Investigation of an FPGA-Based Acoustic Gas Thermometer for Monitoring Indoor Temperature Distribution Two-Dimensionally

Acoustic gas thermometry is a technique that reconstructs the 2-D temperature distribution of a gas medium using the acoustic velocities of multiple propagation paths in a region of interest (ROI). In recent years, this technology has gradually replaced traditional temperature measurement devices in combustion industries because acoustic gas thermometers can be installed on side walls and are resistant to dust interference. However, they are too loud for indoor applications, such as intelligent buildings. Thus, monitoring indoor temperature distribution with more innovative and easier approaches has become a widely discussed topic. Some researchers have tried to replace the siren sound source with ultrasonic transducers, but such ultrasound gas thermometers can only handle small ROIs or have unknown dynamic hotspot-tracking abilities. To tackle this problem, this research proposes an indoor 2-D acoustic gas thermometer that can immediately monitor a large ROI's 2-D gas temperature distribution. By enhancing the transmitting and receiving of ultrasonic signals with a stacked transducer and previbration method (PVM), the hardware alone can implement the proposed time-of-flight (TOF) calculation algorithm. The system drastically reduced the effort of the computation units and was able to acquire the 2-D temperature distribution in our experiment in less than 3 s. Additionally, a graphical user interface (GUI) was developed to display and record the information, including the 2-D gas temperature distribution of the entire ROI, the temperature profile of the selected cross section, the temperature values of specific positions, and the velocity of each acoustic path. The relative standard deviations of acoustic velocities measured at room temperature and the heated environment were less than 2%. Finally, experiments involving a moving heat source were conducted to validate the hotspot-tracking capability of the proposed system. The system tracked the heater's location successfully when it moved 5 cm per 10 and 30 s. Thus, the study demonstrated successfully that the proposed 2-D gas acoustic thermometer can quickly and accurately measure the temperature distribution and follow the hot spot within a large ROI, such as an intelligent building's indoor space.