The continuous torque density of conventional electric machines is determined by the size of the air-gap area and the back-iron depth, which are determined by the power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation. Despite the high coercivity of neodymium or samarium-cobalt PMs, continuous torque density is virtually the same amongst electric machines with optimally designed armature winding sets. Continuous torque density relates to method of cooling and permissible period of operation before destruction by overheating of windings or PM damage.
What determines continuous torque density?
size of the air-gap area and the back-iron depth

According to reciprocity, the efficiency of an antenna used as a receiving antenna is identical to the efficiency as defined above. The power that an antenna will deliver to a receiver (with a proper impedance match) is reduced by the same amount. In some receiving applications, the very inefficient antennas may have little impact on performance. At low frequencies, for example, atmospheric or man-made noise can mask antenna inefficiency. For example, CCIR Rep. 258-3 indicates man-made noise in a residential setting at 40 MHz is about 28 dB above the thermal noise floor. Consequently, an antenna with a 20 dB loss (due to inefficiency) would have little impact on system noise performance. The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR).
In what type of programs would low efficiency antennas not make a difference in effectiveness?
receiving

The length of the pitch for international adult matches is in the range of 100110 m (110120 yd) and the width is in the range of 6475 m (7080 yd). Fields for non-international matches may be 90120 m (100130 yd) length and 4590 m (50100 yd) in width, provided that the pitch does not become square. In 2008, the IFAB initially approved a fixed size of 105 m (344 ft) long and 68 m (223 ft) wide as a standard pitch dimension for international matches; however, this decision was later put on hold and was never actually implemented.
What is the range for the length of fields for non international matches in meters?
90120 m