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.
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