Diagnostics & Control
Research Centre
Smart Materials (Lenses)
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Smart Materials
Smart Lenses
Optical lenses have existed since the time of ancient Greece and Egypt, yet have remained relatively unchanged since that time. Although the materials used to built lenses has been improved, the same key problem still exists with all traditional lenses – namely, that they possess one fixed focal length. In order to focus with these lenses, the distances between the lens and the object and image planes must be adjusted. Although recent advances in engineering have developed lenses with a number of difference focal lengths (such as graded-index and progressive addition), these do not represent a truly variable focal length lens.
Our own interest in these materials stems from biomedical engineering. The World Health Organisation has estimated that over 35 million people are in need of low vision care, with this number expected to rise. Many of these people will require multiple pairs of lenses, which is both wasteful and expensive. The Diagnostics and Control Research Centre (DCRC) is working on the development of a new type of lens, which can dynamically alter its focal length in response to an electrical signal. It is hoped that in the future this lens can be used to treat those people suffering from vision problems. There are also many other uses for a variable focal length lens, including aerospace, communications and military applications.
Variable Focal Length Spectacle Lenses Employing “Smart” Technology
The main aim of the present work is to develop piezoelectric transparent lenses made from functional polymers that could be used to produce variable focal length lenses. This research is a collaborative project between the Auckland University of Technology’s Diagnostics and Control Research Centre (School of Engineering) and the University of Auckland’s Department of Optometry (School of Medicine).
If successful, “smart” lenses will create a revolution in the manufacturing industry and influence the entire range of optical instruments, including spectacles, microscopes, telescopes and binoculars. The Diagnostics and Control Research Centre’s research in this field can be divided into two main areas:
Optimisation of the Optical Properties of Piezoelectric Materials for Optical Applications
This research focuses on improving the transparency and rigidity of polyurethane and other prospective smart polymers. Initial investigations have been conducted that involved an extensive experimental program including complicated heating, drying and stacking processes. These tests have shown the potential of these materials to function as smart lenses. A full understanding of the mechanical, piezoelectric and electrical characteristics is still outstanding, but is essential for developing the final shape of the lens and the development of an electronic circuit to drive the material. The latter requires state of the art technology and requires further development and improvement.
Current research is investigating the optical, piezoelectric and physical properties of these smart polymers for use in smart lenses. Several testing procedures including X- Ray diffraction, UV, visible Spectrophotometers and Infrared Spectroscopy are being utilized to investigate the characteristics of these materials. An appropriate electrical circuit is also being developed to suite the present application.
Optimisation and Modelling of Optical Properties of EAPs
The feasibility of using electroactive polymer (EAP) hydrogels as materials in a changeable focal length lens has also been investigated by our group. Gel polymers are inexpensive, easy to manufacture, transparent and have good voltage-to-strain conversion and this makes them very attractive for use in optical applications. Previous work has focussed on identifying and controlling the various parameters such as crosslinker concentration and degree of neutralisation, which affect the various polymer gel properties. These properties include the optical transparency, structural rigidity and electroactive response. Thus far, an optical transmittance of greater than 70% has been achieved for light in the range of 400-700nm.
The transmission of an electrical signal to the gel has also been investigated in order to determine the ideal shape, location and material for the electrodes used in smart lens applications. Many different materials were tested with mixed results. The structural and optical properties of the polymer gels were also tested using a variety of experiments, including various swelling experiments as well as some non-traditional experiments. The results were positive, although some anomalous results were obtained. This behaviour is attributed to limitations in the currently available body of knowledge on gel swelling processes.
Recently, research has also been conducted on the development of a finite-element model (FEM) to describe the gel swelling processes. It is hoped that this research can be used to aid in the design of future lenses and actuators built with these materials. Specifically, this work aimed to:
- Improved comprehension understanding of material formulation of gel swelling models
- Qualitative adaptation of discrete models to realistic polymer gel materials.
- Develop the appropriate algorithm to implement the computer simulation of the model.
- Establish experimental design to produce a polymer hydrogel to verify the model developed.
- Determine the suitability of the polymer hydrogel for use a material for smart system application.
- Investigate validity of the proposed model by experimentation.