Imaging system for leak detection
An imaging system and method for leakage detection uses schlieren imaging to locate and characterize a flow of pressurized gas with a refractive index different than ambient air. In particular, a schlieren imaging system includes a collimated light, a knife-edge spatial filter and a 4F telescopic imaging system is used to create an image of a device under test (DUT). The DUT is pressurized and monitored for leaks. When a leak is present and in the monitored plane of the DUT, contrast variation illustrates the presence, location and character of the leak. For example, a waterproof/leakproof mobile device may be evaluated for leakage between layers of modules, such as leaks in the housing of a waterproof electronics case. This detection can allow identification and characterization of the leak point via visual identification.
1. A method for evaluating leaks in a device, the method comprising:
emitting a light signal;
modifying the light signal to create a collimated light signal;
filtering the light signal to create a filtered light signal;
sensing the filtered light signal to create a sensed image;
placing a device under test in an object plane along the collimated light signal such that an image of the device under test appears in the sensed image;
directing a pressurized gas into an interior volume of the device under test;
evaluating contrast in the sensed image; and
based on the step of evaluating contrast, determining whether the pressurized gas is leaking through one or more leak paths from the interior volume of the device under test.
2. The method of claim 1 , wherein the pressurized gas has a refractive index different from air.
3. The method of claim 2 , further comprising determining the magnitude and character of the leak in the device under test based on the contrast in the sensed image.
4. The method of claim 1 , wherein the device under test is configured to be a hermetically sealed device.
5. The method of claim 1 , wherein the step of emitting the light signal comprises emitting an incoherent light signal emitted by a light emitting diode.
6. The method of claim 1 , wherein the step of emitting the light signal comprises emitting a coherent light signal emitted by a laser.
7. The method of claim 1 , wherein the step of sensing the filtered light signal to create the sensed image comprises capturing the sensed image with an image sensor.
8. The method of claim 7 , wherein the step of evaluating contrast in the sensed image is performed by a controller operably connected to the image sensor.
9. The method of claim 1 , wherein:
the evaluating the contrast in the image comprises:
receiving a background-subtracted image;
applying image metrices to measure and analyze the background subtracted image; and
recording and storing image measurements and analytics, and
the determining whether the pressurized gas is leaking from the interior volume of the device under test comprises classifying aspects of the background subtracted image based on image metrices applied and measurements received.
10. The method of claim 9 , the method further comprising dividing the background subtracted image into regions of interest and regions of non-interest.
11. The method of claim 9 , wherein the classifying step further comprises predicting labels such as no leak, small leak, or large leak.
12. The method of claim 9 , wherein the classifying step further comprises predicting leaky regions.
13. The method of claim 1 , wherein the light signal is emitted by a point light source.
14. The method of claim 1 , wherein the light signal is modified to a collimated light signal by a collimation lens positioned to receive the light signal.
15. The method of claim 1 , further comprising receiving the collimated light signal at a 4F imaging telescope.
16. The method of claim 15 , wherein the light signal is filtered to create the filtered light signal by a spatial filter positioned at a Fourier plane of the 4F imaging telescope.
17. The method of claim 15 , wherein the filtered light signal is sensed to create the sensed image by an image sensor positioned at an output side of the 4F imaging telescope.
18. The method of claim 15 , wherein the object plane where the device under test is placed is located between a collimation lens positioned to receive the light signal and the 4F imaging telescope.