Patents.
4,942,580; 4,986,623; 4,996,884; 4,998,259; 5,001,716; 5,003,544; 5,003,567; 5,011,284; 5,013,151; 5,018,810; 5,018,857; 5,018,859; 5,022,731; 5,022,760; 5,026,131; 5,026,161; 5,027,367; 5,034,613; 5,034,951; 5,042,889; 5,048,026; 5,048,938; 5,052,003; 5,052,011; 5,056,885; 5,058,972; 5,064,265; 5,064,284; 5,064,288; 5,067,134; 5,068,525; 5,071,208; 5,074,665.