摘要:
An apparatus for actively damping vibrations in an element (30) which is secured to a support (28) comprises: an actuator (10, 40) locatable at a point adjacent to the point of attachment (29) of the element to the support and operable to apply force between the element and the support. A sensor (34) is associated with the element to produce a signal in response to vibration of the element and control means (36) is provided to operate the actuator in response to said signal to apply a force to the element to damp vibrations therein.
摘要:
In an endoscope, the tip (1) which contains passages for viewing means and light guide means is made of plastics material, for MR compatibility purposes, and an r.f. receive coil (19) of the endoscope is provided with a fiducial (17) having its own r.f. receive coil (16), to make it possible to track movement of the r.f. receive coil.
摘要:
The invention relates to a piezo-electric transformer circuit (200) incorporating a piezo-electric transformer (10) comprising a multi-element primary region (12) and a single element secondary region (14) mutually joined together. In operation, the circuit (200) applies a drive signal to the primary region (12) to excite the primary and secondary regions (12, 14) into longitudinal resonance, thereby generating a high potential signal at the secondary region (14). The drive signal is derived from the signal at the secondary region (14) in a self oscillating feedback loop configuration. The transformer (10) is fabricated from a hard piezo-electric ceramic material having a dielectric loss of substantially 0.005 or less at 1 kHz. Although such a hard ceramic does not provide as high a charge coefficient as softer piezo-electric ceramic materials, it is found that hard ceramics provide surprisingly improved energy conversion when used in piezo-electric transformer power supplies.
摘要:
In magnetic resonance imaging apparatus employing magnetic gradient fields in a phase-encode and in a read-out direction for spatially encoding excited MR active nuclei in a region of interest of a patient, in which a reduced number of readings in the read-out direction is taken, thereby creating an aliased reduced field of view image, at least two r.f. receive coils are used together with sensitivity information concerning those coils in order to unfold the aliased image to produce a full image while taking advantage of the reduced time of collection of data. In accordance with the invention, sensitivity information is collected at a lower resolution than that at which the image information is collected.
摘要:
In magnetic resonance imaging apparatus employing magnetic gradient fields in a phase-encode direction for spatially encoding excited MR active nuclei in a region of interest of a patient, in which a reduced number of readings in the phase-encode direction is taken, thereby creating an aliased reduced field of view image, a pair of r.f. receive coils is used together with sensitivity information concerning those coils in order to unfold the aliased image to produce a full image while taking advantage of the reduced time of collection of data. In accordance with the invention, the phase sensitivity pattern of each coil over the region of interest is different from that of the other coil.
摘要:
An optical link (10) is described for transmitting a microwave signal (30) in modulated optical form over an optical fibre (24). The optical link (10) has a transmitter (12) and a receiver (18). The transmitter (12) splits and converts the microwave signal (30) into two separate optical signals (34 and 36), each of which represent either the positive varying part of the microwave signal (30) or the negative varying part of the microwave signal (30). The receiver (18) combines the two separate optical signals (34 and 36) and converts them back into the microwave signal (30).
摘要:
An identification tag (300) is provided comprising a multilayer assembly incorporating, in sequence, a metal backing layer (320), a bulk structural layer (330), a piezo-electric layer (340) and an electrode layer (350). The electrode layer (350) incorporates antennae structures for receiving interrogating radiation comprising a first radiation component at a relatively lower frequency and a second radiation component at a relatively higher frequency. The electrode layer (350) also incorporates a structure (390, 400) for modulating a second signal generated in response to receiving the second component by a first signal generated in response to receiving the first component to generate a modulated signal which is re-emitted as reflected radiation from the tag (300). The presence of the tag (300) is determinable from modulation components present in the reflected radiation, thereby distinguishing the tag (300) from other objects capable of reflecting radiation, but not modulating it.