The drumhead is tens of trillions times (10 followed by 12 zeros) smaller in volume and 100,000 times thinner than the human eardrum and could ultimately contribute to making the next generation of ultralow-power communications and sensory devices smaller and with greater detection and tuning ranges, according to the team at Case Western.
"Sensing and communication are key to a connected world," explained Philip Feng, an associate professor of electrical engineering and computer science and corresponding author on a paper recently published in the journal Science Advances. "In recent decades, we have been connected with highly miniaturised devices and systems, and we have been pursuing ever-shrinking sizes for those devices.
"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.
Researchers said that their work was focused on measurements, limits and scaling which would be important for essentially all transducers.
While those transducers may be developed over the next decade, Feng and his team have already been able to demonstrate the capability of their key components, the atomic layer drumheads or resonators, at the smallest scale yet.
Their work represents the highest reported dynamic range for vibrating transducers of their type. To date, that range had only been attained by much larger transducers operating at much lower frequencies-like the human eardrum, for example.
"What we've done here is to show that some ultimately miniaturised, atomically thin electromechanical drumhead resonators can offer remarkably broad dynamic range, up to ~110dB, at radio frequencies (RF) up to over 120MHz," Feng said. "These dynamic ranges at RF are comparable to the broad dynamic range of human hearing capability in the audio bands."
Key to all sensory systems is the dynamic range, which is the ratio between the signal ceiling over the noise floor and is usually measured in decibels (dB).
Human eardrums normally have dynamic range of about 60 to 100dB in the range of 10Hz to 10kHz, but that quickly decreases outside this frequency range.
The vibrating nanoscale drumheads are made of atomic layers of semiconductor crystals (single-, bi-, tri-, and four-layer MoS2 flakes, with thickness of 0.7, 1.4, 2.1, and 2.8 nanometers), with diameters only about 1 micron.
They are constructed by exfoliating individual atomic layers from the bulk semiconductor crystal and using a combination of nanofabrication and micromanipulation techniques to suspend the atomic layers over micro-cavities pre-defined on a silicon wafer, and then making electrical contacts to the devices.
These atomically thin RF resonators have also excellent frequency "tunability," meaning their tones can be manipulated by stretching the drumhead membranes using electrostatic forces, similar to the sound tuning in much larger musical instruments in an orchestra, Feng said.
The study revealed that these small drumheads only need picoWatt (pW, 10^-12 Watt) up to nanoWatt (nW, 10^-9 Watt) level of RF power to sustain their high frequency oscillations.
"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."
