THE EFFECT OF STANDARD WAVE CONDITIONS ON DRY SUIT INSULATION WHEN MEASURED ON HUMANS
Testing of immersion suits is commonly conducted in calm or circulatory water. Several investigators have argued that this is an unrealistic test for a suit that is designed to protect a human from hypothermia in open ocean conditions. In support of this argument, Steinman et al. (1) and Romet et al.(2) reported a significant reduction of suit insulation in turbulent water when compared to still water by an average of about 30% when measured on humans. Such differences were found for loose-fitting wet suits but were not investigated for dry suits. Recently, Sowood et al. (3) reported a reduction of dry suit insulation by about 30% in turbulent water (wave height of 60 cm) compared to still water when tested on a thermal manikin.
Immersed clo insulation in marine work suits using human and thermal manikin data.
The immersed clo value of a series of 11 marine work suits has been measured using both humans and a thermal manikin. In still water, there is no significant difference in the measurements. Turbulent water significantly reduces the immersed clo value. The manikin errs on the safe side and consistently overestimates this decrement in insulation, and the reasons for this are discussed. Not intended to replace human physiological testing, the manikin is an excellent apparatus for the examination of conditions not easily or ethically possible to represent using humans. A good fitting suit with efficient neck, wrist and ankle closures which reduce flushing of water is essential to make an effective marine work suit.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.