The challenge of miniaturizing devices and systems is also achieving a broader dynamic range of detection for small signals such as sound, vibration, and radio waves.
Atomically thin “drumheads” were developed that are able to receive and transmit signals across a radio frequency range far greater than what the human ear can hear. In addition, the drumhead is tens of trillions of times smaller in volume and 100,000 times thinner than the human eardrum.
The work was focused on measurements, limits, and scaling that would be important for essentially all transducers. The 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, such as the human eardrum, for example. Ultimately, miniaturized, atomically thin electromechanical drumhead resonators can offer broad dynamic range up to ~110 dB, at radio frequencies (RF) up to more than 120 MHz — ranges comparable to the broad dynamic range of human hearing capability in the audio bands.
Dynamic range 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 100 dB in the range of 10 Hz to 10 kHz, and our hearing 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 thicknesses of 0.7, 1.4, 2.1, and 2.8 nanometers with diameters of 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 microcavities predefined on a silicon wafer, and then making electrical contacts to the devices.
The drumheads require only a picoWatt (pW, 10-12 Watt) up to nanoWatt (nW, 10-9 Watt) level of RF power to sustain their high-frequency oscillations.