surface acoustic wave based wireless mems actuators

Surface Acoustic Wave based Wireless MEMS Actuators for

Biomedical Applicationsby

Sukanta BhattacharyyaRegistration # 1651210007

Tuesday, April 11, 2023Surface Acoustic Wave based wireless MEMS actuator 2

Agenda

IntroductionSurface Acoustic Wave (SAW) sensorDevice DesignSAW sensor operationSAW based wireless microactuatorMaterial selectionFabrication process flowOperationAdvantage and disadvantageApplicationsConclusionReferences


Introduction

Micro-Electro-Mechanical Systems (MEMS) technology has made it possible to fabricate small size, and high performance implantable devices to meet critical medical and biological needs such as in–vivo drug delivery, Lab–on–a–Chip (LoC), surface acoustic wave devices, polymerase chain reaction (PCR) etc.Actuators are one of the important components in Bio-MEMS, especially for fluid manipulationSurface Acoustic Wave (SAW) devices are used to develop micromachines such as ultrasonic micromotors and fluid transfer methodologies such as flexural micropumps


Surface Acoustic Wave (SAW) sensor

Surface acoustic wave sensor is a class of MEMS device which is based on the modulation of surface acoustic waves to sense a physical phenomenon.


Device Design

The basic surface acoustic wave device consists of a piezoelectric substrate, an input interdigitated transducer (IDT) on one side of the surface of the substrate, and a second, output interdigitated transducer on the other side of the substrate. The space between the IDTs, across which the surface acoustic wave will propagate, is known as the delay-line.


Surface Acoustic Wave (SAW) sensor

Fig 1: Surface Acoustic Wave sensor


SAW sensor operation

SAW technology is based on the piezoelectric effect.

Fig 2: Surface Acoustic Wave sensor operation


SAW sensor operation contd..

Input Interdigitated Transducer (IDT) transduces electric signal to acoustic waves when the two ends of IDT are subjected to sinusoidal signal.Alternating polarity(+-) develops between the fingers of IDT resulting in generation of electric field.Direction of electric field changes alternatively between the adjacent set of fingers creating alternate regions of tensile strain and compressive strain (mechanical vibrations) thus producing mechanical waves.Waves produced at the surface of the piezoelectric substrate known as surface acoustic waves.


SAW sensor operation contd..

Acoustic waves propagate through the region of delay line between the two IDTs.At the output end the propagated waves are picked up by the output IDT.Waves are converted back to electric signal by piezoelectric effect which is then measured and calibrated.


SAW based wireless microactuator

Fig 3: SAW based wireless microactuator


Material selection

The SAW based microactuator is similar to the normal SAW sensor only differing in the actuator part.SAW substrate: The SAW substrate is generally made of quartz. Lithium Niobate (LiNbO3) is also used as it is best suited for Rayleigh wave propagation.IDT: Made of highly conductive low cost materials such as copper (Cu), aluminum (Al), gold (Au), tungsten (W), and titanium (Ti).


Material selection contd..

Microactuator: A thin conductive plate (conductive material) is placed over the output IDT with a small air gap in between that acts as the actuator. Also made of materials such as Silicon (Si) or Silicon Nitride (Si3N4) and the bottom surface of the microactuator can becoated with a thin conductive material such as Gold, Platinum or Aluminium.Input IDT is connected to a micro-antenna for wireless interrogation.


Fabrication Process flow


Operation

Working principle is similar to that of normal SAW sensor. Only difference is that the wireless SAW uses the RF waves as the exciting source for the generation of Rayleigh waves at the input IDT that propagate in the forward direction towards the output IDT.RF is an electromagnetic wave having a frequency between 3 kHz to 300 GHzThe RF signal is fed to the SAW device through the microstrip antenna


Rayleigh waves are a type of surface acoustic wave that travel on solids. They can be produced in materials in many ways, such as by a localized impact or by piezoelectric transduction.Rayleigh waves include both longitudinal and transverse motions that decrease exponentially in amplitude as distance from the surface increases.

Fig 4: Ray Leigh waves


Actuation mechanism: electrostatic actuationA thin conductive plate is placed on top of the output IDT, which is separated by an air–gap. The conductive plate does not alter the mechanical boundary conditions of the SAW substrate, but causes the surface to be equipotential and the propagating electric potential to be zero at the surface of the conductive plate. As a result, an electrostatic force is generated between the conductive plate and the output IDT in the SAW device causing micro deformations or microactuation in the conductive plate


Advantages

• High biocompatibility• Reliable • Low power operation• Small size• Simplicity fabrication• Cost effectiveness• Fast fluid actuation


Disadvantage

One disadvantage of SAW is that Rayleigh waves are surface-normal waves, making them poorly suited for liquid sensing. When a SAW sensor is contacted by a liquid, the resulting compressional waves cause an excessive attenuation of the surface wave.


Applications

Widely used in micro fluidics for studying the manipulation of fluids.Also used to develop micromachines such as ultrasonic micromotors and fluid transfer methodologies such as flexural micropumps


Conclusion

A brief introduction about the SAW sensor is highlighted at the beginning stating the device layout and working principle which is followed by a detailed explanation about the wireless based SAW microactuator. We talked about the fabrication process that is involved in the making of such a device and later we focused on some merits and demerits of the SAW based microactuator.


References

1. Surface Acoustic Wave Based Wireless MEMS Actuators for Biomedical Applications Don W. Dissanayake, Said Al Sarawi and Derek Abbott, The School of Electrical and Electronic Engineering, The University of Adelaide Australia. SA 5005

2. A Fabrication Study of a Surface Acoustic Wave Device for Magnetic Field Detection by Matthew L. Chin

3. www.google.com4. www.wikipedia.com5. Google images

http://www.google.com/

http://www.wikipedia.com/


THANK YOU

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