakthroughs in energy efficiency and storage and beyond.”

Monitoring blood with a patch
Engineers at the University of California San Diego created a wearable patch that uses ultrasound to monitor blood flow within the body.

Most wearable patches sense activity occurring on or directly under the skin. This device, however, can continuously monitor blood flow, blood pressure, and heart function as deep as 14 centimeters inside the body. Worn on the neck or chest, the researchers said it could help alert patients to early cardiovascular problems.

“This type of wearable device can give you a more comprehensive, more accurate picture of what’s going on in deep tissues and critical organs like the heart and the brain, all from the surface of the skin,” said Sheng Xu, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering.

In addition, the ultrasound beam can be tilted at different angles and steered to areas in the body that are not directly underneath the patch. “With this patch, we can probe areas that are wider than the device’s footprint. This can open up a lot of opportunities,” Xu added.

“Sensing signals at such depths is extremely challenging for wearable electronics. Yet, this is where the body’s most critical signals and the central organs are buried,” said Chonghe Wang, a former nanoengineering graduate student at UCSD, now at Harvard University. “We engineered a wearable device that can penetrate such deep tissue depths and sense those vital signals far beneath the skin. This technology can provide new insights for the field of healthcare.”

This soft, stretchy skin patch uses ultrasound to monitor blood flow to organs like the heart and brain. (Credit: UC San Diego Jacobs School of Engineering)

The patch is constructed of a thin sheet of flexible and stretchable polymer that adheres to skin. Embedded in it is a 12 by 12 array of millimeter-sized ultrasound transducers, each individually controlled to create an ultrasound phased array. This allows all the transducers to be synchronized, producing a high-intensity ultrasound beam that can penetrate up to 14cm in the body. Alternatively, the transducers can transmit out of sync, which allows the beams to be steered to different angles.

When the ultrasound waves penetrate through a major blood vessel, they encounter movement from red blood cells flowing inside. This movement changes or shifts how the ultrasound waves echo back to the patch, which is picked up by the patch and is used to create a visual recording of the blood flow. This same mechanism can also be used to create moving images of the heart’s walls.

“With the phased array technology, we can manipulate the ultrasound beam in the way that we want,” said Muyang Lin, a nanoengineering Ph.D. student at UC San Diego. “This gives our device multiple capabilities: monitoring central organs as well as blood flow, with high resolution. This would not be possible using just one transducer.”

Wirelessly charging multiple devices
Researchers from Aalto University and Xidian University propose a design for wireless chargers that could power up multiple devices at once, without requiring them to be in a fixed place.

The new system creates power transfer channels in all directions, in comparison with many other free-position wireless charging schemes that require a transmitter to detect a device’s location and send energy in its direction.

“What sets this transmitter apart is that it’s self-tuning, which means you don’t need complex electronics to connect with receivers embedded in devices. Since it self-tunes, you can also move the device freely within a wide charging range,” said Prasad Jayathurathnage, a post-doctoral researcher at Aalto University.

To achieve this, the team focused on the design of the coils in the transmitter. By winding the coils in a specific way, they create two kinds of electromagnetic fields: one going outwards and the other around. These fields couple the receiver and transmitter to achieve efficient power transfer.

The transmitter is currently 90% efficient at up to 20 centimeters, with reduced efficiency at longer distances. The team said that the peak-efficiency range could grow as the technology is improved.

“For now, the maximum range at peak efficiency is dependent on the size of the transmitter and receiver.  With the right engineering, we could shrink them down,” Jayathurathnage said.

Safety tests are still needed to ensure the electromagnetic field generated is safe. The team has applied for a patent on the transmitter and is also working on wireless charging for industrial and warehouse robots.