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Showing papers on "Phased array published in 1993"


Book
30 Nov 1993
TL;DR: Details of Element Pattern and Mutual Impedance Effects for Phased Arrays and Special Array Feeds for Limited Field of View and Wideband Arrays are presented.
Abstract: Phased Arrays in Radar and Communication Systems. Pattern Characteristics and Synthesis of Linear and Planar Arrays. Patterns of Nonplanar Arrays. Elements, Transmission Lines, and Feed Architectures for Phased Arrays. Summary of Element Pattern and Mutual Impedance Effects. Array Error Effects. Special Array Feeds for Limited Field of View and Wideband Arrays.

2,233 citations


Journal ArticleDOI
TL;DR: An investigation into methods of modeling the radiation patterns of phased arrays that include the effects of radiative mutual coupling that accurately predicts the patterns of small and medium-size arrays of equally spaced elements is presented.
Abstract: Results from an investigation into methods of modeling the radiation patterns of phased arrays that include the effects of radiative mutual coupling are presented. The approaches are based on either the principle of pattern multiplication or the use of active element patterns. Theoretical derivations of the various active element pattern methods are presented. A new method, the hybrid active element pattern method, is introduced. It accurately predicts the patterns of small and medium-size arrays of equally spaced elements. Example arrays of center-fed dipoles are analyzed to verify and illustrate the representations. The results are general and can be applied to arrays of any type of element. The array patterns computed using both the classical pattern multiplication approach and the methods based on active element patterns are compared to those computed using accurate numerical codes based on the method of moments. >

376 citations


Patent
19 Aug 1993
TL;DR: In this article, a communications satellite payload is carried by one satellite of a plurality of such satellites in a low earth orbit (LEO) constellation to provide worldwide communications, and a multi-element phased array of receiving antennas is also disclosed, wherein each element of each phased array is utilized for each individual one of the received or transmitted beams.
Abstract: A communications satellite payload provides for efficient communications between user devices, such as hand held cellular telephones, and terrestrial gateways that may be connected to world-wide public telephone and telegraph (PTTs) networks. The satellite payload simultaneously supports a plurality of independent antenna beams, for example 12 or 16 beams, on both the uplink and downlink for user devices employing full duplex communications. The satellite payload furthermore supports an identical number of full duplex channels between a terrestrial gateway and the satellite. The communications satellite payload is carried by one satellite of a plurality of such satellites in a low earth orbit (LEO) constellation to provide worldwide communications. Downlink beam forming occurs prior to final amplification of transmitted signals, thereby reducing losses within the beam forming equipment. A multi-element phased array of receiving antennas and a multi-element phased array of transmitting antennas is also disclosed, wherein each element of each phased array is utilized for each individual one of a plurality of received or transmitted beams.

301 citations


Journal ArticleDOI
TL;DR: The Letter describes a new balanced antipodal Vivaldi antenna that retains the wide bandwidth characteristics while reducing the crosspolarisation by 15dB across an 18:1 band.
Abstract: The conventional Vivaldi antenna typically has a bandwidth of less than 3:1, limited by the feed line to radiating slot transition. The antipodal Vivaldi antenna removes this limitation but gives very high crosspolarisation which is undesirable for phased array applications. The Letter describes a new balanced antipodal Vivaldi antenna that retains the wide bandwidth characteristics while reducing the crosspolarisation by 15dB across an 18:1 band. Measurements are presented that compare the performance of existing antenna structures with this novel antenna element.

192 citations


PatentDOI
TL;DR: A system architecture and communication methodology for significantly reducing the size of an aircraft antenna required to provide full broadcast quality video communications with an aircraft via a satellite communications link includes a combination of video bandwidth compression, spread spectrum waveform processing and an electronically steered, circular aperture phased array antenna that is conformal with an airframe surface of the aircraft.

150 citations


Patent
21 Jul 1993
TL;DR: In this paper, a transponder location and tracking system with a phased array antenna mounted at a toll collection station includes a plurality of antenna array elements for receiving a signal from a trans-ponder mounted on a vehicle and for providing an output signal representative of the location of the vehicle in response to the defined angles of arrival.
Abstract: A transponder location and tracking system having a phased array antenna mounted at a toll collection station includes a plurality of antenna array elements for receiving a signal from a transponder mounted on a vehicle and for providing a plurality of antenna element electrical signals. A plurality of phase detectors are provided for comparing the phase of the electrical signals to provide a plurality of phase difference signals. A plurality of angle-of-arrival calculation processors is provided for converting the phase difference signals to spatial signals to define the angles-of-arrival of the vehicle transponder signal. A position calculation processor is included for providing an output signal representative of the location of the vehicle in response to the defined angles-of-arrival. In a preferred embodiment, the transponder location and tracking system includes a plurality of receiver processing devices for amplifying and filtering the electrical signals from each antenna element. The phase detectors then compare the phase of the electrical signals to a reference element signal. Each phase detector provides a digital representation of the phase difference signals. The spatial signals represent the angle-of-arrival of the vehicle transponder signal. The position calculation processor operates on the spatial signal to determine the vehicle transponder position. A tracking mechanism is provided to plot the location of a moving vehicle along the roadway.

111 citations


Journal ArticleDOI
TL;DR: In this article, a photonic in-phase/quadrature (I-Q) RF phase shifter utilizing two integrated optic Mach-Zehnder modulators has been tested.
Abstract: A photonic in-phase/quadrature (I-Q) RF phase shifter utilizing two integrated optic Mach-Zehnder modulators has been tested. This phase shifter demonstrates the capability of 360 degrees phase control, >

103 citations


Journal ArticleDOI
TL;DR: In this paper, a true-time delay, optically controlled phased array antenna system whereby a large number (100-2500) of antenna elements can receive a series of microwave delays via use of a coherent optical carrier signal is described.
Abstract: A true-time delay, optically controlled phased array antenna system whereby a large number (100-2500) of antenna elements can receive a series of microwave delays via use of a coherent optical carrier signal is described. Both transmit and receive antenna arrays are described, and the signal-to-noise ratio for a 128 channel system is calculated to be approximately 40 dB with an optical link loss of only approximately 3 dB for a 1 GHz instantaneous bandwidth at a wavelength of lambda 1.55 mu m. It is shown that the use of coherent optically controlled phased array antennas provides improved controllability and immunity from noise and system losses over other architectures currently being investigated. >

94 citations


Journal ArticleDOI
TL;DR: It is shown that the method, even if developed for the analysis of large arrays, is able to handle small arrays and the results obtained are good even for single patches.
Abstract: A method for the analysis of large phased arrays of microstrip patches is presented. It is based on an infinite array approach where the edge effects are taken into account through the convolution with a proper window function. In the first step, a rigorous Green's function corresponding to a finite array of elementary sources is derived. This Green's function is then used to analyze the finite phased array of microstrip patches. Results are shown for the active impedance and element patterns of several arrays, and compared with measurements or, in the case of small arrays, with results obtained by a rigorous element-by-element approach. It is shown that the method, even if developed for the analysis of large arrays, is able to handle small arrays. Indeed, the results obtained are good even for single patches. Although the method has been developed for the microstrip phased array case, the results are general and are valid for any phased array with a rectangular grid. >

91 citations


Journal ArticleDOI
TL;DR: This paper theoretically analyzes the performance of a subspace separation technique based on orthogonal projections (OP) for adaptively suppressing interference in phased arrays and shows that the weight vector calculated using OP converges more quickly to the optimal solution than the SMI weight vector.
Abstract: Several recent studies indicate the promise of subspace separation principles when applied to adaptive jammer suppression in phased array antennas. This paper theoretically analyzes the performance of a subspace separation technique based on orthogonal projections (OP) for adaptively suppressing interference in phased arrays; the theoretical performance predictions are validated using computer simulations. This analysis holds for the case when it is possible to differentiate between the vector spaces spanned by jammers and additive noise. The performance parameters used are (a) the average residual interference (jammer plus noise) power at the output of the adapted array as a function of the number of jammer snapshots used for calculating the weight vector, and (b) the similarity of the adapted array pattern to the design pattern away from the jammer locations. The performance of the OP-based subspace separation technique is compared with the sample matrix inversion (SMI) algorithm. It is shown that the weight vector calculated using OP converges more quickly to the optimal solution (infinite number of interference snapshots) than the SMI weight vector. Further, in contrast to the SMI adapted pattern, which exhibits large sidelobe levels away from the jammer locations, the OP adapted pattern closely follows the design pattern both in the mainbeam and in the sidelobe region away from the jammer locations. >

83 citations


Journal ArticleDOI
TL;DR: In this paper, a performance monitoring/fault isolation and correction (PM/FIC) system for an active phased-array antenna has been developed and tested using a transmission line signal injector embedded at the radiating aperture together with a phase-toggling technique for signal detection.
Abstract: A built-in performance-monitoring/fault isolation and correction (PM/FIC) system for an active phased-array antenna has been developed and tested. This PM/FIC system employs a transmission line signal injector embedded at the radiating aperture together with a phase-toggling technique for signal detection. Hardware components for a demonstration test-array have been developed, fabricated, and assembled. Eight active elements are fed by four dual-channel transmit/receive (T/R) modules in a column array. Far-field range tests and fault correction tests have also been performed to demonstrate the PM/FIC functions on this test array. Good results have been obtained from these tests. The measurement accuracy of the phase-toggling method is compared with an HP8510 measurement system. >

Journal ArticleDOI
01 Oct 1993
TL;DR: In this paper, the angle estimation problem with an adaptive phased array radar is considered, and correction values for the slope and bias of the adaptive monopulse ratio for a planar array are derived for the adaptive sum and difference beam outputs without correction.
Abstract: The angle estimation problem with an adaptive phased array radar is considered. Because of the adaptation, the shape of the sum and difference beam is perturbed, therefore the usual monopulse formula produces errors if applied to the adaptive sum and difference beam outputs without correction. Correction values are derived for the slope and bias of the adaptive monopulse ratio for a planar array, and it is shown by example that this corrected adaptive monopulse procedure may be applied to the subarray outputs of a large array with partial digital beamforming. The bias can be further reduced by iterating the procedure, resulting in a ‘multistep corrected adaptive monopulse procedure’. This technique is also applicable to subarray output data. The method is applicable to arbitrary planar or volume arrays.

Journal ArticleDOI
TL;DR: A passive spatial light beam deflector based on a channel waveguide phased-array concept is presented and diffraction gratings patterned by electron-beam lithography couple light into and out of the device.
Abstract: A passive spatial light beam deflector based on a channel waveguide phased-array concept is presented. Diffraction gratings patterned by electron-beam lithography couple light into and out of the device. Phasing is achieved electro-optically with indium tin oxide/AlGaAs Shottky junctions. Discrete beam steering is first demonstrated with a 43-element rib waveguide array at an 850-nm wavelength. A sawtooth electrode keeps the device length short and the electrode surface small. Continuous deflection over a ±7.2 mrad range at a 900-nm wavelength is then reported. A set of seven sawtooth and offset electrodes permits addressing any point within this range. The beam has a width of 1.5 mrad, and the maximum modulation voltage is −8.5 V.

Patent
30 Nov 1993
TL;DR: In this paper, an active transmit phased array antenna system for generating multiple independent simultaneous antenna beams to illuminate desired regions while not illuminating other regions is proposed. But the antenna array is not designed to be used for any specific application.
Abstract: An active transmit phased array antenna system for generating multiple independent simultaneous antenna beams to illuminate desired regions while not illuminating other regions. The size shape of the regions is a function of the size and number of elements populating the array and the number of beams is a function of the number of beam forming networks feeding the array. All the elements of the array are operated at the same amplitude level and beam shapes and directions are determined by the phase settings. The active transmit phased array antenna includes a plurality of antenna elements disposed in a hexiform configuration. Each antenna element is identical and includes a radiating horn capable of radiating in each of two orthogonal polarizations. The horn is fed by a multi-pole bandpass filter means whose function is to pass energy in the desired band and reject energy at other frequencies. The filter means is coupled into an air dielectric cavity mounted on substrate. The air dielectric cavity contains highly efficient monolithic amplifiers which excite orthogonal microwave energy in a push-pull configuration by probes in combination with amplifiers placed such that they drive the cavity at relative positions 180 degrees apart. Phase shift means and attenuator means in the substrate are connected to the amplifiers in the cavity to determine beam and direction and for maintaining the signal amplitudes from each of the antenna elements at an equal level.

Journal ArticleDOI
TL;DR: In this article, the impulse directivity patterns of laser-generated longitudinal acoustic waves have been computed for duraluminum samples in the thermoelastic regime and steel sample in the ablation regime.
Abstract: Focused ultrasonicwaves have been generated in a solid by irradiating its surface with a multiple beam‐pulsed YAG laser. A set of 16 rectilinear sources is used, equivalent to a phased array of ultrasonic transducers. Longitudinal waves are focused in the sample by introducing an appropriate time delay between each laser pulse. The elastic waves are detected either by a broadband optical heterodyne probe to analyze the wide ultrasonic signal spectrum (0–20 MHz), or by a narrow‐band piezoelectric transducer to achieve the sectorial acoustic beam scanning of the sample. Neglecting heat diffusion in the solid and considering the source as a surface center of expansion, the impulse directivity patterns of laser‐generated longitudinal acoustic waves have been computed. Experiments performed on duraluminum samples in the thermoelastic regime and steel samples in the ablation regime are presented and compared with this analysis. It is shown that a high focusing and a significant improvement of the signal sensitivity for longitudinal waves can be achieved with this technique.

Patent
14 Sep 1993
TL;DR: In this paper, the authors proposed an efficient radio communication between a base station and a mobile station by selecting the direction of a communication beam in a direction in which a signal with the highest electric field strength is received at a point where a scanning means scanning surroundings intermittently is located.
Abstract: PURPOSE:To attain efficient radio communication between a base station and a mobile station by selecting the direction of a communication beam in a direction in which a signal with a highest electric field strength is received at a point where a scanning means scanning surroundings intermittently is located. CONSTITUTION:A base station 101 executes scanning by a major beam in every direction in tow-dimension or stereoscopically by changing the directivity of an antenna mechanically or electrically intermittently, in response to the transmission rate concretely such as every 5msec in the case of 200kbps. A mobile station 107 receives the major beam and measures the electric field strength at a received point and informs the result of measurement to the base station 101, which fixes its direction of the major beam in a direction in which a signal with a highest electric field strength is received afterward. Thus, a new radio wave transmission channel Bb is found out corresponding to the reception environment of the mobile station 107 and the direction of the major beam is corrected. Furthermore, when the direction of the antenna is electrically changed, for example, a phased array antenna or the like is used.

Patent
22 Feb 1993
TL;DR: In this paper, a distributed phase and gain controller is proposed to calculate the necessary phase shift for each antenna element, taking into account the phase-and gain errors associated with the TR module associated therewith.
Abstract: An antenna array (10) includes a plurality of antenna elements (12), each of which is associated with a transmit-receive TR module (14). The antenna elements and their associated TR modules are grouped into sets, which in the illustrated embodiment are sets of four. Each set of four TR module/antenna elements is associated with one phase and gain controller (18 X ), which is part of a distributed phase and gain controller. The beam direction is commanded by a central radar control computer (RCC) (22), which transmits beam direction and other information to all the separate phase/gain controllers. Each separate phase/gain controller accesses local memory to obtain data relating to the location within the array of those antenna elements which it controls. Each phase/gain controller then calculates the necessary phase shift for each antenna element it controls, taking into account the phase and gain errors associated with the TR module associated therewith. The calculation is performed separately for the transmit and receive modes. While the described controller calculates for both transmit and receive modules, in a transmit-only or receive-only system, only transmit or receive-mode values, respectively, need be calculated.

Journal ArticleDOI
TL;DR: Multipoint foci have been synthesized by applying the pseudoinverse field conjugation method to a single ultrasonic transducer coupled to a polystyrene lens that is capable of generating strongly localized, controlled temperature fields for hyperthermia.
Abstract: Multipoint foci have been synthesized by applying the pseudoinverse field conjugation method to a single ultrasonic transducer coupled to a polystyrene lens. The lens design is based on phased array calculations are then fabricated on a computer-controlled milling machine. The measured beam patterns from the lenses agree closely with the beam patterns predicted by theory for the equivalent phased arrays. Temperature distributions from thermal modeling and those measured in tissue equivalent phantoms show that the lens system is capable of generating strongly localized, controlled temperature fields for hyperthermia. >

PatentDOI
TL;DR: In this article, the complete 2N element aperture is realized at each beam angle with two firings of the transmitter and the receipt of echo signals from two different sets of N transducer elements.
Abstract: A phased array sector scanning ultrasonic imaging system includes a transducer array with 2N separate transducer elements and a transmitter and receiver with N separate channels. The complete 2N element aperture is realized at each beam angle with two firings of the transmitter and the receipt of echo signals from two different sets of N transducer elements. The echo signals from the two firings are coherently summed to form a single receive beam. Two different patterns are provided for selecting which transducer elements to energize and receive from during each of the two firings.

Journal ArticleDOI
TL;DR: Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager, and can enhance detection of low contrast lesions using large phased-array apertures.
Abstract: In clinical applications using large apertures, a significant number of phased array elements may be blocked due to discontinuous acoustic windows into the body. These blocked elements produce undesired beamforming artifacts, degrading spatial and contrast resolution. To minimize these artifacts, an algorithm using multiple receive beams and the total-least-squares method is proposed. Simulations and experimental results show that this algorithm can effectively reduce imperfections in the point spread function of the imager. Combined with first-and second-order scatterer statistics derived from multiple receive beams, the algorithm is modified for blocked element compensation on distributed scattering sources. Results also indicate that compensated images are comparable to full array images, and that even full array images can be improved by removing undesired sidelobe contributions. This method, therefore, can enhance detection of low contrast lesions using large phased-array apertures. >

Journal ArticleDOI
TL;DR: The authors describe a four-coil surface phased-array coil for magnetic resonance (MR) imaging of the temporal lobes that is 1.67 times or more better than that obtained with a standard quadrature head coil in the region of the hippocampi.
Abstract: The authors describe a four-coil surface phased-array coil for magnetic resonance (MR) imaging of the temporal lobes. On the basis of measurements in a phantom, the signal-to-noise ratio of the array is 1.67 times or more better than that obtained with a standard quadrature head coil in the region of the hippocampi. The higher sensitivity of this phased array permits use of imaging pulse sequences for which the head coil is inadequate.

Journal ArticleDOI
TL;DR: A method is presented for the evaluation of optimal amplitude and phase excitations for the radiating elements of a phased array hyperthermia system, in order to achieve desired steady-state temperature distributions inside and outside of malignant tissues.
Abstract: A method is presented for the evaluation of optimal amplitude and phase excitations for the radiating elements of a phased array hyperthermia system, in order to achieve desired steady-state temperature distributions inside and outside of malignant tissues Use is made of a detailed electromagnetic and thermal model of the heated tissue in order to predict the steady-state temperature at any point in tissue Optimal excitations are obtained by minimizing the squared error between desired and model predicted temperatures inside the tumor volume, subject to the constraint that temperatures do not exceed an upper bound outside the tumor The penalty function technique is used to solve the constrained optimization problem Sequential unconstrained minima are obtained by a modified Newton method Numerical results for a four element phased array hyperthermia system are presented >

Patent
14 May 1993
TL;DR: In this article, an ultrasonic phased array imaging system which includes a normal mode and an adaptive mode of operation is described, where the adaptive mode adjusts the delay associated with each element in the transducer such that the average image brightness of the region of interest is maximized.
Abstract: Disclosed is an ultrasonic phased array imaging system which includes a normal mode and an adaptive mode of operation The adaptive mode adjusts the delay associated with each element in the transducer such that the average image brightness of the region of interest is maximized Also disclosed is a method of correcting for phase aberration using selected elements of an ultrasonic array specific to each element of the array to correct each element of the array It is further disclosed that the use of corrected elements to correct subsequent elements in the array results in more accurate phase aberration correction In a preferred embodiment, the determination of the maximum average image brightness is performed more accurately through the use of selectable transducer array elements and previously corrected data during adaptive processing

Patent
05 Nov 1993
TL;DR: In this article, a diode laser includes a body of a semiconductor material having an active region therein which is adapted to generate radiation and emit the radiation form a surface of the body, and separate reflecting mirrors at opposite sides of the active region with at least one of the mirrors being partially transparent to the generated light.
Abstract: A phased array of semiconductor laser elements is provided in which the percentage of light which propagates into different diffractive orders is modified by an optical element. The diode laser includes a body of a semiconductor material having an active region therein which is adapted to generate radiation and emit the radiation form a surface of the body, and separate reflecting mirrors at opposite sides of the active region with at least one of the mirrors being partially transparent to the generated light to allow the light generated in the active region to be emitted therethrough. The optical element may take the form of a modification in the arrangement of the semiconductor laser elements, or an array of microprisms, or an external mirror to modify the percentage of light which propagates into different diffractive orders.

Patent
30 Jul 1993
TL;DR: In this article, a radar system that includes an ultra wideband radar signal processor for electronically scanned arrays that utilizes frequency offset generation (FOG) to achieve beam steering as compared with phase shift and time delay techniques of conventional radars is presented.
Abstract: A radar system that includes an ultra wideband radar signal processor for electronically scanned arrays that utilizes frequency offset generation (FOG) to achieve beam steering as compared with phase shift and time delay techniques of conventional radars. The device comprises a transmit antenna, a chirp generator connected to the transmit antenna and a first summing circuit, a receiver antenna connected to the first summing circuit, a Doppler de-ramping chirp circuit connected to a second summing circuit, the output of the second summing circuit connected to an amplitude and weighting circuit and the output of the amplitude circuit connected to a spectrum analyzer of a Fast Fourier Transform (FFT) circuit. The signal processing consists of mixing the target returns with the transmitted signal to obtain a video beat note signal. This video beat note signal is mixed with a Doppler de-ramping chirp waveform which is matched to the desired target velocity. The output is amplitude weighted and the FFT algorithm applied. To achieve beam steering for the detection of off boresight targets, a phased array with distributed receivers is required. Also, frequency offset generation must be incorporated into the Doppler de-ramping chirp generator.

Journal ArticleDOI
TL;DR: In this paper, the use of optical fiber arrays to generate shear and surface waves was investigated and the results showed that the array enhances signal generation in the forward direction for both shear wave and surface wave.

Proceedings ArticleDOI
28 Jun 1993
TL;DR: In this article, a performance monitoring/fault isolation and correction (PM/FIC) system for a smart skins phased array antenna with active transmit/receive modules has been developed and tested.
Abstract: A performance monitoring/fault isolation and correction (PM/FIC) system for a smart skins phased array antenna with active transmit/receive modules has been developed and tested. This system employs a built-in transmission line signal injector embedded at the radiating aperture together with a phase toggling technique for signal detection. The authors present the design of a demonstration test array and the PM/FIC system test results. The PM/FIC system can be used to provide the performance monitoring of the array. A low-sidelobe distribution can be also achieved using the PM/FIC system. In the application to self-correction, a fault correction algorithm has been developed and incorporated into the demonstration model. >

Journal ArticleDOI
TL;DR: In this paper, an approach for the design of optically synchronized millimeter-wave local oscillators based on a subharmonically injection-locked phase-lock-loop technique is introduced.
Abstract: An approach for the design of optically synchronized millimeter-wave local oscillators based on a subharmonically injection-locked phase-lock-loop technique is introduced. The experimental results support the desired goal of frequency and phase coherency, phase shift control of millimeter-wave oscillators, and self-oscillating mixing to downconvert a millimeter-wave RF signal. Experimental results and theoretical analysis show the advantages of the proposed approach: large locking range of two subharmonically locked oscillators, lower FM noise degradation, and smaller phase error caused by frequency detuning. >

Patent
08 Jun 1993
TL;DR: In this article, a digital signal processing method and apparatus for beam forming utilizing an N-element phased array antenna is presented. But the beam signal is generated separately weighted in amplitude and phase at each of the N elements of the antenna.
Abstract: A digital signal processing method and apparatus for beam forming utilizes an N-element phased array antenna (1). For transmit side beam forming of an agile beam to be steered in a direction between three adjacent orthogonal beams three copies of complex envelope samples for the required beam signal are generated, separately weighted in amplitude and phase (4) and fed into an N-part inverse FFT processor (3) via three input ports (7a, 7b and 7c) which correspond to the three adjacent orthogonal beams, and inverse Fast Fourier Transformed therein into the required beam as a weighted combination of the three adjacent orthogonal beams for passage to the elements (2) of the phased array antenna (1). For receive side beam detection of an agile beam received from a direction between three adjacent orthogonal beams, baseband complex envelope samples of signals received on each of the N elements (2) of the antenna (1) are input to the DFT processor (3) and discrete transformed into N orthogonal beam signals, the three orthogonal beam signals (5a, 5b and 5c) output from the processor 3 which correspond to the three orthogonal beams are separately weighted in amplitude and phase at (4) and combined into an output signal (10) which is the baseband complex envelope of the required beam signal.

PatentDOI
TL;DR: In this article, three approaches for increasing the sensitivity of an acoustic sensor by optical amplification are described. And a multi-element sensor array suitable for linear array or phased array imaging is presented.
Abstract: An acoustic sensor, useful as an ultrasonic transducer, microphone or hydrophone, uses an optical lever to amplify the motion of the sensor surface and convert it to an electrical signal for image processing. A beam of light (15) from a laser is directed at an oblique angle onto a reflective surface (13) coupled to a sensor membrane (31). The reflected light (16) strikes a position-sensitive light detector (PSD) (17) generating an electrical signal indicating the position of the light spot on the PSD (17). When an acoustic wave strikes the sensor membrane (31), the small movements of the reflective surface (13) result in large motions of the spot of light on the PSD (17), thereby amplifying the acoustic signal. Also disclosed is a multi-element sensor array suitable for linear array or phased array imaging. Three approaches are disclosed for increasing the sensitivity by optical amplification: 1) the vibrating mirror (46) is part of a cantilever that increases the angular deflection of the incident light beam (15); 2) a stationary mirror (M2) is positioned approximately parallel to the vibrating mirror surface; the reflected light beam is reflected back onto the vibrating mirror (M1), and picks up another increment of the acoustic signal with each reflection; 3) the effective movement of the optical lever is increased within a small volume by the use of two stationary mirrors (M3, M4) to increase the path length from the vibrating mirror (M1) to the position-sensitive detector (17). Two chopped light beams may be directed at a single vibrating surface (M1), and phase-locked loop circuitry used to reduce the signal-to-noise ratio.