Ever since the introduction of electronic telecommunication and navigation devices, electronic circuits have seen extensive use in the underwater environment. For such applications, the design engineer must carefully examine the range of options available, to ensure optimum performance under the extreme conditions accompanying this environment.
The IFW (Institute for Production Engineering and Machine Tools), University of Hannover is currently involved with investigations for the use in subsea robotics. In the past the work focused primarily on seals, motors and tool-changing-mechanisms for water depth of up to 1200 meter/Tonshoff et al., 1987.
This report covers recent research into the operation of electronic devices in a high pressure environment equivalent to a water depth of 1200m. The research was carried out at the IFW in cooperation with the GKSS Research Centre Geesthacht.
The performance of electronic components is guaranteed by the manufacturer for particular operational and environmental conditions. These conditions are given in specifications and standards and can, for both user and manufacturer, form the basic obligatory arrangement for the testing and operating of the components. However, electronic circuits are also used outside the conditions specified in the standards. The components may be subjected to additional influences due to electromagnetic, mechanical and radiation effects.
Even in the underwater area, with its extreme pressure and corrosive environment, electrical circuits have found extensive use. There are theoretically a number of ways to operate electronic devices in underwater equipment, as shown in Fig. 1. The gas medium is the option normally chosen, since this represents the normal operational environment. In particular instances, for example with saturation diving, it may be advantageous to subject the device to the full ambient pressure. Alternatively, solid materials can be used to completely enclose the device. Either a thin layer or a larger block of material can be used, another alternative is to surround the device with an inert liquid medium. The device can be placed in a housing filled with the liquid medium. The device can be placed in a housing filled with the liquid, and can be protected by a thick-walled housing against the ambient pressure. Otherwise the device can be subjected to the full ambient pressure by means of a pressure equalization membrane in the wall of the thin-walled housing.
Fig 1 Variations in the different capsule types
All these capsule types have their own particular advantages and all are feasible solutions to the problem in hand. The appropriate solution must be chosen by considering the advantages and disadvantages of the cost, manufacturing and operating characteristics.
The research at the IFW focused on the operation of electronics, subjected to the full ambient pressure, within a liquid capsule. The advantages and no pressure differential is created at the plugs and seals. Additionally, this type allows the best constructional and assembly design, giving the engineer the free choice of shape and, particularly, size of the capsule.
Should a device be operated at full ambient pressure the behavior of electronics and the thermal power dissipation in such an environment have to be investigated.