Recently, improvements in instrumentation have provided the option of gas- or air-coupled ultrasonic testing as a realistic alternative to immersion or contact testing. In this paper we present theoretical and experimental results on resonant sound transmission methods mediated by ultrasonic coupling directly through ambient air. Although these methods are not new [1], they have only recently been considered for MHz applications. Advances in transducer technology [2–5] have further improved signal to noise ratios.