Change of mass can be viewed as a general feature of the interaction of the chemical species with the sensor. From the measurement point of view the determination of mass is generally called gravimetry. Although scales and balances are standard equipment in any laboratory, they are not usually regarded as sensors. On the other hand, when we talk about microbalances and microgravimetry(1) we regard them as sensors. Owing to their small size, high sensitivity, and stability, piezoelectric crystals have been used as microbalances, namely, in the determination of thin-layer thickness and in general gas-sorption studies.(2) The incorporation of various chemically sensitive layers has enabled the transition from microbalance to mass sensor and has resulted in the explosive growth of piezoelectric sensors in recent years.(3) The major advantages of mass sensors are their simplicity of construction and operation, their light weight, and the low power required. Measurement of the frequency shift is one of the most accurate types of physical measurement. Compared with electrochemical sensors the measurement is conducted in a monopolar mode, i.e., only a single physical probe is necessary. Mass sensors have high sensitivity and can be used for a very broad range of compounds. However, the corollary is high vulnerability to interferences. Piezoelectric crystals are relatively inexpensive and readily available.
KeywordsResonant Frequency Frequency Shift Quartz Crystal Surface Acoustic Wave Delay Line
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References for Chapter 3
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