US-12622593-B2 - Pressure sensor

US12622593B2US 12622593 B2US12622593 B2US 12622593B2US-12622593-B2

Abstract

A pressure sensing apparatus comprises an elongate first sensor device in a beam configuration supported at at least one longitudinal end by a rigid support structure and having a deflectable portion. A chamber is disposed adjacent a first, internally-facing, face of the first sensor device. An envelope hermetically seals the first sensor device and the chamber from an ambient environment external to the pressure sensing apparatus. The envelope comprises a flexible membrane disposed over and coupled to a second, externally-facing, face of the first sensor device and extending along at least one or two sides of the first sensor device and the chamber. The sensor device may be a surface acoustic wave device coupled to an RF antenna.

Inventors

Mohammad Reza Bahmanyar
Longfang Zou

Assignees

IMPERIAL COLLEGE INNOVATIONS LIMITED

Dates

Publication Date: 20260512
Application Date: 20210309
Priority Date: 20200309

Claims (20)

1 . A pressure sensing apparatus comprising: an elongate first sensor device in a beam configuration supported at at least one longitudinal end by a rigid support structure and having a deflectable portion; a chamber disposed adjacent a first face of the first sensor device; an envelope hermetically sealing the first sensor device and the chamber from an ambient environment; the envelope comprising a flexible membrane disposed over and coupled to a second face of the first sensor device and extending along at least one or two sides of the first sensor device and the chamber, in which the rigid support structure comprises a housing having a trench within which the first sensor device is positioned, and the flexible membrane comprises a polymer which encapsulates the housing to form the envelope, in which the housing comprises first and second electrically conductive portions separated from one another by an electrically insulating portion, each electrically conductive portion coupled to a respective electrical terminal of the first sensor device, and in which the first electrically conductive portion of the housing is substantially longer than the second electrically conductive portion to form a ground plane, and the second electrically conductive portion of the housing is coupled to an antenna.
2 . The pressure sensing apparatus of claim 1 configured such that pressure applied to the flexible membrane at the second face causes deflection of the flexible membrane disposed over the deflectable portion of the first sensor device and displacement of the flexible membrane along said at least one or two sides of the first sensor device and the chamber.
3 . The pressure sensing apparatus of claim 1 in which the flexible membrane of the envelope surrounds the first sensor device, the chamber and the support structure along at least a portion of a longitudinal axis of the first sensor device.
4 . The pressure sensing apparatus of claim 3 in which the flexible membrane forms a sleeve extending along the longitudinal axis and around the first sensor device, the chamber and at least a portion of the support structure.
5 . The pressure sensing apparatus of claim 4 in which the support structure comprises two longitudinal end portions which each close a respective end of the sleeve to form the hermetic seal of the envelope.
6 . The pressure sensing apparatus of claim 5 in which the longitudinal end portions each comprise an electrically conductive cap which is bonded to the respective end of the sleeve around its circumference to form the hermetic seal.
7 . The pressure sensing apparatus of claim 1 in which the elongate first sensor device is supported at each longitudinal end by the rigid support structure and the deflectable portion is a deflectable central portion between the opposing longitudinal ends.
8 . The pressure sensing apparatus of claim 7 in which a base of the rigid support structure comprises a second sensor device extending parallel to the first sensor device adjacent the chamber.
9 . The pressure sensing apparatus of claim 8 in which the rigid support structure further comprises a pair of spacers separating the base and first sensor to form the chamber, the spacers each comprising an electrically conductive material coupled to a respective electrical terminal of at least one of the first sensor device and the second sensor device.
10 . The pressure sensing apparatus of claim 9 in which the envelope comprises an electrically conductive material electrically coupled to a first one of the spacers and forming a ground plane enveloping at least a part of the first sensor device.
11 . The pressure sensing apparatus of claim 9 in which the electrically conductive material of a second one of the spacers is electrically connected to an antenna extending away from the envelope.
12 . The pressure sensing apparatus of claim 11 in which the antenna comprises a resilient material having an expanded shape memory configuration defining a substantially linear axial portion and an off-axis laterally extending portion, the material resiliently bendable into a substantially linear configuration for delivery of the apparatus via a catheter.
13 . The pressure sensing apparatus of claim 1 in which the flexible membrane comprises a metal material soldered, welded or otherwise bonded directly to at least one electrically conductive end cap of the envelope.
14 . The pressure sensing apparatus of claim 1 in which the flexible membrane comprises a metallised polymer bonded to at least one electrically conductive end cap of the envelope and electrically continuous therewith by an electroplated layer.
15 . The pressure sensing apparatus of claim 1 in which the flexible membrane comprises a glass material forming the envelope as a closed-ended capsule sealed around at least one electrical connection passing therethrough.
16 . The pressure sensing apparatus of claim 15 in which the closed-ended capsule is sealed around at least two electrical connections passing therethrough, and further including an electrically conductive sleeve disposed around the capsule electrically connected to one of the electrical connections to form a ground plane around the capsule.
17 . The pressure sensing apparatus of claim 1 in which ends of the trench of the housing are narrower to support the respective electrical terminals of the first sensor device and wider therebetween to enable unrestricted displacement of the deflectable portion.
18 . The pressure sensing apparatus of claim 1 in which the flexible membrane is coated with one or more layers of material to increase the hermeticity of the envelope.
19 . The pressure sensing apparatus of claim 1 incorporated within an intracranial shunt apparatus.
20 . The pressure sensing apparatus of claim 19 further including a valve within the intracranial shunt apparatus, the valve being configured for control by an output of at least the elongate first sensor device.

Description

The present disclosure relates to pressure sensors operable to monitor an ambient pressure by deflection of an element within an enclosure by pressure exerted on the enclosure via a flexible membrane. Elevated intracranial pressure (ICP) is a dangerous condition that can be caused by severe head injuries and other pathological problems. Continuous and accurate measurement of intracranial pressure (ICP) is considered a valuable means of management of patients suffering from ICP hypertension. The volume of the intracranial cavity is constant under normal conditions. The maintenance of a steady ICP depends on the volume of its contents, which include brain tissue (˜80%), venous blood (˜3 to 4%), arterial blood (˜6 to 7%) and cerebrospinal fluid (CSF) (˜10%). As brain tissue is relatively incompressible, steady ICP requires balancing the inflow and outflow of the fluid components. In other words, there must be a balance between the inflow of arterial blood and the outflow of venous blood from the head, as well as between the rate of CSF production and drainage. Some changes in mean ICP are expected under regular physiologic conditions, including changes in posture, brain activity, cardiovascular function, respiratory function and adrenergic tone. Elevated ICP can result from any mechanism that increases the volume of blood or CSF. Alternatively, ICP can also increase by the addition of a fourth component, such as a mass, intracranial haemorrhage or cerebral oedema that expands beyond the ability of the system to compensate. As ICP increases, mean arterial pressure (MAP) is increased, primarily through a rise in cardiac output, in order to maintain a steady cerebral perfusion pressure (CPP), which represents the pressure gradient driving cerebral blood flow and hence oxygen and metabolite delivery. In the presence of elevated ICP beyond the ability for compensation through elevation of MAP, CPP will be compromised and cerebral ischemia may follow. When ICP is sufficiently elevated, the pressure differential between the intracranial cavity and the spinal canal can cause the downward motion of brain tissue (i.e., herniation), which can compress vital brainstem structures, and subsequently lead to severe neurological outcomes including death. Untreated hydrocephalus has a 50-60% death rate, while survivors having varying degrees of intellectual, physical, and neurological disabilities. The most common neurological and neurosurgical pathologies that require ICP monitoring are traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), and hydrocephalus. Conventional invasive ICP monitoring systems require a wire, optical fibre or tube penetration of the skin. Such wired systems may limit patient transport and movement and may have high risks of infection, which can prevent long term usage. Some commercial telemetry ICP systems may offer the possibility of long term and continuous ICP monitoring. However, the sizes of the implantable and external device components and the cost of the system can limit their applications due to the wireless transmission method of inductive coupling, which, in nature, requires large coils. Elevated ICP can be treated by intracranial shunts, i.e. tubes that drain CSF into other parts of body (e.g. the abdomen). Shunts may be made from two tubes. One is inserted into the ventricle at one end and connected to a valve at the other end. The valve adjusts CSF flow from the brain into the second tube. However, current technology shunts can be prone to failures because of issues ranging from shunt obstruction, disconnections, fracture, over drainage or underdrainage. Therefore a ‘smart shunt’, i.e. a shunt integrated with a wirelessly readable pressure sensor, is desirable to improve reliability, control, precision and monitoring. It is desirable to provide a pressure sensor that can have some or all of the following features: to be fabricated to have a very small size; to be wirelessly readable; to be powered using wireless technology. As reproduced in FIGS. 1 to 3 of this disclosure, GB 2571141 describes an implantable cardiovascular pressure sensor 1 which comprises rigid enclosure 2 arranged for holding a compressible fluid or a vacuum 3 sealed within the rigid enclosure by a flexible membrane 4. An elongate compliant member 5 comprising a piezoelectric material is provided within the enclosure and the flexible membrane 4 is coupled to the elongate compliant member 5 to transfer external fluid pressure load 6 to the elongate compliant member 5 to cause deflection of the elongate compliant member 5. The pressure sensor 1 comprises a first acoustic wave device 10 provided by the piezoelectric material of the elongate compliant member 5 for sensing deflection of the elongate compliant member 5. The membrane 4 may include at least one flexible feature arranged to reduce rigidity in the membrane. For example, such a flexible feature may include a corrugation of the membrane 4 arranged to reduce