Rectangular split-ring resonators with single-split and two-splits under different excitations at microwave frequencies

In this work, transmission characteristics of rectangular split-ring resonators with single-split and two-splits are analyzed at microwave frequencies. The resonators are coupled with monopole antennas for excitation. The scattering parameters of the devices are investigated under different polarizations of E and H fields. The magnetic resonances induced by E and H fields are identified and the differences in the behavior of the resonators due to orientations of the fields are explained based on simulation and experimental results. The addition of the second split of the device is investigated considering different configurations of the excitation vectors. It is demonstrated that the single-split and the two-splits resonators exhibit identical transmission characteristics for a certain excitation configuration as verified with simulations and experiments. The presented resonators can effectively function as frequency selective media for varying excitation conditions

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

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

Embroidered Rectangular Split-Ring Resonators for the Characterization of Dielectric Materials

In this paper, we report an embroidered rectangular split-ring resonator (SRR) operating at S band for material characterization based on the differences in dielectric parameters. We designed, fabricated and characterized SRR sensors on a conventional fabric that can be conformally attached over the surface of samples under investigation. The structures are made of conductive threads and can be embroidered on any dielectric fabric at low cost using conventional embroidery methods. We have demonstrated material characterization capability of the sensors using a specific design with a length of 60 mm and a width of 30 mm. We wrapped the sensors on low-density polyethylene (LDPE) bottles filled with deionized (DI) water and common solvents (ethanol, methanol, isopropanol and acetone) in our experiments. We measured the nominal resonant frequency of a specific sensor wrapped around an empty bottle as 2.07 GHz. The shifts in resonant frequencies when the bottle was filled with the solvents follow the dielectric constants of the solvents

Integrated Sensing and Actuation Capabilities of Flexible Surface Acoustic Wave Devices with Metallic and Polymer Layers

Flexible and bendable devices have become the key elements in the development of next-generation point-of-care systems and wearable technologies. In this paper, we report flexible surface acoustic wave (SAW) devices that are composed of a multilayer substrate; SAW devices are basically made of interdigital transducers (IDTs) that are patterned on a piezoelectric layer. In our fabricated devices, thin film of zinc oxide (ZnO), as the piezoelectric layer, is deposited on substrates made of trilayer of thin metal films (Nickel/Copper/Nickel) on top of a polyethylene terephthalate (PET) layer. We have characterized the devices in radio frequencies, and we have measured the response of the device to the temperature and the Ultraviolet (UV) light. Also, we have tested the actuation capability of our fabricated devices. We have successfully demonstrated that our fabricated devices can be employed as an integrated platform for sensing and actuation purposes using a single structure

An Ultra-compact Metasurface and Specklemeter-Based Chromatic Confocal Sensor

The development of ultracompact lightweight optical instrumentation that can be used on-machine and to carry out in-process measurements is vital in realizing improved manufacturing processes, increasing the quality of parts being made while saving time and energy by reducing scrappage rates. Only incremental progress is being made in developing suitable instrumentation based on conventional components, such as traditional refractive elements, as fundamental limits in terms of size and weight are already reached. Here, we demonstrate a chromatic confocal sensor that utilizes the natural chromatic aberration found with a basic hyperbolic metalens to realize an ultracompact and simple probe. Furthermore, we demonstrate how this can be combined with a compact specklemeter as the detection element, thus realizing the whole sensing system in a compact manner. Even with the proof-of-principle instrument in its preliminary and unoptimized state, we achieve the successful recovery of the location of a scatterer, as it is scanned over a 227 μm range, with a standard deviation of error in the position of 1.37 μm. Sensors of this form can be deployed in areas where traditional instrumentation would typically impede the manufacturing processes, increasing the number of processes that can have metrology applied directly and providing real-time feedback to improve manufacturing outcomes.</p

Flexible Platform of Acoustofluidics and Metamaterials with Decoupled Resonant Frequencies

The key challenge for a lab-on-chip (LOC) device is the seamless integration of key elements of biosensing and actuation (e.g., biosampling or microfluidics), which are conventionally realised using different technologies. In this paper, we report a convenient and efficient LOC platform fabricated using an electrode patterned flexible printed circuit board (FPCB) pressed onto a piezoelectric film coated substrate, which can implement multiple functions of both acoustofluidics using surface acoustic waves (SAWs) and sensing functions using electromagnetic metamaterials, based on the same electrode on the FPCB. We explored the actuation capability of the integrated structure by pumping a sessile droplet using SAWs in the radio frequency range. We then investigated the hybrid sensing capability (including both physical and chemical ones) of the structure employing the concept of electromagnetic split-ring resonators (SRRs) in the microwave frequency range. The originality of this sensing work is based on the premise that the proposed structure contains three completely decoupled resonant frequencies for sensing applications and each resonance has been used as a separate physical or a chemical sensor. This feature compliments the acoustofluidic capability and is well-aligned with the goals set for a successful LOC device

A Flexible PVDF-based Platform Combining Acoustofluidics and Electromagnetic Metamaterials

Acoustofluidic devices have been demonstrated effectively for liquid manipulation functionalities. Likewise, electromagnetic metamaterials have been employed as highly sensitive and wireless sensors. In this work, we introduced a new design combining the concepts of acoustofluidics and electromagnetic metamaterials on a single device realised on a flexible PVDF substrate. We characterise the operation of the device at acoustic and microwave frequencies. The device can be used in wearable biosensors with integrated liquid sampling and continuous wireless sensing capabilities

Integrated sensing and acoustofluidic functions for flexible thin film acoustic wave devices based on metallic and polymer multilayers

Surface acoustic wave (SAW) devices are generally fabricated on rigid substrates that support the propagation of waves efficiently. Although very challenging, the realisation of SAW devices on bendable and flexible substrates can lead to new generation SAW devices for wearable technologies. In this paper, we report flexible acoustic wave devices based on ZnO thin films coated on various substrates consisting of thin layers of metal (e.g., Ni/Cu/Ni) and/or polymer (e.g., polyethylene terephthalate, PET). We comparatively characterise the fabricated SAW devices and demonstrate their sensing applications for temperature and ultraviolet (UV) light. We also investigate their acoustofluidic capabilities on different substrates. Our results show that the SAW devices fabricated on a polymer layer (e.g. ZnO/PET, ZnO/Ni/Cu/Ni/PET) show enhanced temperature responsivity, and the devices with larger wavelengths are more sensitive to UV exposure. For actuation purposes, the devices fabricated on ZnO/Ni/Cu/Ni layer have the best performance for acoustofluidics, whereas insignificant acoustofluidic effects are observed with the devices fabricated on ZnO/PET layers. We propose that the addition of a metallic layer of Ni/Cu/Ni between ZnO and polymer layers facilitates the actuation capability for the acoustofluidic applications while keeping temperature and UV sensing capabilities, thus enhancing the integration of sensing and acoustofluidic functions

Flexible and integrated sensing platform of acoustic waves and metamaterials based on polyimide coated woven carbon fibers

Versatile, in situ sensing and continuous monitoring capabilities are critically needed but challenging for components made of solid woven carbon fibers in aerospace, electronics and medical applications. In this work, we proposed a unique concept of integrated sensing technology on woven carbon fibers through integration of thin film surface acoustic wave (SAW) technology and electromagnetic metamaterials, with capabilities of non-invasive, in-situ and continuous monitoring of environmental parameters and biomolecules wirelessly. Firstly, we fabricated composite materials using a three-layer composite design, in which the woven carbon fiber cloth was firstly coated with a polyimide (PI) layer followed by a layer of ZnO film. Integrated SAW and metamaterials devices were then fabricated on this composite structure. Temperature of the functional area of the device can be controlled precisely using the SAW devices, which can provide a proper incubation environment for biosampling processes. As a demonstration for an ultraviolet light sensor, the SAW device could achieve a good sensitivity of 56.86 ppm/(mW∙cm-2). On the same integrated platform, the electromagnetic resonator based on the meta-materials has been demonstrated to work as a glucose concentration monitor with a sensitivity of 0.34 MHz/(mg/dL)

Embroidered rectangular split-ring resonators for material characterisation

In this paper, we report an embroidered rectangular split-ring resonator (SRR) operating at S band for sensing applications. We designed, fabricated and characterized the SRR sensor on a fabric that can conformally cover the surface of samples under investigation. The structure can be embroidered on any dielectric fabric at low cost using conventional embroidery methods. In addition, the method is suitable for the fabrication of large-scale arrays to cover large surfaces. We have demonstrated material characterization capability of the sensors using a specific design with a length of 60 mm and a width of 30 mm. We wrapped the sensors on low-density polyethylene (LDPE) bottles filled with deionized (DI) water and ethanol in our experiments and measured their resonant frequencies using a vector network analyzer (VNA). We measured the nominal resonant frequency of a specific sensor wrapped around an empty bottle as 2.06 GHz with a quality factor of 411. The shifts in resonant frequencies when the bottle was filled with ethanol and DI water are 42 MHz and 66 MHz, respectively