Some New High-Frequency Wattmeters Operated by Forces Arising from a Rate of Change of Electromagnetic Momentum

The concept of momentum associated with moving energy in an electromagnetic field is particularly valuable as a means of interpreting the mechanism by which mechanical forces arise from reflection, absorption, or a progressive change of stored energy in the field. Three new types of wattmeter are described: 1) absorbing the angular momentum of a rotating field at 10 MHz, 2) reversing angular momentum by means of a half-wave plate in a circularly polarized field at 10 000 MHz, and 3) employing a gradient of stored energy in a dielectric at 35 000 MHz. Details are given of each of these instruments, calling attention to their particular advantages and limitations.