Abstract: A water level gauge according to one aspect of the present invention includes a first communicator configured to receive a first wireless signal indicating an absolute value of water pressure from a water pressure sensor device capable of measuring the absolute value of the water pressure, and a water level calculator configured to calculate a water level on the basis of the absolute value of the water pressure indicated by the first wireless signal received by the first communicator and an atmospheric pressure measured by a barometer.

Abstract: A method of manufacturing a resonant transducer having a vibration beam includes: (a) providing an SOI substrate including: a first silicon layer; a silicon oxide layer on the first silicon layer; and a second silicon layer on the silicon oxide layer; (b) forming a first gap and second gap through the second silicon layer by etching the second silicon layer using the silicon oxide layer as an etching stop layer; (c) forming an impurity diffusion source layer on the second silicon layer; (d) forming an impurity diffused layer in a surface portion of the second silicon layer; (e) removing the impurity diffusion source layer through etching; and (f) removing at least a portion of the silicon oxide layer through etching such that an air gap is formed between the first silicon layer and a region of the second silicon layer surrounded by the first and second gaps.