Ink cartridge for ink level management apparatus

摘要

An ink cartridge for an ink management system includes a piston having a stepped back surface for improved reflection of ultrasonic acoustic waves through presentation of flat surfaces normal to the incident waves, thus permitting the piston to possess a preferred cone shape and structural rigidity. Heights of steps are preferably separated by even multiples of one-quarter wavelength of incident acoustic waves to avoid destructive interference from multiple reflections. Improved reflectivity overcomes problems with using an acoustic range finder to measure the position of the piston.