Conformal coating is a thin film used for protecting printed circuit boards (PCBs) from harsh environmental conditions, which reduces the failure rate of PCBs. The thickness of conformal coating is one of the key factors determining the protection efficacy on PCB. Therefore, the thickness measurement is highly desired to qualify the conformal coating. In this study, we propose to employ high-resolution spectral-domain optical coherence tomography (SD-OCT) for measuring the conformal coating thickness. An SD-OCT with axial resolution of 1.72 μm is developed. The system can provide cross-sectional imaging of the conformal coating layer. Then a boundary detection algorithm is developed to identify the coating layer from the OCT image and eventually calculate the thickness of the coating layer. Our proposed method is evaluated through comparing with metallographic slicing method, which cuts PCB into cross-section and measure conformal coating thickness under a microscope. The results demonstrate that our method produces a very consistent measurement results as compared to metallographic slicing method. In addition to the good accuracy, our algorithm’s computation load is low (about one hundred milliseconds per B-scan), indicating the potential to achieve on-line inspection of coating thickness.
Optical coherence tomography (OCT) is now a popular high resolution optical imaging technology capable of providing three-dimension images of internal microstructures within biological tissues. To date, the most successful application of OCT has been in ophthalmology, where the technology has become an indispensable diagnostic tool. It has proven able to image the structural changes due to various eye diseases. Besides, those structural changes may also be associated with certain physiological conditions, for instance, vessel density changes resulting from intraocular pressure change. Intraocular pressure (IOP) can also serve as an important physiological marker for the diagnosis of ophthalmic diseases. Therefore, in this study, we aim to develop ophthalmic OCT combined with a novel flexible pressure sensor for retina imaging and intraocular pressure measurement. A swept source OCT (SS-OCT) system is designed, and its axial resolution is about 5 μm. The OCT system is specially designed to allow for both anterior and posterior eye segment imaging. The anterior eye segment imaging is dedicated to measure the contact area between the pressure sensor and the cornea, which is needed by the pressure sensor to calculate the intraocular pressure. This system will be a versatile ophthalmic imaging platform: (1) conventional anterior and posterior eye imaging; (2) intraocular pressure measurement. Further, it will serve as a useful tool aiding in eye disease diagnostics in clinics.
Intraocular pressure (IOP) is the pressure exerted by the eye contents on the eyeball wall and is used to maintain the shape of the eyeball. It may cause glaucoma when the dynamic balance of the generation and excretion of aqueous humor in the eyeball is broken. The Goldmann applanation tonometer (GAT) based on the Imbert-Fick principle is considered to be the reference standard for glaucoma diagnosis in clinics. OCT is widely used for eye screening by imaging structural changes caused by various eye diseases. In this paper, we have developed an OCT-assisted transparent flexible force sensing system (O-FPSS) for IOP measurements. In general, the hybrid O-FPSS consists of a droplet-based flexible transparent force sensor placed over an optical coherence tomography imaging lens, in which the IOP measured once the apex of the cornea is flatted by the sensor. According to the Imbert-Fick law, when cornea is flattened, the pressure applied by the sensor equals to the IOP. Specially, the droplet-based capacitive flexible force sensor is consisted by two flexible conductive membranes, and an ionic is sandwiched in between, in which the force applied on the cornea can be monitored by the output. The sensing membrane deforms uniformly upon contacting the cornea, leading to the expansion of the droplet and an increase of the overall capacitance. On the other hand, to get the flatten area between the sensor and the cornea, a swept-source OCT (SS-OCT) is used to record the interfacial with a resolution of 5μm.
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