How does an ultrasonic sensor work?
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It is like SONAR.  A high frequency sound is emitted that bounces off surfaces inside your body.  The bounced back sound is collected and is used to generate a picture of your insides.
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Capacitive sensor panels are coated with a material that stores electrical charge. When the monitor is touched, a portion of the charge is transferred to the user, decreasing the panel's capacitive layer. Electronic circuits then measure the ensuing alteration and calculate where the touch event occurred. \n\nA capacitive touch screen panel is coated with a material, typically indium tin oxide, that conducts a continuous electrical current across the sensor. The sensor therefore exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes - it achieves capacitance. The human body is also an electrical device which has stored electrons and therefore also exhibits capacitance. When the sensor's 'normal' capacitance field (its reference state) is altered by another capacitance field, i.e., someone's finger, electronic circuits located at each corner of the panel measure the resultant 'distortion' in the sine wave characteristics of the reference field and send the information about the event to the controller for mathematical processing*. Capacitive sensors must be touched with a conductive device being held by a bare hand or a finger, unlike resistive and surface wave panels that can use anything that can point, such as a finger or stylus. Capacitive touch screens are not affected by outside elements and have high clarity.\n\n    * Better said: When a user touches the screen, he/she draws some of the current from the circuit. The resulting changes to the electric field can be observed and the ratios of the fields according to the 4 corners of the screen can be calculated to obtain the position of the disturbance (the touch).
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Two techniques: analog and digital.\nAnalog: the sound is a variation of air pressure.  This variation is "measured" by a microphone (or similar), to convert the pressure differences into variations of voltage.\nThis voltage variation is then used, after amplification, to act upon a "stylus" (in the case of Edison) that "vibrate" on a cylinder of soft wax, animated by a rotation and a horizontal translation.  The variations of the stylus can be read afterwards by retarting the process, this time fromt the stylus to a speaker.\nLater, the voltage variations where converted in magnetic variations that were "written" to a wire first, then to a tape (tape recorders).\nNowadays, the same voltage variations are "sliced" and measured many times per second, converted in numeric value, and it is the number that is recorded on some disc or solid state memory: this is the digital recording.
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If pizometer is the correct spelling, I am not sure what it is.\n\nA piezometer is an instrament used to measure pressure.
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* There are horizontal and vertical rows of electrodes below it that form a grid. These layers with electrodes are charged with a constant alternating current (AC). \n\n    * As the finger touches the electrode grid, the current is interrupted and the interruption is detected by the circuit board. \n\n    * It works by sensing the capacitance. The human finger is an electrical conductor, and when you place your finger on a TouchPad, a tiny capacitance forms between your finger and the metal electrodes in the TouchPad.\n\n    * The TouchPad sensor's sensitive analog electronics measure the amount of capacitance in each of the electrodes. By measuring which electrodes have the most capacitance, the TouchPad can locate your finger to an accuracy of better than 1/1000th of an inch.
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Constant current source, diode junction for temperature sensing, and a gain/offset circuit for scaling to 10mV/deg C.\n\nIf you look at the diagram in the product folder, its pretty easy to see whats going on.\nhttp://www.national.com/pf/LM/LM35.html\n\nThey get the accuracy without taking 2 measurements at different current levels, as is commonly done in diode temperature sensors, by wafer trimming.... which is why the LM35 costs so much more, than a simple diode sensor. The current source, and gain/offset circuitry uses minimal real estate on the die, with interconnects and physicial handling issues consuming almost as much as the circuit needs. The cost is a funtion of the extra time needed for trimming, and of course the manufacturing yield.
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A transducer is an element that converts some force to an electrical signal. A microphone converts sound waves to a signal. A speaker receives an electrical signal and generates sound.\n\nYou can use a speaker as a microphone, by plugging it into a mic input! So, it really can be both.
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A sphygmomanometer (note spelling) works by completely cutting off the blood flow with high pressure, and then gradually decreasing that pressure until blood flows again.  The nurse determines this by listening with a stethoscope.  When she first hears blood begin to flow with a loud sound, that is the systolic blood pressure.  When the sound is no longer heard, that is the diastolic blood pressure.  So the cuff just reports how much pressure it is applying.  The nurse has to determine at what point the body responds.
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A miniature microphone (electret) and signal amplifier to trigger the device.\n\nWith the proper associated components (coil, capacitors, resisters) the operation can be activated only by a limited frequency range or volume or both.
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Maybe the following picture will give you an idea:\nhttp://pg.photos.yahoo.com/ph/dpeter508/detail?.dir=/c51a&.dnm=b97fre2.jpg&.src=ph\n\nThis is a binary pattern painted on the shaft, with three sensors (red dots in the pic).  The outermost sensor will detect black and white squares, and can determine rotational speed based on the rate that the black and white squares go by.  As the shaft rotates, the sensors will detect the 3-bit pattern painted on the shaft at any point.  If the shaft is turning in one direction, the pattern will appear to "count up" or down depending on direction.
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To be honest, I am not quite sure...but perhaps diagnostic sonography involves only an image and cardial/vascular (cardio-vascular??) involves not only an image, but doppler ultrasound.\n\nHere is an excerpt from a medical textbook, "Basic Radiology"\nby Michael Y.M. Chen, Thomas L. Pope, Jr., David J. Ott \nMcGraw-Hill, 2006\n\n"Ultrasonography\n\nDiagnostic ultrasound is a noninvasive imaging technique that uses high-frequency sound waves greater than 20 kilohertz (kHz). A device known as a transducer is used to emit and to receive sound waves from various tissues in the body. The transducer is placed against the patient's skin with a thin layer of coupling gel. This gel displaces the air that would otherwise reflect virtually all of the incident ultrasound beam. As sound travels into the patient, wave fronts spread out, diminishing the overall beam intensity. Beam attenuation also occurs secondary to partial tissue absorption with associated heat conversion. At tissue interfaces, the beam is partially reflected and transmitted. The reflected sound waves, or echoes, travel back to the transducer, are converted into electric signals, and then amplified. The amplitude of the returning wave partially depends on the degree of beam absorption. A shade of gray is then assigned to each amplitude, with strong echoes being typically assigned a shade near the white end of the spectrum and weak echoes given a shade near the black end of the spectrum. In addition, the depth of the reflecting tissue can be calculated from the known total beam travel time and the average sound velocity in human tissue (1540 meters/second). Limitations of this modality are based on its operator-dependent nature, sensitivity of equipment to slow flow, variable visualization of midline abdominal organs (pancreas) or vasculature when obscured by overlying bowel gas, and inability of sound waves to penetrate gas or bone.\n\nUltrasonography has many common applications that involve imaging of the abdomen [liver, gallbladder (Fig. 1–6), pancreas, kidneys], pelvis (female reproductive organs), fetus (routine fetal surveys for detection of anomalies), vascular system (aneurysms, arteriovenous communications, deep-venous thrombosis), testicles (tumor, torsion, infection), pediatric brain (hemorrhage, congenital malformations), breast, and chest (size and location of pleural fluid collections). In addition, ultrasound-guided interventions have been used for facilitating lesion biopsy, abscess drainage, and radiofrequency ablation."\n\n"Doppler ultrasound is used primarily to evaluate vascular flow by detecting frequency shifts in the reflected beam, utilizing a principle termed the Doppler effect. This effect occurs when a sound emitter or reflector is moving relative to the receiver of sound. Objects moving toward the detector appear to have a higher frequency and shorter wavelength, while objects moving away from the detector appear to have a lower frequency and longer wavelength. If the ultrasound beam strikes a reflector (vessel wall, heart) moving toward it, the reflected sound will have a higher frequency than the original beam. The reflected sound will be of lower frequency than the original beam if the reflector is moving away when the beam strikes it. The Doppler shift is the frequency difference between the original beam frequency and the reflected beam frequency. These frequency differences are used to calculate the corresponding flow velocities, from which a Doppler waveform, or tracing, can be generated. This tracing depicts the relationship between velocity and time and is unique to the flow pattern within the vessel. Color flow Doppler assigns colors (blue and red) to structures according to their motion toward or away from transducers. This information can be superimposed on a gray-scale image.\n\nEndoluminal sonography uses a high-frequency catheter-based transducer (9–20 MHz) to image structures beyond the lumen of
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Piezo is apparently a term derived from the Greek word piezein, meaning to "squeeze or press". Essentially, the idea is that the movement of certain crystals creates an electric potential, and in some cases the opposite can happen (an electric potential can create movement). The movements are all on a very small scale, too small to really see with the naked eye. Check the wiki page for more info; they have more specifically about piezo motors in there, though the gist is about the same: electricity from small movements in crystals.
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This small control device allows electrical applicances to be turned on and off by sound.  The way it works is that a small microphone element is connected to a circuit that controls a triac or an SCR.  A triac or SCR is an electrical component that can be switched on or off with a smaller control voltage, supplied by the microphone.  When a sound is detected, the small voltage triggers the triac or SCR on.  Another sound will turn it off.  This type of device will only work for direct electric devices, for example lights or motors.  Electrical appliances that have internal remote power circuits, like most modern TVs and stereo equipment, won't work with the sound device.\n\nA more complex device is available that actually senses the frequency of a sound which then is used to turn on or off one of several devices.  For each device that you want to control, there is a separate triac or SCR circuit.  There is an extra control circuit built in that only activates one triac or SCR depending on the frequency detected.\n\nThese sound control devices are becoming more impractical as other more sophisticated means of controlling electrical appliances are produced.  It now seems that infra-red remote controls are the preferred portable devices since they can be programmed to work with many devices and are just as inexpensive.
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what sort of sensors are u interested in. if it is light then it can be measured using photoconductive or ptotovoltaic devices.
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ultrasound is anything over what the human ear can hear over 20 kHz.\nUltrasound is produced by a transducer, this can both emit and detect ultrasound. By varying the size of the pizoelectric discs frequency of the emited ultrasound is altered.\nThe higher the frequency the better anatomical detail however less penatration is attchived.\n\nthere are 3 main types of scan\n\nA-scan (ampitude mode)\nThis shows the differenc between tissue interfaces and is used in mesurement e.g foetal skull maturity\n\nB-scan (brightness mode)\nThis shows a 2D image in a specific plane. It shows different types of tissue in gray scale. This is shown in real time. This is used to image abdominal areas.\n\nM-scan this shows the way tissue interfaces alter with time. Moving traces produce a wavy line on the screen where static interfaces produce a straight line m scans are used in cardiac imaging to show valves of the heart.
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Piezoelectric crystals will deform when a voltage is applied to them. If the voltage is an alternating one, they will deform one way, then the other way,. If the voltage is alternating rapidly, the crystal will flex rapidly. If the alternating signal is in the audio range, the crystal will emit sound. (Some very small, lightweight headphones work this way.)\n\nThe opposite is true also. When the crystal is mechanically deformed (vibrated), it will generate a tiny voltage. So they can also be used as microphones. Some piezoelectric crystals are actually ceramic materials. \n\nThey will respond at ultrasonic frequencies, and so are used as transducers-- sources and sensors.\n\nThe way the crystal is made inside is that there are layer upon layer of the same kind of molecule lined up, all in the same direction. These molecules are usually polarized, with a free electron on one end and none at the other end.\n\nSo if a thin film of metal is electroplated on both sides of the crystal (and you have to cut the crystal carefully, to make sure you have the molecules lined up right) you can solder wires to those metal platis and use them as electrodes. When a voltage is applied to one side, the molecules want to rotate in place (without stepping out of formation) as far as they can. The electrons repel one another, and this is what causes the deformation.\n\nWhen the polarity of the voltage reverses, the molecules want to rotate the opposite direction (again, without steping out of formation.) The electrons are repelling on the opposite side.\n\nIf too high a voltage is applied, the molecules break formation, and the crystal cracks. The voltage causes a little spark like an electric arc, that ruins the device.\n\nIn addition to the man-made ceramic materials, quartz, tourmaline and Rochelle Salts have these properties. Radio hams use quartz crystals to keep their transmitters on the right frequencies.\n\nIf you are intersted in things of this type, I suggest taking electronics courses. It will be a challenge, but you seem to have an interest, and I know you will enjoy someday being able to build your own ultrasonic devices, like rangefinders and echo-locators. Good luck!
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Check out this page:\nhttp://www.americanpiezo.com/piezo_theory/index.html