Enhanced Sensitivity of a Love Wave-Based Methane Gas Sensor Incorporating a Cryptophane-A Thin Film

Abstract

A Love wave-based sensing chip incorporating a supramolecular cryptophane A (CrypA) thin film was proposed for methane gas sensing in this work. The waveguide effect in the structure of SiO2/36° YX LiTaO3 will confine the acoustic wave energy in SiO2 thin-film, which contributes well to improvement of the mass loading sensitivity. The CrypA synthesized from vanillyl alcohol by a double trimerisation method was dropped onto the wave propagation path of the sensing device, and the adsorption to methane gas molecules by supramolecular interactions in CrypA modulates the acoustic wave propagation, and the corresponding frequency shifts were connected as the sensing signal. A theoretical analysis was performed to extract the coupling of modes for sensing devices simulation. Also, the temperature self-compensation of the Love wave devices was also achieved by using reverse polarity of the temperature coefficient in each media in the waveguide structure. The developed CrypA coated Love wave sensing device was connected into the differential oscillation loop, and the corresponding gas sensitive characterization was investigated. High sensitivity, fast response, and excellent temperature stability were successfully achieved.

Optimization of AIN Composite Structure Based Surface Acoustic Wave Device for Potential Sensing at Extremely High Temperature

“…It is well-known that the acoustic energy is confined in the piezoelectric crystal surface within several wavelength depths. Hence, the perfect matching layer (PML) can be used to reduce the thickness of the Si substrate, which can save the calculation time and effectively suppress the spurious waves from the interface reflection [14]. The corresponding material constants are revealed in the series literature [18][19][20][21].…”

“…Furthermore, the most important is that the fabrication of AlN based SAW devices can be compatible with conventional silicon technology [12]. On the other hand, platinum (Pt) and its alloys are widely known for its high thermal and chemical robustness, and are commonly used in micro-machined devices operated in an extreme environment like, for example, sensors and micro heaters [13,14]. Therefore, a combination of Pt and the AlN substrate provides an effective way of building a high-temperature sensor.…”

Portable Low-Cost Electronic Nose Based on Surface Acoustic Wave Sensors for the Detection of BTX Vapors in Air

“…In this research, we intend to highlight the electronic nose prototype developed with Love-SAW sensors, as they present the advantages of a great surface confinement of the acoustic energy by the guide layer (which increases the sensitivity to gases) and the capacity to propagate the waves across the solid-gas interface without suffering excessive acoustic wave attenuation [16,17]. In addition, Love-SAW sensors have revealed a higher sensitivity to gases than Rayleigh SAW sensors [18].…”

“…Different SAW devices are supported by the electronic nose we developed, such as Rayleigh, shear horizontal, Love, multi-guiding layer Love, etc. [18,20,25]. Despite the fact that a similar design is used for SAW devices, each of them works at different frequencies, and consequently the electronic nose was designed to support frequencies from 120 MHz to 200 MHz; the low-pass filter can be modified with a cutoff frequency to up 1 GHz.…”

Enhanced Sensitivity of a Hydrogen Sulfide Sensor Based on Surface Acoustic Waves at Room Temperature

“…The adsorption in sensitive thin-film modulates the SAW propagation by a so-called mass loading or viscoelastic or acoustic–electric effect, depending on the physical class of the sensitive thin-film itself. Considering the photo-lithographical fabrication technique and sensing topological structure, the SAW gas sensor exhibits some unique advantages, such as its low cost, fast response and high sensitivity, which was reported successfully for sensing H 2 , CH 4 , NO 2 , SO 2 and various chemical agents since the pioneering work of Whltjen et al [2,3,4,5,6,7,8,9,10]. Among them, some SAW gas sensors can detect gases such as NO 2 [11], CH 4 [12], and C 2 H 6 O [13] at room temperature.…”