a continuous , non - invasive fetal heart rate measurement is produced using one or more ultrasonic transducer array patches that are adhered or attached to the mother . each ultrasound transducer array is operated in an autonomous mode by a digital signal processor to obtain data from which fetal heart rate information can be derived . each ultrasonic transducer array patch comprises a multiplicity of subelements that are switchably reconfigurable to form elements having different shapes , e . g ., annular rings . each subelement comprises a plurality of interconnected cmut cells that are not switchably disconnectable . the use of cmut patches will provide the ability to interrogate a three - dimensional space electronically with ultrasound , using a transducer device that is thin and lightweight enough to stick to the patient &# 39 ; s skin like an ekg electrode . the ultrasound device can track the fetal heart in three - dimensional space as it moves due to the mother &# 39 ; s motion or the motion of the unborn child within the womb .