Electrowetting-on-dielectric (EWOD), in which microdroplets are manipulated using electrical inputs, has drawn a great deal of attraction with applications of digital lab-on-a-chip and hot-spot cooling. In most EWOD actuations, the commonly used powering method is wired transmission, which may not be suitable for isolating and employing EWOD devices in hard-to-reach areas. In this study, we investigate wireless power transmission for EWOD utilizing inductive coupling. Since EWOD is typically operated by a high-input voltage although the current is minimal, wireless EWOD also requires a similarly high voltage at the receiver, unlike conventional inductive coupling. To meet this condition, the resonant inductive coupling method at a high resonant frequency is introduced and investigated. To optimize the transmission efficiency, we study the effects of many parameters, such as the frequency, inductance, and capacitance at the transmitter and receiver, the gap between the transmitter coil and receiver coil, and the droplet size, by measuring the voltage at the receiver and the contact angle of the droplet placed on a wirelessly operated EWOD chip. In addition, by applying amplitude modulation to the resonant inductive coupling, wireless AC-EWOD, which generates droplet oscillations and is a common mode for EWOD droplet handling, is also achieved. Finally, it is successfully demonstrated that a droplet is transported laterally by using an array of electrodes, which is also powered by an amplitude-modulated wireless signal.
Recently, it has been shown that amplitude modulation (AM) in a wireless EWOD (electrowetting on dielectric) via magnetic induction facilitates the transmission of a low frequency message signal and then the oscillation of droplets at a low frequency. This process requires demodulation to recover the message signal from the high-frequency AM signal. As a key contribution, this paper theoretically and experimentally shows that the EWOD-actuated droplet has the inherent functionality of demodulation. That is, the EWOD droplet itself demodulates a supplied AM driving voltage, and as a result the contact angle of the droplet directly follows the message signal without any artificial demodulation circuit. A theoretical explanation of this inherent demodulation property is developed using a time-varying Lippmann-Young (LY) equation. In addition, experimental results are presented to substantiate the inherent demodulation functionality of an EWOD droplet.
Electrowetting-on-dielectric (EWOD) is one of the most versatile methods used to control the wettability of liquids using electrical input. In most applications, EWOD is applied using physical wiring, which may restrict its application to implantable EWOD devices. In order to resolve this issue, we have studied and developed a wirelessly powered EWOD by using planar coils at the receiver that are fabricated out of a printed circuit board (PCB) by means of standard micro photolithography. Unlike conventional, bulky, spool coil type, the planar coil type lends itself to compact design and easy integration with EWOD chips. The present wireless powering principle is based on magnetic induction, which is very efficient when the transmitter and receiver coils are close to each other. The voltage obtained at the receiver is much higher than typically required EWOD voltages (>50 V) using a high transmission frequency (~MHz). The span of the EWOD contact angle is over 40°. In addition, amplitude modulation (AM) is implemented in the present wireless powering setup, followed by demodulation, in order to oscillate droplets at low frequency. This technique ensures smooth and reliable droplet movements. The wirelessly powered EWOD is used to transport a droplet and is mounted in a mini-boat which it powers and propels.
Recently, EWOD (Electrowetting on dielectric) has attracted a great deal of interest with applications of digital lab-on-a-chip in which microfluids are manipulated in a discrete form of droplets using electrical inputs. In most EWOD applications, the commonly used powering method is wired transmission, which may not be suitable for implantable lab-on-a-chip applications. In this paper, we will investigate wireless power transmission for EWOD utilizing the inductive coupling. Unlike the conventional inductive coupling, wireless EWOD requires a high voltage (> 50 V) at the receiver side which is connected to the EWOD chip since EWOD naturally operates under high input voltages. To satisfy this condition, the resonant inductive coupling method at a high resonant frequency is introduced and investigated. To optimize the transmission efficiency, we study the effects of many parameters such as the frequency, the inductance and the capacitance at the transmitter as well as receiver, the gap between the transmitter coil and receiver coil, and so on, by measuring the voltage at the receiver and the contact angle of droplets placed on wirelessly operated EWOD chip. In addition, by introducing amplitude modulation (AM) to the resonant inductive coupling, wireless AC electrowetting which generates droplet oscillations and is one of the commonly used operational modes is also achieved.
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