Energy in Focus
Using waves as tools thanks to their energy
Waves transport energy that can be used and applied in various ways: directly, by converting it into another form of
energy or by focusing it on one point.
Focusing on the Target
We can focus sunbeams with a magnifying glass to collect their energy in one point – and start a fire. Other types of waves can also be used in a targeted way by focusing them on one point.
In focal therapy for the treatment of prostate cancer, ultrasound waves are directed at the diseased tissue to heat and thus destroy it. This is achieved with a lens that concentrates sound waves – in a similar way that a magnifying glass concentrates sunlight.
Radiosurgery also treats tumours with focused waves. Here, individual gamma rays are directed at the tumour, for example by a mobile robot arm, from lots of different angles. While the tumour is hit by all the rays, the surrounding healthy tissue is only exposed to the low doses of individual rays.
It is a great challenge to focus energy onto a target and at the same time minimise its effect in other areas. This is especially true when waves propagate inside a complex structure – such as the human body or the interior of the Earth.
Heat from Waves
A black shirt looks black because it hardly reflects any light. Instead, it absorbs almost all the light and converts it into heat. That is why we get warm in the sun especially fast when we wear black clothes. The shirt gets warm because the sunlight causes the atomic particles in the fabric to vibrate.
Food can be heated in a microwave oven because it contains water, which absorbs the energy of the microwaves. The electrically charged water molecules are turned back and forth by the oscillations of the waves, causing them to rub against each other and generate heat.
Absorption is also used to reduce the fogging of car windows. A windscreen fogs up when it is colder than the surrounding air, causing water droplets to condensate on it. A new type of coating absorbs mainly the infrared radiation of sunlight, causing the windscreen to warm up. As the difference in temperature between the air and the windscreen is smaller, fewer droplets are formed.
The Power of Motion
The energy of water waves is expressed in their motion: in the open sea it is a regular up-and-down motion, in increasingly shallow coastal waters the waves build up and break.
We can use the motion of a breaking wave for surfing as various different forces act on the surfboard. If we succeed in bringing them into balance, we can keep the board on the water surface and let the wave carry us forward while we use our body weight to control the direction and speed of the surfboard.
Wave power plants convert the motion energy of ocean waves into electricity. There are various technical approaches to this, but most of them are still being tested.