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Atomically Thin Synthetic Eardrum Offers Cat-Like “Hearing” Capability

Case Western Reserve University researchers are now reportedly designing a wearable device that can send and receive signals at radio frequencies even greater than those we can hear with our natural ear.

Nicknamed the “drumhead”, it is 10,000,000,000,000 times smaller in volume and 100,000 times thinner than the human eardrum and can detect a much wider range of signal than other similar devices.

Their work will likely contribute to making the next generation of ultralow-power communications and sensory devices smaller and with greater detection and tuning ranges.

Sensing and communication are key to a connected world,” said Philip Feng, an associate Professor of electrical engineering and computer science and corresponding author on the paper. “In recent decades, we have been connected with highly miniaturized devices and systems, and we have been pursuing ever-shrinking sizes for those devices.

Illustration of ultrasensitive optical interrogation of the motions of atomically thin drumhead nanoelectromechanical resonators (made of atomic layers of MoS2 semiconductor crystals). Credit: Case Western Reserve University

The challenge with miniaturization: Also achieving a broader dynamic range of detection, for small signals, such as sound, vibration, and radio waves.

In the end, we need transducers that can handle signals without losing or compromising information at both the ‘signal ceiling’ (the highest level of an undistorted signal) and the ‘noise floor’ (the lowest detectable level),

” Feng said.

Dynamic range is the ratio between the signal ceiling over the noise floor and is typically measured in decibels (dB). Human eardrums typically have a dynamic range of about 60 to 100 dB in the range of 10 Hz to 10 kHz, and human hearing rapidly drops outside this frequency range. Other animals, such as the beluga whale or common house cat can have comparable or even broader dynamic ranges in higher frequency bands.

The vibrating nanoscale drumheads built by Feng and his team are composed of atomic layers of semiconductor crystals (single-, bi-, tri-, and four-layer MoS2 flakes, with a thickness of 0.7, 1.4, 2.1, and 2.8 nm), with diameters only around 1 µm.

Comparison of dynamic ranges and frequency bands of the eardrums of humans, other animals, and atomically thin drumheads. (Image: Case Western Reserve University)

In order to duplicate this effect, the researchers needed to construct the ‘eardrums’ on an atomic level. They used a combination of nanofabrication and micromanipulation to suspend atomic layers over a silicon wafer.

The team then made electrical contacts to the devices. Even for all its tiny size, the resonators show frequency “tunability,” according to the researchers, which means that tones can be manipulated by stretching the drumhead membranes through electrostatic forces. It would be similar to tuning a kettle drum in an orchestra, Feng noted.

Not only having surprisingly large dynamic range with such tiny volume and mass, they are also energy-efficient and very ‘quiet’ devices,” Feng said, “We ‘listen’ to them very carefully and ‘talk’ to them very gently.”

In search of the perfect burger. Serial eater. In her spare time, practises her "Vader Voice". Passionate about dance. Real Weird.