Don W. Dissanayake

Radio frequency controlled microvalve for biomedical applications

In this paper we propose the use of a RF controlled microvalve for implementation on a PZT substrate for biomedical applications. Such device has a huge range of applications such as parallel mixing of photo-lithographically defined nanolitre volumes, flow control in pneumatically driven microfluidic systems and lab-on-chip applications. The microvalve makes use of direct actuation mechanisms at the microscale level to allow its use in vivo applications. A number of acoustic propagation modes are investigated and their suitability for biomedical applications, in terms of the required displacement, device size and operation frequency. A theoretical model of the Surface Acoustic Wave (SAW) device is presented and its use in micro-valve application was evaluated using ANSYS tools. Furthermore, the wireless aspect of the device is considered through combining the RF antenna with the microvalve simulation by assuming a high carrier frequency with a small peak-to-peak signal. A new microvalve structure which uses a parallel type piezoelectric bimorph actuator was designed and simulated using ANSYS tools. Then, further optimization of the device was carried out to achieve a better coupling between electrical signal and mechanical actuation within the SAW device.

Design and Characterisation of Micro-Diaphragm for Low Power Drug Delivery Applications

Micro-fabricated diaphragms can be used to provide pumping action in microvalve and microfluidic applications. In this paper, a design for a micro-diaphragm that features low power and small area is presented. The diaphragm is actuated using a Surface Acoustic Wave (SAW) device that is interrogated from an RF signal to provide secure actuation operation. The micropump is targeted for in vivo nano-scale drug delivery and similar applications. For low power micropump operation, it is important to design the diaphragm with a higher flexibility while maintaining the stability. Analysis is carried out using ANSYS simulation tools with different design methods and materials. Results achieved from analytical and Finite Element Modeling (FEM) methods are compared and discussed to decide on optimal dimensions for the diaphragm.

Electrostatic Microactuator Design Using Surface Acoustic Wave Devices

An integration of low power operated Surface Acoustic Wave (SAW) devices with the electrostatic microactuators for microfluidic and similar applications is presented in this chapter. Passive, low power, and small area devices can be interrogated wirelessly using SAW devices, which can respond to a uniquely coded signal for a secure and reliable operation. The novel approach relies on converting the interrogating coded signal to surface acoustic wave that is then correlated with an embedded code. A theoretical analysis of how the actuation mechanism operates is carried out and simulation results of the new microactuator are discussed. At the initial analytical stage, for simplicity, a basic SAW delay line structure is used to generate an electrostatic field between output interdigital transducer (IDT) of the SAW device and a thin conductive plate (actuator), which is placed on top of the output IDT. The static and transient displacement analysis of the actuator is carried out using ANSYS simulation tools. A comparison between the static displacements obtained from ANSYS based simulations and Rayleigh-Ritz based analysis is also presented and discussed.

Finite element modelling of surface acoustic wave device based corrugated microdiaphragms

This paper presents modelling and analysis of microdiaphragms that are designed for implantable micropump applications. Microdiaphragms are considered to be a major component of micropumps. A securely operated, electrostatically actuated, fully passive micropump is designed using a novel method, which is based on surface acoustic wave (SAW) devices and wireless transcutaneous radio frequency (RF) communication. The device is capable of extracting the required power from the RF signal itself, like RFID (ID: identification device) tags; hence the need of a battery and active electronics is negated. Moreover, a SAW correlator is used for secure interrogation of the device. As a result, the device responds only to a unique RF signal, which has the same code as was implanted in the SAW correlator. Finite element analysis (FEA) based on code from ANSYS Inc. is carried out to model the microdiaphragm, and a Rayleigh–Ritz method based analytical model is developed to investigate the validity of the FEA results. During the FEA, a three-dimensional model of the diaphragm is developed and various kinds of corrugation profiles are considered for enhancing the device performance. A coupled-field analysis is carried out to model the electrostatics–solid interaction between the corrugated microdiaphragm and the SAW device. In modelling microdiaphragms, selection of appropriate material properties and element types, application of accurate constraints, and selection of suitable mesh parameters are carefully considered.

Corrugated micro-diaphragm analysis for low-powered and wireless Bio-MEMS

Surface acoustic wave (SAW) device based wirelessly operated, batteryless and low-powered microdiaphragm structures have been investigated and presented in this paper. These diaphragms are intended to establish the actuation mechanism for micropumps and similar microfluidic devices. The actuation method of the diaphragm relies on the electrostatic coupling between the diaphragm and the output Inter digital transducer (IDT) of the SAW device. In this paper, the theory governing the SAW device based novel actuation mechanism, is elaborated using the parallel plate approximation in electrostatic actuation. To validate the theoretical model, a finite element model (FEM) is developed using ANSYS simulation tools and presented. Different design methods are considered to enhance the deflection of the diaphragm for a low input voltage. As such, inclusion of corrugations around a flat square-shaped diaphragm and selection of different bio-compatible materials for various sections of the diaphragm are analysed at the simulation level. Deflection of the diaphragm is obtained as a function of the electric potential at the output IDT of the SAW device, and compared with results obtained from published research.

Surface Acoustic Wave Device Based Wireless Passive Microvalve for Microfluidic Applications

There are vast advantages of using a SAW device based micro-valve in Micro Electro Mechanical Systems (MEMS) and Nano Electro Mechanical Systems (NEMS) such as secure, reliable and low power operation, small size, simplicity in construction and cost effectiveness. In this paper, a Surface Acoustic Wave (SAW) based microvalve that generates micro actuations for micro-fluidic and similar applications is presented. The microvalve is batteryless and can be actuated wirelessly. The security of the device is enhanced by using a coded SAW correlator that is integrated as part of the microvalve. A theoretical analysis of how the actuation mechanism operates is carried out and simulation results of the new micro-valve structure are discussed. ANSYS simulation tool is used to design and simulate the micro-valve structure. Characteristics of the microvalve actuator in terms of displacement for different operating conditions are also discussed.

Modelling and simulation of wirelessly and securely interrogated low-powered actuators for bio-MEMS

This paper presents modelling and analysis of microactuators that are designed for implantable bio-MEMS applications. Microactuators are considered to be a major component of microvalves and micropumps. A novel interrogation methodology is implemented, which is based on surface acoustic wave (SAW) devices and wireless transcutaneous RF communication. This unique combination of technologies results in a novel microactuator that can be remotely and securely interrogated by an RF system, with the advantage of no power requirements at the actuator site. ANSYS based finite element analysis (FEA) is performed to model the microactuator, and a Rayleigh‐Ritz method based analytical model is developed to investigate the validity of FEA results. During FEA, a 3D model of the microactuator is developed, and a coupled-field analysis is carried out to model the electrostatic‐solid interaction between the microactuator and the SAW device. Consequently, detailed 3D modelling and transient results are presented, and the low-powered microdisplacements at low frequencies are clearly demonstrated. (Some figures in this article are in colour only in the electronic version)

Wireless Interrogation of a Micropump and Analysis of Corrugated Micro-diaphragms

In this chapter, Surface Acoustic Wave (SAW) device based wirelessly operated, batteryless and low-powered microdiaphragm structure is investigated. These diaphragms are intended to establish the actuation mechanism for micropumps and similar flow control devices. The actuation method of the diaphragm relies on the electrostatic coupling between the diaphragm and the output Inter Digital Transducer (IDT) of the SAW device. The theory governing the SAW device based novel actuation mechanism is elaborated. A Finite Element Model (FEM) is developed and analysed using ANSYS tools. Different design methods are considered to enhance the deflection of the diaphragm for a low control voltage. As such, inclusion of different types of corrugations, and selection of different bio-compatible materials for various sections of the diaphragm are analysed. Deflection of the diaphragm is obtained as a function of the electric potential at the output IDT of the SAW device and compared with results obtained from published research. Corrugation types such as pure sinusoidal, arc sinusoidal and toroidal types are included in the analysis. Effective meshing requirements that are specific to the presented model are considered and a mesh is developed to achieve converged results. Results show that the use of corrugations around a square-shaped diaphragm with carefully chosen materials results in better performance than that of a flat diaphragm.

Finite element analysis of wirelessly interrogated implantable bio-MEMS

Wirelessly interrogated bio-MEMS devices are becoming more popular due to many challenges, such as improving the diagnosis, monitoring, and patient wellbeing. The authors present here a passive, low power and small area device, which can be interrogated wirelessly using a uniquely coded signal for a secure and reliable operation. The proposed new approach relies on converting the interrogating coded signal to surface acoustic wave that is then correlated with an embedded code. The suggested method is implemented to operate a micropump, which consist of a specially designed corrugated microdiaphragm to modulate the fluid flow in microchannels. Finite Element Analysis of the micropump operation is presented and a performance was analysed. Design parameters of the diaphragm design were finetuned for optimal performance and different polymer based materials were used in various parts of the micropump to allow for better flexibility and high reliability.