Jan Peter Specht

Combating the health effects of particulate matter (PM) pollution requires affordable and reliable real-time air quality monitoring. The potential for large-scale manufacturing of acoustic-wave-based sensors makes them an interesting option for low-cost, low-power particle sensing applications. This article demonstrates a solidly mounted resonator (SMR) PM sensor with improved sensitivity through thermal modulation of the device. A novel, complementary metal oxide semiconductor (CMOS)-compatible SMR with an integrated microheater was designed, manufactured, and tested. In simulations, it was found that particle deposition increases both the heat loss and the thermal time constant of SMR. The effect of this on the resonant frequency shift of the device caused by particle deposition is investigated closely in this work. The sensitivity of the devices to particle deposition was tested experimentally with and without temperature modulation by placing the device in a test chamber and allowing the randomized settling of aerosolized particles on its surface. The unmodulated sensor demonstrated a particle mass sensitivity of ~40 Hz/ng while the mass sensitivity of the temperature-modulated device was shown to improve by a factor of nearly $\times 5$ to 190 Hz/ng. Temperature modulation also improved the detection limit from 100 to 50 ng. Further experiments were conducted by adding an impactor mechanism to have a more controlled measurement setup. To this effect, a thermophoretic particle deposition mechanism was added to the device to enhance its performance. It was demonstrated that the repeatability of measurements was significantly improved, making the device a promising low-cost technology for air quality monitoring.

The increase in air pollution and its effect on human health, is highlighting a growing demand for ubiquitous low-cost air quality monitors. Acoustic resonators have significant potential to satisfy this need. Solidly mounted resonators (SMR) are of special interest, because they have the advantage of being small and can be integrated into smart CMOS systems for air quality monitoring. This paper presents a CMOS-based SMR with a resonant frequency of about 2 GHz and a Q-factor of ca 200. The device comprises an integrated microheater with multi-purpose potential for temperature frequency modulation, temperature control, enhanced device sensitivity, sensor self-cleaning and use of single sensor as a virtual sensor array.

Pollution by particulate matter (PM) poses a serious and growing risk to human health. Film Bulk Acoustic Resonators (FBARs) have been proposed as a low-cost way to monitor particle concentration. This paper presents particle detection by a 1.1 GHz aluminium nitride based FBAR designed and fabricated by SilTerra Malaysia. The FBARs are used in a differential configuration with one sensing and one reference device in a system comprising a microchannel with an electric microfan and a thermophoretic precipitator microhotplate array for improved sampling. A custom-built test chamber was designed to characterise the device at different levels of particulate matter concentration in air. The particle feed rate into the test chamber was varied between 9.5, 19, 43, 66 and 94 μg/m ³ s. The FBAR frequency was found to decrease with increasing particulate matter concentration in the test chamber air. The experiments were conducted with and without the microchannel and it was found that the sampling channel increased sensitivity of FBAR resonant frequency to particle concentration per cubic meter of air from 5 Hz/ μgm ^-3 to 20 Hz/ μgm ^-3 . The detection limit in this test was estimated at ca. 50 μg/m ³ , which is around current European limits for PM10 pollution. In addition, the use of the sampling microfan to aid cleaning of FBARs after particle measurement was also investigated and found to be feasible especially for lower particle concentration.

Biosensors play a key role in medical diagnostics, and acoustic wave technology such as solidly mounted resonators (SMRs) applied to this field is one of the latest developments with great potential. This study seeks to explore the potential application of SMRs to detect and quantify prostate-specific antigen (PSA) for the screening and diagnosis of prostate cancer. The primary results show promising frequency shift of SMR sensors coated with Polydimethylsiloxane (PDMS) to different liquids. The SMR frequency is 1.082, 1.084 and 1.088 GHz, respectively, to air, deionized water and toluene (liquid) presence. These sensors have great potential as an accurate, low-cost method for measuring PSA and biomarkers for cancer and other diseases.

This paper presents the development of a low cost and low power wearable Electronic Nose with IoT connectivity for detecting synthetic urine. This system was designed with the ultimate aim to relieve the burdens associated with urinary incontinence for both sufferers and healthcare workers in hospitals and care homes. Commercially proven metal oxide (MOX) gas sensors for Volatile Organic Compound (VOC) detection such as the SGP30 and MiCS-5524 series of gas sensors were used, as well as the custom-made WO3, SnO2 and CuO MOX sensors developed at the Microsensors and Bioelectronics laboratory at the University of Warwick. A web-application was created to facilitate real-time monitoring over the MQTT protocol and indicate when urine has been detected. The capabilities of the IoT for this purpose allow for enhanced patient mobility and simultaneous patient monitoring. An artificial neural network was used to classify synthetic urine from other odours. The model was able to identify synthetic urine with 100% accuracy based on prior training and testing datasets.

Indoor and outdoor air pollution is known to cause many health problems. In order to improve air quality it is essential to monitor relevant parameters and identify sources of pollutants. This paper presents the design and development of a low-cost, portable Internet of Things (IoT) Indoor Air Quality (IAQ) monitoring system with 30 hours of battery life. The unit is intended for the monitoring of total VOCs, CO 2 , PM2.5, PM 10 , temperature, humidity and illuminance. The system can be used for both real-time measurements as well as hourly and daily averaging, in low power modes, and interfaces with a custom Blynk smartphone app, developed for easy user engagement. The device calculates a qualitative air quality index from measurements taken in-situ, based on United States Environmental Protection Agency (EPA) standards. Environmental data is used by the system to provide recommendations, such as increasing ventilation or reducing activity levels, which can help users improve their air quality. This system can be used as a node to monitor air quality in large scale networks for Smart Cities.

Monitoring particulate matter concentrations is of particular importance within the overall assessment of indoor and outdoor air quality and its impact on human health. Bulk acoustic wave (BAW) technology offers low cost, robust alternative to widely employed optical measurements. However, due to its reasonably new application within the area of particulate measurements, an in-depth characterisation of this technology to temperature and humidity variations that are inevitably present within the indoor and outdoor environment is necessary step in order to determine its suitability for possible commercialisation. This work presents the characterisation of the temperature and humidity dependence of solidly mounted resonators for particulate matter sensing. Both theoretical results, obtained through modelling and simulation, and experimental result, obtained within the laboratory conditions, are analysed and compared. A 1.5 GHz resonator with a zinc oxide thin film is modelled using a one-dimensional equivalent circuit model, and finite-element methods based on both two-dimensional model and the three-dimensional model. The simulation results show that the temperature dependence of the resonator is strongly dependent on the material properties and crystal structure of the zinc oxide film. Our models estimate the temperature coefficient of frequency to be -30 to -40 ppm/Centigrade. This theoretical temperature dependence was comparable to experimentally measured value of ca. -49 ppm/Centigrade. In addition to temperature characterisation of discrete devices, the resonator was combined with read-out circuitry, which was also simulated and tested experimentally. The temperature coefficient of frequency in this case was found to be much higher at -220 ppm/Centigrade demonstrating the necessity for temperature control or temperature compensation within the complete system in practical applications. The effect of humidity was also investigated. The experimental mean resonant frequency shift per percent increase in relative humidity of the ambient air was found to be -3.8 kHz/%RH, while the models showed negligible sensitivity to humidity variations. Finally, preliminary experiments were conducted within the controlled lab environment showing promising result for possible application of this technology in particulate matter monitoring. The resonant frequency shift of approximately 300 kHz was measured after mass loading the sensing area of the resonator with estimated 24 ng of standard Arizona dust particles.

This work presents the first results for the production of highly efficient solar cells with industrial processes using the PERC structure. Two batches of FZ and Cz wafers were conducted to prove the applicability of a transfer from the clean room to an industrial standard. The front and rear side metallization was done by a new pilot system using the sputtering technology. The investigation of solar cell results, series resistance, contact resistance and a optical analysis are discussed later on.