Stein Kuiper

Variable-focus liquid lens for miniature cameras

The meniscus between two immiscible liquids can be used as an optical lens. A change in curvature of this meniscus by electrowetting leads to a change in focal distance. It is demonstrated that two liquids in a tube form a self-centered lens with a high optical quality. The motion of the lens during a focusing action was studied by observation through the transparent tube wall. Finally, a miniature achromatic camera module was designed and constructed based on this adjustable lens, showing that it is excellently suited for use in portable applications.

Experimental Validation of the Invariance of Electrowetting Contact Angle Saturation

Abstract Basic electrowetting theory predicts that a continued increase in applied voltage will allow contact angle modulation to zero degrees. In practice, the effect of contact angle saturation has always been observed to limit the contact angle modulation, often only down to a contact angle of 60 to 70°. The physical origins of contact angle saturation have not yet been explained successfully and unequivocally. At best, scientists have produced multiple disconnected hypotheses (droplet ejection, charge injection, a thermodynamic limit, etc.) that do not satisfactorily hold for the large body of electrowetting experimental results. Herein we experimentally demonstrate that when using DC voltage, electrowetting contact angle saturation is invariant with electric field, contact line profile, interfacial tension, choice of non-polar insulating fluid, and type of polar conductive fluid or ionic content. The selected experiments were performed and designed using conventional electrowetting materials, without bias toward supporting a particular theory. Because the experimental results show such a strong invariance of saturation angle to multiple parameters, electrowetting saturation parallels many of the trends for Taylor cone formation. However, the contact line geometry is distinct from a Taylor cone, suggesting that some other (though related) form of electrohydrodynamic instability might cause saturation. Although this work does not unequivocally prove what causes contact angle saturation, it reveals what factors play a very limited or no role, and how dominant factors causing saturation may change with time of voltage application. This study thereby provides additional direction to the continued pursuit of a universal theory for electrowetting saturation.

Electrowetting without Electrolysis on Self-Healing Dielectrics

An electrowetting system with protection against dielectric breakdown is presented. It comprises an electrolyte and a Parylene-C film deposited on an aluminum electrode. The system demonstrates virtually instantaneous self-healing (within 100 ms) after dielectric breakdown under both DC and certain AC electrowetting conditions. DC current response during electrowetting on intentionally damaged Parylene-C is presented. Also presented is a characterization of DC offset voltages and duty cycle percentages required for electrolysis free AC electrowetting between 10 Hz and 4 kHz.

Variable-focus liquid lens for portable applications

The meniscus between two immiscible liquids can be used as an optical lens. A change in curvature of this meniscus by electrowetting leads to a change in focal distance. We demonstrate that two liquids in a tube form a self-centered tunable lens of high optical quality. Several properties were studied, such as optical performance, electrical characteristics and dynamic behavior. We designed and constructed a miniature camera module based on this tunable lens and show that it is very well suited for use in portable applications.

Zoom camera based on liquid lenses

A 1.7× VGA zoom camera was designed based on two variable-focus liquid lenses and three plastic lenses. The strongly varying curvature of the liquid/liquid interface in the lens makes an achromatic design complicated. Special liquids with a rare combination of refractive index and Abbe number are required to prevent chromatic aberrations for all zoom levels and object positions. A set of acceptable liquids was obtained and used in a prototype that was constructed according to our design. First photos taken with the prototype show a proof of principle.

Variable liquid lenses for electronic products

The design, manufacturing and application of variable liquid lenses are discussed. The interface between the two immiscible liquids that forms the lens can be altered with a voltage. Results are presented of applying this lens in miniature autofocus and zoom cameras, in optical recording and in illumination systems.

Control of an electrowetting-based beam deflector

We experimentally demonstrate the feasibility of a small, low-power beam deflector based on electrowetting. The beam deflector deflects light by refraction at the flat interface (meniscus) between two immiscible and density-matched liquids, namely, a nonpolar oil mixture and an aqueous salt solution. The liquids are contained in a square pyramidal frustum with electrode-covered faces. The electrodes can be separately driven by voltage sources in order to control the contact angle between the meniscus and the frustum faces. By controlling the voltage on all four electrodes, a flat meniscus is obtained that can be tilted independently in two perpendicular directions. We present a capacitance-based feedback driving scheme and demonstrate that it can be used for accurate control of the meniscus shape and tilt. Independent, continuous, and accurate beam steering through an angle of ±6° was achieved on two deflection axes.

Electrowetting-based optics

Electrowetting is electrostatic manipulation of liquids. It can be used to displace and deform volumes of polar liquids. A very promising application area is optics. The surface of a volume of liquid can be used as a tunable lens and displacement of the liquid can change the refraction, diffraction or transmission of light when passing through the liquid. In this paper we describe a selection of various tunable optical components that make use of electrowetting, ranging from refractive and diffractive lenses to diaphragms and displays.

Miniaturized ultrasound scanner by electrowetting

An ultrasound imaging technology based on electrowetting has been developed and integrated in a miniaturized ultrasound scanner. The feasibility of scanning the ultrasound beam of a single-piston transducer in a three-dimensional space by using electrowetting is demonstrated. The technology has a high potential to be embedded in devices where size restrictions do not allow the use of traditional ultrasound phased-array transducers.

Zoom camera based on variable-focus liquid lenses

A zoom camera was constructed based on two adjustable lenses. The strongly varying lens shapes make an achromatic design complicated. Special liquids are required to prevent chromatic aberrations for all zoom levels and object positions