Surface wave sensors can be utilized in a number of sensing applications. Examples of surface wave sensors include devices such as acoustic wave sensors, which can be utilized to detect the presence of substances, such as chemicals. An acoustic wave (e.g., SAW/SH-SAW/Love/SH-APM) device acting as a sensor can provide a highly sensitive detection mechanism due to the high sensitivity to surface loading and the low noise, which results from their intrinsic high Q factor.
Surface acoustic wave devices are typically fabricated using photolithographic techniques with comb-like interdigital transducers placed on a piezoelectric material. Surface acoustic wave devices may have either a delay line or a resonator configuration. The change of the acoustic property due to the flow can be interpreted as a delay time shift for the delay line surface acoustic wave device or a frequency shift for the resonator (SH-SAW/SAW) acoustic wave device.
Acoustic wave sensing devices often rely on the use of piezoelectric crystal resonator components, such as the type adapted for use with electronic oscillators. In a typical flow sensing application, the heat convection can change the substrate temperature, while changing the SAW device resonant frequency. With negative temperature coefficient materials such as LiNbO3, the oscillator frequency is expected to increase with increased liquid flow rate. The principle of sensing is similar to classical anemometers.
Flow rate is an important parameter for many applications. The monitoring of liquid (e.g., blood, saline, etc.) flow rate within a human body can provide important information for medical research and clinical diagnosis. Such measurements can provide researchers with insights into, for example, the physiology and functioning of the heart and other human organs, thereby leading to advances in medical, nutrition and related biological arts. Blood/liquid flow rate measurements can also provide useful information regarding the safety and efficacy of pharmaceuticals and the toxicity of chemicals. It is believed that the use of passive, wireless acoustic wave devices for flow rate monitoring can provide for great advances in physiological, pharmaceutical and medical applications to name a few. Surface acoustic wave sensors have the potential to provide flow sensor systems with higher sensitivity and wider dynamic ranges than the solid state flow sensor devices currently available.