Table 1.

Comparison of delay line and resonator SAW sensors.

Delay Lines	Resonators
Change of delay time is measured: material constant is temperature coefficient of delay (TCD)	Frequency shift is measured: material constant is temperature coefficient of frequency (TCF = −TCD)
Wide band device: sharp peaks in time-domain	High Q-factor needed for sharp peaks in frequency-domain -> narrow resonance.
Differential measurement is easy due to multi peak design	Differential measurement requires multiple resonators
Wide band operations allow for wide temperature shift	Too wide temperature shifts might shift the sensor’s resonance frequency out of the dedicated ISM-band
Devices are relatively long ~>4–6 mm, measurement corresponds to mean value over delay path ~2 mm	Resonators can be small and allow point-like measurements
Sophisticated phase tracking required	High resolution frequency reading needed