Optical system for measuring diameter, distribution and so forth of micro bubbles and micro liquid drop

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam;
• and
• measuring numbers of interference fringes in the respective out-of-focus images corresponding to the micro gas bubbles or the micro liquid droplets to determine diameters and distribution of the micro gas bubbles or the micro liquid droplets;
• wherein said out-of-focus images are captured with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said sheet-shaped parallel laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane.

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• and
• determining a center of each of said out-of-focus images, thereby determining a center position of the corresponding micro gas bubble or micro liquid droplet.

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• subjecting each of the out-of-focus images to Fourier transform to obtain a frequency;
• multiplying the obtained frequency by a length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image;
• and
• determining a diameter of the micro gas bubble or the micro liquid droplet on a basis of the number of interference fringes.

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing two image frames at a micro time interval Δt, the two image frames each containing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam, the linear out-of-focus images being captured from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• calculating cross correlation between the two captured image frames for each linear out-of-focus image in the two captured image frames to obtain a displacement Δsi of each linear out-of-focus image;
• and
• determining a velocity ui of each micro gas bubble or micro liquid droplet from the following relationship:
• ui=Δsi/Δt (6).

A method of measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said method comprising the steps of:

• applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• determining a center of each of said out-of-focus images, thereby determining a center position of the corresponding micro gas bubble or micro liquid droplet;
• subjecting each of the out-of-focus images to Fourier transform to obtain a frequency;
• multiplying the obtained frequency by a length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image;
• determining a diameter of the micro gas bubble or the micro liquid droplet on a basis of the number of interference fringes;
• capturing two image frames containing the linear out-of-focus images at a micro time interval Δt;
• calculating cross correlation between the two captured image frames for each linear out-of-focus image in the two captured image frames to obtain a displacement Δsi of each linear out-of-focus image;
• and
• determining a velocity ui of each micro gas bubble or micro liquid droplet from the following relationship:
• ui=Δsi/Δt (6).

An apparatus for measuring a diameter, distribution and so forth of micro gas bubbles and micro liquid droplets, said apparatus comprising:

• laser beam application means for applying a sheet-shaped parallel laser beam to a space in which micro gas bubbles or micro liquid droplets are floating;
• imaging means for capturing linear out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam, which is applied by said laser beam application means, from a lateral direction which is at a predetermined angle to a direction of travel of the laser beam with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of said laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction perpendicular to said plane, said linear out-of-focus images extending in a direction of said plane in correspondence to the micro gas bubbles or the micro liquid droplets;
• center position measuring means for determining a center of each of said out-of-focus images to thereby determine a center position of the corresponding micro gas bubble or micro liquid droplet;
• diameter measuring means for subjecting each of the out-of-focus images to Fourier transform to obtain a frequency, multiplying the obtained frequency by a length of the out-of-focus image to obtain the number of interference fringes in the out-of-focus image, and determining a diameter of the micro gas bubble or the micro liquid droplet on a basis of the number of interference fringes;
• and
• velocity measuring means for capturing two image frames containing the linear out-of-focus images at a micro time interval Δt, calculating cross correlation between the two captured image frames for each linear out-of-focus image in the two captured image frames to obtain a displacement Δsi of each linear out-of-focus image, and determining a velocity ui of each micro gas bubble or micro liquid droplet from the following relationship:
• ui=Δsi/Δt (6).