Development of electromagnetic metamaterials and surface acoustic wave transducers on a single device geometry

Zahertar, Shahrzad (2021) Development of electromagnetic metamaterials and surface acoustic wave transducers on a single device geometry. Doctoral thesis, Northumbria University.

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Abstract

Ageing population and health challenges associated with it shows us the importance of continuous and remote health monitoring using inexpensive, low-power, sustainable, and simple to use Lab-on-Chip (LoC) devices. LoC systems aim to bring in the whole laboratory process onto a small chip. Although crucial effort has been invested into this field, a marketable product is yet difficult to attain. An important reason is that LoC systems are developed via the integration of different devices and even technologies that are tailored for an individual task. A streamlined integration of these on a single platform is challenging, especially considering complicated fabrication processes. There are two fundamental mechanisms that have important roles in development of a LoC device; i.e. sensing and fluid manipulation.

The aim of this thesis is to investigate a new method of bringing biosensing and fluid manipulation capabilities on a single structure that can be integrated in various biosensing platforms. The sensing capability is realised using metamaterial-based electromagnetic split ring resonators (SRR), and the fluid manipulation capability is realised using surface acoustic waves (SAWs). The functionalities are performed on a single structure fabricated on different rigid and flexible substrates. SRR-based sensors have drawn much attention in different fields such as material characterisation, biosensing, strain sensing and remote sensing attributed to their simple design and fabrication, reliability and high quality factor. SRRs are metallic structures that are fabricated on a dielectric substrate and operate at certain resonant frequencies. Their operational frequency depends on their geometry and the effective permittivity of the materials surrounding them. However, these structures are incapable of manipulating fluids. On the other hand, SAW actuators have been extensively studied for their ability in different microfluidic functionalities, namely, streaming, pumping, separation, jetting and nebulisation. SAW actuators consist of Interdigital Transducers (IDTs) that are patterned on a piezoelectric substrate. By applying radio frequency (RF) power to the IDTs travelling surface waves are generated, which is the driver of the microfluidic functions.

In this thesis, a general methodology for the integration of sensing and fluid manipulation capabilities in a single device is described based on four different designs introduced as separate chapters, which can be beneficial in LoC applications. These fabricated devices have been employed as wireless sensors in microwave frequency range and utilised as a SAW actuator by applying power in radio frequency range. In addition, a flexible embroidered SRR is also introduced in this thesis that can be utilised in daily items based on fabrics towards continuous monitoring applications.

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