This is the portion of the electromagnetic spectrum that has a frequency just below the visible spectrum.

Answer: Radiowaves, infrared radiations.

Explanation:

First things first, the electromagnetic spectrum is an array of radiations which result from the interference of an electric and magnetic component.

The portion of the electromagnetic spectrum which can be seen using the eye is termed the visible spectrum.

This visible spectrum have a range of wavelengths with lower limit of 380 nm and an upper limit of 740nm.

The electromagnetic radiations that have a frequency below the visible spectrum are Radio waves which may be microwaves in their highest frequency forms and also we have the infrared radiation.

Infrared Light