simple past tense (passive voice)

Screen-printed electrodes were fabricated using a model 247 screen-printer

 It took a shorter time than expected to dissemble the goods 

More than seven different types of antennae were investigated

The compounds were tested at 25⁰C, in a buffer solution, to which the agents were added

describing samples selected for this study 

or

 specially designed or chosen materials or equipment

All chemicals were of top grade 

The buffer solution had a pH value of 6.80 

Many different metals were used and each device contained several tens of components

describing general populations from which the samples were taken

 or

 conventional material

present tense

More than 90% of all the computer appliances people use are selected by someone other than the user

These users are typically under the age of 50.