From automobile to aeronautic with biomedical, all applications domain uses sensors. Some of them are frequency-output. The coming of new piezoelectric materials opens a door to applications not accessible nowadays and specially at high temperatures. Gallium orthophosphate (GaPO4) is one of these new piezoelectric materials with high coupling factor. This book is about design and realisation of different GaPOs sensors working in acoustic bulk waves. The first part consists to study temperature sensibility and stability building analytical model of vibrating beam in length...