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.
The capability to wirelessly control fluid flow through a microvalve can emerge as an attractive technology enabling various biomedical applications such as remote drug delivery and in vitro diagnostics. Contactless powering of such a microvalve is best addressed by near-field inductive coupling due to its close proximity to the external interrogator. In this paper, we propose the use of the same technique for secure remote interrogation and powering of a human implantable, surface acoustic wave (SAW) correlation-based, passive microvalve. This is carried out by interrogating the microvalve with a Barker sequence-encoded BPSK signal. A numerical and experimental analysis of the biotelemetry link for the microvalve was undertaken in the vicinity of numerical and physical human body phantoms, respectively. To accurately account for the path losses and to address the design optimization, the receiver coil/antenna was solved simultaneously with the transmitter coil/antenna in the presence of a human body simulant using three-dimensional, high frequency electromagnetic FEM modelling. The received relative signal strength was numerically and experimentally derived for a miniature (6 mm × 6 mm × 0.5 mm), square spiral antenna/coil when interrogated by a handheld 8 cm × 5 cm × 0.2 cm square spiral antenna/coil in the near-field. Finally, the experimental results agreed well with the FEM analysis predictions and hence ascertained the applicability of the developed system for secure interrogation and remote powering of the newly proposed microvalve.
A wireless microvalve would have a wide range of applications, including biomedical applications such as fertility control and nano-litre drug delivery. Arguably the most important aspect for such a device is a secure method to actuate the valve, such that it is not actuated through the spectrum of electromagnetic radiation already present in the surrounding environment. Additionally, many of the possible applications are sensitive to electromagnetic (EM) radiation so the device should be designed to only require the minimum amount of EM input to actuate the valve. To overcome this problem, we propose the use of a coded interdigital transducer (IDT) to respond only to a coded signal. For the wireless microvalve to be useful in biomedical applications, the IDT's response to a specifically coded RF signal must be much greater than its response to another coded RF signal, even if the two codes are very similar, i.e. improve the signal ratio of the device. In this research we demonstrate a number of code sequences that have a correlation function such that the peak response is unique and can be used to provide a high signal-to-noise ratio (SNR) surface acoustic wave. That results in a unique activation of the device when the interrogating RF signal code sequence matches the stored code sequence in the device. Also we will investigate the trade-off between the needed code length to ensure secure operation and the area constrain of the device within the context of biomedical application. For this purpose, the IDT is modelled as a pulse compression filter, which correlates the input signal with a stored replica.Keywords: microvalve, SAW, IDT, biomedical applications, coded actuators INTORDUCTIONA wireless, battery less microvalve uses no direct electrical power but makes use of the interrogating signal to provide the needed actuation. Such a device can be placed in an inaccessible location thus opening up new host of applications such as flow regulation, on/off switching and sealing of liquids, gases or vacuums [1][2][3]. For this purpose we utilise an IDT configuration with the SAW device. The IDT transforms this incoming RF signal from the antenna to a SAW and vice versa. Wireless interrogation of the device is possible by connecting the IDT to an antenna. The SAW generated by the IDT propagates along the piezoelectric substrate. The principles of SAW and the SAW generation mechanism in the microvalve are discussed in a previous publication [3]. The high energy density and small size make SAW devices attractive for actuator applications. But on the other hand the device requires a high input power level to drive it, hence it is important to have an efficient antenna design and ensure that the device will only trigger to a uniquely coded RF signal. Both of these objectives can be achieved by modelling the IDT as a pulse compression filter thus combining the narrowband, high Q-factor operation of a band pass filter with a coded reception scheme. The coding gain further improves the Q-factor [4]. Since the wirel...
We present a normally closed, remotely actuated, secure coded, electrostatically driven active microvalve using passive components. This is carried out by utilizing the complex signal processing capabilities of two identical 5 × 2-bit Barker sequence encoded acoustic wave correlators. An electrostatically driven microchannel, comprising two conducting diaphragms as the top and bottom walls, is placed in between the compressor interdigital transducers of the two correlators. Secure interrogability of the microvalve is demonstrated by finite element modelling of the complete structure and the quantitative deduction of the code dependent microchannel actuation. Furthermore, the influence of the excited acoustic modes of the correlator on the microchannel deflection is investigated to optimize the microvalve design.
Numerical simulations of SAW correlators so far are limited to delta function and equivalent circuit models. These models are not accurate as they do not replicate the actual behaviour of the device. Manufacturing a correlator to specifically realise a different configuration is both expensive and time consuming. With the continuous improvement in computing capacity, switching to finite element modelling would be more appropriate. In this paper a novel way of modelling a SAW correlator using finite element analysis is presented. This modelling approach allows the consideration of different code implementation and device structures. This is demonstrated through simulation results for a 5×2-bit Barker sequence encoded SAW correlator. These results show the effect of both bulk and leaky modes on the device performance at various operating frequencies. Moreover, the ways in which the gain of the correlator can be optimised though variation of design parameters will also be outlined.
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