This paper reports a novel hybrid acoustic energy harvester. The harvester utilizes both the electromagnetic and piezoelectric conversion mechanisms simultaneously to convert the ambient acoustical noise into electrical power for self-powered wireless sensor nodes. The proposed harvester is comprised of a Helmholtz resonator, two magnets mounted on a piezoelectric plate, and a wound coil located under the magnets. The harvester is characterized both under harmonic and real random acoustical excitations. In-lab, under harmonic acoustical excitation at a sound pressure level of 130 dB and frequency of 2.1 kHz, an optimum power of 2.86 μW (at 114 Ω optimum load) is obtained from electromagnetic conversion and 50 μW (at 1000 Ω optimum load) is generated by the piezoelectric harvester’s part. Moreover, in real acoustical environment of a domestic electric generator the peak voltages of 40 and 123 mV are produced by the electromagnetic and piezoelectric portions of the acoustic energy harvester.

This paper presents a K-band bulk acoustic wave (BAW) resonator constructed from an Al _0.72 Sc _0.28 N periodically poled piezoelectric film. The resonators exhibited dominant resonance responses around 20 GHz, approximately four times higher than the resonance frequencies of similar unpoled devices fabricated on the same wafer. Resonators with a quality factor ( Q_p ) of 160 and an electromechanical coupling ( k ² _t ) of 8.23% were achieved. The figure of merits (defined as FoM_I = k ² _t Q_p and FoM_II = f_p FoM_I ×10 ^-9 ) of the resonator are 13.2 and 274 which are higher than most reported acoustic resonators operating at K-band (18 GHz to 27 GHz) or higher frequency. The experimental results suggest that periodically poled BAW resonators are promising for emerging RF filter and oscillator applications at K-band frequencies.

In this paper, by using 0.35 μm 2P4M CMOS MEMS technology, a Thermoresistive Micro Calorimetric Flow (TMCF) sensor with two packaging designs were systematically investigated: Open-space (O-Type) and Probe-with-channel (P-Type) designs. In comparison with the O-Type design, the P-Type sensor showed an 80% enhanced sensitivity with a relieved tilt angle effect on the mainstream airflow detection. Accordingly, the P-Type packaged flow sensor for HVAC gained a prominent normalized sensitivity (S*) of 228 μV/(m/s)/mW, while also having a low power consumption (P) of less than 4.2 mW. Moreover, within the linear range of -2 to 2 m/s, an accuracy of ±0.05 m/s was achieved, thus enabling this robust flow sensor (repeatability < 0.2%) for indoor airflow measurements even in a variable ambient environment. Furthermore, the proposed P-Type TMCF sensor and its wireless multi-sensor module were applied for the development of personalized ventilation (PV) and the monitoring of predicted mean vote (PMV), both of which confirm the functionality of the developed sensor for indoor airflow measurements in the HVAC system.

In this paper, we report a two-dimensional (2D) Thermoresistive Micro Calorimetric Flow (TMCF) sensor by using a 0.35 μm 2P4M CMOS MEMS technology. For the airflow, the fabricated and the open-space packaged 2D flow sensor system achieved the highest normalized sensitivity of 32 mV/W/(m/s) with respect to input heating power and gain. To overcome the sensor output drifting issue due to the locally redistributed fluid flow near the bonding wires, a digital signal conditioning algorithm using the inverse distance weighting (IDW) method, instead of the conventional fitting method with sine and cosine function, was proposed. Accordingly, the calibrated 2D flow sensor showed an improved velocity accuracy of ±4% and the angle accuracy of ±3° for an input airflow from 0 to 20 m/s. Therefore, the developed highly sensitive 2D TMCF sensor will be a promising device for the airflow measurement in the smart buildings and the meteorological monitoring system. [2019-0259]

This article presents 19-GHz bulk acoustic wave (BAW) resonators realized in a periodically poled piezoelectric film (P3F) microfabricated in a commercial XBAW process. The polarization of the three layers comprising the P3F film are realized via a combination of as-grown (two-layer) and electrically poled (one-layer) aluminum scandium nitride (AlScN). To improve the series ( ${Q}_{s}$ ) and maximum ( ${Q}_{\max }$ ) quality factors, the device is constructed by connecting two-BAW resonators in series, which lowers the effect of the via resistance when compared with a traditional single BAW. Resonators achieved ${Q}_{\max }$ of 531 (with ${Q}_{s}$ of 348 and ${Q}_{p}$ of 264) and ${\text {FoM}}_{{os}}$ (defined as ${\text {FoM}}_{{os}} = {{f}_{{s},{p}} {Q}}_{{s},{p}} \times {{10}}^{-{9}}$ , where ${Q}_{{s},{p}}$ is the quality factor at series ( ${f}_{s}$ ) or parallel ( ${f}_{p}$ ) resonance frequency) of 6542 at 18.8-GHz frequency, which is higher than most of the state-of-the-art piezoelectric BAW resonators operating at similar and higher frequencies. The experimental results indicate that the P3F BAW resonators are promising for applications in emerging RF communication systems.

In this article, we report a predicted mean vote (PMV) index based micro Human Thermal Comfort Sensing (HTCS) system with multiple MEMS sensors. The system consists of a wireless multi-sensor (CMOS MEMS air velocity, MEMS relative humidity (RH) and MEMS air temperature) module to measure three environmental parameters and a smartphone App with a novel motion analytics algorithm (for estimation of metabolic rate) and personal factors (clothing insulation) input. While the majority of the reported HTCS systems are bulky and takes only environmental parameters into consideration, the developed system utilizes MEMS technology for sensors’ fabrication and measures the essential environmental and human factors involved to compute human thermal comfort. Furthermore, the developed HTCS system shows much better accuracy (±0.13) than its commercial and reported counterparts (±0.17 to ±0.4). Moreover, the packaged HTCS system is placed in a testing room to monitor the PMV. The experimental results indicated that our micro PMV-based HTCS system is promising for smart HVAC system integration in the era of the Internet of Things.