Transparent Electroactive Ceramic for VR Headsets
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Solution Overview
Problem
Existing virtual reality and augmented reality eyewear devices face challenges with optical quality due to light scattering from electroactive ceramic materials, particularly due to variations in refractive index, porosity, domain walls, and grain boundaries, leading to degraded optical performance.
Innovation Solution
The development of an electroactive ceramic layer with a small domain and grain size, sandwiched between conductive electrodes, which is capacitively actuated to deform and improve optical performance, maintaining high transmissivity and clarity even under applied electric fields, by using materials like lead titanate and lead zirconate titanate with specific dopants and processing techniques to achieve a dense, transparent, and stable optical element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electroactive ceramic materials are used in optical assemblies, then actuation capability is achieved, but light scattering occurs due to refractive index variation, porosity, domain walls, and grain boundaries, degrading optical quality
Solution Approach 1:
The patent changes the microstructural parameters of the electroactive ceramic by reducing grain size to sub-micron scale (less than 10 micrometers, preferably less than 1 micrometer) and controlling domain size. This parameter change reduces the scattering cross-section and minimizes optical degradation while preserving actuation functionality
Solution Approach 2:
The patent uses composite structures by combining electroactive ceramic particles or grains within a matrix material. This composite approach allows the ceramic to provide actuation while the overall structure maintains optical transparency by distributing scattering centers and reducing their individual impact
2Length of moving object
If thin layers of electroactive piezoceramics are used, then intrinsic transparency is achieved, but variation in refractive index between materials and adjacent layers causes light scattering
Solution Approach 1:
The patent applies local quality by ensuring that the electroactive ceramic layer has uniform microstructural properties (grain size, domain size, density) throughout its thickness. This uniformity minimizes local variations in refractive index and reduces light scattering at interfaces with adjacent layers
Solution Approach 2:
The patent optimizes the thickness parameter of the electroactive ceramic layer to balance transparency and actuation effectiveness. By controlling thickness along with grain size and density, the patent minimizes interface-related scattering while maintaining sufficient actuation capability
3Reliability
If ferroelectric materials are used, then spontaneous polarization and domain formation occur, but domain walls and birefringent boundaries scatter light
Solution Approach 1:
The patent changes the domain size parameter by applying specific electric field treatments and controlling processing conditions to reduce domain size. Smaller domains mean fewer and less extensive domain walls, reducing light scattering while maintaining the necessary spontaneous polarization for actuation
Solution Approach 2:
The patent applies preliminary poling treatments during manufacturing to establish a stable domain configuration before the device is put into service. This preliminary action reduces the formation of random domain walls that would scatter light, while preserving the material's ability to respond to applied fields
4Ease of manufacture
If conventional electroactive ceramic processing is used, then material formation is achieved, but porosity and large grain boundaries cause optical scattering
Solution Approach 1:
The patent changes the processing parameters including sintering temperature, time, and atmosphere to achieve high density with minimal porosity. It also controls cooling rates and applies post-processing treatments to achieve fine, uniform grain structures that reduce scattering while maintaining manufacturability
Solution Approach 2:
The patent incorporates sintering aids and dopants as composite components during processing. These additives facilitate densification at lower temperatures, reduce grain boundary formation, and eliminate porosity, thereby improving optical quality without significantly complicating the manufacturing process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in an optically transparent and stable electroactive ceramic layer with minimal change in transmissivity, haze, and clarity when exposed to electric fields, enhancing the optical quality and performance of virtual and augmented reality devices.
Implementation Method 1
Electroactive materials, including piezoelectric and electrostrictive ceramic materials, can change their shape under the influence of an electric field
Implementation Method 2
leverage one or more characteristics of electroactive materials, including the piezoelectric effect to generate a lateral deformation (e.g., lateral expansion or contraction) as a response to compression between conductive electrodes
Data Source
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AI summary
An electroactive ceramic, which may be incorporated into a transparent optical element, has an average grain size of less than 200 nm, a relative density of at least 99%, and a transmittance of at least 50% within the visible spectrum, while maintaining a d33 value of at least 20 pC/N. Optical properties of a layer of the electroactive ceramic, including transmittance, haze, and clarity, may be substantially unchanged during actuation of the optical element by voltage application.