A. Depari

Model and Experimental Characterization of the Dynamic Behavior of Low-Power Carbon Monoxide MOX Sensors Operated With Pulsed Temperature Profiles

Wireless sensor networks for home automation or environment monitoring require low-cost low-power sensors. Carbon monoxide (CO) metal-oxide (MOX) sensors could be suitable in terms of device cost, but they show some severe limits, such as the need to be heated, which means large power consumption and the need for complex and frequent calibration procedures, which increases the overall cost. This paper investigates the possibility to partially overcome these limits by a low-cost detection system based on a suitable commercial sensor (TGS 2442, Figaro, Inc.) and an ad hoc measurement technique exploiting specifically tailored temperature profiles. To this aim, the authors study the dynamic behavior of low-power CO MOX sensors operated with pulsed temperature profiles by means of two approaches: 1) sensor modeling and 2) experimental evaluation. To analyze how the sensor dynamic response changes as a function of the CO concentration, the authors individuate a temperature profile, which ensures satisfactory sensitivity to the target gas and very low power consumption. Moreover, some parameters describing the sensor response shape are selected, which prove to be significant in terms of both robustness to environmental conditions and calibration simplicity.

A CMOS Integrable Oscillator-Based Front End for High-Dynamic-Range Resistive Sensors

A new oscillating circuit is proposed to estimate the resistance and parallel parasitic capacitance of resistive chemical sensors. The circuit is able to reveal the resistance in a wide range (from tens of kiloohms to more than 100 GOmega) due to the adopted resistance-to-time technique. In addition, the parallel capacitance (up to 50 pF) can be estimated. The circuit, which does not need any initial calibration, is very simple and compact and is suitable to be integrated with a standard CMOS technology to obtain a low-cost and low-power device for a sensor array interface. Different kinds of post layout simulations concerning the CMOS integrated implementation have been conducted. Experimental results obtained using a discrete prototype board, both on passive components and on real sensors (metal-oxide sensors), have shown good linearity and reduced percentage error with respect to the theoretical expectations.

A New and Fast-Readout Interface for Resistive Chemical Sensors

The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of resistive values that the sensors can show. In addition, some sensors could have baseline resistive values up to tens of gigohms. To avoid the use of expensive picoammeters or the use of circuits adopting scaling factors, different solutions have recently been proposed, exploiting the resistance-to-time conversion (RTC) technique. They show good linearity and are suitable for the integration in a chip together with the elaboration unit, but they may require long measurement time (tens of seconds) if high resistance values need to be estimated. In addition, they may suffer the influence of a sensor parasitic capacitance, in parallel with the resistive component. In this paper, a new method is proposed to reduce the measuring time, keeping the advantages offered by the RTC approach and including a parasitic capacitance estimation feature. Particularly, an effective architecture, based on moving thresholds, has been proposed, simulated, and experimentally tested with commercial resistors (values between 1 M¿ and 100 G¿) and capacitors (values between 1 and 47 pF). Finally, a fast sensor transient, due to a rapid change in the heating power, has been acquired with the proposed instrument and compared with a similar transient analyzed with a classical RTC approach. This test has shown the applicability of the interface for solutions requiring detailed information of the sensor response, such as the characterization of new sensors (e.g., nanowires) or the behavior analysis during nonstandard thermal profiles.

A CCII-Based Low-Voltage Low-Power Read-Out Circuit for DC-Excited Resistive Gas Sensors

In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the read-out of DC-excited resistive gas sensors, based on Second Generation Current Conveyors (CCIIs). This low-cost fully integrable front-end is able to evaluate the resistive behavior of gas sensors, without any preliminary calibration, operating a Resistance to Time ( R-T) conversion and exciting the sensor with a DC voltage. Through the use of CCIIs, all the Current-Mode (CM) benefits in LV LP integrated architecture design are achieved. The developed interface, designed at transistor level, is able to operate with a low supply voltage (plusmn0.75 V), showing a low power consumption of about 700 muW, and, hence, it is suitable for portable applications. Both CADENCE simulations on the designed integrated solution and experimental results, achieved using a PCB prototype, have shown a linear characteristic and a good agreement with theoretical expectations, for more than four decades of resistive variation. Experimental measurements, conducted employing low cost commercial components (AD844 as CCII and Figaro TGS 2600 device as resistive gas sensor), have confirmed the good performances of the developed read-out circuit as resistive gas sensor interface.

USB sensor network for industrial applications

This work proposes a USB solution for sensor networking. First, a network architecture has been presented having as the primary objective its integration with an existing infrastructure: for this reason, a USB to Ethernet gateway has been introduced. Then, many aspects of industrial applications have been considered in order to realize a suitable solution: insulation problems and low-cost implementation has been tackled. Working prototypes of each network component have been defined and realized: host-gateway, insulator, and hub. Several commercial devices can be used as sensors. Finally, some experiments have been carried out: timing performances, network activities and power consumption have been tested.

A New Low-Cost Electronic System to Manage Resistive Sensors for Gas Detection

In this paper, a new electronic system for gas detection is presented. Particular attention is focused on electronic noses that employ several resistive sensors. New resistive sensors may have high value due to new substances (TiO2) or to low-cost fabrication process and, supposing to use these sensors together with traditional ones (SnO2), a novel instrument to manage high-value resistive sensors varying over a wide range, from kilohms to gigohms is required. The proposed hardware approach is a modular architecture which takes advantage from an improved resistance-to-period converter, where sensors are DC powered. Experimental results show a relative standard deviation below 0.01% and a relative displacement to the reference line less than 1% over six decades if commercial resistors are considered. A prototype has been realized to manage up to eight sensors, detect and estimate substance concentrations, and communicate results to the Internet.

Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor

Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10

Evaluation of Bluetooth Hands-Free profile for sensors applications in smartphone platforms

) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.

Transcranial magnetic stimulation distinguishes Alzheimer disease from frontotemporal dementia

Nowadays, the wide diffusion of smartphones has completely changed the interaction of people with the surroundings. In fact these devices are equipped with a large number of sensors, like GPS receiver, 3-axis accelerator, which can enrich the user experience, collecting data from the external environment. Moreover, additional sensors can be used to enlarge the set of data providing information usually not available in a smartphone, like biomedical data. Usually, Bluetooth is used to connect external sensors to smartphone. Several commercial solutions are already available on the market. Unfortunately, different types of smartphone require the use of dedicated external sensors, due to the different Bluetooth data profile supported by the different Operative System (iOS, Android). In this paper the Bluetooth Hands-Free profile has been evaluated to transmit sensor information to smartphone, since it is the only profile supported both by Android as well as iOS devices. A prototype of a photoplethysmographic sensor with Hands-Free interface has been realized and interfaced to commercial smartphone, showing the feasibility of this approach.

A complementary metal oxide semiconductor—integrable conditioning circuit for resistive chemical sensor management

Objective: To determine whether a transcranial magnetic stimulation (TMS) multiparadigm approach can be used to distinguish Alzheimer disease (AD) from frontotemporal dementia (FTD). Methods: Paired-pulse TMS was used to investigate short-interval intracortical inhibition (SICI) and facilitation (ICF), long-interval intracortical inhibition, and short-latency afferent inhibition (SAI) to measure the activity of different intracortical circuits in patients with AD, patients with FTD, and healthy controls (HC). The primary outcome measures were sensitivity and specificity of TMS measures, derived from receiver operating curve analysis. Results: A total of 175 participants met the inclusion criteria. We diagnosed 79 patients with AD, 64 patients with FTD, and 32 HC. We found that while patients with AD are characterized by a specific impairment of SAI, FTD shows a remarkable dysfunction of SICI-ICF intracortical circuits. With the use of the best indexes, TMS differentiated FTD from AD with a sensitivity of 91.8% and specificity of 88.6%, AD from HC with a sensitivity of 84.8% and specificity of 90.6%, and FTD from HC with a sensitivity of 90.2% and specificity of 78.1%. These results were confirmed in patients with mild disease. Conclusions: TMS is a noninvasive procedure that reliably distinguishes AD from FTD and HC and, if these findings are replicated in larger studies, could represent a useful additional diagnostic tool for clinical practice. Classification of evidence: This study provides Class III evidence that TMS measures can distinguish patients with AD from those with FTD.