Development of ball surface acoustic wave gas chromatograph for environmental monitoring in spacecraft and its application on the ground

For on-site analysis of surface materials on the moon, planets, and small bodies and for the monitoring of air quality in crewed spacecraft, we have developed a portable gas chromatograph (GC) equipped with a ball surface acoustic wave (SAW) sensor. In this study, we fabricated a 10 cm cube GC that implements the forward flush method using two metal micro-electro-mechanical-system (MEMS) columns coated with different stationary phases in microchannels fabricated by wet etching and diffusion bonding of stainless-steel plates. Using this GC, we succeeded in analyzing 10 kinds of gas within 10 min. In addition, for the application of the ball SAW GC on the ground, we also developed a palm-sized GC with a single metal capillary column and used it in the analysis of the headspace gas of sake. We showed that the ratio of peak areas differed among odorants depending on the brand and brewing process of sake.

Characterization Studies of a GC based SAW Sensor System for Potential Detection and Identification of Toxic Environmental Gases/Vapors

The characterization of a custom-designed GC-based SAW e-Nose sensor system is presented here to study the sensing ability of the sensor system to detect and identify low medium and high toxic vapors. A semi-automated multi-vapor generator generates vapors of chemical compounds that are then exposed to the sensing system to examine its performance under various concentrations. Time-domain verses frequency response of GC-SAW Sensor is noted for repeated cycles against different chemical compounds like xylene, 1,2 dibromoethane, dimethyl sulfate, triethyl phosphate, nitrobenzene, phosphorous trichloride being tested. The generated data is examined using a principle component analysis (PCA) technique to detect a unique response for an individual chemical compound. Experimental results are reported.

Surface Acoustic Wave-Based Flexible Piezocomposite Strain Sensor

A surface acoustic wave (SAW), device composed of polymer and ceramic fillers, exhibiting high piezoelectricity and flexibility, has a wide range of sensing applications in the aerospace field. The demand for flexible SAW sensors has been gradually increasing due to their small size, wireless capability, low fabrication cost, and fast response time. This paper discusses the structural, thermal, and electrical properties of the developed sensor, based on different micro- and nano-fillers, such as lead zirconate titanate (PZT), calcium copper titanate (CCTO), and carbon nanotubes (CNTs), along with polyvinylidene fluoride (PVDF) as a polymer matrix. The piezocomposite substrate of the SAW sensor is fabricated using a hot press, while interdigital transducers (IDTs) are deposited through 3D printing. The piezoelectric properties are also enhanced using a non-contact corona poling technique under a high electric field to align the dipoles. Results show that the developed passive strain sensor can measure mechanical strains by examining the frequency shifts of the detected wave signals.

Modelling and Simulation using Finite Element Method of Surface Acoustic Wave Biosensor for Gas Detection Application

A surface acoustic wave (SAW) sensor detects changes in physical properties such as mass and density on its surface. Compared to other types of sensors, SAW sensor have a good stability, high selectivity and sensitivity, fast response, and low-cost. On the other hand, to design and optimize a SAW biosensor requires a long process including time and cost using conventional methods. Therefore, numerical simulation and computational modelling are useful and efficiently conduct analysis for the SAW biosensor. In this paper, a numerical simulation technique is used to analyse the SAW device sensitivity for the application of gas detection. The SAW biosensor can detect very small mass loading by changing its sensor resonance frequency. The two-dimensional (2D) device model is based on a two-port SAW resonator with a gas sensing layer. We made two design of SAW biosensor device with frequency of 872 MHz and 1.74 GHz. A gas with vary concentration from 1 to 100 ppm were used to determine the change of the device resonance frequency. As a result, the high frequency (1.74 GHz) device, shows that the resonance frequency is shifted larger than to the low frequency (872 MHz) device. In addition, the high frequency device offers five times more sensitivity than the low frequency device. By changing the sensor design, the sensor characteristics such as sensitivity can be altered to meet certain sensing requirements. Numerical simulation provides advantages for sensor optimization and useful for nearly representing the real condition.

A Novel Love Wave Mode Sensor Waveguide Layer with Microphononic Crystals

Surface acoustic wave (SAW) sensors have been applied in various areas with many advantages, such as their small size, high sensitivity and wireless and passive form. Love wave mode sensors, an important kind of SAW sensor, are mostly used in biology and chemistry monitoring, as they can be used in a liquid environment. Common Love wave mode sensors consist of a delay line with waveguide and sensitive layers. To extend the application of Love wave mode sensors, this article reports a novel Love wave mode sensor consisting of a waveguide layer with microphononic crystals (PnCs). To analyze the properties of the new structure, the band structure was calculated, and transmission was obtained by introducing delay line structures and quasi-three-dimensional models. Furthermore, devices with a traditional structure and novel structure were fabricated. The results show that, by introducing the designed microstructure of phononic crystals in the waveguide layer, the attenuation was barely increased, and the frequency was shifted by a small amount. In the liquid environmental experiments, the novel structure with micro PnCs shows even better character than the traditional one. Moreover, the introduced microstructure can be extended to microreaction tanks for microcontrol. Therefore, this novel Love wave mode sensor is a promising application for combining acoustic sensors and microfluidics.

Development of Wireless and Passive SAW Temperature Sensor with Very High Accuracy

A surface acoustic wave (SAW) temperature sensor with high accuracy was developed and wirelessly characterized in this work. The sensing chip with reflective delay line pattern was simulated using typical coupling of modes (COM) model and prepared by the standard photolithographic technique. Sharp reflection peaks with high signal-to-noise (SNR) were observed from the developed sensing chip operating at 433 MHz. Referring to the frequency-stepped continuous wave (FSCW)-based transceiver, planar antennas, and the developed SAW chip, the wireless and passive temperature sensor system was built. Adaptive Least Mean Square (LMS) algorithm was used for the first time in the SAW sensor signal processing to significantly improve the system SNR, and the corresponding phase fluctuation is down to only 3∘. High temperature sensitivity of 36.5 ∘C and very high accuracy of ±0.2 ∘C in the range of −30 ∘C∼100 ∘C were achieved successfully by wireless measurement.

AN INVESTIGATION OF THE SENSITIVITY OF POLYMER-COATED SURFACE ACOUSTIC WAVE-BASED GAS SENSORS IN THE DETECTION OF VOLATILE ORGANIC COMPOUNDS

Surface acoustic wave sensors (SAWs) are excellent at detecting volatile organic compounds (VOCs) since a sensing layer can be created by spreading a thin film of material across the delay line. This critically enhances performance as it is sensitive to the physical phenomena of interest. This study aims to provide a thorough investigation of the sensitivity of polymer-coated SAW-based gas sensors to VOCs using simulations via the finite element method (FEM). As such, quartz was chosen as the piezoelectric substrate while polymeric materials were chosen as the sensing layers due to their high sensitivity, low energy consumption, short response time, performance at room temperature, and reversibility after exposure to an analyte. The polymeric materials chosen were: (1) polyisobutylene (PIB), (2) polydimethylsiloxane (PDMS), (3) polyisoprene (PIP), (4) polyimide (PI), and (5) phenylmethyldiphenylsilicone (OV25). The VOCs chosen for investigation were: (1) dichloromethane (DCM), (2) trichloroethylene (TCE), (3) 1,2-dichloroethylene (DCE), and (4) carbon tetrachloride (CCl4). The performance of each polymer-coated SAW sensor was evaluated in terms of frequency shift and sensitivity to each VOC in FEM simulations. Our study found that the PIB-coated sensor had the highest sensitivity (4.0571 kHz/ppm) to DCM vapor and good sensitivity (45.257 kHz/ppm) to TCE vapor. However, the performance of each polymer-coated sensor varied depending on the type of VOC being tested. As an example, while the OV25-coated sensor was more sensitive (52.57 kHz/ppm) than the PIB-coated sensor (53.54 kHz/ppm) to TCE vapor regardless of the concentration, the PIB-coated sensor was more sensitive to DCM vapor at both low (4.06 kHz/ppm) and high (3.54 kHz/ppm) concentrations than the OV25-coated sensor. Therefore, the results of our FEM simulations indicate that polymer-coated SAW-based gas sensors are highly capable of self-powered VOC detection. ABSTRAK: Sensor gelombang akustik permukaan (SAW) adalah sangat baik dalam mengesan sebatian organik meruap yang tidak stabil (VOCs), kerana lapisan pengesan dapat dihasilkan dengan melapis nipis bahan pada lapisan garis tunda. Cara ini dapat menambah baik prestasi kerana ianya sensitif kepada fenomena fizikal yang dituju. Kajian ini bertujuan bagi menyediakan kajian menyeluruh terhadap kesensitifan sensor gas berasaskan SAW bersalut polimer pada VOC menggunakan simulasi melalui kaedah unsur terhingga (FEM). Oleh itu, kuarza dipilih sebagai substrat piezoelektrik manakala bahan polimer dipilih sebagai lapisan penginderaan berdasarkan kepekaan tinggi, penggunaan tenaga rendah, respon masa singkat, prestasi suhu bilik, dan faktor keboleh-balikan setelah terdedah kepada analit. Bahan polimer yang dipilih adalah: (1) polisobutilena (PIB), (2) polidimethilsiloxana (PDMS), (3) polisoprena (PIP), (4) polimida (PI), dan (5) phenilmethildiphenilsilikon (OV25). VOC terpilih bagi kajian adalah: (1) diklorometana (DCM), (2) trikloretilena (TCE), (3) 1,2-dikloroetilena (DCE), dan (4) karbon tetraklorida (CCl4). Prestasi setiap sensor SAW bersalut polimer dinilai berdasarkan peralihan frekuensi dan kesensitifan pada setiap VOC simulasi FEM. Dapatan kajian menunjukkan sensor bersalut-PIB mempunyai kesensitifan paling tinggi (4.0571 kHz/ppm) terhadap wap DCM dan kepekaan yang baik (45.257 kHz / ppm) terhadap wap TCE. Walau bagaimanapun, prestasi setiap sensor bersalut polimer adalah berbeza bergantung kepada jenis VOC yang sedang diuji. Sebagai contoh, sensor bersalut OV25 adalah lebih sensitif (52,57 kHz/ppm) daripada sensor bersalut PIB (53,54 kHz/ppm) pada wap TCE tanpa mengira kepekatan. Manakala sensor bersalut PIB lebih sensitif terhadap wap DCM pada kedua-dua kepekatan rendah (4.06 kHz/ppm) dan tinggi (3.54 kHz/ppm) daripada sensor bersalut-OV25. Oleh itu, hasil simulasi FEM menunjukkan bahawa sensor gas berasaskan SAW bersalut polimer adalah sangat berpotensi sebagai pengesan VOC berkuasa sendiri.