Microwaves are detected by which of the following?

Microwaves are primarily detected using an aerial and receiver system. An aerial, often referred to as an antenna, is designed specifically to capture electromagnetic radiation in the microwave frequency range. The receiver then processes the signals picked up by the aerial, converting the microwave energy into a form that can be analyzed or utilized.

This setup is commonly employed in various applications, including communication systems and radar technology. The combination of the aerial's ability to sense microwaves and the receiver's capability to interpret these signals makes this option the most suitable for detecting microwaves effectively.

Other options, while they might be capable of detecting different forms of energy, are not specifically designed for microwaves. For instance, photovoltaic cells are primarily used for detecting light and converting it into electrical energy, while thermal sensors detect changes in temperature and are useful for measuring infrared radiation rather than microwaves. Piezoelectric devices generate an electric charge in response to mechanical stress and are not typical detectors for electromagnetic waves like microwaves.