Droplet sensor

A droplet sensor comprising:

• an optical cover that forms part of a spheroid, a major axis of the spheroid being a vertical axis;
• a light emitting and receiving device disposed at a position offset from a first focal point of the spheroid along the major axis;
• and
• a reflector disposed in vicinity of a second focal point of the spheroid,
• wherein the light emitting and receiving device includes a light emitting element and a light receiving element;
• wherein both the light emitting element and the light receiving element are provided on a same side of the second focal point;
• wherein the light emitting and receiving device, and the reflector, are arranged along the path of the major axis;
• wherein the optical cover has an effective detection area between the light emitting and receiving device and the reflector,
• wherein the reflector is a non-detection area;
• wherein the effective detection area has a total internal reflection characteristic that (i) satisfies a total internal reflection condition at an interface with a gas, and (ii) does not satisfy the total internal reflection condition at an interface with a liquid,
• wherein the reflector reflects, towards a light receiving surface of the light emitting and receiving device, light totally reflected by the effective detection area, or reflects, towards the effective detection area, light directly incident on the reflector from the light emitting and receiving device;
• wherein the reflector does not have a total internal reflection characteristic that (i) satisfies the total internal reflection condition at the interface with the gas, and (ii) does not satisfy the total internal reflection condition at the interface with the liquid;
• and
• wherein the reflector is an area that reflects all light arriving from the effective detection area.