Lie Detector

In radio, a detector is a device or circuit that extracts information from a modulated radio frequency current or voltage. The term dates from the first three decades of radio (1888-1918). Unlike modern radio stations which transmit sound (an audio signal) on an uninterrupted carrier wave, early radio stations transmitted information by radiotelegraphy. The transmitter was switched on and off to produce long or short periods of radio waves, spelling out text messages in Morse code. Therefore, early radio receivers did not have to demodulate the radio signal, but just distinguish between the presence or absence of a radio signal, to reproduce the Morse code "dots" and "dashes". The device that performed this function in the receiver circuit was called a detector.[1] A variety of different detector devices, such as the coherer, electrolytic detector, magnetic detector and the crystal detector, were used during the wireless telegraphy era until superseded by vacuum tube technology.

After the invention of amplitude modulation (AM) enabled the development of AM radiotelephony, the transmission of sound (audio), during World War 1, the term evolved to mean a demodulator, (usually a vacuum tube) which extracted the audio signal from the radio frequency carrier wave. This is its current meaning, although modern detectors usually consist of semiconductor diodes, transistors, or integrated circuits.

Lie Detector

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In a superheterodyne receiver the term is also sometimes used to refer to the mixer, the tube or transistor which converts the incoming radio frequency signal to the intermediate frequency. The mixer is called the first detector, while the demodulator that extracts the audio signal from the intermediate frequency is called the second detector. In microwave and millimeter wave technology the terms detector and crystal detector refer to waveguide or coaxial transmission line components, used for power or SWR measurement, that typically incorporate point contact diodes or surface barrier Schottky diodes.

One major technique is known as envelope detection. The simplest form of envelope detector is the diode detector that consists of a diode connected between the input and output of the circuit, with a resistor and capacitor in parallel from the output of the circuit to the ground to form a low pass filter. If the resistor and capacitor are correctly chosen, the output of this circuit will be a nearly identical voltage-shifted version of the original signal.

An early form of envelope detector was the crystal detector, which was used in the crystal set radio receiver. A later version using a crystal diode is still used in crystal radio sets today. The limited frequency response of the headset eliminates the RF component, making the low pass filter unnecessary.

More sophisticated envelope detectors include the grid-leak detector, the plate detector, the infinite-impedance detector, transistor equivalents of them and precision rectifiers using operational amplifiers.

A product detector is a type of demodulator used for AM and SSB signals, where the original carrier signal is removed by multiplying the received signal with a signal at the carrier frequency (or near to it). Rather than converting the envelope of the signal into the decoded waveform by rectification as an envelope detector would, the product detector takes the product of the modulated signal and a local oscillator, hence the name. By heterodyning, the received signal is mixed (in some type of nonlinear device) with a signal from the local oscillator, to give sum and difference frequencies to the signals being mixed, just as a first mixer stage in a superhet would produce an intermediate frequency; the beat frequency in this case, the low frequency modulating signal is recovered and the unwanted high frequencies filtered out from the output of the product detector. Because the sidebands of an amplitude-modulated signal contain all the information in the carrier displaced from the center by a function of their frequency, a product detector simply mixes the sidebands down into the audible range so that the original audio may be heard.

Product detector circuits are essentially ring modulators or synchronous detectors and closely related to some phase-sensitive detector circuits. They can be implemented using something as simple as ring of diodes or a single dual-gate Field Effect Transistor to anything as sophisticated as an Integrated Circuit containing a Gilbert cell. Product detectors are typically preferred to envelope detectors by shortwave listeners and radio amateurs as they permit the reception of both AM and SSB signals. They may also demodulate CW transmissions if the beat frequency oscillator is tuned slightly above or below the carrier.

AM detectors cannot demodulate FM and PM signals because both have a constant amplitude. However an AM radio may detect the sound of an FM broadcast by the phenomenon of slope detection which occurs when the radio is tuned slightly above or below the nominal broadcast frequency. Frequency variation on one sloping side of the radio tuning curve gives the amplified signal a corresponding local amplitude variation, to which the AM detector is sensitive. Slope detection gives inferior distortion and noise rejection compared to the following dedicated FM detectors that are normally used.

A phase detector is a nonlinear device whose output represents the phase difference between the two oscillating input signals. It has two inputs and one output: a reference signal is applied to one input and the phase or frequency modulated signal is applied to the other. The output is a signal that is proportional to the phase difference between the two inputs.

The phase-locked loop detector requires no frequency-selective LC network to accomplish demodulation. In this system, a voltage controlled oscillator (VCO) is phase locked by a feedback loop, which forces the VCO to follow the frequency variations of the incoming FM signal. The low-frequency error voltage that forces the VCO's frequency to track the frequency of the modulated FM signal is the demodulated audio output. The phase-locked loop detector should not be confused with the phase-locked loop frequency synthesizer, which is often used in digitally-tuned AM and FM radios to generate the local oscillator frequency.

The Jefferson Lab Radiation Detector and Imaging Group, headed by Dr. Drew Weisenberger has the primary mission of supporting detector development for the experimentalnuclear physics research program using the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. For more than 30 years, the group has been involved in numerous collaborations resulting in many application-specific radiation-imaging systems based on technology used in nuclear physics research. The group has worked directly in the development and testing of several detectors for the original three experimental halls (Halls A, B and C) and for the new Hall D. The Detector Group has access to the experimental halls in order to perform tests on detector components under experimental conditions

In addition to open laboratory areas and tools available to the general research personnel at Jefferson Lab, the Detector Group has a 1300 ft2 laboratory work area available to it exclusively on the Jefferson Lab campus. Within this lab there are various pieces of equipment, materials and tools necessary for detector development and testing. These items include sealed radioactive calibration sources, digital and analog oscilloscopes, dark boxes for detector and scintillator testing, high voltage supplies, several computer workstations interfaced to VME based, stand alone FPGA JLab developed flash analog to digital electronics and two tabletop 3-D printers to build prototype and finished plastic parts.

The Group has technical capabilities applicable not only to nuclear physics radiation detector development, but also to application spin-offs of the detector technology. Jefferson Lab has been awarded over fifty US patents based on inventions developed by the Detector Group members.

The Compact Muon Solenoid (or CMS) detector sits at one of these four collision points. It is a general-purpose detector; that is, it is designed to observe any new physics phenomena that the LHC might reveal.

An unusual feature of the CMS detector is that instead of being built in-situ like the other giant detectors of the LHC experiments, it was constructed in 15 sections at ground level before being lowered into an underground cavern near Cessy in France and then reassembled. Engineers found that building sections above ground, rather than constructing them in the cavern with all its access and safety issues, saved valuable time. Another important conclusion was that sub-detectors should be made more easily accessible to allow for easier and faster maintenance.

The Short-Baseline Near Detector (SBND) will be one of three liquid argon neutrino detectors sitting in the Booster Neutrino Beam (BNB) at Fermilab as part of the Short-Baseline Neutrino Program. MicroBooNE and ICARUS are the intermediate and far detectors in the program, respectively.

SBND is a 112 ton active volume liquid argon time projection chamber (LArTPC) to be located only 110 m from the BNB neutrino source. The detector is currently being assembled and is anticipated to begin operation in 2023.

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