1. Department of Optical Engineering Zhejiang University Department of Optical Engineering Zhejiang University Advanced Sensor Technology Lecture 2 Jun. QIAN

2. Department of Optical Engineering Zhejiang University Lecture 2 Basic Intent Overview the basic sensor terminology in product data sheets, and in the technical literature. Overview the basic sensor terminology in product data sheets, and in the technical literature. Case study: off-the-shelf accelerometers, ADXL150 v.s. LIS331. Case study: off-the-shelf accelerometers, ADXL150 v.s. LIS331. Then, a summary of the basic electronic circuits we will be covering in the course is presented. Then, a summary of the basic electronic circuits we will be covering in the course is presented.

3. Department of Optical Engineering Zhejiang University Where do Sensors Come From? We are going to cover a significant fraction of modern sensors, We are going to cover a significant fraction of modern sensors, some sort of invention some sort of invention Interesting to think how such things come to be Interesting to think how such things come to be Many researchers out there competing to invent, design, build and sell sensors which are going to next big wave in industry Many researchers out there competing to invent, design, build and sell sensors which are going to next big wave in industry This competition has been going on for decades This competition has been going on for decades What are the basic facts at work? What are the basic facts at work?

4. Department of Optical Engineering Zhejiang University Basic facts : R&D of modern sensors Some of the people working in this business have great resources at their disposal. Some of the people working in this business have great resources at their disposal. Researchers at national labs or big industrial labs, where access to state of the art materials and equipment is key to finding the next really important sensor. Researchers at national labs or big industrial labs, where access to state of the art materials and equipment is key to finding the next really important sensor. Access to resources (people, equipment,…) is a big advantage. Access to resources (people, equipment,…) is a big advantage. Market Drive- an important driving power Market Drive- an important driving power If the Auto Industry says it is interested in buying 20 million gyroscopes at a price of $10 each every year, you can be sure that hundreds of people are trying to meet that challenge. So, there are some industries which get to set the challenges which are the focus of inventor interest. If the Auto Industry says it is interested in buying 20 million gyroscopes at a price of $10 each every year, you can be sure that hundreds of people are trying to meet that challenge. So, there are some industries which get to set the challenges which are the focus of inventor interest.

5. Department of Optical Engineering Zhejiang University Introduction to sensor terminology A sensor is a device A sensor is a device which converts a physical phenomena into an electrical signal. which converts a physical phenomena into an electrical signal. As such, sensors represent part of the interface between the physical world and the world of electrical devices, such as computers. As such, sensors represent part of the interface between the physical world and the world of electrical devices, such as computers. The other part of this interface is represented by Actuators, which convert electrical signals into physical phenomena. The other part of this interface is represented by Actuators, which convert electrical signals into physical phenomena. For a virtual reality game glove, it is better to have both. For a virtual reality game glove, it is better to have both.

6. Department of Optical Engineering Zhejiang University Exemplary Interfaces Cockroach with steering wheel Implanted E-retina Implanted bionic ear

7. Department of Optical Engineering Zhejiang University Introduction to sensor terminology Characterization and data sheet Characterization and data sheet since the output of the sensor is an electrical signal, we tend to characterize sensors in the same way we characterize electronic devices. since the output of the sensor is an electrical signal, we tend to characterize sensors in the same way we characterize electronic devices. The data sheets for many sensors are formatted just like electronic product data sheets. The data sheets for many sensors are formatted just like electronic product data sheets. However, there are many formats out there, and nothing at all like an international standard for sensor specifications. However, there are many formats out there, and nothing at all like an international standard for sensor specifications. We will encounter a variety of interpretations of sensor performance parameters, and sometimes a lot of confusion will emerge. It is important for you to realize that this confusion is not due to our inability to explain the meaning of the terms - it is a result of the fact that different parts of the sensor community have gotten comfortable using these terms differently. We will encounter a variety of interpretations of sensor performance parameters, and sometimes a lot of confusion will emerge. It is important for you to realize that this confusion is not due to our inability to explain the meaning of the terms - it is a result of the fact that different parts of the sensor community have gotten comfortable using these terms differently.

8. Department of Optical Engineering Zhejiang University Data Sheet: Purpose and Format The data sheet The data sheet is primarily a marketing document. is primarily a marketing document. It will be designed to highlight the positive attributes of the sensor, emphasizing some of the potential uses of the sensor, It will be designed to highlight the positive attributes of the sensor, emphasizing some of the potential uses of the sensor, might neglect to comment on some of the negative characteristics of the sensor. might neglect to comment on some of the negative characteristics of the sensor. In many cases, the sensor has been designed to meet a particular performance specification for a specific customer, and the data sheet will concentrate on the performance parameters of greatest interest to this customer. In many cases, the sensor has been designed to meet a particular performance specification for a specific customer, and the data sheet will concentrate on the performance parameters of greatest interest to this customer. In this case, the vendor and customer might have grown accustomed to unusual definitions for certain sensor performance parameters. In this case, the vendor and customer might have grown accustomed to unusual definitions for certain sensor performance parameters. As a potential new user of such a sensor, it is initially your problem to recognize this situation, and interpret things reasonably. As a potential new user of such a sensor, it is initially your problem to recognize this situation, and interpret things reasonably. So, expect that you will encounter odd definitions here and there, and expect that you will find that most sensor data sheets are missing some information that you might be most interested in. So, expect that you will encounter odd definitions here and there, and expect that you will find that most sensor data sheets are missing some information that you might be most interested in.

9. Department of Optical Engineering Zhejiang University Sensor Classification Passive sensor does not need any additional energy source and directly generates an electric signal in response to an external stimulus; a thermocouple, a photodiode, piezoelectric sensor. Active sensor The active sensors sometimes are called parametric because their own properties change in response to an external effect and these properties can be subsequently converted into electric signals. For example, a thermistor is a temperature-sensitive resistor. These variations (presented in ohms) directly relate to temperature through a known function. a resistive strain gauge in which electrical resistance relates to a strain.

10. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Transfer Function: Transfer Function:. This function establishes dependence between the electrical signal S produced by the sensor and the stimulus s. S =f (s), s : the stimulus; S: electrical signal output e.g. S =a +bs Linear, b: sensitivity, a: offset Usually, this relationship is represented as a graph showing the relationship between the input and output signal, and the details of this relationship may constitute a complete description of the sensor characteristics. Usually, this relationship is represented as a graph showing the relationship between the input and output signal, and the details of this relationship may constitute a complete description of the sensor characteristics. For expensive sensors which are individually calibrated, this might take the form of the certified calibration curve. For expensive sensors which are individually calibrated, this might take the form of the certified calibration curve.

11. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Span or Dynamic Range: Span or Dynamic Range: A dynamic range of stimuli which may be converted by a sensor is called a span or an input full scale (FS). It represents the highest possible input value that can be applied to the sensor without causing an unacceptably large inaccuracy. Signals outside of this range are expected to cause unacceptably large inaccuracy. Signals outside of this range are expected to cause unacceptably large inaccuracy. This span or dynamic range is usually specified by the sensor supplier as the range, in which other performance characteristics described in the data sheets are expected to apply. This span or dynamic range is usually specified by the sensor supplier as the range, in which other performance characteristics described in the data sheets are expected to apply.

12. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Accuracy: Accuracy: Generally defined as the largest expected error between actual and ideal output signals. Generally defined as the largest expected error between actual and ideal output signals. Sometimes this is quoted as a fraction of the full scale output. For example, a thermometer might be guaranteed accurate to within 5% of FSO (Full Scale Output) Sometimes this is quoted as a fraction of the full scale output. For example, a thermometer might be guaranteed accurate to within 5% of FSO (Full Scale Output) Hysteresis: Hysteresis: Some sensors do not return to the same output value when the input stimulus is cycled up or down. Some sensors do not return to the same output value when the input stimulus is cycled up or down. The width of the expected error in terms of the measured quantity is defined as the hysteresis. Typical units : Kelvin or % of FS The width of the expected error in terms of the measured quantity is defined as the hysteresis. Typical units : Kelvin or % of FS

13. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Nonlinearity (often called Linearity): Nonlinearity (often called Linearity): The maximum deviation from a linear transfer function over the specified dynamic range. The maximum deviation from a linear transfer function over the specified dynamic range. There are several measures of this error. There are several measures of this error. The most common compares the actual transfer function with the `best straight line', which lies midway between the two parallel lines which encompasses the entire transfer function over the specified dynamic range of the device. The most common compares the actual transfer function with the `best straight line', which lies midway between the two parallel lines which encompasses the entire transfer function over the specified dynamic range of the device.

14. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Resolution: Resolution: The resolution of a sensor is defined as the minimum detectable signal fluctuation. The resolution of a sensor is defined as the minimum detectable signal fluctuation. data sheets generally quote resolution in units of signal/Root(Hz) data sheets generally quote resolution in units of signal/Root(Hz) or they give a minimum detectable signal for a specific measurement. or they give a minimum detectable signal for a specific measurement. If the shape of the noise distribution is also specified, it is possible to generalize these results to any measurement If the shape of the noise distribution is also specified, it is possible to generalize these results to any measurement

15. Department of Optical Engineering Zhejiang University Resolution Resolution describes the smallest increments of stimulus which can be sensed. When a stimulus continuously varies over the range, the output signals of some sensors will not be perfectly smooth, even under the no-noise conditions. The output may change in small steps. typical for potentiometric transducers, occupancy infrared detectors with grid masks, and other sensors where the output signal change is enabled only upon a certain degree of stimulus variation.

16. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Noise: Noise: All sensors produce some output noise in addition to the output signal. All sensors produce some output noise in addition to the output signal. If the noise of the sensor is less than If the noise of the sensor is less than the noise of the next element in the electronics, the noise of the next element in the electronics, or less than the fluctuations in the physical signal, or less than the fluctuations in the physical signal, in which case it is not important. in which case it is not important. Many other cases exist in which the noise of the sensor limits the performance of the system based on the sensor. Many other cases exist in which the noise of the sensor limits the performance of the system based on the sensor. Noise is generally distributed across the frequency spectrum. Many common noise sources produce a white noise distribution, which is to say that the spectral noise density is the same at all frequencies. Johnson noise in a resistor is a good example of such a noise distribution. Noise is generally distributed across the frequency spectrum. Many common noise sources produce a white noise distribution, which is to say that the spectral noise density is the same at all frequencies. Johnson noise in a resistor is a good example of such a noise distribution. For white noise, For white noise, the spectral noise density  Volts/Root(Hz). e.g. using 10Hz filter: the spectral noise density  Volts/Root(Hz). e.g. using 10Hz filter:

17. Department of Optical Engineering Zhejiang University Sensor Performance Characteristics Definitions Bandwidth: All sensors have finite response times to an instantaneous change in physical signal. All sensors have finite response times to an instantaneous change in physical signal. many sensors have decay times, which would represent the time after a step change in physical signal for the sensor output to decay to its original value. many sensors have decay times, which would represent the time after a step change in physical signal for the sensor output to decay to its original value. The reciprocal of these times correspond to the upper and lower cutoff frequencies, respectively. The bandwidth of a sensor is the frequency range between these two frequencies. The reciprocal of these times correspond to the upper and lower cutoff frequencies, respectively. The bandwidth of a sensor is the frequency range between these two frequencies. Human ear, e.g. 20-20KHz or response time 50ms-50  s Human ear, e.g. 20-20KHz or response time 50ms-50  s These definitions are adapted from those in These definitions are adapted from those in J. Fraden, AIP Handbook of Modern Sensors, Physics, Designs, and Applications, American Institute of Physics 1993 J. Fraden, AIP Handbook of Modern Sensors, Physics, Designs, and Applications, American Institute of Physics 1993

18. Department of Optical Engineering Zhejiang University Accelerometer ADXL150 from Analog Devices General Description General Description   50g  Resolution 10mg  Surface micromachined  Low noise: S/N>80dB  Single axis  Sensitivity: 38mV/g; Two scale factor 36mV/g, 76mV/g  Zero g drift: 0.4g over industrial temp range, 10x improvement over the ADXL50  Power consumption 1.8mA  Hermetic package

19. Department of Optical Engineering Zhejiang University Accelerometer ADXL150 from Analog Devices Theory of Operation Theory of Operation  Fabricated by Surface micromachining  Depositing poly-silicon on a sacrificial oxides layer, which is then etched away leaving the suspended sense element  Differential capacitance sensor  42 capacitance unit cells for sensing  12 unit cells for electrostatically forcing the beam during a self-test  Built-in circuitry for driving the sensor and converting cap change to voltage

20. Department of Optical Engineering Zhejiang University Accelerometer ADXL150 from Analog Devices

21. Department of Optical Engineering Zhejiang University Close-up of a packed accelerometer

22. Department of Optical Engineering Zhejiang University Package Drawing

23. Department of Optical Engineering Zhejiang University Specifications

24. Department of Optical Engineering Zhejiang University Time Response

25. Department of Optical Engineering Zhejiang University Output v.s. Frequency

26. Department of Optical Engineering Zhejiang University Output Noise

27. Department of Optical Engineering Zhejiang University Zero g Temperature Drift

28. Department of Optical Engineering Zhejiang University Noise Spectral Density

29. Department of Optical Engineering Zhejiang University Applications In IPHONE 4

30. Department of Optical Engineering Zhejiang University

31. Department of Optical Engineering Zhejiang University

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33. Department of Optical Engineering Zhejiang University Summary Sensor performance characteristics Sensor performance characteristics Transfer function Transfer function Sensitivity Sensitivity Dynamic range Dynamic range Hysteresis Hysteresis Temperature coefficient Temperature coefficient Linearity Linearity Accuracy (nonlinearity, temp effect, zero drift) Accuracy (nonlinearity, temp effect, zero drift) Noise (dep. on Bandwidth of filter) Noise (dep. on Bandwidth of filter) Resolution Resolution Bandwidth Bandwidth