Ultrasound

The invention: 

A medically safe alternative to X-ray examination,
ultrasound uses sound waves to detect fetal problems in pregnant
women.

The people behind the invention:

Ian T. Donald (1910-1987), a British obstetrician

Paul Langévin (1872-1946), a French physicist

Marie Curie (1867-1946) and Pierre Curie (1859-1906), the French husband-and-wife team that researched and developed the field of radioactivity

Alice Stewart, a British researcher

Sonar

The invention:

A device that detects soundwaves transmitted
through water, sonar was originally developed to detect enemy
submarines but is also used in navigation, fish location, and
ocean mapping.

The people behind the invention:

Jacques Curie (1855-1941), a French physicist
Pierre Curie (1859-1906), a French physicist
Paul Langévin (1872-1946), a French physicist