An ultrasonic monitor implemented on a PCB includes a transmission medium. The transmission medium may be biocompatible and implemented as an oil-based transmission medium, a gel pad, or a combination thereof. Ultrasonic signals are transmitted between the ultrasonic monitor and a living subject through the transmission medium. An air gap is formed in the PCB underneath transducer elements to provide for more efficient signal transmission. The entire ultrasonic monitor may be encapsulated in plastic, a transmission medium, or both to provide water resistant properties.