High-Frequency Effects and Radiated Energy
For inductors or capacitors in circuits, the field energy must be returned to the circuit twice per cycle at the sinusoidal frequency of interest. If the frequency is so high that energy cannot return in phase with the current or voltage generating the field, the energy is said to be radiated. When field energy leaves a circuit, it returns through a process of reflection. Space is divided into cones emanating from the field source, and as the cone diameter increases, the characteristic impedance of the transmission space changes. Outgoing waves reflect a small amount of energy at each surface, resulting in complex forward and backward motion of field energy. Maxwell’s equations, formulated in the mid-nineteenth century, explain these fundamental field relationships.
Application of Radiators in Daily Operations
Radiators, operating in a range from around 10 kHz to gigahertz frequencies, are used for data, voice, and video transmission. Lower frequency radiators communicate with underwater craft, while radar transmitters operate in the gigahertz range. Commercial transmitters typically exceed 500 kHz, with military radar transmitters being the most powerful in the gigahertz range. In urban environments, electromagnetic radiation from these sources is pervasive. Military applications may use intense radiation to disrupt aircraft, highlighting the importance of understanding radiation and radiation hardening (shielding).
Explanation of Field Patterns and Energy in Electronics
Field patterns in electronics, depicted for various conductor configurations, extend into space. However, in structures like coaxial cables, fields are confined within the cable. In electronics, field energy from inductors and capacitors typically stays within the components. As components decrease in size, a larger proportion of field energy storage exists around the components. Conductors interconnecting circuit elements also have fields extending into space. The assertion that fields extend into space is clarified by considering that fields represent energy, and energy cannot be moved instantaneously. At the speed of light, it takes approximately 1 nanosecond for an electromagnetic field to traverse 1 foot.