| In daily life or in industrial production,the participation of particles is very common.Size characterization is one of the most important parameters of particles.Measurement methods commonly used include light extinction method,light scattering method,ELPI and SMPS.Although these methods can obtain the particle size distribution,but can not directly obtain the shape information of particles.Microscope is also used in the observation and measurement of particles,but in industrial applications,the microscope has the following disadvantages:1.the price is expensive;2.the use of objectives leads to small depth of field and FOV,but large device which is inconvenient to carry;3.lens and other optical devices are exposed to the environment which makes it not suitable for the use under factory environment;4.to image clearly is not easy.In view of the problems existing in the above measurement methods,a lensless particle imaging and measurement scheme based on spherical wave digital holography is proposed.Spherical wave source is easy to obtain,and spherical wave holography has a series of important characteristics.By numerical simulation combined with experimental methods:Firstly,the effect of the measured object's relative position on the resolution was studied.The results show when light source and sensor plane were fixed,with the distance of the object and light source to reduce,holographic fringe magnification is increased,but the numerical aperture of the system is reduced,so the overall resolution of the system firstly increased and then decreased;The effect of light coherence on the resolution was studied,and found that when the system has a high magnification,the system resolution is very sensitive to the coherence of the light source,and the use of partially coherent light led to the high frequency loss of holographic fringe;and for the approximate non pre amplifier type,resolution is not very sensitive to the coherence of the light source.The system has high numerical aperture,resolution mainly depends on the sensor pixel size;The super resolution holographic is explored.It was found that the super-resolution reconstruction restored the missing high frequency components of the original hologram.In the experiment,the original hologram sequences with sub-pixel displacements are obtained by moving the light source of the non-magnified system.The super-resolution reconstructed result of 25 holograms is compared with the hologram using x20 fold objective lens.Both the results have reached 228.11p/mm.The super-resolution reconstructed image is bright,high contrast,and the field of view is the same as the sensing area of the CMOS sensor.The field of view of the hologram using ×20 fold objective lens is only 1/20 of that.Based on the above research,cheap materials such as LED,CMOS sensor chip are used to develop a lens-less holographic particle measuring device.The main body of the device is processed by 3D printing,and the size is about 5cmx 5cmx 7cm.The effective pixel size of the calibrated device is 1.35?m,and the effective measuring range is about 3?3000 ?m.Using the device to measure 25 ?m standard particles,the computed average diameter is 25.84 ?m with a relative error of about 3.36%.A software has also been developed,which can assist the device to obtain particle size information.The device has the advantages of small size,simple operation and clear image result,which can meet the basic requirements of particle observation and measurement. |
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