The ultrasonic sensor system is similar to that used by bats. Dolphins also use ultrasound for sensing and communication. Other biologically inspired sensors are possible.
Whiskers – on cats, moles, seals
Allow physical detection of objects
Allow animal to move through narrow passage
Robots can have wires which act the same way.
Noses – various animals can detect odours
Electronic ‘noses’ have been made
Electric eels, sharks, rays, catfish can all detect electric fields. Birds detect magnetic fields for navigation. Many animals use visible light… but that requires processing.
Some birds navigate using the Earth’s magnetic field – and for robots we can have devices called magnetometers, which can measure the strength of, and sometimes, the direction of magnetic fields.
Non bio-inspired sensors
Recently man has developed lots of other sensors:
Infra-red
Laser range finders
Microwaves
Radar
Terahertz
These are similar to ultrasonic in that it emits a signal, and awaits echoes – hence you can determine position. Sometimes if you want to detect changes – how quickly is position changing – the speed of the object. The so called continuous wave radar does this.