and 14 there is a thin coating of conductive material 16 and 18 best seen in fig2 these coatings may be screened onto the surfaces of the plates and fired they may be screened on in the form of conductive pastes or they could be in the form of tin oxide by way of specific examples the fired conductive layer may be formed of copper gold or tin oxide for example as shown in fig2 the plates 12 and 14 are spaced apart and sealed together with the coating of conductive material 16 and 18 on the inner opposed surfaces by a peripheral frit 20 of glass or other nonconductive material in practice this peripheral frit layer 20 and the plates 12 and 14 are preferably of substantially similar material from the standpoint of coefficient of thermal expansion this configuration forms a gap 22 between the conductive coatings 16 and 18 by way of example the frit may be made of glass particles having two different melting points with the firing of the glass frit being accomplished at a temperature intermediate the melting points of the two glasses included in the glass frit the two plates 12 and 14 may be accurately spaced apart in accordance with the size of the particles included in the higher melting point glass frit 20 in practice the spacing between the plates 12 and 14 may be in the order of from 1 2 of a thousandth of an inch up to about 20 thousandth of an inch with a spacing of between one and two thousandths of an inch being practical for many applications concerning the thickness of the diaphragm.