I found a basic patent for a device from 1990. I developed a new device with great improvements and updated for technological advances but its utility is identical in purpose to the original device.
Whether you can patent your new device depends on whether 1) someone else has previously made the same invention or, if not, whether 2) your invention is an obvious design in view of what has been invented before your invention.
Simply because your invention and the old design have the same utility does not necessarily mean you cannot get a patent. However, the more changes and more improvements you have made over the old design improves the likelihood of you getting a patent.
Yes, you can patent the new device as long as the improved device is novel and is not obvious over the previous device itself (e.g., common sense improvement) or in combination with other devices or disclosures in patents. If your improvement has something unexpected or superior property or advantage, that would certainly help. Utility may be the same but its performance can be better, e.g., greater efficicency. Please work with a patent attorney in determining whether it would be possible to patent it. Good Luck!