Abstract. This paper describes the design and testing of the first miniaturised metallic triplebeam tuning fork resonant sensors for use in force, pressure and torque measurement applications. The new devices with 9mm length vibrating tines have resulted in over a 40% in size when compared to previously tested resonators. The four fold increase in operating frequency to 26 kHz, with Q factors in air up to 4000, provides additional benefits for resolution, accuracy, range and overload capability. Measurement repeatability of at least 0.02% of span levels for torque transducers employing the sensors are quoted. Results of characterisation over the temperature range -30 o C to +90 o C are given. IntroductionResonant sensors have been used in a wide range of sensing applications, such as load, pressure, torque and fluid flow characteristics [1]. The key element of these sensors is the resonator, an oscillating structure, which is designed such that its resonance frequency is a function of the measurand. The most common sensing mechanism is for the resonator to be stressed as a force sensor. The applied stress effectively increases the stiffness of the resonator structure, which results in an increase in the resonator's natural frequency. The resonator provides a virtual digital frequency output, which is less susceptible to electrical noise and independent of the level and degradation of transmitted signals, offering good long-term stability. The frequency output is also compatible with digital interfacing and no analogue-to-digital conversion is required, therefore maintaining inherent high accuracy and low cost. The first successful metallic triple-beam tuning fork (TBTF) resonant sensor with thick-film drive/pickup elements [2, 3, 5] has a resonating 'tine' element length of 15.5mm and an overall sensor length of 23.5mm, a thickness of 0.25mm and beam widths of 1mm, 2mm and 1 mm. The gap between the beams was 0.5mm. However, this device is too large for current force/torque and pressure sensing applications. The challenge has been to reduce the sensor dimensional footprint and if possible enhance sensor performance.
A piezoelectric FPW-sensor has been developed for a point of care device in this work. The Bio- MEMS FPW-sensor consists of an electrode configuration termed as an interdigital transducer (IDT) placed on a membrane. An input IDT excites and an output IDT detects the propagating acoustic waves through a PZT layer. Design optimizations and fabrication improvements of the FPW-sensor led to significantly reduced attenuation of the wave signal and the damping of the propagating waves between the IDTs. The working principle of mass loading is shown using different low-viscous liquids. A densitydependent sensitivity of -0.39 MHz/g/cm³ was evaluated. After the membrane was functionalized, the Bio-MEMS FPW-sensor was used to measure a specific chemokine in complex solution. By design improvements, the resolution was significantly increased from 0.7 Hz/nM to 14 Hz/nM.
Point of Care devices for medical applications are becoming more and more widespread. The advantage of having test results after a very short period and without any laboratory creates is beneficial for doctors in developing countries far away from laboratory infrastructure to clinical devices disburdening in-house laboratories for example in case of an outbreak of an epidemic. Especially infectious diseases are one of the world's leading cause of morbidity and death [1]. Viral respiratory infections are a major cause of burden of disease in children. Annual human respiratory syncytial virus (RSV) related death are around 253.000, mainly in developing countries. It accounts for up to 6.7 % of mortality of children younger than 1 year. Therefore, RSV is the second most important global cause of death during infancy. Furthermore, RSV infection has been linked to an increased risk in the development of childhood wheezing and asthma in later life [2,3]. Fast and cheap diagnostic, independent from laboratory infrastructure, will have a high impact on the healthcare system. Highly sensitive microelectronic biosensors have a superior sensitivity and accuracy compared to paper stripes. The higher miniaturization potential and production stability accompanied by a better readout simplicity makes them a cheaper alternative to optical systems. In this paper a hybrid microelectronic-microfluidic packaging strategy for a disposable for two different microelectronic biosensor platforms will be presented, targeting the diagnostic of RSV. The multiplexed detection of both, host and pathogen biomarkers in the same sample will lead to a rapid, cheap and accurate diagnosis and prognosis, providing almost real-time results. Platform 1, the BioGrFET sensor uses a graphene field effect transistor (GrFET). The liquid sample containing the biomarkers flows over the sensor's surface with probe molecules, where the target molecules (specific biomarkers) of the fluid can be immobilized. The charge of the biomarker on the surface changes the charge carrier density inside the graphene which can be detected by measuring the graphene field effect transport characteristic. Platform 2, the BioMEMS sensor is a micro electro mechanical system (MEMS) having a very thin membrane carrying the active sensor structure, offering additional challenges to device packaging. The liquid sample, containing the biomarkers, flows over the membrane's surface with detection molecules, where the specific biomarkers of the fluid can be immobilized. With the specific biomarkers on the membrane's surface changes the mass and therefore the resonance frequency of the membrane which can be read out. Specific packaging challenge for both sensors is to develop packaging technology flows that allow to add the sensor functionalization during packaging and leaves this functionalization intact until the packaging processes are finalized, which implies a process selection with reduced thermal and mechanical load on the delicate functionalized sensors. This challenge has been ma...
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