One alternative to the purely mechanical approach is to use water. That's the principle behind the design of the Hydro-Massage Chair invented by Frank J. Arzt. Arzt's design allows the user to experience an invigorating massage using jets of water, yet remain perfectly dry.
His design includes a waterproof membrane similar to the kind found on a waterbed. The backrest for the chair contains the membrane. The front of the membrane -- the side that is in contact with the user's back -- is restrained by a series of bars. Without the bars, the membrane becomes misshapen whenever the pressure of the water inside it changes. Valves at the top end of the membrane allows users or the manufacturer to fill the membrane cushion with water.
Along the back of the membrane are a series of nozzles. The nozzles connect by tubes to an electric pump, and a heating and cooling system. The pump re-circulates the water inside the chair, pushing it through the nozzles to create the massage sensation. The user sits back in the chair and receives a massage from the water jets. The heating and cooling system can adjust the water's temperature to the user's preference.
Arzt's patent suggests that the nozzles could include a rotor inside the nozzle's central passageway. The rotation of the rotor causes the water jet to rotate as well, increasing the area of impact on the user. By pulsing the water through the nozzles, the chair could simulate the tapping sensation you can get from some mechanical massage chairs.
Although Arzt filed his patent in 2000, the market hasn't been flooded -- pun intended -- with hydro massage chairs. This could be due to the fact that massage chairs are still a small market for much of the world or perhaps the manufacturing process is too complex. But there are dry hydro-massage tables and mattresses on the market, so we may still see a chair variation in the future.
Some massage chairs use another technique that relies on air. How do massage chairs use air to relax an aching back? Keep reading to find out.