Quasi-synchronous thermocompensation for ISFET-based ionometric devices. Part 1: Theory and simulation

Solid-state ion selective transducers, as an alternative to the traditional liquid electrolyte-filled glass electrodes, are known for over four decades now, and find their use in various areas of industry and applied science, such as in vivo analysis of the ions activity in biological and medical research, monitoring of toxic and aggressive environments, and biosensors design. However, along with potential advantages — short response time, small size, chemical inertness and durability — solid-state devices also possess certain inherent drawbacks — namely intrinsic noise, drift and instability of sensing properties, and cross-sensitivity to various interfering environmental conditions — that inhibit their widespread acceptance. Further improvement of the fabrication technology and methodology of application of these devices is thus still an important practical task even today. This paper is a first part of the two-part work dedicated to the problem of compensating the temperature dependence of a solid-state ion selective transducer output. Specifically, presented work considers the possibility of using ion-selective field-effect transistors (ISFET) that serve as primary transducers in an ionometric device, as temperature sensors. This allows compensating the temperature dependence of ionometric signal without substantial complication of the ionometer structure, and eliminates the need to include a separate thermometric channel as part of the instrument. Ionometric and thermometric channels are combined into a unified measuring path, with the sensor functions separated in time. The ISFET operation modes are switched by changing polarity of the bias voltage, and thus direction of the current flowing through the sensor. The authors propose a corresponding secondary transducer structure and simplified schematic illustrating the implementation of its key components. The concept’s applicability is supported by the circuit simulation results. Some aspects of the practical implementation of the proposed concept will be presented further in the upcoming second part of the paper.

Piezo-Optical Transducers in High Sensitive Strain Measurements

New piezo-optical sensors based on the piezo-optical effect for high sensitive mechanical stress measurements have been proposed and developed. The piezo-optical method provides the highest sensitivity to strains compared to sensors based on any other physical principles. Piezo-optical sensors use materials whose parameters practically not change under load or over time, therefore piezo-optical sensors are devoid of the disadvantages inherent in strain-resistive and piezoelectric sensors, such as hysteresis, parameters degradation with time, small dynamic range, low sensitivity to strains, and high sensitivity to overloads. Accurate numerical simulation and experimental investigations of the piezo-optical transducer output signal formation made it possible to optimize its design and show that the its gauge factor is two to three orders of magnitude higher than the gauge factors of sensors of other types. The cruciform shape of the transducer photoelastic element made it possible to significantly increase the stresses in its working area at a given external force. Combining compactness, reliability, resistance to overloads, linearity and high sensitivity, in terms of the all set of these parameters, piezo-optical sensors significantly surpass the currently widely used strain-resistive, piezoelectric and fiber-optic sensors and open up new, previously inaccessible, possibilities in the tasks of measuring power loads.

Development of an Integrated System for the Automatic Viscosity Correction of a Ceramic Slurry for the Investment Casting Process

Background: Starting from a wax model of the mold, which is later discarded, investment casting is used to make almost finished metal cast parts. The term "investment casting" is derived from the use of a ceramic liquid mixture (slurry), in which the model is repeatedly immersed (invested) to form, layer by layer, the shell which has to be filled with molten metal. The liquid of the slurry tends to evaporate so that the viscosity of the former increases and a correction is needed. Objective: The study aimed to investigate the simplest way to measure slurry viscosity and automatically correct it. Methods: Numerical and experimental tests have been implemented to correctly assess the proposed method. An integrated system for the automatic correction of slurry viscosity is realised which comprises: a reservoir of slurry including means for mixing it; a transducer which continuously measures the slurry viscosity; a pump that gradually feeds the diluent into the slurry to keep its viscosity constant; and a device, governed by the continuous viscosity measurement, that operates the pump. Results: It has been proved that the developed system is able to integrate the slurry viscosity continuous measurement with gradual addition of diluent into the slurry, so as to have a fully automated operation that can make corrections, whenever necessary, on the basis of the transducer output. Conclusion: The developed system works properly by keeping the slurry viscosity within a fixed range. A patent has been recently deposited to protect the integrated system for the automatic correction of slurry viscosity.

Experimental Studies of an Eddy Current Transducer with Spatially Periodic Fields

The purpose of this study is to perform a comparative analysis of the experimentally obtained and calculated values of the measuring windings total EMF amplitudes of the eddy current transducer with spatially periodic fields when magnetic and nonmagnetic cylindrical product are placed in it. To realize this goal in the work, a transducer with translational symmetry of excitation magnetic field has been developed. Translation symmetry typical example is the field of a long current conductor. The paper considers quasi-static electromagnetic field with the wavelength that exceeds characteristic transverse dimensions of conductor and cylinder. As the study result it is seen a satisfactory coincidence of the calculated and experimentally obtained values of the EMF of the transducer output signal in the cases of the product absence and with variety of products. As for example for measuring windings with angular coordinates φ = 30° and 60° an error of voltage values difference is less than 10%. The study shows that the advantage of such transducers while operating on one fixed frequency is capability to perform the multi-parameter testing on account of processing of certain amount of some spatial harmonics of excitation field.

New Devices for Measuring Forces on the Kayak Foot Bar and on the Seat During Flat-Water Kayak Paddling: A Technical Report

The purpose was to develop and validate portable force-measurement devices for recording push and pull forces applied by each foot to the foot bar of a kayak and the horizontal force at the seat. A foot plate on a single-point force transducer mounted on the kayak foot bar underneath each foot allowed the push and pull forces to be recorded. Two metal frames interconnected with 4 linear ball bearings, and a force transducer allowed recording of horizontal seat force. The foot-bar-force device was calibrated by loading each foot plate with weights in the push–pull direction perpendicular to the foot plate surface, while the seat-force device was calibrated to horizontal forces with and without weights on the seat. A strong linearity (r2 = .99–1.0) was found between transducer output signal and load force in the push and pull directions for both foot-bar transducers perpendicular to the foot plate and the seat-force-measuring device. Reliability of both devices was tested by means of a test–retest design. The coefficient of variation (CV) for foot-bar push and pull forces ranged from 0.1% to 1.1%, and the CV for the seat forces varied from 0.6% to 2.2%. The current study opens up a field for new investigations of the forces generated in the kayak and ways to optimize kayak-paddling performance.

Implementation of Silicon-on-Insulator (SOI) Control Electronics to Accelerometers for High Temperature Applications

The requirement to install control systems integrated with sensors in high temperature environments has posed a challenge to the traditional limit of 125°C for conventional electronics. There is a need to operate at temperatures of 200°C and above in restricted space for example in down-well, aero-engine or geothermal applications in combination with high pressures, vibrations and potentially corrosive environments. Piezo-electric accelerometers based on ferro-electric ceramics have been used in a wide range of applications for measuring vibrations, fluid flow and turbulence and are capable of operating as a transducer alone at temperatures up to 250°C, which has made them attractive in sensing applications for down-well drilling and aero-engine health and usage monitoring. However, the electronics traditionally used to carry out the signal conditioning and processing (e.g. charge to voltage conversion, filtering) has been limited to a qualification limit of 125°C, which results in a reduced sensitivity of the transducer output as the signal conditioning and processing cannot be performed close to the sensor. With the development of Silicon-On-Insulator (SOI) semiconductor technology, which can operate at temperatures of up to 250°C, many of the signal conditioning and processing operations can be carried out in-situ with the accelerometers to create a new generation of high temperature products. In addition, the integration of many of the functions that used to require discrete components into one SOI based device has led to further miniaturisation opportunities and a protection against obsolescence of specialist analogue devices. This paper will describe the migration of the traditional low temperature electronics to a high temperature SOI based ASIC device and the implementation of high temperature electronics packaging technology to instrumentation for piezo-electric accelerometers, leading to products that are suitable for high temperature monitoring in restricted spaces in down-well drilling and aero-engine applications.