An overview of nanoacoustics in nanotechnology


Nanoacoustics has advanced rapidly with continuous and considerable growth in capabilities and refinement of techniques. This article discusses nanoacoustics, its applications including nanoacoustic sensing, nanoacoustic manipulation, and nanoacoustic characterization, and its future prospects.

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What is acoustics?

The term “Acoustics” is derived from the Greek word “akoustos”, which means “heard”. Acoustics is the science that deals with the production, transmission, control and effects of sound. Acoustics covers a range of topics including noise control, ultrasound in the medical field, thermoacoustic refrigeration, bioacoustics, SONAR for underwater navigation, nanoacoustics, seismology and electroacoustic communication.

Ultrasound has sound frequencies above the hearing range, usually 20 kHz. Usually, ultrasound is generated by transducers that use piezoelectric material to convert electrical energy into acoustic energy using the inverse piezoelectric effect.

Context of nanoacoustics

With advances in nanoscience in the 1980s, nanotechnology began to attract attention in various sectors of the research community. Advances in nanomaterials and nanodevices for ultrasound investigations have revolutionized conventional methods of using ultrasound.

In recent years, the introduction of various nanoscale materials to support the identification and treatment of different diseases has gained increasing interest, becoming an important area of ​​medical ultrasound. Nowadays, nanotechnology relates to various ultrasonic instruments capable of monitoring and controlling nanoparticles.

Nanoacoustic characterization

Scanning Acoustic Microscopy (SAM):

High frequency sound waves have short wavelengths and are used to develop acoustic microscopes. These microscopes have a resolution similar to optical microscopes. Scientists have used this idea of ​​nanoacoustics in microscopy to develop scanning acoustic microscopes (SAM).

Earlier microscopes that used SAM techniques provided resolution down to 10 μm. Later, the evolved version could work with wavelengths up to 260 nanometers. This technique is primarily used for biology, imaging internal structures in materials, and characterizing optically opaque samples.

Atomic Force Acoustic Microscopy:

The resolution of SAM is limited. Therefore, to characterize material properties at submicrometer resolution, another technique, Atomic Force Acoustic Microscopy or AFAM, is used. This technique is used to characterize and map mechanical properties down to the nanometric scale. For example, according to recent studies, this technique has been used to accurately measure the dynamic Young’s modulus of materials such as nanocrystalline ferrites with nanoscale resolution. The resolution of this technique is up to 10 nanometers.

Nanoacoustic manipulation

With scientific advancements in nanotechnology such as nanofabrication, biomedicine, and materials engineering, the manipulation of nanoparticles, nanodroplets, and nanocells is essential. These manipulation functions include orientation, trapping, sorting, concentration and assembly of nanoobjects.

Researchers have created many alternative tactics to accomplish these manipulation functions, categorized into electrical, optical, microfluidic, magnetic, AFM, mechanical, and acoustic methods.

Each approach has its own set of disadvantages, but when compared, acoustics-based systems have several advantages over other techniques. For example, acoustics-based techniques can provide various manipulation functions. These methods also do not require specific manipulated sample properties and can be performed using simple device structures.

Nanoacoustic detection

Surface Acoustic Wave (SAW) devices respond to mechanical, electrical, chemical and other disturbance signals. The reactive properties of these devices also allow them to be used as SAW sensors.

These nanoacoustic sensors are advantageous due to their low cost, high sensitivity, superior response time and compact size. In addition, SAW-based nanoacoustic sensors exhibit exceptional stability, selectivity, and linearity due to appropriate design of IDT sensing surfaces and piezoelectric substrates.

In addition to SAW-based sensors, various nanoacoustic sensors are also under development. For example, scientists have developed a flexible pressure sensor made by placing gold nanowires between 2 sheets of PMDS. This nanoacoustic sensor showed fast response, high stability, high sensitivity and low power consumption. These properties and the mechanical flexibility allowed this sensor to observe heart rate in real time as well as detect small vibrational forces.

Future prospects

Nanoacoustic manipulation has shown great promise in a variety of applications, including nanofabrication and biomedicine. However, many questions about the underlying principles of SAW generation inside microchannels remain unanswered.

Moreover, advanced research is needed to improve our understanding of these phenomena. Future prospects of nanoacoustics for practical application include the integration of high precision and controllability devices.

Functionalization of SAW devices for improved selectivity should be an important area of ​​research due to the characteristic advantages of SAW-based detection platforms. SAW-based sensing research should continue to search for new sensing materials to improve performance and expand the range of applications.

Additionally, there is a need to improve current SAW-based nanoacoustic sensors, as one of the limitations is that they require expensive electronic sensing systems, such as network analyzers, to effectively record device behaviors. Therefore, small portable data collection devices that can be packaged into highly integrated and cost-effective systems will be needed in the future.

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References and further reading

Kelf, T. Introduction to Nano Acoustics. [online] Timkelf.com. Available at: http://www.timkelf.com/research/ResearchNanoAcoustics.html

Peng, C., Chen, M., Spicer, JB and Jiang, X. (2021). Nanoscale Acoustics (Nanoacoustics): A Comprehensive Literature Review. Part I: Selected materials, devices and applications. Sensors and Actuators A: Physics, 332, 112719.https://www.sciencedirect.com/science/article/pii/S0924424721001825?via%3Dihub

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