Patent Description:
An example refers to an emitter for emitting radiations, e.g. a visible light emitter or infrared (IR) emitter or mid IR (MIR) emitter.

An example refers to a fluid sensor, such as gas sensor. The fluid sensor may include an emitter and a detector. The detector may be a photoacoustic sensor (PAS), a light sensor, an infrared (IR), and more in particular a MIR sensor.

Examples refer to an emitting method and a sensing method, e.g. for measuring the concentration of a fluid (e.g. a gas).

A fluid sensor (e.g., a gas sensor) may be used for detecting the quantity of a target fluid in a target environment. The fluid sensor may be, for example, a micro mechanical electric system (MEMS) device, and may imply the use of a microcontroller.

A fluid sensor may comprise an emitter for emitting radiations at a particular wavelength onto a target environment. The target environment is in general replenished with a target fluid, whose amount (or concentration) is to be measured. The radiations shall have a specific wavelength associated to the target fluid, to excite the molecules or atoms at their characteristic wavelength (e.g., wavelength of maximum absorption typical of a target gas). A detector, downstream to the target environment, is illightened by the radiations propagated through the target environment. At the detector, an electric signal indicative of the propagated radiations is measured. From the electric signal, the amount or concentration) of the target fluid in the target environment is obtained.

In some cases, the detector is a photoacoustic detector including a microphone. The microphone includes a microphone membrane which is either inside the target environment or is inside a sealed environment replenished with a reference fluid. In any case, pressure of the target fluid and/or reference fluid changes by virtue of the photoacoustic effect, i.e. by virtue of a change in pressure (inside the target environment or is inside the sealed environment), caused by the interaction of the radiation (at the specific wavelength) with the molecules of the target fluid and/or reference fluid. The change in pressure is an acoustic wave, which deforms the microphone membrane, causing the generation of an electric signal indicative of the acoustic wave. The acoustic wave is associated to the impinging radiation, which is in turn associated to the amount or concentration of the target fluid. Hence, by analyzing the electric signal generated by the microphone, it is possible to arrive at having information on the amount or concentration of the target fluid.

In other cases (e.g. for non-dispersive infrared, NDIR, sensors), the detector may be a thermal detector, and perform thermal measurements associated to the impinging radiation at the specific wavelength, also arriving at a measurement of the amount or concentration of the target fluid.

The emitter may include an electrical conductor, which dissipates electric power by Joule effect, irradiating the target environment with radiation at different wavelengths in accordance to the temperature reached at the conductor. The temperature of the conductor follows a law of the type <MAT>, i.e. the optical power of the emitted radiation is proportional to the temperature raised at the power of <NUM>. The wavelength is also in function of the temperature, even though not with the same law. It is possible to directly measure the temperature TCONDUCTOR of the conductor.

However, this is not an easy task: the temperature TCONDUCTOR of the conductor can easily be larger than <NUM>, which is not a temperature easily measured or directly controlled (in particular for a MEMS device). Moreover, the transducers that transduce the temperature TCONDUCTOR of the conductor may output voltages which are not easily managed by a microcontroller. This in general requires the use of Zener diodes for saving the microcontroller and static converters (e.g. direct-current/direct-current, DC/DC converters) for reducing the voltages are regularly used.

Techniques for reducing the equipment are therefore pursued.

In addition, there are some issue in the measurements as performed by the detector. In some implementations, the emitter does not send radiations continuously, but in periodic fashion (impulse train). For example, the emissions may follow a squared signal, such that "hot" periods (where the Joule effect causes the temperature to arrive at the temperature necessary for emitting the radiation at a specific wavelength) are alternate to "cold" periods (where not power is provided to the conductor, i.e. no Joule effect is present, and the temperature of the conductor decreases).

However, it has been noted that in this way the measurements are suboptimal. The measurements obtained from the electric signal (e.g., as obtained by the microphone or as subsequently processed) are notwithstanding affected by errors due to thermal phenomena, which render the measurement difficult to be obtained. For example, thermoacoustic waves may be generated, which transfer unwanted heat, which notwithstanding arrives to the detector and introduces errors in the detection.

Techniques for reducing the errors due to thermal phenomena are also pursued.

In particular, it would be preferred to have an emitter which generates radiations without unwanted dependencies on the voltage and on the ambient temperature.

<CIT> discloses a gas sensor and a method for controlling it. Different duty cycles are defined for having a variable light source output. <CIT> relates to an infrared spectrophotometer comprising an electric heater as an infrared light emission source. <CIT> relates to the field of modulated sources for optical sensors to measure the chemical composition in fluids.

In accordance to an aspect, there is disclosed an emitter for emitting radiations at a specific wavelength, according to appended independent claim <NUM>, comprising inter alia and as further defined with claim <NUM>,.

It is not necessary to have a sensor directly measuring the temperature of the Joule-heated emitting electrical conductor.

Hence, negative effects of the change of the ambient temperature are circumvented.

The controller may define, for at least one hot or cold period, the duty cycle in dependency of:
the at least one temperature-indicative measured value, so that a high ambient temperature is compensated by a low high-average power duty cycle, and vice versa.

The controller may define, for at least one hot or cold period, the duty cycle also in dependency of:
at least one voltage-indicative measured value indicative of the voltage which is applied to the Joule-heated emitting electrical conductor as measured, so that a high voltage is compensated by a small duty cycle, and vice versa.

Hence, the variations in the voltage at the Joule-heated emitting electrical conductor are compensated.

In accordance to an example, the controller (<NUM>) may be configured to define, for at least one cold period, the low-average power duty cycle as the duty cycle causing a decrement of electrical power with respect to the high-average power, wherein the decrement is constant irrespective of the ambient temperature.

Accordingly, the sensed value is more reliable and negative effects of thermoacoustic phenomena are compensated.

During an initialization procedure, the controller may be configured to control a variable voltage subjected to the Joule-heated emitting electrical conductor and modulated according to a duty cycle, the duty cycle being variable between:.

This may permit to also compensate for negative thermoacoustic phenomena.

There is provided a sensor for determining characteristics of a fluid, comprising:.

The sensor may operate according to an initialization procedure which provides multiple emissions and detections, through the detector, for different known amounts of fluid, so as to individuate a detection law mapping amounts of fluid onto reading units to be converted into amounts of fluids, wherein the sensor is configured, in operation, to define the low-average power duty cycle in such a way that the decrement between the high-average power and the low-average power is the same of the decrement between the high-average power and the low-average power experienced during the initialization procedure.

According to another aspect of the invention, there is provided a method for emitting radiations at a specific wavelength according to appended independent claim <NUM>, comprising inter alia and as further defined with claim <NUM>,.

There is provided a sensing method for determining characteristics of a fluid, comprising:.

In accordance to an aspect, there is provided a non-transitory storage unit storing instructions to cause the device of claim <NUM> to execute the steps of the method of claim <NUM>.

Throughout the description, reference is prevalently made to "gas", even though it is intended that it is valid for a fluid.

<FIG> shows a schematized example of fluid sensor <NUM>. The sensor <NUM> may include an emitter <NUM> (e.g., optical emitter, light emitter, IR emitter, etc.) and a detector <NUM> (e.g., optical detector, light detector, IR detector, etc.). The sensor <NUM> may be, for example, a non-dispersive infrared (NDIR) sensor or a photoacoustical sensor (PAS). The sensor <NUM>, the emitter <NUM>, and the detector <NUM> may be MEMS devices.

The emitter <NUM> may emit a radiation <NUM> at a specific wavelength λ<NUM> (which may be chosen to be, for example, the characteristic wavelength of a particular fluid to be measured). The radiation <NUM> may be or include light. The radiation <NUM> may be or include infrared (IR) radiation (e.g. MIR radiation). The radiation <NUM> may include laser radiation. The radiation <NUM> may be at a specific wavelength λ<NUM>, in the sense that it is at a narrow band, which includes the particular wavelength λ<NUM>. The narrowband may be approximated to an interval [λ<NUM>-δ λ, λ<NUM>+δλ], with δλ a small incremental wavelength.

The sensor <NUM> may include a detector <NUM> which receives radiation <NUM> emitted by the emitter <NUM>. The detector <NUM> may be, for example, a light intensity detector or a photoacoustical detector. If the detector <NUM> is a photoacoustical detector, it includes a microphone which transduces variations of pressure (acoustic waves, sound) onto electrical signals.

An optical filter <NUM> may be interposed between the emitter <NUM> and the detector <NUM>. The optical filter <NUM> may include a photonic crystal structure. In alternative, the optical filter <NUM> may be a Fabry-Perot filter. The optical filter <NUM> may be understood as a wavelength selective structure providing the radiation <NUM> in an even more restricted narrow band, still containing the specific wavelength λ<NUM>. , the band becomes [λ<NUM>-dλ, λ<NUM>+dλ] with dλ << δλ. It is noted that the optical filter <NUM> may be considered a part of the emitter <NUM> even though it is explicitly shown in the schematization of <FIG> for clarity.

Accordingly, an optical path <NUM>, <NUM> is defined between the emitter <NUM> and the detector <NUM>. In the optical path <NUM>, <NUM>, the radiation <NUM> passes through a target volume <NUM> (target environment) in which a target gas (or more in general a target fluid) is present. The target gas absorbs and emits photons at a specific wavelength (each gas being characterized by a specific wavelength, which is the wavelength <NUM> or <NUM> which is intended to be transmitted by the emitter <NUM>). Accordingly, the radiation <NUM>, after having propagated through the target volume <NUM> (and after having excited the molecules or atoms of a specific gas of which it is intended to measure the amount or concentration), is used for determining the properties of the fluid, e.g. by measuring its quantity or concentration of the gas. In particular, electrical signals may be processed at the decoder, the electrical signal being indicative of the radiation reaching the detector <NUM>.

In some examples, the detector <NUM> is enclosed in a sealed volume in which a reference gas is present, hence permitting to measure the quantity or concentration of the target gas placed (in the target volume <NUM>) outside the closed volume. In other examples, the target gas directly arrives inside the detector <NUM>, and its amount or concentration is directly measured by the detector <NUM>.

Another schematic drawing of sensor <NUM> (which may the same of <FIG>) is shown in <FIG> (reference can also be made to <FIG>). The sensor <NUM> includes a Joule-heated emitting electrical conductor (heater) <NUM>. The joule-heated emitting electrical conductor <NUM> may be of the type having a suspended heating membrane anchored to sustaining elements. The heating membrane may be heated by Joule effect. By virtue of its temperature, the joule-heated emitting electrical conductor <NUM> generates radiations according to the Planck's law (the hotter the heater <NUM>, the smaller the wavelength λ<NUM>).

The Joule-heated emitting electrical conductor (heater) <NUM> may be heated by Joule effect at a temperature that causes the emission of the radiation <NUM> at the wavelength λ<NUM> (or its filtered version <NUM>, the optical filter <NUM> not being shown). After having propagated through the target volume 204a (which is replenished of target gas to be measured) the optical radiation reaches a sealed volume (e.g. PAS volume) 204b. The sealed volume 204b contains a fixed known amount of a reference gas. The radiation excites the molecules or atoms of the target gas in the target volume 204a and the reference gas in the sealed volume 204b. Radiation <NUM> passes through a transparent window <NUM> and the sealed volume 204b, and causes a modification of the temperature within the sealed volume 204b, which in turn modifies the pressure and causes a membrane <NUM> of a microphone <NUM> to be deformed accordingly. An electric signal <NUM> may therefore be generated. The electric signal <NUM> may provide information regarding the amount or concentration of the target gas in the target volume 204a.

The PAS detector may be substituted by a detector which directly converts the radiation entering through the window <NUM> into an electrical signal and in that case, there would be no microphone <NUM> and no membrane <NUM>, but in any case, an electric signal indicative of the quantity of the target gas would be notwithstanding obtained. It is also to be noted that, in any case, it is not necessary that the volume of the detector <NUM> is closed, but it is also possible to have an open volume sensor, without reference gas inserted in a closed volume.

As can be seen from <FIG>, the Joule-heated emitted electrical conductor <NUM> may be structurally and constructively made so that:.

It is noted that, following the Planck's law, at the sub-emission temperature TCOLD some negligible emission at the wavelength λ<NUM> could notwithstanding be caused. For example, the radiation intensity may be reduced to less than <NUM>% or even less than <NUM>% or less than <NUM>% at the sub-emission temperature TCOLD. Here, when referring to the sub-emission temperature, it is imagined that the amount of emission at the wavelength λ<NUM> is negligible and is approximated to <NUM>. Notably, when referring to sub-emission temperature (TCOLD), reference can be made to a range of sub-emission temperatures (e.g. TAMBIENT ≤ TCOLD ≤ TCOLD,MAX < THOT).

It is also to be noted that the sub-emission temperature TCOLD is not necessarily one single pre-defined temperature value. A range of sub-emission temperatures may therefore be defined (i.e., the range of temperatures at which the radiation at the wavelength λ<NUM> is not generated or is negligible). Therefore, in subsequent passages, reference is prevalently made to "a sub-emission temperature" to indicate that the sub-emission temperature is not necessarily at one single temperature value.

To the contrary, as will be shown below, the emission temperature THOT (which, for a particular gas, may be ideally one single value) can be controlled with high accuracy by relying on techniques discussed below. Therefore, in subsequent passages, reference is prevalently made to "the emission temperature THOT", in the sense that it is intended to reach a particular emission temperature value.

In particular, emission at the Joule-heated emitting electrical conductor <NUM> may be controlled so that:.

The variable voltage vDD (see also <FIG> and <FIG>) at the Joule-heated emitting electrical conductor <NUM> is here also indicated as a signal <NUM>. The signal <NUM> may be the understood as combining the effects of the following two signals:.

The signals <NUM> and <NUM> may be understood as PWM signals, and the resulting signal <NUM> may understood as the combination of the modulations of the two PWM signals <NUM> and <NUM>. An impulse train is therefore generated. As it will be explained later, the signals <NUM> and <NUM>, modulated one inside another, cause the Joule-heated electrical conductor <NUM> to operate according to two different modes:.

As will be shown later, the HF signal <NUM> is responsible for reaching and maintaining the emission temperature THOT during the hot periods and to be maintained at a sub-emission temperature (smaller than the emission temperature THOT) during the cold periods. The LF signal <NUM> is responsible for timing the alternation of the hot periods with the cold periods.

In some examples, the LF signal <NUM> may be a two-state periodic signal divided into two semi-periods, each semi-period having the time length of one half of the period of signal <NUM>. <FIG> shows that a period <NUM> of the LF signal <NUM> is being divided into two semi-periods <NUM> (i.e. hot periods) and 472c (i.e. the cold periods). It is to be noted, however, that it is not necessary that the period <NUM> is exactly divided into two semi-periods of equal length, but different subdivisions are possible. In general terms, it may be understood that the period <NUM> is subdivided among hot sub-periods <NUM> (i.e. the hot periods) and cold sub-periods 472c (i.e. the cold periods), with reciprocal lengths which are variable according to the particular implementation.

The LF signal <NUM> may have a frequency between <NUM> and <NUM> or <NUM> (e.g., <NUM>). This frequency is appropriated for permitting the transmission of pulses of radiations at the specific wavelength λ<NUM> (during the hot periods) alternated to the absence (during the cold periods) of radiations at the wavelength λ<NUM>. The frequency range between <NUM> and <NUM> or <NUM> is particularly appropriated for permitting an effective detection at the detector <NUM> (e.g., when the detector <NUM> is a photoacoustic detector, the microphone <NUM> may reliably detect sound in the range between <NUM> and <NUM> or <NUM>).

The HF signal <NUM> may be understood, for example, as a digitally controlled PWM, which modulates the voltage of the Joule-heated emitting electrical conductor <NUM> between:.

The PWM of the HF signal <NUM> has a high duty-cycle in the hot periods <NUM> (thus providing high average power to the Joule-heated emitting electrical conductor <NUM>), and a low duty-cycle in the cold periods 472c, so as to reduce the average power provided to the Joule-heated emitting electrical conductor <NUM>. The duty cycle for a PWM is in general an adimensional, positive number (or a percentage) comprised between <NUM> and <NUM> (or <NUM>% and <NUM>%). The duty cycle indicates the relative proportions between the time length of the high voltage value and the time length of the <NUM> voltage or low voltage value in a particular whole period: e.g., if the duty cycle is <NUM>, the high voltage value is never achieved; if the duty cycle is <NUM> (or <NUM>%), the high voltage value is continuously applied; if the duty cycle is <NUM> (or <NUM>%), both the high voltage value and the <NUM> voltage or low voltage value are alternated for the same time length, and the average voltage applied to the heater <NUM> is VDD/<NUM>. In this case, however, the high duty-cycle in the hot periods <NUM> is defined so as to reach the emission temperature.

<FIG> shows an example <NUM> of an emitter (e.g. the emitter of <FIG> and/or 1b). The emitter <NUM> includes the Joule-heated emitting electrical conductor (heater) <NUM> as the element generating the radiation <NUM> under the effect of a variable voltage vDD. The voltage vDD (signal <NUM>) may be fed to terminals <NUM> and <NUM> of the Joule-heated emitting electrical conductor <NUM> under a control <NUM> exerted by a controller <NUM>. The terminals <NUM> and <NUM> may be connected to conductor lines <NUM> and <NUM>, respectively. Line <NUM> may be imagined as at mass, and line <NUM> may be fed by a constant potential VDD > <NUM> (or lines <NUM> and <NUM> are simply at different polarities or potentials). A switch <NUM> may separate a proximal branch 208b (at the constant potential VDD > <NUM>) and a distal branch 208a (connected to the terminal <NUM>), hence causing the alternance between VDD and <NUM>. The variable voltage vDD may be provided to the Joule-heated emitting electrical conductor <NUM> as pulses of fixed voltage amplitude VDD controlled by the switch <NUM> controlled by the controller <NUM>. (In alternative embodiments, different solutions can be used. In some cases, the variable voltage vDD could be directly provided by the controller <NUM>). The switch <NUM> may be, for example, a metal-oxide-semiconductor field-effect transistor, MOSFET, and the control <NUM> may be connected to the gate of the MOSFET, while the terminals associated to the switch <NUM> may be the source and the drain of the MOSFET (one of the source and the drain being connected to the distal branch 208a, and the other one being connected to the proximal branch <NUM>).

The control <NUM> may be understood as controlling the PWMs of the signals <NUM> and <NUM>. The controller <NUM> may include or be connected in input to a timer <NUM>, which provides a timing signal <NUM>' controlling the LF signal <NUM>: the timing signal <NUM>' may control the transitioning from a hot period to a cold period and vice versa. The timer <NUM> may be or include a phased locked loop, PLL, circuit and/or may be fed by an external clock input (not shown).

The emitter <NUM> may include, or be connected in input to, a voltage sensor <NUM> (which, in <FIG> is shown as an internal to the controller <NUM>, but it can also be an external component). The voltage sensor <NUM> may be connected to the lines <NUM> and <NUM> (e.g. the branch 208a and the line <NUM>) which feed the terminals <NUM> and <NUM> of the Joule-heated emitting electrical conductor <NUM> (in particular, when the switch <NUM> is present, the portion of terminal <NUM>, is placed downstream to the switch <NUM>). In examples, the voltage sensor <NUM> may be connected to only one of the two conductor lines <NUM> and <NUM> (e.g., when the line <NUM> is already connected to the mass, it may be not necessary to also connect the voltage sensor <NUM> directly to the conductor line <NUM>, by virtue that also the voltage sensor <NUM> may be connected to the mass). In examples, the voltage sensor <NUM> may be substituted by another electric sensor (e.g., current sensor) which provides a measurement associated to the voltage. In any case, the voltage sensor <NUM> provides at least a voltage-indicative measured value <NUM>', which gives information on the actual voltage experienced by the Joule-heated emitting electrical conductor <NUM>. The voltage-indicative measured value <NUM>' may be in the digital domain, for example. It has been noted that, even with the extremely precise control of the variable voltage vDD and/or of the switch <NUM>, some unwanted variations of voltage can, notwithstanding, appear. Therefore, by sensing the voltage vDD actually provided to the Joule-heated emitting electrical conductor <NUM>, it is possible to obtain a more efficient control.

It has been understood that it is not necessary to measure the input voltage VDD in real time. It is possible to measure the input voltage VDD before subjecting the Joule-heated emitting electrical conductor <NUM> with the variable voltage vDD.

The emitter <NUM> may include a temperature sensor <NUM> (which, in this case, is shown as being part of the controller <NUM>, but can also be provided as a separate element). The temperature sensor <NUM> may provide a temperature-indicative measured value <NUM>' (e.g. in the digital domain), which is indicative of the ambient temperature TAMBIENT.

It has been understood that the ambient temperature TAMBIENT may be measured as the initial temperature of the Joule-heated emitting electrical conductor <NUM> when the Joule-heated emitting electrical conductor <NUM> is in thermal equilibrium with the environment. Therefore, the ambient temperature TAMBIENT may be simply obtained by measuring the temperature of the Joule-heated emitting electrical conductor <NUM> before the start of subjecting the Joule-heated emitting electrical conductor <NUM> with the variable voltage vDD. Hence, the measurement of the ambient temperature TAMBIENT does not require the presence of an additional temperature sensor which somehow "senses the environment temperature". Rather, the temperature sensor <NUM> may simply be applied directly to the Joule-heated emitting electrical conductor <NUM>. It is may be simply provided that the Joule-heated emitting electrical conductor <NUM> is switched off for a pre-defined amount of time which sufficient to reach the thermal equilibrium with the environment. Basically, the reading of the temperature-indicative measured value <NUM>' may temporally precede the process of subjecting the heater <NUM> with the variable voltage and the consequent process of emitting the radiations at the wavelength λ<NUM>. Notably, instead to TAMBIENT, reference could simply be made to TCONDUCTOR,INITIAL.

The controller <NUM> may include a PWM controller (duty-cycle definer) <NUM>, which may be input by any of the voltage-indicative measured value <NUM>', temperature-indicative measured value <NUM>', and a timing signal <NUM>'. Accordingly, the controller <NUM> may define the duty-cycle for the hot periods and the duty-cycle for the cold periods, and determine the transitions between the hot periods and the cold periods (and vice versa), by exerting the control <NUM> (on the basis of at least one of the timing signal <NUM>', voltage-indicative measured value <NUM>' and temperature-indicative measured value <NUM>'), according to the specific implementation for the voltage control.

It is to be noted, however, that the control <NUM> is not necessarily established in real time: simply, the input voltage VDD and the ambient temperature TAMBIENT may be measured before starting to feed the Joule-heated emitting electrical conductor <NUM> with the variable voltage vDD. Hence, before starting the impulse train, the high duty-cycle and the low duty-cycle are defined and do not change during the emission.

In some examples, the voltage is controlled in real time.

The controller <NUM> may have a chip structure, and all or at least part of its elements may be provided inside of one single structure (e.g. a package structure). At least one of the timer <NUM>, voltage sensor <NUM>, and temperature sensor <NUM> may be internal to the chip structure or external to it.

The controller <NUM> may also be the element that controls the operations of the detector <NUM> and, more in general, the operations of the sensor <NUM>. The controller <NUM> may include a PWM controller <NUM>, which is here shown as driving the control <NUM>.

<FIG> shows, in scheme (a), a graph showing the variable voltage vDD (signal <NUM>) in time. Scheme (b) is a magnified scheme of portion <NUM>.

As can be seen, the variable voltage vDD is defined, according to a variable duty cycle, as being between the value <NUM> (or another low-voltage value) and VDD.

Scheme (a) shows a sequence, having period <NUM>, of the LF signal <NUM>. Each period <NUM> is, in turn, subdivided into different sub-periods:.

(As explained above, <FIG> shows the sub-periods <NUM> and 472c being two semi-periods of exactly same length, but this is not general, and different lengths and different subdivisions are possible).

The subdivision of the LF signal <NUM> in consecutive periods <NUM> may be controlled, for example, by the timing signal <NUM>' e.g. based on the timer <NUM>.

As can be seen from scheme (a) of <FIG>, the hot periods <NUM> and the cold periods 472c are characterized by different duty cycles: while in the hot periods <NUM> the duty cycle is high, in the cold periods 472c the duty cycle is low.

Accordingly, in the hot periods <NUM>, a high-average power is provided to the electrical conductor <NUM>, while a low average power (greater than <NUM>) is provided to the electrical conductor <NUM> in the cold periods 472c. The duty cycle in the hot periods <NUM> causes the temperature of the Joule-heated emitting electrical conductor <NUM> to reach the emission temperature at which the radiation at the intended wavelength λ<NUM> is generated. On the other side, it has been understood that also the low average power may be defined in such a way to reach a constant decrement of the average power in the cold periods 472c with respect to the average power in the hot periods <NUM> (the constant decrement does not change with the ambient temperature).

Scheme (b) of <FIG> shows the duty cycle during a hot period <NUM>. (An analogous graph would be obtained for the cold periods 472c, apart from the fact that the reciprocal lengths of the slots would be different). As shown in scheme (b), the variable voltage vDD may take, during high voltage slots <NUM>, the high voltage value VDD, while for low voltage slots <NUM>/the variable voltage vDD may take the value <NUM> (or another low voltage value). The relative length of the slots <NUM> and <NUM>ℓ is determined by the duty cycle (e.g. as defined by the PWM controller <NUM>). The duty cycle is based on a timeperiod indicated with <NUM>, which is much smaller than the thermal time constant τthermal. Scheme (b) of <FIG> shows a more elongated extension of the high voltage slot <NUM> with respect to the low voltage slot <NUM>ℓ, and this is expectable as scheme (b) relates to a hot period <NUM>. In the cold period 472c, the length of slot <NUM> would be much shorter and the length of the slot 474ℓ would be much longer.

As explained above, the duty cycle may be defined by the controller <NUM> (and in particular by the PWM controller <NUM>) on the basis of at least one of the voltage-indicative measured value <NUM>' and the temperature-indicative measured value <NUM>'. The time variation <NUM> of the high voltage slots <NUM> may be modified, for example, in accordance to the particular voltage control that is implemented.

<FIG> shows an example scheme of the sensor <NUM> with simplified operational blocks (which may be understood as both, elements of the sensor <NUM> and as method steps). At the side of the emitter <NUM>, a duty cycle calculation block <NUM> (which may be understood as corresponding to the PWM controller <NUM>), may have, in input, the voltage-indicative measured value <NUM>' ( <MAT>) and the temperature-indicative measured value <NUM>' ( <MAT>). The PWM controller <NUM> may output a control <NUM> (intended for controlling the signal <NUM>) for subjecting the Joule-heated emitting electrical conductor <NUM> to the variable voltage vDD.

At the detector <NUM>, a gas (or fluid) measurement block <NUM> may be provided. When the detector <NUM> is obtained based on the photoacoustic sensing (e.g. it comprises the microphone <NUM>), a vibration of the membrane is caused converted into an electric signal <NUM>. The signal <NUM>, in its original analog version of in a digital version, may be provided to an output calculation block <NUM>.

The final measured value <NUM> (e.g. concentration and/or quantity of the fluid) may be output (e.g. provided to a display peripheral or otherwise signaled to a user, and/or transmitted or stored in a storage memory, such as a flash memory or a register) by the output calculation block <NUM> as a final measurement value (or more in general, as characteristic of the fluid).

The emitter <NUM> (and the sensor <NUM>, as well) may have, at block <NUM>, the knowledge of a relationship between the electric signal <NUM> and the real amount of the gas (or fluid), e.g. in ppm (parts per million). An example in provided in graph (a) of <FIG>, showing in ordinate a reading unit u (obtained from the signal <NUM>) and in abscissa the real ppm amount of gas (to be output as value <NUM>). It has been understood that the real amount of gas and the signal <NUM> (value u) are bound to each other through a linear function (linear detection law), which is shown in graph (a) in terms of u = u(ppm) + u(<NUM>), where u(ppm) is the expected measurement (proportional to the gas amount), and u(<NUM>) is an unwanted offset associated to the temperature.

The slope of the linear function u = u(ppm) + u(<NUM>) is associated to the ambient temperature: hence, different ambient temperatures will in principle cause different functions with different slopes. This result can be seen by comparing, in <FIG>, graph (a) (TAMBIENT=<NUM>) and graph (b) (TAMBIENT=<NUM>). Hence, in principle, a signal <NUM> as collected by the sensor <NUM>, could result in an incorrect measurement.

Graph (a) also shows an offset u(<NUM>) in the linear function. Also in this case, the offset may in principle vary in different measurements. Besides the intended irradiation at the specific wavelength λ<NUM>, other unwanted thermal phenomena (e.g. thermoacoustic waves) have been observed. These unwanted phenomena may in principle change the offset u(<NUM>), thus causing a different reading at block <NUM> and a misrepresentation of the amount of gas.

However, the present techniques permit to cope with these inconvenients. Here below an exhaustive explanation is provided.

In general terms, the temperature of the conductor <NUM> (heater) is TCONDUCTOR = TAMBIENT + ΔT (which, in the hot periods <NUM>, becomes THOT = TAMBIENT + ΔTHOT), where ΔT is the increment of temperature due to the electric power Pel provided to the Joule-heated emitting electrical conductor <NUM>. The general formula TCONDUCTOR = TAMBIENT + ΔT becomes THOT = TAMBIENT + ΔTHOT in the hot periods <NUM>, and TCOLD = TAMBIENT + ΔTCOLD in the cold periods (notably, TCOLD is not necessarily pre-defined, and simply needs to be a sub-emission temperature which generates a null or negligible amount of radiation at the wavelength λ<NUM>). If TAMBIENT = <NUM> and the emission temperature required for emitting radiation at a specific wavelength λ<NUM> is THOT = <NUM>, then during a generic hot period <NUM> the electric power Pel,HOT shall provide an increment of temperature which is ΔTHOT = THOT - TAMBIENT = <NUM> - <NUM> = <NUM>.

During a generic hot period <NUM>, the electric average power Pel,HOT is conditioned by the high-average power duty cycle DHOT (e.g., the length of the slot <NUM> divided by the length of timeperiod), and may be the average of the power along the length of timeperiod <NUM>. In practice, the electric power Pel,HOT may be expressed as an average power expressed by <MAT> where Vdd is the high voltage value provided to the terminals <NUM> and <NUM> of the Joule-heated emitting electrical conductor <NUM>, and Rel,HOT is the electrical resistance [Ω] of the Joule-heated emitting electrical conductor <NUM> (the electrical resistance Rel in general varies with the temperature, and this may be mirrored by assuming that the resistance in the hot periods is different from the resistance in the cold periods, i.e. Rel,HOT ≠ Rel,COLD).

It has indeed been noted that, in general, the increment in temperature ΔT is proportional to the average power Pel for a proportionality coefficient which is the thermal resistance <MAT>, which is the same of <MAT>. This provides <MAT> (with D generic duty cycle, Rth generic thermal resistance, Rel generic electrical resistance, Vdd constant high-voltage value) which, in a generic hot period <NUM>, becomes ΔTHOT = Rth,HOT · <MAT>.

Putting together the results above, it follows that the temperature of the Joule-heated emitting electrical conductor <NUM> obeys to the rule: <MAT> which, in the generic hot period <NUM>, becomes <MAT>.

One could imagine that, in order to define the high-average power duty cycle DHOT, the temperature of the Joule-heated emitting electrical conductor <NUM> should be sensed in real time. However, it has been understood that this is not necessary.

In fact, it has been understood that, instead of the temperature of the Joule-heated emitting electrical conductor <NUM>, it is possible to detect the ambient temperature <MAT> (or another temperature-indicative measured value <NUM>') and the actual voltage <MAT> (or another voltage-indicative measured value <NUM>') which is experienced at the terminals <NUM> and <NUM> of the Joule-heated emitting electrical conductor <NUM>. It has been understood that, from THOT = <MAT>, the duty cycle DHOT can be easily obtained.

The controller <NUM> (and in particular the duty-cycle definer <NUM>) may therefore calculate DHOT, so as to provide to the Joule-heated emitting electrical conductor <NUM> with the power necessary for emitting, during the hot periods <NUM>, the radiation at the wavelength λ<NUM>.

Hence, in the hot periods <NUM>, the high-average power duty cycle DHOT may be controlled on the basis of the required emission temperature THOT, at least one voltage-indicative measured value (<NUM>') and at least one temperature-indicative measured value (<NUM>') as acquired measurements, so as to define the duty cycle necessary to reach maintain the emission temperature.

As explained below, in examples the at least one voltage-indicative measured value (<NUM>') and at least one temperature-indicative measured value (<NUM>') may be obtained before start of the provision of the voltage to the Joule-heated emitting electrical conductor <NUM>, and the value of the high-average power duty cycle DHOT may therefore be calculated in advance, and maintained subsequently, without further adjustments in real time. Hence, for a complete session of measurements, DHOT may remain constant.

Therefore, during the hot periods <NUM>, a compensation of the ambient temperature TAMBIENT may be performed: irrespective of the value of TAMBIENT, the intended emission temperature THOT will be reached and maintained. Analogously, a compensation of VDD may be performed: the intended emission temperature THOT will be reached and maintained.

During the cold periods 472c, radiation at the wavelength λ<NUM> is not to be emitted by the Joule-heated emitting electrical conductor <NUM> (or at least should be emitted in a negligible amount). Hence, in the cold periods 472c the duty cycle DCOLD shall be reduced, so as to reduce the average power (Pel,COLD) provided to the Joule-heated emitting electrical conductor <NUM>, to reduce the temperature and ideally up to avoid the emission.

It has been understood that it is preferable, during the cold periods 472c, to continue to feed the Joule-heated emitting electrical conductor <NUM> with an amount of low-average power Pel,COLD having an offset (decrement) ΔPel, in respect to the high-average power Pel,HOT, which is constant for all the measurements and does not change in respect to the ambient temperature. Hence, during the cold periods 472c: <MAT>.

In accordance with examples of the present technique, the constant ΔPel may be defined for example during an initialization (calibration) process <NUM> (discussed below) and is not meant at changing. It has been noted, in fact, that by keeping always the same constant decrement ΔPel, the offset u(<NUM>) in <FIG> does not change for different measurements, even if taken at different ambient temperatures. Accordingly, during the cold periods 472c the heat transfer caused by the thermoacoustic waves is compensated.

Accordingly, the decrement of power ΔPel in the cold periods in response to the hot periods is fixed. This effect pre-compensates a possible offset in reading the u(<NUM>), which is accordingly known and does not need to be compensated a posteriori.

It is now explained how to define the low-average power duty cycle DCOLD to be used in the cold periods 472c. Most of the explanations follow those carried out for the hot periods (see above).

During a generic cold period 472c, the electric low average power Pel,COLD is conditioned by the low-average power duty cycle DCOLD. The electric power Pel,COLD may be expressed as an average power expressed by <MAT> where Vdd is the (constant) high voltage value provided to the terminals <NUM> and <NUM> of the Joule-heated emitting electrical conductor <NUM> in the cold periods <NUM>, and Rel,COLD is the electrical resistance of the Joule-heated emitting electrical conductor <NUM> at a sub-emission temperature.

Putting together the results above, it follows that the temperature in the cold periods 472c is <MAT> may vary during a generic cold period, since we are not necessarily interested in having a constant TCOLD.

As explained below, in examples the at least one voltage-indicative measured value (<NUM>') and at least one temperature-indicative measured value (<NUM>') may be obtained before start of the provision of the voltage to the Joule-heated emitting electrical conductor <NUM>, and the value of the low-average power duty cycle DCOLD may therefore be calculated in advance (e.g. together with the calculation of the high-average power duty cycle DHOT), and maintained subsequently, without further adjustments in real time. Hence, for a complete session of measurements, DCOLD may remain constant.

In the cold periods we have not interest in reaching a particular temperature, but we simply need to avoid (or render negligible) the emission at the specific wavelength λ<NUM>. However, as it will be explained later, notwithstanding a control may be performed so that the decrement ΔPel of the power from the hot periods to the cold periods remains constant, irrespective of the ambient temperature and/or the input voltage VDD.

<FIG> shows method <NUM> for explaining a way according to which the emitter <NUM> may operate (the operations specific of the detector <NUM> are not shown).

At step <NUM> an original initialization is performed. Subsequently, measurement operations are performed at <NUM> (iteration <NUM> refers to the fact that multiple measurements may rely on the same initialization <NUM>).

During the initialization <NUM>, the emitter <NUM> (and the sensor <NUM> in general) operates as above (e.g. by generating impulse trains according the duty cycles as above and emitting radiations in hot periods and cold periods as above). Any of the operations <NUM>-<NUM> (discussed below) may therefore be performed during the initialization <NUM>. It is only requested that multiple known amounts of fluid are measured at the same ambient temperature and at the same constant decrement ΔPel is used between the hot periods and cold periods. At the end of the initialization <NUM>, a linear detection law (e.g., such as in graph (a) of <FIG>) may be obtained for the particular ambient temperature.

For example, during the initialization <NUM>, the controller <NUM> may control a variable voltage subjected to the Joule-heated emitting electrical conductor <NUM> and modulated according to a duty cycle, the duty cycle being variable between:.

During the initialization procedure, the decrement between the high-average power and the low-average power may be maintained constant and the ambient temperature is also maintained constant. The controller <NUM> may be configured, during a measurement operation <NUM> (i.e. subsequently to the initialization <NUM>), to define the low-average power duty cycle in such a way that the decrement between the high-average power and the low-average power is the same of the decrement between the high-average power and the low-average power experienced during the initialization procedure.

Analogously, the sensor <NUM> may be understood as being configured to perform the initialization procedure <NUM>, wherein the initialization procedure <NUM> provides multiple emissions and detections, through the detector <NUM>, for different known amounts of fluid, so as to individuate a detection law mapping amounts of fluid onto reading units to be converted into amounts of fluids. The sensor <NUM> may be configured, in operation, to define the low-average power duty cycle in such a way that the decrement between the high-average power and the low-average power is the same of the decrement between the high-average power and the low-average power experienced during the initialization procedure.

The initialization procedure <NUM> may operate like in the normal measurement operations <NUM>. For example, the temperature measures <NUM>' and/or the voltage measures <NUM>' may be performed identically. In some examples, the initialization procedure <NUM> may be performed at a pre-defined ambient temperature and a pre-defined supply voltage VDD, e.g. using high-precision machinery.

During measurement operations <NUM>, the results obtained at the initialization <NUM> will be used. In particular, in operations, the emitter <NUM> will define the duty cycles so as to present the same constant decrement ΔPel used in the initialization at any possible ambient temperature.

As can be seen in <FIG>, the emission (step <NUM>) operated as in <FIG> may be actually preceded by at least one of:.

The iteration <NUM> refers to the fact that several pulses may be generated with the same precalculated duty cycles.

Even if not shown in <FIG>, during the initialization <NUM> the detector <NUM> detects the signal <NUM> and provides the output based on the linear law previously defined.

In some examples, the initialization <NUM> is not necessary, and other methods may be used (e.g., reference data obtained by simulation, etc.). In some other examples, the initialization <NUM> may be performed multiple times (e.g. when it is intended to re-initialize the emitter).

<FIG> shows four graphs (a), (b), (c), and (d) which permit to appreciate advantages of the invention.

Graph (a) shows the linear function u [ordinate] which maps the real amount of gas [abscissa: ppm]. In principle (e.g. the technique discussed here), this graph is valid only at TAMBIENT = <NUM> (which may be the ambient temperature at which the initialization <NUM> has been performed). As can be seen, u(ppm) follows linearly the real amount of gas, but is subjected to the offset at <NUM> ppm (i.e. u(<NUM>) > <NUM>). As explained above, the offset is proportional to the decrement ΔPel of average electric power from a hot period to the subsequent cold period (i.e. u(<NUM>) ∝ ΔPel). The slope of u(ppm) is proportional to the emission (hot) temperature (here indicated with Tmax,<NUM>), i.e. <MAT> (where Tmax,<NUM> is the hot temperature reached by starting at <NUM>, without the above discussed compensation at hot periods). The sensor <NUM> may have the knowledge of graph (a).

Graph (b) shows the output when the ambient temperature is <NUM> (without the techniques discussed above, e.g. those that compensate the ambient temperature during the hot periods). If the different ambient temperature is not compensated and the duty cycle at the cold periods and the hot periods are not modified with respect to the case of graph (a), by virtue of Tmax,<NUM> > Tmax,<NUM> (where Tmax,<NUM> is the hot temperature reached by starting at <NUM>, without the above discussed compensation at hot periods), the slope <MAT> is increased: the new relationship is shown in graph (b), but this time the sensor <NUM> has no knowledge of it, and it could provide an incorrect measurement <NUM>.

With the present techniques, however, it is possible to cope with this inconvenient at the emitter. Graph (c) shows an advantageous effect of the present techniques (in particular the compensation at the hot periods). Here, with TAMBIENT = <NUM> (like in graph (b)), we have that at any ambient temperature the emitter is subjected to the same emission temperature THOT = Tmax,<NUM>, and the slope can be reported to <MAT>. This is the effect of having compensated the hot periods <NUM> by modifying the duty cycle to take into consideration the ambient temperature and the voltage at the heater <NUM>. This result has been obtained by assuming that, in the cold periods, the conductor <NUM> is permanently off (DCOLD = <NUM>). However, unwantedly, the offset u(<NUM>) is not maintained constant but is reduced. This could also cause an incorrect reading of the amount of gas.

It has been understood that, by using, in the cold periods 472c, the low-average power duty cycle DCOLD defined in such a way that the reduction of power is constant throughout the measurements (e.g. the same as in the initialization), also the offset diminution is compensated. The advantageous effect is depicted in graph (d). As can be seen by comparing graphs (a) and (d), at the ambient temperature of <NUM> the function u(ppm) appears the same of the function u(ppm) at the ambient temperature of <NUM> (i.e. no slope change and no offset error with respect to the situation in graph (a)).

Another example can be understood with the comparison of a <NUM>st scenario at TAMBIENT,1st scenario = <NUM> and a <NUM>nd scenario at TAMBIENT,2nd scenario = <NUM>. At first, the hot periods are here taken into consideration: :.

Hence, the difference between the electrical power in the first scenario and the electrical power in the second scenario is determined to be ΔPel,HOT,1st scenario-2nd scenario = Pel,HOT,1st scenario - Pel,HOT,2nd scenario = <NUM> mW - <NUM> mW = <NUM> mW. This ΔPel,HOT,1st scenario-2nd scenario of <NUM> mW in the hot periods causes the offset drift at the detector, which sees the absolute power as a baseline u(<NUM>) (due to thermoacoustic phenomena).

The cold periods average power has to be adapted to cope with the thermoacoustic phenomena by choosing the following constant value 380mW for ΔPel:.

Hence, ΔPel,HOT,1st scenario-2nd scenario ≠ <NUM> would cause an unwanted offset drift, implying a deviation between of the input power, which is demanded to remain stable (in this case <NUM> mW). By keeping ΔPel = Pel,HOT - Pel,COLD = constant, it is possible to move from the situation of graph (c) to that of graph (d): the offset and the slope end to be the same of graph (a), and the amount of gas can be easily measured.

We may imagine, for example, that the <NUM>st scenario is the scenario at the initialization <NUM>, and the <NUM>nd scenario is the scenario during a measurement operation <NUM>: we have the same, constant decrement of electrical power ΔPel as provided to the heater <NUM>.

For a generic measurement, the following duty cycles may be defined:.

For example, the compensation of ΔPel (so that it remains constant) may be done when calculating the low-average power duty cycle DCOLD (e.g. from ΔTCOLD = TCOLD - TAMBIENT = <MAT>). The compensation of the ΔPel may be performed on line, by increasing (or respectively reducing) the input power with the same absolute power in the cold periods and in the hot periods.

In one example, from the general formula <MAT> we can obtain <MAT> and, by imposing ΔPel = costant and DHOT being previously calculated, DCOLD can be obtained (e.g. at step <NUM>).

Above, reference is often made to dynamically controlling duty cycles (e.g. in cold periods and hot periods). However, it is noted that there are several possible techniques for choosing the duty cycles. For example, it is not necessary that the duty cycle is varied abruptly (e.g., from the hot period to the cold period, or based on a detection of a voltage ripple, etc.). Also the duty cycle may be smoothed, filtered, etc., and this also applies to the signals <NUM>' and <NUM>' which are taken into account for dynamically defining the duty cycle. Further different modulations may be chosen which are based on the same duty cycle, but this is known.

Important achievements are obtained at the emitter, since the generated radiations results substantially independent of the ambient temperature and the input voltage. Hence, the invention can result valid also for an emitter which is used for emission generation, and which could also not be used for gas sensing (and independent from the results associated to the graphs of <FIG>, for example): what is obtained is notwithstanding an emitter which emits at a precise specific wavelength without negative effects due to the ambient temperature and the supply voltage. A stable emission source is generated which does not depend on ambient temperature and supply voltage.

In particular for a fluid (gas) sensor, the effects of the thermoacoustic waves are greatly reduced. The detector <NUM>, placed in the same case of the emitter <NUM>, would be otherwise subjected to the effects of the thermoacoustic waves. By defining a stable ΔPel, however, the effects of the thermoacoustic waves are compensated.

Moreover, DC/DC converters and Zener diodes may in principle be avoided, since variations of the supply voltage are compensated.

In some examples, one or more of the most important method steps may be executed by such an apparatus.

Depending on certain implementation requirements, examples of the present techniques can be implemented in hardware or in software.

Some examples according to the present techniques comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, examples of the present techniques can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine-readable carrier.

Other examples comprise the computer program for performing one of the methods described herein, stored on a machine-readable carrier.

In other words, an example of the present techniques is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further example of the methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein.

A further example of the present techniques is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein.

A further example comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

A further example comprises a computer having installed thereon the computer program for performing one of the methods described herein.

A further example according to the present techniques comprises an apparatus or a system configured to transfer (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver.

In some examples, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some examples, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein.

Claim 1:
An emitter (<NUM>) for emitting radiations (<NUM>, <NUM>) at a specific wavelength which is the characteristic wavelength of a particular fluid, comprising:
a Joule-heated emitting electrical conductor (<NUM>), configured to emit radiations (<NUM>) at the specific wavelength at an emission temperature at which radiations at the specific wavelength are emitted,
a controller (<NUM>) configured, in operation, to control a variable voltage (vDD) subjected (<NUM>) to the Joule-heated emitting electrical conductor (<NUM>) and modulated according to a duty cycle, the duty cycle being variable between:
a high-average power duty cycle, during hot periods (<NUM>), so that the Joule-heated emitting electrical conductor (<NUM>) is subjected to a high-average power to reach and maintain the emission temperature to emit radiations at the specific wavelength; and
a low-average power duty cycle, during cold periods (472c) alternated to the hot periods (<NUM>), so that the Joule-heated emitting electrical conductor (<NUM>) is subjected to a low-average power to reach a temperature smaller than the emission temperature so that the Joule-heated emitting electrical conductor (<NUM>) does not emit, or emits only a negligible amount of, radiations (<NUM>) at the specific wavelength, wherein the low-average power duty cycle is smaller than the high-average power duty cycle,
characterized in that
the controller is configured to obtain at least one temperature-indicative measured value (<NUM>') indicative of the ambient temperature provided by a temperature sensor (<NUM>),
wherein the high-average power duty cycle and the low-average power duty cycle are defined based on the at least one temperature-indicative measured value (<NUM>') indicative of the ambient temperature as measured.