The Precise Determination of the Dielectric Properties of Alumina

There are three methods for the determination of the dielectric properties of material in sheet form: the Hartshorn-Ward ´resonance-substitution´ technique (BS 2067), the Lynch method using a transformer bridge (BS 4542) and the two fluid immersion method. These methods may be used at frequencies up to 1 MHz, and, in this range, it is shown that the two fluid immersion method offers advantages for permittivity measurement but is not suitable for determination of tan ¿. A modified form of Q meter is then described for use in the frequency range 1-100 MHz where application of the resonance substitution method permits dielectric loss measurements to be made with a precision of better than five microradians. Measurements at microwave frequencies are made by resonant cavity techniques and comparison is made between the value of permittivity determined at 1 MHz by a cross checkable two fluid method, and those calculated from the high frequency values of permittivity and dielectric loss.